8hp Briggs Engine Problems

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  #1  
Old 01-14-13, 10:24 AM
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8hp Briggs Engine Problems

Hi everyone. I have recently acquired a Bobcat Snowblower. The engine was built in 79 so I assume the machine was manufactured the same year. The guy I bought it from found it in a barn. From what he told me, it had been sitting in there for quite some time. He bought it from the barn guy and decided to sell it. When I bought it he told me it had no spark. I've done points on many Briggs engines before so this was no problem for me. When I took off the flywheel to reveal the spark, I noticed that the plunger that sets the motion for the arm that touches the condensor was jammed and ceased. So I decided to leave it all in tact and install an electric ignition (magneto that bypasses the points alltogether) I gapped the magneto as close to the flywheel as possible without touching and put it all back together. Got a good clean spark.

The next bit that I tackled was the gas tank, fuel line and carb. Looks like gas sat in the tank while the machine sat in the barn for who knows how many years. Cleaned the gas tank out so there was no residue in it and took the carb off to be ultrasonic cleaned which has worked very well on other engines. Put it all back together and got nothing, not even a puff of smoke.

So I took off the original carb and put one from another Briggs engine I have. I have two Snowbird 262's and the carbs are almost identicle. Minor differences in the throttle linkages and the jet inside the carb (brass jet that threads inside the carb and can only be taken out when the high idle adjustment screw is taken out) This particular carb was leaky but the engine started up with it. Lots of white smoke at first. Could only get it running with full or almost full choke and for only about 30 seconds at a time at most.

Decided to try the original carb again. Recleaned it, new gaskets and set the adjustment screws 1.5 turns out each. Carb filled with gas but no dice. Put the leaking carb back on and could only get the engine to fire for about 10 seconds at a time. Got it to fire on full open choke however.

I decided to try one more carb. I have a running Snowbird 262 with a carb that is properly adjusted. So I decided to use that since this engine starts always on one pull even in the cold (not bad for an engine built in 62)

After putting that carb on the Bobcat, I got nothing out of the engine. I know I am getting gas and I have spark but I simply don't get it. The engine only seems to want to run with the carb that is leaking (same exact carb as the Snowbird carb). It won't run with the tightly sealed carburetors that do not leak. The leaking carb gave me an exhaust backfire once (small flame) which I believe means too much gas was being dumped into the cylinder and the fuel was still burning when the gas was being exhausted (correct me if that is wrong). I checked the valves and piston and all are working as they should.

I might try today to put the original Bobcat carburetor on the running Snowbird and see if it works. In the meantime, can anyone here figure this out? I am completely stumped. I'm thinking maybe the spark is weak but I made sure that I got the correct replacement part for the electric ignition. Any help is greatly appreciated. I attached pictures to give you an idea of what I am working with. I will supply model #'s if needed.


http://i291.photobucket.com/albums/l...ps906947b1.jpg
 
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  #2  
Old 01-14-13, 08:05 PM
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I see you had the flywheel off. That fact, and the mention of a backfire says that you might want to go back and check that flywheel key. If it wasn't torqued well enough or if the crankshaft had oil or grease on it at all, it may be sheared.
 
  #3  
Old 01-15-13, 12:03 PM
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Hi Cheese. Thanks for the response. I was actually reading another thread on this site before I decided to post about my engine. Thread can be found here: http://www.doityourself.com/forum/ou...has-spark.html

So I did a quick check of the key already and it looked okay to me. Should I take the flywheel off to check it though? I made sure to crank the flywheel back on when I put it all back together. I got a big nut that fits on the shaft and tightened it against the flywheel while a breaker bar until I couldn't crank it any further.

I saw in the other thread mentioned above something about still getting spark even if the key is sheared. I am still confused though that even if it is sheared, how come it will only run with one specific carburetor? All 2 of the 3 carbs were identical, the third had only minor differences.
 
  #4  
Old 01-15-13, 03:51 PM
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It looks like yours has a cranking ratchet, not a nut. Did you put a nut on in place of it?

