RL250

[BOGWHEEL]

Hi all
Chasing some know-how please, on setting / checking the timing on a RL250.
As the sytem is not on a suzuki, i was going to mark the case at TDC and then the flywheel at 2.8mm BTDC, and then use a strobe.
But i was also told if the ignition has auto advance / * that this may not work.
Is there a simple way to check if the system is faulty please?

Also before i go to the trouble of doing a leak test, could an air leak upset the running at only up to 1/4 throttle and when engine braking? My past experience with air leaks made the bike very difficult to start and once going would rev it's tits off.

signed
desperate

[David Lahey]

If you are using a timing strobe that is triggered by a pickup on the HT lead, the strobe will flash when a spark happens.
However something that may trick you up is that some strobes are limited in how many flashes they can do per second and some electronic ignitions provide more than one spark per revolution. In this way the timing light can be tricked and set off the flash at positions other than the one you are interested in. I discovered this on my wife's DT175 which sparks just before BDC as well as just before TDC. I think it is due to the ignition relying on the position of the flywheel magnets to trigger the spark. Some bikes might even spark more than twice per revolution! Hows that for a wild idea?
Maybe the RL250 ignition uses something other than the magnets to trigger the spark so it might not be an issue on yours- I don't know
I do know that I mucked around for a long while checking the advance curve on an electronic ignition I put on my TY175, because the strobe was being triggered by sparking at BDC as the revs went up. The symptom was that the flywheel mark appeared and disappeared as the revs changed while the fixed mark stayed illuminated throughout.

[BOGWHEEL]

Thanks David
The guy said something about if it has auto advance / * you need to time it at full advance (went over my head, so didn't go any further)
Any thoughts on the air leak?
Trying to pin down things to find my running problem ( It has some symptoms of running lean but also the same as i have experienced with the timing being out on a points system (pre igniting) . It idles, but a surging idle, an when you give it a handful of throttle it is a joy, even from tickover. Also it starts very easy hot or cold.
Motor has just had new seals and bearings (problem was there before this also) i have removed the exhaust as it had a very slight weep of oil at the gasket. The back of the gasket against the barrell was totally covered with spooge and exhaust port was totally wet.
Have also swapped out 3 different carbs.

[David Lahey]

Not sure about the logic of setting the timing at full advance. I would have thought that the timing at idle RPM (ie when fully retarded) would be the critical setting on your motor.

Yes surging with throttle slide down and running well when slide open or part open is a typical sign of air leakage. The exhaust connection is not important for preventing air leaks as it doesn't go below atmospheric pressure there.
Other possible air leak sites are;
cylinder base gasket
rubber connector tube between carby and barrell (very common leakage site)
gasket between aluminium inlet connector and barrell
engine casing centre gasket (seen a few of these on rebuilt Bultaco motors but if it did the same surging thing before the rebuild then ???)

If it does the same surging thing with three different carbies then it is not likely to be the carby causing it - unless they all have the same fault!

[BOGWHEEL]

Cheers
Will set up for a leak test - didn't think the exhaust would matter, have had older bulls that leaked there and had no or little effect on running.
Spark plug screws in very easilly and doesn't seem to be able to be nipped up any.
Head needs re-tensioning after every ride. (no oil leaks from head or base gaskets though)
Last carb is new OKO with new inlet rubber to suit. (sorry, bought from guru at ClassicTrial UK all set up from - huge difference even with dodgy running motor)
On a different note - you get what you pay for. Dropped the OKO slide when taking it off the cable, and now have two nicks in it. Really soft material!

thanks