TRX250R.ORG
Workshop => Carburetor, Intake, and Exhaust => Topic started by: pinned250r on July 04, 2013, 09:53:35 AM
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Last year i rode Morse250r's stock cylinder with an RB racing drag port on it, insane. So i went ahead and had it done to my cylinder, We have the exact same set up(40.5, trx5 cm, esr elim kit, same plug, pilot, main, needle, and clip position, and mine has no bottom end. Lost alot of rideability. It boggs/cuts out hard 1/2-WOT, We decided its just too rich, agreed? Thinking of going up on my needle clip and down on the pilot. Any input/reinforcement?
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I did forget, Johann has the cr ignition, im just running oem, but RB said it shouldnt make a huge difference, it didnt on the dyno.
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are you gapping the spark plug tight?
not all motors are the same some times its the carbs sometimes its just different.
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When you say it bogs and cuts out hard, is it a smooth bog or blubbery and smokey?
Need to figure out if its a lean or rich bog......
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Definitely a blubbery bog, I think it's just getting too much fuel in the top, and I will definitely make sure to gap the next plug right.
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Definitely gap the plug at .018. Then work on the jetting. You should be able to tell if its rich at wot by reading the plug. What size main are you running now? Move the main a couple sizes and see if it gets better or worse.
A lean bog will almost feel like the motors cutting out. Rich will bluber and smoke a bunch.
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Right, i dont think its the main thats the issue, plug is right where it needs to be at a WOT run, its the half throttle to 3/4 that blubbers out on me, I went 4 turns out on the air screw(supposedly its equivalent to 1 size down on the pilot) and it helped a little, I am running a 52 pilot, think im gonna drop a 48 in it.
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And go up a clip position.
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Adjust your air screw for the highest idle and then turn it in a quarter turn or so. If you are out over 2.5-3 turns put in a smaller pilot. If you are out less than 1.5 or so you need a bigger pilot. Make sure the motor is warmed up good when doing this. What does a plug chop look like? Once you get the pilot close you can work on the needle/main.
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sounds like a float height issue. fearlessfred has a trick to adjusting the floats without completely removing the carb. hopefully he will help.
john
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I didnt even think about float height, I have been meaning to adjust that anyways due to a little fuel leaking after shut down.
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I didnt even think about float height, I have been meaning to adjust that anyways due to a little fuel leaking after shut down.
That could very well be your smoking gun! Too much fuel in the bowl will certainly throw your jetting off.....
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What needle are you running? Diameter such as going from D"" to C"" series will lean out 1/2 to 3/4 throttle. I'd check float level though that could be prob. What slide cut away you using also? All this I'm talking about is related to a keihin though.
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seemed to me when i rode it that it was fat 0-1/2 throttle it wouldnt build any power i was constently shifting to keep the thing in the power to get me around.
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Two port jobs are never they same, so it each one will need a little tweaking here and there.
Did they just run it on the dyno to get power figures or did they do in initial tuning on it. Should be pretty easy to get it on there and see what the a/f looks like.
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If fuel is coming out of the overflow,it could be causing your problems.the fuel level ,when correct is even with the seam ,if it is to low it would cause poor throttle responce (not what your describing),to high to were its coming out the overflow that would cause what your describing.I think the diff. in the ign. would have an effect ,but I don't believe that is bigger problem
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It is possible it could be the difference between the two ignitions. Maybe try an counterbalance holder that is adjustable where you can add or take away a little timing and see how it feels.
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Well upon inspection I had a Rees chip, I picked up some vf2s and installed today. throttle response is better, but didn't get a chance to ride it. Going out tomorrow and bringing all jets along. I will keep y'all updated. Thanks for the variety of answers!
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All great advice given previously, I would still first adjust the float level if its wanting to spill a little fuel, before you do any jetting changes or even leave the house, then go after the plug gap then needle and maybe air screw to fine tune the lower bottom end range of throttle pull.
