carb leaks gas

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  #1  
Old 02-10-11, 12:49 PM
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carb leaks gas

On the four-stroke Briggs/Stratton engine on my pressure washer the carb leaks. I noticed it after some no-starts, gas dripping out down out of the air cleaner assembly. I can turn off the petcock at the gas tank to stop it, but of course upon opening the petcock again it starts leaking, bad. When I uninstall the carb from the engine and empty the bowl, and then re-install the bowl to the carb and re-install the carb to the engine, and then open the petcock from the gas tank, no leakage occurs from the carb. Then when I go try to start the engine, it still doesn't even begin to start. And then upon removing the air cleaner assembly to inspect the carb again, I can see that its been flooding, gas dripping out of it. Then if I open the gas tank petcock again, gas comes dripping out of the carb big time until I close the petcock. I looked at the float and needle valve and seat, it looks fine. From my description what could likely be making the carb leak gas like this?
 
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  #2  
Old 02-10-11, 02:17 PM
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I assume your carb. has a bowl and a float on the bottom. If so I would remove the bowl and inspect the float to see if it's gotten any fuel inside or become "water logged". Then I would inspect the needle valve that the float actuates. This is what meters fuel entering the carb. The pointy end should have a nice straight V with no grooves or pits. Look up in the hole for the needle and see if it's seat has any nicks, scratches or bits of varnish or dirt stuck to it.

If the float is too heavy from being water logged or if the valve is not seating well it will allow fuel to pour into the carb. uncontrollably, flooding the engine and spilling gas out the carb.
 
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Old 02-10-11, 02:39 PM
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I've inspected the float and there is no indication of fuel within it. The needle valve has a nice straight V with no pits or grooves. And up in the hole http://i207.photobucket.com/albums/b...1/IMG_1514.jpg it looks un-scratched and pretty darn clean to me. I'm still stumped, so any further advice appreciated. thanks

Note: I'd been operating the engine just recent to this happening, and it had been running fine. It's not like its been sitting for a long time with old gas in it. It's been running and has good fresh gas.
 
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Old 02-10-11, 04:03 PM
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Boy, it looks nice and clean. If you re-assemble the needle valve and float, then turn the carburetor upside down and look at the float. It should be parallel to the rim of the carb.

Try putting the carb back together, re-install it on the engine and turn on the fuel shut-off valve but don't start the engine. Just watch it for a few minutes. Does fuel start pouring out an overflow in the carb or out the throat of the carb? If fuel's not pouring/dripping out try to start it. Does fuel start pouring out when trying to start?
 
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Old 02-10-11, 04:39 PM
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Originally Posted by Pilot Dane View Post
Boy, it looks nice and clean. If you re-assemble the needle valve and float, then turn the carburetor upside down and look at the float. It should be parallel to the rim of the carb.

Try putting the carb back together, re-install it on the engine and turn on the fuel shut-off valve but don't start the engine. Just watch it for a few minutes. Does fuel start pouring out an overflow in the carb or out the throat of the carb? If fuel's not pouring/dripping out try to start it. Does fuel start pouring out when trying to start?
With the needle valve and float assembled and with the carburetor turned upside, the float is parallel with the rim of the carb but not exactly parallel. Not sure if you can tell by this picture, http://i207.photobucket.com/albums/b...1/IMG_1524.jpg but in real life here it's not exactly parallel unless I push/hold the float down manually with my finger to make it spring down a little to make match just level. Is it supposed to be exactly parallel?

When I put the carb back together and reinstall it on the engine and open the fuel shut-off valve but don't start the engine and watch it for a few minutes, no fuel pours/leaks out of the carb. When trying to start I'm certain it begins pouring/dripping out then. Because when it didn't/doesn't start and I put it up on the workbench and take the air cleaner assembly out of the way to look at the carb throat I can see that there's been flooding/dripping, and will continue to flood/drip out the carb throat as long as the fuel shut-off valve is open.
 
