Newbie needs timing and mixture advice for LA360 engine, please.

[David Womby]

I need some VERY basic advice. Keep the explanations simple, please, because I am a complete newbie to V8s and 4bbl carbs. My engine experience before has only been on Jaguar L6 EFI engines.

My car (1964 Bristol 408) has the following installed:

1978 Monaco 360 engine.
Mopar Performance Cam 4452761.
Summit Racing Carb SUM-M08600VS.
Distributor Pertronix PNX-D141701.
Coil Pertronix PNX-45001.

The exhaust manifolds are stock iron castings.

The car runs fine at all speeds. It lopes more loudly at idle than I would like but I think that's due to the cam. My main problem is it uses a lot of gas (less than 10mpg) and the exhaust smells of it. I assume it's too rich but I always was taught to make sure thhe timing is right before adjusting the mixture. So, here's my questions:

1. What should the timing be for that cam and distributor combination?
2. How do most folks set the mixture on these carbs - vacuum gauge or by ear based on revs or what?

Thanks for any help.

David

 

[66 Sat]

Mate I'm no expert here but nobody has chimed in yet so I'll start:
1. Timing I think should be about 10- 12° initial and 36° all in - I think.
2. Carb - can't help sorry, I have a local guy who does all my tuning for me. I do need to learn though so I'm interested in the other responses.

 

[72sunroof]

I need some VERY basic advice. Keep the explanations simple, please, because I am a complete newbie to V8s and 4bbl carbs. My engine experience before has only been on Jaguar L6 EFI engines.

My car (1964 Bristol 408) has the following installed:

1978 Monaco 360 engine.
Mopar Performance Cam 4452761.
Summit Racing Carb SUM-M08600VS.
Distributor Pertronix PNX-D141701.
Coil Pertronix PNX-45001.

The exhaust manifolds are stock iron castings.

The car runs fine at all speeds. It lopes more loudly at idle than I would like but I think that's due to the cam. My main problem is it uses a lot of gas (less than 10mpg) and the exhaust smells of it. I assume it's too rich but I always was taught to make sure thhe timing is right before adjusting the mixture. So, here's my questions:

1. What should the timing be for that cam and distributor combination?
2. How do most folks set the mixture on these carbs - vacuum gauge or by ear based on revs or what?

Thanks for any help.

David

The all in timing needs to be 34 to 36 without vacuum advance attached at 2500 rpm
You need get a vacuum gauge and see how high you can get it at idle by leaning the idle circuit out. You turn the screws in a quarter turn at a time until the vacuum starts dropping then turn them out till it stop going up...
Clean all your plugs or replace them please number each plug to the cylinder , if you replace keep the old ones, drive the car then pull all them and "read" them they should be tan not black not white.
Here is detail on how to fully read the plugs
http://members.uia.net/pkelley2/sparkplugreading.html
Then adjust jets if needed. Always go up or down 2 jet numbers.
Also 10 may not be far off from the mileage with your set up.

 

[David Womby]

Mate I'm no expert here but nobody has chimed in yet so I'll start:
1. Timing I think should be about 10- 12° initial and 36° all in - I think.
2. Carb - can't help sorry, I have a local guy who does all my tuning for me. I do need to learn though so I'm interested in the other responses.

Thanks. All help is appreciated!

David

 

[David Womby]

The all in timing needs to be 34 to 36 without vacuum advance attached at 2500 rpm
>
>
Also 10 may not be far off from the mileage with your set up.

Thank you. Very helpful but a bit depressing if 10mpg is the best I can do. However, I can live with it as the car is driven only for fun and weekends.

David

 

[Moms68]

Thank you. Very helpful but a bit depressing if 10mpg is the best I can do. However, I can live with it as the car is driven only for fun and weekends.

David

I’d check the plugs as others have suggested. Sounds like way too much fuel or not enough timing.
I have a 340 in my B body and it does amazingly well on gas. I switched to a Quick Fuel 650 a few years ago…had a Demon before that.

 

[Master Gunner]

Always tune for the highest vacuum possible, going back and forth until there is no more gain, then richen about 1/8 to 1/4 turn on both sides. Recheck and confirm your timing. Your carb and cam should work well together, but probably could use exhaust work. You stated you have factory manifolds, but not if you have dual exhaust. Even with the "log" manifolds a true dual exhaust system would really help your motor breath better,
and you might find a mile or two per gal increase.

Mark

 

[David Womby]

I’d check the plugs as others have suggested. Sounds like way too much fuel or not enough timing.
I have a 340 in my B body and it does amazingly well on gas. I switched to a Quick Fuel 650 a few years ago…had a Demon before that.

Thanks, I'll do that.

Always tune for the highest vacuum possible, going back and forth until there is no more gain, then richen about 1/8 to 1/4 turn on both sides. Recheck and confirm your timing. Your carb and cam should work well together, but probably could use exhaust work. You stated you have factory manifolds, but not if you have dual exhaust. Even with the "log" manifolds a true dual exhaust system would really help your motor breath better,
and you might find a mile or two per gal increase.

Mark

It has dual exhausts. 3.25" I think. No catalytic converters and a single simple muffler on each pipe.

David

 

[David Womby]

I’d check the plugs as others have suggested. Sounds like way too much fuel or not enough timing.
I have a 340 in my B body and it does amazingly well on gas. I switched to a Quick Fuel 650 a few years ago…had a Demon before that.

 

[David Womby]

I didn't have much time today but I pulled the plug from #1. It looks ok to me.

David