96 RM 250 Jetting Issues

[boscoholic]

In need of help. I have a stock 96 RM 250 and I typically run 100 octane race gas with a 52:1 Spectro oil mix. I ran out of race fuel so I put some super unleaded (91 octane) in with a 52:1 mix. The bike hated it! Fired up, ran for about 3 seconds and died. It was fouling the plug left and right. I cleaned the plug and it fired up and died again (this went on several times). I pulled the carb and reeds to make sure everything was in order. The main jet was a 165 and the pilot was 52. It was recommended I run a 175 main and 55 pilot, so I swapped them out and changed the plug with a BR8EG. The bike fired up and ran, but it smoked like a chimney and eventually fouled the plug again. I drained the fuel tank, put the old jets back in, cleaned my stock plug and filled the bike with 100 octane race gas (52:1) and viola, it seems to run fine (although there is some knocking going on occasionally - sounds like someone inside the engine with a hammer trying to get out). I don't want to blow anything up, but am confused with the jetting. It seems the bike runs good with the lean jet, but is it too lean? I have a Pro Circuit works pipe on the way and they are saying to use a 175 main and 55 pilot when I put it on, but after today I think I might stick with what's in it now. Any advice is appreciated.

 

[whenfoxforks-ruled]

What is your compression ratio?Leave the 52 pilot and put the 175 main in and check the needle position.52:1,what the heck is that?

 

[boscoholic]

Not sure what the compression ratio is. As far as I know everything is stock (not bored). Also trying to find out when the last top end was done (I bought it two weeks ago). Needle clip is in position 3. 52:1 is what Golden Spectro calls a 12 ounce bottle mixed with 5 gallons of fuel. I talked to a bike shop about it (owner used to race a 96 RM250) and he concurred that is ok for the bike. I took it out again and it ran great, but I pulled the plug and there carbon build up (not the light tan it's suppoed to be). Looks a little rich still (and I haven't swapped back to the 175 main yet). Also, what is teh stock needle for this bike? Suzuki lists about 10 different ones - at least mine is on the list R1467NS.

 

[whenfoxforks-ruled]

You need the book,it will explain everything! The needle you have is the smallest number of like 8 different styles and sizes.

 

[boscoholic]

I got the book ordered. I looked through another book I have for my KX 125 (Clymer) so at least I would gain a little knowledge of how the jetting works. While specifics will vary from bike to bike the principle is basically the same. However, even teh Clymer book doesn't say much about needles (different sizes). It basically just says move the clip up to richen the mixture and down to lean it. I'm just trying to get a good neutral starting point and move from there so I know what's being done as I do it rather than try to figure out what the previous owners have done and why.