Need carb and/or timing help

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shadango

shadango

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Have been fighting with my fish (318) for a while now.....

My problem is an erratic idle.....from what I was told the engine was rebuilt 10-15k ago to stock specs, except for a double roller timing chain, internally. It has an edelbrock performer intake manifold and an edelbrock performer 750 cfm (#1407) 4v carb, electric choke (which is working).

The car has a brand new engine wiring harness, electronic control unit, voltage regulator, ballast, coil. All have checked out after being tested.

Also, a reman distributor with new pickup and reluctor was installed yesterday.

Checked for vacuum leaks and found none....

Compression is about 145 when hot acorss all cylinders and the yseem to hold compression.

Timing when I got the car was set at a huge 18* initial.......I tried setting total timing to 38*, which left the initial timing at around 14 I think it was.

At 4, 6 8 & 10 degrees initial timing the idle doesnt change much but the throttle response is HORRIBLE......very boggy.........so I bumped it back up to around 10-12 * and the reponse is somewhat better but still boggy and the idle is the same.......

SO, figuring ignition and timing is ok, I moved on to carb.

I found that the IMS didnt have a huge affect on the idle....found that could be due to too high idle rpms, so I made sure it is at around 800 in park at idle. I can get a very small change to happen with the iMS screws but the engine still idles poorly.

First tried going from the orange springs for the metering rods to blue. No change....then went up to the pink springs and no difference I could percieve.

One other thing I noticed that it is doing....it idles rough and lumpy and at about 800 rpm.....if I gas it a few times the rpms stay high , around 1300-1400....if I tweak the throttle screw back just a hair the rpms drop right back down.....(and the linkage isnt binding or anything)......

Manifold vacuum at 800 rpms is measuring 4-5" hg .......when I drop it into gear, rpms go to 400-500 and like 1" HG of manifold vacuum...........the engine just wants to die....

I feel like I am going in circles....

Was thinking about checking the float settings but I cant find the gaskets locally and have to order them...not sure if I could pull the airhorn assembly and check the floats and jets etc and then reassemble without new gaskets or not.,

I just feel like I must be missing SOMETHING.....

......could my control module be hooked up wrong somehow? The (new) wiring harness I have had plugs for the 5 pin control unit and the 4 pole resister......I figured if I had any of that stuff wrong it wouldnt run at all...

Any ideas?
 
Seems as though that is either not a stock cam or it was installed one tooth retarded.
 
Your vacuum should not be that low unless you have some serious cam. I would double check for leaks. Does'nt take much & could just be loose carb,misplaced fitting or vacuum line prob. Are you running vacuum advance & is it a stock distributor or mopar performance. You need to know the advance built in to your dissy.

Oldschoolcuda
 
Don't pick a timing mumber using total and accepting what the intiail turns out to be. That's ***-backwards. Set you intial to what the engine wants, not want someone on here tells you it should be. Do it with a vacuum gauge, highest reading at the desired constant idle speed. Find the highest point, back it off 1", and lock the distributor down. Get your initial timing reading with a light.

You'll probably have to limit the mechanical advance in the distributor.

Then adjust the carb to highest vacuum reading, leanest setting.

The big idle drop could be a vacuum leak, primary throttle blades too far open. Any number of things.

If you think you may have a vacuum leak, take everything that drags vacuum from the carb/manifold and plug it. Car runs better, you know it's something that is hooking up to the carb/manifold causing an issue. Localize the problem.
 
Sure sounds like a vacuum leak. My set up just did the same thing; it was a carb stud set too high.
 
Thanks guys.

Well, I decided earlier to go ahead and pull the carb top off and check the bowls etc.

The primary jets were hard to read but I think they were the correct ones....numbers were hard to read.... the carb is using the out-of-the-box jetting (.113) and rod (071x047). I swapped out the jets for the other set I have just in case.

Was hoping to maybe find bowls full of dirt, crap or something.

No such luck.....a little dirt in the very bottom but nothing crazy.

What I did find was that the floats were way off. The drop is supposed to be 15/16" to 1" and they were at like 1 1/2". The rise was off too...way off.....SO I set the rise at 7/16" and that brought the drop into spec.

Put the orange springs back in and bolted everything back up.

Checked the flow from the fuel pump while it was off...seemed strong enough....

ALso set the accelerator pump to the first hole (lowest setting) instead of the highest......the off-idle bog seems to be almost gone.....

The idle is still lumpyt and the engine still gives a strange shake now and then......but I am pretty much able to keep the engine idling in drive (so far)......its very low idle, about 400-500 rpm......If I set it any higherm, then it is too high in neutral...

Took the car out for a spin and the off-idle power is still bad......not bogging this time....more like just no power....but if I baby it off idle and get it to midrange and up it goes pretty good! Also doesnt seem to vibrate quite as much as it did.

I have been all over it looking for leaks.....there are only a few vacuum ports on the carb:

-- pcv valve, and that hose is ok.
-- hose to distributor, and that is new
-- manifold vacuum prot is capped off (even replaced the cap to be sure)
-- rear brake vacuum port is plugged.

I have sprayed brake cleaner and carb cleaner around the manifold mounting areas and along the carb base, etc....NOTHING.

