Help, cant get it to idle

[1BAD68]

Swapped my old 340 cam for a Comp Cams XE275HL in my 318.
The engine ran fine before, fired up with no choke instantly hot or cold and idled great. I didn't change anything on the edelbrock 1407 carb in fact it came off with the intake in one piece.
I did a normal 20 minute cam break in at 2000 rpm and all that, everything good.
Now here's the problem. ..
It seems to run good but it's like when it transitions from high idle to the idle circuit, it drops so low that it just kills the engine. For example I can set it at 1100 rpm and its fine, then I turn the idle screw out and it will just drop from 1000 to 500 and stumble then die. Also, when idling at say 1100 and putting it in gear will make it drop out and die.
I checked for vacuum leaks, reconnected vacuum advance, adjusted timing, took carb apart and cleaned, mixture screws, etc but no difference. I'm stumped.   

[Charger-Bodie]

Vacuum leak?

[1BAD68]

I checked for vacuum leaks but none found

[Charger-Bodie]

It would only be if it were sucking oil in from from the lifter area.

[BSB67]

I checked for vacuum leaks but none found

How did you check?

[Charger-Bodie]

I checked for vacuum leaks but none found

How did you check?

Ran out of things to check. Pulled the intake ,found oil in a couple runners in the head.


Is there a good way to check for that?

[1BAD68]

I checked for vacuum leaks but none found

How did you check?

I used propane. Symptoms are a lot like a vacuum leak so is there a better way?

[1BAD68]

Used a smoke machine today, found a small leak at the corner of the manifold. Sealed it up and seems better, it will idle fine at 800 like it used to although it has a definite lope to it.
Still dies when pit in gear 

[BSB67]

Used a smoke machine today, found a small leak at the corner of the manifold. Sealed it up and seems better, it will idle fine at 800 like it used to although it has a definite lope to it.
Still dies when pit in gear 

put you hand over the carb.

[1BAD68]

put you hand over the carb.

Okay... now what?

[c00nhunterjoe]

Post the cars reaction. Does it instantly die? Does the idle raise slightly before it dies?

[1BAD68]

Dies instantly, I'm guessing too rich?

[1BAD68]

So I can adjust the mixture screws 3 turns out and set idle at around 800, then when I put it in gear the idle only drops 100-200 rpm and doesn't die but... If its sitting in park the rpms gradually go up to around 1200-1400 or so.
If I lean it out, it just dies when shifting into gear. I'm so frickin baffled I'm ready to park it for winter.

[firefighter3931]

Try bumping up the base timing and see how it responds. That cam is quite a bit bigger than a stock cam and will reduce idle vacuum making carb adjustments more challenging. 

My Guess is that the base timing is set too low and this engine combo wants more spark lead. 


Ron

[BSB67]

Dies instantly, I'm guessing too rich?

No.  Dies instantly - likely no leak.  Slight increase then dies, vacuum leak.

[69wannabe]

Ron beat me to it, it's gonna have to have alot more initial timing at idle to keep up with that size cam. Maybe start at 15 to 18 degrees BTDC and work with the carb from there. It's sad to say but that 1407 eddy carb not the best choice for a performance carb. Maybe time for a good holley double pumper or a good proform!!!!

[1BAD68]

OK I tried more base timing as well as less timing and it doesn't improve, I'm leaning towards it being maybe a mechanical problem.
My old cam had a gross valve lift of .440 and tapped lift of 260. New cam has gross valve lift of .525 and tapped lift of 275.
Could the pushrods be the wrong size? I have the magnum heads which have 1.6 ratio ratio rocker arms vs the 1.5 stock rocker arms, could that be part of it?
Could the valves not be closing all the way or something?
I took it on the street last night and gave it a little, it had no power and made an unusual  "BWA BWA BWA BWA BWA BWA" sound from the exhaust like half the engine wasn't firing.

[1BAD68]

I measured 7.65 for pushrod length, if I add .030 for preload it's 7.68.
I broke the cam in using 7.60 pushrods then replaced with 7.70 I know thats not exact but I had those in hand and the book says .02 to .06 for preload. Should be ok right?

[firefighter3931]

I measured 7.65 for pushrod length, if I add .030 for preload it's 7.68.
I broke the cam in using 7.60 pushrods then replaced with 7.70 I know thats not exact but I had those in hand and the book says .02 to .06 for preload. Should be ok right?

As long as the hyd lifter plunger is not bottomed out you should be fine. the .020 -.060 spec is correct 

Did you modify the heads for the increased valve lift ? Change the valvesprings ? Measure retainer to guide clearance and coil bind ? Piston to valve clearance ?

Lots of things can go wrong when upgrading to a bigger cam and care needs to be taken when making those changes 


Ron

[1BAD68]

I bought the heads assembled. They're EQ magnum heads 62cc and they advertised these as good for up to .600 lift.
My cam must be off a degree or something because no matter what I do there is pretty much no change. The idle surges, plugs are sooty, it has no consistent rythym in the exhaust. It fires up instantly like it always did though.
Well looks like I'm ripping it apart again 

[firefighter3931]

Before tearing it apart run a compression test to see how things stack up. If you have a bent valve or some mechanical problem it will show up in the test results.

Was the cam degreed in ? If so, what was/is the installed intake centerline ?

Have you checked the idle vacuum reading ? How much manifold vacuum is it producing ?


Ron

[1BAD68]

I didn't degree the cam.
Compression test will be first on the list tomorrow, don't know why I didn't think of that.
Thanks

[1BAD68]

Here's my compression readings over the lunch hour. Took these dry/wet, engine was cold.

#1. 175/175
#2. 124/134
#3.151/160
#4. 161/165
#5.132/150
#6. 167/172
#7. 154/155
#8. 150/155

[firefighter3931]

Here's my compression readings over the lunch hour. Took these dry/wet, engine was cold.

#1. 175/175
#2. 124/134
#3.151/160
#4. 161/165
#5.132/150
#6. 167/172
#7. 154/155
#8. 150/155

Those numbers are interesting ; #2 & #5 are lower than the others 

The proper way to test is to bring the engine up to operating temp. Try warming it up and perform a wet/dry retest and see what you come up with.  Make sure the throttle is wide open and disconnect the coil.

It could have a valve seal issue on those two weak cylinders or it could be rings....



Ron

[1BAD68]

Good news, bad news.

The good news, I decided to clean up the plugs before putting them back in so I could see if it was running rich/lean while warming it up.
Noticed the little ends of the plugs that the wire snaps onto was loose on around half of them, tightened all of them and installed. Fired it up and it was idling smooth, no surging and even had a nice rhythm to the exhaust. So I decided to take it for a test drive, it has a bog off the line when you really put your foot into it but otherwise pulls nice and strong. Pretty much all the symptoms are gone.
I pulled all the plugs and wanted to recheck the compression but ran out of time. But they are all a nice tan color, I'll have to warm it up and recheck compression later today.

The bad news, there really isn't any except that I am kicking myself for not noticing the plugs earlier. I spent hours trying to figure this out. Thankfully Ron, I took your advice and didn't start ripping it apart again.

[1BAD68]

I uploaded a video of the new cam...

https://youtu.be/iLmD6KJhb9Y

I love seeing the looks on people's faces when I'm sitting next to them at the stoplight 

[firefighter3931]

That sounds great ! 

Glad you found the issue....it's often the simple things that we overlook that come back to bite us in the azz 

You sure that's a 318 ?  Sounds like a mean 440 


Ron

[c00nhunterjoe]

Sounds good. The bog can be eliminated with tuning. What carb is on it again?