Fast idle and a few other problems

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Alan L said:
yes i think distortion due to over tightening etc either in the body or float bowl is a likely explanatio, thank you.
I will investigate and get back
al
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Hi
There are a few answers on this forum about straightening the Amal carb body . I Think the last one was "Amal de-warping jig" dated March22 2020 . If you go down the carb slide resleeve path contact Allan 02 4632 7202 he has been doing this for decades and advertises in the Classic Clatter the journal of the Classic and Enthusiasts Motorcycle Club NSW .
Paul
 
Can't you just pull the air cleaner to verify the slides are closing, hot or cold?
 
You will never guess how long a piece of string is (That's why they made the saying)

Not used in a long time then there is little choice but to remove the exterior bolt on parts and start servicing and confirming the actual condition.
Pull the carburetors, strip and clean them along with freshly lubricated cables, move to the next item.
#
The flanges on my brand new Premiers were not flat which was a surprise (after lapping the inlet manifold faces and countersinking any holes including those for the studs)
 
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I had a slide jam open on a single amal setup. Happened after a longish run. Stopped for five minutes to fuel up. Just prior to restart I happened to twist the grip and discovered it did not fully return to closed. After poking around the carb, found the float bowl to be too hot to touch. Seems the heat soak to the carb was enough to distort the slide bore. After it cooled, grip suddenly rotated fully closed.
I fitted the insulator type "gaskets" 'tween the head and single manifold and another 'tween carb and manifold. Completely solved the hot float bowl and never had another jam open.
Since moving to dual carbs, I still use insulators for peace of mind.

Abrupt clutch action? Might in center clutch basket be notched excessively? Mine was acting up and turned out to have deep notches. New hardened center from CNW solved it.
 
Tornado said:
I had a slide jam open on a single amal setup. Happened after a longish run. Stopped for five minutes to fuel up. Just prior to restart I happened to twist the grip and discovered it did not fully return to closed. After poking around the carb, found the float bowl to be too hot to touch. Seems the heat soak to the carb was enough to distort the slide bore. After it cooled, grip suddenly rotated fully closed.
I fitted the insulator type "gaskets" 'tween the head and single manifold and another 'tween carb and manifold. Completely solved the hot float bowl and never had another jam open.
Since moving to dual carbs, I still use insulators for peace of mind.

Abrupt clutch action? Might in center clutch basket be notched excessively? Mine was acting up and turned out to have deep notches. New hardened center from CNW solved it.
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Part of the problem might be, the Bakelite insulator is fine but heat once stopped can get to the manifold through the cap screws who's heads are in contact with the manifold bypassing the insulator.
From the manifold to the carburetor heat transfer is just a matter of parked time.

On early Moto Guzzi's the manifold fastener holes have a counterbore in which a thick Bakelite washer inserts with a washer (replaced with brass) on top of it for the cap screw , that stops heat transfer via that path.
Maybe the Commando cap screw could have a insulating washer of some sort under its head.

Fast idle and a few other problems
 
High idle post-warm-up is almost always air leakage. I would try spraying some ether or carb cleaner around suspected sources to see what affects idle. It has to be something that opens up when the engine is hot. A constant leak or incorrect timing would affect idle when cold, also. If it's due to a sloppy slide-to-carb body fit, spraying at the top where the cables emerge should make a difference. The manifold-to intake port junction is also suspect. I like to spray the bakelite insulators with aluminized silver paint prior to assembly. Another way to check is to cap the balance tube pipes, which would isolate the leak to one side or the other. After allowing it to high idle for a bit, pull the plugs and check for differences.
 
Danno said:
High idle post-warm-up is almost always air leakage. I would try spraying some ether or carb cleaner around suspected sources to see what affects idle. It has to be something that opens up when the engine is hot. A constant leak or incorrect timing would affect idle when cold, also. If it's due to a sloppy slide-to-carb body fit, spraying at the top where the cables emerge should make a difference. The manifold-to intake port junction is also suspect. I like to spray the bakelite insulators with aluminized silver paint prior to assembly. Another way to check is to cap the balance tube pipes, which would isolate the leak to one side or the other. After allowing it to high idle for a bit, pull the plugs and check for differences.
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Ive seen pics of those insulators sandwiched between standard gaskets to give better sealing. The insulators are hard and do not seal well on their own. I use Hylomar blue as it seems to hold up well and no discernable air leaks. Disassembly/cleaning easier than setting sealants like Yamabond.
 
