I've heard of, but never seen the pipes cherry red...

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Nov 28, 2009
I think I've only run the Commando once at night since I got her. No blinkers, dark, 1.5 million people about... just don't like it, which is why I'm (eventually!) going to get some indicators!

Anyway, fired her up last night in the dark. Not sure if it was because I warmed her up fpr 2-3 minutes while stationary or not, but damned if the right side pipe didn't have about ten (10) inches of visibly red pipe for maybe 8-10 inches. Thought "Maybe because I'm stationary?"

Glanced at the left pipe, she was still dark. Killed the engine. Fired her up just now, sounds like she's missing (probably on the left side). ANyway... what fear, or calm, can you guys tell me about this cherry red hot pipe?? Mega-TIA, guys! ~Gary
Check your right side carb's low speed mixture setting. Sounds like it's a tad too lean.
Hi Gary,
I have seen a couple of bikes do that, in both instances the mechanical advance had froze (rusted), which of course made the bike run retarded (timing wise) and I suppose passing still raw fuel into the pipes where it then burned. However, you say that this is happening on one side only but, if you still have points its possible to have incorrect timing on just one cylinder. Timing is a relatively quick check and I recommend doing that before playing with the carbs.

Worst case - burnt exhaust valve or adjusted too tight, more likely lean or timing/AAU issue.
Peel turned her 2-1 bright red all the way to the megaphone in a few seconds d/t Boyer timing going bonkers d/t magnets hitting the trigger wire terminals.
Much more likely a timing issue than fuel so follow the prior advice. Can't imagine a valve hanging up to do this. Air leak leanness may make less heat d/t less fuel.
Mine got cherry red about 6" down just after before timing a new ignition setup. super advanced.
I can wrench a little bit. Not like some of you guys can, but a little bit. So I spent the last day or two off and on thinking WHAT could make it fire that much hotter, although nothing (apparently) has changed. Decided to much air (bellows) could 'stoke the fire' much hotter. Went and then checked the rubber BOOT between the carb and the combustion chamber. Sure enough, it has cracked well open. I can push the tip of my pocket knife into the crack. Well, to long a story. Enough said, she's sucking in a lot of air, rubber split at least half way around, sucking air the entire split.

1.) Guys... am I right, this would cause her to run a lot hotter in the chamber? Leaner? (Leaner equals hotter?)

2.) In any event, I need the 'mikuni' rubber boot. Anyone know where I can track this thing down? That 'Brit bits' (Old Brits?) place some have mentioned? TIA for any info, guys. ~Gary
Are your referring to the bellows that connects the carburetor to the air cleaner? If so, unless the air cleaner is totally clogged, a split in the rubber of the bellows would not affect the air/fuel ratio enough to cause the head pipes to run cheery red hot.
Hi again Gary,
Give Sudco a call, their number is 323 728 5407
I would have looked up the part number for you but I don't know what size carb(s) you have. If you go onto their website you can download their entire catalog and price list on PDF, glad you found your problem.

"Went and then checked the rubber BOOT between the carb and the combustion chamber. Sure enough, it has cracked well open"

Absolutely will cause the problem you are seeing! It COULD have caused a more serious problem - burnt valve, for example. I'd check compression and, if both cyls are about the same, just replace the boot. I'll bet that will make it right!
I recall similar from 1974, returning home from evening class, on the motorway link road.

Me on my MKv 750 commando & my mate on his '69 rocket 3. Off the line & round the roundabouts I got way ahead but a couple of miles further on he would always come past me, probably about 120 ish, with the 3 inti 2 manifold glowing cherry red, & his grin as wide as could be!

Hey-ho, happy days!

Yes, of course, Mikuni . . . . but I 've never known those to split, get hard yes, maybe crack along the top . . . especially the neoprene type .. .. . sounds more like the bellows between Amals and stock air filter pan.
Ah... I came back for something else, but glad I did. As some of you noted, I mis-spoke with 'mikuni'. Slip of my tongue. It is an Amal. Now, for the reason I've come back here, and believe me, I am swollowing some pride! Hope you guys recall I stated I can wrench only a little bit, not like you guys (blush). I cannot seem to find this part I need, and this is mostly because I do not understand what the carb is, how to differentiate it from other Amal carbs, etc. I've checked many-many sites, no luck. The only stamping on the (single) carb that I can find is as follows: R2036 beneath that stamp, is stamped '300'. So, R2036 and 300. The rubber has two (2) bolts to the manifold, with the after end clamped to the carb. The bike is a '73 850 commando. Like I said, I have looked through manuals, parts manuals, websites from England, USA, etc. How the hell to I find and order one of these things?? As is... am I simply to try to give the split thing a 'temporary fix', and try to seal it with a wrapped piece of tire tube cut to fit, adheared on via silicon? Again, I am embarrassed in my ignorance that I cannot find this thing... anyone??? When I find a pic of it at the Amal site... it doesn't show the same rubber, instead it shows one that appears to be held on by a clamp on both end, so I cannot use it. Again, it attaches the carb to the manifold.
THREAD CLOSURE: many of you were correct, it turns out to be a Mikuni rubber mounting flange, part #VM34/200, which is why I could not find this part at all in any Norton publications. Guess I should have thought 'outside of the box', initially. Well, now I know, and it's always good for this novice to learn a LITTLE more about this cool bike... though I wish I hadn't lost a week or two of riding! Thanks to each and every one of you guys nice enough to try and assist! I do appreciate it! ~Gary
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