ok guys on my flht, i put together a small motor this year, its a 10.5 to 1 80 inch with screamin eagle heads, ev51 camshaft, and i just took off a heavily modified keihin cv, the problem im having is that between 55 and 65 in high gear, the bike is completely flat, so i had put the keihin together from parts i had, so i figured something was up with it. so i installed a brand new mikuni, and its just as flat, so with that being said, its standing off fuel like crazy in that rpm range too, so what gives any ideas how to correct it before i yank his cam out, thanks chad.

 

also running stock ignition, would a bad voes cause this ?

 

When I had VOES problems it made slow speed running a nightmare, but got better at normal road speeds. Stock ignition has a strange advance curve, to help keep noise down for emissions, so it could be with that cam it will give you problems, also your compression sounds high to me. What exhaust are you using?

 

The stock ignition could be your problem, the curve isnt't very aggressive. What happens if you back off on the throttle a little bit when this is happening??

 

im running a thunderheader, and yes 10.5 is high for a bagger, but with the bathtub chamber of the screamin eagle head, detonation isnt a problem. and mia, its weird, its like it takes more throttle position to get thru 50-65 and once above 65, its really nice and you can actually back off the throttle,

 

Have you tried adjusting the needle? If it was me I would run it at the flat spot for a few mins and do a plug chop....go from there.....

 

After I had put my evo back together with se heads, se 57 cam, mikuni carb and all the other bits. I was running stock ignition with se coil it had bad flat spot and top end felt like fuel starvation, changed the ignition system to single fire crane HI4e and what a difference.
I know people say dual fire and/or single fire makes no difference and have dyno tests to prove it.
If you do some searching on the web you will find info to do with wild cams, valve overlap, timing and single/dual fire ignition, it is in theory possible to have an issue with the wasted spark.

I believe that with wild cam you can experience problems, also as already stated the stock ignition was built around fuel economy and noise regulations, a good aftermarket ignition is built for performance/efficient burn.

I have tried the ignition in stock curve with VOS and race mode no VOS it is currently in race mode cant really tell any difference, need to get bike on a dyno to set up/test different settings.

Nothing to do with the issue you have but it’s also worth looking at is replacing your fuel tap with a high flow item, I had to.

 

After I had put my evo back together with se heads, se 57 cam, mikuni carb and all the other bits. I was running stock ignition with se coil it had bad flat spot and top end felt like fuel starvation, changed the ignition system to single fire crane HI4e and what a difference.
I know people say dual fire and/or single fire makes no difference and have dyno tests to prove it.
If you do some searching on the web you will find info to do with wild cams, valve overlap, timing and single/dual fire ignition, it is in theory possible to have an issue with the wasted spark.

I believe that with wild cam you can experience problems, also as already stated the stock ignition was built around fuel economy and noise regulations, a good aftermarket ignition is built for performance/efficient burn.

I have tried the ignition in stock curve with VOS and race mode no VOS it is currently in race mode cant really tell any difference, need to get bike on a dyno to set up/test different settings.

Nothing to do with the issue you have but it’s also worth looking at is replacing your fuel tap with a high flow item, I had to.

 

When we talked I forgot to ask what pipes are you running? If they are open drag pipes you could try adding some back pressure by drilling the ends of the pipes and putting a 1/4"X1 1/2" bolt with a 1" stack of flat washers on it. It seems that the complete system is mismatched in that RPM range. You probably have some reversion that is leaning out the engine just before it gets "up on the cam" cuasing a slight lean condition that the stock ignition has problems firing efficiently. Keep us posted and don't be afraid to call again if you need more help.
John