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Old 02-10-11, 05:50 PM
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For that type of leakage, it's nearly always the float/float valve/float seat. Considering the low cost vs the hassle of continually dismantling the carb, it's a good idea to replace all three.
 

Last edited by marbobj; 02-10-11 at 06:05 PM.
  #7  
Old 02-10-11, 06:30 PM
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I referenced the specific Briggs part number for the needle and seat for the carb on my engine, and apparently the seat looks like this when it's removed from the carb (as shown here with the needle): Inlet valve needle & seat for Briggs 398188 - eBay (item 130484413050 end time Mar-10-11 11:16:01 PST)

So if my current seat looks like this one, which it does, what exactly could be the problem with it? It looks just fine to the naked eye down in there, how could it be preventing the needle valve from closing, if that's what's happening? Also, mine doesn't seem to be made of brass... ??

Any further comments appreciated! Thanks
 
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Old 02-10-11, 06:50 PM
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Basically any time that style carb drips gas it's almost always something in the bowl. It's a really simple system but it relies on that little needle valve tip being able to form a good seal against the seat. The tinniest leak will let fuel into the bowl when it shouldn't. A little leakage is no biggie when the engine is running at a good pace but it can be a real problem when trying to start a cold engine.

Getting the correct fuel level in the bowl is critical to making the carb work. The float keeps fuel at a specific level. The air flow through the throat of the carb creates a venturi suction that draws the fuel of from the bowl, through the jets and into the airflow. Since the venturi suction is pretty weak a minor difference in the fuel's level in the bowl can have big impact on how much fuel flows up through the jets. If the fuel in the bowl is too high, the engine floods.

I have had some luck resurrecting them by pushing the needle up into it's socket hard with my thumb. You can also try spinning the needle to try and polish the mating surface with the seat.
 
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Old 02-10-11, 08:55 PM
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The problem with the needle and seat mating usually isn't apparent to the naked eye. It has to do with two perfectly concentric shapes mating. Over a long period of time, exposure to vibration, gasoline, heat and cold will affect that fit, regardless of their composition. the needle and seat used to be made of steel/brass, then a neo tip was put on the needle. Now you see the seat and tip of the needle made out of neoprene, nylon, or some type of plastic.

If the two components became slightly misshapen but maintained their position they could very well still seal. However, the vibration of the engine can rotate the needle slightly out of the position that allows the sealing and you have a leak. Shake it a little and the flow stops, only to start again with a little more engine vibration.
 
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Old 02-11-11, 08:54 AM
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Thanks for those explanations which helps me understand the basic function/operation as well as the importance that the needle valve should seal so perfectly. It looks as if the solution then is to for me to install a new needle and seat. I'll have to order one and wait for it as there's no place locally that stocks it.

Upon close examination the surface of this seal looks to be of a red/orange colored rubber type material, and as I mentioned looks nice and clean and perfectly intact to the naked eye. I even looked with a magnifying glass and it looks fine, but of course (as explained) that doesn't mean much.

The operation of the float on the hinge pin, up and down seems fine, no apparent problem. With the carb off the engine, I did try hooking a short clean hose to the end of the fuel inlet on the carb, and pushed and held on the float so it'd hold the needle into the seal hole, and blew (with my own breath) on the hose to see if it would be airtight. It did hold airtight, until I released the float/needle and then there would be air flow. So it seems it seals, but apparently not with gas and with during actual operating conditions?

I might try to push the needle in hard with my thumb, per Pilot Dane's suggestion, and see if I can "resurrect" the seal, at least temporarily.

thanks again
 

Last edited by sgull; 02-11-11 at 09:23 AM.
  #11  
Old 02-11-11, 09:20 AM
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Originally Posted by sgull View Post

I did try hooking a short clean hose to the end of the fuel inlet on the carb, and pushed and held on the float so it'd hold the needle into the seal hole, and blew (with my own breath) on the hose to see if it would be airtight. It did hold airtight, until I released the float/needle and then there would be air flow. So it seems it seals, but apparently not with gas and with during actual operating conditions?

