jaredi

I've got an Edelbrock 750 manual choke (1407) on a Performer RPM intake with a 234/234 .488/.488 cam on a 350 thats been punched .040 over and estimated 9.7:1 static compression.

The car seems to run pretty good under any decent amount of throttle, but at idle and just higher, it gets a bad bad miss. Sounds like its running on 5 cylinders. Add throttle, just enough that it is accelerating and it will run fine but as soon as you back your foot out of it just a hair, starts missing again.

I took it down the road and had it in third gear and under light throttle it was missing and carrying on so I downshifted manually and brought the revs up over 3000 and tried to maintain speed and it started missing and cutting out even at RPM.

I changed the plugs today thinking that could be the problem. I'm running Delco R44TS. The R45TS that I pulled out were a shade darker than tan.

Where should I go from here?

Thanks,
Jared

Apeiron

Is it a new carb?

gapimpin

had the same problem with my 1406 600cfm edelbrock... it was running rich but once i changed the rods back to stock size and put some blue springs in it everything was ok.

jaredi

It is not a new carb, it was on the engine/trans wen I bought it. I rebuilt it already, which it needed. The guy I bought it from acted like it ran good when they had it running.

There for a while it was acting fine but now it's doing it again and I do not know what I changed to make it start acting bad again. I've played with the idle screws to no avail...

I think my step up springs are red and I have no idea what size metering rods are in it.

Apeiron

Does it still run if you turn the mixture screws all the way in?

jaredi

Oh no, I can kill it with the mixture screws.

I changed the step-up springs today and it had the red/orange/rust colored ones in it. Here are the results:

Pink - Not much difference.
Blue - Seemed to like them, noticably better.
Gold(?) - About like the blue.
Natural finish - About the same as Pink.

The rods have 7147 stamped on them.

Apeiron

How did you set the idle mixture?

jaredi

Set the idle mix by screwing them all the way in then backed out 2.5 turns and hooked up a vacuum gauge.

I'm not getting any more than 10-12" no matter what. Vacuum practically does nothing but fluctuate between 10-12" all the way to 6 turns or so but at that point it burns my eyes so I've got it at about three turns out right now. It doesn't burn my eyes and pulls 10-12ish inches so I decided to leave it be. When I was adjusting it, it seemed to have little to no effect on the problem. If you think it is worth trying I'll go and fiddle with it some more but whatever I did before with it seemed to have little bearing on the missing.

Should I be pulling more vacuum? I think even with that cam I would be able to get 15 or so out of it...

Thanks

gapimpin

whats the lsa on that cam? im running a 503/510 224/230 112lsa and im getting around 18hg constant... sounds to me like you need to do a tune up... plugs wires cap rotor and if that doesent work you could reset valve lash... i had mine too tight when i first installed my motor and the valves hung open to the point i was only getting 1o-12hg out of it.

Apeiron

How well did you clean it when you rebuilt it?

jaredi

LSA is 114°. It is Summit cam 1106. Yeah I know I know... I didn't buy it.

Cap/Rotor/Wires/entire distributor/Coil are all new. I ohmed the wires out and I wasn't sure how to use the ancient ohmmeter that I had but I was able to determine that they're all fine or they're all shot to hell

When I rebuilt it I sprayed almost three whole cans of Gumout carb cleaner through it. I sprayed it through every hole I could find in the thing. The only thing I didn't do was blow air through it. I thought perhaps I should have just bought the bullet and got a whole bucket of carb parts cleaner but decided against it because I didn't know if there were small pieces that I hadn't taken apart that could be damaged by the parts cleaner.

Also, I suppose my valve lash could be out a bit because I've never adjusted them with it running, but would it allow it to run perfect at higher throttle load if the valves were too tight?

Apeiron

Right now I'm thinking you've got something plugging up an idle circuit.

jaredi

That is possible because when I did rebuild it, it was full of crud and rust. It had rust all in the bottom of the bowls, covering the jets completely. I've never had a carb before and didn't know where the jets were. I had to find a picture of one on the intarweb before I realized they were all obscured by the rust that was built up.

So think I should pull the carb off and soak it, or would pressurized air do the trick? If I'm thinking correctly all I will need is the air horn gasket correct? Or is this necessary since the gasket is only ~2 weeks old?

Apeiron

If the gaskets are new, chances are you'll be able to reuse them all. Take the whole thing apart, soak the body and the pieces overnight in carb cleaner, and rinse them out well. Use a can of carb cleaner with the plastic straw, and/or compressed air to blow out every passage and tube before you put it back together.

You used the 1477 rebuild kit originally?

jaredi

Yes I used kit 1477 about 2 weeks ago trying to solve this problem. Maybe I'll be able to find someone with a bucket of carb cleaner instead of shelling out ~$20 for the stuff.

Fun stuff. I'll do that tonight hopefully and get back with results.

Thanks for the advice.

Apeiron

You can get a gallon of CRC Tyme-1 carb cleaner for around $30, it'll last you a looooong time.

jaredi

OK So I soaked it in Berryman carb cleaner for a couple hours and presto, most of the cars problem is gone. There is still a hint of stumble there but it is a.) not bad at all and b.) possibly caused by a vacuum leak because I heard one while I was driving.

I never realized just how big that carb is. I'm in a search for a pan that is both large enough to fit the carb in and small enough so that the liquid will cover the carb entirely. Once I get something that fits that bill I'll take it apart and soak it again to be sure I got it all and replace the carb gaskets.

But first I gotta fix another problem tat just sprung up.... Header gasket let loose last night when I test drove it. LOL.

Thanks for the help guys