Need some help.....swapped cams

-
MoparMagic0069

MoparMagic0069

Well-Known Member
Joined
May 27, 2011
Messages
56
Reaction score
22
Location
Spring Mills, Pa
I know everyone has there opinions on the 284/484 Purple Shaft cams, well my grandfather and I put one in my 71 Swinger with a 340 yesterday.....the 340 is out of a 68 GTS dart so it has really good compression and the "X" heads, it's bored 30 over as well and has long tubes on it. Well we got everything in started it up, it fired up instantly and sounded great. So after a little breaking in my Pap (who's done Mopars for over 40 years) went to set the timing so we could get the idle set....and now the problem, it won't idle. It has one of the edelbrock carbs that look like the original style carbs, well the air/fuel mixture screw on the drivers side does absolutely nothing....and the idle screw is so touchy! You barley turn it and the idle runs clear up to 1200, you barley move it the other direction and it falls and than shuts off. Any suggestions?....
 
First off, did you degree the cam, or line up the dots?

Second, you may have the throttle blades open too far. If you can close them and get the idle where you want, you'll need to do some other mods.


I will tell this. If that is the cam on the 108 or 106 LSA, it will need some work done to the carb to clean up the idle. Since it uses metering rods rather than a power valve, you have to make sure the metering rods aren't being pulled up because you have no vacuum.

There is a bunch going on here. You need to thin the herd by taking out 1 issue at a time. Like ignition timing. As much initial as you can get. The minimum I use is 10 in the distributor and 15 on the crank for 35 total. If you have to, pull some out of the distributor and put more on the crank. Then deal with the vacuum issue.
 
I ran the exact cam in a 360. Ran and idled perfect. I idled my car at about 800 rpms in park. It would idle all day at a stop light, no issues.
I think your issue is the carb. I would look no other place but the carb to start with.
 
318willrun said:
I ran the exact cam in a 360. Ran and idled perfect. I idled my car at about 800 rpms in park. It would idle all day at a stop light, no issues.
I think your issue is the carb. I would look no other place but the carb to start with.
Click to expand...


True.

But if they didn't degree the cam, they have no idea where it is. If it's straight up, that means it's running 1.5-2* RETARDED if the TC&G are brand new.

What if it's in 2* retarded where it's at?

He needs to verify ICL first. Then work on the tune up.
 
yellow rose said:
True.

But if they didn't degree the cam, they have no idea where it is. If it's straight up, that means it's running 1.5-2* RETARDED if the TC&G are brand new.

What if it's in 2* retarded where it's at?

He needs to verify ICL first. Then work on the tune up.
Click to expand...
I think if it's cam timing, it would be off a bit more to make it act up like he describes. Not sure 2* either way would kill it so dramatic as he is experiencing. Have an effect on how it performs? Yes.
First - I would start with the carb because it's a suspect, it's on top (easy to get to), cheap to tune. Perhaps I'd borrow a Holley that's known to run good and see how it responds.
Second - I would prove a cam lobe didn't go flat. That's free. Remove the valve covers, paint a white mark on the push rods, and see if the push rods rotate by watching the mark.
 
As for me I would just pull the distributor around until the rpm peaked and then back off the curb idle screw. This of course after I checked for a honking big vacuum leak! Like a cracked hose to the pcv, or the brake booster.
The unresponsive mixture screws tell the story; the blades are open too far. The too-far open blades tell the story that the idle timing is insufficient. The touchy speed screw tells the story that the Vcan may be activated, or the dropping butterflies are choking the transfers which are supplying fuel, to compliment the vacuum leak.
Happy hunting; you got 3 minutes! Clamp the hoses and....PULL!
 
AJ/FormS said:
As for me I would just pull the distributor around until the rpm peaked and then back off the curb idle screw. This of course after I checked for a honking big vacuum leak! Like a cracked hose to the pcv, or the brake booster.
The unresponsive mixture screws tell the story; the blades are open too far. The too-far open blades tell the story that the idle timing is insufficient. The touchy speed screw tells the story that the Vcan may be activated, or the dropping butterflies are choking the transfers which are supplying fuel, to compliment the vacuum leak.
Happy hunting; you got 3 minutes! Clamp the hoses and....PULL!
Click to expand...
Certainly sounds like vacuum, and I was assuming vacuum leaks to be part of the carb check.
 
AJ/FormS said:
As for me I would just pull the distributor around until the rpm peaked and then back off the curb idle screw. This of course after I checked for a honking big vacuum leak! Like a cracked hose to the pcv, or the brake booster.
The unresponsive mixture screws tell the story; the blades are open too far. The too-far open blades tell the story that the idle timing is insufficient. The touchy speed screw tells the story that the Vcan may be activated, or the dropping butterflies are choking the transfers which are supplying fuel, to compliment the vacuum leak.
Happy hunting; you got 3 minutes! Clamp the hoses and....PULL!
Click to expand...


That's what I'm saying. Butterflies are open too far. That's why I asked about cam timing. If it's retarded 3-4*'s or even more, the late closing intake will cause low speed reversion, which makes the carb 300% rich, so you have to crank the butterflies open to make it run and now it's even worse.

Like eating your tail...eventually you get to the.............................................crack pipe.
 
MoparMagic0069 said:
I know everyone has there opinions on the 284/484 Purple Shaft camslook like the original style carbs, well the air/fuel mixture screw on the drivers side does absolutely nothing....and the idle screw is so touchy! You barley turn it and the idle runs clear up to 1200, you barley move it the other direction and it falls and than shuts off. Any suggestions?....
Click to expand...

