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Author Topic: High idle rpm  (Read 52 times)

lonsomecrow

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High idle rpm
« on: Today at 01:28:28 PM »
I recently changed handlebar, throttle and clutch lever. Also with the help of Mike_D I have Mikuni TM 32 Carb on it.
We tried different combination of jets to get the correct setting. This is what we have finally:

Needle :P8,
main: 195,
Pilot:   p30

Now the motorcycle runs fine but the only constant issue is the low idle rpm. Every time I stop (like at traffic signal) the rpm rises sharply and the moment gear is engaged, rpm comes down to normal. It happens most of the times but not everytime. I could not figure out what the problem is everything looks fine to me.
I was wondering if it is because of throttle or clutch lever because i replaced them? Or may be wrong carb jettings?
Any suggestions.

I have Goldstar exhuast and K&N Filter with the Carb


ace.cafe

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Re: High idle rpm
« Reply #1 on: Today at 01:39:47 PM »
Well, I think that the P8 needle jet is a little excessive. Probably a P6 would be the most needle jet needed.

You have some clutch drag, which is not unusual, and that is what is pulling the rpms down when you put it in gear.

However, the typical high idle issue at stoplights usually comes from setting the carb when the bike is not fully warmed up. Try setting the idle speed at full warm engine. Depending on how the mixture is set, sometimes the idle goes high, or sometimes it stalls out. I have seen both symptoms. After doing that, then, it might be a little stubborn when cold, but that's a good thing because it makes you wait until it is warmed up some before you ride off hard.

« Last Edit: Today at 01:42:15 PM by ace.cafe »

High On Octane

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Re: High idle rpm
« Reply #2 on: Today at 01:42:16 PM »
If it is intermittent, another possibility is that your throttle cable may be routed wrong and is hanging up a bit.  Does it idle fine when sitting in neutral or rev on it's own if you turn the handlebars one way or the other?
Scottie J  ~  Bulldog Kustoms Denver  ~  1958 Enfield/Indian Trailblazer - The Blackhawk

lonsomecrow

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Re: High idle rpm
« Reply #3 on: Today at 02:00:52 PM »
If it is intermittent, another possibility is that your throttle cable may be routed wrong and is hanging up a bit.  Does it idle fine when sitting in neutral or rev on it's own if you turn the handlebars one way or the other?

Turning the handlebars has no effect on it. RPM rises sharply only when it is sitting in neutral gear. The moment I engage the gear, rpm comes down to normal

lonsomecrow

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Re: High idle rpm
« Reply #4 on: Today at 02:05:28 PM »
Well, I think that the P8 needle jet is a little excessive. Probably a P6 would be the most needle jet needed.

You have some clutch drag, which is not unusual, and that is what is pulling the rpms down when you put it in gear.

However, the typical high idle issue at stoplights usually comes from setting the carb when the bike is not fully warmed up. Try setting the idle speed at full warm engine. Depending on how the mixture is set, sometimes the idle goes high, or sometimes it stalls out. I have seen both symptoms. After doing that, then, it might be a little stubborn when cold, but that's a good thing because it makes you wait until it is warmed up some before you ride off hard.

Ace, you are right. Mike_D had also suggested me to set idle when the engine is warm. I'll try that again.
Regarding jets, we started with P6 but it was popping a lot. We tried P4 and popping from the exahust was even more. P8 has no too negligible. I may try P6 again after this idling issues is fixed and see how it responds?
Thanks

ace.cafe

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Re: High idle rpm
« Reply #5 on: Today at 02:18:05 PM »
Ace, you are right. Mike_D had also suggested me to set idle when the engine is warm. I'll try that again.
Regarding jets, we started with P6 but it was popping a lot. We tried P4 and popping from the exahust was even more. P8 has no too negligible. I may try P6 again after this idling issues is fixed and see how it responds?
Thanks

It is important to get the air bleed screw setting correct. This can cause popping if it is off. If you try the P6, and get some popping, try making the bleed screw a little richer.

High On Octane

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Re: High idle rpm
« Reply #6 on: Today at 02:45:29 PM »
Turning the handlebars has no effect on it. RPM rises sharply only when it is sitting in neutral gear. The moment I engage the gear, rpm comes down to normal

Definitely tuning then.  :)  +1 to what Ace just said.
Scottie J  ~  Bulldog Kustoms Denver  ~  1958 Enfield/Indian Trailblazer - The Blackhawk