port time changing

[2stroker]

Hi,

After a long search through the forum, I would like to share my experience with you Gassers:

I have just raised the cilinder on my 300 to clear the exhaust port (total amout of gaskets of 1,35 mm!), and have cutted the head to achieve the compression of 180 psi cold and 165 psi warm engine. The squish is about 1,5 outside to 2,4 mm inside edge. For now I will not reshape the combustion chamber, and I measured it 23 cc.

What is the main difference between aligned porting and the previous setup?

the question is: should I re-time the ignition to compensate the porting time change?

The bike has N1EG needle on first clip, 178 main and 38 slow. The spark plug seems to be ok, but the bike does not run well from idle to half throttle, beeing hesitating like too rich until the power valve opens. These symptoms already were present before changing port timing.

I removed a long time ago the 2 shims from power valve preload. Could it be the reason for the hesitation?

Thank you in advance,

Carlos

[hannesd]

seems to me you acted before informing yourself of what you were about to do?
what gave you the idea of trying to do this mod if you don't know the purpose of it?
what was wrong with it before?

no offence, but it just made me curious (as i am by nature),eager to learn.

hope some one can shed a light on this topic

ciao, hannes.

[2stroker]

In other 2 strokes I had, piston clears the exhaust port. I was advised to do this on GG300 to get all the power and hi-rev, as I use to ride on fast tracks, at hi speeds. For this reason, I would not raise the compression beyond 170 or 180 psi.

Good rides,

Carlos

[jostby]

Originally Posted by 2stroker

Hi,

These symptoms already were present before changing port timing.

Carlos

I think you got ahead of yourself. Though fixing (?) the port timing may be a good idea I think you have jetting issues that should have been addressed first.
Check out the jetting "sticky" in the Intake/Carb 2-Stroke forum to see how you compare to others on this board.
I'm not up on needle sizes but your slow jet seems awful small. I run a 48 on my '00 and a 46 on my kids '04 (250's).

[2stroker]

I just find a broken reed valve blade!....

I never suspected of it because I put a new set some months ago.

That should be the main reason for the rich idle and hesitating accelerating.

I will ride it next weekend and let you know.

[2stroker]

Concerning about the port timing change, can anybody tell me if I will improve the bike raising the cilinder to clear the exhaust port?

[Keg]

Raising the cylinder will give you better exhaust port timing and give you better top end. Doing this will mean it is worth modifying the head to get the right squish. 0.9 - 1.3mm squish with 26-29cc's in the chamber is pretty good.

[2stroker]

Hi Keg,

26-29 cc for a GG300, is a bit hi-compression, dont you think?
And Hi-compression is not good for hi revs.

Please correct me if I am wrong.

Regards

[hannesd]

Originally Posted by 2stroker

I just find a broken reed valve blade!....

I never suspected of it because I put a new set some months ago.

That should be the main reason for the rich idle and hesitating accelerating.

I will ride it next weekend and let you know.

now did it help the rich idle, by replacing the reeds?

[elemetal]

If you had to replace the reeds so soon it sounds like something's not right in there. Might just be that lean pilot causing a backfire that's trashing the reeds. 38 is pretty small compared to just about averyone on here. If I remember correctly 23cc is stock head volume so 26-29cc would lower compression. I just did the opposite of you (dropped the cylinder rather than raise it) so that the low end is still a usable tractor. Have to see if it hurt the over-rev, if so I'll need to re-shape the bowl.