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dropping to idle is hesitant

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Guys,

New engine running real nice, however idle is smooth until you blip, then it doesn't return to normal idle speed until you restart engine or engage the drive-train and engage the clutch a little

this issue is ongoing from pre-engine replacement so has to be the carb.

I'm satisfied the throttle cable adjustment is fine.

Is this the float jamming in the FCR?

Thanks for the help so far, bike is running great and I've learnt loads!

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That's the black plastic thumbscrew on the side of the carb right?

I tried turning it to the left a fair few rotations, didn't seem to make any difference to my idle speed?

However after fiddling with it a bit the bike seems to return to idle quickly after being revved.

My understanding of an idle screw is that I should be able to back the idle off until the engine runs lumpy, then increase it until it smooths out.

Is my idle screw jammed, or do you have to turn it for ever for it to make any difference?

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Sounds like your turning the chock. The Idle knob is below the bottom of the carb and is white on mne.

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The chock? What's that? have you got an FCR?

No, didn't notice that you have an E.

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"My understanding of an idle screw is that I should be able to back the idle off until the engine runs lumpy, then increase it until it smooths out."

I think your understanding would be the fuel screw. The idle adjust knob does exactly that, speeds up the idle or slows it down.

Yes, the idle adjuster is the black knob just above the float bowl gasget, the choke, which im sure your aware of is the one which just misses the fuel tap on the tank and pulls in and out.

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Tarka,

Just to clarify, I'm not talking about the fuel screw I am talking about the idle knob.

What I mean is that it should be fairly sensitive? I.e. if I turn it to the left a rotation or two the bike should be pretty much stalling due to the idle speed being too low. I should then be able to increase it until the engine runs smoothly.

Sure the same logic could loosely be applied to the mixture screw when leaning out or richening the mixture.

Now the issue I have is that my idle screw doesn't really seem to affect the idle much at all, if any? How sensitive should it be? Is mine jammed? Its stiff to turn.

It is a 'used' FCR, in that it is the original carb off my 'E' model DR-Z, and I have just put an SM engine in, and used my carb etc.

Cheers,

Con

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Check to make sure that the throttle wheel on the carb (Where the cables hook into) is not touching the frame. I had this problem and it was causing my idle to hang when releasing the throttle as it was making contact with the frame just before hitting the stop screw. I just had to loosen the clamps, tweak the carb and re-tighten.

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a useful point, and I will check that. However I still need some advice on the state/operation of my idle screw.

Cheers,

Con

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If you turn the idle stop... yes, it is sensitive. Half a turn from where it's at would either make it stall, or idle at 2500 rpm.

I think the post above should have been the "Choke." The choke has a black knob. If the choke is leaking a little, it will cause a high idle, and twisting it, may help seat the seals.

But either way... if you got it do come back to normal, good. The FCR seems to be very sensitive on the idle adjustment since I see this topic come up often, and I know on my personal bike, it is a very fine adjustment where the idle comes back quickly, but doesn't stall.

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Yeah I'm quite aware about what knob the choke is :banana:

i turned the idle a few turns to the left, expecting it to stall but it didn't.

Then upon reving the bike it would just stall.

So I turned it roughly back to where I thought it was to start with, and the issue seems to have gone.

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An air leak could also give you the same effect ,also the slide upside down in the carb.

If you solved it by turning idle to the bottom ,could indicate that the slide is hanging inside the carb.

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A worn fcr will have the same problem. Did you have the carb apart? If the vacuum release plate is installed on the slide wrong it will act like this also. Or it may just be normal wear and tear.

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I've not had anything but the AP diaphragm out personally. (to do the eddie mod).

Can you get a rebuild kit for FCRs? How easy are they to rebuild?

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Are you sure the boots are tight...not just snug. With the bike at a steady idle...shoot some carb cleaner at the boot joints. If the idle changes...you have an air leak...an dneed to tighten your clamps.

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What RToth said. Also, the end of the idle adjuster is the stop for the throttle wheel so when its turned it will always affect the idle, it cant not. Try turning it a little then blip the throttle a little to let the idle settle better. Its also better to set it with the moter fully warmed up. You might also want to lube the part between the black knob and the throttle wheel stop. Its curved so if its dry it will be tight to turn.

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