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post #1 of 13 (permalink) Old 10-19-2013, 12:34 AM Thread Starter
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Unusual rev

So I have noticed my bike revving with no throttle usually soon after starting the bike with choke. what's weird is the fluctuations in rpms. It can be at normal rpms(1100) and then jump up to 3k and sit there while idling and then after taking off it will drop. Is there anything anyone has encountered that might cause this? Recently installed new throttle cables. They work like a charm. Any help is appreciated.
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post #2 of 13 (permalink) Old 10-19-2013, 10:54 AM
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I'm not sure of what you are saying here. When you start the bike (cold) with the choke, the RPMs will go up as the bike warns up. That's why he choke is a progressive lever, so you can slowly back it down while it does.

You should not ride with the choke on. If you are saying that the bikes RPMs rise and fall after the bike has warmed up and ridden a few miles, you have a leak in your boots or a clog somewhere.

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post #3 of 13 (permalink) Old 10-19-2013, 11:00 AM
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Revs

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Originally Posted by Timmah6859 View Post
So I have noticed my bike revving with no throttle usually soon after starting the bike with choke. what's weird is the fluctuations in rpms. It can be at normal rpms(1100) and then jump up to 3k and sit there while idling and then after taking off it will drop. Is there anything anyone has encountered that might cause this? Recently installed new throttle cables. They work like a charm. Any help is appreciated.
My 2002 VN-750 revs higher during warm up and I just close the choke back back down a litle and it runs fine after that. BTW, the so called experts say to just warm it up about 15 seconds to get the oil distributed properly and then drive it gingerly without over revving it for the first couple of miles. Claiming thats the way to warm up any modern day engine without letting it idle wasting gas.
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post #4 of 13 (permalink) Old 10-19-2013, 11:03 AM
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Originally Posted by Knifemaker View Post
I'm not sure of what you are saying here. When you start the bike (cold) with the choke, the RPMs will go up as the bike warns up. That's why he choke is a progressive lever, so you can slowly back it down while it does.

You should not ride with the choke on. If you are saying that the bikes RPMs rise and fall after the bike has warmed up and ridden a few miles, you have a leak in your boots or a clog somewhere.
Oop's Knifemaker, didn't know you had made that post saying basically the same thing as I did! Ten lashes!
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post #5 of 13 (permalink) Old 10-19-2013, 11:35 AM
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It is normal for the rpms to go really high with the choke all the way on. Mine will quickly go over 3000 rpm after the choke has been on all the way for a few seconds. You need to back off the choke to keep the rpms down. As KM said, do not ride it with the choke on. I warm mine up until the needle on the temp gauge reaches the second mark from the left before taking off. If it only does this with the choke on, I'd say it is normal. If you get fluctuations in idle speed with the choke off, then something is wrong.

I had an issue where the idle would remain around 3,000 rpm with the choke off, for 10-15 seconds after blipping the throttle, before returning to normal. It turned out to be a bad diaphragm on the coasting enrichener on the front carb. But many things can cause a fluctuation in idle speed. A vacuum leak, plugged jets or a passage in the carb, problems with the enrichener system including the cable, problems with the throttle and cable, problems with the vacuum diaphragms on the top of the carb.

Does it do this only when the choke is on?

I am a motorcyclist, NOT a biker.


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2001 Yamaha XT225, heavily modified
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post #6 of 13 (permalink) Old 10-19-2013, 12:14 PM
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Geezy, the most I let anything warm up is 1 minute.
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post #7 of 13 (permalink) Old 10-19-2013, 12:17 PM Thread Starter
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I tried to be clear. The choke is completely off and the rpms fluctuate with no throttle with the bike just sitting there.
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post #8 of 13 (permalink) Old 10-19-2013, 12:19 PM
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Geezy, the most I let anything warm up is 1 minute.
I only let mine warm up longer than about 15 seconds is when I go on the "Frozen Toe" rides in 30 degree temps.
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post #9 of 13 (permalink) Old 10-19-2013, 03:16 PM
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Geezy, the most I let anything warm up is 1 minute.
same here..

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Originally Posted by Timmah6859 View Post
I tried to be clear. The choke is completely off and the rpms fluctuate with no throttle with the bike just sitting there.
a few rpm fluctuation is gonna occur.. jumping a lot means a leak someplace
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post #10 of 13 (permalink) Old 10-20-2013, 03:08 PM
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Quote:
Originally Posted by Timmah6859 View Post
I tried to be clear. The choke is completely off and the rpms fluctuate with no throttle with the bike just sitting there.
Well then, it can be a leaky carb boot, a clogged idle jet, torn diaphragm in the carb or other blockage, cylinder cutting out or even water in the gas.

I'd start with some SeaFoam and check the boots. Clean/replace the plugs and check for loose connections in the ignition system. Make sure the carb vents are clear.

Not holding a steady idle can encompass alot of things unfortunately.....

If it did not do this until you replaced the throttle cable I'd start there to make sure it's functioning properly.

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