Having problems jetting my 250R correctly.

[Blown 331]

I know there are tons of threads and stickys on this but I'm having a weird problem. I've mostly jetted 4 strokes which seem easier to me unless thats just what I'm used to. And 4 strokes seem a little more forgiving if you are off, or maybe thats just me.
Anyway I've got an 85 250R running just one layer of head gasket, fresh wiseco, boysen rad valve, ESR pipe and 36mm flat slide. Running 32 to 1 Honda synthetic premix with 93 octane. Air filter is clean.
I started out with a 175 main with air box lid off. This was obviously rich, it seemed to cut out or jerk up top, similar to choke being on. So then I dropped down to a 170 main. All the rest of my main jets have a star on them but the one says 170RD, not sure what that means or if it matters. Anyway it seemed a bit better. But was still kinda jerky around 3/4 throttle and up. So then I put the air box lid on. Normally this should richen it up but it seemed to run better which was opposite of what I was thinking should happen. I thought I was still rich up top but richening it more with the air box lid made it run better? But I know the 175 main isn't the answer. Thoughts?

[edog]

As far as I know on the jets. There tolerances are different on manufactures.

[Blown 331]

As far as I know on the jets. There tolerances are different on manufactures.

So you are thinking because most of my jets have a star on them and the on in there now says 170RD that could be throwing me off?

[Daddio]

That is a definite possibility. A 170 jet sounds about right though. If you are going to be running the airbox lid on jet it with it on.

[edog]

So you are thinking because most of my jets have a star on them and the on in there now says 170RD that could be throwing me off?

It depends on the size difference in the jets. A 170 In a the star...I think thats Keihin and the 170D uknown to me.

If you look at them do the wholes in them look bigger than the other one?

[edog]

That is a definite possibility. A 170 jet sounds about right though. If you are going to be running the airbox lid on jet it with it on.

That's how I jetted my R.

I also richened it up a little on the needle.

[Blown 331]

That is a definite possibility. A 170 jet sounds about right though. If you are going to be running the airbox lid on jet it with it on.

I want to run it without the lid for more power and I keep this bike out of wet conditions anyway. But aside from the possiblity of me using 2 different types of jets wouldnt it mean that adding the lid (richening) to the 170 and running it better mean that I'm lean with the lid off? That doesn't sound right, I'm confused.

[Dammit!]

That star is actually a K if I remember right. Been a while since I looked at them. The RD is just a different brand and I wouldn't be concerned about using them. The tolerances might be off a tad but when you find the right one it won't matter who made it.

Start way too big then go backwards. If it ran better with the lid on, take it back off and throw a 190 in there. It should be obviously too big. Then try 185, 180 and if it's starting to show improvement use smaller steps like 178, 175, 172 until you find the right one. Remember, main jet is WOT. Ignore how it runs below that until it's running clean at WOT. After you get that down, work on the needle clip (and taper if you need to) then adjust the air screw.

Also worth noting, 93 octane and a single layer gasket is not a good combo. Personally I think 93 is borderline on a bone stock R. You might just be experiencing a detonation problem. Get some 100 or 110 fuel and see what happens.

[Blown 331]

That star is actually a K if I remember right. Been a while since I looked at them. The RD is just a different brand and I wouldn't be concerned about using them. The tolerances might be off a tad but when you find the right one it won't matter who made it.

Start way too big then go backwards. If it ran better with the lid on, take it back off and throw a 190 in there. It should be obviously too big. Then try 185, 180 and if it's starting to show improvement use smaller steps like 178, 175, 172 until you find the right one. Remember, main jet is WOT. Ignore how it runs below that until it's running clean at WOT. After you get that down, work on the needle clip (and taper if you need to) then adjust the air screw.

Also worth noting, 93 octane and a single layer gasket is not a good combo. Personally I think 93 is borderline on a bone stock R. You might just be experiencing a detonation problem. Get some 100 or 110 fuel and see what happens.

Thanks, and big thanks on the octane recommendation. I thought I might have heard a bit of detonation but didn't think I was anywhere near enough compression for that. Stock is around 8 to 1, I think and 10 to 1 should be ok on 93 octane. Of course I'm basing this on 4 stroke experience again.

[Dammit!]

Throw the 4-stroke stuff out the window.

[Blown 331]

Throw the 4-stroke stuff out the window.

That's what I figured, well I'm totally lost then. lol.

[oscarmayer]

don't forget about the needle heigth adjustment. stick i beleive is on #3 bot if you move it higher it is leaner. if your rich, go to the 2nd from the top and see what happens.

top end could be lean or rich but i imagine it's lean. put a fresh plug in , drop in a 175 jet and set the needle to #2 clip like i said. now start and ride it (with air box lid on) and sing it a few times and come back and pull the plug. look at what it's saying. the coloring will help you determine what's going on.

if it's black, your rich, if it's just plain white or even powerdy, then it's too lean, if there's a nice carmel coloring, it's just about perfect. from there you also have ignition that could be causing an issue.

