Ive asked before with no real help but lets try again PLEASE... Bike stumbles at half
 

throttle, runs great everywhere else. If Im at half throttle(highway speed) and its stummbling I can pull out the choke and the stumble goes away. I have changed carbs, R/R, Air filter. I havent changed plugs in the new motor though and I did notice a small gas leak from the petcock when I had the tank off putting the new motor on the bike. Im thinking this is a vacuum issue causing this and its possibly coming from the petcock gasket but I would like some of the Gurus from this sites opinions.

Your help is appreciated in advance,

Chris (BDK)

I'm no guru, and I'm guessing, but what you describe, especially it clearing when you pull out the choke, sounds more like a carb/jetting issue to me than a vacuum problem.

Whatever gurus there are around here might be more help if you detail what exhaust you are running, are the carb jets and needles stock or after market and if so what is the set up? Are the air filter and airbox stock or aftermarket/modified? Are you sure that the carbs are fully seated in the manifold booties and all four bands are tightened down? Is the TPS set properly? Are you certain it is a "half throttle" condition not a "constant throttle" (as opposed to accelerating throttle) condition?


Seems to me also that if it was caused by a gas leak at the petcock it would be worse under acceleration than it would be tootin' along at half throttle.

Well I changed carbs and it didnt change the problem so I ruled out the needle/jet issue ( I was leaning that way to start with ) The air filter and box are stock and unmodded. The carbs are seated good i checked that thourougly and the bands are tight. Now the TPS Im not sure about. I got this problem AFTER A MOTOR SWAP ;) I swapped airbox and all so the TPS may be a bit out of adjustment. The only mods to my bike are a 15 front sprocket and Graves exhaust also.

Does this info help with the diagnosis any more?

Thanks again

Chris

If the choke fixes it it's lean. That can be improper jet sizes or a vacuum leak bypassing the carbs.

Like I said, I'm no expert, I'm guessing. But if the carbs are seated good and your vacuum hoses are where they belong and have no holes, I'd check the tps. Before I adjusted mine from 860+ to 499 my bike wouldn't exactly stumble, but felt goofy like it was fighting itself a little at constant throttle and small throttle changes weren't smooth.

If you have a multimeter it only takes a few moments to check the tps resistance.

But it still sounds like a carb/jetting problem to me. You say you changed the carbs but do you know what main jets are in them and are they the right size to run with the
Graves exhaust? Do the carbs have the OEM needles or aftermarket maybe set too low?

I don't know anything about the Graves exhaust but assume it flows freer than stock and if much so the stock jets and needles would leave you running lean, especially noticeable at constant throttle, which is what sounds like is happening.

One other thing. Did you sync the carbs? Even when everything else on my VTR is dialed in, I have to sync the carbs every time I pull them or it won't run right. And even when they are in spec per the manual, my bike runs better when I take the time dial them in better than mere spec.

Not sure on the needles and jets on the carbs with the new motor but it only had 4300 miles on it and was on a layed down 2004 model that had no other visible mods so Im *assuming* it was all stock. Its doing exactly the same with these carbs as it did with my old ones on the new motor ( I swapped carbs because I wasnt sure how long this motor had sat) Im gonna try the TPS as soon as I get a chance. Thanks a ton for your help I really appreciate your time. I will let you know what happens.

thanks again,

Chris

You guys are all over the obvious stuff but if all the obvious stuff doesn't work it sounds like an intermittent air leak into the intake or manifold. Go back over all your rubber and look for the smallest of imperfections. Likely you'll run across a major problem. Best of luck and keep us posted.

nuhawk is right and one of the things I'd check is the O rings that seal the carb bodies to the bottom of the airbox.

I'd do these easy-quick things first but if problem persists, and since you haven't done it yet, I'd pull and open those carbs and see what is in them.

The VTR carbs can be a pain in the ass to dial in and plenty of guys fook 'em up good way before 4300 miles. I had mine off 5 or 6 times before I got them jetted real good for my slip ons.

will do man

Not at all a safe assumption. When someone lays a bike down and wants to sell it he's going to replace the easy stuff with the fresh stock items he removed, but he's not going to take the time to undo all the difficult mods he made that aren't initially apparent... i.e. carb work.

First, where was the petcock leaking from? The fuel nipples or the vacuum nipple? How about the nipple from the bottom? That one's the vent and shouldn't have anything going to it.

If the petcock is not the problem then I think you just need to rejet. You can get by with shimming the needles with small washers but jetting will net you better rideability overall.

