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Recently purchased 900ss 1981 seller said it used to run rich on back cylinder (been stored for 4 years)so got the baby home and got to work after check over tried firing up did fire up but only on right side so took back carb off gave it a good clean this time it fired up on both pots but was spitting and back firing on back pot after a couple of minutes i noticed left hand down pipe glowing red hot stopped bike let call down and adjusted mixture screw but still seems to get hot to worried to run it long just in case it gets red hot again any ideas?thanks phil

Hi Phil

1. What plug are you running? In the 1980 owner's handbook I have, it lists Champion L88A (altho' Walker says otherwise!). The modern NGK equivalent for this (Ducrappis always seem to prefer NGK to Champion) is usually listed as B5HS BUT it's generally reckoned that the B7HS is the one to go for.

2. You're leaking air around the carb isolaters - the bits of rubber between the manifolds and the heads. These go hard with age and leak, causing pre-ignition. Replacements can be got from Tony Brancato (UK), Steve Allen (US), Damien Birch (AUS), Andy Nienhagen (Germany) and others.

3. Compare the jets and needles with the regular factory fitments. It's just possible that someone has fitted some seriously wrong stuff.

According to Falloon, a 81 SS fitted with 40mm AD/AS Dell'Ortos should have a K5 needle (and use the middle groove), a 152 main jet, 60 pilot, 265AB needle jet, and 60/3 slide. These are also the main and the pilot listed in the owner's handbook I have. (Walker differs slightly, quoting a K4 needle and a 60/1 slide, but these differences aren't that significant).

If 32mm CS/CD carbs, the owner's handbook says 122 main and 55 pilot -but doesn't say anything about the slide or needle. Walker gives K16 needle (middle groove); 60/3 slide; 265AB needle jet. (Typically (!), Falloon is slightly different with a 62 pilot).

Also, these carbs do need to be very clean to work properly. Modern fuels gum them up very easily - so be prepared for getting them overhauled by someone who knows what they're doing (e.g. Mike at JRS).

4. The ignition is desparately over-advanced. Let's hope not, because re-setting it requires the use of a special tool - which you can hire from the DOCGB (join if you're not a member, btw) - but it's not especially easy to use - altho' the tool hire Secretary, some bloke called Steve Wynne (!!), will advise.

HTH

Ciao

Craig in UK

Hi thanks Craig ,plug thats in at moment is bp6hs, have the isolaters on order, running 40mm carbs, needles seem ok, while i have carb off is it worth squirting some cleaner at the valves as it looks coaked up or would this create more problems? I will let you know how it goes when i have fitted new rubbers ,Hope its not ignition trouble many thanks again Phil

Fitted new carb rubbers bike will not start now had plugs out noticed that plug sparks when turning ignition off is this normal also when turning over bike seems to spark at plug on every stroke also back fires sometimes when turning off anyone have any ideas thanks phil

Hi Phil

This is a characteristic of a Hall effect ignition system - I can't now remember the science of it, but I'm sure you could find the explanation somewhere on the web :-)

It isn't something to be worried about - or, at least, that's what I've always been led to believe. Others may now advise otherwise, of course ...

The fact that the bike isn't now firing would make me suspicious of the ignition. (If you're getting backfiring, that at least tells you that fuel is arriving in the cylinders - albeit with the caveat that it doesn't necessarily mean that it's arriving in the correct air-fuel mix or in the right quantity.)

You could be suffering from the common problem of the insulation coming off the pick-up wires. If these wires short out, the ignition will fail or spark at the wrong time, with the consequence that the engine won't fire/will run rough/will backfire, cut-out etc.

You might like to consider taking the clutch casing off to do a visual inspection ...

HTH

Ciao

Craig in UK

Don't run it again until you personally check to make certain that the valves are properly adjusted and that the timing is correct when checked with a strobe light.

I have for the second time noticed this when running the engine around dusk time! The vertical cylinder header pipe "glows" red hot directly from the cylinder head exhaust outlet. And I'm talking about the vertical head only. Could this be a symptom of "cold" spark plugs or the other way round, ie: too "hot" spark plugs? The next step is to get the carbs checked which I'll probably do anyway.
Anybody with some suggestions?
Cheers,
Steve

I have seen this many times. Each time it was *after* I had rebuilt the carbies and was in the process of doing a sync on the carbs. NOTE: this didn;t happen every time, just a few times I saw it, when the carbs were desperately out of whack.....

As soon as the carbs were sync'd correctly, the glowing stopped.

This is NOT a good thing. You should NOT run the bike until you correct this.

I highly suggest that you get a big fan and put it on HIGH setting so it is blowing directly onto the engine to help keep it cool while you do the sync.

Doing a sync by ear and/or feel is NOT doing a sync, it is geting it maybe close to right........ You need carb stix to do the job correctly and exactly. Dellortos work wonderfully when set exactly right. But they MUST be set exactly right to work wonderfully.........