2150 2b hard start/Carb Black Magic

Hey bullnose’ers,

Been tinkering on my 84 302 2b truck over the summer and have had a consistent issue I’ve been trying to solve.
On start up it takes quite a bit of engine cranking before coming to life- mostly when cold/after sitting, but still a similar situation after being warm.
Also has a bit of stumble off of a stop, sometimes stalling when cold.

At first I thought it may have been a timing issue with the hard starts, but it idles and runs smooth, so I assume it’s a fuel pressure issue or moreso something in the accelerator pump circuit since there’s no similar issue at cruising speed or higher rpm.

I bought this truck with 55k mi after it sat for a while. At 55k it got a new fuel pump, fuel filter and gave it a time up. Have driven it another 1k and the issue has been relatively the same.
I’ve recently replaced the accelerator pump diaphragm and check valve which has help that stumble a little bit.
I’m trying to go through each circuit of the carb to learn more as I go and hopefully solve the issue, but any thoughts or suggestions are greatly appreciated.
Next will be replacing the fuel filter just in case the tank had some debris that’s starting to clog the new one, then also cleaning/replacing the fuel bowl and check ball & weight in the carb.

Thanks,
Mark

Have you checked to see that you actually have two streams of gas squirting into the carb when you hit the throttle?  Pull the air cleaner and look down into the carb as you hit the throttle - with the engine off.

I've had the nozzles on the 2150 plug due to debris in the fuel, and that can cause the problems you describe.

To unplug them I use a strand of copper wire from a multi-strand piece.  Most copper is hard enough to push the debris out w/o damaging the brass shooters.

Hey Gary,

Thanks for the comment- and that sure would be the common sense thing to do first before replacing the accelerator pump diaphragm!! Always start with the simple fixes first :D
I was going to check out the two jets next along with the ball and weight assembly.  Hopefully that help solves the issue.
And maybe I'll pick up some wisdom along the way;)

THere's no such thing as a fuel pressure issue with a carburetor, at least not a low one. Too much would cause the float to lift and the carb would over fill and find it's way into the venturi on it's own. There's either fuel in the bowl of the carb or there isn't.

Thanks for clarifying.
Yeah- I guess I didn't clarify what I meant.  I understand that this is different than something like a fuel-injected system with electric fuel pump- just trying to describe the issue of what I believe to be a lack of fuel being fed into the carb at low RPM during acceleration, leading to stumbling or stalling.

“On start up it takes quite a bit of engine cranking before coming to life”

Like Gary states, accelerator pump action needs to be checked. But also, on startup/cold startup, the choke needs to be checked, is the choke set to high idle (fast idle cam)? Is choke butterfly 90% closed ?

"lack of fuel being fed into the carb at low RPM during acceleration, leading to stumbling or stalling."

“Fed into the carb” - Do you mean from the fuel pump? Or Fed through the Carb circuits via the Jets, Venturi, Transfer Slot?

What I do to prove some fuel bowl issues is to pull the top off the carb, unplug the coil wire, crank the engine to see how the fuel level looks and to watch the action of the float & needle valve.  I lay a clear piece of plastic on top of the fuel bowl to minimize the fuel splash.

It is rare that the fuel bowl level affects the idle performance and initial rpm advance, since the fuel demand is minimal.
 
Also, off idle hesitation can be a transfer slot issue (Throttle plate position at idle.)

I didn’t see where this carb was cleaned or blown out completely, so some of the circuits could have debris in them.

You can also take a close look at timing during initial acceleration to see how the timing is advancing.

Is your engine still computer controlled ?