I thought you were getting it to fire up on one carb a little, but barely. A flooding carb will add more gas to the fuel air mix and possibly help it run with late timing (sheared key). You said the carb that runs fine on one engine won't even start this one, right? I'm still thinking sheared key. Did you install a new plug?
 
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Old 01-15-13, 04:46 PM
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I did use the nut only to tighten the flywheel onto the shaft. I then put the starter clutch back in its place. Sorry for the confusion. I realize this whole thread is probably a little confusing!

You are correct, I did get it to fire on one carb. I got it running for maybe 30 seconds at a time with almost a full choke. But what you are saying makes sense. If I am still getting spark with a sheared key, the carb dumping too much gas into the engine might still get it to fire. Hence why the two good carbs aren't doing anything for it. Okay, I will have to check the key again then. I'll take the flywheel off this time to check it.

Do you think that putting in the electric ignition may have messed this up? Say if the unit is no good but is still producing a spark; just a weak spark. Or perhaps I didn't gap it correctly? Every source I have checked has said to place a business card between the flywheel and the magneto to set the gap. Thanks for the help!

I just had to log back on to edit this because I just remembered something. The electric starter on this machine has been shearing little bits of metal off the flywheel teeth. As soon as I noticed, I stopped using the starter. Do you think that a sheared key could cause the flywheel to have just enough play to make this happen?
 
  #6  
Old 01-15-13, 09:19 PM
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You have to get the clutch that tight. Tightening it with then nut doesn't do anything because you took the nut back off. You didn't put oil or grease on the shaft or flywheel bore did you?
 
  #7  
Old 01-16-13, 10:16 AM
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No I did not. And I did get the clutch that tight when I reinstalled it. I've done a lot of points on Briggs engines so I am fairly familiar with the process of disassembling and reassembling. I have never bypassed the points however, this was my first. Which is why I am thinking that the error would lie in the installation of that. But I still have to recheck the key. Which means taking the flywheel off. I checked it last week after reading that thread I posted and it looked fine, completely in tact. Of course maybe it did somehow shear and I can't tell because it is sandwiched in that small space.

But just to set the above straight, I did crank on the starter clutch and I did not apply any grease/oil anywhere near the shaft of the flywheel.
 
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Old 01-16-13, 06:35 PM
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Okay... Just trying to cover the bases. I still want to put reservations on the flywheel key, mainly because it's what I would check from here, even if I just saw it during the ignition conversion. How about a new plug... did you try that? If so, and the key is intact, then what about compression? I don't recall you mentioning that it is in acceptable range. Since your ignition is working, I doubt that the armature air gap is a problem, but you should have it gapped at .010". Line the flywheel magnets to the coil, put a business card between them if you don't have brass feeler gauges, and let the magnet pull the coil to it and tighten the screws, then roll the card out and it will be gapped properly. The shavings from the starter are most likely because of the wrong gear on the starter. It should have a nylon gear on it.
 
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Old 01-19-13, 08:34 AM
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Thank you Cheese. I appreciate all your input. I will check the key today and buy a new spark plug for it. If that does nothing, I will move on to compression. Again, thanks for the help! I'll post later to let you know how it went.
 
  #10  
Old 01-20-13, 01:11 PM
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Key is in tact and not sheared. Where should I go from here?
 
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Old 01-20-13, 03:28 PM
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How about the other stuff mentioned in my above post?
 
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Old 01-27-13, 11:30 AM
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Put it back together last week. Reset the gap anyways. Gave it a pull and it started. So I tried working the choke and throttle to see if I could get it running but nothing. Eventually it just died and wouldn't start when I pulled. The good news however is that it started with one of the good carbs. That hasn't happened before. I also put a newer spark plug on it (J19LM, same as the one that was on there).

I am going to try today putting the original carb on. The original carb has a jet with 4 holes in it and the 2 other carbs have a jet with only two holes in it. But now that I got it running with 2 of the 3 carbs I have, I might as well see if it'll run with the original.

Another added bit of info is that I have a Gilson Snowblower with the same engine on it. It is one year newer than the Bobcat but it at least has the same carb. So I could also try that carb.

Could you explain to me how to check the compression? Air blasts out of the spark plug hole when I take the plug out but I know there is a more accurate way of testing than that.
 
