briggs carb problem, I think

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  #1  
Old 11-29-04, 12:25 PM
amoto
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briggs carb problem, I think

I'll give the whole story...

This fall, I bought a used snowblower that the owner told me that he had it running the previous season. It has an 8hp B&S model 190402, type 0898-02.

It wouldn't start. No spark. I pulled the cover off and found a mouse nest, and chewed electrical. I have an old 8hp vertical shaft B&S that I pulled the electrical component off. The vertical shaft has the non-points style ignition. It also has electric start which I also pulled.

I installed the "new" ignition parts along with the generator, starter and flywheel. I also pulled the carb apart and cleaned out the jets, etc.

With the new ignition, I was able to get the engine to start and run, it was tough to start - required lots of starter fluid. But it ran okay. The carb leaked due to damaged gaskets. It aslo would not restart when hot.

I figured that the carb needed a rebuild. Bought the carb rebuild kit and installed.

Now the thing won't run. It will start and putter for a couple of seconds before dying. If I turn it over with out the plug wire on, then remove the plug, the plug is dry.

However, after it does it puttering thing, there is gas dripping from inside the carb.

I've got the needles set to the initial start settings, 1 turn out on upper and 1.5 turns out on lower needle. I initially had the float set up correctly - completely flat when upside down.

My thoughts were that the thing was flooding, so ive adjusted the float to shut gas off sooner, but same symptoms.

Please help, this thing is driving me nuts. I've never had to take a small engine to a shop, this might be my first...

Thanks,
ANdrew
 
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  #2  
Old 11-29-04, 12:44 PM
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The gas dripping from inside the carb is an indication that the float isn't shutting the gas off like you thought. When something like that happens it's usually because the needle isn't seating properly or because the float itself isn't adjusted right. If you have the instructions from the carb overhaul kit, carefully adjust the float height as per those instructions. Make sure the needle is properly connected to the float and that the needle seat was replaced with a new one and is screwed in tight. The float must be free to move up & down and the needle must not jam in the seat. If you have one of those 'mighty vac' hand pumps you can usually use that to determine if the needle/seat system is working right. At this point I'd say that's your most likely culprit.
 
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Old 11-29-04, 01:21 PM
amoto
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Thanks for the reply.

I originally had the float set to the correct position according to the instructions on the rebuild kit.

It was also leaking.

I don't have a vac unit, but the way I checked the float is to blow (with my mouth) on the gas inlet. While blowing, I turn the carb upside down, and I can't blow anymore.

I've adjusted the float so that when the carb is upside down, the float is higher in the air. THis should shut the float off sooner.

The thing that puzzles me is that I think the spark plug should be getting damp if i turn the engine over with the plug wire disconnected. Unless the carb flooding is not allowing gas into the cylinder...
 
  #4  
Old 11-29-04, 04:27 PM
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Little raw gas (liquid state) will go into the cylinder unless you have the choke on. Your idea of blowing into the carb to check the needle & seat will work too. That's the way I used to do it until I sprang for the vacuum pump. With the carb completely dry you should be able to put a small spoon full of gas into the spark plug hole and start & run for a second or two. Unless you can do that you have problems other than those that involve the carb. Try that quick test to see. You should be able to get that engine to start on the first or second pull. It might take some work but if you don't you'll be cussing that machine this winter when you have bumper deep snow in your driveway and you have to refuel a time or two to get all that snow cleared.
 
  #5  
Old 11-30-04, 06:30 AM
amoto
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It will actually run for a couple of seconds without manually adding gas or starter fluid.

Even with the choke closed, the plug is not getting wet.

I've got the throttle wide open, and the choke closed, but the engine just sort of putters, like is idling. Then dies. I can do this once or twice then it won't fire at all.

I'll let it sit, then can do it all over again.

If it is flooding itself, will the spark plug get wet?

I've checked the float bowl by removing the bottom adjustment screw, and lots of gas comes out.

I've got the shut off wire completely unwired from the safety/start circuit to make sure that something wasn't killing it electrically.

Could my ignition be dying after it runs for a couple of seconds? I've got one of those spart testers, and the spark looks okay while I pull on the starter cord. Is any other ways to test the ignition unit?
 
  #6  
Old 11-30-04, 09:44 AM
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It sounds like you are doing all the right stuff with the carb. There's another factor to consider. Your carb can't function properly unless there's sufficient air flow in the carb throat. That air flow comes from the piston decending in the cylinder. If you have problems there, either from bad gaskets (cylinder head - carb to intake) or from defective and/or stuck piston rings the air flow will be insufficient to get or keep the engine running. Try checking the compression. You must do that properly to get usefull readings. Make sure that the throttle is blocked open and that the choke is fully off. Pull the engine through several times and watch the compression guage. You should see at least 80 psi, 100 or more would be great. Less that 80 psi means that you will most likely have lots of trouble starting the engine. If you find the compression low, try squirting 30W crankcase engine oil into the spark plug hole. Don't be afraid to squirt several times. Try the compression test again. If you see a marked improvement of compression after squirting in the oil that's almost a sure indication that your problems are due to poor sealing of the cylinder caused by worn out, stuck, or broke piston rings. Of course poor compression could be caused by poorly seating valves, but then you wouldn't see any improvement of compression following the oil squirt test if that's the case.

