need some info on a Jr. Magoo's motor

[addicted]

Sorry guys, but I know this is where to find Paul.

I bought a 99 GP1200 from a guy on pwct called njstxr. I can pm you his name if that helps.

It's a 1mm over 65U with a R&D head and it was ported by Jr. Magoo's. He told me that he had to run a mix of super and av gas in it. I want to keep it pump gas only.

Could you tell me if I can get away with just cutting the domes to drop the compression, or does the porting require race gas? The seller wasn't too technical and said that's what you told him to do, but didn't remember why.

Here's a few pics. I can get measurements and pics of whatever you need. I have to tear it down anyway because it blew out the rear seals:bigeyes: Oh yeah, I've never seen rear seals blow before, or even have the lip and spring totally removed. Any idea what would cause that?

Thanks,
Mike

 

[CoreyLKN]

As far as i know compression has alot more to do with what gas you need to run then porting. Do you know what the compression is on it? I dont know if you can cut the doems to lower compression, i always thought that it raised it. You could just run an aftermarket head too.

 

[addicted]

He said it was pushing about 160- that's alot for a tripple. It was partially disassembled, because he was going to part it out, so I can't check the compression yet. If needed I'd cut the domes to make them larger so the cc's go up. . . or just buy new domes.

 

[FLY6584]

As far as i know compression has alot more to do with what gas you need to run then porting. Do you know what the compression is on it? I dont know if you can cut the doems to lower compression, i always thought that it raised it. You could just run an aftermarket head too.

Porting definitely affects what gas you have to run. I'm not sure exactly why it affects it, but I do know that I am able to run 93 octane with the 35cc domes (185psi) that are in my stock 701, but once I have porting done I won't be able to run 93 with those same domes anymore.

 

[addicted]

That's how I understand it too. Porting opens up a whole other can of worms.

 

[feartheride]

hydro lock could blow seals but never seen it happen

 

[CoreyLKN]

Porting definitely affects what gas you have to run. I'm not sure exactly why it affects it, but I do know that I am able to run 93 octane with the 35cc domes (185psi) that are in my stock 701, but once I have porting done I won't be able to run 93 with those same domes anymore.

Hmm, never heard that before. Guess i'm gonna have to rethink the setup i was gonna run.

 

[addicted]

hydro lock could blow seals but never seen it happen

Yeah, I've heard that and a bad backfire, but the spring and the part of the seal tha the spring sits on, on both seals is gone. I actually found some of it in the bottom of the hull. What's amazing is that the motor isn't blown:shock:

 

[Jr.]

Hi Mike, Yes, I know the motor well. It was owned by a guy named Mike. He was a pretty hard core surf rider for a runabout guy.

If you like, call me tomorrow & I'll tell you all you need to know about you motor. I have the spec sheet from when it was built.

ski ya, Paul

 

[addicted]

Awesome! Thank you.

 

[keefer]

You can't beat that for customer service. 42 minutes from first post till you get a reply from the man himself. Not to mention its after hours. :hail:

 

[Boris]

You can't beat that for customer service. 42 minutes from first post till you get a reply from the man himself. Not to mention its after hours. :hail:

Not only that but the man has a record of the specs.:hail:

 

[keefer]

Documentation of any system is a pain and requires extra time, but it pays dividends down the road. I learned this a long time ago in the information technology field. It has saved my butt and saved me from reinventing the wheel over and over again. Not to mention the old noodle dont retain like it used too.:biggthumpup:

 

[Big Kahuna]

Porting definitely affects what gas you have to run. I'm not sure exactly why it affects it, but I do know that I am able to run 93 octane with the 35cc domes (185psi) that are in my stock 701, but once I have porting done I won't be able to run 93 with those same domes anymore.

Why not????? I am running 35cc domes on my TLR Ported cylinder, have been for years.

 

[Mile9c1]

160psi on 93 octane seems reasonable.

But to answer the only question we can really answer w/o knowing your engine specs, yes, lowering the compression will lower the octane requirement. In every case. But of course you won't make as much power with lower compression :Banane01:

 

[SuperJETT]

160psi cranking compression on a triple is WAY more running compression than 160psi on a twin.

 

[jeepmark4x4]

160psi cranking compression on a triple is WAY more running compression than 160psi on a twin.

Why would the dynamic pressure be more than static just on a triple? I'm just wondering why 160psi is high for a triple and not a twin.

 

[SuperJETT]

The way I understand it, because the exhaust pulses are only 120 degrees apart, they combine slightly and it increases your dynamic compression. Running triple pipes eliminates that.

I could be wrong, maybe the guys on greenhulk.net could answer better.

 

[Idok]

Porting definitely affects what gas you have to run. I'm not sure exactly why it affects it, but I do know that I am able to run 93 octane with the 35cc domes (185psi) that are in my stock 701, but once I have porting done I won't be able to run 93 with those same domes anymore.

why not?

35cc's with stock porting shuould produce 180 plus or minus 5

Paul has rec'd me to run 33cc's with his porting to retain that same compression.....




if you run 35's with your ported cyl you'll push about 165....that exactly what I have in my current boat and I think its perfect! not to much and not too little!








oh, and the stock compression on a 65U is 120-125ish.....FWIW

 

[FLY6584]

why not?

35cc's with stock porting shuould produce 180 plus or minus 5

Paul has rec'd me to run 33cc's with his porting to retain that same compression.....




if you run 35's with your ported cyl you'll push about 165....that exactly what I have in my current boat and I think its perfect! not to much and not too little!








oh, and the stock compression on a 65U is 120-125ish.....FWIW

I was just told by a few people on the boards that I would be ok for now with using 93 with my 35cc domes, but once I had the motor ported I would either need to run higher octane or run smaller domes.

Maybe I misuderstood them. :dunno: