Detonation? Re-Jet Time?

[JoeDoomsday]

Hi Folks-
Recently put together a build with some of the higher end performance parts, which I never really fooled around with before.

I'm running the CNC High Compression Head, the Ported Cylinder with the Dio Reed intake, and the Thruster exhaust.
I also upgraded the magneto and CDI.

What I'm experiencing is once the bike is up to speed with the throttle, instead of being smooth sounding, it's almost like machine gun fire from the exaust. Giving it more throttle immediately stops this.

I was recommended before I even talked about this, to rejet the carb due to the set up, to a fatter jet-
It seems to run just fine other than that machine gun sound when I let off...its almost like a series of backfires.

I've checked the plugs for rich/lean, and the plug color is light brown to black.

I'm scratching my head. With that spark setup, its definitely burning off the gas, so I doubt it would be a typical backfire in the pipe from built up gasses...

I'm not sure what could be causing it other than detonation, or perhaps the jet not supplying enough gas, therefore the rejet that was suggested.

Any ideas or thoughts, lemme know. I'm going dead from it coming out of that Thruster pipe.
I knew ahead of time it would be loud, but its REALLY loud and I'm getting ugly looks from the local fat and bored Cops.

 

[Chainlube]

I think what you have is normal for that pipe, look for a little muffler for the end to avert the ugly stare.

Detonation is a condition found in more 4 stroke motors from a build up of carbon in the combustion chamber, when the carbon gets hot, it just lights the fuel even before it's compressed.

 

[Guest-907788]

I think what you have is normal for that pipe, look for a little muffler for the end to avert the ugly stare.

Detonation is a condition found in more 4 stroke motors from a build up of carbon in the combustion chamber, when the carbon gets hot, it just lights the fuel even before it's compressed.

Cool! Thanks- ironically I just saw the muffler extention

 

[JoeDoomsday]

If your running a "F2 thruster" it works as a big straight pipe and has no proper expansion.

I was thinking the same thing last night...
I might, for experimental sake, slap the old stock pipe on and give the bike a run, and see if there is any difference. If not, I'll look Into a different pipe.

 

[Chainlube]

The stock pipe is a proven winner in performance over a scooter pipe or baby expansion chamber.

 

[Street Ryderz]

Hi Folks-
Recently put together a build with some of the higher end performance parts, which I never really fooled around with before.

I'm running the CNC High Compression Head, the Ported Cylinder with the Dio Reed intake, and the Thruster exhaust.
I also upgraded the magneto and CDI.

What I'm experiencing is once the bike is up to speed with the throttle, instead of being smooth sounding, it's almost like machine gun fire from the exaust. Giving it more throttle immediately stops this.

I was recommended before I even talked about this, to rejet the carb due to the set up, to a fatter jet-
It seems to run just fine other than that machine gun sound when I let off...its almost like a series of backfires.

I've checked the plugs for rich/lean, and the plug color is light brown to black.

I'm scratching my head. With that spark setup, its definitely burning off the gas, so I doubt it would be a typical backfire in the pipe from built up gasses...

I'm not sure what could be causing it other than detonation, or perhaps the jet not supplying enough gas, therefore the rejet that was suggested.

Any ideas or thoughts, lemme know. I'm going dead from it coming out of that Thruster pipe.
I knew ahead of time it would be loud, but its REALLY loud and I'm getting ugly looks from the local fat and bored Cops.

Doesn't sound like detonation issue just to rich and 4 stroking under lite/no load,a good muffler on the end of the thruster pipe will help with the sound and down jetting will clean up the 4 stroking.If you listen to the bike in this video it's just a little rich so that when under little to no load it 4 strokes and cleans up when more throttle or load is seen.

 

[Street Ryderz]

I would NOT put a stock pipe on a dio reed setup you will just over heat it and damage you're engine,Detonation is common is 2 stroke engine for many reasons like too much compression,improper squish or lean jetting causing excessive heat.If it is detonation it's very easy to identify just take the head of and look at the piston top it will be all pock marked with little divot's around the edges.You wont hear detonation through the pipe as this happens in the compression part of the stroke before the exhaust port is open,you hear it in the cylinder and has a very distinct pinging sound.It's also not the size of chamber in the head that contributes to detonation it's the lack of squish control most aftermarket heads are not higher compression than stock they just have a better chamber with better squish area and far more cooling area.

 

[JoeDoomsday]

The stock pipe is a proven winner in performance over a scooter pipe or baby expansion chamber.

Gotta disagree with you on this;
Earlier I decided to see for myself if it WOULD ( this was before I read this) and sure enough, after running both pipes, the Thruster pipe definitely let's me top out a little higher, and a little bit additional torque..
It isn't DRASTIC by any means but definitely noticeable

 

[Street Ryderz]

Gotta disagree with you on this;
Earlier I decided to see for myself if it WOULD ( this was before I read this) and sure enough, after running both pipes, the Thruster pipe definitely let's me top out a little higher, and a little bit additional torque..
It isn't DRASTIC by any means but definitely noticeable

A bigger pipe with better suited header dia would improve that again noticeably,the stock pipe even gutted is WAY to small for even a lightly modified engine!

 

[JoeDoomsday]

Im writing this a couple weeks after....
I picked up one of those VooDoo 'Expantion' chambers with the small muffler on the end for a good price off that ebay sight boygofast. ( im not pushing advertisements- but the prices are good and shipping is far faster than the other companys)

First few days I simply didnt like it.
I fiddled and retuned the carb, and after dialing everything in, turns out this pipe DOES add a good high end take off.

I was having some low end bog out, so I drilled a few holes into the muffler for some release. Sure enough, it solved the low end bog out and even though I violated the muffler rule, it was still far quieter than that F2 pipe. Im liking it so far.
Now, that High Compression cnc head was, to be honest, TOO high of a compression and I solved it by adding an extra head gasket- that micro amount of extra room gave it exactly what it needed. Now its responsive, consistant, and winds out pretty well...

Been running good past few days. Just waiting for the next minor set back- seems to be some small thing every week to fiddle and fix... but hell, with this epidemic I dont have anything better to do.
Matter of fact I need to check the rear wheel bearings today.