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Old 02-27-2004, 08:42 PM
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Question How to port PW80 exhaust?

     

I bought my grandson a PW80 a while back. I have no experience with motorbikes, and am a complete novice with them. My grandson and I have taken the washer out of the exhaust, drilled the airbox, and taken the spark arrestor out of the silencer, and drilled holes in the spark arrestor tube to help tune it. These modifications helped immensely, but grandson wants more response if possible. We read on the pw80 thread to port exhaust. Does anyone know any good books that might help on this subject? Does Eric Gorr's "Motocross & Offroad Performance Handbook cover this subject?
Thanks in advance to all help.
Buck
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Old 02-27-2004, 09:24 PM
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Default Re: How to port PW80 exhaust?

Hi Buck,
Well sorry I don't know how to port the exhaust, but I can tell you they make a lot of aftermarket parts to make those bikes go faster. FMF makes a full exhaust which looks sweet. They also make a power up kit that includes different reeds and some other stuff. I was playing around on e-bay and found a lot of stuff. My little nephew just got one so we have been checking out all the trick parts they make.
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Old 02-28-2004, 06:44 PM
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Default Re: How to port PW80 exhaust?

As much as I admire your will to hop up that little bike, If he is really using the motor to its full potential its time to get him an mx 85 or 65 (whichever fits best).

A pw-80 was my first bike!
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Old 02-28-2004, 07:37 PM
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Default Re: How to port PW80 exhaust?

A PW80 was my first bike as well. If your grandson feels comfortable on the PW but just needs a little more pep then the FMF fatty pipe should be worth taking a look at. If he just feels as if he has completely outgrown the power and needs something more than an motocross bike is in need.
As for the porting I do not know about it but I believe it would be best to just leave it alone.
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Old 02-28-2004, 08:00 PM
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Default Re: How to port PW80 exhaust?

make sure you got the jetting and carb operating to it`s full potential...number 1 tuning hop up and often overlooked...eric gorrs book is a good investment...have fun with the little rooster
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Old 02-29-2004, 12:23 PM
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Default Re: How to port PW80 exhaust?

Thanks for the feedback, they are all appreciated.
Buck
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Old 03-04-2004, 01:21 PM
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Default Re: How to port PW80 exhaust?

Buck, the beauty of that bike is that cylinders are cheap. It also came from the design era where everything you did seemed to help it out. Had you done any drilling on something designed since the 80's you probably would have lost power.

We still have a garage full of pw50's and one pw80. They are low on compression and slow on porting. Lap the head and cylinder,,,drop the head gasket and add the corresponding amount to the base gasket and see what you get! We have used heavy tin foil ie aluminum foil for head gaskets, but something like "copper seal seems" to work well. If you really like it you can go further by building a spacer and milling the head and cylinder top. Keep about .030 clearance between the extreme edge of the squish band and the piston,,,,as always watch your jetting and use good fuel as a base.

No philosophy here, as you just asked what you could do.
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Old 03-26-2004, 09:58 PM
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Default Re: How to port PW80 exhaust?

Andy, I took the head and cylinder to a friends machine shop and got them milled, I had my grandson do all the mechanical work, pulling the head and cylinder, installing the base gaskets and using copper coating in place of the head gasket. It made a marked improvement in the little bikes performance. Unfortanetly the copper seal didnt last, blowing the head seal after about 20 minutes riding. I had grandson pull head and put in aluminium foil for head gasket, and after riding it hard for roughly 3 hours this evening it held, and is running great. Grandson thanks you, and I thank you.
Buck
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Old 03-26-2004, 10:17 PM
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Default Re: How to port PW80 exhaust?

awesome! good luck on the lil bike
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Old 03-26-2004, 10:19 PM
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Default Re: How to port PW80 exhaust?

Raise the exhaust .080"...widen the exhaust .160" each side...mill the head .080"...relieve the squish .080"...cut the squish 10 degrees .080" from the edge. Hope this helps. tdub
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Old 03-27-2004, 07:55 PM
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Default Re: How to port PW80 exhaust?

