Acceleration oddity

[BigBear]

So...on my way into work this morning, I was accelerating (harder than normal in 3rd gear) to merge onto the highway.

 

The engine responded quite well to the twist...but as it started to wind up, the engine appeared to gain more power...almost like another couple of carb jets opened up...the same kind of feeling you get when you accelerate faster than you let the clutch out.

 

So that begs the question...WTH? The carbs are synch'd, and adjusted approx 3.5 turns out.

 

Other than the above, the bike is running pretty good.

 

Any suggestions on what to check? Sure seems like a carb / fuel delivery anomaly.

 

:confused24:

[djh3]

Hmm I'm sure some wayyyy more knowledgable guys on carbs than me will chime in, but my couple of ideas are. 1) You say accelerated quicker than "normal". Maybe just cleaned some gunk out, plugs jets etc. Back in the day when I worked in a garage before we did a tune up we use to take the car for a drive and stand on it hard a few times to blow out the carbon etc. 2)You forgot what the power band felt like. Seriously I would think if it idles correct and your milage aint in the crapper the carbs would be close. I also remember from working in the shop that quickly closing the throttle at say 60 or so and letting it loose some speed cleared jets out along with closing off the throat of the carb with your hand. We used to spray some water down the carb to break up carbon deposits once they started with the cat converters and there wasnt any spray cleaners at the time to use.

[Flyinfool]

It is possible that you were just reaching the power band for the first time in a long time, these engines like to rev and do not make a lot of power or torque at lower RPMs.

You might finally have reached the RPM that she wants to run at and she was rewarding you for it.

[SilvrT]

I'm confused...

 

Are you saying that the engine revved up but the bike didn't? If it was that, then your clutch is slipping.

 

Or are you saying that you felt a burst of power as the engine's revs reached a high rpm? If it was that, then you just got her into the power band.

[we2riders]

I know one thing about these Yammies, if the carb diaphrams are not in the best of shape they will do some crazy sneaky things, I had a diaphram coming loose from the slide that acted like I had gremlins poking their little fingers in a mainjet hahaha.. On the other hand, like already mentioned,, if ya aint been above 4800 rpm in a while it can be be a high spot for the day...

[we2riders]

another thought,, it wasnt like the clutch was slipping a little was it?

[SilvrT]

another thought,, it wasnt like the clutch was slipping a little was it?

 

LOL... isn't it a PITA to read all the posts before posting yourself ... I do that all the time .. only to discover later somebody beat me to it.

[we2riders]

LOL... isn't it a PITA to read all the posts before posting yourself ... I do that all the time .. only to discover later somebody beat me to it.

 

aint that the truth!!!!! but at my age I get to blame it on slowwwwwwwww fingers doing the typin and a short term memory and a.d.d. and,,,,, wait a minute,, to old to make excuses anymore,,, how bout oppps hahahahahaha

[BigBear]

I'm confused...

 

Or are you saying that you felt a burst of power as the engine's revs reached a high rpm? If it was that, then you just got her into the power band.

 

[SilvrT]

 

yup, these bikes will do that ... maybe more noticeable in 3rd and 4th gears .... give 'er full twist and let the rpms/speed build and then WOOOOOOOOOOO!!! feels like an afterburner kicked in (almost).

 

Just imagine what a shot of nitro would do at about the same time LOL!

[dingy]

Just imagine what a shot of nitro would do at about the same time LOL!

 

Might let you know what that feels like this spring.

 

 

Gary

[SilvrT]

Might let you know what that feels like this spring.

 

 

Gary

 

Anything you say (about that then) can only be believed by first-hand experience....

[Trader]

Or....just a long shot....it's been running on 3 cyl and for some unknown reason, it decided to kick in on all 4???? Maybe the colder temps caused a bad connection to "heal"???

 

From what I understand ...(although I could be wrong...somebody correct me if I am)....you can have the carbs sync'ed and still only be running on 3.

[mraf]

Tailwind! Burritoes! Worm-hole! Momentary gravity release! Total tire traction! Gas fart! I give up. You pick.

[naturbar]

It should be obvious........ you hit the nitrous button by accident..........

[Flyinfool]

It is possible that you were just reaching the power band for the first time in a long time, these engines like to rev and do not make a lot of power or torque at lower RPMs.

You might finally have reached the RPM that she wants to run at and she was rewarding you for it.

 

I'm confused...

 

Are you saying that the engine revved up but the bike didn't? If it was that, then your clutch is slipping.

 

Or are you saying that you felt a burst of power as the engine's revs reached a high rpm? If it was that, then you just got her into the power band.

 

LOL... isn't it a PITA to read all the posts before posting yourself ... I do that all the time .. only to discover later somebody beat me to it.

 

YUP!!

 

So did we solve the issue yet?

[V7Goose]

I have no idea what bike you have, but if i understood your post correctly, then it sounds like you have some clogged pilot jets.

 

A CV carb runs primarily off the pilot jets anywhere in the first 1/4 throttle , and they still provide significant amounts of fuel in conjunction with the main jets up past 1/2 throttle. Only above 1/2 do the main jets provide enough fuel to make the additional fuel from the pilot jets mostly insignificant. And a CV carb does not use an accelerator pump to overcome the initial rush of air when opening the slides (which pulls the needle out of the main jets), so there is an inherent lag in how fast the main jet fuel jumps in the mix. The slides are deliberately delayed on the first throttle twist, and the pilot jets MUST be able to supply the additional fuel needed from the opened butterfly valves until the revs climb enough to support the opening slides.

 

So what is going on is that most likely your idle adjustment is cranked up to allow some fuel through the mains at idle to compensate for your plugged primaries. It will seem to run OK, but not actually near as good as it will with clean carbs (and you will have that delay you described). You can verify this by checking the vacuum level at idle - if the engine is not pulling 10" Hg, then either the engine is worn or the butterflies in the carbs are being held too far open.

Goose

Edited November 29, 2012 by V7Goose
spelling

[Wrench]

I have no idea what bike you have, but if i understood your post correctly, then it sounds like you have some clogged pilot jets.

 

A CV carb runs primarily off the pilot jets anywhere in the first 1/4 throttle , and they still provide significant amounts of fuel in conjunction with the main jets up past 1/2 throttle. Only above 1/2 do the main jets provide enough fuel to make the additional fuel from the pilot jets mostly insignificant. And a CV carb does not use an accelerator pump to overcome the initial rush of air when opening the slides (which pulls the needle out of the main jets), so there is an inerrant lag in how fast the main jet fuel jumps in the mix. The slides are deliberately delayed on the first throttle twist, and the pilot jets MUST be able to supply the additional fuel needed from the opened butterfly valves.

 

So what is going on is that most likely your idle adjustment is cranked up to allow some fuel through the mains at idle to compensate for your plugged primaries. It will seem to run OK, but not actually near as good as it will with clean carbs (and you will have that delay you described). You can verify this by checking the vacuum level at idle - if the engine is not pulling 10" Hg, then either the engine is worn or the butterflies in the carbs are being held too far open.

Goose

 

If his public profile is correct it's an '08 Venture. Just trying to help.