After searching a ton of threads, I didnt find a similar instance with similar symptoms so I just need advice on which route to choose.

I just recently did a rebuild and weber swap on my 79 20R pickup. It has a new coil, distributor, plugs, wires, and weber 32/36 with fuel regulator. I did a full smog delete and flat sanded/sealed the weber adapter plates as best I could. The truck starts up fine once warm and idles on its own very easy. however when I try giving it throttle, it barely revs a little then boggs and wants to die as you apply more throttle. that combined with the rich smelling exhaust makes me think its too rich. I have done the weber tuning guide multiple times and have played with mixture positions but nothing seems to help much. my options next are:

1) get an LCE adapter plate to verify no vacuum leak
2) get a lean rejet kit
3) pursue some friendly yotatech advice

 

Verifying no vacuum leak spraying carb cleaner around the base of the carb, and all your emissions and vacuum areas, not by buying a different adapter.

What's your timing set at? Who rebuilt the engine?

 

I did the rebuild myself. And the timing is zeroed at TDC with the point at #1. I will try the leak test later today. Any other ideas besides a small vac leak?

 

Yes, check your timing the right way with a light and set it between 5 btdc (stock) and 8 btdc (what these engines equiped with webers usually like). As for vacuum leaks it is also easy to check, and I think it would have trouble idling. Remember that lean conditions sometimes have the symptoms of rich. But please set your timing correctly first..

 

Yeah I'm somewhere above 8 with my 20R and Weber.

But yeah, definitely check for vacuum leaks.

 

Full desmog eliminates nearly all of your vacuum leak issues. You should be able to rule out vacuum leaks rather quickly since you should only have a distributor advance and brake booster vacuum hoses. I am assuming that you didn't leave any gaping holes in your manifold where there should be a plug? I have a desmog thread in my signature below if you need help with some of the desmog particulars.

I'm suspect of this - were the plates used? Why did you feel the need to flat sand them? I would definitely recommend the LCE spiral adapter even if this isn't the root cause of your problem.

Try the leak test first. Make sure you get all around the base of the carb and the mating surface between the intake manifold and head. If there are no problems there then you're look at timing, advancement or spark issues.

Now I'm going to go on the assumption that you knew what you were doing during the rebuild and that everything (particularly the timing chain) was installed correctly. The next steps would be to:
1-Check all fuel delivery (lines, filters, tank, etc) for clogs and verify that your fuel pressure regulator is putting out the correct pressure (around 2.5-3.5 PSI for Webers). Get a gauge if you don't have one already. This will also ensure that your fuel pump is working properly.

2-Check the timing. Get a timing light - this whole timing by sound thing is nonsense if you do not have a baseline timing to start with. You should be at 5* BTDC at around 950 RPM with the vacuum advance pinched. Like the guys said above, some engines like more advanced timing with Webers and such - I was around 8* to with my Weber.

3-Once you get the timing set, verify that the vacuum advance on the distributor is working properly. If you have a dual diaphragm distributor, make sure you have the vacuum hoses going to the proper location - the distributor port closest to the radiator goes to the carb (Sub/Idle Advance) and the port closest to the head goes to the manifold (Main/Port Advance). If your distributor is not advancing properly then it will not allow even time (advance) to burn the fuel, thus causing a seemingly rich environment. Check the contacts and rotor on the distributor as well if you are using the original one.

4-Check your spark. Make sure your spark plugs are properly gapped and adequately firing. A weak spark can cause failure to ignite the additional fuel.

5-If this is a used or rebuilt Weber, then there is no telling what jets are in it, but all Webers are jetted from the factory for sea level use. If you are in a high altitude such as Denver then you'll likely have to get larger jets, but this doesn't seem to be your issue if you are getting too much fuel.

That should keep you busy for an afternoon. Let me know how it goes for you.

 

Twice I've had the advance unit on the distributor go bad, to where it would leak air/vacuum internally and would no longer advance the timing. Mine is the dual diaphragm version. Luckily LCE sells those, or did last time. If it happens again I'm not putting in another one until I have some idea why.

 

mallory unilite check it out I have one and a hyfire 6al box solves all

Sent from my iPhone using YotaTech

 

I don't see them for an '81, and it looks like they are NLA for the older trucks. It uses only a mechanical advance?

Did it change your mpg from the original distributor?

 

Would you recommend using an electronic fuel pump for a weber 32/36? (Carter 4070?) I've been having the same issues and I'm thinking its the fuel supply... new carb, but seems like the jets are clogged or irregular fuel supply...

 

First put a regulator on it and make sure the fuel pressure does not exceed 2.5 psi. The 32/36 cannot take more than that.

 

I installed a regulator and an inline gauge when I put the new carb on. It's at 3 psi... if I try to go less the screw comes out of the regulator... I'm gonna start a new thread for my 22r, too much to complicate this thread.

 

For street applications this type of regulator is decent. 1 - 6 psi range.
https://www.summitracing.com/parts/mrg-9710