# B/S 18hp Blowback through carb



## MJ42N8SON (Jun 12, 2009)

I have read through the forums and have cleaned the carb, took off and cleaned, checked the Flywheel key. I have spark (new Spark plug). It runs fine initially, but approximately 10 minutes later, it starts with backfiring. I also put on a new fuel filter, and replaced the gas. Model is 31D177, Type is 0235EI and code is 92D. This thing is kicking my butt and I have been working on it off and on for two weeks. Any other suggestions would be appreciated.
Thanks, MJ


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## octaneman (May 13, 2009)

Hi Mj42N8SON

Does it backfire through the carburetor or the exhaust ?


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## MJ42N8SON (Jun 12, 2009)

It's throught the carb. I do know the muffler needs replaced. But it's like it runs great for ten minutes or so, then it wants to start "blowing back through" the carb, and then it starts cutting in and out.


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## octaneman (May 13, 2009)

The timing is slightly advanced, check the flywheel key it maybe partially sheared off. A broken or partially sheared key will make the engine buck, kicks back, backfire.
Replace the key.


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## MJ42N8SON (Jun 12, 2009)

I removed the flywheel. No problem there. The key was in it's original condition. Could it possibly be the "ignition coil"? Maybe it's working, just not correctly?


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## Zed101 (Jun 9, 2009)

Is it possible that the cam gear/chain or method of driving the cam shaft is worn and maybe a bit of stiff until warmed up and gets some oil to make it loose and float around easier?
My reasoning is linked to my 69 chev v8 that had a nylon coating on the cam gears. It wore down quite a bit and sometimes would jump a tooth. When it did all [email protected]#$!#$# would break loose! Didn't want to run, backfired, hard to start and then all of a sudden would slip back into proper place and run quite well! (Now have a steel double row chain and gears) No more problems!
Just a thought!


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## octaneman (May 13, 2009)

If the ignition coil is suspect then the only way to verify it is by using a spark tester to visually see the spark's intensity, length, strength, and duration. Readings will have to be taken with an ohm meter when the engine is dead cold and then hot to see if the spark is intermittent. Since the flywheel key is ok and nothing is out of place, spin the flywheel and look if there is any evidence of binding, scoring, governor misalignment, or metal to metal contact. Check the air gap and see if it has shifted. if everything checks out, look to the carburetor choke and see if it's working properly. If it's the diaphragm type, the diaphragm sometimes gets stiff and gas leaks into the automatic choke.


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## MJ42N8SON (Jun 12, 2009)

If I choke it slightly it seems to run like it should until a load is put on it. Once a load is put on it, then it begins to start blowing back through the carb. I have cleaned thae carb out pretty good. It is a butterfly choke. ANy suggestions?


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## k2skier (Sep 30, 2008)

Check valve clearance when it's warm and acting up. If the intake valve doesn't fully close it will cause all sorts of running problems.
I'm assuming it's an OHV V-twin Intek. 
Also make sure it has good voltage to the afterfire solenoid when it craps out.


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## MJ42N8SON (Jun 12, 2009)

What is the afterfire solenoid?


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## k2skier (Sep 30, 2008)

MJ42N8SON said:


> What is the afterfire solenoid?


It's the part that goes into the bottom of the carb with 2 wires connected to it, a cylinder shaped item about 1" across and about an inch long, it also is the float bowl nut.


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## mstpops (Oct 21, 2009)

hi there k2skier make sure you set the valves @ 1/4 inch past tdc on power stroke try 0.003" inlet and 0.005 " exhaust also try a leak down test - @ tdc compression stroke - air escaping from inlet valve indicates - worn or burnt valve and or seat letting mixture blow back when it should be trapped in combustion chamber, air excaping from ex valve indicates same thing as inlet valve - check inside your air cleaner if it looks like its slightly wet with a light petrol / oil mix - possible blown hd gasket between cyl and push rod tunnel 
if this unit is a ohv model single cyl model they are famous for it - make sure push rods are not bent push rods are alloy ( btm one ) for inlet and steel (top one ) for exhaust also check for cyl head flatness - 

have a look it may help cheers mstpops


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