Carb problem or electrical
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Cruiser
Joined: Jul 2010
Posts: 189
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Carb problem or electrical
I have a dead stock '97 Evo that I know is running too lean with the factory set-up.I have to leave the choke on for a long time to get it to warm up to proper idle.I just started getting a funny sort of backfire at 3000 rpm's.In lower gears it is more pronounced but happens in all gears at about 3000 rpms.Its not real loud but is definately there.It kind of feels like it is missing also.It is like a "pop-pop"and I feel a slight hesitation as it hits 3000. I assume it is the lean set-up,but wonder if it may be ignition related.Anybody got any ideas?Also,would resetting the idle mixture affect the mixture across the entire range,or do I have to re-jet the other circuits in the carb?I planned on leaving any carb adjustments until I change the pipes,but now think I have to at least do the idle mixture to get it a bit richer.
Road Warrior
Joined: May 2010
Posts: 1,382
Likes: 4
From: Kennewick, WA
I have a dead stock '97 Evo that I know is running too lean with the factory set-up.I have to leave the choke on for a long time to get it to warm up to proper idle.I just started getting a funny sort of backfire at 3000 rpm's.In lower gears it is more pronounced but happens in all gears at about 3000 rpms.Its not real loud but is definately there.It kind of feels like it is missing also.It is like a "pop-pop"and I feel a slight hesitation as it hits 3000. I assume it is the lean set-up,but wonder if it may be ignition related.Anybody got any ideas?Also,would resetting the idle mixture affect the mixture across the entire range,or do I have to re-jet the other circuits in the carb?I planned on leaving any carb adjustments until I change the pipes,but now think I have to at least do the idle mixture to get it a bit richer.
Just adjust the idle mixture screw until you get the maximum RPM out of it at idle and give it a try.
The choke being used too long indicates too lean of a pilot jet or whatever circuit they are called on your Harley. The hesitation in the midrange could be too lean in the needle or needle jet, try raising the needle first. Again my carb tuning experience is based on Mikunis and a few similar types, so just google your carb and you should be able to find diagrams and tuning recommendations.
Carb tuning is more throttle position related than engine RPMs. I used to put a piece of tape on the grip and another next to it on the housing with markings for 1/4, 1/2, 3/4 and full. I'd just check the problem against the throttle position to determine what jets were affecting the hesitation or bog.
Does the bike run okay higher than 3,000? If so your ignition is probably fine.
Outstanding HDF Member
Joined: Oct 2010
Posts: 2,706
Likes: 14
From: Near Frankenmuth, MI
Before you "tinker" with your carb and settings check for an intake leak. Remove air filter and use carb cleaner to spray the manifold behind the carb. Use the tiny tube to pinpoint the spray in the area of the intake. If the engine speed changes when spraying you have an intake leak. Replace seals and you could be back on the road in no time at all.
Start randomly adjusting the carb and you may have issues only a repair shop can straighten out.
Start randomly adjusting the carb and you may have issues only a repair shop can straighten out.
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