As you can all see, it is clear that tryce does not actually have a 60 horsepower yzf. He is
obviously a midget, and rides a souped up PW-80.
:
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Old 03-28-2004, 12:43 PM
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Default Re: How to port PW80 exhaust?

LOL Tryce has been outed. And we see that he works on a certain number pattern,,,,.080 and .160. probably .040 etc.

This is one cylinder that you can improve with about anything.

But it is good to see that you got the boy involved in the work. Invaluable. May he never need a "mechanic". And if he does, he will be wise enough to pick a real one.

Did you add to the base gasket yet (in other words raised the cylinder and advanced the porting as well as extending the time they are open)? It does a good portion of what raising the ports do. As Tryce suggests,,widening them helps and if that is all you do, it won't detract from the low end power either. But your grandson sounds like he would be ok with raising them a little,,so start stacking on some base gaskets, or cut a thicker one and see where you like it .
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Old 03-28-2004, 01:12 PM
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Default Re: How to port PW80 exhaust?

Andy, we bought some gasket material that was the next thickness up, from what was on it. We cut two base gaskets out of this material and AJ installed them when he put it back together. I showed him where the ports were cut in the cylinder walls, and explained to him that by raising the gaskets, we were really raising the ports, making it port faster. He bought Eric Gorrs book, and we use it for his 1/2 hr reading assignment he has every school night. I then quizz him on what Eric was explaining. Seems to make his reading homework we assign him go down easier that way.
Once again, thanks to everyone that contributed to my question, they all were of great help to a mechanical challenged grandad and a youngster thats hungry to learn.
Buck
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Old 03-28-2004, 02:16 PM
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Default Re: How to port PW80 exhaust?

I think it is very important when teaching someone, whether it be junior of an older one, to not only show them how, but WHY...good job. Tdub
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Old 03-28-2004, 11:51 PM
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Default Re: How to port PW80 exhaust?

I think you are doing the right thing Buck. I found a copy of E Gorr's book, and it is really, really good. I didnt read all of it, but what I saw was right on save a few editing errors. Kids need to read and read lots. Some are motivated to read what the school gives them, and some aren't. By giving him things he can read about subjects he is enthused about, you kill two birds with one stone so to speak. I did similar with my son (now 23). He is confident to take anything apart from a Yamaha to a Piper, and put it back together. He starts every job my opening his manuals before the tool box.
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Old 03-29-2004, 12:06 AM
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Default Re: How to port PW80 exhaust?

Oh,,sounds like a trip back to your friend's machine shop and milling the carb may soon be in order,,,we did one of the PW50's and it shows,,,.060" should be easy. You will have to jet up a little as the vacuum drops on the engine side when you go bigger on the carburetor, so find your main jet size and get a couple of larger ones. Building this a step at a time will show your grandson how to look for performance, and what makes the most difference. Change too much at once and gain or lose you dont know what to blame it on.

FYI Buck, we used to mill our own heads on glass using a store front jewelry case (after hours of course) with emery cloth taped on it. Most of what I told you started out as a means of hopping up a Hodaka Ace 90 circa 1966.

As you get further into this one you may wish to disconnect the oil pump and run premix, if you havent already. If you are still running the pump and want to keep it, you may wish to upgrade oils. A synthetic that works in pumps or premix would be my choice.

If I am not mistaken, Terry Cable used to offer a fork kit for this one and it was cheap. If not look for an old KDX 80 (early 80's vintage or go on ebay) the swap to the front off of it will made a difference. By now your grandson should be running out of suspension.

TRYCE, you got any specs on a pipe for this one?? We cut 1.5 out of the center of the stock one and almost 2 inches out of the header (before we realized we had gone too far) after raising the ports. I wish we still had that particular 80 around.
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Old 03-29-2004, 06:02 AM
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Default Re: How to port PW80 exhaust?

TRYCE, you got any specs on a pipe for this one?? We cut 1.5 out of the center of the stock one and almost 2 inches out of the header (before we realized we had gone too far) after raising the ports. I wish we still had that particular 80 around.

No never messed with the stock pipe. Try www.paxracing.com
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