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AT LOW RPM AND TAKE OFF I'VE GOT SOME SERIOUS NOISE FROM THE LEFT ROCKER COVER. I CHECKED THE VALVE CLEARANCE, BUT I CAN'T GET GOOD VACUUM FROM #4 CARB. I'VE HAD THE CARBS OFF & N SO MANY TIMES, I'VE GOT IT DOWN TO 20 MINUTES. BEING AN AIRCRAFT MECHANIC HAS TOUGHT ME MUCH PATIENCE WITH TROUBLESHOOTING. BUT EXPERIENCE ALWAYS RANKS HIGH WHEN PROBLEMS ARISE. A LITTLE GUIDANCE WOULD BE GREATLY APPRECIATED. DOES ANYONE HAVE A GOOD FLOW DIAGRAM OF THE CARBURETOR SET-UP?

J DUB
 

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How's the compression on the left bank? Ahh... Paris in the spring! No vacuum in #4could be a valve problem. When did the noise start? Have the timing belts been replaced recently?
 

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I thought #4 carb had a fixed vacuum on the 4 cylinder Wings. That would be why you can't get a variable reading. When you balance the carbs, you use #4 as the reference carb to set the others against.
 

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#3 carb is the reference cylinder. Compression is good and fuel supply. Once I get up to about 2500 rpm and some speed , she runs like a champ.
 

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Noise + low vacuum might = burnt exhaust valve. How do you define "low vacuum?" What are the vacuum readings? Easy to get +/- 10 inches from being out of tune.

Its possible to be quite low just from being out of synchronisation. The reference cylidner is the one thats non-adjustable. The rest have to be synched to it. Weak ignition also causes "valve noise" when cylinders fire out the exhaust valves, which in turn fries valves.:shock: It sounds exactly like metal on metal noise.
 

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Hi Dave, thanks for the response. Vacuum at #3 is 5 inches at 2000 rpm. I adjusted 1 and 2 to 5 inches, but when I got to #4, as I was adjusting and the gage was coming up in the positive range, my rpm started coming down and killed it. Keep in mind that I have only one vacuum gauge, so I don't know what's goin on with the other three. I guess to relly do this procedure I need to know what I'm inducing on the other cylinders. Why are those vacuum gauges so hard to find? I think I will take out the valves. No matter how muchadjusting I do, there's no headway. Thanks again for the help. Spring is on the way.

J DUB
 

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J DUB wrote:
Hi Dave, thanks for the response. Vacuum at #3 is 5 inches at 2000 rpm. I adjusted 1 and 2 to 5 inches, but when I got to #4, as I was adjusting and the gage was coming up in the positive range, my rpm started coming down and killed it. Keep in mind that I have only one vacuum gauge, so I don't know what's goin on with the other three. I guess to relly do this procedure I need to know what I'm inducing on the other cylinders. Why are those vacuum gauges so hard to find? I think I will take out the valves. No matter how much adjusting I do, there's no headway. Thanks again for the help. Spring is on the way.

J DUB
5 inches is way too low, should be 20- something on idle (1100-1500 RPM). Time for a compression check. Reading should NEVER go positive, that indicates backfire or leaking valve.

Synch is not easy, change one cylinder and it affects the others because the cylinders are tied to a common crankshaft. But there are bigger fish to fry before that.

If a compression test doesnt show a burnt valve, remove the carbs and gauge the throttle plate openings with a piece of wire to set them "close. One carb badly out can seriously mess the rest up.
 

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J DUB wrote:
Hi Dave, thanks for the response. Vacuum at #3 is 5 inches at 2000 rpm. I adjusted 1 and 2 to 5 inches, but when I got to #4, as I was adjusting and the gage was coming up in the positive range, my rpm started coming down and killed it. Keep in mind that I have only one vacuum gauge, so I don't know what's goin on with the other three. I guess to relly do this procedure I need to know what I'm inducing on the other cylinders. Why are those vacuum gauges so hard to find? I think I will take out the valves. No matter how muchadjusting I do, there's no headway. Thanks again for the help. Spring is on the way.
J DUB, with vacuum readings like you have (especially that positive reading) unless you are running a turbo or blower I would strongly suspect your vacuum gauge as being defective..

With all cylinders at 3"-5" of vacuum at 2000 RPM that engine would not run as the carbs would basically be wide open..

OR-- you have a severely plugged exhaust system & at those vacuum readings that engine wouldn't even pull the bike down the road..

Check your vacuum gauge on a car engine at idle (probably 20"+ at idle if gauge is good..



JDC
 
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