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Old 01-27-13, 04:44 PM
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Turn the engine backwards and when it comes to the compression stroke, give it a good spin and see if it has enough compression to bounce the flywheel back. If it hits the compression stroke and the flywheel just stops, then we need to investigate more. If it bounces back the other way, the compression should be ok.
 
  #14  
Old 02-01-13, 07:50 AM
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Did what you said and the flywheel did bounce back in the opposite direction.
 
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Old 02-01-13, 10:46 AM
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Sounds like the compression should be okay.
 
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Old 02-01-13, 12:22 PM
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Tried starting it today after buying a new E3 replacement spark plug. I got backfires more than puttering. Any idea as to why I keep getting the backfires? It looks like the carb is always too full of gas and the backfires seem to be coming from the exhaust.
 
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Old 02-01-13, 07:17 PM
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And this is with a carb that is verified to be good and will run fine on a different engine?
 
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Old 02-02-13, 09:00 AM
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Yes. The carb that is on it is from a Snowbird built in 1962. The Bob-cat was built in the late 70's, engine was built in 78. Like I said, there are minor differences in the carbs. The throttle assembly which is just a different linkage and then the jet gas nozzle inside the carb. The Bobcat's carb has a nozzle with 4 holes in it, the Snowbird carb has a nozzle with 2 holes in it. Both Snowbird carbs made the engine fire as I've said before. The Bobcat carb seems to be dead, I get nothing out of it.

But I'm thinking that maybe these minor carb differences are the cause of the issues. Snowbirds have a 6hp Briggs and the Bobcat has an 8hp. I do however have an 8hp Gilson that was built in 79 with a Briggs. Only one year newer than the Bobcat. Same engines so I will try the carb from the Gilson to see if it makes a difference at all.
 
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Old 02-02-13, 12:46 PM
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The Brigs

Just for laughs, what about the points & condenser the hinge for lack of a better term might need a drop of oil, and maybe a dab of grease on the point cam, or just a cleaning of the contacts, or new points and condenser. Popping isn't usually a fuel problem.
Sid
 
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Old 02-02-13, 12:58 PM
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Hey Sid. I replaced the points with an electric ignition module. So I have good strong clean spark.
 
  #21  
Old 02-02-13, 02:46 PM
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Yeah, I forgot what I read, sorry.
Sid
 
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Old 02-02-13, 02:56 PM
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No worries at all! If you think of anything else, let me know.
 
  #23  
Old 02-03-13, 06:31 AM
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Could a valve be hanging up when it gets to speed?
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  #24  
Old 02-17-13, 06:45 PM
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Late response to this but I tried to carb from the Gilson. Unfortunately, I could not get the carb apart to clean it because the jet or gas nozzle would not come out and it is only a brass screw. It didn't start. And the Gilson didn't start with the original carburetor from the Bobcat. So I'm thinking it is a carb issue.

I am looking at a brand new carb right now for $58. It is a lot but will be worth it if the carb is indeed the issue. What else should I check before buying the carb? Keeping in mind it did run with the carb from the 6hp SnowBird.
 
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Old 02-18-13, 06:14 AM
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The B&S

Not a bad price. At least for that money you will know for shure.
Sid
 
  #26  
Old 02-18-13, 10:21 AM
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Just a Thought......

This is really more of a question than an answer. Does anyone remember when some Briggs point engines had reverse polarity magnets on the flywheel? I know for years after the magnatron came out you could send your flywheel to B&S and they would re-polarize for no charge so it would work with the add on chip and later the magnatron ignition. The problems reverse magnets caused sound much like the problems with this engine. Just thought with this thing all over the place it might be a valid thought.

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Old 02-18-13, 12:40 PM
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I have thought it sounded like a carburetor issue from the beginning, but in the original post we were told that a properly adjusted good working carb was put on it and it still wouldn't run. I don't know what carbs were put on it, or how suitable they are for the engine though. I still think it's a carb problem. If you did put a working carb from the same series engine on it and it would run fine on one engine and not on this one, then I guess it's not the carb, but I'm not so sure about what has been done and what worked or didn't work now.