I might try to push the needle in hard with my thumb, per Pilot Dane's suggestion, and see if I can "resurrect" the seal, at least temporarily.

thanks again
You can do the same sort of test using gas. Just assemble the carb but leave it off the engine. You can hook a hose and some sort of supply of gas to it and let it sit and wait to see if it leaks. Might even be able to use the fuel line and gas tank of the mower itself. I have a small gas can with the vent nipple perfect size for fuel line that I use.
 
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Old 02-11-11, 09:31 AM
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Originally Posted by BFHFixit View Post
You can do the same sort of test using gas. Just assemble the carb but leave it off the engine. You can hook a hose and some sort of supply of gas to it and let it sit and wait to see if it leaks. Might even be able to use the fuel line and gas tank of the mower itself.
Not to repeat myself unnecessarily here, but I did mention previously how when I put the carb back together and reinstall it on the engine and open the fuel shut-off valve but don't start the engine and watch it for a few minutes, no fuel pours/leaks out of the carb. When trying to start I'm certain it begins pouring/dripping out then. Because when it didn't/doesn't start and I put it up on the workbench and take the air cleaner assembly out of the way to look at the carb throat I can see that there's been flooding/dripping, and will continue to flood/drip out the carb throat as long as the fuel shut-off valve is open.

So my above procedure seems to be basically what you're suggesting except that I had the carb on the engine when doing it (I guess just to keep it stabilized/level there). thanks
 
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Old 02-11-11, 09:36 AM
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I have had them sit for more than half an hour or so before showing signs of leaking. Testing it off the engine also prevents contaminating the oil with gas.

Good luck
 
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Old 02-11-11, 09:49 AM
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Originally Posted by BFHFixit View Post
I have had them sit for more than half an hour or so before showing signs of leaking. Testing it off the engine also prevents contaminating the oil with gas.
Hmm, okay I didn't try letting mine sit for very long, just a few minutes and then I'd look and say "still dry, what the ****!?" I'm gonna leave it sit for a good long while next time then go look.

And glad you mentioned about the gas into oil contamination. Since this has been happening I would think I should make sure to change the oil when/if I ever get this carb leak fixed. Right? Also I suppose its not a good idea at all to even try to be running the engine even for a short period if there's suspected gas contamination into the oil?
 
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Old 02-11-11, 09:53 AM
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I am assuming the engine has compression. When you pull the start cord you feel it get tougher to pull and the engine makes a little "pugh" sound?

Have you checked for a spark? Remove the spark plug. Connect the spark plug wire to the plug then hold it so the plugs' tip or threads of the plug are touching a metal part of the engine. Then pull the cord and see if the plug sparks.

Here's another test to help narrow it down to confirm if it's the carb causing the problem. Remove the air cleaner and move the throttle to the full throttle (open) position, no choke. Spray a quick 1/2 second shot of ether or a 1 second shot of WD-40 into the throat of the carb. Then pull the cord and see if it sputters, tries to start or runs for a second. If you don't have anything to spray in the carb you can remove the spark plug and pour about 1 tsp of gas into the cylinder. Re-install the spark plug and pull the cord several times to see it it fires or runs for a few seconds. If it runs then you know everything in the engine (compression & spark) are OK which only leaves fuel (carburetor).

If possible when testing the carb. and trying to debug leave the air cleaner off. It makes is easier to see what's going on.
 
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Old 02-11-11, 10:29 AM
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If the engine has a dipstick pull it and check the oil level. If it is noticeably higher then I would change it before running the engine. If it appears to be at its normal level I'd leave the old oil in there until you get this problem worked out, but make sure to change the oil before you run it for any length of time.
 
