Board logo

throttle sticking at 4000?
robby - 19/4/11 at 10:02 AM

got mikuni flatslides on my gsxr1100 motor and throttle keeps sticking about 3 - 4000 revs.
cable not sticky, spring - very heavy! - takes it back to idle screw no bother, but still runs fast.
if i brake in a high gear, the revs come down, not to tickover, but in line with the speed i'm going - and sticks there, anywhere beyween 2 and 3k.
cleaned wi carb cleaner, and canna see anything sticking or tight.
any ideas?
cheers, robby

phoenix70 - 19/4/11 at 10:33 AM

could it be an air leak somewhere?

adithorp - 19/4/11 at 12:21 PM

Think someone else had something similar last week. Seem to remember something about a vac pipe on no3?

The other thing that comes up occationally is the clamp screws catching the throttle spindle.

lewis - 19/4/11 at 12:36 PM

I have the same issue (twin 45s on a pinto) can't work out why it's doing it,I can't see any obvious air leaks and been running fine prior.

matt_gsxr - 19/4/11 at 12:53 PM

Are the throttle plates closing or not? I put an additional spring on my accelerator pedal, but I think from what you say this isn't the problem.

Have you real flat slides, or are these the stock Mikuni carbs with butterflies and a vacuum operated slide?

Matt

p.s. another gsxr1100 is always nice to see (although mine is water cooled)

robby - 19/4/11 at 03:38 PM

ha ha matt! there's no manyof us about!
thanks all, will try and get another look tonight.
oh, and they are flatslides.

cosmick - 20/4/11 at 05:43 AM

Are these Proper Flat slide Carbs? ie non CV type carburettors, if so, the vacuum is high when you shut the throttle at any RPM and the slides will get drawn towards the inlet side of the carb and stick. this was common on early bikes which is why all bikes went mostly to CV type carbs. The amount of effort required to open 4 flat slide carbs was huge in comparison to CV. Also. Every set of flat slides was fitted with a closing cable to make the slides fall when shut. If you force your carbs closed, you will probably find that they return to correct idle. However if you just let go of the throttle, you may find the revs hang up due to the slides not shutting fully.
If this is the case, then a very strong return spring needs to be fitted to do the job of the missing closing cable.

robby - 20/4/11 at 08:53 PM

cheers cosmick.
aye, proper flatslides.
got the return spring round as far as it'll go - you're right, it would be a twat to turn on a twist grip!
hope to have a poke at it tomorrow - if i take the filters off, should i be able to see if slides are up, or will there be too little movement to tell?
will try forcing it back when it sticks to see if a spring on a short return cable would solve it.
thanks!

matt_gsxr - 20/4/11 at 09:03 PM

quote:
Originally posted by cosmick
Are these Proper Flat slide Carbs? ie non CV type carburettors, if so, the vacuum is high when you shut the throttle at any RPM and the slides will get drawn towards the inlet side of the carb and stick. this was common on early bikes which is why all bikes went mostly to CV type carbs. The amount of effort required to open 4 flat slide carbs was huge in comparison to CV. Also. Every set of flat slides was fitted with a closing cable to make the slides fall when shut. If you force your carbs closed, you will probably find that they return to correct idle. However if you just let go of the throttle, you may find the revs hang up due to the slides not shutting fully.
If this is the case, then a very strong return spring needs to be fitted to do the job of the missing closing cable.


I had typed that too although less eruditely (the vacuum makes it difficult for the slides to close), but I made the mistake of guessing you didn't really have flatslides. They were far too expensive for me!!!

Do you have to get through IVA. I have heard that those expensive carbs can be a struggle at low RPM and hence your emissions might be a struggle.

I got my Mikuni 40's through (eventually using magic), but subsequently went EFI as I struggled with leaks and stuff (and I love changing things).

Matt

[Edited on 20/4/11 by matt_gsxr]

robby - 21/4/11 at 08:27 AM

hi matt.
got them cheap from a mate!
aye, trouble wi sva, but examiner was very helpful... got there in the end.
hoping to get a look at it today, usual, never getting time...

robby

cosmick - 21/4/11 at 09:09 PM

The amount that the slides stay open is minimal. so you will struggle to see the slides sticking. they will reurn most of the way and then stick as the vacuum increases as the slide closes. Another way to check if this is the problem is to kill the motor when the revs hang up. Then restart the engine and see if the RPM has gone back to normal idle. If this is the case, then it is definately slides sticking due to vacuum.
Hope that helps.

cosmick

robby - 22/4/11 at 01:35 PM

yeah, did that, they were sticking up. feel a bit daft now i've found the problem - 2 of the screws holding the arms that lift the slides had slackened off a wee bit, letting the arms move a baw hair on the shaft...
thanks for everyones help!

matt_gsxr - 22/4/11 at 01:50 PM

Thanks for the update. I have made all those mistakes too.

robby - 23/4/11 at 12:42 PM

took it out for a test drive, no sticky throttle, but got stuck in 3rd gear! no power going to compressor for shifter. gonna be one of those years...

matt_gsxr - 23/4/11 at 02:46 PM

I wondered what that medical gas cylinder was doing.

robby - 25/4/11 at 01:43 PM

ha! didn't realise i'd managed to get photo's on here! was sitting here thinking "how the bleep did he see the bottle?"!