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ViragoTechForum.com XV750 Hesitation at low rpm ??? (solved)

#1: Question Hesitation at low rpm ??? (solved) Author: vira-go Post Posted: Thu Jun 03, 2010 5:47 am

I just bought the bike a couple of months ago, 1994 XV750. It was running pretty rough when I first bought it. I have put tons of new parts on it, new rocker arms and shafts, new camshafts, new head gaskets, new carburetor joints. New o-rings, brake pads and hoses. I adjusted the valves. Took the carbs and cleaned them, put it all back together and tried adjusting the mixture...

Now it runs fine at idle but if I crack the throtle open a bit it struggles to go, if I keep opening the throttle then it revs up like crazy. It does the same thing when I try to ride it, at low rpm it stumbles and if I keep pull the throttle it takes off really fast.

Plugs are really black.I can see a bit of black smoke when reving up. Pilot screws don't make much difference.
Fuel level is about 5mm lower than it should, it was the only way to get it to have a decent idle.

Any ideas?

Thanks

#2:   Author: mark75 Post Posted: Thu Jun 03, 2010 6:56 am

Howdy vira-go. Welcome to VT.

has Mikuni's, right?
"enricher" circuit diaphragms ok?
battery good and hot?

#3:   Author: vira-go Post Posted: Thu Jun 03, 2010 10:42 am

Thanks Mark!

Yes Mikunis. Brand new battery, 100 % charged

The enricher diafragms looked good but I will check them again today... I am for sure missing something...

#4:   Author: mark75 Post Posted: Thu Jun 03, 2010 9:03 pm

maybe Grazingazer or one of the guys that are better diagnosticians than me will chime in.

#5:   Author: slipknotking490 Post Posted: Fri Jun 04, 2010 5:19 pm

my 82 xv750 is having the same problem if i fix it ill let you know what it was

#6:  Re: Hesitation at low rpm ??? Author: kfabel Post Posted: Fri Jun 04, 2010 5:22 pm

i have a 1982 xv750j. i just had the carbs rebuilt by the local Yamaha guys and i have this same exact problem. the bike is pretty tight, only 5800 loving miles. i would love to know where to look. i'm assuming it's not the carbs unless they need fine tuning

#7:   Author: slipknotking490 Post Posted: Fri Jun 04, 2010 5:32 pm

kfabel and vira-go are you running aftermarket exhaust

#8:   Author: kfabel Post Posted: Fri Jun 04, 2010 5:37 pm

No stock everything . . my exhaust had one small hole that i plugged

#9:   Author: slipknotking490 Post Posted: Sat Jun 05, 2010 2:12 am

im running straight pipes so im gonna have the carbs rebuilt and rejetted hopefully that will solve the problem ill let you know the results

#10:   Author: grazingazer Post Posted: Sat Jun 05, 2010 6:43 pm

vira-go wrote (View Post):
I just bought the bike a couple of months ago, 1994 XV750. It was running pretty rough when I first bought it. I have put tons of new parts on it, new rocker arms and shafts, new camshafts, new head gaskets, new carburetor joints. New o-rings, brake pads and hoses. I adjusted the valves. Took the carbs and cleaned them, put it all back together and tried adjusting the mixture...

Now it runs fine at idle but if I crack the throtle open a bit it struggles to go, if I keep opening the throttle then it revs up like crazy. It does the same thing when I try to ride it, at low rpm it stumbles and if I keep pull the throttle it takes off really fast.

Plugs are really black.I can see a bit of black smoke when reving up. Pilot screws don't make much difference.
Fuel level is about 5mm lower than it should, it was the only way to get it to have a decent idle.

Any ideas?

Thanks
check your air filter for being dirty

#11:   Author: kfabel Post Posted: Sun Jun 06, 2010 12:17 pm

Brand new K&N air filter

#12:   Author: vira-go Post Posted: Mon Jun 07, 2010 8:07 pm

Problem solved!!!

It was the plastic washer that goes on top of the carb needle. I put it under the needle washer instead, my bad!

A friend who is a motorcycle mechanic figured it out, but I am not out of the water just yet. I took the bike to emissions and CO is too high 7.2 and it should be 5 or less.

I took the bike out today for the first time. I did not care about the 108 temperature out there, very pleased with the machine, very pleased.

Thank you all for your posts.

Now I just have to figure out the CO problem.

#13:   Author: vira-go Post Posted: Mon Jun 07, 2010 8:08 pm

I forgot to mention I am using stock exausts.

#14:   Author: mark75 Post Posted: Tue Jun 08, 2010 2:32 am

FWIW: heard of a product (on another forum) called RxP that supossedly helps with emissions.

we have been dodging that EPA bullet around here so far, so I have no personal experience with emissions testing.

if after looking it over, you decide to try it, let us know what you find.

#15:   Author: slipknotking490 Post Posted: Tue Jun 08, 2010 10:45 pm

figured out my problem it was just junk gas

#16:   Author: mark75 Post Posted: Wed Jun 09, 2010 2:42 am

slipkk - shoot a little Seafoam in there to help keep carbs clean after the bad gas.

#17:   Author: vira-go Post Posted: Sat Jun 12, 2010 1:53 am

More good news, I passed emissions!!!

My friend said he would help me but I could not wait. I turned the carb screws in until the engine almost stopped, then I turned the screws out until the backfiring on deceleration stopped. I got it down to 3. in CO. I am a happy man again.

slipknotking490 I am glad you figured out your problem.
ViragoTechForum.com XV750 Hesitation at low rpm ??? (solved)


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