Hesitation at speed

CBXter · Post by **CBXter** » Wed Apr 23, 2008 12:30 pm

Don't know if it's carb/fuel or timing issue, but when I'm at speed 60-65 mph and I try mild to fairly rapid throttle roll-on increase in 5th gear, I get hesitation and slight sputtering with hardly any increase in speed, however if I go through all the gears from a stop with fairly hard acceleration I get no hesitation and she runs up past 80 mph with no problems. It seems like a fuel starvation type issue, or maybe timing is not advancing fully at the 60-65 mph/5000 rpm area when I increase throttle. But if it's fuel starvation or timing issue, why don't I have the problem when I start from a stop and run it through all the gears under fairly hard acceleration? Any other ideas?

alimey4u2 · Post by **alimey4u2** » Wed Apr 23, 2008 5:28 pm

Possibly sticking vacuum slides...anyone agree ??

dan1995 · Post by **dan1995** » Thu Apr 24, 2008 9:30 am

accelerator pump not working

CBXter · Post by **CBXter** » Fri Apr 25, 2008 9:35 am

Did complete rebuild and ops check on carbs, none of the above mentioned items occured, new accelerator pump, and all slides moved freely.

alimey4u2 · Post by **alimey4u2** » Fri Apr 25, 2008 10:24 am

Mechanical ignition advancer sticking ??

EMS · Post by **EMS** » Fri Apr 25, 2008 11:39 am

Maybe it is just the normal "torque lack" in the mid-range of the early engine which is more recognizable at low rpm roll-ons. It all depends on what you are used to from other bikes in these conditions and your subjective feeling may indicate a problem which isn't really one at all

CBXter · Post by **CBXter** » Fri Apr 25, 2008 3:07 pm

Have taken advancer off also and thoroughly cleaned and lubricated, everything looks quite functional, have dyna ignition but still had problem before that with stock pickups and coils.
This seems a little more than a slight hesitation EMS, it's almost like trying to punch through a barrier but not having enough something to break through. hard to explain, kind of like having a partial rev limiter kicking in when I'm at cruise speed 60-65 mph and I want to accelerate enough to pass someone, that's about the best description I can give.
And like I said previously this only happens in this type of cruise speed scenario. If I am starting from a stop or even slower speeds and accelerate briskly she winds right up to whatever speed or rpm range that I want to go with no hesitation.

EMS · Post by **EMS** » Fri Apr 25, 2008 3:19 pm

I see what you are saying, CBXter. But remember, this engine is not a torque monster. It makes its power at higher rpm. Max torque comes in at 8,000., and below 4000, there is not much happening at all. The bike is geared to reach 135 mph in 5th and 117mph in 4th. If I would want to accelerate from 60-65mph, I'd drop down from 5th to 4th.
But anyway. What air cleaner are you running on the intake? You don't by any chance have pods, do you?

alimey4u2 · Post by **alimey4u2** » Fri Apr 25, 2008 3:25 pm

A strobe light will check the functionality of the advancer through the rev range. It would then come down (possibly) to fuel/ air ratios across the range. I use my trusty NAPA exhaust gas analyser strapped to the guages with the sniffer stuck up one exhaust to get a true reading under load whilst riding. Could be mid range jetting causing the problem, once the engine is through the mid range ( under light load,) the main jets take over...
Without the luxury of an exhaust gas analyser, you could run the engine in the troublesome range for a period of time & immediately whip the plugs out & view the reading ?? If you run it hard on the main jets does the bike slow down eventually ( like it's starving ?) If that is the case, check the fuel tank cap vent hole for a partial blockage. Could be the pipes fitted are very inefficient at a certain rev range or is this a new phenomenon ?

415ZR1 · Post by **415ZR1** » Fri Apr 25, 2008 9:54 pm

CBXter · Post by **CBXter** » Sat Apr 26, 2008 2:02 am

415ZR1, I know it's definitely not the choke plates because I don't even have a choke cable hooked up, don't need it here in sunny Florida LOL, just one less thing I have to worry about or replace, but thanks for the input.

alimey4u2, I'm leaning more in your direction, must be advancer/timing issue or possibly some type of fuel starvation thingy, but I can't understand why it only occurs at cruise speed when I roll on the throttle in 5th gear and not when I run briskly through the gears from a stop or moving more slowly. I mean it doesn't happen if I'm in 5th going 30 or 40 mph and roll on the throttle, only at the higher cruise speed. I dumbfounded about it.

Also, what would cause the advancer not to function properly, I have thoroughly taken apart, cleaned and lubed the advancer, there doesn't appear to be anything to me that would wear out except the little springs, do they ever have to be replaced? They seem to have good tension, they would be the only things I would think might wear out.

Thanks for all your inputs, I'll keep troubleshooting and hope I find the problem.

daves79x · Post by **daves79x** » Sat Apr 26, 2008 7:13 am

CBXter:
Have you made any changes to intake or exhaust plumbing since it last ran well? Or has it always ran this way? Some aftermarket pipes are notorious for creating a flat spot right where yours is. Hard to jet out. A drop-in K & N filter will sometimes cause this as well. It's carburation, combined with intake/exhaust issues that are causing the problem. Are your carbs totally stock? You can jet richer on the bottom and mid-range and see what happens. Shim the needles .020 inch and maybe go from 65 to 68 or so on the primary mains. Don't go richer on the secondary main (the 95 jets). Unless you have individual filters. Then all bets are off and you have to go way up on the mains. I need to know EXACTLY what you have and maybe I can help you more.

Dave

CBXter · Post by **CBXter** » Sat Apr 26, 2008 10:18 pm

Yes Dave, I have some of the extras you say might be the problem, I'm running X-pipes for exhaust, I have a drop-in K&N air filter, and I have 100's/70's for my jet sizes. What do you recommend with this information Dave?

P.S. I have acquired some nice stock exhaust pipes that I was planning to put back on the bike instead of using my X-pipes if you think that will help.

daves79x · Post by **daves79x** » Sat Apr 26, 2008 11:07 pm

I don't have any experience with the X-pipe, but you should have jetting enough for most aftermarket pipes. I've heard of some leaness experienced when putting a replacement K&N in the stock airbox. If it is easy enough for you to try just putting the stock pipes on and leave all else as-is, I'd do that first and see how the bike responds. The jetting you have with the stock pipes and K&N should be pretty close.

You say the slides all move freely - make sure you didn't 'ding' a dome when installing them. I've see it happen more than you would imagine. The slide will stick or just operate in a short range. I take Q-Tips soaked in Berrymans and thoroughly clean the towers on the slides and the receptacle in the dome. It's the only to make sure some varnish isn't forming there to hang up the slides.

When you put in the new accelerator pump, did you visually confirm it's operation? You should gas the carbs up on the bench and operate the throttle to see how the pump works. Most don't work right, if at all, without some fiddling.

I'd try the pipe change first and see what happens. That may totally fix it.

Dave

CBXter · Post by **CBXter** » Sun Apr 27, 2008 4:37 pm

I bench tested the accelerator pump and it was pumping out massive amount of gas and all six squirt tips were shooting out a nice stream of gas. I thoroughly cleaned the carbs using Mike Nixon's carb cleaning book, everything seemed to be operating very well as far a the carbs go.
I'll get my stock pipes on and see if there's any change, thanks for the inputs all, hope it fixes with the pipe change out.
Dave, my jet sizes 100/70's you say should be good with the stock pipes and drop-in filter?