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Keihin ZX9R carb throttle return springs
FASTdan - 7/4/10 at 06:48 AM

This is the second set of this type of carb we have used and on both occasions the throttle does not return to the idle position quickly - especially if you back off with the pedal slowly this causes the revs to remain around at around 1500rpm dropping off slowly despite there being no throttle applied. It is not a cable issue as I have checked that the cable has gone slack.

Its a bit of an unsettling feeling when you dont have proper engine braking.

Anyone else encountered this? I suspect most bike carbs are like this as the springs are probably lighter duty to match the bike type throttle......

Any remedies?

YQUSTA - 7/4/10 at 06:55 AM

Have you added a second spring or are you just using one?

I have an extra spring at the carb end others have put it at the peddal end.

David Jenkins - 7/4/10 at 07:04 AM

My Honda CBR600 carbs used to have 2 throttle cables - pull-open and pull-shut - that came from the twist grip. This is probably to prevent the rider getting wrist fatigue from holding against a strong spring for a long period.

I put about 75mm of throttle cable on the pull-shut side, with a washer, longish spring, another washer and a clamp. Now, when I take my foot off the throttle this spring shuts the butterflies.

I experimented with spring strengths until I found one that worked well. Don't go too strong, as you may overload the mechanism.

cd.thomson - 7/4/10 at 08:19 AM

Hi Dan,

Same issue here, infact the engine nearly revved itself to destruction when I first set the pedal up!

I just bought a random throttle return spring off ebay and hooked it on between one of my camcover bolts and the throttle quadrant on the carbs. It's got a lovely feel now

blakep82 - 7/4/10 at 11:04 AM

works ok on mine, but maybe the cable could do with some lubrication, and also the shafts on the carbs themselves?

one of mine was completely jammed up. thought it was broke, but a few minutes twisting the shaft open and closed with oil applied and stuff saw it turning so free, it didn't even need the main spring in the middle.
mine snap closed real fast when the pedal's released now

Slater - 7/4/10 at 11:12 AM

I did the same as David Jenkins, there is a pic in my archive, I have some spare springs too if you need some sent.

Keith

FASTdan - 7/4/10 at 11:49 AM

quote:
Originally posted by Slater
I did the same as David Jenkins, there is a pic in my archive, I have some spare springs too if you need some sent.

Keith


Thanks for the offer - we have a fair few random extension springs kicking around at work i was going to have a play with, but if i get stuck i'll give you a shout.

Blake, I've soaked the throttle spindles in GT85 but didnt seem to help. I dont think its the cable because I can pull the cable back toward the carb (ie giving it full slack) yet the throttle still closes very gradually.

I'll have a play with some springs, cant be too hard to sort (i hope!).