Snap Crackle, Pop

I am getting a snap crackle and pop at and above 5000rpm. This happens egaully with 4 different ignitions including the Joe Hunt Mag, 2 Powerarcs, and a Surefire. Also with different carb setups.

I am checking for a broke brand new beehive spring but all looks and sounds (ping) good and equal. I am also looking at cam timing and see that intake lift is around .165 and exhaust is around .145 at TDC as suggested for this cam.

I am wondering is cam chain got loose and would cause these issues. I have the mk3 cover and looking in to the inspection hole it does not seem particulaly loose with 3/8" at the looses point and 3/16" at the tightest.

One no brainer that has slipped my brain is chainging the spark plugs but the different ignitions take different plugs anyways. The plug look good and no smoke is coming from the bike. Piston top are clean. Idles well and cruizes fine below said rpm's with good low and mid range to 4500 where it starts to go bad.

I will be screwing in the pressure guage later today to check for inequalities.

Again, this is with various carb and ignition systems all showing the same symptoms.

Ugh, this is how my Peel Combat acted after over rev event, just fine up to 5000 then like hit a wall of spitting popping and pooping out on power. It'd spin on up to redline, if I was going down hill but not otherwise. I most suspect in Peel case it was the cam chain tension getting jerked out of it and a cam lobe ground down adding to the miss timing of slack chain some how bouncing analog boyah nutzo like it over advanced. Another thing may be bad terminal or broken copper in ignition power path that only acts up at 5000ish rpm. Ugh, 5 ignitions systems loss of leisure and ride time, ugh. Oh yeah, had another event where Peel would start ok and idle and low throttle ok but soon as got some speed and throttle she'd miss fire and loose power till one day just quit. Found the tail light woven earth cable was bouncing against a power lead and shorting out running voltage. Nothing like a Commando to test your sanity and will power and pure luck.

If your are using a grade 7 NGK plug [or equivalent] you might want to go to an 8 or a 9.

7's are too hot for a motor with a few power adders and can cause your symptoms. Jim

PS. If that doesn't do it I would put one extra heat insulating washer under each spring.

comnoz said:

If your are using a grade 7 NGK plug [or equivalent] you might want to go to an 8 or a 9.

7's are too hot for a motor with a few power adders and can cause your symptoms. Jim

PS. If that doesn't do it I would put one extra heat insulating washer under each spring.

Click to expand...

No joy with the 8's or 9's, Jim. God, I do not want to pull the head.

Going to take a look at the cam chain and geartrain in there.

God, I do not want to pull the head

Click to expand...

Boy is that refreshing attitude yet no help to face my current nothing left but bite bullet or stay in denial.

pete.v said:

comnoz said:

If your are using a grade 7 NGK plug [or equivalent] you might want to go to an 8 or a 9.

7's are too hot for a motor with a few power adders and can cause your symptoms. Jim

PS. If that doesn't do it I would put one extra heat insulating washer under each spring.

Click to expand...

No joy with the 8's or 9's, Jim. God, I do not want to pull the head.

Going to take a look at the cam chain and geartrain in there.

Click to expand...

I have pulled the rocker spindles and aired up the motor through the spark plug holes to change the springs, but it's still no fun. Jim

Hows the snap crackle pop happening? Is it revving on the stand or out on the road? Accelerating or backing off? As seems carbs, ignition and plugs have been examined, how about a detail check on the header pipe joints? Maybe a stray wire flopping around? A loose connector?

ML said:

Hows the snap crackle pop happening? Is it revving on the stand or out on the road? Accelerating or backing off? As seems carbs, ignition and plugs have been examined, how about a detail check on the header pipe joints? Maybe a stray wire flopping around? A loose connector?

Click to expand...

During accelleration on the road. Pipes are virtually new. All electronics are isolated and swithed off with magneto. I have even removed the grounding shut off wire just in case of some random feedback.

Can you identify if the exhaust noise is different between the left and right pipes? Things seem to point to a combustion breakdown at that RPM, and if its on one side and not the other then maybe a valve is the issue. But if its on both sides I think 2 valve springs busting at the same time very very unlikely. I do know that if cam chain timing, is one 1 pin out, it causes the motor to hit the wall around 4,000 but I can't say if its the same effect as you are experiencing.
If you rev the motor to 5,000 on the stand (or at least upright on its wheels) and hold it there does the problem appear? Because if it doesn't I suspect that when under load as in running on the road, the carburetion (or lets call it the induction) is pulling way too much air. How that's happening I can't figure out as I guess you've done all the manifold joint checks? And likewise, the right gasket rings in the exhaust ports? Alternative - Small Roadster tank experience tells me this is like carbs running low on fuel, done the flow check?