Puch exhaust port match

So, I'm either about to do something really stupid or my first semi difficult moped mod.

I want to match my performance exhaust (techno estoril) to the cylinder exhaust port.

I have a pretty good grasp of how to do it and have all the right tools, I just want to know:

Is this a good idea?

I mean, I always hear people talk about port matching with regard to matching the cylinder to the case, but I don't hear much talk of exhaust porting... is this because its not a big deal or what? It seems like it should make a decent difference in helping the flow, and given that I have a stock cylinder and carb, it's really the only thing that needs to be "matched"... and I'm not interested in reshaping the stock stuff right now.

So should I do it? Damn, I'm probably going to anyway just thought I should check in first and see if anybody would let me know if I'm being totally retarded.

Thanks dudes!

Re: Puch exhaust port match

Yea that is a good thing to do. The cylinder end of the port can be made more wide too

Re: Puch exhaust port match

use a red sharpie parker and trace a line on the inside of youre cylinder around the ports as a guide to haw much material you are taking out.

also I would strongly recommend finding a spare cylinder

to fall back on just in case you cut too deep if you know what I mean!

Re: Puch exhaust port match

Are you running it on a kit? Opening up a cylinder's exhaust usually has the effect of reducing the amount of low-end power a cylinder has in exchange for more top-end.

Re: Puch exhaust port match

what about just ramping the bottom of the port to reduce turbulence, and keeping the cylinder wall original?

Re: Puch exhaust port match

I don't think this guy knows the difference between the exhaust port window and the exhaust port outlet. I think he's just talking about matching the exhaust port outlet, the part where the header of the pipe bolts on to the cylinder, which is quite safe. Changing the size and shape of the actual port window in the bore of the cylinder is MUCH riskier mod, though mostly it depends on how well you understand how things work, and know EXACTLY what you're doing.

Re: Puch exhaust port match

Hey Ando and everybody else,

This is basically what I did. All I did was grind down the gasket and bottom of the port so there is a sloping wall from the actual pipe openng into the cylinder. I didn't change the cylinder wall except for maybe the bottom 1/4" or so which now has a wider lip and gradual slope.

The bike now runs more poorly, but I think its due to the fact that I have to readjust everything I had adjusted for my previous setup... jet, needle, idle, timing, etc.

It is now much louder, and the sound of it firing can be heard much more clearly right around the cylinder / pipe joint. I dunno if this is good or bad sign.

It SOUNDS like the bike has more balls, but it runs way worse.

I had been running a 64 jet, so I upjetted to a 66 assuming that the better air flow would lead to a leaner mixture. When I pulled out the plug it was sickening and black after having been a perfect medium brown before. So I downjetted to a 62 just to see what would happen. With the 62 it seems to be 4 stroking right before 30 mph, which didn't happen before. I can't imagine this setup needing a smaller jet than 62, but a plug chop seemed to confirm I'm running a little too rich...

Could this be a needle adjustment issue? Pretty sure it's at stock setting right now. Should I lean out the needle a little more and then put the bigger jet back in?

The other thing I'm considering is possibly I fucked up the compression somehow, because going by the spark plug color chart I found mine looks like one of the options that has low compression as a possibility...

Any ideas?? Could I have fucked it up? It seemed like I did a fairly flawless match for what it was... but who knows. What do you guys think?

Re: Puch exhaust port match

And yes,

I know the DIFFERENCE between the window and outlet, I just described what I was doing badly and am pretty new to port, intake, outlet matching etc. so pardon my bad explanation skills and please ask me to clarify if it seems like something I said was wrong or doesn't make sense. Sorry fellers.

Re: Puch exhaust port match

I'm pretty sure that if you lowered the exhaust window its fucked. Everything I read says you can rase the window a little. But if you lower it the window stays open longer and you lose the next stroke's mixture. But all thats conjecture.

Re: Puch exhaust port match


Woke up this morning and checked it out again. Disassembled the carb again only to find that the needle clip was totallly fucked up. It was bent so that it was resting on both like, the bottom notch and the 2nd from the top notch.... don't ask me how. Must have gotten bent when I was cleaning and reassembling.


After I fixed that, it ran WAY better but I think was too lean so I upjetted again (back to where I was) and now it runs fantastically. The noise of the firing is still the same (noticeably louder)... could it be that I need to adjust the timing again??? Or do you think the wider opening could just have made it louder?

Regardless, It seems like I gained 1 MAYBE 2 mph out of the mod, plus everything just seems to run "smoother" for lack of a better word while at and around top speed.

Provided the noisy firing isn't a drastically bad sign of something.. I think I was fairly successful. I would definitely recommend this mod as an easy entry into getting used to what it's like to actually grind away metal on the cylinder without running too much danger of ruining everything.

And Paul, I didn't even touch the actual port window whatsoever... just the outlet, so I don't think I ruined anything... at least not too bad.

Re: Puch exhaust port match

Good to hear.

Re: Puch exhaust port match

shit talkin' hippy /

new exhaust gasket...

Re: Puch exhaust port match

yes, new gasket. maybe double check how tight those exhaust bolts are.

Re: Puch exhaust port match

Im planning on doing this same thing - opening the exhaust outlet to match the boss pipe. Have a set of small files, wondering which dremel bits work the best for this sort of thing?

Re: Puch exhaust port match

tungsten carbide, get one where the carbide part has a greater circumference that hte peice that goes into the dremel.

Just ramp the port so that it matches your exhaust gasket and take out any humps in the port.

If (and only IF) you do a really good, smooth job. (and its a stock puch cyl)

widen the exhuast port window 1mm, then champher.

then see how it runs, if its awesome and you still did a good job raise the exhuast window .5mm

then take the cyl off, put the piston in the cylinder at TDC (make a sharpie mark on the cyl while its still on the bike with the head off)

and look through the intake port, is the piston skirt covering up the intake port?

If yes, then shave in down until its completely clear.

THEN, look in from the clyinder skirt side with the piston at TDC. are the top parts of the arch in the piston covering up the ports? If so shave those down too!

You be flyin' 40mph or better

Re: Puch exhaust port match

Ok well I think I will start with just matching the exhaust output to the header. If that goes well maybe I will widen the port a little with some of my small files. I hesitate to raise the window as I would assume that would fuck the timing.

Can you give me some insight on the technique for chamfering that works well for you. Do you go in there with some really fine sand paper or file or what?

Re: Puch exhaust port match

Those Dremel sanding drums with a coarse grit are ideal for making nice round enlargments. I tried one of those rubber like tools that have grit in the rubber to chamfer some ports and it did a wonderful job.

Re: Puch exhaust port match

Oh yea I take the shap edge off rings with that rubber tip tool too. Just stay off the face

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