Varitronic timing

[Jeff t]

Fitted this over winter on My GP imola, franspeed with 30 phbh, when it's low down so up to 4.5k revs it runs lumpy is the only way to describe it. Had it on the dyno at weekend and the jettingis bang on which I needed to rule out because of another issue I had.
Anyway I set fast tick over at around 20 degrees so tonight I have doubled checked everything tdc, the markings re-strobed it and all looks ok and is set up as I thought. Would changing the fast tick over help this or could it be something else. On the graph from the dyno from 3.5k to about 4.5k rpm the line is like a squiggle that a kid would draw but once it gets to 4.5k the line is as you would expect so smooth line and that reflects how it rides. I can't upload the dyno results as I wouldnt know where to start.
The only other thing tonight when I tried to start it because the earth wire wasn't connected to Earth the engine it wouldn't start and I've read that Variatronic can be temperamental if not we'll earthed.

Any thoughts?

[dscscotty]

Check all earths etc are good, and advance your ignition timing @ tickover to around 24' BTDC, Imola's can be a bit hit and miss with port timings, and often need setting to achieve the best from the kit.

[Raveydavey]

The Varitronic doesn't start retarding to about 4.5k revs, so it's running flat at 20deg before that. An engine should run fine at 20 so I doubt changing the timing at fast idle will have any effect but it doesn't take long to try it. I love being wrong I've had lumpy performance from a Varitronic but at high revs. It turned out to be a broken earth strap.

[a-teamlambretta]

what flywheel did you have before, was it a full weight or even a semi lightend one? . varitronic flywheel is light and therefore you will have a lumpy tickover due to not enough inertia . i used to have my imola/varitronic set at a slightly faster idle to compansate . hope this helps ,cheers simon

[Jeff t]

Thanks for the help, I've changed the timing and made sure the earths are good, although I thought the same as it would have been running at19 degrees before I fitted the kit on static timing. It's not tickover's thats the issue its running at low revs then as it reaches 4.5 revs it goes ok. I've not had chance to run it yet will try over the weekend.
Cheers

[Jeff t]

Went out earlier and it seems a lot better, will give it a proper run tomorrow.

[Jeff t]

Went out at weekend and it's no better, I've checked everything even fitted an extra earth wire, starting to think it maybe something else as I stripped the top end at the same time. Only seed of doubt is sealing the cylinder head as its the first time I've only used silicone would an air leak have the same effect.

[a-teamlambretta]

reeds ok ?

[Jeff t]

Checked the reads all look ok, cylnder head looks ok I'm struggling now could it be the stator ?

[Norfolk]

Interesting reading your problem with Varitronic ignition. My scoot has one fitted and I am experiencing exactly the same problem.
I don't have a rev counter but at engine speeds below approx 4K the engine runs for a better word like a bag of nails, over that speed the whole engine gives a jolt and runs as sweet as a nut. I have tried the ignition at several settings ranging from 17 to 24 degrees, nothing changed the way the engine jolted and run smoothly, so I will be following this thread with interest.
For interest it has Ancillote exhaust, PHBH 26 carb, stage 5 tuned and lightened flywheel. Adjusting the mixture screw makes very little difference with the smoothest running with the screw nearly full in.

[Jeff t]

Sounds exactly the same as mine, I am convinced now it's either stator or cdi but not a clue about electrics so will see if I can get a spare to try.

[Norfolk]

Do you find that when checking the timing with a strobe light the timing mark appears to jump around quite a bit, I assumed this was because of the double spark the Varitronic is supposed to produce

[dickie]

Do you find that when checking the timing with a strobe light the timing mark appears to jump around quite a bit, I assumed this was because of the double spark the Varitronic is supposed to produce

When I strobed my varitronic I found it nice and stable until around 4000rpm when it jumped 180. My strobe (and I believe all the common or garden ones) are only good up to around 8000rpm. Off topic slightly but my point is simply that mine didn't jump around; might just be slight differences between strobes

[Jeff t]

No on the strobe it's ok seems stable and as the revs increase starts to move towards TDC, where it was stange was on the dyno up to around 4.5k revs the line is eratic and then smoothes out at 4.5k revs and is ok which is in line what it feels like to ride so shite at the start then kicks in and rides great.

[Wack]

The first time I fitted a varitronic I found I had to come down on the atomiser to let the motor run smoothly so why not try that or lean the needle off just to see?

[Fast n Furious]

Do you find that when checking the timing with a strobe light the timing mark appears to jump around quite a bit, I assumed this was because of the double spark the Varitronic is supposed to produce

This can happen if the the pickup alignment is on the raggy edge. Any wear in the magneto crank bearing won't help. It can also happen if the magneto ignition coil is producing an unstable voltage level to the CDI

[Jeff t]

I checked and cleaned the earth wire, and changed the atomiser from 266 to 264 and it now runs a lot better, I think changing the atomiser made all the difference. Thanks for the help.
Cheers

[Norfolk]

I will have to do that to mine and see what happens. I already know the earth leads are all just fine, I have checked them and fitted extras all over the place