Commando will not accelerate

terencem58 · Aug 5, 2013

Hi all, i recently refurbished my 1970 commando AMAL's with new jets and cleaned them up etc but after refitment the engine will not rev without the odd coughing and splutter
i have checked for leaks and replaced the connecting air tube but same result
the bike starts well and idles normally but when the throttle is opened it will not rev above 3000rpm without a lot of spitting out the exhausts
i bought the bike about 12 months ago and this is the first time i have heard it running so no history of what it was like before the AMAL refurbishment
any ideas?

DogT · Aug 5, 2013

It worked fine before the new jets? Are you sure you got everything installed correctly and the correct/same part numbers? If it was working fine before, it should work better with new parts. Mine did.

Torontonian · Aug 5, 2013

Usual sick running like that is plugged up idle jets. The gas goos up from sitting a long time. Fine wire or micro drill bit with carb cleaner and compressed air works.

Hobot · Aug 5, 2013

Pilots screw up low end below 3000 rpm. So Suspect inhaling air leaks, a needle slipped its clip or float hang up maybe. I've also bumped wires working on carbs that only rattled loose about some rpm. Can't ignore plugs might be fouling form prior mis tune or just phase of the moon. You've been alerted water in bowls can do this not being sucked up till giving some gas flow. Look under after dark too.

Rohan · Aug 5, 2013

Chronic problems like that could even be blocked or partly blocked main jets.
Again, gunge from sitting around filling the base of the floatbowls...

Time for some carby cleaning ?

VintAge · Aug 5, 2013

terencem58 said:
i bought the bike about 12 months ago and this is the first time i have heard it running so no history of what it was like before the AMAL refurbishment

I think this is the important statement. It begs the questions: What else, if anything, have you done prior to starting it for the first time? Why did you choose to redo the jets - just as part of a routine carb cleaning? Most of the responses so far have assumed the problem must be carburation but, if you never heard the bike run before, it theoretically could be anything.

If you're sure you've reassembled the carbs correctly, used the correct parts and done the adjustments carefully, and cleaned and checked the fuel system thoroughly - including measuring fuel flow to and through the carb needles and seats - then it could be time to check (or double check) the ignition system too. If nothing comes to light quickly, then providing the forum with a complete list of everything you've done to get the bike ready to run might be instructive. Good luck,

Rohan · Aug 6, 2013

Actually, in the light of Andy's good points, the FIRST thing you try on something like this is NEW spark plugs.
Then go fault tracing...

Tugging on the individual throttle cables to each carb, to ensure that each cylinder will rev individually can also assist considerably.
If both cylinders have the problem is different than if the problem is only in one cylinder...

batrider · Aug 6, 2013

Are you operating the choke correctly? The choke slides need to be pulled up in normal running so the choke cable should be under tension.

Welcome to Nortondom.

Russ

MFB · Aug 6, 2013

So many possibilities here, both carby and ignition related.
Here's some more for your check list (if still on points ignition):

AAU unit. It's not stuck on full retard is it?

Condensers

Coils

Just think how satisfying it will be when it's all sorted.

terencem58 · Aug 7, 2013

I bought the commando in what was called 'running condition' however when i came to start it for the first time i found that tickling the AMAL carbs delivered no fuel
i took the carbs off and stripped them down to clean the bowl and other parts while checking bowl function and changing the o-rings
then because of blocked main jets i simply ordered new 220 jets and fitted these using same needles as original
the carbs went together fine and i used new gaskets and then reassembled on the bike - cables are free-running without any snatching
once fuel was tickled and bowls filled it started with second kick but then the problem of not being able to increase revs started - each time i try and increase revs there is popping and spluttering from the exhausts
the commando has boyer electronic ignition, a dual coil and bosch platinum plugs - they look a little sooted from idling at 1000rpm
i checked for air leaks and rechecked exhaust fitment etc and fitted new connecting air pipe
new fuel in tank
any thoughts?

chilly · Aug 7, 2013

Try some ordinary Champion N3 or 4 or NGK equivalents , my mates Commando just wouldnt run right, we tried all the usual stuff to get it to run right , as a last resort we changed his fancy expensive iridium plugs for my standard Champions , it ran just perfect .

Never bothered to try the plugs in the first place as they were new , just as an aside there are a lot of repro plugs out there doing us no favours .

Nortiboy · Aug 7, 2013

terencem58 said:
i took the carbs off and stripped them down to clean the bowl and other parts while checking bowl function and changing the o-rings
then because of blocked main jets i simply ordered new 220 jets and fitted these using same needles as original

Have you mechanically cleaned the idle pilots jets ?. You need fine wire or a #78 drill. If the carbs were bad enough to block main jets the pilots are blocked for sure.

