cold carb?? By sitticuss (Read 687 times)

[sitticuss]

I took my scoot out and actually opened up the throttle a bit for the first time since I put in the BBK.... It didn't run smooth at more than half throttle.. I went home to adjust the carb and noticed it was cold not cold as in not warm but actually COLD??? The temperature today was 75. My carb is a 19mm 2t with a #90 main jet

[twowheeler]

Who measure the temp of their carb? I dont think it means a thing.

[sitticuss]

Just been trying to figure out what the deal is with my carb. I've tried everything..never seen a carb that cold with condensation dripping off the sides. It wont"t hold the idle and it spits gas. tried moving the needle changing the pilot jet..even tried another carb i have thats the same. at idle i can hear it suck air in every revolution from four feet away....I've been thinking maybe its to small for my BBK

[Alleyoop]

What size BBK did you put in a 72cc? If its spitting out fuel your MAIN JET is to big. For a 72cc try a #80 or #85 Main.
Alleyoop

[sitticuss]

I put in the 47.6mm aluminum kit from scrappydogs. I tried the 85 it still does the same thing. and at about half throttle it fades in and out. With the 90 from 1/4 full throttle it works good. I did a plug chop at WOT with the 90 and the plug looked good. during acceleration at just over 1/4 throttle there is a drop and then over reving for a few a few seconds then it runs fine throughout the power band

[FrankenMech]

Carbs will freeze up under the right conditions. Usually prolonged periods of constant throttle will freeze up the worst. They have charts for aircraft to help identify dangerous conditions. When a scoot or any ground transport freezes up it is usually not a big problem but if an aircraft loses power.....

[Alleyoop]

Like I figured it is a 72cc BBK, what kind of AIR FILTER do you have on it. Did you leave the AIR BOX on or put on some Free Flow Air Filter? I am just telling you how it is, a #90 main jet for a 72bbk is to much. There are hundreds of guys with the 72bbk and they will tell you the same thing, your flooding the poor little thing. You say you tried the #85 and it did the same thing, so looks like the #80 might be the right combo, but you do what you want.

People always make that mistake they slap in a BBK and 99.9 percent always over jet the carb or get a carb that is to big. They think they can now pour a gallon of gas and get a lot more power. Just so you know a BBK gets you more low end power so it will get up to speed a lot quicker. But don't expect top end out of it for that you need to work on the CVT and Tranny Gears now that the motor has more power.
Alleyoop

[sitticuss]

Your the first one to suggest. I should go down even smaller than a #85..The few other opinions i've gotten is i should need at least a #100 with the BBK and performance filter I am using. My feeling is my 19mm carb should be more than enough even for a 90cc. I am just looking to cruise at 45. I was using a #74 before the BBk with the same filter and it worked fine. My stock air box was falling off because all of the mounting tabs had broken due to fatigue,and I couldn't find a replacement. Personally I don't like the foam filters. I am just concerned my problem might be with the BBK. I will down size the jet and put the stock air box on tomorrow too see if that helps

[sitticuss]

Well none of that worked... so i am going to just order a new replacement 50cc kit and put it back to stock. I'll do some more studying and hopefully my next attempt will be more successful. Thanks for everybody's help and patience with my dumb questions.

[mikey34]

I Wouldn't stop now, and Alley Everybody's scoot is different I guess, cause my Vento 50CC, has a 1.01 main jet... and it runs great through the whole power-band. I just don't have the gear length to let my baby fly yet, Alley is right about changing up the CVT, I would research All about the CVT if you want more speed. I would change my secondary, and final gear, with a little more weight in the Variator, with 1k springs...

[Alleyoop]

Well I said my peace, I don't care if everyone's scoot is different, A MOTOR CAN ONLY TAKE SO MUCH AIR AND FUEL PERIOD. People that say I put in a 100 or whatever main jet do not realize they are really loosing a lot of power but they believe by pouring in a GALLON OF GAS they are TEARING up the ASPHALT.

Have a good day and may the Force be with you I am done.
Alleyoop

[sitticuss]

I opened my cvt today and found two rollers that were stuck in the variator slides.. i also found out the space between the variator and the fan where the belt rides was 2mm thinner than my original when assembled. Put my old variator back in and...bingo no more surge on acceleration. I switched my rollers from 5 to 6.5. It raised my top end and lowered the rpms. Didn't notice any drop takeoff so i might try a heavier roller.. I have a 1.5k main spring for my clutch I might go there next..I don't want stiffer clutch springs the last thing i need right now is a higher rpm launch. My cvt cover has a bearing which supports the clutch so i can't run mine with the cover off like some of you lucky guys...My BBk came with a racing piston, or what i call a flat head not the rounded head I had...sorry i'm not sure what the actual proper terms for them are....So the length of the new cylinder and the postion of the wrist pin on the piston were different. Anyway what i am saying is I no more now then when I put it in and i think i can do better on the gasket spacing etc. to get my squish down right now i am at 1.84 mm. I read that if the reeds are going bad that could cause the carb to spit. I looked at the reeds and their good. I held my hand next to the opening of the intake manifold with the carb off and turned over the engine it sucked air but did not blow back any. But it also didn't seem to sucvk that much either. So i am just going to pull the BBk and do a little inspection, tweaking and measuring. I am going by the assumption now that if i tweek my squish band I will get more suction at lower rpms. Or that i made a mistake somewhere putting it together. I didn't do a compression test after the install because i don't have a compression tester. I don't have or can afford a lot of tools right now. So thanks for the encouragement. The gears will be next i haven't got that far yet.

[sitticuss]

Your just spoiled alley your used to all the fancy tools and new parts....lol

[Alleyoop]

Dec 6, 2013 13:44:07 GMT -6 @sitticuss said:

Your just spoiled alley your used to all the fancy tools and new parts....lol

HAHAHA, no not spoiled at all just know my crap. I used to build my own hotrods and race every Saturday and Sunday. Still have one of my Hotrods 1969 firebird. So tuning a 1 cylinder little motor is a piece of cake.
Alleyoop

[sitticuss]

I just thought this forum was about helping...not making fun of someone who is doing his best to learn. I think that says a lot about your character. but that's ok i guess I'm sure no one ever helped you out.