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skerwath

Active member
Joined
Nov 10, 2013
Messages
41
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Location
Texas
My Car
1971 Mach 1 351C 2V
I gotta 71 Mach 1 with a 351C 2V inside. I replaced the intake manifold with an Edelbrock Performer intake and slapped an Edelbrock Thunder AVS 650 on top of it. My problems are that the engine will idle fine, but when I adjust the fuel/air screws I get no RPM increase or decrease when adjusting the left one(passenger side). Only changes when adjusting the right screw(driver's side). When I put the car in gear, she stalls and starts to backfire. I've searched for vacuum leaks, but so far I haven't found any. I move all the old vacuum plumbing over from the Cleveland intake. When I had it on the road after the swap, the engine would sputter, surge, and stall. When I open the throttle, I get a high pitched squeal, and I've checked for belts slipping. Is this all related? The reason I switched everything over, I was tired of rebuilding the autolite 2100 every time the car sat for an extended period. Any points in the right direction will be greatly appreciated.

20121126_160255.jpg

 
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You may need to try slowing the idle speed down a bit then try to adjust the idle mixture screws until best vacuum is achieved. If the idle speed is set to high the carb idle circuit becomes not functional. A severe vacuum leak is very possible and worth checking out. Good luck.

 
The left air/fuel circuit in the carb is plugged, or major vac leak.

Disassemble, remove adjustment screws and clean every orifice and transfer port with carb cleaner and compressed air. Gotta be spotless, and not just pretty to the eye.

Squeal could be from a bad/slipped/improper sealing base gasket.

My bet is on the carb.

 
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Sounds like a vac leak. I had the same problem which ended up being the stock 4V carb spacer. I swapped out with a cheap Mr Gasket spacer and she ran fine.

I'd also double-check timing, but I'm assume that's the very first place you checked.

 
Did you just do the swap to the Performer intake? Our Cleveland engines are prone to vacuum leaks due yo improperly sealed intake manifolds. You really have to use a lot if gasket sealer in the front and rear valleys.

 
Yep, vacuum leak for sure. Rear of intake manifold. Gotta wait for engine to cool before ripping it apart :-(

 
When my buddie and I did my intake, we used a tube of gasket sealer that you can put in a caulking gun. Made it easier to make a mound of it along the front and rear edge.

 
On a Cleveland, I'd suggest NOT sealing around the intake ports themselves with RTV, only the water ports, end rails and corners.

Gas will eventually swell the RTV and turn it to snot, then get sucked in causing another leak.

Been there.

I'd first glue the gasket to the head (with a little 3M spray adhesive or dabs of contact cement) to keep them from slipping, then apply sealer where desired and install.

 
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I thought a cleveland was a dry intake with no water passing through it:huh:
Nope, got two water ports in it.
Maybe you just found your problem:dodgy:

"The radiator hose locations differ between the Windsor and Cleveland engines; the Windsor routed coolant through the intake manifold, with the hose protruding horizontally, while the Cleveland had a dry manifold with the radiator hose connecting vertically to the cylinder block above the cam timing chain cover."

 
I thought a cleveland was a dry intake with no water passing through it:huh:
Nope, got two water ports in it.
Maybe you just found your problem:dodgy:

"The radiator hose locations differ between the Windsor and Cleveland engines; the Windsor routed coolant through the intake manifold, with the hose protruding horizontally, while the Cleveland had a dry manifold with the radiator hose connecting vertically to the cylinder block above the cam timing chain cover."
Ditto on the dry intake - you have a Cleveland or a Windsor?

Windsors have a valve cover that is flat across the top front to back with rounded corners.

Clevelands have a dented or bent valve cover across the top with more square corners.

- Paul

 
From my experience:

After rebuilt my Holley carb, I had the same problems, first because one of the gasket from a kit was not right for my carb, then the two bowls was not enough tight. After change a gasket and then tight the bowls (primary and secondary), I could adjust the 2 fuel/air screws. Note that the engine will stop when you close close screws.

Manu

 
From my experience:

After rebuilt my Holley carb, I had the same problems, first because one of the gasket from a kit was not right for my carb, then the two bowls was not enough tight. After change a gasket and then tight the bowls (primary and secondary), I could adjust the 2 fuel/air screws. Note that the engine will stop when you close close screws.

Manu
True enough. I fixed my vacuum leak with a new gasket. Rear of the intake was leaking. Trying to get the idle right. It still wants to stall when accelerating. When I got the car, the front vacuum fitting was capped and the vacuum diaphragm on the distributor was open. With these both capped, I set the timing at 6 degrees like the service manual says, but when I ran a vacuum line from the fitting to the distributor, my timing advanced to 16 degrees. I'm scratching my head. I replaced the points with a petronix unit. Flipping through the service manual, it shows a vacuum tree with three ports on the front of the manifold. One of those I assume is supposed to go to the other side of the carb. It maybe why I am stalling in gear. The rpm's are not dropping when I put it in gear, but I did notice a lot of energy being dumped into the tranny when I shift it. It's making the tires bark, and I have to keep a firm foot on the brake when I shift. If it's not one thing, it seems to be another.

 
What you are describing seems normal.

The vacc advance will do that, that is normal.

A very high initial advance will also put extra pressure on the box as described.

It seems to me that you're not far off.

It seems like a lot of little things need to be adjusted, that's all.

Back to basics, tune the car with the dizzy vacc disconnected and all vac lines plugged.

set initial timing to 8-10 adv.

Once that is done, drop the idle revs down to about 900 in Park or neutral.

That's it... you can confirm that the idle circuit is working by slowly closing one mixture screw at a time.

If it feels like it's about to stall, that's good. Put it back to 1/14 or 1/12 turns out.

Do the same to the other side.

Tell us what you find.

Make sure the vacc at the tranny modulator is sealed properly, no leaks.

 
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