The Dodge Challenger Message Board

Greetings all! I have been reading many posts on this board and find you all extremely knowledgeable! It is great to have a forum like this. I have a 1970 with a 340 replacing the original 318. It has a Holley carb and a recently installed rebuilt 904 transmission. I understand the basics about engines, but have not had a lot of experience doing the work. I believe the engine is running very rich. I smell it while I am driving. I just picked up new points and condenser today, but I am thinking I may need to find some help to make sure the timing is correct. Might there be another cause to the rich running? I car usually coughs a couple times after turning off the ignition (not cool) and it pings pretty bad when under moderate to heay acceleration. I have been running premium fuel and lead additive. What advice do you have?

Adjust the timing to 10 degrees advanced. Make sure your vacuum advance is working or better still install an electronic ignition system and do away with the points set-up (mine cost me US$80 second hand).
I no longer use the lead replacement additive to my premium fuel. As it was described to me, it's like making a dilluted 2 stroke mix, will foul your plugs and is never going to replace the lubricating qualities of lead. I'm addressing my situation once and for all by having the heads rebuilt with stainless steel valves and hardened seats. While I appreciate that not everyone will do this until necessary, I have had no apparent problems running mine to date without the additive and only use high octane premium unleaded - never the premixed "lead replacement' fuel available as this stuff fouled my plugs within 2000 miles.
Have your carby checked for mixture, choke slightly sticking on etc. This is the most probable cause for the rich smelling exhaust. Pinging is usually down to timing. Hey - I'm no expert either (as the other MB members know) but this is my opinion for what it's worth. Cheers...

There is quite a bit on this board about tuning carbs if you want to learn how Mike. The other way is to find a place with a 'rolling road' dynometer that can tune your carb mixture not only at idle but also when driving.

There are four or five mixture bits to tune on the carb. First you have to tune the idle mixture and engine speed. Then measure vacuum and check the power valve rating. Then you have to set the correct jet size on the primaries. After that the jets on the secondaries. Finally you have to make sure the accelerator pump squirter is the right size.

If you break it all down to one step at a time it is not as complicated as it sounds. You just need to get your head around how each bit works.

I would start with adjusting the timing to 36-38 degrees at 3000 rpm. (I have tried to set the timing at lower rpm´s but without any good result). If that doesn´t work, I would go on with tuning the carburator. Good luck!

Christer is talking about total timing there and not initial timing Mike and it is not going to effect your mixture if the carb is set rich.

(Message edited by roppa440 on August 07, 2003)

Other things to consider (Basics I guess, but worth mentioning):

1) Are the spark plugs/wires ok (Do all of the cylinders get a good spark)? A simple way to check if the engine is running on all the cylinders is to feel on all of the headder tubes one by one (bleech your finger with water and CAREFULLY touch the headder tubes one by one for instance. Then you can watch the small water marks on the headders and see how long time it takes for them to disappear) and then compare how fast the different tubes get hot after you start the engine. If there is an obvious difference in heat between different tubes you might have a problem with one or several cylinders not running properly. (This check method does not work if you run cast iron manifolds or at least it is harder to feel/see the difference)

2) Are there any vacuum leaks around the intake or somewhere else? If you pour a small amount of liquid (I am not sure if water is ok. Dave?)on the place where you think you have a vacuum leak, and you notice a difference in the engines rpm, you may have a vacuum leak at that place.

I hope this makes sence to you.

I meant moisturize (NOT bleech). Sorry!

A bad vacuum leak can make the power valve open in the carb making it rich. A bad leak usually results in the rpms going up and down by themselves. Other vacuum leaks can make the carb leaner rather than richer.

But all this is just guess work. It might just be a leaky gasket in the carb dripping fuel in or it might just be something simple like the idle mixture screws too far out. Only YOU can tell. We can only guess.

A good way to see if you have a vacum leak I have found is to cup your hand over the top of the carb while the car is running if the idle picks up then most likely you have a vacum leak but if it dies out right away then most likely you don't. You don't want to close off all the air when doing this but most of it.