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post #1 of 9 (permalink) Old 04-27-2010, 04:25 PM Thread Starter
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Idle Adjustment Help Needed

Hey guys, the idle adjustment screw (that handy black knob) is MIA on my bike (thanks previous owner), im trying to figure out which screw under the carbs is the idle adjust. There are two that i see, the one closer to me is for balancing and the other one is basically a throttle stop screw, in that the screw length determines where the throttle plate is positioned when at rest. Is the throttle stop screw the same as the idle adjustment?

Just in case your curious, my bike idles beautifully when first started with a little choke, smack on 1000rpm. When the bike is warm and the choke is off completely the idle speed is at about 1500rpm. I figure if I can adjust the idle a tad lower I can compensate with the choke until she's warmed up. Thanks in advance for the help guys.
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post #2 of 9 (permalink) Old 04-27-2010, 05:16 PM
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You've got it right.

However, a 500 rpm diff in idle after warmup is a bit curious. With a "smack on" cold idle with no choke indicates a too rich fuel adjustment on both carbs. Ignore the idiots that claim the adjustment screw on the forward lower part of the carb body is an air screw. It's not, it's a fuel metering screw.

You're running rich, way rich. Make sure the carbs are properly sync'd at warm idle (service idle specs proceedure) then adjust the missing screw (handle) to 1000 rpm. Then start backing INWARDS on each carb by 1/8 turns until the RPM's stop increasing. That's called Lean-Best-Idle. Now set the idle speed with the missing screw/knob you referred to earlier.

How do I know? 84,700 miles on an 86 and a documented one million miles on two wheels.

Go Fish.
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post #3 of 9 (permalink) Old 04-27-2010, 05:22 PM
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Quote:
Originally Posted by AlwaysOnTwo View Post
You've got it right.

However, a 500 rpm diff in idle after warmup is a bit curious. With a "smack on" cold idle with no choke indicates a too rich fuel adjustment on both carbs. Ignore the idiots that claim the adjustment screw on the forward lower part of the carb body is an air screw. It's not, it's a fuel metering screw.

You're running rich, way rich. Make sure the carbs are properly sync'd at warm idle (service idle specs proceedure) then adjust the missing screw (handle) to 1000 rpm. Then start backing INWARDS on each carb by 1/8 turns until the RPM's stop increasing. That's called Lean-Best-Idle. Now set the idle speed with the missing screw/knob you referred to earlier.

How do I know? 84,700 miles on an 86 and a documented one million miles on two wheels.

Go Fish.
i am curious as to what idiots you speak of i dont know of anyone here who said it is an air screw it is a fuel metering screw. second what has crawled up your a#% today we are all here to help. and as far as how far you have ridden on two wheels this isnt a contest of one upmanship i could really care less


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post #4 of 9 (permalink) Old 04-27-2010, 07:54 PM Thread Starter
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Hey, just wanted to re-iterate, i DO have the choke on slightly when cold idling, thats when it idles perfectly at 1000rpm. As the bike gets warmed up the idle speed increases to around 1500, thats with the choke off. It is running a bit rich, but not by very much. Is it possible that the idle has just been set too high?

I'd dive right in but the awkward location of the screw (missing the damn knob) makes me want to gather up all the advice I can before I get to it.
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post #5 of 9 (permalink) Old 04-29-2010, 03:12 AM
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my idle adjuster knob is gone also so i went to autozone got a carb adjust screw set took my dremel made the biggest bit a little bigger to fit works great you can adjust idle with tank on and room to spear good luck my freind
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post #6 of 9 (permalink) Old 04-29-2010, 11:29 AM
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Ordinarily, when you start one of our bikes, and I'm going by my own bike that ran perfect, in my opinion, I'd pull the choke on a little more than half way. The bike would start and at first idle pretty slow, but within a few seconds it would rise to around 2000 rpms, and I'd slowly back off the choke til it idled at 1500 or so, and a few seconds more and it would start to rise up to around 2000 or so and I'd push the choke off a little more, repeating this process trying to keep the bike at around 1500 rpms until it warmed up enough to idle on it's own. Usually it would idle at around 800-900 on it's own, until I rode for a few minutes, and would eventually idle at 1100 once it had reached full operating temperature.

It is normal for the bike to idle a little slow until it is fully warmed up. If it settles at 1500 rpms, fully warm, (after you've ridden for a few miles) and doesn't rise and fall inconsistently, then I would say that your idle stop adjustment is off a little and needs to back off so it can idle at 1100. Before adjusting this, I would make certain that your throttle cables are not binding in any way, and that the throttle snaps back to the stop every time like it should. You can check this with the bike shut off. If that's all good, then go ahead and warm your bike by riding a few miles and then adjust the idle stop. Then when you have it idling at around 1100, ride the bike a few days and see if things continue to stay where they are at.

I'd imagine you will probably have to use a little more choke to start the bike after this adjustment, but in my opinion, that is how it's supposed to be. After you adjust the idle, I'd be curious to see if it doesn't start to act exactly like my bike did the whole time I had it. Let us know! Good luck!

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post #7 of 9 (permalink) Old 04-29-2010, 01:32 PM Thread Starter
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Hey fellas, thanks for all the responses, you guys make this forum rock. Ive got the same warm up routine that Fergy does, put on choke about halfway until it revs and then coax it back into a nice even idle. I do have a little inconsistency on the gauge at warm 1500 idle, im estimating it to be up to about 150 rpm up or down. When its cold idling i dont have any movement on the needle, its a thing of beauty (plus my gauges dont vibrate so much). Oh and my throttle cable are clean and snappy, I just did them last week.

I found my idle adjust screw by rolling the throttle and checking where the cable housing makes contact with the screw to keep the throttle plate open. I suspect that mine is different from other vulcans, it looks like a mechanic the bike was brought to (in its previous life) replaced the idle adjust with a phillips head machine screw, (a spring fitted under the head of the screw). I should mention that im not looking at the sync screw, i made double sure of that. Anyways, i cant imagine that the stock plastic knob somehow drives a phillips head screw to make adjustments so Im pretty sure this is a little improv going on. Only problem is its impossible to get to the screw with any phillips head device, of which ive got several. If thats not bad enough, the damn thing doesnt have a hex head. I might have to pull the tank and see if I can weasel in from above.

Im hoping that Fergy's right and Ill just compensate for a slow cold idle with some good ole choke. Ill let you guys know how it goes, thanks for all your help.
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post #8 of 9 (permalink) Old 04-29-2010, 06:14 PM Thread Starter
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OK, so I got a little lucky. Like my friend Pete says, "the sun even shines on a dogs ass once in a while". After a little noodle scratching I unbolted the tank, shifted it to the right a bit and managed to snake down a foot long phillips head onto the throttle stop. I seriously thought I was going to have to pull the carbs just to adjust the thing. I gave it about 3/4 turn out and when the bike was hot the idle was too low, like 600-700, didnt sound healthy and i got a few backfires (not popping). I went the other way and ended up with an idle of about 1900. Went back some and with the bike hot (no choke of course) i now have an idle of about 1300. One measly thread makes quite a difference.
Its not exactly where I want it but I figure Ill ride with it for a few days and see if all is going well.
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post #9 of 9 (permalink) Old 04-29-2010, 08:52 PM Thread Starter
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Just an add on to my previous post, my 1300 idle increased to about 1600 when the bike was fully warmed up i.e thermostat in open loop. I turned it back out about 1/5 of a turn, no time to ride it more tonight though. Does seem awefuly finnicky though.
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