The magnet in the flywheel isn't the problem most likely, since the reverse polarity magnets were found on the cast iron engines only... if I recall correctly. This engine is aluminum, and it was running with a different carb albeit improperly.
 
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Old 02-18-13, 01:29 PM
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First carb used: Original carb from the machine. It was cleaned and put into an ultra sonic for deep cleaing. Never made the engine run.

Second carb: From a 6hp Snowbird built in 1962. Different from the original carb in that the jet/gas nozzle and bottom adjustment screw were slightly diff. sizes and style. Engine ran on this carb for about 30 seconds at a time on full choke.

Third carb: From my other 6hp Snowbird. Same exact machine as the previous, same exact carb as well. Engine ran for only about 10 or so seconds before not being able to run at all. Mostly got backfires from this carb (also got backfires from the previous carb)

Fourth carb: From an 8hp Gilson. One year newer than the Bobcat (1979). Same carb. However, this carb was fairly gummed up. The plan was to rebuild it but unfortunately I could not get it apart because the jet/gas nozzle screw would not come out. Carb went onto the machine as was and did not get the engine to fire.

I placed the Bobcat carb onto the Gilson and the Gilson did not fire up.

Flyhweel key not sheared, compression check was good. Valves and pistons moving freely as they should. New spark plug, clean gas tank, fuel line and removed old gas filter (straight gas line now, no filter). Gas comes out freely and cleanly. Carbs checked for gas each attempt and all were filled. Ignition coil/magneto from a used engine purchased on Ebay. Checked the spark with a spark checker and it is indeed getting good clean spark.
 
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Old 02-18-13, 06:58 PM
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Can you drip fuel into the carb and keep it running?

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Is it paranoia if they really are out to get you?
 
  #30  
Old 02-20-13, 11:04 AM
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Haven't tried that. I've noticed a lot of gas coming from the carb while it starts and stops, mainly from the choke. Although the carbs from the 6hp and 8hp briggs are the same size, I think they are somehow different internally and that is the cause of the crappy running with the 6hp carbs on the 8hp engine. I bought the new carb a few days ago. Should be here by Friday. Hopefully it all goes well and works because I heard that MA is getting another foot of snow this weekend.
 
  #31  
Old 03-11-13, 12:38 PM
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Couldn't get it to run with the brand new carb. It tried to and wanted to but didn't. I took the new carb off and put it on the Gilson. Started up first pull. So carburetor isn't the issue. Could it be spark? Maybe the electric ignition that I got for it off ebay was bad?
 
  #32  
Old 03-11-13, 05:43 PM
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Is it possible the coil is put on backward?? There is an inside & outside to these I believe.. Roger
 
  #33  
Old 03-13-13, 09:24 AM
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Nope. It can only mount one way, at least this style of coils
 
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Old 03-13-13, 10:02 AM
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The coil on these can be flipped over and installed upside down. Worth a look I guess, but I don't recall an upside down coil ever sparking at all.
 
  #35  
Old 03-16-13, 08:19 AM
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module

Hi, I've used a few of the electronic ignition modules, and had good luck on some but at least 1 where I had a good spark, but the engine just wouldn't run right. I finally fixed the original points and condenser and it ran fine. I don't know if it didn't spark at the right time or what, but if there's a way to go back to the points and condenser, it might be worth a try. Good luck- Steve
 
  #36  
Old 03-18-13, 09:29 AM
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I bypassed the original points because the plunger that sets the motion for the points condenser was stuck and looked melted. I couldn't get it out and I figured it would be easier to just bypass them completely and also the best way to save time. I could go back to the original points but I am not sure how I would fix the plunger.
 
  #37  
Old 04-22-13, 12:34 PM
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thought i was the only one with this problem. same deal with the carb,and same carb as in picture. rebuilt after soaking overnite,blown out and rebuilt. valves ground,lapped,and clearance set to specs. new coil,points and condenser. new plug w/strong blue spark. new gas and filter. flows good thru gas line. was leaking from around plug,so i used teflon tape to seal plug. still only wants to barely fire on full choke. will fire with starting fluid and open choke.
 
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