Eviljohn
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| posted on 19/9/17 at 09:33 AM |
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Revs drop slowly to idle
Hi all. Hope you're well. Doing bike carb conversion on mk2 polo, only thing that isn't stock is electronic ignition on refurb'd
dizzy. All bolted on and fired up. Just sorting few niggles it seems to have.
Firstly: can anyone tell what it's called when it takes a while for revs to drop back to idle when throttle is blipped or actually driving?
Second: is there a way to identify the carbs i have or what bike they came off? I have snapped the long spring off the idle adjust screw. Screw still
works,i just snipped the rest of the spring off and made a small cut with a hacksaw in the "head" of the screw so i can fit a screwdriver
in to adjust. Just wondering so i can replace the it at some point if i need to. Thanks for stopping by and any guidance you can give. Much
appreciated.
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David Jenkins
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| posted on 19/9/17 at 10:02 AM |
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Bike carbs often used 2 cables when on the bike - one to open the throttle and the other to close it when the twist grip is turned back. If yours is
like that then you'll need to provide some form of return force to close the throttles properly.
My solution on CBR600 carbs looks like this:
It's very hard to see, just on the left of the picture alongside the edge of the nosecone. It's a bit of throttle cable, a spring and
something to hold the spring in place. This compresses when I open the throttle, and closes everything once I lift my foot.
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Slater
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| posted on 19/9/17 at 01:42 PM |
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For your first question..............See this thread, with a pic of my solution.
Linker to thread
Also if you search on here for "throttle return spring" it will give you a few other suggestions.
Why do they call Port Harcourt "The Garden City"?...... Becauase they can't spell Stramash.
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Eviljohn
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| posted on 19/9/17 at 03:06 PM |
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Thanks Mr. Jenkins. I did find your in depth thread when i was looking into bike carb conversion and did read it quite a few times.
I think it may be the lack of return spring. Everything else seems to be okay. The carbs were bench balanced before being sent to me, but i will be
sure to double check that.
Mr. Slater, thanks for your reply too. I have a vacuum balance bar connecting vacuum hose from each runner on the manifold to the vacuum advance
system. No hunting on idle so assuming no leaks anywhere. Will work on return spring and see what that does.
Thanks again gents. Much appreciated.
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jacko
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| posted on 20/9/17 at 06:29 PM |
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engine
you can see the extra spring going from the carbs to the rocker cover
jacko
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Eviljohn
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| posted on 20/9/17 at 08:46 PM |
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I can. Thank you. My rocker cover is a fair bit further away but i'm on the case of figuring out a way to attach a return spring. Thanks again.
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MikeRJ
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| posted on 21/9/17 at 09:06 AM |
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quote:
Originally posted by Eviljohn
Firstly: can anyone tell what it's called when it takes a while for revs to drop back to idle when throttle is blipped or actually driving?
Either a purely mechanical issue with the throttle as other have mentioned, or this can be caused by a weak mixture due to incorrect jetting or an air
leak.
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Eviljohn
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| posted on 21/9/17 at 08:48 PM |
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Had a slight issue with starting and then blowback when first fired up, but tightened up the manifold bolts and that got rid of the blowback.
Haven't adjusted any of the pilot screws yet so not sure how far out they are at this point.
Have checked the throttle return again and if i'm honest it doesn't seem to snap shut as i would expect from other threads i have read. I
have picked up a couple of different springs that i can try out so will have a go with those. Haven't checked out main jets yet . Was looking to
get it as close as i could myself before rolling road. But finding one that deals with carbs near me is proving difficult. Found two but they are
crazy busy with other projects.
Thanks again for guidance. It all helps.
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Eviljohn
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| posted on 13/10/17 at 12:11 AM |
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Used some jb high heat epoxy to stick an eye on the back of the engine block. Then hooked a spring from that to the throttle linkage on the carbs.
Just snaps shut again real quick. Will have to wait until it fires up to see how it works. Definitely feels a lot quicker to close.
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