Time Warp said:
Part of the problem might be, the Bakelite insulator is fine but heat once stopped can get to the manifold through the cap screws who's heads are in contact with the manifold bypassing the insulator.
From the manifold to the carburetor heat transfer is just a matter of parked time.

On early Moto Guzzi's the manifold fastener holes have a counterbore in which a thick Bakelite washer inserts with a washer (replaced with brass) on top of it for the cap screw , that stops heat transfer via that path.
Maybe the Commando cap screw could have a insulating washer of some sort under its head.

View attachment 79496
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I agree the fasteners are a path for heat transfer. Also, I think the one carb into two intake ports manifold is less able to shed heat compared to two single manifolds for dual carbs. Less surface area and bigger lump of alu for the single carb mani.
Note in my case the float bowl was not excessively hot while out riding nor immediately after stopping, just after a five minute stop, heat soak period. With my insulator use, things stay cool even after such stoppage.
 
It is also possible that there is no slack in the cables so then the slide or slides will drop no further no matter how much you back off the idle screw.
 
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Alan L... any updates...?

Please don’t be one of those ungentlemanly types who disappears leaving the plot open ended ...
 
Alan L said:
The bike is a perfect starter, almost always first prod with an appropriate tickle when cold. It instantly settles into a perfect idle. However, once warm, the idle stubbornly hangs up around 2000rpm. From reading the forum I’m led to believe it’s slide wear.
# Does over-tightening the carburettor to the manifold lead to distortion of the body contributing to the problem?
# Does simply fitting new slides help with this problem?
# Should I have the bodies rebored and sleeved? Who would perform this work in Australia? I really don’t want to fit a single Mikuni.

Wow, is that front brake useless. I always thought I had large strong hands but at 62 and with a condition called Dupuytrens Contracture I can barely slow the bike down. I Have a reduced master cylinder kit ordered so I hope that helps, otherwise I will have to rethink the front brakes
# I have heard that Ferodo Platinum pads gives improved stops, is this correct?
# Does anyone have any other suggestions.
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Like some already mentioned: is there enough slack in the cables? Second: are the carbs adjusted at a warmed up engine? Are the choke slides still on it? Rather than worn slides, false air comes from warped flanges. Sand them flat on a piece of waterproof sand paper on a glass plate. Worn slides will make an engine hickup when giving some throttle after closed throttle. Slides are more prone to stick when opened, rather than closed. And do not mix up the throtle stop and air mixture screw.

Depending on how much you wish to spend on your front brake, but even more depending on how much you value original looks, sleeving the master and mounting a steel braided line up front are the way to start. Exotic calipers, modern big discs and big adapter plates make you bike break heavenly, but I don't like the looks of them. And their price.
 
NIX said:
Like some already mentioned: is there enough slack in the cables? Second: are the carbs adjusted at a warmed up engine? Are the choke slides still on it? Rather than worn slides, false air comes from warped flanges. Sand them flat on a piece of waterproof sand paper on a glass plate. Worn slides will make an engine hickup when giving some throttle after closed throttle. Slides are more prone to stick when opened, rather than closed. And do not mix up the throtle stop and air mixture screw.

Depending on how much you wish to spend on your front brake, but even more depending on how much you value original looks, sleeving the master and mounting a steel braided line up front are the way to start. Exotic calipers, modern big discs and big adapter plates make you bike break heavenly, but I don't like the looks of them. And their price.
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No ,do not sand the flanges, Straighten the carb body there are many posts on this.
 
Dick Casy, 389 Amal Mono repair - straighten flange -, on U tube has instructions.
Sorry cannot post thread -you need a vice, big long sprocket to fit in place of slide and feeler gauges.
 
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Fast Eddie said:
Alan L... any updates...?

Please don’t be one of those ungentlemanly types who disappears leaving the plot open ended ...
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Hi Eddie,
more investigation but no solution, particular ensuring the slides are reaching the bottom with idle screw removed. A quick change to new Amal premiums would be definitive.
It is not external air leaks, I believe the air is flowing past worn slides. Otherwise it starts and runs very well.
I will keep on it but last few days have been spent installing RGM reduced diameter master and mucking about with lever geometry.
Coming out of hibernation it’s surprising how many small problems and mis-adjustments I’m finding.
The good news is that every little problem solved incrementally improves the bike.
Put new K81 tyres on yesterday and in classic form managed to pinch a tube, my specialty.
Weather in Southern NSW is turning to crap with rain falling and temps dropping, as soon as things improve it will be time to take it for a decent ride
regards
al
 
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