Ok, So It Started but...

[Silverback]

the story so far:

http://www.7173mustangs.com/thread-help-me-get-this-thing-started

Well, I got it to start and sort of run, but not well enough to try to drive it. The basic problem is that it will start, but I can't get it to run consistently below 2000rpm. If I back of the throttle screw enough to get it below that it just won't stay running without constantly blipping the throttle.

Basics:

• 71 351C, supposed to be an M code but has 2bbl heads, weiand xcelerator manifold, edelbrock 600cfm carb and a mallory unilite distributor
  
• rebuit carb
  
• new plugs
  
• seeing 28* advance and 18" vacuum @ ~2100rpm
  
• New fuel pump, added an inline filter, new gas...
  
• Called edelbrock and they suggested to check
  
  could be a vacuum leak- spray simple green around all the manifold gaskets... Nothing (but the back of the manifold is leaking oil), vacuum seems like it might be OK for that rpm
  
• leaking needle and seat assembly in the carb (put new ones in),
  
• timing (again, 28* at 2100, that seems reasonable)
  

I honestly can't figure out what else to look at/try... thoughts/help?

 

[hyena429]

I think that manifold is too much for a stock 2v cleveland my self...I would'nt put a single plain manifold on stock build...that xcelerator manifold runs 2000-6500 rpm range , and they work best with at least a 9.5:1 compression ratio..at the very least.... and 280° or more of cam duration....Im going 450 horse in my cleveland and im not even thinking about runing a single plain my self.....but it should still idle...And its hard to tell vacuum if you can get it down low enough....I would give it a compression test....If you have a tester...If not...They are not expensive and good to have around

 

[Jeff73Mach1]

My single plane intake 4V low compression lots of duration and lift solid cam engine easily idles at 700 rpm, I don''t think it is the intake.

Check your cap and rotor and the condition of your plugs and wires.

 

[Totalled]

Sounds like a classic big vacuum leak. Check all around the ports on the carb. Edelbrocks have a threaded port on the back of the base that needs to be plugged, and isn't always obvious.

 

[droptop73]

Is the intake designed for 2v heads? if not you may have massive vacuum leaks.

 

[hyena429]

My single plane intake 4V low compression lots of duration and lift solid cam engine easily idles at 700 rpm, I don''t think it is the intake.

Check your cap and rotor and the condition of your plugs and wires.

Weidlands web site ....They dont recomend that manifold for any less compression than 9:50:1 and above..and 280 duration.....So if this is a stock 2v compression it will be only 8:1ish with less than 275 duration i think....which would be big time issues with runing on idle.......if its a 4v intake on a 2v cleveland...could be a issue....Plus 4v clevelands can use a single plane much better than a 2v......Im just saying...I think thats a bad match for a typical 2v cleveland..Unless that motor is built more than average with some milled head work...Its just a waste and cause you more harm than benifit....If he not runing enough compression it will be some big issues...and needing more throttle just to stay alive......But i would give it a quick compression check just to make sure something else isnt going on.

 

[marks73]

My single plane intake 4V low compression lots of duration and lift solid cam engine easily idles at 700 rpm, I don''t think it is the intake.

Check your cap and rotor and the condition of your plugs and wires.

Weidlands web site ....They dont recomend that manifold for any less compression than 9:50:1 and above..and 280 duration.....So if this is a stock 2v compression it will be only 8:1ish with less than 275 duration i think....which would be big time issues with runing on idle.......if its a 4v intake on a 2v cleveland...could be a issue....Plus 4v clevelands can use a single plane much better than a 2v......Im just saying...I think thats a bad match for a typical 2v cleveland..Unless that motor is built more than average with some milled head work...Its just a waste and cause you more harm than benifit....If he not runing enough compression it will be some big issues...and needing more throttle just to stay alive......But i would give it a quick compression check just to make sure something else isnt going on.

+1 to that. If you have verified you don't have a vacuum leak this would definetly be the next step.

 

[Silverback]

I think that manifold is too much for a stock 2v cleveland my self...I would'nt put a single plain manifold on stock build...that xcelerator manifold runs 2000-6500 rpm range , and they work best with at least a 9.5:1 compression ratio..at the very least.... and 280° or more of cam duration....Im going 450 horse in my cleveland and im not even thinking about runing a single plain my self.....but it should still idle...And its hard to tell vacuum if you can get it down low enough....I would give it a compression test....If you have a tester...If not...They are not expensive and good to have around

I have both a compression and a leakdown tester, but haven't even thought to run a test. I know that it has at least decent compression since it's pretty close to impossible to turn over by hand with the plugs in, and no problem with them out. I suppose that I can run the test and get some better idea what shape it's in, but I don't think it's a compression problem

WRT to the combination, I have no idea what's in the engine. I'm sure that a bunch of the work that I found on this car was done by a speed shop, and based on how it was done i'm thinking that the car was used as a drag car for a bit (all the rubber lines replaced, double return spring, battery tray modified...). I also found receipts for some speed parts, but again, no idea what's in the engine.

My single plane intake 4V low compression lots of duration and lift solid cam engine easily idles at 700 rpm, I don''t think it is the intake.

yea, that's basically what i'm thinking, I doubt that the cam is big enough that it is the reason that I can't get it to idle down. It doesn't sound lopey at all where it is running.

Check your cap and rotor and the condition of your plugs and wires.

