Can't get jetting corrected

[sick 96 250]

I have 96 RM250 with boyesen reeds and cage and a fmf fatty pipe. I haven't been able to ride much lately due to school but when i took it out last it ran bad. It was really hard to kick over but eventually it would fire up. If i would try to go from idle to wide open the bike bogs down then catches back up with the gas. It was running a 45 pilot and a 168 main with the clip in the second slot on the needle. I changed the pilot to a 55 and the main to a 175 and the clip back to the 3rd slot. The bike fires up a lot easier now but still having the same throttle response when i try to get on it. The plug doesn't look to bad, actually looks the right color now. I cleaned the air filter but the problem still persisted so I have a new one on the way just in case. Any other tips on how to straighten this out would be sweet. The temp in the summer is 80-90 degrees with pretty high humidity and i ride at sea level.
Thank You

 

[biglou]

55 pilot is probably way too big! I'd suggest going to a 42 or even a 40 if it is very hot where you are. Clip in the 2nd or 3rd slot from the top is a good starting poing as well.

Set the choke, start it, after you take the choke off and let it warm up, adjust the air screw for the highest idle speed. You'll hear it start to blubber, then go the other way until it does it again, set it in the middle of those two extremes and then take her for a spin and see how she responds.

 

[sick 96 250]

since i have been messing with the jetting the lower the pilot the harder it gets to start no matter what clip position, wouldn't a 42 or 40 lean it out way to much. When i had the 45 in the bike was running rough and sometime started to overheat. Only with the air screw all the way in and the idle way down would the throttle respond correctly but soon as the gas was let off it would die. If i should go a 42 or 40 what mix should i run? 40:1 or 32:1?

 

[ScottS]

I think when you said that you have not ridden much lately that mey be a clue- the jetting didn't change while it was parked, so if it ran good with that jetting in the past you should not have to be changing things much - if it is running lean and hot even though big lou thinks the pilot is already too big then it sounds like some passages in the carb are plugged - maybe a thorough cleaning is in order as if it has been sitting you may have varnished something up.

 

[TWRT]

How about air leaks? We had a older bike that needed constant jetting changes (and needing rich jetting). After getting new crank seals, we had to lean the bike way back to get it to run right. Plugged up carb is a thought also.

 

[sick 96 250]

when i said haven't ridden it much I mean since i got back from school, i had the at school with me and thats when i put the fmf pipe and boyesen stuff on it. I cleaned the carb several times to make sure nothing was stuck in it because its when i got home it started acting up. A clogged carb was my first guess also but it ran great when the air screw was turned all the way in and the idle was down, just when the throttle was closed it would stall very quick. Other than it not responding from a closed throttle to wide open the bike runs strong and has a lot of power. I'll take a look at the seals also, i was thinking about that earlier but never got the chance to look. Was it the crankshaft oil seals or different seals? Thanks for the advise, any other ideas are more than welcome

 

[RM 2 fif T]

anyone have a 96 rm250

anyone have a 96 rm250 jetted correctly with an aftermarket pipe and reeds that could help me out. I can get it to dial in. I ride at sea level and currentll have a 168 main, 52 pilot, and needle on the 3rd clip. The bike has a problem going from closed throttle to wide open, it bogs then the rpms catch up and its good. Is it possible to be the exhaust valve or possibly a crank seal? When i first bought the bike i was at school and it had a 45 pilot, 169 main and needle on the second clip but i have no clue what mix the guy was running before. With jetting that lean would it of been 50:1 or somewhere in that area? Someone please help me :bang:

 

[TWRT]

The crank seal on the right(sitting on the bike) is the oil side seal. The one on the left is the air side seal. If replacing one, I would do both. A bad oil side seal will tend to make the bike run rich. A bad air side seal will tend to make it run lean. Do a search and look for air leak testing and seal replacement, things like that.

 

[CaptainObvious]

When a two-stroke becomes hard to start, and the jetting suddenly seems wrong, it's a good sign that you are in need of a top end. Have you done a compression test?

 

[sick 96 250]

does anyone have any type of answer for this????

 

[sick 96 250]

The top end is farely new with minimal hours on it i think. I bought the bike out at school and it ran very strong low and top end. The thing was i never new the mix the guy was running before me so i think that may be the factor. When i started thinking of it the only time the bike ran real good is when I bought the bike and it still had a full take from the previous owner so i emptied the tank last night of my 32:1 mix and i am going to go for a 40:1 or 50:1 mix with the original jetting from when i bought the bike.
45 pilot
168 main
2nd clip on needle
With these setting the bike ran crappy after i put the 32:1 mix in it. The way it ran good was if the air screw was all the way in and the idle was down.

Thanks for all the help so far, keep em coming guys

hopefully this works with the new mix but i will still check the seals

The bike starts on the first or second kick with a 55 pilot and a 172 main with 3rd clip but still has the throttle response problem no matter what i try so that i why i am going to try my old settings from when i bought it with a different mix

 

[ScottS]

More oil (32:1) than less oil (50:1) will lean the bike out because the oil replaces gas. The volume of air stays the same at a given RPM so you are leaner-

It is possible the gas was not mixed right ?