The advance is stoxk as it is a reman stock distributor.

I very well might have a cam in this thing and that could explain the rough idle.....I have been wondering if, as ramcharger suggested, I have a cam or if what is in there is a tooth off....guess the only way to find THAT out is rip the front of the motor apart and look for the timing marks, right?

Crackedback, will try your suggestions......I did look at vacuum when I was setting timing this last time...didnt seem like changing timing did much.....?? Only way to get more vacuum was to bump up the throttle speed.....

Someone suggested that because of my low vacuum I need to plug the air bleeds for the idle circuit and that will bring my idle back....

Anyone have a picture of where these would be on a Edelbrock 1407?
 
Checked the flow from the fuel pump while it was off...seemed strong enough....
You need a gauge.
Stumble off idle- are the throttle plates showing more than .040 of transfer slot at bottom? you may be not using the idle circuit.
Pull it and turn it upside down and check. If your curb stop idle shows more than .040; you need to drill holes in the front primary plates. Start at 1/16"
 
I just found that the grommet for my pcv valve is torn......leaving a gaping hole and it was sucking some air........So I pulled the hose off the carb and plugged it...didnt change much but glad I found that.

( Its a mopar performance cover......which by the way is seeping oil THRU the cover...like it has a hairline crack or something....I'd do it now but have no new cover gaskets....... :stomp: )

green1...."transfer slot"...ok, this newbie is lost.....is that just the gap between the primary plates and the side of the barrel?

What I think is strange is how the idle gets "stuck" up high and then if I tweek the throttle screw out just a hair it drops down.....if I try it by hand, it doesnt work as fast.....maybe I have some bindage somewhere I am not seeing?

I have a fuel pressure test gauge....but I need to pick up some connectors etc to hook it up....

I
 
green1 said:
Checked the flow from the fuel pump while it was off...seemed strong enough....
You need a gauge.
Stumble off idle- are the throttle plates showing more than .040 of transfer slot at bottom? you may be not using the idle circuit.
Pull it and turn it upside down and check. If your curb stop idle shows more than .040; you need to drill holes in the front primary plates. Start at 1/16"
Click to expand...

Hey green....I installed a fuel pressure gauge inline.....I am showing 6.5-7 psi at idle, and it gets a little erratic when the idle drops real low.....

edelebrock says the pressure needs to be no more than 6 I think, 5.5 ideally. So either the gauge is wrong or my pressure is too high.....I may pick up a regulator at pep boys and try that. But if it were the pressure being too high, wouldnt it want to flood out?

As it stands, it will idle in park at 800 rpms....if I rev the engine or touch the throttle, it jumps to 1200 or so.....and wont come back down....

In drive, it drops to 500 rpms....too low.....and wants to sputter bad off the line.....even a small pop thru the carb if I am not careful...if I baby the throttle and get to around 1200 rpms or so I can pull out and acclerate OK...still feels boggy but pretty strong.

Maybe this cam is just too big.

I havent measured the transfer slot at you suggest yet.....Can I pull the carb, check it and replace without a new base gasket? I am waiting for one to ship to me...its on backorder from edelbrock.

What does drilling the plates do.....let more air in, right?

Where should I set the throttle screw when I measure the exposure of the transfer slot?

And if I do drill the plates and it truns out that it doesnt help, what is the fix to go back? Would I need to replace the plates or could I safely JB Weld? Wouldnt want something breaking off and going into the motor.....
 
If you have ruled out vacuum leaks a big drop in rpm between neutral an drive is an indication of not enough initial timing. If you have a cam with a lot of duration 18 or more initial is not uncommon. Like previously mentioned you will have to limit the total in the distributor to keep it in the 34-36 range that sb open chamber heads like. This is where an aftermarket distributor like the mopar performance unit that has adjustable mechanical advance will makes tuning easy.
 
Make sure your timing is correct before you tune your carb. I think you need to go back and take a look at that reman distributor. It's possible the mechanical advance is kicking in at the ragged edge of where you're tying to set your idle (ie: the springs are too weak).

Here's an excerpt from page 4 of document titled, "Timing is everything":

By having the advance kicking-in at or below idle, the engine idle speed will tend to hunt or hang up to a higher speed as the timing kicks up and down. With an automatic, this problem is even worse, with idle speed and smoothness artificially boosted by the centrifugal advance. Toss it in gear and the normal pull-down of RPM also will take down the advance, retarding the timing and pulling the rug out from under the engine. All of these erratic idle woes are the reason to provide a buffer of a couple hundred RPM from idle speed for the centrifugal advance curve kick-in.

Here's a link to the entire document. Worth reading. http://www.jefframin.org/library/distributorRecurving.doc
 
green1 said:
Checked the flow from the fuel pump while it was off...seemed strong enough....
You need a gauge.
Stumble off idle- are the throttle plates showing more than .040 of transfer slot at bottom? you may be not using the idle circuit.
Pull it and turn it upside down and check. If your curb stop idle shows more than .040; you need to drill holes in the front primary plates. Start at 1/16"
Click to expand...

Alright.....I figured I have tried everything else, so would try this.

