Freshly rebuilt amal 932 carbs with stay up floats, anodized slides viton tipped float needles etc. Bike runs well after warmed up but will not idle unless I take it for a short ride first. I also noticed that when I sit at idle the bike will eventually falter unless I tickle the carb, then the revs will increase and slowly fade and shut off after a minute. I have thouroghly cleaned the idle air circuit with guitar string and raised the float height with no luck. Any ideas?
72 Commando idling issue
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Mr. Rick
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I guess this depends on what you mean by a short ride. My bike will not idle properly unless it's warmed up, and i live in a pretty warm place. Takes about 2 minutes with some choke and the throttle held slightly open.
What idle speed are you after? Mine won't run below about 1050 (indicated) so I set the idle screws to hold it there and I can sit at a stoplight without stalling.
What idle speed are you after? Mine won't run below about 1050 (indicated) so I set the idle screws to hold it there and I can sit at a stoplight without stalling.
I generally warm it up with a 5 min ride around the neighborhood. I feel like the issue is that the fuel level in the carbs may be too low to sustain idle, however I have the float height set as high as I can without overflow through tickler.
I have a Boyer black box ignition.
I have a Boyer black box ignition.
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Your carb is not like modern fuel injection, its tuned to be correct when the engine is warm, until it get there its not tuned so Amal give you the tickler to add fuel and a choke to allow you to compensate. I either give it another tickle or use the choke, after a few mins on the road its fine.
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Ignition timing plays a role. If too retarded the idle is poor. Combats don't idle as well as other Commandos anyway. Set your idle speed at or slightly above 1000 rpm. If you have new carbs...the idle jets should be #25. To set idle mixture turn the air screws in to the stop back out 1.5 turns, run engine warm then turn in until the engine falters, back out until engine falter, then set in the middle of the two positions. Of course before any of this make sure the slides are open exactly the same on the idle stop screws (I use a drill bit as a guage).
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Fuel level or float height will not cause this problem IMO. Fuel starvation is the other end of the spectrum. Your carbs are not going to run out of fuel at idle unless they are almost empty...
Are your throttle cables in good order and adjusted properly? Something sticking slightly in there could cause this.
Are your throttle cables in good order and adjusted properly? Something sticking slightly in there could cause this.
Deets55
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Check and see if the slides are dropping freely. Remove the carb tops, remove everything from the slides including the needle. Then see if they drop to the bottom easily. I had something similar happen as a result of overnighting the tops, it caused the slide in one carb to hang up. It didn't happen all the time, the problem only occurred when the out side temperature was low and the bike was shut off and then started a couple of minutes later. Usually when I stopped for gas. Took a while to hunt the problem down. So check yours with a hot and cold engine.
Pete
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New spark plugs and clean out pilots again.
dennisgb said:
Dennisgb can you elaborate on how the throttle cables could result in this issue? Once warm my bike idles well at just over 1000rpm but will eventually shut off after about 1 min of idle. I can prevent the bike from shutting off by ticlking the carbs which seems to reset the clock and give another minute of smooth idle. I have new throttle cables and I believe they are in order. Thanks
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Have you tuned the pilot system by using the mixture screw to get highest idle, the 1.5 turns out is only a starting point to get you going. Get the engine to operating temp and tune the idle circuit using the mixture screws then set the idle speed using the throttle stops to reduce the extra revs, then check again, if it's currently too lean or rich then it will not idle for long.
kommando said:
I have attempted to adjust the mixture screws. I start at 1.5 turns out but I don't seem to notice a significant change in idle by turning 1/4 turn in either direction. Seems to run OK at 1.5. I have been following the "Bushman carb tuning" guidance online. Test rode today and after long ride the idling issue appears to have been resolved but is idling close to 1500 (if my tach is accurate). Any issues with idling this high?
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If the mixture screw has no effect on idling then its normally means there is a blockage or restriction in the pilot circuit, not uncommon on new Amals to find swarf has been left in the pilot passageways but they have been improving. You would also have problems starting if there was a blockage or if it did start then you need to keep the throttle open to keep a fast idle. But 1/4 turn would not tell you that.
1500 is a bit high, I prefer 1100 but you should be able to get 900 with a higher risk of stalls, 1500 will reduce the engine braking effect on closed throttle and create heat if stuck in stop go traffic.
Bushmans is a good resource.
1500 is a bit high, I prefer 1100 but you should be able to get 900 with a higher risk of stalls, 1500 will reduce the engine braking effect on closed throttle and create heat if stuck in stop go traffic.
Bushmans is a good resource.
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djsktr said:
If the choke is actually bringing RPM's back then my guess would be the same as others here...pilot (idle) mixture circuit is dirty or adjusted improperly.
My thought on the cables is if they are hanging up due to lube or some other issue they could hold the throttle position so you are not getting a proper stop (idle speed) adjustment and if they break loose then the slides are making the stops but they are adjusted too low thus closing off the opening and stalling the engine.
o0norton0o
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illf8ed said:
ILLF8TED, has it right... I've copied my comment from another thread I posted in and will paste it below. It explains why you can't set the idle mixture screw by just turning the screw while the bike idles, without using the throttle on and off as you make very small adjustments... I've never had another norton owner support my method and reasoning, so I assume that those who know are close mouthed, or fewer people actually know how amal idle mixture screw settings interact with the other chosen parts of the carb as you accellerate.
ME from another thread said:
It should make sense to you that as you lift the inner carb body to accellerate, your idle mixture setting now begins to interact with the needle and needle jet, so you need to tune your idle mixture setting to make that transition as smooth as possible...
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djsktr said:
That may indicate that the float needles are sticking in the valve, or for some reason not opening. At higher speeds, vibration may be helping them to open.
Does it idle any better with a full fuel tank?
If you have brass float needles, it's possible that aluminium ones will open more readily.
But this is mostly guesswork on my part.
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Have you verified that you have no air leaks? Did you replace the o-rings that sit between the carb and the intakes when you changed the carbs? Did you remember to install them? Are the intake manifold bolts to the heads snug? Try to eliminate ALL sources of air leaks.
Are you POSITIVE your petcocks are flowing fuel properly? If you have clear gas line can you verify fuel flow? Have you opened BOTH petcocks while it is running to see if it makes a difference?
Are you POSITIVE your petcocks are flowing fuel properly? If you have clear gas line can you verify fuel flow? Have you opened BOTH petcocks while it is running to see if it makes a difference?
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