Ok I have been trying to figure this 250r carb out for way too long. Time to ask someone who would actually know. I am running a 40 over cylinder...a stock head...a 185 main...mixing at 40:1...my needle jet is in the middle...my idle/choke is turned up about 1/8 of an inch...the thing idles perfect. I also just had a complete top end rebuild

Now here is the problem...when I start out if i hit the throttle any harder than 3/4 the engine will cut, in any gear. I originally thought that it was starving for gas so I bumped up the main jet to a 180 then to a 185. It is still doing it. Now I think that it may be getting to much gas. One reason that I think this is because when it cuts out it reminds me of how the engine sounds if you choke a warm engine. I also tried flushing the carb to clean it, but to no avail. I would appreciate any and all advice. I am getting desperate(and getting sick of my friend taking all the holeshots on his 416). Thanks

 

Try raising the needle so it runs richer. My bike does the same thing when it running out of gas or the gas valve is shut off so I think it might be starving for fuel.

 

BEFORE YOU DO ANYTHING ELSE DO A PLUG CHOP!!!!!

Don't go messing with the needle yet!!

If you don't know, I will tell you how, but do one. It sounds as if your main jet is too large, hence, the cutting out at high revs. The main jet will have no effect whatsoever on your idle or your low-end less-than-half throttle. It appears that you're not having a problem there, but only 3/4-full WOT.

If your plug comes out black/oily, go one size smaller on the main jet and check again. Use a fresh plug for each check. Keep going smaller until you get a brown plug. Then stop, you got it.

Oh yeah, the word is spode in case you're wondering![img]i/expressions/face-icon-small-happy.gif[/img]

 

Is it a stock carb?...reeds?...filter ?...air box? &lid ?.
get a bunch plugs,a selection of main jets ..(if ya don't already) that will let you go down as for as 148 or 150 ...(150 stock for 87 I beleive) & do what traperb says
bet it will run good ,close to a stock set-up..

 

From past use of 250r's, we had the jetting at about 155 to 160 on the main. The piolet should be around a 45 or 48. Go back to these numbers and see how it runs and then take a plug reading. Boring the cylinder over should not have any effect on jetting if you are just going 1 or 2 sizes from what you had if it was jetted correct before and you had no porting done. !80 is way to big if it is a stock carb, even with major engine work.

 

DS650DAVE is close, stock main jet for an 87 R is a .152, needle in the middle.

I've seen people run cylinders bored 120 over with no effect on jetting.

Do the plug chop!

I've seen jet sizes on the Rs go way crazy and still work, each of these little beasts has it's own combo that will work. I've seen stockers with no air box, FMF and stock reeds work great with a .175. I've seen 330 kits with 39mm carbs run the same size and both were dialed in. Who knows what will work until you start doing the basics on the tuning.

Plug chopping can take a lot of time and seems like a hassel, well, IT IS! You gotta do it anyway or it'll never run right.

The thing is, once you get it dialed, you're gonna be so happy you did it!

 

Ok I guess I forgot some info then...the reeds are from a CR, i am running without an airbox lid, and the carb is stock.

Now explain how this plug chopping works please. I will do anything to help tune this engine. I am gonna drop to a 160 main and 45 pilot and work up from there. Thanks guys