choke has to be on

i have a 78 chappy lb50 and when i start it the choke HAS to be on. it wont start if not, even if its been running for hours. sometimes it bogs out and i have to put the choke on to keep it alive. does anybody know why this is?

choke has to be on

Well, let's think this through.

When the choke is on, airflow from the air filter is blocked, causing a vaccum effect that pulls more gas from the main jet into the engine. (A "rich" mixture).

So, if your engine won't run without the choke, it means that the bike is getting too much air, and not enough gas. Sounds like either the gas flow to the carburetor is impeded, or that the main jet in the carb is clogged.

Check the easy stuff first:

a) drain tank - look for rust in your gas

b) remove petcock, and clean it out

c) Remove fuel line, and clean it out (Can-O-Air from electronics stores work pretty well if you don't have an air compressor)

NOTE: Do not leave an empty tank in a humid location for a long period of time - even overnight might be bad in some weather. When the gas evaporates, the steel on some tanks can _immediately_ start to rust. Always replace the petcock and put a few ounces of two-stroke mix gas into the tank and close the fuel cap before you stop working on the bike for the day. You never know when you'll next have a chance to work on it... and a rusted out tank is a nasty surprise.

(Unless your tank is just packed with rust. In that case, search this group for 'tank rust' and follow the great advice from gurus who know a lot more about it than I)

Once your fuel system is clean, you should clean the carburetor (which can be quite buried in some mopeds - get a shop manual if possible, a digital camera if not!):

a) Remove carb (put a clean rag on the engine where you removed the carb so that dirt won't get in your engine)

b) Disassemble carb (take plenty of pictures if you don't have a shop manual!)

c) Clean carb with carb cleaner (NOT gasoline) to remove varnish

d) Clean carb with compressed air to blow out loosened varnish

e) Repeat (c) and (d) until cleaned.

f) Reassemble carb, and perform a blow-test. (see below)

g) Reassemble bike, turn on petcock (count to 10 to let the gas fill the carb), and try to start it.

The Blow Test

On a cleaned, working carb (empty of gasoline!), you should be able to blow into a tube attached to the fuel intake easily when the carb is right-side up, and not easily at all when the carb is upside down. (This is a really quick and dirty check to make sure you've reassembled the float valve properly before you put the carb back on your bike)

Re: choke has to be on

well, considering the gas tank is plastic, i really doubt that rust is my problem here. i just got done rebuilding my carb for the 4th time in about 3 months. i cleaned out my petcock about a month ago. maybe i should again? its also a 4-stroke, that may help, since you were talkin about 2-strokes, but thanks for the help, ill go through it again.

and how do i get less airflow? just by adjusting the jets on the carb?

Re: choke has to be on

First, I dug up this place in NZ that's selling Chappy manuals, if you don't have one:

And a French Chappy Web Site ("Babelfish-ized for your conveniance": ) that seems to have a lot of info about that specific moped.

Second, you may want to try adjusting the idle screw on the carb. See the french chappy site for details, under 'Carburation'. It has a labelled cross section picture of the carb that should make it more clear.

Re: choke has to be on

wow, thank you. that blow test worked like a charm. i havent put the carb back on yet, but when i do i hope it works. thanks again.

Re: choke has to be on

If it sat for a long time before you got it I would suspect dried out main oil seals. This causes air to be sucked into the engine leaning the mixture out. Running with the choke on re-balances the mixture (kind of).

Re: choke has to be on

that could be the problem. it sat in pieces for about 5 years before i got it. where would the oil seals be located and how many should there be?

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