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My 1960 283 with 4 barrel will not idle unless it is just about fully choked and then while at idle pulls about 18 on the vacuum gage. When I open the choke more than about 3/16" it dies. I've checked the intake with propane at every gasket and jetted propane under the manifold through the vent pipe opening next to the distributor and no leak is evident. I thought perhaps it was a carb problem so using an adapter I put on a good 2 barrel with the same result: When the engine is fully warmed up it stalls unless choked.
Background: I just replaced the timing chain and installed the correct intake manifold. I'm using a WCFB that I've rebuilt and double checked before testing with the 2 barrel mentioned above. I installed the distributor with #1 facing forward. The engine timing is correct and the compression is 125 on every cylinder. Does anyone have any suggestions.
 

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It sounds like it's running very lean. Fuel pump?
 

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The fuel pump is fine. The carb is full of fuel. The accelerator pump is working. When the carb is taken apart it has plenty of fuel inside and the idle circuit is all clear.
 

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If I have a leak between the intake and the heads wouldn't it have shown up when I forced propane into the cavity below the intake manifold? Can you think of any other possiblility? What do you think about my 125 compression?
 

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I have a '59 283 with an unknown year 4-bbl intake that uses the Rochester 4G. The carb has an area underneath the rear that overhangs the intake pad by about 1/16", causing a good-sized vacuum leak. I had to get a gasket that would cover that gap & glue it with plenty of liquid Permatex so it would seal. I later found an intake that had a slightly larger pad at the rear.
 

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125 compression is good if they all have that. It is more important that they all be uniform tho. 10% variation from the highest cyl. to the lowest is about the largest acceptable spread. 20 years ago I had a 59 283 with 100 in every hole. It is still in the family and running fine, after being my nephew's daily driver all through high school.
At this point it seems you have tried to cover all the areas that may leak. I never used the propane leak test myself. I may catch flak for this but I always used Berryman's carb clean. Then I had a section of vacuum hose hooked to my stethoscope that I could pinpoint the tiniest leak with. You can do the same thing with a section of vacuum hose to listen through.
 

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Discussion Starter #9
The propane torch works great. (Don't light it) In the same way that the torch flame comes to a point you can use the torch to pinpoint a small area. I just can't find any leak but I still suspect there is one somewhere.
 

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Can you clarify how you did the propane test under the intake?
 

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This old 283 has a breather draft pipe that hangs down the side of the engine to vent the crankcase. On my engine I've removed the breather and attached a PCV valve to the opening. I simply fed propane into the cavity and I would assume that if there were vacuum leakes that the propane would have been sucked in and the rpm's would have increased. Rather than a suction however there is a small amount of venting from the cavity under the intake because it's connected to the crankcase. My PCV will draw the crankcase fumes into the base of the carb for a cleaner running engine once I resolve this strange problem.
 

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Discussion Starter #13
I suppose it's possible but the blow by is very faint and my propane presure is a bit higher. I've forced propane into the chamber with no result. I was able to get the 2 barrel to respond properly after correcting the adjustment and tightening it down a bit. I think my problem is in the WCFB carb. I've cleaned and rechecked but it just will not idle unless choked.
 

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I'd go thru the carb again and make sure every passage is open, especially the idle circuit and vent passages! There must be a clog somewhere!
 

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I installed the new chain and gears and it could not have changed. If a gear were marked incorrectly I don't think I would have 125 compression and I doubt if the ignition timing would have been so easy to set correctly. I have not taken the time to set up a dial indicator and check it by the book.
 

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Wayne Hagopian said:
I installed the new chain and gears and it could not have changed. If a gear were marked incorrectly I don't think I would have 125 compression and I doubt if the ignition timing would have been so easy to set correctly. I have not taken the time to set up a dial indicator and check it by the book.
Seems like ya got ome of those frustrating ones, it's probably a simple one and when ya find it you'll enjoy a few beers ,,..
 

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I had this exact same problem with my 350 Chevy. I sprayed carb cleaner for 2 days over every possible place I thought a vacuum leak may occur and nothing showed up. Just by accident I was looking at some close up photos of the Holly carb I had and noticed 2 vacuum ports that mine did not have. Under carefull examination I discovered that two brass fittings, covered with a rubber plug, had just fallen out of the carb, leaving two big holes for vacuum to escape. The carb was over 20 years old, so I could not complain. I replugged the two holes and the problem was resolved. I have even seen vacuum operated plungers on the inside of the carb itself cause a problem, where you could not check it with anything. I'll bet you have a vacuum leak somewhere. If possible, I would put another carb on there and see if you still have the problem.
 

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Wayne,

I think the problem is in the carb. It is drawing clean air from inside the carb itself. You may have one of the gaskets misaligned or the wrong one for that year carb. If you still have the old gasket match it up and see if all the holes match. Check the "compression" pattern on the gasket. It could be drawing air from a passage way that you can not get propane to.

You did not mention which trans you are running so maybe the vacuum line going to the modulator valve has a leak.

Also check the vacuum booster hose. Just clamp it off with locking pliers.
Lastly check the vacuum line to the PCV. Just calmp it off and see if the engine runs without being "choked".

Good Luck
Scholman
 
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