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Old 02-11-11, 10:34 AM
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Originally Posted by Pilot Dane View Post
I am assuming the engine has compression. When you pull the start cord you feel it get tougher to pull and the engine makes a little "pugh" sound?
Have you checked for a spark? Remove the spark plug. Connect the spark plug wire to the plug then hold it so the plugs' tip or threads of the plug are touching a metal part of the engine. Then pull the cord and see if the plug sparks.
Yes I'd say the start cord gets a little tougher to pull and the engine makes a little (definitely little) pugh sound. Hard for me to say for certain though whether the feel of the cord while pulling seems too easy (its not too much tougher, or maybe the same, than I recall when things were working normally).

When I do the spark check test you suggest, is it necessary at all to have the carb installed onto the engine?

Also, in regard to the next test you suggested to see if I can get it to fire or run a few seconds (ether, WD40, or gas), it seems I should probably not perform that with this carb installed while its having this leak issue? Comment please. thanks
 
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Old 02-11-11, 11:19 AM
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The test by adding the gas to the cylinder or using ether/WD-40 can pretty much be used in place of the other two tests. If you can get it to fire or run it's a good indication that you have spark and compression. I just mention the other tests in case you don't have ether or WD-40 handy or aren't comfortable putting raw gas in the cylinder.

I usually do this test with the carb on the engine. Just use some common sense whenever gasoline is present. You can have the fuel shut off valve turned off. You DO NOT want fuel dripping from the carb, puddling nearby and you certainly do not want your hands or clothes soaked in gas in case the engine backfires. After all, it is gasoline which is highly flammable and you don't want a fire. For the same reason you should not smoke or play with matches while working with gasoline.
 
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Old 02-11-11, 11:43 AM
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If the engine has a dipstick pull it and check the oil level. If it is noticeably higher then I would change it before running the engine. If it appears to be at its normal level I'd leave the old oil in there until you get this problem worked out, but make sure to change the oil before you run it for any length of time.
+1. Good chance that gas is sleaking into the crankcase and thinning out your oil.
 
  #20  
Old 02-11-11, 12:18 PM
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Well I filled the re-assembled carb with gas with the carb off the engine and let it sit for over an hour and there was absolutely no sign of leakage/seepage. Similar to what I tried yesterday but only let it sit a few minutes then before attempting to start (and it didn't start) but then bringing back in only to discover it leaking badly again until I shut off the petcock valve from the tank.

So I've pressed the needle valve into the seat firmly with my thumb and remantled the float and bowl onto the uninstalled carb, and the bowl is still full of gas with no sign of leaking after over an hour of sitting. I even picked it up and shook/vibrated it some to maybe try to simulate the engine vibration to some extent, and that didn't cause it to leak either.

Getting ready to install it back onto the engine, it's necessary to rotate the carb considerably off level in order to re-engage the governor link shaft (hooked end) into the grommet on top of the throttle shaft lever (on top of the carb). But I'm concerned by doing that with gas full in the bowl that this extreme tilting could affect the float position and the quick odd angle could jar the needle tip out of it's now non-leaking position into the seat. So is it best to first remove the bowl and then install the carb and then re-install the bowl? Especially considering the apparent current issue that the valve has not been making adequate seal? I'd actually rather just install it with the bowl on (either full or empty of gas) because it's quite a bit easier that way. Comment please.

By the way I went ahead and did the spark test as described, and there definitely is nice blue sparking which appears while pulling the start cord.
 
  #21  
Old 02-11-11, 02:35 PM
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Did you check the float for leaks while you had it apart? You could submerge it in a container of water and check for bubbles. A slow leak or one that starts with vibrations would be very difficult to catch.

Steve
 
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Old 02-11-11, 02:43 PM
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Originally Posted by 2ndgencamaro View Post
Did you check the float for leaks while you had it apart?
No I didn't actually test the float for leaks. I could I suppose. Seemed light and empty of any any possible fluid inside when I was handling it and looking at it close, but I guess that's not really a test.