I agree but this was bought from an auction after the guys insurance "totaled" the bike so I dont know if he had access to it to remove parts. Im sure it went to the tow yard and then to the auction..... I hope

I think it was leaking from the actual gasket but Im not certain. I was thinking it was maybe from me standing it on its end while I was changing the motor so I just wrote it off. Im certain I have the PIVLIR issue taken care of though;) . The leak was really small and it doesnt lose any fuel now with it on the bike.

Im leaning now toward the o-ring seals on the bottom of the air box because I dont recall seeing them on the new airbox or the TPS but adjusting the TPS sounds like a job in itself so Im gonna take NuHawks (I think thats who it was) advise and chase down the easy stuff first.

Thanks a great deal guys... keep the brain storming coming.. this site is the best!!!!


Thanks again,

Chris

The seals between the airbox and the carbs are a formed rubber o-ring that seats in a recess on the carb body. They generally never come out unless you intentionally take them out.

Well I personally didnt take them out thats for sure :D . I also thought about it and the TPS is mounted to the carbs right? So when I changed carb setups I changed TPS sensors also and the problem didnt change with the different setups so that should rule out the TPS and the carbs because the first set of carbs ran perfect on the previous motor before the cct failure. :confused::confused::confused:

Respectfully and with all good will, I think you are assuming things that you would be better served by taking 30 or 40 minutes to actually check out.

Dont worry, Im not going to take anything out of context but what are you meaning? I didnt have this issue until I swapped the engine. When I did the swap I used my old carbs because I didnt know how long the 'new' ones had been sitting but I got the 'stumble' so I swapped back to the carbs that came on the new engine and the issue didnt change. My old air filter was nasty but the new one had only 4300 miles so it was very clean (looked new) so I used it and the new air cleaner and I didnt change plugs,which in hindsight was a dumb move. I used all the sensors that came with the new engine.....Ummm I know Im rambling but I just got off the bike and I want to make sure I say everything I did (even if it may not make sense :D ) I even tried using a little bit of seafoam additive in it and it didnt change a thing. I guess Im gonna just take the tank off as soon as I get my land finished for my new home and look everything over really good and see what I missed. It runs entirely to well to be anything serious so it must be something I looked over, I guess or I hope.

The great thing about a Superhawk is you dont have to ride very long to run out a full tank of fuel so its easy to mess with taking the tank off:o:o



I cant thank you guys enough for your help,

Chris

BDK;

What I was thinking when I wrote that is this;

You've had several guys suggest that based on their experience, it sounds like a carb/jetting problem.

You are assuming, because it happens with both sets of carbs, that it can't be.

But even if the the second set of carbs are bone stock, which you can't know unless you check them out, there is enough variation on VTRs from bike to bike, let alone year to year, that the same carbs could have worked well with the old engine and your Graves exhaust but not with the new engine and Graves exhaust. I'd also consider that the difference between a dirty plugged up air filter and a fresh one could be the difference between running OK with stock jetting and having a flat spot or stumble 'cause the stock jetting is a bit lean for your exhaust.

I'm just saying I think it a mistake to rule out the carbs unless and until you pull them, check them out and fiddle with them a bit, maybe open the mixture screws, go up a main jet size etc.

And whether it is the carbs, tps or anything else you hook up to a different engine from a different bike, I don't think it safe to assume it will work exactly the same without any adjustment.

Makes sense, Im just trying to avoid boogering with those touchy @ss carbs man. Your probably right though because the old air filter looked like it was off an old diesel truck so it probably fattened it up enough to compensate for the exhaust or at least enough to where I couldnt notice.

BDK;

Believe me, as someone who has TWICE had to visit my friendly Honda dealer and spend $33 for the parts package with the cheese-ass plastic enrichment valve fastener (which ought to cost .29) , I understand your reluctance to pull down the carbs.

The good news is that once you've done it 5 or 6 times it gets easier!

I also discovered after spending that $66 that if willing to work at the bike instead of the work bench, I could access the pilot screws, float bowls and vacuum chambers without detaching the choke cables.

Cool deal..... but I dont have the first clue as to how to even take these things apart right much less do anything to them correctly:rolleyes:

Its about riding season guys so what size jets do you think I should try? Or do you suggest me going with th .040 shim job I have in the second set of carbs already and just seeing where that gets me? If you think taking the shims out and jetting is best I may try that. Let me know what you think.Which jets to change and size to go to if possible.

Thanks in Advance

Refresh my memory. What mods?