Dieseling

[Chevynation]

It’s almost like it’s a bleed off port or something. Not sure how they routed vacuum lines for the original vehicle. The carb only has three ports. The port on the front for pcv, the port on the passenger side which I thought was full manifold vacuum, and the port on the driver front which should be ported. I didn’t test that one but it didn’t appear to be manifold the way it was routed. I don’t have any ports on the baseplate. My manifold has a hole behind the carb so I installed a fitting for my power brake hose connection. Same way it was from the factory on my car. Do I have to drill the baseplate for a manifold vacuum port?

[Kenth]

Now you are "robbing" air from the idle bypass source, that´s why you see low vacuum in the side manifold vacuum source.
Instead of cutting the gasket you should have drilled the hole a bit further to the next location in float bowl. Then you will get full vacumm signal in the side manifold port, and a fully functional idle bypass air.

[Chevynation]

Now you are "robbing" air from the idle bypass source, that´s why you see low vacuum in the side manifold vacuum source.
Instead of cutting the gasket you should have drilled the hole a bit further to the next location in float bowl. Then you will get full vacumm signal in the side manifold port, and a fully functional idle bypass air.

I’ll get a new gasket. You’re a genius. That next port would’ve been perfect so I’ll drill to that hole.

[Chevynation]

I might just epoxy the vacuum port hole thats currently exposed from shaving the gasket and drill to the next hole like you said so I don’t need a new gasket at the moment. However, if I need a new gasket should I shave it so that the bypass hole on the base plate is fully showing and not just maybe 1/4 of the hole. The majority of the gasket is just covering the hole. It is fine on the main body and the driver side hole is centered perfectly on the base plate. I would’ve thought it shouldn’t be blocking the hole. Is this not considered a restriction and should be left alone? Thanks again.

[Kenth]

No need for epoxy.
A new gasket will cover the unwanted hole and solve the idle bypass issue as the slotted hole in gasket acts like an air channel leading air to were it´s needed.

[Chevynation]

No need for epoxy.
A new gasket will cover the unwanted hole and solve the idle bypass issue as the slotted hole in gasket acts like an air channel leading air to were it´s needed.

For the time being I just drilled to the next hole and put epoxy in the first hole so it’s not robbing the idle bypass air. Everything works as it should now. Can’t wait to take it out and get gear soaked to see how it acts.

[Chevynation]

Everything went smooth but when I set the idle and drive it and it gets hot it will go up.  I figured it was normal since it heated up. So I lowered it and then I get down the street and it’s higher again. I’ll set it at 750 and it will go up to 1000 by the next time I stop. My throttle return spring is pulling the lever back to the screw so I’m not sure why the idle keeps going up. I can’t find any vacuum leaks. Should I try to reduce the idle bypass holes? My curb idle is pretty much backed all the way out at this point. If I pull on the throttle lever towards the stop then the idle will drop but no spring will be able to pull the lever back that tight to lower the idle. My throttle shaft bushings were replaced when it was rebuilt so I’m not sure why I can lower the idle by forcing the lever to the closed position. Idle bypass holes at .136 currently.

[Kenth]

Check for weak distributor centrifugal weight springs, or binding weights, not returning the advance when letting off to idle speed.

[Chevynation]

Tried that. I’m using a billet distributor and I’m using a heavy and medium spring. Repeatedly tried to see if anything was sticking. I can’t see me having to use two heavy springs.

[Chevynation]

Went up to a heavier spring. I’ll post back later this evening.

[Chevynation]

Two heavy springs worked. I’m still thinking about taking some idle bypass air out. With 18 initial plus 10 manifold vacuum advance it will idle no lower than 750 without touching the curb idle screw.

[Kenth]

Set initial to 10-12° and use the ported source for vacuum advance.

If this don´t work, check the sizes of upper and lower idle circuit airbleeds, idle tubes size (at the lower end), downchannels size and idle mixture needle holes size.

[Chevynation]

I’ll have to measure everything because it’s not happy at all at 10-12 degrees initial. It likes the 18 initial. Even with 18 initial and removing the vacuum advance I can’t notice an idle drop but looking at the timing it does retard so my pickup is indeed advancing when connected. I limited it to 10 degrees all in at 1.5 - 2” below idle vacuum. The ported vacuum advance port does not work with the carb since the main body was replaced. I never tried to make it work since I was only worried about manifold vacuum to my vacuum advance. I’m not a fan of ported to be honest. I was under the impression that I could simply remove some idle bypass air since it only affects how much the primary blades have to be open in order to get it to idle and nothing else. Essentially like closing the throttle blades.I would imagine doing so would require me to have to close the idle mixture screws in. The rest of the carb works fine. Responsive everywhere etc. Idle mixture screws are responsive as well. It can just idle with the throttle blades closed which is almost where I want the idle but not quite and I want the throttle blades to be open a small amount at idle i would think. I don’t want to recalibrate the carb and mess with everything that’s working fine. Just reducing the idle bypass air hole sizes in the baseplate by maybe .010 at a time won’t fix the issue?

[Cliff Ruggles]

Just some info for those reading and following this thread.

ALL of the issues here are fundamental.  Too much camshaft and LSA too tight for the CID and compression ratio of the engine.

For sure "rowdy" tight LSA cams sound great but the overlap causes reversion, low vacuum at idle/poor signal to the carb and loss of throttle response and power at low RPM's. 

Doesn't mean we can't make things work but for sure the engine is NOT going to do well without running a LOT of initial timing and opening up the idle system to supply it with enough fuel to be happy at idle speed. 

It will also like a lot of idle bypass air to keep the throttle angle low so too much transfer slot isn't exposed and they don't "run-on" or "diesel when we shut they down........FWIW.....