I am not sure if the difference between 32:1 and 50:1 would cause your problem, but if you mixed it incorrectly it could be a problem. Easy enough to verify-

The crank seals leaking may be the issue- most seals leak when the crank starts to go- sometimes the crank will be going bad, if you put new seals in it will run OK (usually long enough to sell it) then they begin to leak beause the crank is moving around too much.
If your mixing wasn;t the problem you should either get the tools to do a leak down test or take it somewhere where they will doa good leakdown test - otherwise trying to fix a leaky engine is a waste of time

If you to determine that the crank seals are the culprit verify the crank play is in specification before you replace the seals.

The oil side seal would make the bike smoke like crazy- I think you would notice that, but the dry side is harder to diagnose

When the crank seal leaks it allows the engine to suck air in around the crank- when it does this, not only is teh air unfiltered it is entering the engine after the carb, so it is leaning the mixture out- sometimes the seals will seal at idel but of you rev the bike up or put it under a load it starts to suck air.

Make sure also it is lot leaking around the reeds. You mentioned a Boyeson reed cage, maybe it;s not installed right or is not sealed properly

 

[sick 96 250]

I'm possitive the mix was done correctly because I first mixed a tank in my gas can then when it responded with the throttle like i was saying i used my friends mix who had just filled the can with gas and measured out the oil to mix. I checked the reeds and they looked fine, almost new, but how do they need to sit on the cage? flat? When i looked at them the one side was completely flat and the other was up a very little. Why would the bike run great when i had the 45 pilot and 168 main in with the clip on 2nd notch when the air screw was turned all the way in? or if the air screw was set at around 2 turns out and the choke on it had perfect response. Any ideas of how much i should go up on the jets from this point? This is the main reason i feel it is the jetting along with the ratio of gas. How hard is it to check the seals, i'm pretty handy with taking things apart such as this but never had to before. Jetting was always my problem for some reason. Thank you for the advise so far, hopefully i am getting closer to the problem.

Oh and the bike has a tendensy to smoke when i whip the throttle and it bogs then catches up, a nice cloud comes out then is goes to normal if this helps any

 

[dirt bike dave]

I checked the reeds and they looked fine, almost new, but how do they need to sit on the cage? flat? When i looked at them the one side was completely flat and the other was up a very little.

The reeds should seal flat against the cage. A reed that is slightly warped can cause extreme difficulty in cold starting. You might want to flip that reed over to see if it lies flat - if not, replace it.

If the reed is warped, turning the airscrew in or richenging the pilot jet may have been a 'bandaid' that worked temporarily.

Also, I have heard that some of the mid '90s RM250s had problems with the carb bodies. Apparently, over years of use and vibration, microscopic cracks can appear between the float bowl and the venturi. I have talked to one guy that had this happen and heard of one other, and in both cases the only cure was to replace the carb. In your case, I would focus on the reeds first, and hope that solves the problem.

 

[sick 96 250]

I heard there were a lot of problems with the 96 carb because of the idle adjuster being the choke and it was hard to set correctly. I'll check the reed tomorrow but anyone know if other carbs match up for this bike, i know someone who has a PWK carb from a 96 kx 250 and someone who has a PWK from a 99 RM 125, anyone know if these are all the same carbs or not or if i can put it on my bike? Thanx for the help so far

 

[TWRT]

Do you think the previous own had race gas in it? Doesn't race gas use different jetting than pump? Just wondering, since you said it ran good until different gas was put in.

 

[sick 96 250]

that was a possibility i thought of but the bike doesn't have a lot of race stuff on it so even when i put pump gas in i changed the jetting and still had the same problem, i re did the top end a few days ago and came across a problem in which i was careless and got coolant in the crank so I have to get it out today then i will post if i still have the same problems.

 

[sick 96 250]

everything fixed, new top end was needed it seems

 

[reelrazor]

does anyone have any type of answer for this????

You have gotten a few. It is my belief that you have an air leak of some kind, possibly a crank seal, but also possible that the base gasket and/or intake gaskets/boot are bad. You could go to the trouble to pressure test it, or you could remove the ign. side cover, start it and wave a propane torch around(unlit but with the gas on) suspect areas(including under the flywheel). If the run condition changes when the torch is near anything, you have found your leak.

Also RV6 is right, when compression is falling off they tend to get hinky and inconsistent. Just because the top end is 'fairly new' doesn't mean everything is good.

Your 32:1 mix may well have leaned out the fuel supply(more oil in the fuel taking up volume in the jets). Let's hear what a modern mix ratio does for you. The original jetting should at least let the bike run. Work from there and make ONE change at a time.

If you have any doubt about your reeds seating, flip them over.

 

[sick 96 250]

i did flip the reeds but there was a little gap still so i was able to get new carbon fiber reeds from boyesen and the bike is running great, i went back to stock jetting then dropped a few size on the main and on the pilot and the bike hits hard through everything and doesn't give me a smoke trail anymore. I upped the mix from 32:1 to 40:1 using mobile MX2T and it seems cleaner. I feel everything is good but i will do a pressure check also, thanx for all the help