Hi folks, I've got a bit of a niggle under the bonnet (1600 type 1 lump) and wondered if anyone could shed some light on it? The last couple of times I've set the timing I've noticed that it isn't particularly stable- it probably flicks by a couple of degrees every so often- which it really shouldn't as the timing on the 123 dissy should be rock solid... I thought it might be due to a vac leak somewhere and I've just replaced the manifold boots as one had perished and I thought this might have helped but it appears not- just checked with the strobe and still the same. Have done the spray test for leaks in the manifold system but can't find any so just wondering if it could be a vac leak or whether there could be something else at fault that would cause this lik the coil or leads? Any help gratefully received, cheers oracle Olly
You have to be careful of cheep strobe lights if the sensor is too near the plug or too near the dissy you get false readings try moving the sensor when you do it to make sure its not this
Everything else A OK? Carb tip top( choke fully disengaging) and tuned correctly, may need jets blowing if its flicking now and again. Rev limiter rotor arm? Can be sods. Now over to our more learned colleagues
Hmmm, hadn't considered this- I do generally put the sensor very close to the spark plug and it's one of the cheapo Gunson ones...will give this a try. Cheers
Hey there, Everything else should be in good shape. Carb was tuned not long ago and choke disengages fine as far as I know. Standard rotor arm and dissy is only a couple of years old so don't suspect any issues with the 123. I forgot to mention that all this is at idle with the vac line off (and plugged). Haven't yet tried it at high revs/max advance but will ry and get out at lunch to see how the land lies! Cheers
I you just looking at what the strobe shows or can you hear it too? What is leading you to be playing with the timing? Before messing with a dissy or anything else make sure all your valve clearances are spot on. Ensure that all your HT leads and connections to plugs are 100% spot on. No point having a flash dissy if everything else is garbage. What's the condition of the distributor shaft, timing gear? If there is any play or wear inside that won't help things.
Cheers Joker- just checking it as I removed the dissy to get at the manifold to replace the boots, shouldn't have changed (and hadn't) as i left the clamp on but also wanted to see if changing the boots had helped if it was to do with a vac leak. Did the tappets a few hundred miles ago and just fitted new plugs- have some new leads on order as they're pretty old and it could be that the connections aren't as good as they once were... As for the dissy shaft and timing gear I'm not sure- I'll have a look in Bentley but is it relatively easy to remove and check for wear or is it something to be done at rebuild time? Thanks fella, Olly
I had a problem like this . Turned out the distributor clamp was bent and holding the distributor base away from the block which allowed the drive to slop around. And another time I was not paying attention and let the RPM climb above 1000 while setting the timing - this made the centrifugal advance cut in and made everything bounce around - rpm and timing.
As matty said, I think it's likely to be your strobe gun. It's most unlikely that a 123 would start generating random ignition pulses - there's no real mechanism for this, given how it works. You can check for play in the dissy drive simply by gripping the rotor arm and trying to waggle it. It should be rock solid. I wouldn't think this is your problem.
timing on a good engine with good components will appear to vary to a certain extent...If it's running well, I wouldn't be too concerned could be that the electronic ignition module is much more sensitive to small changes in voltage regulation/alternator ripple, and it is this that you are seeing on the strobe....
if it was an old duffer, circa 1974, I'd agree, but a new 123 Dizzy shouldn't have much if any play in it...the dizzy drive may have some lash in it but this would be taken out as soon as you install and turn the dizzy...having said that all these worn bits rotating around at hundreds of RPM can add up to lumpy running.
Thanks for your comments chaps. No play in the dissy drive from what I could tell but mikedjames might be onto something as I looked and my dissy clamp is a bit bent and the dissy isn't rock solid against the case. Also noticed yesterday that whenI drove home the choke was still on one notch ( about 2.5miles and 10 minutes) but it was bloody cold so maybe not a problem... There didn't seem to be a tendency to stall when braking to a stop at least though so hopefully free of leaks fgollowing manifold boot replacement
