running but not idling

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rgierer
Cucciolo - the Lil Pup
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running but not idling

Post by rgierer » Mon Oct 10, 2011 7:44 pm

The bike 1974 750GT. I have had the bike 8 weeks.

Among many other things I have rebuilt carbs, gone to Dyna coils and a Dyna S. The bike starts on the first kick but wont idle. I tried the adjustment on the side of the carb and it just doesn't get the bike to idle.

On most bikes there is a way to set up the idle so you can at least have it run while you synch and adjust carbs.

It seems to run slow enough but if I release the throttle the bike will die. This is all done without the choke being on.

Im looking for an idea or two.

robin
new owner of 1974 750GT

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abmartin
SSD900 Darmah
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Post by abmartin » Tue Oct 11, 2011 4:49 am

Have you adjusted the throttle stop screws?

Bruce
1979 900SS
Fredericton, NB
Canada

rgierer
Cucciolo - the Lil Pup
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Post by rgierer » Tue Oct 11, 2011 5:58 am

If by throttle stop scews, you mean the screw on the side of the carb that gently lifts the slide, then yes.
new owner of 1974 750GT

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Craig in France
Cagiva Gran Canyon
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Re: running but not idling

Post by Craig in France » Tue Oct 11, 2011 9:28 am

rgierer wrote: Among many other things I have rebuilt carbs ... <snip>
Gotta ask ...

Are you confident whoever did it knew what they were doing, Robin :? ?

Just askin' :) ...

Ciao

Craig

rgierer
Cucciolo - the Lil Pup
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Post by rgierer » Tue Oct 11, 2011 2:07 pm

The same question I was asking myself. I will take that as gentle guidance that i should go through the carbs again paying special attention to the idle circuit.

Thanks
new owner of 1974 750GT

rgierer
Cucciolo - the Lil Pup
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Post by rgierer » Tue Oct 11, 2011 2:55 pm

But recognize, I am still happy! It will start easily and run on 2, count them 2 cylinders. It has brakes that stop and lights that work. The gas tank is clean. Heck it even has new tires.

I have no trouble at all visiting the carbs again.
new owner of 1974 750GT

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BevHevSteve
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Post by BevHevSteve » Wed Oct 12, 2011 4:31 pm

Upon thinking about this quandry, I would do the following:

intake manifold insulators good? Check by squirting chemtool [carb cleaner] around them while biek is running - just a little bit! - if the idle increases they are bad. Replace them PLUS exhaust gaskets to seal up both sides of the head.

Look at the slides - specifically the bottoms where the slide screws hit - are they worn out to the point that the slide screw isn;t doing anything when you turn them in? If the other ramps are good, swap slides carb to carb and the screws will be hitting new ramps and that might cure the problem.

Back to the slides - they they in good shape or are they scored badly etc?

Did you read there here and follow the advise given exactly to sync them?
http://www.bevelheaven.com/~BB/phpBB2/v ... c.php?t=10
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Spub
Mach 3
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Post by Spub » Tue Nov 15, 2011 2:10 pm

+1 what Steve just said. If bike will not idle (assuming carbs balanced and jets are correct and valves are adjusted correctly), first, most likely culprit is a vacum leak. Places where this can occur is, as Steve says manifold gaskets, manifolds themselves, and any of the places where air can come into the carb, most likely: idle screw (does it have "O" ring at seat?), fuel/air screw (same), carb top cap and rubber boot over throttle cable adjuster screw. Also, slides in good order? If all of that checks, then perhaps check static ignition timing spot on? If that checks, then compression loss? It took me a good month going over all of these things before I was able to get my 900SS to idle reliably. Your bike likely does not have 40MM dellortos, so it should idle fairly reliably, if all of the above checks out.
1982 Laverda 180 JOTA, 1975 Moto Morini 3 1/2 Sport, 1993 Moto Guzzi Daytona, 2010 KTM Adventure 990, 1974 Laverda SFC #17188

ducadini
860 GT / GTS
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Post by ducadini » Thu Nov 17, 2011 12:53 am

Shouldn't You be looking at the mixturescrews first ?
Check if the tips are the same (2 different types) and washer/o-ring/spring are good.
1.5 turns out should give a reasonable startingpoint.
If there's a vacuumleak, the bike should run higher right after closing shutting the gas.

cu
j
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mizike77
860 GT / GTS
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Post by mizike77 » Thu Nov 17, 2011 2:50 am

from steve...Look at the slides - specifically the bottoms where the slide screws hit - are they worn out to the point that the slide screw isn;t doing anything when you turn them in? If the other ramps are good, swap slides carb to carb and the screws will be hitting new ramps and that might cure the proble




Thats where I would look first. My Darmah had that same issue...
79 Darmah
78 900 GTS
86 F1B
80 SSD
02 Harley FXD
72 H2 750 triple
08 KTM 300XC
there has yet to be a motorcycle line made that is as satisfying to ride, hear and look at as the ducati bevels

radecal
Parallel Twin
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Post by radecal » Thu Nov 17, 2011 10:09 pm

Big question! What shape are the carbs in?
Did the bike sit for a long period of time before you got it?
If so, a problem can surface where the idle circuit can be gummed up from the fuel going off. The passageways in the idle circuit can be restricted to the extent that it will not idle but will happily chug away on a partially open throttle or above.
I have had 4 sets of carbys in this state and the only way I fixed it was to strip the carbys and use a good detergent in an ultrasonic bath to remove the crap from the galleries and passageways of the idle circuits. Ensure all passageways are blown clear with air as well at the end.
Just helped a bloke out on the Bevelhead list who just picked up a GT as well and was experiencing similar issues.
Regards,
RAD

rgierer
Cucciolo - the Lil Pup
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Post by rgierer » Fri Dec 16, 2011 5:34 am

Carbs are clear, channel was blocked. Success Thank you
new owner of 1974 750GT

radecal
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Post by radecal » Sat Jan 07, 2012 3:03 am

Glad to be of assistance mate.
RAD

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