B/S 18hp Blowback through carb

MJ42N8SON · 06-12-2009, 05:54 PM

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

**octaneman** · 06-14-2009, 09:30 AM

Hi Mj42N8SON

Does it backfire through the carburetor or the exhaust ?

MJ42N8SON · 06-14-2009, 11:48 AM

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.

**octaneman** · 06-15-2009, 06:27 AM

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.

MJ42N8SON · 06-15-2009, 07:31 PM

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?

Zed101 · 06-15-2009, 07:45 PM

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 !@#$!#$# 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!

**octaneman** · 06-15-2009, 08:34 PM

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.

MJ42N8SON · 06-16-2009, 04:14 PM

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?

k2skier · 06-16-2009, 10:24 PM

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.

MJ42N8SON · 06-18-2009, 08:43 AM

What is the afterfire solenoid?

k2skier · 06-18-2009, 09:51 AM

Quote:

Originally Posted by MJ42N8SON

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.

06-12-2009, 05:54 PM	#1 (permalink)
MJ42N8SON Registered User Join Date: Jun 2009 Posts: 5 OS: windows xp	B/S 18hp Blowback through carb 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

06-14-2009, 09:30 AM	#2 (permalink)
octaneman Mentor Join Date: May 2009 Posts: 498 OS: WINXP	Re: B/S 18hp Blowback through carb Hi Mj42N8SON Does it backfire through the carburetor or the exhaust ?

06-14-2009, 11:48 AM	#3 (permalink)
MJ42N8SON Registered User Join Date: Jun 2009 Posts: 5 OS: windows xp	Re: B/S 18hp Blowback through carb 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.

06-15-2009, 06:27 AM	#4 (permalink)
octaneman Mentor Join Date: May 2009 Posts: 498 OS: WINXP	Re: B/S 18hp Blowback through carb 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.

06-15-2009, 07:31 PM	#5 (permalink)
MJ42N8SON Registered User Join Date: Jun 2009 Posts: 5 OS: windows xp	Re: B/S 18hp Blowback through carb 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?

06-15-2009, 07:45 PM	#6 (permalink)
Zed101 Registered User Join Date: Jun 2009 Posts: 39 OS: Win XP Prof, SP-3	Re: B/S 18hp Blowback through carb 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 !@#$!#$# 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!

06-15-2009, 08:34 PM	#7 (permalink)
octaneman Mentor Join Date: May 2009 Posts: 498 OS: WINXP	Re: B/S 18hp Blowback through carb 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. Last edited by octaneman; 06-15-2009 at 08:40 PM.

06-16-2009, 04:14 PM	#8 (permalink)
MJ42N8SON Registered User Join Date: Jun 2009 Posts: 5 OS: windows xp	Re: B/S 18hp Blowback through carb 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?

06-16-2009, 10:24 PM	#9 (permalink)
k2skier Registered User Join Date: Sep 2008 Location: Oregon Posts: 313 OS: XP Home-SP3 My System	Re: B/S 18hp Blowback through carb 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.

06-18-2009, 08:43 AM	#10 (permalink)
MJ42N8SON Registered User Join Date: Jun 2009 Posts: 5 OS: windows xp	Re: B/S 18hp Blowback through carb What is the afterfire solenoid?