UBF24BS carb question - starting

[STEVENM63]

So thanks to Bob, I got my ignition wires sorted on my 250 nc. Now my problem is starting. I have good spark and compression, so I am checking the carb. One thing that I noticed is that my UBF24BS carb does not have a choke. Is this normal? It does have the tickler.

I have gotten in to fire after kicking and kicking and kicking. It will run for a few seconds while working the throttle and then it dies. Then more kicking. What starting procedure should I use without having a choke? How many times should I tickle the carb? Also, how many turns out should the air screw have?

Thanks
Steven M

[john jupiter]

Hi Steven
I beleive that one has the air restrictor that slides up and down on the slide. It doesnt work well as a choke. I had the same problem with getting mine running, then i was able to clean the tiny idle jet that is buried pretty deep in the body of the carb. Now it starts and idles with one kick no mater if rhe "choke" is up or down.
The idle jet is so tiny it gets really clogged, i cleaned mine with a very small torch cleaner.

[DewCatTea-Bob]

[quote= STEVENM63 ...
" my UBF24BS carb does not have a choke. Is this normal? "

____ No, as it came stock with the air-block (that's made to fit through the throttle-slide).
__ The choke-setup is-not of much use (except perhaps in weather with air-temp that's too cold for riding), which is probably why the choke-block has been removed.



" It does have the tickler. "

____ That's far more useful (than the choke-setup) for cold-engine starting !



" What starting procedure should I use without having a choke? "

____ First thing, turn-on a fuel-petcock and allow fuel to finish flowing down-into the carb.bowl,, and-then, tickle the 'tickler' no-longer than it takes to see just a single drop of fuel come-out, just before kicking-over the engine.



" How many times should I tickle the carb? "

____ Defining a single 'tickle' as a quick down-press of the float-depressor (until it bottoms-out) and-then instantly releasing it (as soon as it has bottomed-out),, a cold engine (in cold air) may require 3 or 4 'tickles' and a warm engine may need just 1 or 2 tickles, (while a hot engine should-not need any tickling).



" how many turns out should the air screw have? "

____ I think the fuel-mix screw (in this carb.model) actually adjusts the fuel-flow through the idle-circuit, rather than the amount of 'air',, (or perhaps it's the other-way-around, I just know and only recall that it's the opposite adjustment-method of most other carb.models !).
__ The adj.screw should be set as lean as possible without causing high-RPM shutdown-throttle exhaust-backfiring.
Start-out at about 1.5 full-turns (outward from fully-seated), and-then re-adjust (as needed) from that adj.screw setting-point.


Hopeful-Cheers,
-Bob

[STEVENM63]

Thanks for the responses. I've checked and cleaned the jets and the internals for the carb, but the engine just doesn't seem to be getting fuel in to the cylinder when the engine is kicked over. This carb does have a velocity stack on it with no filter and I'm wondering if that is affecting my intake vacuum. If I cover the velocity stack opening with my hand and kick the engine over, I get suction and gas on my hand. This would lead me to believe that I don't have restriction in the jets, since I am getting fuel up into the chamber. I'm just thinking that perhaps I'm not able to draw it into the cylinder.

Am I on to something or grabbing at straws?

Steven M

[DewCatTea-Bob]

[quote= STEVENM63 ...
" This carb does have a velocity stack on it with no filter and I'm wondering if that is affecting my intake vacuum. "

____ Perhaps so, but certainly not by any amount that would make any real difference.
__ What motorcycle did "This carb" come from originally ?
And haven't you ever tried the original 'SSI' carb ?
Don't you have any other suitable carb to try-out (in place of the one you're currently trying) ?



" If I cover the velocity stack opening with my hand and kick the engine over, I get suction and gas on my hand. "

____ That's pretty-much normally expected !



" since I am getting fuel up into the chamber. I'm just thinking that perhaps I'm not able to draw it into the cylinder. "

____ Have you tried using a spray-bottle (filled with gasoline) to squirt some fuel in through the throat ?



" Am I on to something "

____ Unless the carb itself is reasonably suspect, then I'd say you're probably-not on-to something along that line of suspicion.
__ Have you got the engine that your carb came off-from, or any other bike, which you can test-out that carb on ?

____ Your other/previous thread had left me to gather that you've already-before had the engine running,, so if-so, then what-all else have you since changed (that you can now no-longer get it started-up) ?
__ Please continue forth-ward within your other thread, for also concerning any possibly related start-up issues associated with your present electrical-wiring scheme.


Hopeful-Cheers,
-Bob