Right hand exhaust RED HOT

The backfiring and the red hot exhaust do point towards an ignition issue, unless fuel supply is partially restrictedor maladjustedon the carb feeding the offending cylinder. As a quick check, take off the points cover, check that the points and auto advance are moving freely. Further check will be ignition timing and maybe the spark plugs. Could be a completely wrong plug in the offending cylinder!

I have seen a similar problem a long time ago on my ES2. The cause was a burned exhaust valve. I think the valve burned because that timing was retarded. Like Chris Grimmett said, check compression, just turning the engine over with your thumb over the plug hole will likely reveal the leak, or compressed air applied to the cylinder via the plug hole with both valves closed will let you listen to air coming out of the exhaust pipe.

I concur with the suspicions about the exhaust valve. I too have seen the same symptom. Although not wishing to be a wet blanket, I would have the head off to check the valves etc, and also check carb jets, valve and ignition timing.

Cheers

Alan

This is what happens to NOS dull-chromed 16H silencers when the exhaust valve hangs open - guide problems in my case.

[IMG]http://i248.photobucket.com/albums/gg164/commando16h/M20%20forum/Silencer.jpg[/IMG]

I couldn't believe that it could get so hot so far round, but apparently it can.

Anything else like carbs or timing would have to be a long way out on one cylinder to give those symptoms.

Hi Andrew & welcome to Commando ownership.

When I first got my Commando I had much the same thing happen,bugger to start &the right hand pipe would glow red after about 5 - 10 mins at a fastish idle, (the slowest I could get it to stay running, around 1000 - 1200 rpm, at a guess) lots of popping & banging etc. I too suspected a burnt exhaust valve, however, I found the pilot air screw on the r/h carb had little effect so looked deeper & found the pilot jet (which is just a busheddrilling pressedin tothe alloy on the concentric)was completeley blocked. I had to remove the little plug in the intake face & poke about (thats a technical term, of course) with a piece of wire & an air line to clear it, replaced the plug & hey presto, the bike ran fine once air screwcorrectly adjusted. I'm a trained mechanic & wouldn't have believed it could have had that effect, but it did ! As mentioned, acompression test will soon show up a valve problem but if that checks out ok, may be worth a look.

Hope you get things sorted without too much trouble, once you do, a Commando is a cracking machine.

Regards, Tim

Hi Andy,

You need to remove the ally plug that is in the intake face of the carb which will give you access to the pilot air drillings. The Concentric carb doesn't have a removeable pilot jet like most carbs, there's nothing to unscrew, it's just a bush with a slightly smaller drilling than the alloy body, bloody stupid idea, if you ask me, but there you go. The plug usually has to be drilled out & a replacement refitted, you can make one from a piece of ally rod of the correct diameter or purchase a replacement from an Amal spares supplier. I have managed to remove them in the past with a little gentle heat around the area & then tap the carb intake face down on a bench with the plug just overhanging the edge, sometimes it will dislodge enough to be able to get hold of it with grips & pull it out, if you're lucky.

If you need any further help give me an email address & I'll try sending some pics to ilustrate better what I'm rambling on about. Where are you by the way ? if you're not too far away may be easier to meet up ?

Hope this helps, Tim

You might find these helpful:

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

http://www.amalcarb.co.uk/TechnicalDetail.aspx?id=11

http://www.amr-of-tucson.com/carb_facts.html

By the way, the reason that I would have the head and timing cover off is not just to check the exhaust valve. One can judge the general state of the engine and check the basics. It only takes a couple of hours and might save a very expensive engine rebuild.

Cheers

Alan

When I first bought my Commando in 1975 I had the problem of bad starting and red hot exhausts, took it back to the seller and established that the timing had "slipped" He reset it with a strobe and things were ok until I rode 140 miles home and consumed a tank of oil. One cracked piston(the old type with the slotted oil control ring groove) two new pistons cost me about £26 and I replaced them behind the barrack block at RAF St Athan. I persevered with the points, setting them as per the manual and performance was lively to say the least. Eventually I saved my pennies and bought a strobe light. This established that the fully advanced spark was at about 42 degrees BTDC!! The advance and retard unit was so shagged out that setting it accurately was almost impossible. Saved a lot more pennies and bought a Boyer. The rest as they say is history. Acurate ignition timing is one of the secrets to a civilised Commando and the only way to get close is with a strobe.

Actually Dave, it is possible to time a commando very accurately with a fag paper. If the engine is set to 28 deg BTDC and the paper put between the points, if the auto advance is pushed round to the fully advanced position, the fag paper should be released just as the auto advance hits the stop. I have had very good results doing it that way. Of course, this assumes the points gap is set correctly before you try to time the ignition. You have to do each cylinder separately, of course.

Off topic, but IIRC the manual for Dominators suggests doing it this way.