OOps, I missed the part about only one side not working. If one side does work, then The T-port sync may not be that far off.
So then you may have multiple problems.
Or it may just be a problem on the bad side of the carb. It sounds like the low-speed circuit on that side has gone AWOL. It may be that there is no vacuum problem at all. It sortof appears that the main on that side is working, cuz you did not mention an issue during the break-in. So I'm gonna guess that the problem is restricted to that one circuit.
Unless the valve lash is too tight...
 
im running that cam now, ive had it in 3 different engines in 4 years, it likes 20 initial and i put in fbo limiter plate for 34 total, holley wit 3.5 power valve , idles at 750 all day long, it was alearning curve getting it there though. ive always done dot to dot also, keep pluggin away and youll get it
 
Got the same (almost) exact cam in my 340. Also ran the equivalent cam in a 383. Never had any idle issues. But I always use Holleys too. It isn't all that radical a cam for a 340.
 
Alright sorry I was away today as for what we did for install, we lined the Dots up, the car ran fine before the cam, all you had to do was hit the gas one time for the electric choke and it fired right up and idled great, we put this cam in and it fired right up on the initial start, we got everything broke in then went to get the idle set and now have this issue. We have a carb on another 340 with the 284/484 cam that we know starts and idles great so I guess we are going to make sure the timing is set like you guys all said in other comments and put that good carb on it and see what happens...
 
MoparMagic0069 said:
Alright sorry I was away today as for what we did for install, we lined the Dots up, the car ran fine before the cam, all you had to do was hit the gas one time for the electric choke and it fired right up and idled great, we put this cam in and it fired right up on the initial start, we got everything broke in then went to get the idle set and now have this issue. We have a carb on another 340 with the 284/484 cam that we know starts and idles great so I guess we are going to make sure the timing is set like you guys all said in other comments and put that good carb on it and see what happens...
Click to expand...

Hopefully the cam was ground accurately, if playing around with ignition timing and swapping carbs doesn't do the trick you might need to tear down the front of the engine again and check the actual valve events with a degree wheel and dial indicator... I've heard that cam works better when it's advanced a bit anyways
 
MOPEkidD-3 said:
Hopefully the cam was ground accurately, if playing around with ignition timing and swapping carbs doesn't do the trick you might need to tear down the front of the engine again and check the actual valve events with a degree wheel and dial indicator... I've heard that cam works better when it's advanced a bit anyways
Click to expand...


Yup, should go in at least 2* ahead at a minimum.

The OP has no idea where the ICL is. As I said, if it's installed retarded, it will make it pig rich at idle because you have closed the intake later.
 
when my 284/484 was in 318, my electric choke on 670 avenger didnt always behave so well , usually had to feather it til it warmed up, on the 360 choke works just fine, and i didnt touch the choke adjustment at all, i believe i read somewhere if a cam was a bit too much for the dispacement there could be choke issues.just a thought.
 
Try unhooking the vacuum line on the distributor and see if it idles. If it is ok then your carb blades are letting vacuum to the distributor and advancing too much. There should be no vacuum at the distributor at idle. I had this problem with a larger cam and had to back the distributor timing off some so it would idle with no vacuum in the line. I just plugged the dist vac line for a while and it was ok. When I got time I played with the timming to get it about right so I could back the idle screw down some to close the blades so no vac to dist at idle
 
So last night we took my edelbrock off of my 340 and put the carb off of my Pap's 340, his carburetor has never been apart! EVER! It was on a 70 or 71 340 (not 100% sure anymore but its original to that engine), we put that one on and in a matter of 5 minutes it was idling fine. Got the timing set and everything and it idle great (choppy because of the cam but good), now another problem has shown itself haha with the other cam the headers didn't hit or anything but there wasn't a lot of room between them and the power steering box.....well now with the 284/484 Cam they like to hit the power steering box haha so now just see if we can get more clearance between them and get a carburetor redone for it and it "should" be all good.
 
MoparMagic0069 said:
So last night we took my edelbrock off of my 340 and put the carb off of my Pap's 340, his carburetor has never been apart! EVER! It was on a 70 or 71 340 (not 100% sure anymore but its original to that engine), we put that one on and in a matter of 5 minutes it was idling fine. Got the timing set and everything and it idle great (choppy because of the cam but good), now another problem has shown itself haha with the other cam the headers didn't hit or anything but there wasn't a lot of room between them and the power steering box.....well now with the 284/484 Cam they like to hit the power steering box haha so now just see if we can get more clearance between them and get a carburetor redone for it and it "should" be all good.
Click to expand...
As I thought in post 3, glad you found it!! Have fun.
 
MoparMagic0069 said:
So last night we took my edelbrock off of my 340 and put the carb off of my Pap's 340, his carburetor has never been apart! EVER! It was on a 70 or 71 340 (not 100% sure anymore but its original to that engine), we put that one on and in a matter of 5 minutes it was idling fine. Got the timing set and everything and it idle great (choppy because of the cam but good), now another problem has shown itself haha with the other cam the headers didn't hit or anything but there wasn't a lot of room between them and the power steering box.....well now with the 284/484 Cam they like to hit the power steering box haha so now just see if we can get more clearance between them and get a carburetor redone for it and it "should" be all good.
Click to expand...

A couple SMALL dents will take care of that problem.
 
You must log in or register to reply here.
-

Back
Top