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Engine still surging


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#1 BrokenTractor OFFLINE  

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Posted November 21, 2017 - 04:30 PM

Hello,

 

I put a new Nikki carb on a B&S 14.5HP OHV engine and it still surges. It also backfires thru the carb about once per second. If I hold the choke flap 90% closed it runs smoother but still backfires say every 5 to 10 seconds. I have the fuel/ air mixture screw almost all the way CW, as if there is no more turning it CW. As I recall all the way CW pushes a small needle into a hole to restrict air flow. I think this is correct?

 

I just adjusted the intake valve to .005 and the exhaust to .007 before I ran it. The only other thing is I have the air filter assembly completely off, so basically you can see right into the carb. Not sure if this is adding more air to the problem or not?

 

I don't know what else to do with checks or adjustments. Does anyone have any ideas on this?

 

Thanks,

BT

PS I have about a 10 second video of it running would this help to see it?



#2 larrybl ONLINE  

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Posted November 21, 2017 - 04:59 PM

The back-firing suggests a damaged or worn fly wheel key. I had one do that, and even the key looked OK, but the fix was to replace the key.


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#3 DH1 ONLINE  

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Posted November 21, 2017 - 06:02 PM

I think you need to turn the mixture screw CCW to increase the fuel flow, richen up the mixture. Sounds like you got it too lean.



#4 BrokenTractor OFFLINE  

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Posted November 21, 2017 - 07:48 PM

I think you need to turn the mixture screw CCW to increase the fuel flow, richen up the mixture. Sounds like you got it too lean.

Electric tractors,

 

When I did that it seems to want to stall out. 



#5 EricFromPa ONLINE  

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Posted November 21, 2017 - 07:59 PM

It's not very common on an OHV Briggs for the flywheel key to sheer but that's what it sound like.  Doesn't have to be completely sheered to throw the timing off. Even a slight dent will throw it off.  I had 1 here with a cracked flywheel at the keyway. Stator magnets came loose and busted up the stator and flywheel. 


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#6 jms180 ONLINE  

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Posted November 21, 2017 - 10:34 PM

if  the engine has a lot of hours on it the valves may not be closing complete due to build up or worn seat.


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#7 karel OFFLINE  

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Posted November 22, 2017 - 05:31 AM

I think Larrybl has the right idea. I would start with the flywheel key. I've had that flywheel key throw your timing off, back fire flame thrower with out and air cleaner on thing! Singe your face off Rick!


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#8 BrokenTractor OFFLINE  

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Posted November 22, 2017 - 08:54 AM

Karel I did have a minor flamethrower effect and will do as Larry suggests when the weather clears. This engine is so close to running right.

 

One thing though when I do close the choke 90% it almost runs right. So the question is, "If you close the choke 90% and it almost runs right can the problem still be the flywheel key"?

 

Also in my travels I found this:

 

http://outdoorpoweri...lywheel_key.asp

 

Thanks,

BT


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#9 BrokenTractor OFFLINE  

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Posted November 23, 2017 - 09:56 AM

The back-firing suggests a damaged or worn fly wheel key. I had one do that, and even the key looked OK, but the fix was to replace the key.

Hi Larry thanks for this tip, I have not had a chance to work on the engine since your post. However this makes alot of sense. For the last 7 months I have resigned myself to using starting fluid to get the engine to start. Although you did not mention it ( because I never did ) the whining noise during start is also a symptom I have after doing some further reading. My solution was to use starting fluid directly sprayed into the carb, not knowing about this flywheel key being related. Ironically for 6.5 months it did run well after a difficult start each time. I am hoping your are correct here, otherwise I have no clue where to look next.

 

Thanks again,

Jim  






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