RM250 Loading up, Help!

[psustang89]

Another question about my newly acquired 94 RM250. At full or almost full throttle it loads up and runs/sounds like crap. It sounds like a bike that's not warmed up yet. I did a top end rebuild as soon as I bought it and it's been running like this ever since. I attempted to move the E clip on the needle in the carb up a notch, but it was already at the top. I run 32:1 and I ride woods. I use BR8ES's and it fouls them every hour if I'm lugging around the trails. Air filter is clean. Reeds are good. Is this a carb issue? Jetting? Could it have something to do with the power valve when I did my rebuild? Air Delivery? I'm desperate, please help! :ohmy:

 

[sick 96 250]

yup sounds like your jetting is off

 

[psustang89]

Alright, but how does the jetting suddening become off? Is it typical to have to change jets after a top end rebuild? I know there's a sticky, but any hints for choosing jets?

 

[psustang89]

I wanted to add that I tried running it with the seat off just to get more air through the filter. It seemed to run worse.

 

[psustang89]

Is it normal...

...to have to re-jet after a top end rebuild? I'm being told my jets are off now that it's rebuilt. It's loading up like it's running rich and the carb needle is maxed out on adjustment. If not because of the rebuild, what would cause the jetting to suddenly change?

 

[sick 96 250]

a rebuild can cause you to need a re-jet depending how worn the top end was. Have you tried running it with the choke on after it was warmed up to see if it ran better? If so then you need to richen up the jetting. A good place to start with jetting if on the fmfracing dot come site under the tech area in the jetting specs section. Their specs always seem to be pretty darn close so i would base it off of that and see where you stand. Also if you were running lean you could of did minor damage to the piston and or cylinder.

 

[psustang89]

Sick, I don't think I'm running lean, I'm running rich. The engine is bogging down under full throttle.

 

[sick 96 250]

what is your jetting at now? You also said the needle clip was on the highest clip which is the leanest position in the needle

 

[psustang89]

Correct, the clip is at the leanest point in the needle, so my problem can't be fixed by moving the clip. I'll have to check my current jetting tomorrow and post it.

 

[sick 96 250]

I believe your jetting should be somewhere around this....
Main: 175
Pilot: 48
Needle clip: 2nd slot
Air screw: 1.5 turns out

 

[trial_07]

Are you sure you're too rich and not too poor?

 

[psustang89]

Ha ha ha....you should be a flippin comedian!

 

[endofsilence808]

ive never had a bike need rejeting after rebuild. It could be possible that your valves arent right, ive never raced zukis but thats the first thing i would check. maybe goto stock jets if thats poss. the bike should run ok with that if you really think its the jets. of course i dont trail ride and moto bikes arent really set up to trail ride to well and the needle clip dosent really change the jets that drastic. needle clip spots are more for low end to middle. you said the reeds are ok? how about the gasket for the cage. I never take that apart for a top end.

 

[sick 96 250]

ive never had a bike need rejeting after rebuild. It could be possible that your valves arent right, ive never raced zukis but thats the first thing i would check. maybe goto stock jets if thats poss. the bike should run ok with that if you really think its the jets. of course i dont trail ride and moto bikes arent really set up to trail ride to well and the needle clip dosent really change the jets that drastic. needle clip spots are more for low end to middle. you said the reeds are ok? how about the gasket for the cage. I never take that apart for a top end.

The needle clip is more mid to top I believe. RM's dont have valves like 4strokes do, they have an exhaust valve that opens at a certain RPM but if that wasnt functioning properly the bike would lose all power, dont think it can really effect jetting. The needle clip in my carb made huge change from fouling plugs every hour or two to not changing one plug all day so i would say it does play a decent role

 

[endofsilence808]

dude i think i understand how a 2 stroke works and sounds like you think you do. maybe your bike is hatched. you have not a clue on jetting anyway. i love squids, the only bad thing is they waste my time

 

[endurohero]

You had posted that you have "done a top end" could the piston be in backwards? arrow to the exhuast port side?.Have you checked that the power valves open fully?This can make the bike run like it has a rag in the air box. Struggling to rev free. On the years of rm's 93-95 I have experienced a problem with the needle jet (nozzle) that is part of the carb body and not replaceable separately .This part can wear out over time and cause a rich condition that wont be fixed with a new needle or leaner clip settings the jet accually wears out oval in shape from the needle being draw towards the piston with every intake pulse. A smaller main jet is a band aid solution but there will always be a rich spot from 1/4 -1/2 throttle .I have also seen the cdi boxes that have vibrated through the foam pad on the frame and caused the box to not advance the ignition timing at high rpm (some weird processor problem from vibration) also check your resistance of your plug cap it should be @ 5kohms if not replace it .check the condition of you silencer core if its broken it will cause problems too.Check that you sator pick up coil is within specs aswell.

 

[psustang89]

Piston is in correctly. I have not checked the power valve or my current jetting. It's been 100 degrees the last couple days and I've been stuck at work. I hope to look into it soon and provide an update. To clarify, all electrical systems are fine. The bike "loads up" from 3/4 to full throttle. Runs like a champ until then. I'm going to repack the silencer to eliminate that variable also.

 

[sick 96 250]

dude i think i understand how a 2 stroke works and sounds like you think you do. maybe your bike is hatched. you have not a clue on jetting anyway. i love squids, the only bad thing is they waste my time

Who are you referring to here?

 

[psustang89]

Here we go. I tore into the carb again and found a 182 main and a 52 pilot. I'm assuming that's my problem. I believe stock jetting is a 172 main and I'm not sure about the pilot. Now, should I just return to the stock jetting? Do I change both the main and pilot?

 

[sick 96 250]

Go with the 172 jet and see what happens, if it still loads up a little, drop it another size. I think stock jetting is a little higher than 172 though, I would try a 175 in there first to be safe. From what you say it sounds like your low end is fine, is this correct?

 

[psustang89]

Yep, low end is fine. I was climbing high walls with it 2 weeks ago with no problem. It bogs down on the straight aways. Time to put a call into the shop...

 

[psustang89]

On my way to the shop to pick up the 175 Main...

 

[psustang89]

I ended up getting a 178. They didn't have any 175's and the mechanic said the 178 should clean it up. We shall see...

 

[sick 96 250]

yeah if it loads up still though try to drop lower, almost all cycle shops should have the sizes you need since a lot of carbs use the same jets and stuff

 

[psustang89]

The 178 didn't seem to help much, of course that observation was made by just reving it in my driveway. I hope to get it out this weekend and put it through the paces before making any decisions. Even if it still boggs, I would expect a big improvement in dropping 2 jet sizes!?!?