Timing advance: stock stroke vs 4 mil

[J-Madd]

I bumped up my timing from +5 to +9 on my 4 mil Cub and my stock stroke Cub. The 4 mil starts and idles fine, I haven't rode it yet (compression 180 psi, squish around 0.045). The stock stroker (160 psi, not sure about squish) won't start and it backfires. Running 108 octane in both. Of course I'm gonna back the timing down, but just wondering if the difference is due to the stroke, or if it is just an individual characteristic of my particular motor.... "every motor's different" as the saying goes.

[dajogejr]

Cubs in general like more timing if you keep the squish in check as well as the compression.

I ran my 4 mil on gas @ 185PSI and about 12 degrees timing...but the last 4 degrees came from the curve on my dyna...and the CDI tapers off as the R's raise...

8 on my plate, plus the dyna....

 

A lot of folks are scared to run that high of timing on a cub, mine loved it...so, that's what I'm going by.

I'll get a good idea how much timing my 10 mil on alky likes this weekend...

[bigboybanshee]

I'm running a bunch of timing on my cub too, +7 on the plate and dyna on curve 3...cubs definitely like a lot of timing!!

 

On my stock stroke, stock cylinder last year I never ran anything more than +7 on the plate with a stock CDI. I'd be willing to bet the +9 is too much for stock cylinders. Are your stock cylinders drag ported?

[dajogejr]

J-Madd....

Big Boy is 300lbs, and has a little 4 mil cub motor going LOW 4's (4.1s last I heard before the bottle, right Travis??)

 

on GAS....

 

This is almost unheard of on gas and with a big boy rider....

 

He's obviously doing something very right...and very impressive.

 

I used to have a lot of people bag on me for running so much timing on my old 4 mil cub, just goes to show you there more power to be had if you want to try for it...

[bigboybanshee]

Maybe Saturday! I changed a thing or two since the last runs...but my best pass to date is a 4.21, running gasoline. If it wasn't for you recommending the timing increase I wouldn't have tried it, and boy it REALLY woke my bike up. Went from running 4.40's to 4.20's, stock framed bike!

 

And thank you very much for the kind words, I really appreciate it!!! I'm extremely proud of my little 4mil from F.A.S.T. racing

[375hp banshees]

I'm running a bunch of timing on my cub too, +7 on the plate and dyna on curve 3...cubs definitely like a lot of timing!!

 

On my stock stroke, stock cylinder last year I never ran anything more than +7 on the plate with a stock CDI. I'd be willing to bet the +9 is too much for stock cylinders. Are your stock cylinders drag ported?

 

 

I think he said both were cubs- 1 =stock stroke, 1= 4 mil.

[dajogejr]

Good point...he sure did. I guess we're both not very good readerz or sumthin....

 

Odd...maybe it is a stroker motor thing...maybe the stock stroke has less squish, more compression...or combo...

(Could be the timing on the plate is a little off, too...)

[bigboybanshee]

LOL, yeah...I guess I skipped over that part too Been a long day already and it's only halfway over with....

[wesw]

were the domes from the same people ??

 

if not im leaning the squish band and velocitys were different and with lots of timing it was knocking.

 

 

if same and cut the same, something is fishy.

[J-Madd]

Now that I think of it, the domes did not come from the same people. The 4 mil domes came from Jeff and I think I got the stock stroke BB domes from Precision Powersports, but Jeff put the motor together when he welded my stock crank. I'm sure he checks the squish, I just don't know what it is. I'll try to check it and let everyone know.

 

Also.........When I test out the 4 mil with +9, will I find out if that is too much timing before the motor grenades? Will there be enough warning signs? That is kind of scary , especially with a local race coming up that I happen to be in charge of.

[wesw]

if you desire 9 degrees advance and have the gas and all that, do like 2 wot passes and see if the plugs are still in the head adn pull them out if they look normal, no gray flaky stuff you might be ok.

 

i know it depends on your domes the specs not just the squish to run lot of compression and timing, you get the velocitys and bands too high, and pressures off the chart it will blow up.

 

you might try like 5 degs then up it to like 7 and see if it really makes a difference.

[J-Madd]

Well the 4 mil ran fine, but I didn't pull the plugs out and look yet..motor was too hot and never got around to it when it cooled. The stock stroke motor still backfires and won't start even at stock timing. The pick up coil gap should not have changed, but that has to be it. I'll have to check that Sunday.

 

Thanks. :beer:

[J-Madd]

Well, it wasn't the pickup coil gap, so I tried a different stator and CDI.......still no good. I finally got it to start some how while the flywheel not torqued down, but when I tightened it, the engine wouldn't start and backfired. I found that the key was somehow moving the flywheel out of time, even though it was in the groove and tightened down. I took a flat screwdriver and scraped the flywheel keyway clean of metal deposits that the key had left, and it's fine now with +9 timing. No signs of metal flakes on plugs or detonation on either motor.