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What intake setup is on his bike and what is on yours??
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Sounds great. I will follow instruction Dave.
I have vf2 reeds, 40.5 kehin, and esr airbox elim kit.
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Mine has a upp intake v force3 reeds esr eliminator kit
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ok my idea is out then
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played with the float, all set there, went down from a 150 to a 145 pilot, really cleaned up the low end, now it cuts out on the top, like a lean cut. It never did this before, possible i need to go up a size on the main then? maybe down a needle clip rather?
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What about an air leak?
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Update. Today I went down a clip on the dgh needle(rich) and i couldn't get it to cut on the top end, so that's a bonus, but it's still a little doggy on the bottom end, just not as responsive at johanns, very well could be the cr ignition I think :/ I took the airscrew out another 4 turns for a total of 5.5 turns out(4 turns=1 size lower pilot) and it didn't make as big a difference as going from the 48 to 45. Any other suggestions to help on the bottom End?
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I'm slightly confused. 148 and 145 are main jet sizes. Pilots for that carb would two digit numbers like a 48 or 52. And you should be no more than 2.5 turns out on the air screw.
Start bike and let it warm up. Then turn the air screw in all the way. This will richer the pilot circuit and may cause the bike to stall. Start turning the air screw out quarter turn at a time until you get the highest idle. At a point the idle wont go up anymore. (Make sure you give the motor some time to react to your change) Then turn it back in a quarter turn. If you are more than 2.5 turns out on the screw you need a smaller pilot. If you are less than 1.5 you need a larger pilot.
Start with the clip on the second groove from the top of the needle.
Put at very minimum a 160 main in it as I'm pretty sure a 145 is way to lean.
.018 spark plug gag is key also as stated before.
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This may explain it better than I can.
http://www.duncanracing.com/TechCenter/KeihinCarbJetting.pdf
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good advice Polanda!
I forget the amount of turns on the air screw but its always stuck in my head as 3 turns and 1-1/2 turns was ideal so you had equal adjustment open or closed but I have not messed with the pwk in a long time since I run lectrons all the time now.
Yeah your pilot number are wacky maybe drop the first digit?
If you are cutting out on topend then always up the main jet first that is primarily what it affects. and you should get the main jet sized properly before tuning the needle to much.
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I apologize guys, i am aware the pilot jet is just a 2 digit number. Typo.
I do not plan on running the air screw out that far ever, I remember hearing/reading somewhere than 4 turns out is equal to 1 size down on the pilot, any confirmation of this?
I have a 175 main in it currently and the top end is now good, no cutting out.
My current set up in the carb is as follows
40.5 kehin
175 main
45 pilot
dgh needle, 2nd clip from the bottom
My issue now is on the bottom end, from no throttle to about 1/3 throttle, its just weak. I do have an "aggressive drag port" from RB racing, but as stated previously, Johanns rideability on "the same" port and head work is 10x better than mine, it has a bottom end like an mx bike, where mine lacks that significantly. It could be the ignition difference, but i cant imagine it making such a significant difference. Do i dare go down to a 40 pilot or lower?
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Adjusting the air screw like above will tell you what pilot to use. Does morse have the cr ignition advanced a bunch? That would add low end.
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I go by if the air screw is 3 turns out go the next pilot size smaller
so it looks like you are still rich on the pilot after you get the pilot working with the air screw 1-1/2 turns out adjusted properly. Then put a bigger main jet in it then go after adjusting the needle
Dont go riding the bike WOT until you get a bigger main in it.
(http://www.carbparts.com/keihin/needles_tuning/calchart.gif)
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I know Johann's runs good, I have ridden it. But, a drag port is, a drag port. Ask troy how much bottom end he had with 496cc's!
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My timing is stock position. I know motor to motor you can't compare no two are the same. But mine has a very strong bottom end so much so it's hard to hold down low it likes to wheelie I'd say it has the grunt of mx style porting
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^ and im jealous. I WANT THAT TOO!!!