351w backfiring, will not idle

[Speed3guy]

Hey everyone I have a 1987 Prostar 190 with the 351w. It has electronic ignition and a larger cam. Due to the cam it idles 800-1000rpm. It has run excellent for years but recently it started chugging and backfiring coming off of mid-full throttle to idle. I put new spark plugs in it along with a fresh fuel filter. I always use 91 octane fuel in it, non-ethanol. It will rev quick and run great above 22000 rpm but will not idle for anything. I've tried adjusting the idle on the carburetor with no luck. First thing that comes to mind is the carburetor needs rebuilt. Any ideas? Thanks.

[88 PS190]

Vacuum leak?

[d2jp]

I assume you set the new spark plugs to the proper gap-.035?

Re: idle adjustment - did you try to adjust the idle speed (single screw) or the idle air mixture screws (2 screws, 1 located on each front side of the carb)?

If the carb has never been touched and is the original, a rebuild would be beneficial regardless.

[Speed3guy]

Thanks for the responses. I did gap the plugs correctly. I set the idle adjustment at the beginning of every season. I tried to adjust the idle mixture screws also as it is just dumping fuel. The engine is not stock, it is cammed, aluminum intake, holley double pumper automotive carburetor.

[Gamble]

Carb job.......do that first.

[barneyferd]

I'd look at the underside of your distributor cap too. The points can get corroded or worn. Happened to me on my 2003 Response.