carb or ignition issue
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Cruiser
Joined: Jul 2010
Posts: 189
Likes: 0
carb or ignition issue
Posted this on the Dyna forum,got no replies so thought I'd try here.My'97 Evo has a backfire or ignition miss at 3000 rpm's.I know the stock set-up is too lean,I have to leave the choke on forever to warm up to idle.Could this cause a low "pop-pop" along with a feeling that it is hesitating.It only happens at 3000 in any gear.It is more pronounced in the lower gears,but happens in all.Could it be a problem with the ignition or timing?Also,if I re-adjust the idle mixture to get it a bit richer,will that affect the mixture at medium and higher throttle positions?
Road Captain
Joined: Sep 2010
Posts: 574
Likes: 3
From: AB Canada
A quick way to find out if it's too lean is to pull the enrichener out at the RPM you are feeling a miss, if it cleans up, then you know it's too lean. Fattening up the idle to get rid of a high RPM miss may help a bit but may not be the best way as you'll be too rich at idle, a re-jet is most likely the answer. What mods have you done to the bike? Lots of info on the CV carb out there...
http://www.harley-performance.com/ha...arburetor.html
Here is one link of many.
http://www.harley-performance.com/ha...arburetor.html
Here is one link of many.
Road Captain
Joined: Mar 2008
Posts: 601
Likes: 6
From: Aruba
3000 RPM is about where your idle circuit is removed from the equation and you are running solely on your pilot jet. You state that you know you are running lean. Fix that problem first and then trouble shoot the other. Could be that this will solve your entire problem. Read the carb links. Also google Harley rejet carburetor and the like. Tons of information there. Jets are about $2.50 each. A kit will be around $50 give or take depending on who's you buy and may not have the jet you need, but it will give you a needle with a richer profile and possibly a power tube or such.
Running your bike lean is not good for it. It blues your exhaust which will eventually rust, your bike runs hot, your pistons are really hot, and on and on.
Running your bike lean is not good for it. It blues your exhaust which will eventually rust, your bike runs hot, your pistons are really hot, and on and on.
Thread Starter
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Cruiser
Joined: Jul 2010
Posts: 189
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The bike is dead stock,another clue that the idle mixture is too lean.Wasnt sure if the idle circuit was still active at that rpm,thanks for that 95yj.So I guess from these answers that you guys agree it is more likely a mixture problem as opposed to an ignition or coil problem?Thanks for the replies guys.
Tourer
Joined: Sep 2010
Posts: 471
Likes: 9
From: Far NorCal
My first question is: How long has this been happening?
Did you just acquire the bike? Gas flesh?
If not an intake leak, then sort the carb, if no help, then you got other issues. But my money is on a mid jet, needle and mix adjust or plugged jets.
Good luck and Keep us posted
Recent gas problem:
Since this new corn gas additive we have to be aware of gas turning to varnish in 2-3 months and will plug a jet or two. I have used the same lawn mower for years and never dump the gas, but last week with approx 2 mo old gas had turned to varnish and plugged my mower's carb. It was so bad it had the intake line almost plugged up, besides the float bowl. I couldn't wait to finish the lawns and go run my Blackgirl, since I haven't ridden in 3-4 weeks (even older gas) due to rain up here and sickness. I was worried, but it ran okay!
I liked the old oil connected Pres, not corn connected! No offense to you corn growers, just wanting good gas!
Did you just acquire the bike? Gas flesh?
If not an intake leak, then sort the carb, if no help, then you got other issues. But my money is on a mid jet, needle and mix adjust or plugged jets.
Good luck and Keep us posted
Recent gas problem:
Since this new corn gas additive we have to be aware of gas turning to varnish in 2-3 months and will plug a jet or two. I have used the same lawn mower for years and never dump the gas, but last week with approx 2 mo old gas had turned to varnish and plugged my mower's carb. It was so bad it had the intake line almost plugged up, besides the float bowl. I couldn't wait to finish the lawns and go run my Blackgirl, since I haven't ridden in 3-4 weeks (even older gas) due to rain up here and sickness. I was worried, but it ran okay!
I liked the old oil connected Pres, not corn connected! No offense to you corn growers, just wanting good gas!
Elite HDF Member
Joined: Sep 2007
Posts: 4,468
Likes: 12
From: Bluffton, South Carolina
The idle circuit on a CV carb does not stop supplying fuel at any RPM except 0 RPM's. It supplies about 10% of the mixture at full throttle. However an engine depends on the following circuits, Idle, Intermediate, High speed. These may be called other names depending on who you are talking to. On a CV the idle controls the mixture until about 2500 RPM's the the intermediate and high speed take over.
You might want to try a needle from a 1988 sportster. Also open you carb and check for debris in the circuits and set the idle air screw at 2 1/2-3 turns out, do not drill out the slide or change the stock spring. This solves about 99% of the problems with most carbs.
If this doesn't solve your problem then you may have a loose connection somewhere that doesn't like the vibrations at that particular RPM's. However your efforts will still give you a functioning carb. Hope thsi helps.
You might want to try a needle from a 1988 sportster. Also open you carb and check for debris in the circuits and set the idle air screw at 2 1/2-3 turns out, do not drill out the slide or change the stock spring. This solves about 99% of the problems with most carbs.
If this doesn't solve your problem then you may have a loose connection somewhere that doesn't like the vibrations at that particular RPM's. However your efforts will still give you a functioning carb. Hope thsi helps.
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