need help reading piston burn pattern

[bladefrost]

will try to post more videos so you can see the problem. im having a hard time explaining it in english

[bladefrost]

Spark test 1 gapped 3mm
https://www.dropbox.com/s/2l6xezqob7l9o ... 1.mp4?dl=0

Spark test 2
https://www.dropbox.com/s/31gekhaxjm6l8 ... 2.mp4?dl=0

[bladefrost]

tried to by pass the ignition switch & tried leaner mainjet. it improved. stalling is minized but not completely gone. i dont know wether the leaner jetting is the one that help or the by passed ignition switch. i remember my bike would run very bad or have low to midrange stalling issues using smaller mainjet than a 120, even the 120 still cannot completely get rid of the stalling and if i try a 125 mainjet the topend would be too rich, this was before the piston was modified to improve flame travel and quench clearance is changed to about .040 inch. the stalling is almost gone with the 105 and the by passed ignition switch but not completely gone and the driveability improved alot on todays test. would try to run even smaller mainjet, would try no.100 mainjet tomorrow.

please take a look at my spark test video. that might help

[mag2555]

The spark looks good, but drive the bike somewhere that you can take off the exhaust and run it without getting thrown in jail.

[bladefrost]

The spark looks good, but drive the bike somewhere that you can take off the exhaust and run it without getting thrown in jail.

Okay. One time the police when here at my house. Actually the police station is just near. This exhaust is very loud. It has big hole at the silencer.

[bladefrost]

Another thing i checked valve clearance at tdc and it was tighter than checking it using IC EO method. So i set the clearance using ICEO and when i turn the piston to tdc the clearances would be tighter. Is this because of the design of the cam?

[mag2555]

Any progress in testing the motor with the exh off of the motor?
Also in regards to the exh side of the head if the exh port exit has been ported to match the inlet size of the silencer than you may have a big reversion issue which would explain why the motor runs as it does.
Also a ruff surface or rust inside the silencer can make for a lot of reversion / restriction to exhaust flow and can not be over looked!
I have seen headers with rust scale on the inside knock 18 hp off of a V8 motor at 7500 rpm!

The outlet of the heads exh port needs to be smaller than the inlet of the silencer!
This is why I have been compelling you to please test the motor with the silencer unbolted from the head!!

[bladefrost]

Any progress in testing the motor with the exh off of the motor?
Also in regards to the exh side of the head if the exh port exit has been ported to match the inlet size of the silencer than you may have a big reversion issue which would explain why the motor runs as it does.
Also a ruff surface or rust inside the silencer can make for a lot of reversion / restriction to exhaust flow and can not be over looked!
I have seen headers with rust scale on the inside knock 18 hp off of a V8 motor at 7500 rpm!

The outlet of the heads exh port needs to be smaller than the inlet of the silencer!
This is why I have been compelling you to please test the motor with the silencer unbolted from the head!!

The exhaust port has not been matched sir. It has a D port. The flat floor has been carried throughout the flange. Also the exhaust port is smaller than the manifold. Theres been good results. I by passed the ignition switch and at first its still stalling and i adjusted the carburetor again and now it runs better than ever. Seems that after i by passed the ignition switch and re adjusted everything it runs so much better. The stalling is almost gone and the power is so much better.

I hope this is it. Just need to make the carb perfect and the ignition timing. What also helped is i adjusted the valves using ICEO rather than just putting thr piston at tdc coz i found out it at ICEO the valves would be looser. That also helped alot on how it runs. Can you give me guidelines on how to know what timing to run? How do i know what rpm needs the timing to reach full advance?

I thought just took off the silencer. You mean took off the whole exhaust from the head and run it? Still need to find time to do that. Maybe on sunday we can go to a place with my buddy and test it.

[mag2555]

Good news than!
I can not help you with timing as I have no experience with these motors at present!

[bladefrost]

Good news than!
I can not help you with timing as I have no experience with these motors at present!

But still doesnt make sense coz the ignition switch was working normally. Just cant think of any other part to test that could be the problem.

[mag2555]

A switch can work, but under load it can limit the needed current flow of electricity that the motor needs to run under load"
Your video posting of good spark was not under load!
the spark having to jump the gap with the compression of the motor in running order is a very different thing!

[adam728]

With no dyno you are pretty limited in picking the "best" timing at each engine speed. Best method might be finding a hill, 2 landmarks a good distance apart, and doing some testing. Enter at a determined rpm, pin it at the first line, tree, pole, whatever. See what the engine rpm is at your end point. Adjust timing and repeat. If you find yourself picking up more rpm on the same hill/distance, then it's making more power.


I did some more digging and found a 125cc bike engine we did with a clutch and 5 speed. At WOT timing is 15 deg below 1500 rpm, then climbs linearly to a peak of 36 degrees at 9000 rpm. Stays there till the rev limiter (11K).

It's big brother (200cc) was a similar curve, but with about 8 degrees less timing everywhere. Had detonation issues below 4K, and just didn't want much more than 28-29 degrees at high speed, stopped picking up power.

[mag2555]

Adam will these timing numbers work with is faster burn that he has now since his rework of the piston dome, or should he back 2 degrees out of what you posted?

[bladefrost]

A switch can work, but under load it can limit the needed current flow of electricity that the motor needs to run under load"
Your video posting of good spark was not under load!
the spark having to jump the gap with the compression of the motor in running order is a very different thing!

i hope this is it sir. we'll see if my bike continues to improve with the ignition switch by passed.

[bladefrost]

With no dyno you are pretty limited in picking the "best" timing at each engine speed. Best method might be finding a hill, 2 landmarks a good distance apart, and doing some testing. Enter at a determined rpm, pin it at the first line, tree, pole, whatever. See what the engine rpm is at your end point. Adjust timing and repeat. If you find yourself picking up more rpm on the same hill/distance, then it's making more power.


I did some more digging and found a 125cc bike engine we did with a clutch and 5 speed. At WOT timing is 15 deg below 1500 rpm, then climbs linearly to a peak of 36 degrees at 9000 rpm. Stays there till the rev limiter (11K).

It's big brother (200cc) was a similar curve, but with about 8 degrees less timing everywhere. Had detonation issues below 4K, and just didn't want much more than 28-29 degrees at high speed, stopped picking up power.

what about in drag race sir? i plan to use this bike for drag. will a locking the timing out work?

is it okay to lock out the timing first and determine the highest advances which produces the best power at the top and then go back to adjusting the timing at lower rpm? this bike will reach 14k rpm.

i always though best timing power should be about 36degrees. at 28-29 degrees maybe you are loosing power because the bike needs more octane?

what do you suggest adjusting timing at 500 rpm increments or by 1000 rpm? the cdi is programmable but i can only adjust timing at 2,100rpm up. below 2,100 its timing is 15degrees.