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Discussion Starter #1
I have fitted a new 351C motor to my XC and I am having trouble getting it to idle under about 1200 rpm (as read off factory tacho, which I am told is not reliable!). Also it won't idle in gear (its a C4 auto) at any rpm.

Cam is a Crow with advertised valve timing as follows: inlet 33/73 dur: 286
exhaust: 80/32 dur: 293. Crow say it should idle satisfactorily at 850-900rpm.
They also recommend a hi stall convertor of 2500rpm average stall speed. I have had a custom Dominator convertor built for the car which I am told has a 2300 rpm stall speed.

Carby is a factory rebuilt 750 Vac secondary Holley list #80508 with the factory installed #72 jets. I have tried set of smaller #67 jets but it ran worse. Initial advance is has been set at 12 degress B.T.D.C. (Crow recomended to me 15 degrees) It seems to run best with the mixture screws 1 full turn out from seated but will not idle. I can let it warm up and run without fouling the plugs if I screw the idle speed up to roung 1500rpm.

If anyone has a similar set up I would appreciate any thoughts or comments on what could be wrong. Engine has a mild port job, roller rockers, an Edelbrock Performer manifold and try Y extractors. My engine builder has built several similar motors that run 750s and reckons it isnt too big for the engine's specs. The only difference is I wanted an electric choke on mine. He has looked at the car twice and thinks there is a problem with the carb. It is going back tomorrow to have a new MSD dissy fitted in place of the standard electronic dissy which has been recurved for gas (yes LPG) I suspect this may be a problem but it idled OK (not good just better then now) with the previous 600 Holley (on the new motor) but it was a shitty pollution model with tiny idle ports and it was too lean. (glowing headers and white plugs)

I have given all the information that I have, any help would be most appreciated. Thanks in advance.
 

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Slurry Boostin
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Power Valves?

Any other fuel issues any where else in the rev range?
 

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Discussion Starter #3
The power valve is supposed to have blowout protection whatever that means, (safe power valve!) How does one check it?
 

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I immediately suspect the choke. I suggest disabling the choke and seeing what that does. I would also check for vacuum leaks. I found out the hard way once that a little cap fell off a vacuum plug just inder a bowl ... so I couldn't see it.

Your setup is pretty well the same as mine and mine idles well under 1000 rpm.
 

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Slurry Boostin
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The Vacuum your engine may have could be conflicting with the power valves in your carb.

That is what was happening with mine :) couldn't get it idling nicely all the time.

Now it is perfect =D
 

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Discussion Starter #6
It doesnt seem to have any fast idle, other than when I screw it right up to get it to run. Choke opens up pretty much straight away, this is basically a new carb. Power valve is 6.5. Should this work with my cam? I can get 15 inch Hg vacuum at 1200 rpm. Power valve is supposed to be half your vacuum I think?
 

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Discussion Starter #7
Engine guy has checked it over and he reckons the manifold is warped. He is going to get it milled for me and just for the heck of it jet coated at the same time. Actually jet coated first, then milled. Thanks for you replies. BTW: he diagnosed it by spraying WD 40 on the leaky bit to seal it and it idles OK? Is this bull or what??
 

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Whats traction?
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xcgxl said:
Engine guy has checked it over and he reckons the manifold is warped. He is going to get it milled for me and just for the heck of it jet coated at the same time. Actually jet coated first, then milled. Thanks for you replies. BTW: he diagnosed it by spraying WD 40 on the leaky bit to seal it and it idles OK? Is this bull or what??
Its possible the WD40 could seal, very temporarily. But my bet is he stuffed up the manifold gasket when he installed it and is going to charge you a packet to fix it.

Make sure you make some marks on the manifold in places only you know of, so you can tell if he's taking you for a ride...
 

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Discussion Starter #9
I already suggested to him that the gasket may have been on wrong. I usually use an inlet tray, but he doesnt. I told him that I put a gasket on upside down once and it was blowing oil out one exhaust pipe. He assured me he would not do this. He reckons the manifolds sometimes need machining from new, especailly if the block has been decked etc. We will see what hapens but I reckon you cant go past the old inlet tray. It was important enough for Ford to not save money on so what does that tell you. Anyway this guy has built some pretty tough motors ans should know his stuff. Anyone see the red XD in one of the last burnouts at Summernats on Sunday?? Thats one of his.
 
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