[Blown 331]

That star is actually a K if I remember right. Been a while since I looked at them. The RD is just a different brand and I wouldn't be concerned about using them. The tolerances might be off a tad but when you find the right one it won't matter who made it.

Start way too big then go backwards. If it ran better with the lid on, take it back off and throw a 190 in there. It should be obviously too big. Then try 185, 180 and if it's starting to show improvement use smaller steps like 178, 175, 172 until you find the right one. Remember, main jet is WOT. Ignore how it runs below that until it's running clean at WOT. After you get that down, work on the needle clip (and taper if you need to) then adjust the air screw.

Also worth noting, 93 octane and a single layer gasket is not a good combo. Personally I think 93 is borderline on a bone stock R. You might just be experiencing a detonation problem. Get some 100 or 110 fuel and see what happens.


Quoting this post again. lol. I haven't got the 110 octain in there yet (scary) but I did pull that 170 out and went up to a 180 and it ran great. Still not quite right up top but for sure better than the 170 or 175 and I still have the air box lid on. I just bought a jet kit on ebay. Genuine Keihin jets too. For $18.60 shipped I got a 182, 185, 190, 195 and 200. Those seem WAY too big but that's what it's taking, I don't get it. I started out with a 175 as my base thinking I was starting way too big but turn out it was still small. By the time I take the air box lid off I'll probably end up with a 195 or so. Anyone heard of using a jet that big? Seems weird.

[rdlsz24]

You have to factor in elevation and temp too so maybe the larger jet is good for IL this time of year. How have your temps been in Waterloo? We've been hitting 20's overnight here. I see you are at about 700 feet.

Rob

[Blown 331]

You have to factor in elevation and temp too so maybe the larger jet is good for IL this time of year. How have your temps been in Waterloo? We've been hitting 20's overnight here. I see you are at about 700 feet.

Rob

I'm down by St. Louis. Actually I'm at work in St. Louis right now and my thermometer said 22 yesterday morning. We are getting heavy frost. It was raining this morning and above freezing, I think it was like 38. Supposed to be 60 on Thursday.

[The Goat]

jetting between two identical bikes can be ridiculously different.

I know nothing about 2 stroke, but I do know that my jetting for my 200x is GREATLY different than anyone else on the boards. I'm running a main 25 sizes larger than anyone else with a similar carb from what I've heard.

[Blown 331]

jetting between two identical bikes can be ridiculously different.

I know nothing about 2 stroke, but I do know that my jetting for my 200x is GREATLY different than anyone else on the boards. I'm running a main 25 sizes larger than anyone else with a similar carb from what I've heard.

Well I guess what I have going on does make a little sense then. But I've never heard of a 250R taking a 195 main. wow.

[350Kris]

You could probably keep your 175 jet and install a dial-a-jet...just another option.

[The Goat]

well I'd bet you're detonating.

correct me if I'm wrong guys, but I remember seeing something that two piece base gasket meant 100+ octane...and one piece meant 110+

having said that though....I had a 200x engine with over 185psi of compression, and she ran fine on 87.

[88 Turbo Coupe]

Does your gas staion use 93 with ethanol? Buy a couple of plugs an do a plug chop and stop waisting your time.

[Blown 331]

Does your gas staion use 93 with ethanol? Buy a couple of plugs an do a plug chop and stop waistig your time.

Yes it has up to 10% ethanol. And my thoughts on the plug chop are this. I'm running so lean that its not running correctly when I hit WOT or get close so I sure don't want to do a WOT blast down the road if I'm that lean.

[88 Turbo Coupe]

Well.... you don't do a WOT when you do a plug chop. So whats the problem?

[88 Turbo Coupe]

Btw........ Ethanol is GARBAGE

[Blown 331]

Well.... you don't do a WOT when you do a plug chop. So whats the problem?

So tell me how doing a plug chop to adjust your main jet is going to work if you are not at WOT?


Btw........ Ethanol is GARBAGE

I buy most of my gas in Missouri cause it's cheaper but weather I get it in Missouri or Illinois it is all up to 10% ethanol, not much I can do about that. I know it's not ideal but no one really has problems with it. I can get leaded 110 octane that has no ethanol.

[x.system]

Well I guess what I have going on does make a little sense then. But I've never heard of a 250R taking a 195 main. wow.

My tt bike takes a 220/225 main in the winter months, 175 to 185 in the summer heat but every R motor is different. I would recomend not using those aftermarket jets, I've had a few break off. Be careful with detonation also, it doesn't take much to toast a piston.