Carburetor Swap?

[Bunky]

My 67 GMC has a 74 250 I6. It has the 74 mono jet on it. When I got the truck the carburetor was so nasty and dirty inside I'm not sure how it ran.
I cleaned it and put a kit in the carb. It runs better but has a hesitation on take off and intermittently stalls a lights and coming to a stop..

I have a Weber 36/32 that I was going to put on the truck to replace the mono jet, but have read that it might not be enough should be a 38/38.

So I was thinking of finding an old Rochester 2bbl and put that on the engine instead.

What's others thoughts on these two carburetors?

[geezer#99]

Before swapping any carbs I’d check a couple things.
Check accelerator pump is working. Look in carb and stroke the throttle. You should see some fuel squirting inside.
A lack of enough timing can also cause your stumbling/quitting problem.
What is your initial timing set at?

[Bunky]

Geezer#99

Yes the accelaror pump appears to be working, I'm running a HEI and my timing is at 8 degrees (Vacuum advance unhooked) idling .

[geezer#99]

Bump it up to 12 and see if that helps.

What’s the idle rpm at?

[Bunky]

Originally Posted by geezer#99

Bump it up to 12 and see if that helps.

What’s the idle rpm at?

I adjusted the timing to 12 degrees, take off and stalling much better. I do still have the hiccup when I go to give it fuel when I have been cruising along. Not sure on the idle speed and needs to be adjusted down now that I advanced the timing..

Thanks

[geezer#99]

Once you idle it down then check timing again and try 14.

Do you have a full 12v to the distributor?

[Bunky]

Ok I will give 14 a try.

Yes I did the wire mod to get 12 volts to distributor..

[leegreen]

if you give up on the monojet, I have had good luck so far with amazon clone monojet. https://www.amazon.ca/dp/B073W9QM3K

my original '78 carb always seeped fuel around the butterfly when it was shut off and I could not get a consistent idle.

[Bunky]

Originally Posted by leegreen

if you give up on the monojet, I have had good luck so far with amazon clone monojet. https://www.amazon.ca/dp/B073W9QM3K

my original '78 carb always seeped fuel around the butterfly when it was shut off and I could not get a consistent idle.

I was wanting looking for more power but now I have the power but still have idle issues..

[Bunky]

So we took the truck out for a drive probably 15 miles drove good and idled good. Came out and started right up but wouldn't idle again. Never idled right all the way home.

Might try adjusting the idle up and see if that helps.

[geezer#99]

When you rebuilt your carb, did you set the idle vent screw correctly.

[Bunky]

My carburetor doesn't seem to have that vent

[geezer#99]

Maybe you could contact Mike for a carb recommendation.

https://www.carburetor-parts.com/

[leegreen]

It looks like you have the distributor on the lowest port on the carb? That is probably manifold vacuum so you have full advance all the time. That plus the initial advance is too much at idle.

I'd try the next port up which should only give you the vacuum after the throttle plate cracks open. Then reset your initial timing to 8-10 ish and see if you can get it to idle down.

A vacuum gauge and timing light that can read total advance is useful here.

I'm no expert at this and it seems like every year of monojet might be slightly different, and internet opinions on ported vs non ported vacuum for advance are all over the map, but switching mine to ported vacuum helped a lot.

[Bunky]

Originally Posted by leegreen

It looks like you have the distributor on the lowest port on the carb? That is probably manifold vacuum so you have full advance all the time. That plus the initial advance is too much at idle.

I'd try the next port up which should only give you the vacuum after the throttle plate cracks open. Then reset your initial timing to 8-10 ish and see if you can get it to idle down.

A vacuum gauge and timing light that can read total advance is useful here.

I'm no expert at this and it seems like every year of monojet might be slightly different, and internet opinions on ported vs non ported vacuum for advance are all over the map, but switching mine to ported vacuum helped a lot.

There's no vacuum at idle, so I think it's on the right port.

As far as the idle I think raising the rpma would be better.

[Bunky]

So this afternoon I went out and was looking things over and I found 2 vacuum port covers that were cracked and leaking. I'm hoping that fixes the idle issue. Will try and drive it later this week...