Has anyone else grafted a diaphram carb to a moby or any other piston ported engine? just want to compare notes.
i am trying out a HS7 tillotson and a HL166 tillotson on the orange moby. the hs seems to be giving a very abrupt top end and even though the pipe was getting a bit of a glow on the outside radius my plug didnt read lean. the hl was a little too boggy in the bottom end so maybe that would work on a kitted engine because once it took hold it was awesome times two.
How do you jet those things
diaphram carbys are pumpers so you dont jet them you adjust the fuel orifaces for lo and hi mixtures. the pump action comes from your crankcase so you have to drill into the casing for a pulse fitting. they flow real good cause the venturi doesnt have to be so drastic because of the pump action.
One of the first mobys I bought someone had stuck a Tillotson diaphram carb on. It was 23mm and the rest of the bike was stock. Didn't know it it ran or not. but it sure looked funny.
Wari, I have a Tillotson carb that came with my Mobys when I bought them. Nice to know that it does have some practical use. I will have to look at it and see what the model is, somebody made an adapter to fit it to a Moby intake out of aluminum. How did you rig up the linkage to make it work? The Tillotsons use butterfly valves as opposed to a slide.
plate to bolt to the cylinder then length of pipe then plate to bolt the tilly on. the tilly end has extra so i thread the cable through a threaded hole with a collar so i can take out the slack. same wif the choke and i added a spring so it snaps open. havent had to use the choke yet tho.
oh man i love how pumper carbs perform. i have a little 25cc homelite weedeater motor that i blocked an emissions port on to up the compression to 150ish and put a port matched (larger) zama (chinese clone) carb on. it screams! just need to figure out the throttle cable and get a shaft for it. should be able to mow brush and small trees lol.
however, those pumper carbs are a TOTAL BITCH to rebuild. everything is soo tiny and the little springs wear out. stock up on full rebuild kits, the tiny passages get clogged very easily, the diaphragms harden up, and you have to use new gaskets when you take em apart. and dont forget that the needle does wear out, its under an arm on the bottom of the carb by a tiny fuel well.
I've had a lot of problems- they seem to get overheated, and mid range can be tough to set on them. No matter what size I've used, they spray fuel out the intake and soak the filter.
I've used both walboro and zama.
all 2 strokes spray fuel fog out the intake because of reversion, piston ported engines are worst then reed engines.
the walbro and zama are similar boxes like the hs tilly which seems to be working better then the hl on the overall range but not for top end.
i cant get a good reliable speed run because of the cross wind today and it was peeing rain yesterday grrrrr.
Oh and they make your engine LOUD More intake roar than any other carb no matter what. It usually takes a day of running around, stopping adjusting and re- adjusting to get it right. Then the idle will mess with the top end- It's much simpler to use a stock ish carb. I did find a good manual for the walbros- and a lot of information is available for the bigger diaphragm carbs on ultralight and parasail sites. here
"and theory even":http://www.drystacked.com/Walbro%20Carburetor%20Theory%20ebook1.pdf
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