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A A A A Author Topic: Erratic revs  (Read 749 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?

gm

Re: Erratic revs
« Reply #11 on: 14-Mar-21, 12:19 »
thanks Muzza
sorry about the delay in response.
I think the AC valves are functioning ok.
I have been working through my list of things that may or may not have influence over this problem.
I had swapped the original carbies for the spare set and that seemed to work ok for a time then it went silly with the high revs so I pulled the spare carbies out and put the original ones back in.
I also lubricated the the cables (this was on my list) and tested it today. The revs picked up as the engine warmed. I used the idle adjuster to control the revs then it seemed to settle but after the first fan activation the revs increased I turned the idle down and the revs went down slowly and eventually it stalled. It restarted ok and when the revs went down I gave a slight twist to the idle control and it held idle at 1500 for a bit then started to drop. I used the throttle to increase the revs they went up and didn't come back much. I pushed forward on the hand throttle and the revs came down and almost stalled. I was able to control the revs by the hand throttle but the bike would not idle on its own for very long.
Obviously something seems to be affecting the normal operation of the carbies so could it be as simple as the cables either (i) being old and need replacement; (ii) not being routed properly and catching on the sheath or junk build up inside the sheath; (iii) poltergeist perhaps?
I'd be interested in hearing your thoughts on the matter.
thanks again.
gm

CX PHREAK

Re: Erratic revs
« Reply #12 on: 14-Mar-21, 12:30 »
Have you tried installing the carbs with no cables fitted and operating the throttle from the bellcrank to see what happens?

gm

Re: Erratic revs
« Reply #13 on: 14-Mar-21, 14:38 »
OK thanks I'll try this today

Onetrack

Re: Erratic revs
« Reply #14 on: 14-Mar-21, 15:51 »
(iii) poltergeist perhaps? If you have any advice regarding poltergeists, then maybe you can help me to remove the one that lives inside my mobile phone.
"Young" Les F

gm

Re: Erratic revs
« Reply #15 on: 14-Mar-21, 17:33 »
well Gurus
I ran the 650 without the cables attached and was able to get it to idle at around 1200 were it remained even after being revved out to around 4000 it managed to return to the 1200.  Then I turned it off and restarted, I needed to make some minor turns of the idle screw to get back to 1200 but when I revved the engine this time it stayed up for a while. I adjusted the idle again and brought the engine back to 1200 but each time a revved it higher it would not readily return.  So while it was a little more manageable, a  bit smoother, without the cables attached it just isn't right yet.
While the engine ran at the low revs it had a slight misfire occasionally and I noted a tapping noise in the left cylinder most likely a tappet not tightened or spaced right.
Any ideas - I think we are getting closer to the problem.

One Track I'm not sure if the carby poltergeist is handled the same as the phone poltergeist as the phone poltergeist seem to be far more common and are often dealt with by specialist exorcists. but if we have to perform a ritual on my carby you can try it on your phone I might even try it on my phone and the lap top.

gm

CX PHREAK

Re: Erratic revs
« Reply #16 on: 14-Mar-21, 18:11 »
The idle not coming down may be a mixture issue. You get a hanging idle with a lean mixture. The revs come down but take their time. Try cranking out the mixture screws a half turn.

 I would also be testing for intake leaks as these too give a lean mixture.

 I also wonder if the ATU may be slow to return to base timing.

gm

Re: Erratic revs
« Reply #17 on: 18-Mar-21, 19:06 »
Hi Gurus
Well the saga continues.  I adjusted the valves (it would appear not enough as there is still a tapping sound LHS). I replaced the vacuum line from tank to carby as the old one was a bit hard and may have had some cracks.  I couldn't get the 3.5mm only a very soft silicon 4mm but it seemed to work ok.
I turned the mixture screw out 1/4 turn.
I'm not sure how to test the ATU for quick return?
The Bike started with some coaxing of the the throttle pulley assembly. It was difficult to maintain the revs when cold. The choke didn't seem to have any influence although that's not new.  As it warmed and with some adjustment of the idle control it managed to hold revs at 1200 to 1500 when I revved it to 2000 it was slow to return and when I revved it to 3000 it continued unassisted to 4000 then up to 5000.  I had to pull down on the accelerator pump rod (I think that's what its called) to reduce the revs (the throttle cables are still disconnected). When it moved below 3000 it returned slowly to the 1500-1200 area without assistance.
Also there is a slight increase in revs with the air filter removed.
Does this shed any more light on the problem.
I'll test for intake leaks tomorrow although I'm reasonably confident the system is tight especially with the new vacuum line. But you never know what you'll find on an old bike.
gm

CX PHREAK

Re: Erratic revs
« Reply #18 on: 19-Mar-21, 17:33 »
The ATU can be tested with a decent timing light.

It's messy but doable.

It helps to drain about a litre of oil from the motor and do it on the side stand to cut down on flying oil.

 The timing should advance to between the full advance lines and drop back to baseline at idle.

gm

Re: Erratic revs
« Reply #19 on: 29-Mar-21, 14:37 »
Thanks CX PHREAK
I didn't get that far.
I replaced the vacuum line and reconnected the throttle cables.  the bike would run at around 1500revs but when set lower it was quite rough.  I pulled the RHS plug out and it stopped.  I started it again and pulled the LHS plug and it continued with little affect.  I have spark from the LH plug.
Any ideas?
gm

CX PHREAK

Re: Erratic revs
« Reply #20 on: 29-Mar-21, 14:51 »
Test the pulse generators per the FSM.

Play swaptronics with everything else.

Plugs, caps, coils and igniters and see if you can get the issue to swap sides.

And looking at the fuel side, with the engine running remove the balance port from the intake ans squirt a little fuel through it and immediately block the balance port with your thumb.

 If the motor picks up and starts running on that side the issue is likely fuel.

 If not it's a rubbish spark that collapses to nothing under compression and then the plug gets wet with fuel and stops firing.

I'd also test to see if you actually have compression on that side.

gm

Re: Erratic revs
« Reply #21 on: 09-Apr-21, 17:15 »
Hi again.
Well I swapped the plugs no change nothing happening in the left hand cylinder.  I swapped the leads and still no change so I swapped the ignition coils and still no change.  today I did a compression test and the left hand cylinder scored 0 psi dry test and 75psi wet. The right hand cylinder scored 110psi dry and 175psi wet.  the RHS bounced a lot higher  (over 200psi wet) but it did come back.
This is confusing to me but my conclusion is that the left hand cylinder obviously has a problem while the right hand cylinder isn't great but is functional.
Before this problem occurred  the bike was functioning ok it was not using excessive oil perhaps a bit heavy on fuel from time to time.
I'm thinking this is major surgery removing the pistons and valves.  Am I correct?
gm

Seagrass

Re: Erratic revs
« Reply #22 on: 09-Apr-21, 17:52 »
Did you open the throttle fully while doing the compression test? If not do it again with throttle wide open.

Seagrass

gm

Re: Erratic revs
« Reply #23 on: 14-Apr-21, 18:27 »
Thanks Seagrass
sorry for the delay (the compression tester broke)
 
I tested again with the new tester, throttle open;
Left cylinder       5psi dry       7psi wet ;
Right cylinder 120psi dry    135psi wet. 

Similar result in that the Left does not seem to be sealing.

Seagrass

Re: Erratic revs
« Reply #24 on: 14-Apr-21, 19:06 »
Those figures are so low on the left side that you must have a valve not sealing or a blown head gasket or maybe something else.

Even the right hand cylinder is a bit low, I would have expected around 165 psi

 Check your valve clearances and make sure there is a gap on all valves.

Seagrass

 


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