is there a "downdraft" carb for mopeds?

Most mopeds have horizontal cylinders with a side-draft carb, so they have a right-angle bend in the intake tube. So why don't any mopeds use a down-draft car (like on an American V8 car) and eliminate that 90 degree bend? Are there just not any downdraft carbs small enough?

Re: is there a "downdraft" carb for mopeds?

Zeke Rigg /

there are they are just less common, for example the honda P 50 has a ten mm one. but the more common design is as it is. intakes are easy to make redesigning carbs not so much

Re: is there a "downdraft" carb for mopeds?

Salsa Salsa /

there are so many carbs, get them from other applications. big block has like a 35mm on a ported stock cylinder derby that rips.

Re: is there a "downdraft" carb for mopeds?

Most mopeds have a frame very close above the cylinder which wouldnt leave much room for a carb and intake.

Re: is there a "downdraft" carb for mopeds?

get a membrane carb. install in any orientation. easy to find used ones off old jetskis.

Re: is there a "downdraft" carb for mopeds?

there is pumper carbs made for 2ts that will work in just about angle you put them at. tilson or something like that. they are like the carbs on chain saws and weeders but bigger. when i was a kid i had a go-cart with a mac 7 motor with 2- 22mm downdraft carbs.

Re: is there a "downdraft" carb for mopeds?

Dellorto UA 19

the float can mount any direction so you could mount that as a downdraft or whatever you wanted. it's a super badass carb too.

real tough to come by tho, and usually sell over 200, but the 16's and 18's sometimes pop up for under 100 bucks on the bay.

Re: is there a "downdraft" carb for mopeds?

I have throught about this too for a Garelli I had and there was one very good carb for this. It not only is the perfect size for the big bore kit but would be perrfect for almost any horizontal cylinder.

Just go to the local junkyard and find a Suzuki T125 twin. As a twin it has 2 65cc cylinders and that is the same as the big bore kit. It came with a down draft carb. PERFECT!

I never got a chance to do this as another project took over but here is a picture of the carb in question. At the local junkyard.

2ND TRIP TO YARD 032.jpg

Re: is there a "downdraft" carb for mopeds?

I'm not sure I'd want my carb sitting directly above a hot cylinder, anyway.

BTW, crankcase induction engines like my Bat have nice, straight, horizontal manifolds, and it's no speed demon. I don't think the bend makes a whole lot of difference.

Re: is there a "downdraft" carb for mopeds?

Get a diaphram carb and put the carb any orientation you want, just have to plumb a vacuum line from the carter to the pulse port of the carb.

Re: is there a "downdraft" carb for mopeds?

Maitland Of the Loin /

theres several options

but yeah you would need to drill a hole for the pulse, unless you could route it through a reed valve

Re: is there a "downdraft" carb for mopeds?

The diaphragm relies on pressure differential, so taking both the signal and draw from the same side of the the reeds would not give the pumping action properly.

Re: is there a "downdraft" carb for mopeds?

what you need is one of these tillotson carbs. They are probably readily available on ebay for maybe $20 apeice? Just make a manifold and they will work on anything. No need for a pulse port because it gets it from the pulse in the intake manifold each time the engine sucks for air(every rotation). The hardest part is hooking up a linkage to the throttle cable. It requires an extra linkage rod and mount for your cable to hook up to it properly. The Jet-Ski carbs are way too big.

IMAG0538.jpg
IMAG0539.jpg

Re: is there a "downdraft" carb for mopeds?

32mm too big? lol. yeah you're right. maybe a little jetski.

Re: is there a "downdraft" carb for mopeds?

I haven't seen a Jetski that has used a 32mm carb since the 80's. Most in the nineties had 38-48mm on them. A lot of tuning is required with pop off(spring) pressure and jet sizing although they worked pretty good from the factory

Re: is there a "downdraft" carb for mopeds?

@ Mark: Did you snag those carbs? What did they $$ for them?

@ Joe: straight shot makes a big difference. Check MotoGP tech along with all of the 2T tuning books.

Re: is there a "downdraft" carb for mopeds?

These were there about 2 years ago. The bike had been there for a while. I never bought them but if I had the cost would have been @ 65.00.

I have delt with them for a lot of parts and they will give me a deal once in a while. I posted the picture to show they are out there and what they looked like.

I love anything 2-stroke but sold my modified Garelli to finance my ultimate 2-stroke a 1975 Kawasaki H2 750 Denco.

I loved my Garelli and I had it to 58mph. The person I sold it to got it to 62 after the break-in and leaning out of the jetting.

I was really hot to do the mod to this carb but after hitting 58mph the mod seemed pointless.

« Go to Topic — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account