Cap and rotor are new/spotless, wires were cleaned up and new plugs, no signs of arcing and it's not missing when it tries to die

Sounds like a classic big vacuum leak. Check all around the ports on the carb. Edelbrocks have a threaded port on the back of the base that needs to be plugged, and isn't always obvious.

Pulled the plug, put it back in with teflon paste and capped off all the ports on the carb when I rebuilt it. The manifold has a vacuum port on the back which I tried plugging off.

if I had a leak big enough to cause this would I be seeing this much vacuum at 2000rpm? Unless I missed something obvious, the only place I could have that big a leak would maybe be under the manifold.


I'll totally believe that I might have a totally mismatched combination, but I'd be pretty surprised if that totally prevented it from running below 2000rpm, and my goal right now is to figure that out so I can figure out what the heck the combination in the car is like. Honestly, I'd like to get it running well enough that I could get it to the track and get a baseline, even if it's not right so I know where I started and can document how it goes after I've fixed it...

 

[Utard]

Silverback,

You said that you replaced the needles and seats, so I'm assuming you pulled it off again and went through it again?

Did you check the float level and float drop, choke valve clearance and fast idle linkage?

Could it be the choke?

What size jets and rods are in there?

Might be a total mismatch.

Mine was a royal bastard to keep running, so I pulled the carb for a rebuild, and I saw that the previous owner had put huge jets and tiny rods in it. I put the right size jets in it and 1 size leaner rods and it runs great now.

I've never heard of using simple green to check for leaks. I've always used starter fluid.

Don't forget to check all the way to the power brake booster for a leak.

Also, if your car has AC then you could have a leak at the controls in the dash and starter fluid will never find it.

I found I had a vacuum leak where it plugged into the controls with a vacuum gauge.

Fixing that sure helped it run better and tune easier.

 

[Silverback]

Silverback,

You said that you replaced the needles and seats, so I'm assuming you pulled it off again and went through it again?

Yes, I did

Did you check the float level and float drop, choke valve clearance and fast idle linkage?Could it be the choke?

yep checked all that, and it does it even if it's not on the fast idle cam anymore

What size jets and rods are in there?Might be a total mismatch.

Mine was a royal bastard to keep running, so I pulled the carb for a rebuild, and I saw that the previous owner had put huge jets and tiny rods in it. I put the right size jets in it and 1 size leaner rods and it runs great now.

ARG... I honestly didn't check. Everything that I could identify looked totally stock (honestly, this thing looked a lot like someone took it out of the box, put it on the engine, filled it with fuel and then never ran it, it has fuel varnish on the parts touching what was in the bowl and _no other_ dirt or grim or carbon or anything on it).

I'm actually not sure what markings I'm looking for, but will pull it apart if I have to though I really suspect I'll find that they're stockers.

he thing is that I thought that the rods/jets shouldn't do anything at idle, if I can get it to idle down low enough to be in the idle circuit. When I called edlebrock they basically said that it shouldn't be down in the idle circuit at anywhere near that rpm and I need to figure out why, that and it runs well at that RPM the rods/jets are probably OK (I think, definitely said I'm not in the idle circuit)

I've never heard of using simple green to check for leaks. I've always used starter fluid.

Basically the rpm is up high enough that I was worried and they agreed that the conventional carb cleaner/starting fluid/propane test wouldn't be helpful, but suggested simple green (or anything soapy) would momentarily block off the leak and change the speed. They suggested that this is the only way to check for leaks at higher rpms or with really big cams and carbs.

Don't forget to check all the way to the power brake booster for a leak.Also, if your car has AC then you could have a leak at the controls in the dash and starter fluid will never find it.

I found I had a vacuum leak where it plugged into the controls with a vacuum gauge.

Fixing that sure helped it run better and tune easier.

I orginally checked for leaks there, before rebuilding the carb by disconnecting _all_ the vacuum lines and plugging off all the connections. Right now I have all the nipples on the carb plugged off and only have the line from the back of the manifold connected, that has a new hose (though admittedly I could still have a leak at the brake booster or tranny, this thing is missing a heater and the only other line it has is to a vacuum reservoir).

Again, would I be seeing this much vacuum at one of the small ports on the distribution block if I had a vacuum leak big enough to cause this?

 

[[email protected]]

Boy you've got a really difficult problem. Despite all your checking still sounds like vacuum leak. The other suspicion would be carb. Do you have a good friend with a running compatible engine (by that I mean carb pattern) I would see if swapping for a known good running carb dramatically improves your problem. If it does problem is somehow carb. If it doesn't then not carb related. I emphasize known good running carb because you can't know what you get out of a box.

If you get desperate hopefully you have the orig 2v intake to match those head and you could change it. What a bummer. Hope you get it solved

 

[Silverback]

ARRRGGG!!!

My dad stopped by and was ribbing me for having this thing up in the air in front of the house still, that he bets that it doesn't even run. Turned the key on, pulled the throttle lever a couple times to squirt some gas and pulled the trigger on the remote start... fires right up and idling OK at about 850rpm.

I HAVE NO IDEA WHAT'S DIFFERENT, and didn't get time to check, as soon as I figured out that it was idling at a reasonable speed I also noticed the fan shroud bouncing up and down and remembered that I was trying to figure out how to get the shroud aligned with the fan (it fits the radiator well, but I'm wondering if it's the wrong one because it seems to be about 3/4" too high for the fan) and had both the fan and the shroud loose and shut it off right away before something went flying. The only thing that I've touched that I can think of is the fan and shroud... and topped off the radiator when I noticed it was only half full