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97 Evo acceleration issues

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zman700

Member
Thanks for any and all help, I'm getting frustrated.

I'm having issues with my 97 Fatboy Evo, when cruising at 1/8-1/4 throttle in any gear and roll-on the throttle, it hesitates/stumbles, and then goes. It feels as if it is running at 10,000ft, stumbling because of not enough air/too rich. Plugs look good, it has been dyno'd and charts good. It has the Dynojet kit in with 170 main, dynojet needle, 42 pilot. I tried using the stock needle but was very lean. It also has an EV27 cam, V&H Bigshots, and the Ness Big sucker. Can't find any carb leaks. The accelerator pump is good.

I think it is running too rich when it rolls on. I ride at 4500ft on up usually. What needle is everyone using? And slow jet? Would it help to add a better ignition module?

Thanks!
 
There had to be a time when the bike ran Great and did not have this issue. How long ago was that and did you do anything to the bike since that time. Has the bike just come out of storage or not being used for awhile?

When you say the accelerator pump is "good", what did you check that now makes you say it is good. There is No play in the linkage which would give the squirt some propagation delay?
How does the bike come off idle after sitting at a red light.
 
It ran ok when I bought it stock, a year ago. It is running good with the changes, just can't get rid of the stumble. Thinking it is because of the Dyno needle, but could easily be wrong. The stumble is worse since the cam, though.

I changed the diaphram in the pump, and it pumps a good stream. No play. Runs great from stop to full, only stumbles when cruising and I then roll-on to accelerate.

Thanks.
 
I personally think you would be better sticking with the stock jets and emulsifier but with a 45 or 46 for the slow jet and perhaps a size or 2 bigger than the original main jet
it can be a bit of trial and error getting the jetting good and sometimes it helps to put a few washers to raise the slide needle a wee bit and that will get it on the taper sooner
but the 1/8 to 1/4 throttle is the place where the slow jet is providing the main flow of fuel and a 42 is the stock size if you have air coming in faster and going out faster it will not provide sufficient fuel for the airflow

Brian
 
fin_676 said:
I personally think you would be better sticking with the stock jets and emulsifier but with a 45 or 46 for the slow jet and perhaps a size or 2 bigger than the original main jet
it can be a bit of trial and error getting the jetting good and sometimes it helps to put a few washers to raise the slide needle a wee bit and that will get it on the taper sooner
but the 1/8 to 1/4 throttle is the place where the slow jet is providing the main flow of fuel and a 42 is the stock size if you have air coming in faster and going out faster it will not provide sufficient fuel for the airflow

Brian
Click to expand...

Does this have a VOE switch and is it working?
 
zman700 said:
It ran ok when I bought it stock, a year ago. It is running good with the changes, just can't get rid of the stumble. Thinking it is because of the Dyno needle, but could easily be wrong. The stumble is worse since the cam, though.
Click to expand...

Have you made any jet or needle changes since you put the cam in? Usually, increasing cam duration and overlap will require a richer mixture. Also, you say the plugs look good, too rich would leave the plugs dark and sooty.

I'm thinking it is too lean. I would go up 1 or 2 sizes on the main jet. See if that makes it better or worse. If it is better, go up one or two more on the main, if it is worse go back down 3 on the main jet.

Bob
 
I have put the stock needle back in and it was too lean. I think I will try the stock needle with a 45 slow jet. My wife's 98 runs great with almost the same setup, except she has a SE Ignition Module. Maybe that's what I need to do.

I will also check the VOES, I just read on it and it sounds that checking that would be a good thing to do.

I just keep thinking it is rich for a second when I roll on since it feels the same as being at high altitude with no air.

Thanks all!!
 
I've got a 93 fatboy evo with close to the same setup, I tried the 170 jet first was acting almost the same as your's, I switched to a 165 and that seems to have fixed me right up, my plugs were looking about the same too, but I still went leaner and it runs great now, I ride at around 3700 ft., runs around 40mpg.
 
Thanks to all for the help and advise that was given. I worked through all and finally borrowed a vacuum tester and discovered the vacuum hoses weren't connected tight enough. I got new hoses and went for a ride yesterday and it run great!

Thanks again!

Rich
 
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