Right now I'm kind of awaiting a comment on my concern mentioned in my last post here, before proceeding with any further testing, etc.
 
  #23  
Old 02-11-11, 05:03 PM
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Leave the carburetor together while installing it. You don't havea position in the float/needle valve that will be affected to the point of making it work any differently. It will either work or not work once the engine vibration hits it. the latter is something you can't simulate by shaking the carburetor.
 
  #24  
Old 02-11-11, 05:12 PM
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As many times as you've had the float out I'm sure you would have noticed if it were "water logged" and from your pictures there is no fuel inside.

Something has to be going on that we are missing. I can not figure out why it does not leak until you pull the starter cord a few times. I'm wondering if there is something so stupidly obvious that we're just overlooking it.

When properly installed the needle should be captured when the float tries to push up or pull down on the needle. It's so bloody simple there is not much to go wrong. I've seen the needle stick in the up position when left a long time and the fuel varnishes and glues the valve in place. No fuel gets to the engine and it doesn't run. When the float is waterlogged it sinks, allowing fuel to pour into the carb and it starts dribbling fuel pretty quickly. Similar when the needle valve leaks. The carb drips or dribbles fuel depending on how bad the valve leaks but they leak whenever the fuel valve is open.

At this point try whatever you want putting the carb on the engine. If you think you can get the needle, float and pivot pin in place while the carb is on the engine go ahead and give it a try.

I had an old engine with a leaky needle valve that I never bothered to fix. I got it to run by opening the fuel valve to fill the bowl and then close the valve. Start the engine and then once it's running I open the valve again. The running engine consumed fuel faster than the valve leakd and it works. I just had to remember the startup and shutdown sequence.
 
  #25  
Old 02-11-11, 05:24 PM
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I had an updraft on a Briggs that would leak as soon as it was started. I'd tap the side of it with a block of wood - it'd stop leaking - I'd use it with no problem. Next time I'd go to use it, same thing. I finally broke down and bought the float and needle valve to fix it.

Probably lost the cost of those parts a number of times over in leaked gasoline.
 
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Old 02-11-11, 06:02 PM
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I have yet to find a plastic briggs float leaking or bad...but always a first time, I do still check just as with the brass floats, shake it next to your ear and listen for sloshing. Gas is a mysterious liquid. It will pass where many other liquids or gasses (IE: air and water) will not. Used to check heads on water cooled engines for crack by sealing of the ports and filling with gas, it would seep out of cracks that nothing else would. Poor man's dye penetrant
I have had a couple of Kohler Chinese engines XT-6 and XT-7, that have had leaking carbs. Of course the needle and seat all looked great, but sure enough they leaked and the kit for the thing is the entire carb. The second one I have in the shop now and just got the carb today, it is on a "Husky" (Not as in Husqvarna) Pressure washer.
Kinda curious about how you did your test I described...you mentioned you filled the bowl and waited....did you actually attach a fuel line to the inlet with a supply of gas above the carb so it had head pressure...???

That is the only way the bench test will work....

BTW, I feel the best way to install the carb is completely assembled with empty bowl, that is the reason for the bench test actually. Sometimes if I am still unsure, I might reinstall the carb to the engine, turn the gas on but lean the machine so any leaking fuel will run away from the engine
 
  #27  
Old 02-11-11, 07:56 PM
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Originally Posted by BFHFixit View Post
Kinda curious about how you did your test I described...you mentioned you filled the bowl and waited....did you actually attach a fuel line to the inlet with a supply of gas above the carb so it had head pressure...???
I happened to have a good-sized medical syringe which I used (without a needle attached of course) and the tip fit nicely right into the plastic barbed nipple hose connection of the carb inlet. Took about three syringe loads to fill the carb up with gas. So I suppose this way probably did not provide the head pressure for an adequate bench test.

