340 cam problems • The Dodge Challenger Message Board

by **1269** » 27 Jan 2006 2:17

I purchased a 71 340 for my 70 Challenger and the motor had just been rebuilt balanced and blueprinted with all the paper work to prove it. The only problem was it was in a boat.I have pulled all the marine parts and converted to auto exhaust manifolds water pump etc.When fired up which it starts right up and runs great at a high rpm but when you try to bring down to an idle it dies. I have tried different carbs and have adjusted the timing both retarded and advanced.I have looked for vac leaks and can find none.I have the specs on the cam from Iskanderian and the cam has a cam lift of .293 for intake and exhaust and a valve lift of .445 also for intake and exhaust.The intake opens at 24 before tdc and closes at 66 bdc the exhaust opens 60 before bdc and closes 30 after tdc.Can someone tell me if this cam is what is doing this to my motor or should I look elsewhere.

by **Sal** » 27 Jan 2006 3:46

Sounds alot like a carb problem to me. Would say check fuel pump, but the problem would be the other way around. I don't think its a problem with the cam. Try adjusting carb floats, if you havn't already and check voltage to distributor. Post back when you got it all figured out.

Sal
73/340/4spd

by **dave-r** » 27 Jan 2006 8:49

This is normal for a stock carb on an engine with a hotter cam.

Read my posts about carb tuning. You don't say what make carb it is so the cure will vary. But basically the idle circuits are not delivering enough air and fuel at idle.

The idle mixture screws can in most cases deliver enough fuel but usually not enough air. The simple cure on most carbs is to drill a couple of small holes in the primary throttle blades.

But some carbs have an adjustment that does the same thing.

Welcome to thw world of carb tuning. :wink:

by **1269** » 28 Jan 2006 2:09

I have a Carter 625 comp series and a holley 600 and both act the same way.I will try to adjust the mixture screws on the Carter which I did with the Holley with no luck.I will be honest I have never heard of drilling holes in the primary blades.Thanks for your responses.I will be at it again this weekend.

by **dave-r** » 28 Jan 2006 9:30

Performance Holleys have an adjustment screw that opens the secondary blades slightly. This does the same thing as the hole drilling. Don't know about the carter.

The thing is to get more air in. The bigger the duration the cam the more air you need at idle. Once you have enough air adjust the mixture screws to add the right amount of fuel.

This is where rich/lean indicators come into their own. They make carb tuning easy.

by **1269** » 29 Jan 2006 22:29

I unsrewed the mixture screws on the Carter almost all the way out and it went to and idle when fired. Thanks for your input.I am not a carb man at all if you havn't noticed.But the responses kept me on the right track. I will tune it using your methods on this site. Thanks again the 340 sounds and runs like champ.

by **dave-r** » 30 Jan 2006 9:04

Carters tune differently to Holleys. I'm not sure if by screwing the idle mixture screws out you have added more air or more fuel of what percentage of both. It has been at least ten years since I tuned a Carter and my memory is getting terrible.