Starts easy, idles nice, 5-10 blocks and dies, wait 2 min, same thing again

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CraigT

CraigT

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I'm just finishing work on a 74 Commando Roadster I got recently. The bike ran okay but a bit rough when I got it. I cleaned the tank, carbs, plugs, new battery, brakes, rubber parts, cleaned switches, some rewiring etc.. (has Boyer ignition and a single MK2 Amal carb) My problem: Starts easy, usually one or two kicks, idles nice, runs strong at all throttle positions. Will go for 5-10 blocks usually (sometimes more, once went two miles) then it will quickly sputter and die. If I try to restart immediately, it wont but wait a couple min and it starts right up. Then the same thing over again....5-10 blocks and dies.
I've looked at the plugs and they are black but not too "furry looking"....gas in new and clean....carb is clean...air mixture is one and a half turns CC from seated....valve were just gapped at .008 exhaust and .006 intake.
Any suggestions and or a recommended approach to solving this would be really appreciated.
 
Classic symptoms of fuel starvation. When it begins to stutter open the fuel cap, the vent may be clogged.
 
Fuel screens. They’re (mostly) blocked. Or, there is an obstruction in the passage headed to the inlet needle & seat.
Test by measuring fuel flow at the carb supply hose, time/volume into a catch can.
 
CraigT said:
I'm just finishing work on a 74 Commando Roadster I got recently. The bike ran okay but a bit rough when I got it. I cleaned the tank, carbs, plugs, new battery, brakes, rubber parts, cleaned switches, some rewiring etc.. (has Boyer ignition and a single MK2 Amal carb) My problem: Starts easy, usually one or two kicks, idles nice, runs strong at all throttle positions. Will go for 5-10 blocks usually (sometimes more, once went two miles) then it will quickly sputter and die. If I try to restart immediately, it wont but wait a couple min and it starts right up. Then the same thing over again....5-10 blocks and dies.
I've looked at the plugs and they are black but not too "furry looking"....gas in new and clean....carb is clean...air mixture is one and a half turns CC from seated....valve were just gapped at .008 exhaust and .006 intake.
Any suggestions and or a recommended approach to solving this would be really appreciated.
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maylar said:
Classic symptoms of fuel starvation. When it begins to stutter open the fuel cap, the vent may be clogged.
Click to expand...
You are correct....before I saw your post I went to check the new gas cap I had just put on....It was a manufacturing defect.....there was no breather hole in the new cap seal.
 
Okay, thanks for the people who responded and helped to solve the cutting out problem. Here is another little problem: The clutch slips when asked to really do hard work.....this bike sat around for a few years before I got it....is it possible that the plates are just gummed up or is it more likely I need a new clutch spring?
 
CraigT said:
Okay, thanks for the people who responded and helped to solve the cutting out problem. Here is another little problem: The clutch slips when asked to really do hard work.....this bike sat around for a few years before I got it....is it possible that the plates are just gummed up or is it more likely I need a new clutch spring?
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Only anecdotal experience, but the clutch diaphragm spring is pretty robust and unlikely to give out. Easy enough to open up the clutch and clean the plates though.
 
CraigT said:
Okay, thanks for the people who responded and helped to solve the cutting out problem. Here is another little problem: The clutch slips when asked to really do hard work.....this bike sat around for a few years before I got it....is it possible that the plates are just gummed up or is it more likely I need a new clutch spring?
Click to expand...

It was an annual ritual for me to clean the goo off clutch plates until I learned how to make it work per Dyno Dave's info, links posted by concours above.
They can either slip under load or stick and drag when gummed up.
 
Clutch needs to be serviced.
Disassemble, clean, dress plates.
Reassemble.
Be sure to source a clutch spring compressor. Every Commando owner has one.
Part of ownership.
 
As well cleaning the clutch plates what oil are you running, I learned a very long time ago that motor oil is to heavy except if its a M111 as it needs the heavier oil, but the kick start models I found the ATF F works the best to stop clutch slip, my clutch hasn't slipped in over 35 years since using the ATF F and I am still running the orginal clutch plates that came with my Norton since new with well over 160k mile on them.

Ashley
 
ashman said:
As well cleaning the clutch plates what oil are you running, I learned a very long time ago that motor oil is to heavy except if its a M111 as it needs the heavier oil, but the kick start models I found the ATF F works the best to stop clutch slip, my clutch hasn't slipped in over 35 years since using the ATF F and I am still running the orginal clutch plates that came with my Norton since new with well over 160k mile on them.

Ashley
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I had put 20-50 Castrol Motor oil. Just to be clear....You're saying put ATF F instead of motor oil in the primary case?
 
One other question about the primary case..... When I clean the clutch I want to solve an oil leak....I have a new rubber gasket for the primary case but the case still leaks a tiny bit (I know this is pretty normal) I'm wondering if it's a good idea to ad a little bit of gasket seal to the case while remounting it as well? Has anyone tried this with success or do you have any other suggestions? Also if sealer is a good idea, what type of sealer should I use?
 
Motor oil is no good unless the oil has additives in it for running a wet clutch and a lot of motorcycles oils are made for wet clutch operation, normal motor oil isn't but I been using the ATF F and a lot of Norton owners have also been using it without any problems with slipping clutch.
As for a leaking primary seal most people over tighten the centre bolt which will cause the outer case to warp hence oil leak, it also depends how many times the rubber seal has be reused, I would replace the rubber seal with a new one and do not over tighten the centre bolt, mine has not leaked in many years because I don't over tighten it.
As for gear box oil getting into the primary from the clutch/gear shaft some have that problem and put and fix it by putting a seal on the end of the shaft, I have never had GB oil in my primary and have never had that problem, but I do put grease on my clutch rod and messure how much oil I put in my GB I just put in the amount what the manual recommends.
Gear box oil will make the clutch slip badly.

Ashley
 
CraigT said:
I had put 20-50 Castrol Motor oil. Just to be clear....You're saying put ATF F instead of motor oil in the primary case?
Click to expand...

Yes and only 7floz and no more, I run between 5 and 7floz in mine.
 
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