Don Terrill’s Speed-Talk

steve cowan wrote: ↑Wed Jun 03, 2020 1:18 pm

shoedoos wrote: ↑Wed Jun 03, 2020 7:26 am bump it up to 30 initial and get back to us with the idling results.....

even more timing if you have to just at idle as to try and isolate the problem,try lowering fuel pressure to 4-4.5psi,
fuel pressure and float level have a influence on idle mixture,
and dont be surprised if you only need the secondry idle screws out a quarter of one turn from closed.

PRH wrote: ↑Sun Oct 04, 2020 1:24 pm Through the years I have had various running issues with Holley or Holley style carbs.
The beauty of the modular carb is that you can swap “known good” parts, one at a time, into the problematic unit to isolate where the problem really is.

In doing that, I have found a variety of different ailments........ which are often in the main body.

We used to build a bunch of oval track motors that had to run 4412 carbs.
It was amazing to me how many of those things just didn’t work right.
The first easy test was to swap the metering block right on the dyno.
That rarely solved it. Then I’d swap/add a different main body so all that was left of the original was the baseplate and bowl.
That basically always fixed it. Then I’d put the original metering block back on with the new body........ which almost always ran fine, but was sometimes down a little on power.

In the OP’s situation where the motor wouldn’t idle at all ..... I’d have started with a swap to a known good carb, to make sure that’s really where the problem was.

PRH wrote: ↑Sun Oct 04, 2020 1:24 pm Through the years I have had various running issues with Holley or Holley style carbs.
The beauty of the modular carb is that you can swap “known good” parts, one at a time, into the problematic unit to isolate where the problem really is.

In doing that, I have found a variety of different ailments........ which are often in the main body.

We used to build a bunch of oval track motors that had to run 4412 carbs.
It was amazing to me how many of those things just didn’t work right.
The first easy test was to swap the metering block right on the dyno.
That rarely solved it. Then I’d swap/add a different main body so all that was left of the original was the baseplate and bowl.
That basically always fixed it. Then I’d put the original metering block back on with the new body........ which almost always ran fine, but was sometimes down a little on power.

In the OP’s situation where the motor wouldn’t idle at all ..... I’d have started with a swap to a known good carb, to make sure that’s really where the problem was.

PRH wrote: ↑Fri Oct 09, 2020 10:09 am Through the years, my experience with ootb 4500 carbs is....... they often have low speed/part throttle drivability issues.
However the one thing they usually don’t have a problem with is..... idling.

If the cam is small, and the idle vacuum higher than what would be typical when using a 4500 carb....... you’ll often end up with the mixture screws barely open at all.

PRH wrote: ↑Fri Oct 09, 2020 5:38 pm I’m not going to go back and re-read 8 pages of posts.......

When you pulled that carb apart to go through it....... did you find something “wrong” with it, to the point where you felt that’s why it wouldn’t run?

If not, and it was just std Holley fare........ and it was that far off from working on that motor combo....... maybe it’s not really the right carb for the application?