Expected idle with a Purple Cam

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jabdusty57

jabdusty57

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I'm not looking to start a word war over which cam is the best to use. I know Lunati and Comp make great cams for modern builds. But I'm stuck with what I got for now - I can't afford to drop another $400 into my car for a new cam.

I'm restoring 70 340 Duster. No plans for the strip, I just want a fun street car. I want my wife and friends to drive it also so it's important she have street manners. I bought the car 18 months ago and have not driven it but maybe 100 feet. But I couldn't get it to idle respectively for sure. She would stall at anything below 1400 RPM which I doubt is right.

Since then I have rebuilt the carb, drained the gas tank (gas might been 8-9 months old), fixed a half-dozen engine wiring problems (possible shorts), replaced spark plug wires (a couple were shorting out to the exhaust) and I installed an HEI module and coil. I have not started it since because I still have a few more tasks to complete.

So here's my simple question: I looking for an educated guess - something for me to aim for. Assuming I can tune the carb and set the timing halfway respectably, what could I expect to get the idle speed down to? Here is what I have:

340 bored 0.040 over
10.5 compression
MP 284/484 cam
4-speed
Eddy 1406 600 CFM
Eddy Performer RPM intake
Hooker long tube headers
 
I also have a purple cam in my 360 the 280-474 at first she had a shake hard to tune the fuel mixture in my Holley lol,once I got my timing right she settled down,I think that's were you need to go first timing is everything,what are your spec as for timing.My 360 Idles at 900 and no stalling.Your 340 is build stronger than mine for sure.Different animal but again its timing to tame.
 
I have used that cam several times in the past, in many of my old mopars, and there good cams for street use. That car properly tuned should have no problem idiling at 850 to 900 rpm. first get the timing right, and then adjust the carb.
 
Just like every body said. Timing is the first thing to do. 20 initial is a good place to start. I had the same problem with the 508 I have. Recurved the distributor for 22 initial and problem solved. Most problems are the timing.

Fred B
 
Timing has been a challenge. How do you tell what the timing is when the water pump housing hides the mark beyond about 12 degrees Before TDC? Do I need to buy a special timing gun?
 

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I had no problem with the idle , but when I had the car it had a different carb and that was prior to Brian touching it ? I'm not sure what he did ? The car ran great pulled very strong when I parked it ! It had a brand new electronic distributor new plugs wires carb intake and motor had 2500 miles at most . The only reason I stopped driving it was a leak in the gas tank . I had taken the carb off and used it and the coil on another car . I think Brian messed with wiring or fried some stuff when he put the carb and coil back on it because he called me and said it would not run and messed with it for days .
I'm sure the problem is timing and or carb both . I should have a chance to get the valve covers and pie tin to you soon . Have a blessed weekend !
Jim
 
Search "hillbilly timing tape" and my screen name.

Never buy a timing tape again!
 
jimmer said:
I had no problem with the idle , but when I had the car it had a different carb and that was prior to Brian touching it ? I'm not sure what he did ? The car ran great pulled very strong when I parked it ! It had a brand new electronic distributor new plugs wires carb intake and motor had 2500 miles at most . The only reason I stopped driving it was a leak in the gas tank . I had taken the carb off and used it and the coil on another car . I think Brian messed with wiring or fried some stuff when he put the carb and coil back on it because he called me and said it would not run and messed with it for days .
I'm sure the problem is timing and or carb both . I should have a chance to get the valve covers and pie tin to you soon . Have a blessed weekend !
Jim
Click to expand...

Yes Jim - we'll you better than others the struggles I've had with this. I have found and fixed a lot. Maybe it's time to fire her up again and see what a difference all the changes made. Happy Easter!

Rob - just got the headlight kit in today. It was a breeze with your instructions. Can't wait to see the difference. About ready to call it a day and go look at this timing tape thing.
 
Had the same cam in a 10.5:1 340 and it idled just fine @ 800 in a 4 speed car. Had it turned down as low as 700 to make it sound real choppy. Was it degreed and not installed straight up. Have seen this problem on the mopar cams if installed straight up..
 
I'd be checking for air leaks, if you have one your idle will be quite high. My 383 with Purple cam has a nice low idle - when it had an air leak at the booster it was up around 1400rpm.
Timing marks - I printed off a protractor off the net and used it to mark the harmonic in various positions.
 
Ok - I'm having a REALLY stupid moment. I see the Timing Tape on the link below. The instructions say BTC is always to the right of the stock mark and shows the tape marks moving counterclockwise wise around the balancer.

But look carefully at this picture of my engine. It says "Before" to the left of stock mark. And when I was able get the engine running at a high idle (which I'm sure included some mechanical advance), the timing mark was buried up under the water pump cover, way to the LEFT of TDC. Which way are the marks supposed to move when the timing is advanced? Surely my engine is not running backwards. :banghead:

[ame]http://www.jegs.com/InstallationInstructions/100/121/121-8985.pdf[/ame]
 

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Think clock face for the balancer. Balancer turns clockwise looking at it from front.

tdc mark at 12:00. The tape goes on with the btdc markings going towards 1:00.

The idea for a timing tape is using the 0 mark on your marker/timing cover. If you think about that, if you put your tdc mark at 10 BTDC on the balancer, where would the mark on your balancer be to use the 0 mark?

Read that post I linked, it explains how to mark your balancer at 15 and 30 BTDC.

The explanation in those instructions is correct, ATDC will be to the left of your mark, BTDC to the right. When advancing, the mark will disappear up under the water pump.
 
crackedback said:
Think clock face for the balancer. Balancer turns clockwise looking at it from front.

tdc mark at 12:00. The tape goes on with the btdc markings going towards 1:00.

The idea for a timing tape is using the 0 mark on your marker/timing cover. If you think about that, if you put your tdc mark at 10 BTDC on the balancer, where would the mark on your balancer be to use the 0 mark?

Read that post I linked, it explains how to mark your balancer at 15 and 30 BTDC.

The explanation in those instructions is correct, ATDC will be to the left of your mark, BTDC to the right. When advancing, the mark will disappear up under the water pump.
Click to expand...

Ah hah. Now I get it. Thanks.
 
The cam was degreed it ran fine before when I owned the car there was a middle man in between .
 
jimmer said:
The cam was degreed it ran fine before when I owned the car there was a middle man in between .
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I'm sure it's just a matter of me getting it right Jim. I really doubt the previous owner did anything to the cam. Good to know it was degreed. Like everyone said, I'll start with the timing and if that doesn't bring te desired result, I'll look into the carb. It was pretty nasty when I opened it up.
 
It my be running to lean that cam has a nice idle to it used to run it before I went to 284/528solid lifter wich still idles at 8 to 900 rpm just my 2 cents
 
Here is a link to a video I found on youtube. Shows tach at idle and a little exhaust sound also.

[ame="http://www.youtube.com/watch?v=7aE1uSTkYPo"]1968 plymouth barracuda 340 idle mopar purpleshaft cam, headers, vforce mufflers - YouTube[/ame]
 
I don't think he hurt the cam . I just know he robbed parts off the car and think he might have fried some wiring .
 
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