Why does DT refuse to run without choke on? General carb question.

Hey, I need a pointer. I've torn down and cleaned the carb on this DT400
three times now and it still refuses to run without the choke on. What
gives? What am I missing? It's so clean in and out that you could eat off
of it. What causes a carb to refuse to run without being choked? Help?
Thanks. KM

 

jets clogged, choke is a diff. avenue for gas to get there.

 

Hey, thanks for the posts. Like I said, it's spotless clean--nothing's
plugged. The float needle is perfect. Someone else suggested an airleak,
sez it's running wayyyyy toooooo lean. Any thoughts on this? Thanks. KM

 

That's two votes for clogged jets, though I've ensured (3x) that they're
spotless and smoothly clean inside. Funny, too, I always thought that
chokes dealt with airfllow, rather than gasflow? Like, cupping your hand
over the throat "chokes" it into starting?

Someone suggested airleak and lean running prob. Any thoughts there? My
experience with carbs has been 1. varnished up, 2. clean 'em, 3. lucky they
run good after that. I've torn the whole thing down, and nothing's clogged.

 

If the engine can be made to idle using the choke it's possible to use
aerosol carb cleaner to test for vacuum leaks; if you spray a leak the
engine will speed up a little. It works well on four-stroke engines and
you only have to test the manifold between throttle valve and head.

Sounds like you're dealing with a crankcase-scavenged two-stroke. You
then have to test every seal going into the crankcase...much harder.

good luck!

bob

 

<snip>

The choke decreases air flow into the carb. This increases vaccum pressure
(negative pressure) within the carb which causes more gas to be sucked out of
the jets per number of air molecules flowing through, and thus a richer mixture.

The throttle plate, on the other hand, is below the jets at the bottom of the
carb. so when the throttle is closed the vacuum increases in the intake
manifold, not the carb..

Ben

Ben

http://autos.groups.yahoo.com/group/rockland_mc_riders

 

Will check it out. Thanks for the hint. KM

 

PILOT JET,clean with guitar wire!

Thanks,Ripper
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