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html Follow this to understand and set the carbs. Double check float levels and needle and seat.

To help us diagnose yr issues, can you connect new standard spark plugs and lay them on head ensuring they are well grounded. Kick the motor over slowly (battery should be fully charged check min 12.5 volts at rest. The Boyer is very sensitive to low voltage) You need a fat blueish spark in the gap.

If it was a runner when you bought it, I reckon this forum will sort it quick.

concours · Aug 7, 2013

terencem58 said:
I bought the commando in what was called 'running condition' however when i came to start it for the first time i found that tickling the AMAL carbs delivered no fuel
i took the carbs off and stripped them down to clean the bowl and other parts while checking bowl function and changing the o-rings
then because of blocked main jets i simply ordered new 220 jets and fitted these using same needles as original
the carbs went together fine and i used new gaskets and then reassembled on the bike - cables are free-running without any snatching
once fuel was tickled and bowls filled it started with second kick but then the problem of not being able to increase revs started - each time i try and increase revs there is popping and spluttering from the exhausts
the commando has boyer electronic ignition, a dual coil and bosch platinum plugs - they look a little sooted from idling at 1000rpm
i checked for air leaks and rechecked exhaust fitment etc and fitted new connecting air pipe
new fuel in tank
any thoughts?

That is merely a PARTIAL carb cleaning, without verifying flow through EVERY PASSAGE, you get to do it all over again. Sorry

JimC · Aug 7, 2013

Concours is right. I would warn you that getting air flow through a passage does not verify that there is not a partial blockage. Those little passages need to have a wire run through them. This I say from experience.

Hobot · Aug 7, 2013

Zn Oxide does not dissolve in organic solvents only acids and bases so physical removal is the best way but can boil a few min in vinegar or very strong carb cleaner dip Old float needles tended to beat up seal tip so check that too. Get V8 pack of plugs as some may be bad right out the box, [more than just me found that out the hard way] and plugs tend to get fouled during foul running conditions so has continued my pissed off blank dumbfounded British Iron staring teary eye'd -till on whim, short of shot gunning the dam thing or me put trashed but still good plugs back it for nice instant running joy, again, for as long as that lasts, which should be at least10,000 miles+.

terencem58 · Aug 7, 2013

many thanks for all your ideas of fixing the problem - i will take them off and check the flows then reassemble and try again - good fun...

chilly · Aug 8, 2013

Don't forget those fecking plugs mate , its such an easy first try , worked for us when all else failed , including positive cleaning of carbs with full checks to see if the appropriate fuel bypass holes flowed carb cleaner + pilot jet etc .

Not saying your carbs arn't the problem , but after my experiences , plugs are an easy first try .

Junk those fancy plugs , looks like Boyer doesn't like em :wink:

Good luck
Chill

Nater_Potater · Aug 8, 2013

Hard to verify without partial teardown, but, if never having heard run, could be improperly timed cam. If assembled this way, ignition timing could still have been set correctly even with cam wrong.
Go for low-hanging fruit first; NGK B7ES (or BP7ES if no intake valve interference) If not, then pull the carbs, clean the pilot jets, and make damn sure when you blow air in through idle mixture screw opening, fuel/solvent/carb cleaner shoots out of both small passages in throat where bottom of slide contacts at idle, and especially through port next to fuel inlet seat. Liquid from this port will tell you that the pilot jet is indeed open. If you think you see this port is threaded, it is; don't go looking for a jet to screw into it, though, as there isn't one.
I just went through this twice thinking I didn't get my carbs cleaned the first time, only to find out it was bad plugs (bad plugs; naughty plugs). Like the man said, "Most carby problems are ignition, and most ignition problems are carbys".
Nathan

Bernhard · Aug 8, 2013

I would suggest that after about 6 months or so, (depending on how hot the weather is) petrol has been known to evaporate which leaves grey goo behind which has a nasty habit of blocking up the jets, the pilot jet being a particular difficult one to clear.
You really need access to a 125psi airline, and some carb cleaner. If not then use paint thinners, and a garage tyre airline, with a tubeless valve inserted.

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

mike996 · Aug 8, 2013

I recently had an issue with an idle jet clogging while riding. All was fine for most of the ride until problem started. Got home, did compressed air on both pilot jets with air nozzle sealed to the fitting. This did NOT clear the jet, probing with a .016" guitar string did. So don't be surprised if solvent/air seems to indicate that the jet is clear when, in fact, it is not.

Commando will not accelerate

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