What carb to use on my 86?
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Thread: What carb to use on my 86?

  1. #1
    Senior Member 1986_trx's Avatar
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    What carb to use on my 86?

    I'm running a cool head 20cc dome thick head gasket cylinder decked 67.50mm piston boyesen reeds Reed spacer too open air box uni filter Paul Turner 89 race pipe pc silencer hinson clutch hotrods crank and so on..running 50% 110 octane and 50% 90 ethonal free I'm running a pj38 off a cr500 now and I think it's even bored out. Top end it pulls like crazy but its kind of boggy down low. I run xc what is a good carb? I don't want to kill top end tho

  2. #2
    Senior Member american opel's Avatar
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    35-38mm airstryker carbs are good.

  3. #3
    Senior Member TrailBurner's Avatar
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    Quote Originally Posted by american opel View Post
    35-38mm airstryker carbs are good.

    36mm works great, 38mm also if you have piped. either combo works great.

    Main jet usually 160- 172 rough start, My ported R runs a 162-168 I think, no matter what pipe , go up any it farts on top end.
    Pilot set so it starts on 1st 2nd kick, needle setting middle to start. I'll have to dig my notes out.
    AO, always gives great info !!!
    86 253cc, 40pwk, CT OOF pipe.
    99 583 Formula Z
    74 340 TnT- in progress/restoration
    Owner, hellabrokeNH- coming soon.

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  5. #4
    Senior Member meathead321's Avatar
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    Recommend a 35mm airstryker. The big bore carb is most likely killing your low end You will have a strong top end as well. The reason a smaller carb is better for low end is the induction charge moves faster, mixes and swirls better at lower rpms. Giving you a lot better burn. Hence more low end. I use a 35 airstryker and have gobbs of low end. Great top end as well. I'm running a 168 main jet. You will loose a bit of your top end power from what you have now. But it's a trade off type thing. Up to you. By the way you running 100 octane mixing the fuel as you do. Don't know what compression your running but chances are you could bump it a bit if there is room. Don't go to crazy. actually higher octane fuels have more potential energy than lower octane fuels. More compression is needed to condition the fuel in order to extract that energy.
    Last edited by meathead321; 04-14-2019 at 07:04 AM.
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  6. #5
    Senior Member SandSlinger's Avatar
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    35-38mm air striker for sure.

  7. #6
    Senior Member TrailBurner's Avatar
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    In my experience, bigger carb doesn't kill MY lower end. Gearing it lower if an issue, or go down on pilot and adjust needle. ESR 11 whale pipe I can ride anywhere, but it prefers top end. Losing low end w a pipe is a pipe dream IMO. Jetting correctly clears it up, but I've never had a problem w/ any pipe, I could be totally wrong. Just my opinion. Experience plays a big part.

    I had an ol ESR-7, my friends R had the ol FMF, he would smoke me, He had 36-err38 AS, I had 35 I think. (Both stock porting)
    Also IMO, if you change pipes or do any changes, DO A COMPRESSION check 1st, could be need for Rings. You be scratchin your head, saying I put on performance add ons and it's worse.

    Hence " I put on a new pipe, hard to start or farts on top end/ losing top end" Jetting jetting jetting.

    If I am steering in wrong direction, be polite and correct me,
    86 253cc, 40pwk, CT OOF pipe.
    99 583 Formula Z
    74 340 TnT- in progress/restoration
    Owner, hellabrokeNH- coming soon.

  8. #7
    Senior Member meathead321's Avatar
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    If you absolutely can't nail it jetting, perhaps you should look elsewhere. Like ignition ? I know i'll . probably get bashed for this, But i set my plug gap to .019 out of curiosity. And it fell on it's face. It would load up in 5th and 6th. Missfire badly Could clean it out but it took some doing. Gapped it back up and it runs fine. So it didn't work for me. Not saying that it doesn't work because it makes sense. I just freshened up my top end. I scoped my stator. It runs at 250 VDC at operating RPM. Kicking it i get 180 VDC. and it starts, runs great. Doesn't have a ton of top end power. But i need the low end for gorge riding. Put on a 12 tooth counter shaft sprocket. My ignition system is solid. Just about any electrical diagnosis a wave form viewer is a life saver. I work on cars for some people used to be a mechanic. So that's why i have 1. Very expensive. Cant live without it though. These OBD II cars are pretty straight forward and fairly simple. But electrical diagnosis can get funky. With my vantage ( snapon) i can check every electrical device dynamically. Always finds the problem quickly. Actually on cars you can increase your plug gap as much as .010" Better performance and fuel economy. Need a solid ignition system.
    Last edited by meathead321; 04-15-2019 at 02:24 PM.

  9. #8
    Senior Member TrailBurner's Avatar
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    If you have to set gap smaller, you have a weak ignition system, FACT. This is done on my 74 TNT 340, points n condenser. Also on the millionth of a second per say, adjusts timing in that very short time. But most don't need to think like that, usually very intense engine builders.
    86 253cc, 40pwk, CT OOF pipe.
    99 583 Formula Z
    74 340 TnT- in progress/restoration
    Owner, hellabrokeNH- coming soon.

  10. #9
    Senior Member meathead321's Avatar
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    Exactly. They say a OEM ignition system on a 250R is inherently weak. Don't like to make assumptions but in this case i'm going to assume the stator is to blame. If thats the case why not get an reasonably priced after market stator and be done with it ? I don't think i would run with a .020 plug gap. Knowing something is not quite right. Seems like your asking for trouble. I just can't see getting good performance out of it like that. Guys say they do though.So whatever works i guess.I.ve built a few high performance engines in my day. One of the biggest concerns is the right camshaft. Everybody is a carpenter or a guitar player or a mechanic. One guy i know put in a camshaft with to high of a lift and duration. It wouldn't of been to high but he didn't take into consideration his rocker ratio. Tried starting it and bent a bunch of valves. Then they always put the distributor in and set # 1 on # 1 when the cam gear timing mark is lined up with the crank. On a chevy v8 engine this is # 6 fire position. and the distributor is 180 degrees out. Kinda funny in a way. Lobe separaton is a real big deal with a camshaft as well. That will determine if it's a high rpm or lower rpm cam. Also real big concerning idle quality. Duration has a bit to do with it as well. Unfortunetly Lobe separation isn't in some cam specs so you have to calculate it.
    Last edited by meathead321; 04-15-2019 at 01:23 PM.

  11. #10
    Senior Member acecarlos's Avatar
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    Quote Originally Posted by 1986_trx View Post
    I'm running a cool head 20cc dome thick head gasket cylinder decked 67.50mm piston boyesen reeds Reed spacer too open air box uni filter Paul Turner 89 race pipe pc silencer hinson clutch hotrods crank and so on..running 50% 110 octane and 50% 90 ethonal free I'm running a pj38 off a cr500 now and I think it's even bored out. Top end it pulls like crazy but its kind of boggy down low. I run xc what is a good carb? I don't want to kill top end tho
    Do run .018" to .020" spark plug gap, works Best on 250R OEM IGN's old or new.

    What needle, clip position, AS is set at and jets are in the carb...?

    What temp, humidity, altitude are you riding in?

    Have you measured your 'squish clearance, and what is it?

    NO camshafts, lobes or 4 stroke components in a 250R, so no need to elaborate on what does not concern a 2 stroke...

    Carlos
    Last edited by acecarlos; 04-18-2019 at 09:52 AM.


 
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