I took the carb off the car, took the top off, drained it....my transfer slots are like 4 x .040 or maybe more.........LOL....so they are very much exposed.

So I decided to drill it.

.......... removed , drilled and reinstalled the plates...1/16".

Got her all back together.

But, too late to let her run and test.....kids asleep upstairs, etc.....so just made sure she would start (she finally did once the carb got some gas).......couldnt tell much from the 30 seconds I let her run.

How much improvement should see? Or do I keep going up in size til it does make a diff?
 
70Duster440 said:
Make sure your timing is correct before you tune your carb. I think you need to go back and take a look at that reman distributor. It's possible the mechanical advance is kicking in at the ragged edge of where you're tying to set your idle (ie: the springs are too weak).

Here's an excerpt from page 4 of document titled, "Timing is everything":

By having the advance kicking-in at or below idle, the engine idle speed will tend to hunt or hang up to a higher speed as the timing kicks up and down. With an automatic, this problem is even worse, with idle speed and smoothness artificially boosted by the centrifugal advance. Toss it in gear and the normal pull-down of RPM also will take down the advance, retarding the timing and pulling the rug out from under the engine. All of these erratic idle woes are the reason to provide a buffer of a couple hundred RPM from idle speed for the centrifugal advance curve kick-in.

Here's a link to the entire document. Worth reading. http://www.jefframin.org/library/distributorRecurving.doc
Click to expand...

Yeah, I know timing needs to be spot on first......but I am not sure itst he reman distributor.....the car is acting about the same , timing wise and performance wise , as when I had the original distributor in there.....so not sure that is it.

Although I hear yat hat the stock mech. advance may be too early......probably should had waited and got the performace unit so I could have that adjustability to try.

I am hoping though that having so much of the transfer slot showing is part of the issue and that drilling makes a dent in the issue.

Cross your fingers for me....LOL:toothy10:
 
shadango said:
Yeah, I know timing needs to be spot on first......but I am not sure itst he reman distributor.....the car is acting about the same , timing wise and performance wise , as when I had the original distributor in there.....so not sure that is it.

Although I hear yat hat the stock mech. advance may be too early......probably should had waited and got the performace unit so I could have that adjustability to try.

I am hoping though that having so much of the transfer slot showing is part of the issue and that drilling makes a dent in the issue.

Cross your fingers for me....LOL:toothy10:
Click to expand...

I gan see drilling the blades for a running rich problem but not for idle problem. Imlike others here sounds like vac leak.
 
fishman said:
I gan see drilling the blades for a running rich problem but not for idle problem. Imlike others here sounds like vac leak.
Click to expand...

I had a similar issue with the 318 that I rebuilt in the Duster. Pretty mild combo, 4bbl intake and carb, Comp Cams 224/224 @.050 with *302* heads... Nothing major..

Basically, started the engine up once it went in and ran in the cam, ran OK on idle and then went put in Drive it would die. Event with idle turned up it was hard to keep it running..

I checked a fair few things whether it was the Carb or hose vacuum leaks. In the end did the WD40 trick around the intake and found I had a massive vacuum leak on drivers side intake. Off with the intake (crappy tin gaskets that were there) new set of Felpro composite gaskets and intake back on and she started fine..

I put bet that it's a vacuum leak issue...
 
I'd love it to be a vacuum leak...but I have sprayed several times and nothing.....

I do plan on doing it again today, though, as the carb was off last night for the drilling.
 
fishman said:
I gan see drilling the blades for a running rich problem but not for idle problem. Imlike others here sounds like vac leak.
Click to expand...

Apparantly its an old trick.......go to the bottom of this link and there is a picture of the tranfer slot and throttle blad as well a short explanation....there are many other references on the web to doing it....

http://www.carcraft.com/howto/ccrp_0507_carb_tuning_tips_tricks/carb_tuning_tips.html

The expousre of the transfer slot seems to be the key....my having to open the throttle more due to the big cam (assuming its a big cam) means that more of the slot is exposed which means more fuel.....

Drilling gives the carb the air it needs to idle without going rich...

I dunno......it may not work in my case....but hoping it does.
 
Well, not sure if there is a change or not to be honest......

Had some other distractions today (fuel regulator quit, starving me for gas)......but pretty sure I still have the same issues....alsthough, it seems like it wants to idle lower more often....

Noticed I am not shifting into 3rd when crusing....that may be due to he idle issue.....

Hope that a weekend at Carlisle will cheer me up,,,,LOL
 
Intake gaskets can allow vacuum leaks port to port . Those wont show up with external spraying. If you cup your hands down over the airhorn and the idle smooths and rpm goes up... theres your sign. The oppisite result from test rules out vacuum leaks.
 
I tried this and was able to stall the car out.....although I dont recall if the idle improved at all before stalling, so will have to try again.

I changed out the 750 eddy performer carb for a 600 and still no real change......so that would seem to rule the carb out....

Although I still have yet to try changing the rod springs out from orange to blue.....dont really want to drill the 600.....

I yanked the valve covers and confirmed I have J heads and non adjustable rockers....

DCP_0149.jpg


DCP_0148.jpg
 
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