[updated:LAST EDITED ON 08-May-02 AT 08:07 PM (EST)]Greetings. I have a 1975 460 that I'm trying to get to pass smog. The smog test revealed that the truck is putting out high HC's at idle. I'm running propane only and I can smell some raw fuems comming from the tailpipe. I thought it might be the carb., which is new, out of adjustment. I pulled one of the plug wires off with the engine running but could not really tell much difference, no matter what plug I pulled off. Compression is mostly good. See post in 460 forum. If I pull two off then I can tell a real difference. I pluged in a spare plug into the lead and grounded it to the block. It seems to have a weak spark. Yellow not blue. You can't even hear the spark jump across the gap. I have the duraspark setup. Based on this information, can anybody give me an idea as where the problem might be? Coil or duraspark modual? Is there a test I can perform to narrow it down? I suspect the hesitation is just random cylinders not fireing due to the weak spark, which is why I get the raw gas smell out the tailpipe. But it seems to run fine down the road. The high R.P.M. part of the smog test passed with no problem. Any and all opinions welcome. Thanks for your help.

Forgot to mention: The distibutor looks like a regular points distributor. Looking at the shop manual there is a big differance. It has a regular cap and rotor. I suspect the last owner changed it for some reason. I don't know why he didn't go with what it came with. I only had the truck for about a month and a half. I will be changing it back. Can this also contribute to the weak spark? Thanks again.

 

[updated:LAST EDITED ON 10-May-02 AT 10:02 PM (EST)]Make sure you have about 9 volts at the + of the coil. Do you have points? Check and make sure they are good. I would just go ahead and replace them and the condensor. And I just found out something. I was using the later model duraspark coil with the smooth pin connections on one of my projects that had a points dist. I sold it and the new owner put a regular coil with the threaded connections on it, and it ran better. So it looks like you can't mix and match ignition coils. If you can get the duraspark system back up and running, do it. It will give you a hotter spark than the old points system.

 

Like Franklin says, if you have 9v at the postitive coil terminal, suspect the coil being bad; it may have shorted windings. If you have less than 9v at the coil, maybe 4-5v, then the problem is in the pink resistor wire coming from the ignition switch.