Total loss and back firing problems

[Waternut]

I've blown 2 stock waterboxes and I finally got a metal waterbox and today it back fired. It will always start the first time but if I come back a couple hours later and restart it, it will backfire.

I thought I set up my total loss correctly but after three backfires, I started questioning it. I originally setup the static timing as 36° using the LED and with MSD's circuitry that should mean 31° and I took off another 1° with the dip switches on my single channel system to give me a true timing of 30°. My kawi is set to 29° and runs fine. I fired it up to check the timing with a light and I couldn't figure out what was going on. I only marked half of the flywheel and it looked like the timing marks were jumping back and forth about 5-10°.

I verified my static timing but since TDC has some play in it, I think I was using the wrong end of the play. So I'm guessing my true timing was 35° instead of 30°. Would this have been causing all the backfires?

Also any ideas on why the timing marks looked so funny? Is it just because I only marked up half of the flywheel? Maybe the magnets in the flywheel aren't the same and causing problems?

 

[madscientist]

35* of advance if back fired it would be out of the carb. not the pipe.

 

[Watty]

leaky needle and seat? maye the fuel pressure/heat from the sun is pushing past a leaky n&s causing it to burn the fuel right through to the waterbox?

Alos, if it's a dual pickup, check the timing on both cylinders, one could be a bit out if the pickup has been flipped around to get the wiring neater off the pickup plate.

 

[Waternut]

It's only a single pickup and the ski has been in the garage every time I've started it up.

It could be the needle and seat but I don't know. The pop off on this thing is so incredibly high that my pump and test setup starts leaking before it pops. Last time I rode it, the carb idled and revved very smoothly so I hesitant to think that the carb is poorly tuned. However, I wasn't able to get the carb to pop until around 50-55psi. It's got a 1.5 seat and no markings on the needle. The spring looks shiney silver but based on the pop off pressure, it's probably dull silver.

 

[D-Roc]

i thought only the old anolog system removed 5 degrees from the circuity, not the newer single and for sure not the multi channel system, your timing may not be where you think it is. also to verify your true TDC zero your dial indicator and turn 10 CCW from where you think TDC is and record the number, turn 10 degree CW and compare the number to the first if they don't match then your not at TDC, split the difference and try again, this will find TDC of your dwell time.

 

[Waternut]

The single channel total loss takes 5° off as well. The installation manual says so in big bold print.

I rechecked my TDC mark and it is correct now but was about 5° off before and I backed off the timing on the brain another 6° (temporarily) to be safe. The timing is still jumping a little bit but it appears to be jumping between 22-25° so it could just be vibration of the engine throwing off my eye.

 

[D-Roc]

okay i wasn't sure if it was just the old anolog system that removed 5 degrees. what way was the timing out + or - ? so does it work better now with the timing backed off a bit?

 

[Waternut]

My original TDC mark showed 35° and the new accurate mark shows 40° on the static LED. However, the timing light shows it to be more like 35° with the new mark since MSD takes off 5 and I took off 7 to give me around 23 which is roughly what the light was indicating.

Not sure on better or worse though because it idles and revs fine both ways.

 

[D-Roc]

hmmm interesting indeed. that seems like real safe timing now. i guess you have to ride it to see if it backfires on a startup? maybe you do have fuel leaking in past the needle and seat after you shut it off. the tank would be pressurized after a ride, is there any flames in you pulse line?

 

[Waternut]

I rode it today on the lake and everything was fine. I did manage to backfire my kawi today though which I've only done once. I must be doing something funny...