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FCR Carb throttle issue

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Last night I removed, partly stripped and cleaned my 39mm FCR Carb

I have rectified the idling troubles I was having (at last!)

Only now I have noticed that the throttle isn't snapping back as fast as it should be.

I am worried that this is a spring that spins the throttle disc issue rather than the throttle cable adjustment as it seems sluggish without cables attached

Have I damaged anything that might need replacing?

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Did you have the slide out of the carb? Did you get solvent on the release plate seal? If so, giving it 24 hours or so to evaporate should return the seal to serviceable condition. But never use carb cleaner, it is too tough on the rubber parts.

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Did you have the slide out of the carb? Did you get solvent on the release plate seal? If so, giving it 24 hours or so to evaporate should return the seal to serviceable condition. But never use carb cleaner, it is too tough on the rubber parts.

Thanks for the reply William,

I did use carb cleaner as I already have done with previous carbs and using it seemed to have solved my idling issues.

I didn't take the slide out but I did spray carb cleaner up into the top of the carb a few times.

I just took the top lid off and it is still wet from the cleaner.

I re-attached the throttle cables and still having same problem

I take it I have to wait for the cleaner to evaporate off

If this doesn't solve it I don't know what could be the cause

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Leave the lid off the carb and let it sit at least 25 hours, preferable with the carb off the bike.

Carb cleaner is NG for a FCR.

ok that's great

Thanks

What should I use to clean my FCR???

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Some prefer to use Brake Cleaner, stating that it is less harmful to rubber parts and gaskets. Can anyone confirm this?

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Yup, brake parts cleaner, electrical parts cleaner. Read the can, if it is safe for rubber and plastic, it is safe to use.

Strong solvents like carb cleaner can only be safely used IF you know there are no rubber or plastic parts.

The FCR has internal rubber seals that you do not want to mess with.

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Yup, brake parts cleaner, electrical parts cleaner. Read the can, if it is safe for rubber and plastic, it is safe to use.

Strong solvents like carb cleaner can only be safely used IF you know there are no rubber or plastic parts.

The FCR has internal rubber seals that you do not want to mess with.

That carb cleaner is serious stuff ...Does to rubber like what the old recipe Coca-cola did to your guts...:thumbsup:

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That carb cleaner is serious stuff ...Does to rubber like what the old recipe Coca-cola did to your guts...:thumbsup:

Oh F*£K!

Well let's see if mine recovers....???

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Well throttle issues have resolved themselves (thanks for the advice)

But my engine still isn't idling properly. Throttle response is fine might I add.

The engine is now starting to cut out now when you just blip the throttle slightly.

I also seem to have 2 idle speeds. What I think is the normal idle is too high and when I blip the throttle it drops lower and depending on where the idle screw is, the engine can die

I am at my wits end with this f*%king carb

I don't understand it fully enough to know what to do next.

I use it everyday for work and I go back tomorrow

Any help appreciated muchly

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1-put in a new pilot jet

2 Do this:

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

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I need a diagram with label showing exactly where the fuel screw is on a 39mm Kehin FCR

There's nothing that stood out as one when I took the carb partly apart

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Bottom of the carb. You have the 17mm cap and a hole. Up in the hole is the fuel screw. Which is why so many buy an extended fuel screw.

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Just looking at a site and it mentions the main air jet being turned out by 1 turn.

Mine, when I put carb back together, could possibly be tightened all the way up

Could this be causing my idling problems?

Edited by cbr9rrnut
missed out text

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Bottom of the carb. You have the 17mm cap and a hole. Up in the hole is the fuel screw. Which is why so many buy an extended fuel screw.

Do I need any special tools???

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Just looking at a site and it mentions the main air jet being turned out by 1 turn.

Mine, when I put carb back together, could possibly be tightened all the way up

Could this be causing my idling problems?

I think you read a typo. Do not over analyze things. Main air jets are not adjustable by turning, you have to swap jets.
Do I need any special tools???

Some use a stubby screw driver, some use a special 90 degree tool as sold by Motion Pro. Most just replace the fuel screw with a good brass or stainless steel extrended one/ (No Alloy ones, they can be trouble) A few enterpising folks extend the stocker.

Kientech

Merge Racing

Scotts

Kouba

James Dean

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