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Misfiring at idle when hot, ethanol problem maybe?

  • Thread starter Thread starter gearhead13
  • Start date Start date
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gearhead13

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My bike has had an intermittent issue with misfiring at idle when warmed up, seems to be only in the warmer months. I have had the carbs off numerous times cleaning and adjusting them as well as syncing them.
Lately I have been putting in cheaper gas with the 10% ethanol and now it is doing its misfire, could the ethanol be doing this? can I run a stabilizer to help, or do I just need to buck up and buy the 94 octane with no ethanol? I am thinking of draining the gas and filling it with non ethanol, but is there an additive I could use to help this problem?
 
I have not noticed any problems with the way my bike runs, whether the bike is cold or hot, nor whether the weather is cold or hot. I have no reason to suspect ethanol.

You should know that ethanol has fewer BTUs per gallon than gasoline, so a mixture (typically 10%) that contains ethanol will require just a bit more fuel to get the same energy. Yes, this translates to fewer miles per gallon, but it also means that you might need to adjust your jetting to make sure you are getting enough fuel.

Since you don't mention the bike in question, I am presuming this is concerning the only bike in your signature. I don't know what carbs are on that bike, nor what the stock jetting might be. However, carburetion basics remain the same, so I would not think that you need to change the pilot jet size, only the number of turns on the mixture screws. The needle might need to be raised either half a notch or a full notch, and maybe increase the main jets by one size.

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Some other issues may be things such as timing, ignition, and sometimes coils will act up a little before they go completely south especially once they get heated up a bit. Octane used may also play a role.
 
We've had ethanol in the gas around here forever - when I'm in wisconsin I can find pure gasoline - never noticed much difference though. Same with my boat.... so it's probably not the culprit.
 
I drained the tank today and filled it with non ethanol gas and rode it 120km, same problem, I cant tell if its running on 2 or 3 cylinders, but it sounds like crap, irritating and embarrasing. Plan to take the carbs off tomorrow, clean and adjust them. I have dyna coils, coil relay mod on it so I doubt its ignition related. Strange how this problem only starts when it gets warmer out and only when the bike heats up.
 
Sounds somewhat similar to a problem i had with a GS1000.
After a 15 minute ride 2 cylinders would cut out. Replaced the offending stock coil and it solved the problem.
Something about heat expanding the wiring in/around the coil.
 
It sounds like an electrical issue, no spark. Low voltage at coils or bad coils, bad connections somewhere.
 
Gaerhead..start it from cold and let it idle for maybe 2 minutes and shut it off. Then hold the back of your hand "close" to each header right at the top bend and feel how hot each one is. If one is way cooler than another then you probably have a carb clogged problem. Etiher clogged somewhere or the sync is off a little.

1and 4 should be on same coil and 2 and 3 on then other. So..If 1 is real hot and 4 isnt then its a carb problem. If it was a coil problem it would stand to reason the BOTH 1 and 4 wold be cool because they both use the same coil to fire...follow me here??? Same thing applies for 2 and 3 cylinders.
 
Thanks for all the ideas guys!
I went to tear the carbs off yesterday, pulled the tank off and went to take the throttle and choke lines off and noticed that one of the vacuum caps on the carb tops was missing:p, must have happened when I had it apart to set valve lash, as the cap was nowhere to be seen. Pulled the carbs anyway, checked the pilots for blockage and set the mixture screws 1/2 turn richer.
These little caps go missing quite often. I was thinking of using zip ties on them, but they have to come off for syncing.
Put it back together and went for a ride and it idles nice now at about 12-1 instead of 14-1. ;)
Sure miss my GS some times where you can set idle mixture easily. On this thing you have to pull the carbs off just to adjust them.
 
I run E-10 gasoline in all of my bikes, and have never had a carburetor problem.
 
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