Hi guys, im new to the forum and for my first post I need help from anyone with experience of these bikes.

I bought the bike for a dirt cheap price since the stator magnet has flown off and the previous owner couldn't be bothered with it. I bought a new stator rotor and windings, fitted them, put some oil in and she fired up after cranking for a minute or so (hadnt been started for months). The problem was, the bike would tick over just as it should but as soon as i tried to rev it, the bike would bog down and die just as you would expect from a super lean (or super rich) mixture. I know the bike is now charging and all the electrics seem spot on. I decided to strip and clean the carbs, which are like new inside and there are no signs of ware. Ive now had the carbs apart a few times and im probably more familiar with them than the guy who built them. Obviously i was suspecting the carbs to be at fault but im now more sure than ever that the carbs aren't the problem. The previous owner had the mixture screws set to about as rich as they would go in an obvious attempt to remedy the problem. The bike will rev up if the mixture is set RIDICULOUSLY rich. So what could cause the bike to only run on a really rich mixture?

Any advise will be very much appreciated. And yes ive checked the diaphragms, needles, jets are stock, float heights are spot on. I have been advised by a very experienced mechanic to check cam timing to make sure the chain hasn't skipped a link, which I plan to get my head stuck into over the coming weekend. Once again, any help or ideas would be great, i know im gonna end up kicking myself when i finally figure it out! Cheers.

Could be a million things.  Some obvious things come to mind:

--Do you have fresh gas?  Not months old gas, but fresh gas?
--Check valve clearance.  If nothing else, it's piece of mind.
--Mixture screw is set to about 3 turns out as a conservative starting point.  In = leaner Out = richer.
--Look at the boots between the carbs and the engine.  Any leaks will cause a lean mixture.  Spray some WD-40 all around the carb boots with the engine running.  If the engine speed changes, you have leaks.  Tighten the clamps, or simply get new ones.  Don't forget the O-Rings on the boots.
--Underneath your carb plastic diaphragm caps, there is a little o-ring for the older model carbs.  If missing or worn, it will lean out the mixture.  Make sure it's there and in good shape.  Search the forums, there are pictures of good vs. worn O-Rings.
--Check exhaust bolts to make sure they are tight.  If not tight, it tends to lean out the mixture.

Quote from: jestercinti on June 27, 2012, 01:12:26 PM
Could be a million things.  Some obvious things come to mind:

--Do you have fresh gas?  Not months old gas, but fresh gas?
--Check valve clearance.  If nothing else, it's piece of mind.
--Mixture screw is set to about 3 turns out as a conservative starting point.  In = leaner Out = richer.
--Look at the boots between the carbs and the engine.  Any leaks will cause a lean mixture.  Spray some WD-40 all around the carb boots with the engine running.  If the engine speed changes, you have leaks.  Tighten the clamps, or simply get new ones.  Don't forget the O-Rings on the boots.
--Underneath your carb plastic diaphragm caps, there is a little o-ring for the older model carbs.  If missing or worn, it will lean out the mixture.  Make sure it's there and in good shape.  Search the forums, there are pictures of good vs. worn O-Rings.
--Check exhaust bolts to make sure they are tight.  If not tight, it tends to lean out the mixture.

Thanks for the reply,
Gas is fresh.
Valve clearance does need doing but that wouldn't stop the bike revving up.
As I said the mixture is correct but bike WAS set rich when I bought it which seemed to very slightly ease the symptoms.
There WERE vacuum leaks but I fixed these with new boot o-rings.
Exhaust is on good and tight.
Are you referring to the o-rings for the vacuum ports on the top of the diaphragm caps? If so they seem perfectly fine....

Its probably worth mentioning that both carbs are affected the same and both seem to be doing their job. As I said in OP, im beginning to think more and more that its something to do with the engine rather than the carbs. Its the engine that wont run unless mixture is ABSURDLY rich.... the only thing i have checked is the cam timing and electronic ignition......

Thanks.

You could also go +1 on pilot and +2 on main jet.  These bikes are set lean from factory.

By oring I mean the little tiny o-ring that sits right under the diaphragm caps. It stops vacuum leaks, it's not the diaphragm cap seal, but it's sitting on top of the diaphragm. Do a search on the forum on carb rebuild. It will show the ring in question.

Bad valves clearance has been known to cause idle issues and accel decel issues from stop and go respectfully.

definitely check the valve clearance.  When I restored my 97
valve troubles acted a lot like carb problems.

also, check for carb sync.  pull them off and look at the
butterflies and try to adjust the screw so that there is visually
similar openings when the throttle is completely closed

TJ

The ignition control unit can fail in ways that cause some weird running symptoms - even if the usual spark test shows good spark, can be a different story while the engine is running (or trying to run).

Thanks for the input guys, it looks like my next step is definitely to check the cam timing and do the valve clearances, do any of you guys know where i can buy individual shims? Im based in U.K by the way, thanks.

Dealership, eBay, or members on the forum.