Carb Acceleration Hesitation Symptom

[MasterGuns]

Ever since purchasing this 86 VR in April, I have been chasing an acceleration hesitation problem. Only hesitates when engine is at idle and the throttle is cracked open. The motor does not respond and hesitates and may even die. I have been completely through the carbs, including new sliders and diaphragms. No vacuum leaks at alll anymore. Is this a symptom of running too lean or too rich? Everything else is fine, compression is great, plugs are new, well fairly new, new wires, boost sensor is operational, no problems with the vacuum line to the boost sensor. Valve adjustment is right on. What am I missing? I think is still a carburetion issue but can't pin it down. Any thoughts?

[Yammer Dan]

Idle at 900 RPM's??? If it is too low it will stall.

[MasterGuns]

Idle is at 1100.

[Marcarl]

I would think that your a liitle lean, try doing the same while squirting some WD40 down the throat of the carbs. If this fixes the problem somewhat you're too lean so you have to open the idle mixture screws a little and so have to make adjustments all the way around.

Question though, did you clean the idle circuit or just wash the carbs in place with cleaner?

[Yammer Dan]

Synced them?

[MasterGuns]

Yammer Dan and Marcarl, Both. The carbs were entirely disassembled, vatted then reassembled with a couple parts needing replaced; two air cut off valves. All gaskets and o-rings are new. Job performed by a very good mechanic that has years and years of Yamaha experience. The carbs were just too gummed up for seafoam to correct. Anyway, totally cleaned inside and out; look new. And snyced using my CarbTune. As Marcarl suggested, I, too, thought about opening each idle screw about a 1/2 turn but had a couple beers instead and hit the sack. I will get to your suggestion either tonight or tomorrow morning and advise the results. Even though my old diaphragms appeared serviceable (no holes) she runs much, much better with the new slides/diaphragms. Guess the old ones were not as pliable; too stiff or something.

[Ozlander]

If you're getting good gas mileage, I'd leave it alone. Nobody rides around at 1100 prm and cracks the throttle wide open. Try it at 1500 or 1800. Anyway, you're lean at idle.

[RossKean]

I don't know about these ones but at least some Mikuni carbs have an "acceleration duration" setting which sqirts a little fuel when the throttle is cracked. Prevents a momentary lean condition under acceleration. Otherwise, an overall lean condition might be the issue.

[Yammer Dan]

Seems I've had that problem. And all I can remember is I just kept Sea-Foaming it to death and finally something broke loose. Shouldn't be problem this time or could one of the jets got missed?? Not likely to miss them in all 4 cleaning as you say. I'll keep scratching my head. Might even come up with something. Stranger things have happened. Meanwhile I would just keep riding might be one of those things that just go away after it is run a while. Little Sea-Foam wouldn't hurt it?? Stuff is getting too pricey to use like I used to.

 

Is the Camp Fuel as good a cleaner as Sea-Foam?

[Squeeze]

Check the Air Jets inside the Carb-Throats, they should be 75, 80 or 90. There's a Chance they got mixed up with the other Air Jets behind the Diaphragm(170ish). No need to ask how i know.

[Venturous Randy]

Idle at 900 RPM's??? If it is too low it will stall.

 

My bike idles between 600 and 700 rpm's and does not hesitate.

RandyA

[skydoc_17]

Hey Herb,

Did you do the 5Bikes Needle Mod?

Earl

[Kross Kountry]

If you are too lean you should be able to pull the choke out a little and the symptom will go away.

[Kross Kountry]

I think I just made my Gen 2 do what you are talking about. I tightened my Idle mixture screws 3/4 of a turn each and when I cracked the throttle I got a big hesitation out of the motor. I then pulled the choke about half way out and tried it again. It reved up as if it was normal. I returned my idle mixtures screws back to the original setting and the hesitation was gone. If your gen one carbs are the same as mine: clockwise to lean or counter clockwise for rich. Do this a 1/4 turn at a time. It may take as much as a whole turn to make it go away. I think this only affect the bottem of the RPM's so it should not hurt your MPG.

 

If I'm wrong I'm sure I'll hear about it.

[5bikes]

Try something different. I thought I had a bad #1 carb on one of my Suzukis. Turns out it was #2. I thought I had a lean condition just off idle so I kept richening up the pilot screws. Ended up all 4 were way too rich, now at 1 1/4 turns out (normal is 2+ turns). Thought I had a dirty carb, actually was a bad spark plug, that one took me 10 hours to figure out. Got a old GS1000 Suzuki smoking like a misquito fogger. Thought it was bad rings or valve guides. Turned out it was way too lean and out of synch.

Had a hard starter, turned out it was corroded plug wires. One of my suzuki had 12.6v at the battery but 11v every where else. Finally found a main connector under the headlight that was clean & shiny but actually corroded inside.

Expect the unusual on older vehicles, especially one's that sat more than a few months or driven in humid/rainy climates.

I've rebuilt/cleaned the same carbs 3 times before I got all the bugs out, then it takes 10-20 hours to tune them right. And I know what I'm doing... most of the time.

[Twisted Metric]

On 9/4/2009 at 3:30 PM, Squeeze said:

Check the Air Jets inside the Carb-Throats, they should be 75, 80 or 90. There's a Chance they got mixed up with the other Air Jets behind the Diaphragm(170ish). No need to ask how i know.

lol been there a time or two