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A A A A Author Topic: Erratic revs  (Read 286 times)

gm

Erratic revs
« Started on: 13-Dec-20, 18:47 »
Hi Gurus
I hope you are all well.
As some of you know I have had some issues with the 650 lately and the latest problem is to do with the revs.
I managed to get the motor to run and idle at about 1,100 with the adjusting screw but when the motor warms up to operating temperature the revs climb rapidly to 6,000.
One other strange feature is that when the revs reach the high level they can be reduced temporarily by activating the choke.
Any ideas?
gm

Seagrass

Re: Erratic revs
« Reply #1 on: 13-Dec-20, 19:14 »
Sounds like you have a vacuum leak (leaner mixture revs higher and choke adds more fuel) or maybe your carbies are out of sync.

Seagrass

Seagrass

Re: Erratic revs
« Reply #2 on: 21-Dec-20, 18:29 »
Following up on this I went to visit Graeme today and took my carby balancer and a few other tools with me.

I am at a bit of a loss to know what the cause of the problem might be.

You can start the bike and sort of get it to idle and then as it warms up the revs keep increasing to about 4,000 RPM. There are no detected vacuum leaks (spraying around carby cleaner on boots etc) , all "O" rings are OK and the carby boots look good.

I checked the spark plugs and the right hand plug is running rich and the left plug is normal indicating a possible problem with the right hand cylinder.

I found that if I pushed down on the carby balance adjuster screw (which is attached to the right hand carby) the RPM's would drop to idle. Pushing down on the carby adjuster screw closes the butterfly in the right carby and this is why the idle drops back to normal.

The question is why is the right hand carby butterfly not returning to the correct place on its own?

I have checked the throttle cables have slack and the throttle cables are routed correctly and I cannot see why the butterfly does not return.

Has anyone had this problem before and can advise what we need to do to fix the problem?

Seagrass



CX PHREAK

Re: Erratic revs
« Reply #3 on: 21-Dec-20, 18:40 »
Try putting a little inox on where the throttle shafts enter the carbs and on the linkages.

There is enough cable slack?

Seagrass

Re: Erratic revs
« Reply #4 on: 21-Dec-20, 19:04 »
Sorry I forgot to mention that when I push the carby balancer screw it is under sprung pressure so I am not sure that Inox would help but it is worth a try so thanks.

Seagrass

CX PHREAK

Re: Erratic revs
« Reply #5 on: 21-Dec-20, 21:32 »
These were OK until removed?

The carbs may have moved on the brackets causing misalignment.

 I wouldn't pull them off to check this but if you do have them off remove the vac caps and slides crack all 8 screws and push the top faces of the carb bodies against the edge of the bench and retighten the screws.

gm

Re: Erratic revs
« Reply #6 on: 28-Dec-20, 16:38 »
thanks CX PHREAK and Seagrass
I've been thinking (dangerous, I know). 
I removed the carbies again (getting the hang of it now) but when I looked at removing the vac caps and testing on a flat surface for twisting I noted that there were many things in the way and that perhaps removal of these items might cause twisting (I really don't have a delicate touch) see yellow line on the attached.
There is of course the chance I've misunderstood the instruction.
Just a thought before I start pulling everything apart. If pressing down on the synchronising screw reduces the revs maybe the return spring (yellow arrow) is not tight enough see attached. If I replaced it or put an extra turn on the spring do you think this would reduce the problem?
gm

joethebike

Re: Erratic revs
« Reply #7 on: 28-Dec-20, 18:40 »
Seagrass, I know you checked for air leaks but I will mention the hose from the vacuum port to the fuel tap. No splits in the hose?

Seagrass

Re: Erratic revs
« Reply #8 on: 28-Dec-20, 18:46 »
Joe thanks for the suggestion but I have checked that hose and I am satisfied it is OK.

Seagrass

Seagrass

Re: Erratic revs
« Reply #9 on: 28-Dec-20, 18:47 »
thanks CX PHREAK and Seagrass
I've been thinking (dangerous, I know). 
I removed the carbies again (getting the hang of it now) but when I looked at removing the vac caps and testing on a flat surface for twisting I noted that there were many things in the way and that perhaps removal of these items might cause twisting (I really don't have a delicate touch) see yellow line on the attached.
There is of course the chance I've misunderstood the instruction.
Just a thought before I start pulling everything apart. If pressing down on the synchronising screw reduces the revs maybe the return spring (yellow arrow) is not tight enough see attached. If I replaced it or put an extra turn on the spring do you think this would reduce the problem?
gm

Graham I like your thought BUT as it was OK before you removed the engine it should be still OK.

That spring could not have moved so I doubt it is the cause or solution to the problem.

Seagrass

muzza

Re: Erratic revs
« Reply #10 on: 29-Dec-20, 04:22 »
AC valves ok?

 


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