Throttle Lag until 2000 RPM

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ccgroup

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1993 Vmax, No upgrades.
I have a big lag in the throttle until about 2000 RPM. Has no power with low idle. It stalls if I try leave the line under 2000 RPM.
Just started at the first of the year. Wont Idle, only with choke on.
Work done: Removed and cleaned carbs, Changed fuel filter, changed plugs. Clean fuel and ran Seafoam through it.

Just no power at low rpm.

What next?

Thanks in advance for the help.

Cheers.

Chris.
 

desert_max

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Clean the carbs. Not trying to sound trite, but the symptoms you’re describing suggest classic carburetor issues… specifically the pilot jets. When you cleaned your carbs were pilot jets part of that regimen?
 

ccgroup

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Not trite, good question.
I had them all apart.Pilot Jets, Jet Block and Needle valve. Tore them all down
Cleaned them all out but didn't see any issues.
But no change in lag or power.
 

02GF74

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Were carbs synchronised?

Is the vboost open all the time?
 

Fire-medic

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I am not a paid mechanic.

I agree, it sounds like carburetion. Do you have a thermal gun? What are the temps? Are they consistent from one to another? Remember you need to be pretty-close to the pipe to take a reading, at-least mine does. The 'cone' of sensing widens pretty-quickly with distance from the gun. It's not like the laser pointer you might use in a lecture.

Does it miss? Getting thermal readings will tell you which cyl's are firing and which aren't.
 

ccgroup

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Im not sure about the boost being open, but they were synchronized.
It doesn't run smoothly and spits and coughs a bit until its warm

I will check temps in the morning and let you know.

thanks for the help and info.
 

MaxMidnight

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You can see from the illustration below that it is the pilot jets that control the fueling at small throttle openings which translates into low revs.

Carb Jet operating range.jpg
From what you say I suspect one or more of the idle circuits are still blocked and Mr Medics suggestion of using an i.r. thermometer may help identify the culprit.

What method did you use to clean the carbs?

You have done my first port of call, carb cleaner so next step would be 'The Shotgun'. If that doesn't work you would need to have them ultrasonically cleaned.
 

apsolus

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yeah do that peashooter / shotgun clean. the carbs dont have to be pulled to do that and its quick
 

02GF74

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It a thermal gun necessary?

All you want to do is check that the exhausts are getting hot at the same rate.

This could be done with by touching the exhausts with a wet/damp cloth, you'll clearly will hear if one or more exhausts are not getting hot.

I don't know how long the engine needs to run so the cloth makes a sizzling sound, but once one of them does it, stop the engine and test all 4.
 

Fire-medic

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Yes spritzing a bit of water on a header pipe is the shade-tree way, but you get a better read of what's happening. I used to keep a spray bottle for that, but once I got an infrared thermal gun, better data.
 

sdt354

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yeah do that peashooter / shotgun clean. the carbs dont have to be pulled to do that and its quick
+1 on the peashooter/shotgun for the air jets. The crud that plugs that little piolet jet is usually rock hard. I used a slightly larger drill bit on my Bro's ride. Opening up the jet a tad gave some good results. I'll probably do it again to the next rack I dive into. Or maybe go to 40's on the piolet jet.
 

maleko89

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+1 on the peashooter/shotgun for the air jets. The crud that plugs that little piolet jet is usually rock hard. I used a slightly larger drill bit on my Bro's ride. Opening up the jet a tad gave some good results. I'll probably do it again to the next rack I dive into. Or maybe go to 40's on the piolet jet.
The pfj 40’s worked well for me. I just needed to adjust the screws more slowly since a little turn can go a long way.

Mark
 

V-Four

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+1 on the peashooter/shotgun for the air jets. The crud that plugs that little piolet jet is usually rock hard. I used a slightly larger drill bit on my Bro's ride. Opening up the jet a tad gave some good results. I'll probably do it again to the next rack I dive into. Or maybe go to 40's on the piolet jet.

Are you saying that "opening them up a tad" makes you less apt to have to pull the carbs and go thru the cleaning "routine"?

If so, what (if any) other effects would this have overall? 🤔



The pfj 40’s worked well for me. I just needed to adjust the screws more slowly since a little turn can go a long way.

Mark


Same question , I guess.. any other issues w/ goin to 40's? 🤔 🧐



Thanks Y'all,

🍻
T$
 

Fire-medic

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I've never tried enlarging the pilots. I've thought of it, but I haven't done it. If I did choose something like that, I would replace the pilot jet with the next size larger instead of using a drill to enlarge it.

If I suspect a pilot jet blockage/obstruction, I just remove the carburetors and tear them down. Into the ultrasonic tank, and then a rebuild/re-install. It was intimidating at first, now I know it's what has to be done to fix things properly, and I actually enjoy the labor. I have a set of spare carburetors, so if I want I can remove/replace, and be riding again in several hours. That could probably be 'a couple of hours,' if I was in a hurry, but since retirement, very-little is 'in a hurry.'
 
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Parminio

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I've never tried enlarging the pilots. I've thought of it, but I haven't done it. If I did choose something like that, I would replace the pilot jet with the next size larger instead of using a drill to enlarge it.
This.

Keep it a science, eliminate the guess work, get fully expected results. Odds are, he just got lucky with the drilling.
 

maleko89

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Are you saying that "opening them up a tad" makes you less apt to have to pull the carbs and go thru the cleaning "routine"?

If so, what (if any) other effects would this have overall? 🤔






Same question , I guess.. any other issues w/ goin to 40's? 🤔 🧐



Thanks Y'all,

🍻
T$
No issues other than taking the carbs off the bike. Didn’t notice mpg change at all.
 

sdt354

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Are you saying that "opening them up a tad" makes you less apt to have to pull the carbs and go thru the cleaning "routine"?

If so, what (if any) other effects would this have overall? 🤔






Same question , I guess.. any other issues w/ goin to 40's? 🤔 🧐



Thanks Y'all,

🍻
T$
It is not the only jet that's been enlarged on mine. nOT COUNTING THE M
Are you saying that "opening them up a tad" makes you less apt to have to pull the carbs and go thru the cleaning "routine"?

If so, what (if any) other effects would this have overall? 🤔






Same question , I guess.. any other issues w/ goin to 40's? 🤔 🧐



Thanks Y'all,

🍻
T$

PM'd you
 

Parminio

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Didn't mean to insult your manhood or whatever offense you took, but consider this:

The pilot jet from the factory is .375mm in diameter. The smallest metric drill bit I've come across is .40mm, which is the same as the 40 jet.

Then you have to take wobble into account and the fact that holding an exact 90 degree angle to the hole is, at best, guess work.

So you in all likelihood are running a pilot jet at least .40mm in diameter and probably a bit larger when you add any sort of discrepancy at all.

I understand you're the master of all mechanics, but the fact remains that not everybody is. Best to simply buy the 40 jets to begin with, install them and have them perfect than to drill out the stock ones to the 40, put the whole thing back together, have problems, pull them all, try to ascertain which one you screwed up, replace it...

That was my point.
 

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