Several times previously since I've had this leaking issue I've installed the carb onto the engine minus the bowl, then attached the bowl afterward by screwing on the the high speed jet bolt (pretty sure thats what they call it?) into it underneath. It's not that difficult but rather awkward compared with just installing assembled complete, as it's kinda fumbly trying to hold the bowl on and trying to get the threads of the bolts started in the limited workspace there with the engine mounted on the pressure washer frame. Then, I'd open the supply valve from the tank (head pressure!) but there'd be no leakage out the carb. So then I'd try pulling the rope to start the engine, but it wouldn't start, so I'd give up and go put the unit back on the workbench and then notice it's been leaking badly out the carb since I tried the pull start.

Tomorrow morning I'll be ready to give it another pull start try, for the first time since trying to "resurrect" the seal by pushing down hard on the needle into the seat with my thumb and re-assembling. I anticipate it won't start, and that the carb will probably just leak, like before.

This time, though, per cool idea of BFHFixit, I'll at least tilt the machine a little to try to keep very much gas from just dribbling into the engine.
 
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Old 02-11-11, 08:13 PM
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Normally a leaky carb will not cause a no start condition...

I don't recall you posting the model type and code of the engine....

Maybe that would give us some insight...being able to see just what engine you have....
 
  #29  
Old 02-11-11, 09:47 PM
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Old 02-12-11, 08:35 AM
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How does the oil/level look?
Have you tried a new spark plug?
With a new plug and the petcock off, try a bit of fuel in the plug hole as described previously and see if it will pop.
 
  #31  
Old 02-12-11, 08:45 AM
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Oil level looks to be at the proper level.
Spark plug is a new one, proper one for this engine, obtained from Briggs and installed only two weeks ago.

Results of pop test today with 1 tsp gas into plug hole: On first/second pull got a few relatively weak sounding pops corresponding along with short bursts of short quick blue flame from viewable open carb throat (air cleaner assembly removed). With continued pulling attempts, after the second pull, no popping at all and no indication of wanting to start. Seemed as if there was no spark being produced. Tried a 1-second spray of WD40 into carb throat and tried starting again. Nothing.

Observed open carb throat during and after this, and there is no sign of gas leaking out like before.
 

Last edited by sgull; 02-12-11 at 10:09 AM.
  #32  
Old 02-12-11, 10:18 AM
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Found the cause of the no-start. Center area of Intake valve keeper has broken through, valve loose.
 

Last edited by sgull; 02-12-11 at 11:53 AM.
  #33  
Old 02-12-11, 11:19 AM
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What was the reason for changing the spark plug? Were you having the same problems before changing it?

Might be time to check the valve clearances.
 
  #34  
Old 02-12-11, 11:52 AM
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Originally Posted by BFHFixit View Post
What was the reason for changing the spark plug? Were you having the same problems before changing it? Might be time to check the valve clearances.
Long story short, the compression release mechanism on the camshaft broke in recent past and upon ordering the new part I went ahead and ordered a fresh new spark plug just to have it. And since I had it I went ahead and changed it, (not that the other one was particularly bad-looking). After the repairing the compression release issue, it wasn't long after some fine operation of the machine that the exhaust valve retainer broke. After repairing that it continued to run fine again until some intermittent random-like occurrences of quickly cutting out and stopping abruptly. Upon investigation of this, after to examining the carb for dirt or possible debris and then reinstalling, and then upon further no-start after that, another bench investigation revealed the carb gas leakage issue. Valve clearances were set properly after compression release fix, as well as after last valve retainer fix.
 
  #35  
Old 02-12-11, 12:14 PM
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And here's a pic of the broken keeper: http://i207.photobucket.com/albums/b...1/IMG_1528.jpg

I'm at my wits end about these retainers breaking through like this. In the past (long before the compression release breaking) it's happened before on the intake valve like this time, and not too long ago on the exhaust side. So this is the third time I've had a valve keeper on this engine break. What is the likely cause anyway?
 
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