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B&S engine/carb issues - lack of power

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#1 mark843 OFFLINE  



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Posted June 21, 2017 - 10:42 AM

I have a B&S engine model number 350777-1137-E1 on my JD LX288 and have been running into some issues. I was mowing the lawn last week and the mower slowed down and had a lack of power. I stopped mowing and then took the air cleaner off the engine, and it immediately started to run better. I then noticed that there was some misting gas coming back out of the carb. I also noticed the air filter was wet with oil and gas.


I pulled the carb and everything looked OK but cleaned it the best I could with carb cleaner and air. I did not see any dirt or restrictions in the small holes.I checked the float and there did not seem like any gas was in the float and it felt light. The needle also seemed to look good. when the needle is closed, I could not blow any air through where the fuel line would connect, but with the needle open there did not seem like any restrictions and I could blow air through it just fine.


I adjusted the vales to .005 and also checked compression, which is good, and then disconnected the fuel pump and ran the engine with a few squirts of starter fluid. I did not see any starter fluid come back out of the intake, so this should eliminate the engine being a problem and only point to the carb.


After cleaning the carb and putting it back together (I did not make any adjustments to the settings while I checked the float and needle), I started the mower without the air cleaner on, but it would now only run with it half to three quarter choked. I sprayed carb cleaner all around the outside of the card suspecting an air leak, but their was not a surge in RPMs. This should eliminate a too lean condition and air getting in somewhere and needing to be choked.


At this point I thought I should spend the $150 and just get a carb rebuild kit as I already have a new air filter. I pulled the fuel line again to run the engine to burn up the remaining gas in the bowl. When I did this, I had the engine choked once again, but after about 30 seconds to a minute the engine smoothed out and I let go of the choke and it ran just fine without the choke for another 3 minutes or so until all the gas was gone and the engine stopped.


At this point I am a bit confused. It seems like I am seeing both a lean condition needing to keep the engine choked, but a possible flooding condition with too much gas after I disconnected the fuel pump.


Before I spend $150 on a rebuild kit, would this seem to point to the carb needing to be rebuild, or a potential fuel delivery issue? When I had the fuel line disconnected from the carb and cranked the engine, a bunch of gas did come out ans spilled everywhere. 

#2 secondtry OFFLINE  

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Posted June 21, 2017 - 11:46 AM

  Buying parts before diagnosing the problem is a sure way to waste money. Unfortunately most mechanics today use the shotgun technique. If you replace every thing you are bound to replace the defective part. Have you looked in the manuals section for trouble shooting information. Pictures of the carb might help to jog someones memory. I have a carb on an Onan  that splatters gas all over with the air cleaner off but it runs perfectly. I have seen carbs on Briggs that had a solid brass needle and a rubber seat. blowing air through the fuel inlet on that type of carb can dislodge the seat or if the needle is out blow it across the room. Starter fluid is much more volatile than gas so seeing liquid for long  after spraying would be rare to unlikely and give little valuable information. How the carb handles gas is what is important. The engine running just fine without the choke would seem to indicate the idle circuit of the carb being ok but it says absolutely nothing about what the engine might do under load. You say that when you had the fuel line disconnected from the carb and cranked the engine a bunch of gas did come out and spill everywhere. You didn't indicate where the gas came out of. Much more and more specific information is required to to diagnose your problem accurately. Don  

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#3 dtsh OFFLINE  

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Posted June 21, 2017 - 12:40 PM

By the description of it puffing back out the carb and the air filter being wet, my first guess would be one of your intake valves not closing properly; however, that you said it holds compression suggests otherwise. I agree with secondtry and would not yet buy the carb kit, especially considering it's cost.


Were it mine, I would double check the compression and gap on the intake valves, possibly check to see if there's any slop in the flywheel and check to make sure the magneto hasn't somehow come loose causing the timing to be off. I'd also look at the breather for damage, assuming it has one (spec I'm looking at suggests it does not).


Failing all that, perhaps check the intake valve springs. It sounds to me like some compression is escaping through the intake; be that from timing, valve gap, weak spring causing float, sticking valve, or something else.

Edited by dtsh, June 21, 2017 - 12:51 PM.

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#4 stiemmy OFFLINE  

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Posted June 21, 2017 - 12:48 PM

Check to be sure the flywheel key is not bent, or partially sheered. This will cause these exact symptoms.
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#5 buckhvnter3 OFFLINE  

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Posted June 21, 2017 - 01:12 PM

I have to agree with all 3 replies so far. To save money I'd eliminate all other problems that could be present with what you are describing. Have you done a leak down test? I have seen fuel pump diaphragms fail. I have the procedure on testing them but you'd need a mityvac or a way of putting pressure and then vacuum to it and a gauge. It's saved me a lot of time in diagnosing fuel problems. Also found that an ultrasonic cleaner works magic to carburetors. I bought one from harbor freight for $60 a couple years back and don't have anything bad to say about it except where it was made. Where I work we use one but it's about 3K. Too much for my wallet. Harbor Freight one just takes a little longer but great results. There should be a breather assy. in the valley of the cylinders. You could make sure that it is opening and closing. Starter fluid is very volatile and like secondtry said it would be hard to find that on anything the engine didn't burn.

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