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Author: Subject: Revs drop slowly to idle

posted on 19/9/17 at 09:33 AM Reply With Quote
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

posted on 19/9/17 at 10:02 AM Reply With Quote
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.

The older I get, the better I was...

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posted on 19/9/17 at 01:42 PM Reply With Quote
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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posted on 19/9/17 at 03:06 PM Reply With Quote
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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posted on 20/9/17 at 06:29 PM Reply With Quote

you can see the extra spring going from the carbs to the rocker cover

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posted on 20/9/17 at 08:46 PM Reply With Quote
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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