It sounds like you are on top of the ignition system and have good spark. A nice fat spark isn't good enough, however, if it's not coming at the proper instant. You can have a timing problem on a B & S engine if the flywheel key has partly sheared. Visually inspect the key by looking at the junction between the flywheel and the crankshaft. Those keys are just soft material and are designed to protect your crankshaft if you hit something solid. If you must replace the key don't lubricate the junction between the crankshaft and the flywheel. Doing that will assure the failure of the new key when the engine backfires the first time.

Most small engines will start and run easily but you must have everything in good mechanical condition. Single cylinder engines have little tolerance for bad valves or piston rings. The spark has to be good and at the proper instant. Multi cyclinder engines are much more tolerant of those kinds of failures.
 
  #7  
Old 11-30-04, 05:42 PM
amoto
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Jughead, thanks again for the help.

I just finished messing with the thing again. It's driving me nuts...

The compression is okay. My gauge reads about 120psi, but when I reset, it goes back to 30. So I'm guessing my real compression is around 90psi. (time for a new compression guage)

I did find out where the gas is coming from. There is a brass tube that runs from the bottom of the carb up into the throat at an angle (I believe that it is the main jet). At the bottom of the tube is an adjustment screw. When I turn this screw all the way in and pull the engine over, the gas leak stops. I've tried backing this screw out by 1/4 increments and tried to start the engine at each stop. Still could not get anything more than a few second putter.

It'll be a couple of days before I can work on it, but I'll take your advice and check the key on the flywheel next.

By the way, can the valves be adjusted on these type of engines? If so, does anyone have some instructions on checking and adjusting the valve lash?

Thanks in advance
Andrew
 
  #8  
Old 11-30-04, 08:45 PM
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Usually the only way to adjust the valves is to carefully grind the end of the valve stem down. It's a one way adjustment. Mostly you shouldn't have to do it unless you are replacing a valve. Sounds like the compression is OK. I would start with about a turn and a half out on the adjustment screw. Make sure you don't have a big air leak on the junction between the carb and the engine. If you suck air from a leak there you won't have enough air going through the carb throat to pick up the gas in the carb and the mixture will be way to lean to run. Some of the other guys on here swear by soaking the carb in a good cleaner to make sure all the passages are clear. I've done that before and even used a torch tip cleaner to clear some of the small holes. If you have someone to help you pull the engine you can even use a regular automotive type timing light to confirm that the spark is occuring near the proper instant.
 
  #9  
Old 12-01-04, 12:46 PM
Azis
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I also pulled the carb apart and cleaned out the jets, etc.
The bolt that holds the bowl on has passages in it....were they cleaned?
This is the main metering to the main jet, if fuel can not pass, (usually fuel will flow through it before the needle valve seats) the engine will not get gas, the bowl can fill and come out the overflow.
Try to see if you can keep it running by adding a bit of gas to the carb, just as it begins to die add a bit more, if it continues to run this way then you still have fuel restriction somewhere. Most likely the carb and likley more the bolt I mentioned.

GL
 
  #10  
Old 12-01-04, 01:35 PM
amoto
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Azis

Which bolt are you refering to?

The bowl is held to the rest of the carb by 3 small bolts.

There is a long brass tube that runs through the bowl into the top of the carb which must be removed to seperate the bowl from the rest of the carb. (after the 3 above mention bolts are removed).

The brass tube is hollow and had a bunch of holes in it. This tube was replaced inthe rebuild kit, so all the holes are okay.
 
  #11  
Old 12-01-04, 06:47 PM
Azis
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Doh My bad sorry...I didnt look up engine info was thinking just briggs 8hp

Troubleshooting using gas as I described will still help in diagnosing just the same.
Try gas, not starter fluid if you can help it...
 
  #12  
Old 12-01-04, 06:51 PM
amoto
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Whoo hooo!!

Got it running tonight.

Turns out the flywheel key had been sheared. The flywheel was off location by a fair amount.

I think the cause was that I did not tighten down the pull start mechanism that keeps the flywheel on enough.

Engine seems to run okay. I'll probably try tuning the newly rebuilt carb over the weekend.

One other question... After I got the thing running, I wheeled the snowblower outside (in the dark) so that I wouldn't kill myself with the fumes.

After running it for a few minutes with the throttle wide open, I noticed that the muffler started glowing red. Is this normal? If not, what is the cause?


Thanks again for everyones help!!!

Andrew
 
  #13  
Old 12-01-04, 09:38 PM
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Great job!! Glad you got the engine running. Make sure that you didn't lubricate the junction between the flywheel and the crankshaft or you will shear the key again. You need all the friction you can get. I went through five or six keys finding that out. As far as the muffler goes....everything you see is perfectly normal. If you could see inside the cylinder when the fuel ignites you would see a bright blue flash. Gasoline burns blue just like natural gas. You get some cooling of the combustion products when the cyclinder decends and the gas expands but when the exhaust valve opens what comes out is still plenty hot. You should be in the catagory of 850 degrees F. A while ago I ran a 16 HP Tecumseh without a muffler. There was a nice blue flame coming out of the exhaust port. Quite impressive when the light levels are low. I know that on larger diesel engines with a high throttle setting the exhaust gas runs about 1000 degrees. The exhaust manifolds get cherry red. You can clearly see that when the insulation lagging is removed.
 
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