Poor performance and misfire

[PercyUK]

OK, friends, one to ponder.
Firstly having spent 40 years tinkering and fixing up classic cars in my spare time I like to think that I am pretty handy with the spanners however I have a problem that has got me stumped and a fresh perspective from my jeep buddies may help.
My 1954 Cj3a is fitted with it's original,  I assume, L head engine. I recently fitted new pistons, rings, some worn valve guides and valves, new springs and a hone for good measure.
It's running 130lbs on each pot and giving good oil pressure..... Happy days.
However I have had an annoying random misfire at idle that I may have resolved only by adjusting the timing to about 15 degrees before tdc however the car lacks power when under load such as driving up a moderate incline.
When I blip the throttle the engine will hesitate to the point of stalling.
If I pull the choke out a little it runs noticeably better suggesting a lean mix but here's the problem.
I have fitted new plugs, coil , leads and a complete points based dizzy.
A vacuum test shows 18 to 20 inches in the manifold which is good and the fuel pump is banging out 3.5lbs of pressure.................. And I also replaced the old solex with a new Carter from Joe's motor pool.
I also checked for air leaks in the manifold finding none.
I can't drive the car around with the choke out so I have turned to your collective knowledge to help me fix it.
Go for it.

[scoutpilot]

15º is way too early. Find the highest vacuum reading with the distributor then back the rpm off 100. Lock it down. Adjust the steel idle stop screw to again get the best vacuum reading then adjust the idle mixture screw to 650 to 700 rpm. If this is unsuccessful, then you may be experiencing a problem I've found in a few of the JMP carbs. The throttle shafts and the bores are, from the factory, not to spec. Both should mic out at .3125".

[PercyUK]

Hi, thanks for the reply. I have used the vacuum gauge as described before and set idle and mixture accordingly. If anything the misfire becomes more evident.

[PercyUK]

Just a thought but if the throttle shaft bore was oversize and introducing air I would expect the engine to respond when I sprayed carb cleaner over the carb. I get no such response suggesting that there is no leak but I will have a look.

[scoutpilot]

What is your idle RPM? If it is high you may not notice a change in tempo when performing a vacuum leak test.

Did you set the metering rod with the Carter Gauge? Check for a gap between the top inside of the Metering Rod eye and the pin it is supposed to rest on when the rod is bottomed out in the jet.

[PercyUK]

Hi, no the idle is not high I set it to spec during the process. I will check the metering rod and the float height just incase.
The fact that it seems better with a bit of choke would suggest a leak or carb issue.
I am a little worried that the valve timing might be out by agear tooth or two, is this possible and can I check it without removing the engines front cover?

[scoutpilot]

One step at a time...

[PercyUK]

Both checked again and fine. I also had the misfire when the old solex was fitted and this prompted me to buy the carter to try to isolate the problem.

[scoutpilot]

Look inside the distributor cap for carbon streaking. Are the contacts in the cap brass or aluminum? They should be brass. Plug wires should be copper-core and non-resistant. Spark plugs should be copper-core and non-resistant.

[SteveKfl]

After you finish following Scott's expert experience advice, and if you still have a "miss", I'm just offering "my individual experience" just as an FYI.  "my miss" ended up being from a crack in the intake manifold at the flange area, only offered as another place to check out for "intake leaks", especially since you've added the "changing of carbs info" now.

[PercyUK]

Thanks Steve, that was one of my first thoughts but it is testing fine with no looseness or visible cracks and there is no change when spraying carb cleaner, easy start or gas at the join.

[stony]

I hate to suggest this, but I’ll stick my neck out, sounds like you may have a couple of plug wires swapped.  Double check your firing order 1-3-4-2 counterclockwise. 

[PercyUK]

Hiya, all checked and fine, thanks

[scoutpilot]

What is the condition of the distributor?

[PercyUK]

Hi its brand new, I replaced it with a good quality points one as I couldn't test the one that came with it which was electronic.
I have just stripped and cleaned the pcv valve and found that it had been assembled incorrectly in the past. Hopefully I can test it today.