I got everything wrapped up about 12 minutes before it started pouring here. The first rain in 5 weeks, thank God it waited for today[img]i/expressions/face-icon-small-mad.gif[/img] I wasn't sure which jet to run since I still have the stock carb and the 200 jet I ordered won't be in until tomorrow. I tried to drill a spare jet I had out and it didn't work too good. I must've opened it up too much because it was running pig rich at full throttle.

I went back to my 190 jet and kept the clip at the bottom position, which was good enough for a few minutes of running. The difference is obvious from the midrange on up to the freakin stock rev limiter. It now hits the chip much quicker and will defintely have to be my next mod. I really cant believe how much more midrange it has and no loss of bottom end. When the 200 jet comes in tomorrow it should help out as the plug looks a bit white right now. I might even try to open up the 200 a wee bit, if I can find a right sized drill bit.

I used a dremel and a carbide bit. Usually I get out the die grinder out for cast iron heads but since this was aluminum and there wasn't a lot of cutting to be done the dremel worked great. Here is what I found needed work on the head.: The intake port is very good out of the box. Very little work neede to be done here as the design and cast job is very well thought out. I did match the ports to the intake because of a slight mismatch when the intake is bolted down to the head. The short side radius did need a slight bit of smoothing but not much at all. I left most of the port untouched and even the areas I worked were left rough to help keep the mixture atomized. The biggest help on the intake side had to come from the lip on the chamber side where the valve seat had been cut. Smoothing this out took should help flow into the cylinder.

The exhaust needed a lot more help than the intake. The short side radius had a very sharp edge in it from the valve seat that was left jutting into the port. I gently transitioned it into the port and then went to work on the valve guide boss. After I removed a bit of material around the valve guide boss I went ahead and smoothed the rest of the exhaust port to a mirrored shine to try and keep the carbon from sticking to the walls.

The whole process took quite a few hours because it was my first Rotax head I worked on and I wanted to do it right. It was really more of a cleanup job than a full race port because not much material was removed and it can now retain good velocity at low rpms to help keep all that low end there. I am very happy with the results. I will try to get the quad to Norwalk this coming weekend to see what it will run in the 1/8. The stock CDI(chip) will hurt me but I'd like to see what close to $200 worth of mods can do first. The endcap that I modified myself and a UNI filter are my only other mods (so far)

 

Sweet Rockey! Can't wait to see what the drag difference is.
On jet drilling - get a set of wire gauge drill bits, they are numbered 1-60 with the smallest of them in increments of .001", most averaging around .002 or .003 increments. A #60 is .040" in diameter - these guys are tiny!

 

Oh, and by the way, that's some really detailed info there Rockey. Thanks for sharing. I plan on porting this winter.

 

Any idea where I can pick up a set of drill bits like that? I tried Craftsman and no dice there.

A 200 mikuni is about .080". I would like to step it up in .002" increments

 

Try Machinist tool supply co. that is where I got mine. If you can,t find their # pm me and I will get it for you.

 

Rockey,
do you have any info on how your new ported head works? Did you shave your head while you had it off?


Biggerisbetter.

 

<< Rockey,
do you have any info on how your new ported head works? Did you shave your head while you had it off?


Biggerisbetter. >>



I got it running even better yesterday with a 200 jet. The spark plug is grayish in color which is about right, but I will need to jet up when the weather cools off. It feels absoulutely great! The midrange and top end have made substantial gains. I am going to take it to the track tomorrow evening to see exactly what kind of numbers it can put up because SOTP dyno's are hard to prove. All the work I did to the head was listed above in my original post. I didn't want to shave the head since it is a DOHC design and this would change the timing.

 

Glad to hear your proggress! I have been talking to DSmike about head porting and he makes it sound real easy, And I think I could handle doing the &quot;cleanup&quot; like you did. You mentioned that the reason that you didn't shave your head was the timing. would a timing key make up the difference on say 20 thousands? I know that DSmike has shaved his head(along with port work)and has his DS SCREAMING!!!


Biggerisbetter.

 

.020&quot; probably wouldn't affect the timing much at all. It also would be a negligable gain in hp. A piston change would be the best way to increase compression.

I wish I had some pics for you to look at and see, but unfortuantely the pics I took turned out like crap. If you decide to do it yourself and get stuck anywhere just ask for help.