ok so I have this weird rpm issue. When I ride the bike a feel a little pulse or what seems to be a miss, real slight at about 3500 rpm so today I held it steady in nuetral at this rpm and sure enough it would ever 1 to 2 seconds drop 300 rpms or so then 1 sec or so later pop back up to 3500 and it would continue doing this as long as I held it there. I have tried all sorts of different jetting but no matter which direction I go the problem still is there. My bike is stock except for a BMC air filter. I have a dynojet kit, stock mains, needles on the sixth slot 45 pilots idle screws 2 turns out. Other than the random up and down it pulls real well under harder acceleration just bumps when riding in traffic.

 

I doubt it is the jetting.

Were it my bike I'd turn out the pilot screws to 2.5 turns which is the advice of both Honda and Dynojet, and I'd scrap the BMC air filter for the Honda OEM filter. Do those 2 things and I'd bet it runs fine.

Also realize throttle position for 3500 rpm in neutral is different than throttle position in gear on the road. Also 3500 rpm will be a different throttle position in each gear.

 

Are the carbs in balance?

 

yeah I just balanced them the other day to check if that would solve it. At 2 1/2 turns it was too rich and wanted to die, also fouled my plugs at 2 turns it idles really well. It does the stumble in both nuetral and in the gears doesn't matter, although at 60 + miles an hour you can't feel it anymore. I still need to check my spark plug gap, the shop fubared my bike a while back and I am still trying to sort all the issues out.

 

Suit yourself. The stock bike runs pretty well with 2 and 1/2 turns out on the pilot screws with the OEM air filter. If I installed an after market air filter and it ran rich, meaning LESS air flow with the aftermarket filter, I'd think about losing the aftermarket filter.

 

well Im just stating what it seemed like to me, I may try 2 1/2 turns again considering it was out of ballance before and that may have been what made it run poorly at 2 1/2 turns out. I will try it again. Also I have been running the BMC air filter since I owned the bike and it never used to do this. I would like to keep using it considering the cost of replacing a stock one vs cleaning the BMC. So I take you are leaning on the fact my bike has a lean stumble which can be fixed by a richer idle screw setting?

 

I just don't see how you could be running rich at 2.5 turns out with everything stock except the filter, unless the filter is more restrictive than the stock one.

I tried tuning my bike to the BMC race filter when I put my cans on and couldn't get it to run right. The idle was eratic, when I'd rev it in neutral it would hesitate and hunt, all fluffy and weird. Same or similar to what you are describing.

Ran fine over 4000 rpm under load.

I think it had more to do with flow characteristics than rich or lean, but when I went back to the stock filter I got it running better than ever.

Other folks on the forum say thay cured the low rpm weirdness with aftermarket filters by going to #48 pilot jets, which I didn't try, but that argues for lean beforehand, not rich.

If you could borrow another VTR riders air filter for a ten minute ride it might tell you something. I just know folks who try to tune the VTR to the K&N or BMC filters seem to have a lot more trouble getting it right than folks who stay with the stock filter.

 

I agree on the filter reasoning, I will borrow a filter and see as well. Just seems strange I don't remeber it doing this a yr ago I have never had a stock filter in it for very long. I did try one a while back to fix a different problem turned out my coils were bad. But since I put new coils in it I have't tried a stock filter to see if it will fix this problem though, so between a stock filter and adjusting the mix screws I have a few things to try thanks, I will let you know how it goes.

 

Well as an update here, turns out the shop I took it too screwed up my cam timing. This weekend I put apes on and messed up the front cylinder so I had to retime the cams up front and now my bike is running alot better than before. My guess is when the checked my vavles and replaced a shim up there some careless mechaninc had it one tooth off. Its not like it was running horrible just nueterd a little, now it rips more like it did before, and to think I spent hours on jetting.