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Bolens 800 - High Rev Misfire Issues


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#1 MichaelBeck OFFLINE  

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Posted April 23, 2015 - 04:08 PM

My S8D will idle well however in the upper rev range to full throttle it has a minor misfire, just enough to seem like a surging engine however it is not that. It also requires petrol tipped down the air intake to start but starts on its own after that satisfactorily.

 

What I have done to date on this motor, not all to cure this problem just a list of work: 

 

New Spark Plug - Have tried with a 2nd new plug as well.

New Points and condenser, gapped correctly

Cleaned gas tank and replaced fuel line

Had carb professionally rebuilt - new gaskets, needles, float etc.

New Air Filter

Fresh SAE30 oil

Removed cowling and cleaned fins

Have verified correct valve lash and movement.

 

It will idle happily all day long, perfectly smooth, however under load and predominantly at throttle it putters around no problem but has a steady misfire.

 

Any help much appreciated, have exhausted my expertise on it.

 

Thank You



#2 propane1 ONLINE  

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Posted April 23, 2015 - 04:31 PM

I have no idea what an S8D is, but sounds like adjustment on the carb, and check float setting. It maybe set to low. I would also check your fuel filter, plus the vent on your fuel tank to make sure it is vented to allow fuel to flow. Just some ideas, Noel

Oh, welcome to GTTalk, lots of smart people here to help you out.

Edited by propane1, April 23, 2015 - 04:33 PM.


#3 MichaelBeck OFFLINE  

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Posted April 23, 2015 - 04:41 PM

Thanks for your input Noel - S8D is the engine model - it is a Wisconsin S8D.

It is not a mixture issue - I can do anything with the mixture screw and the problem remains. Tank venting correctly.


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#4 propane1 ONLINE  

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Posted April 23, 2015 - 04:47 PM

Ok, thinking..................... Noel

#5 propane1 ONLINE  

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Posted April 23, 2015 - 04:50 PM

Make sure you have the correct spark plug, ran into that one time. Motor would run , but not correctly. Put proper plug in and worked great. Noel.

Now that I think of that, it happened to me twice.

#6 MichaelBeck OFFLINE  

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Posted April 23, 2015 - 05:01 PM

Spark Plug is a NGK AB6 should be a direct swap for the Champion 16J as spec'd in original manual, NGK Website showed this as the match.


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#7 propane1 ONLINE  

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Posted April 23, 2015 - 05:05 PM

Ok, thinking again............. Noel

#8 Bolens 1000 OFFLINE  

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Posted April 23, 2015 - 05:11 PM

I would always use a Champion in these engines , but thats just me

 

Here's something else to consider assuming the guy who rebuilt your carb did a good job.

 

1) Possible wrong main jet (There are two that look the same but are not) People often get these confused when ordering.

 

2) Warped Carburetor, After years of people taking these apart and tightening them too tight these are known for developing a warp in the center of the bowl, As an easy fix I use a thin strip of JB weld across the warped area , having the JB weld thin all you have to do is run it on the wire wheel a few times to take it off.

The warped carb will cause sporadic running especially at higher RPM's


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#9 MichaelBeck OFFLINE  

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Posted April 23, 2015 - 05:16 PM

Champions are much harder and far more expensive to source here in NZ - I am confident in the work of the carb shop, they machined all the surfaces to get a perfect fit. They do a lot of high end restoration (Vintage Ferraris etc) so I am fairly sure they have this one right. I wish we could buy JBWeld here, carbs aside it would be handy to have.  

What about the flywheel key- how likely is that to have sheared?



#10 Bolens 1000 OFFLINE  

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Posted April 23, 2015 - 05:22 PM

If you want to pay the shipping from USPS I'll gladly sell and ship you some champions and JB weld :thumbs:

 

 

Is your engine running on battery ignition or magneto ignition behind the flywheel?

Chances are very slim the key is sheared they are very heavy duty!



#11 MichaelBeck OFFLINE  

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Posted April 23, 2015 - 05:32 PM

Yes Please - email me  It is the magneto ignition behind the flywheel, Although I did add a battery starter motor but it is a standalone circuit from the ignition circuit.


Edited by Bolens 1000, April 23, 2015 - 05:44 PM.
removed e-mail so spam bots dont get it


#12 propane1 ONLINE  

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Posted April 23, 2015 - 05:35 PM

I doubt it would be a sheared key. It would not run at any speed very well or not run at all. Noel

#13 MichaelBeck OFFLINE  

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Posted April 23, 2015 - 05:35 PM

The other though I had is this - although the line is new and the tank has no obstructions - the flow out the end at carb inlet height isn't as great as I would like, I wonder at throttle with the increased fuel demands it is just not getting enough gas - almost enough but just not quite? Thoughts on that theory gentleman?



#14 propane1 ONLINE  

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Posted April 23, 2015 - 05:37 PM

The magneto may be bad. When they get hot after running for a bit they can act up. Noel.

#15 propane1 ONLINE  

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Posted April 23, 2015 - 05:38 PM

Any pictures. ??? Noel




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