785 Flat Top Jetting and Carb Settings

J

jonmx477

Location
WA
Oh man this is a funny thread to run into. So I ended buying this ski with "carb problems". I quickly found out it was much more than that. Took it out for a couple of test rides to try and figure out what was up. I would have actually described it as an extreme bog. And a read on the plugs gave the same symptoms. Practically soaking wet. But the first thing I noticed on the plug check was that this was on a Rius Racing girdled head with the stock superjet br8hs plugs, so the plug was about a 1/4" up in the plug hole. Threw some br8es plugs in a noticed a lot better power, but still a massive bog. I could run it down river wide open and it would not even rev out. I would guess 1000+ rpm off peak. It was time to pull the head I figured. The second the head came off it was very obvious what I was dealing with. A very noticeable amount of wash around the pistons. Pulled the cylinders took them into work and mic'd everything out and found out this thing was toast. The more I looked into it the more I was surprised I didnt destroy this thing on the water. Cylinder bores varied .002" between the two and the pistons had collasped and the 85.5mm part number now measured 85.24mm. Giving me .013"-.015" clearance ha! Gave up on the 785 part of this motor. Hopped on ebay found a .75mm bored over 61x cylinder that came with a top end kit and threw it on. Put the domes on and checked squish, had none! Took the 25cc domes into work and starting trimming. Guessed on the squish and ended up with about .04". Checked compression...200psi lol. Trimmed 2 more times and got compression down to 170psi. The big bore was so loose I checked it and got just over 150psi, but now I realized it probably should have been 220+psi...it had 3.75mm bigger pistons and approximently 10cc or more smaller domes, and they were kawi pistons and had decked the cylinder down .17". Just to be clear I have no problem with hjm1, sounds like he didn't know what was going on either, but man I would reconsider how good of friend you have cause he gave you a blow up race motor that would have needed rocket fuel to run. I had a decent idea of what I could have been getting into, and it turned out to be just that. But it's all good now cause it's on the water.

What I found
Untitled by Jon Mounter, on Flickr

First cut on domes
Untitled by Jon Mounter, on Flickr

Back to pump gas
Untitled by Jon Mounter, on Flickr
 
Citizen

Citizen

Location
Coeur D' Alene, ID
Sorry to hear you ended up with a turd, very glad to hear you have the skills to fix it and make it work though. As a rule, i tend to run in the other direction of any flattop motor, especially a used one.
 
J

jonmx477

Location
WA
Yea haha. I work with my dad and had to hear about it everyday about how you should never buy a ski with a modded motor. He's built a few in his day so he knows all about how much can go wrong with them. Lesson learned here, but it was kind of fun to go through it and check everything. The ski has all the basic goodies you would put on it, factory b pipe, blowsion internal filler, braap strap, pole limiting rope, cold fusion steer mount with rrp riser bars, bob adjustable foot holds, girdled head, so it should be a pretty good and reliable set up now.
 
Citizen

Citizen

Location
Coeur D' Alene, ID
Live and learn, I had to learn everything the hard way even when my dad tried to save me the trouble, stubborn bastard that I am lol. Not sure where you are located in WA but quite a few of us ride the spokane river in post falls every weekend. Ski has a nice amount of mods, should be bullet proof with the new motor!
 
You must log in or register to reply here.
Top Bottom