Help Please: Surging 302 only when warmed up

[rutkak]

Mustang Gurus,

Here's one I need help with on my rolling restoration 1970 coupe with a 302, C4, stock intake and Motorcraft 2100. The car idles fine when first starting up but right about when the thermostat opens up (180 degrees) 7 mins later she starts surging every 4 or 5 secs. Oh by the way, that's just about the time a small amount of white smoke starts coming from the tail pipes. She's smoked since I bought her but the surging is a recent development. I run water in the radiator so it just smells like fuel but it's white.

She was definitely overheating or close to it until I flushed the system, replaced the water pump and thermostat. I later replaced the rusted up radiator without issue. She stays at a cool 185-195 in hot NC weather.

The carb was rebuilt a month ago and the fuel filter is clean. I've checked for vacuum leaks, cleaned up the carb spacer and replaced the gaskets. I'm pretty confident I'm good other than a slight intake manifold oil leak in the back (might be the problem). As part of routine barn-find car buying I also replaced all the plugs, PCV and fuel pump. The wires look good and the plugs all spark. The dizzy is some weird knockoff low-buck HEI but the tach I hooked up reads the same as my timing light. My timing is set to 10 BDC, anything less and she runs poorly. Vacuum is low at 15/16 and surges to 18. Idle surge is about 200 RPM.

My guess is a head gasket or cracked head is causing the white smoke and the surging is some carb related issue.

What else can I check? What do you guys think?

-KR

 

[Kermit 460]

I"m no guru,but when you said white smoke it made me think head gasket too,the surging maybe water is diluting the gas if it's trying to burn it? I beleive theres a leakdown test for head gaskets,I"m sure someone will chime in that knows more about it.Does it use water?

 

[imusa76]

I was also thinking maybe the intake manifold gasket, when the engine warms up things change shape a little, but maybe just enough to cause a vacuum leak.

the wmoke is it burning water or running rich?

 

[wwhite72]

302's have a wet manifold. Could be the manifold gasket letting water into the heads after the thermostat opens.

 

[marks73]

Stop driving it. Pistons hate water! Sounds like a zipper crack that only opens when it gets hot enough. Get a radiator pressure tester and pump it to about 13 pounds. Let it sit overnight and determine if it will hold that pressure. If it does, it's a metal crack in either the intake, head or block that only seperates when hot. Gaskets don't do that.

 

[rutkak]

Mark,

Roger that. I'll check the radiator pressure when I get my fuel tank back in by Saturday. I ordered the fuel tank kit but CJPonyParts had one of the items on backorder (due to arrive 10 May13) but I cancelled it and reordered through a different site.

To answer Kermit - I only run water in the radiator. I've checked the radiator with the cap off when it first starts up and when it's warm and there are no bubbles. There is no oil in the coolant as far as I have noticed but I haven't it driven it that much due to a whole host of other things I'm tinkering with. The engine was fairly gunked up when I bought and I haven't seen any milky oil after the oil change a month ago. The white smoke is definitely not consistent though either in frequency or thickness but ALWAYS starts as soon as the thermostat opens up when it hits 180.

Would a car running rich push out white smoke? I leaned it up too much the other day and it was doing the same thing.

KR

 

[rutkak]

The surging problem ended up being something wrong with the Motorcraft 2100 2V carb. I swapped in an Autolite Carb and it cleared up. I still have the white smoke so I'm working that piece now. I'll post results when I figure out what was wrong with the carb, but I took a good bit of it apart last night and it all looked fine. I also used some carb cleaner to spray out the ports and small pieces so we'll see if something was just caked up with one of the jets.

I noticed that the surging decreased a tad when I screwed in the right (driver's side) fuel/air mixture screw.

 

[72HCODE]

Since you determined it was the carb. On the 2100 check the float level make sure it isn't low.

Surging or idle rolling from a carb is caused by lean fuel mixture.

Like others said it could of been a head gasket or intake gasket as well.

 

[rutkak]

Since you determined it was the carb. On the 2100 check the float level make sure it isn't low.

Surging or idle rolling from a carb is caused by lean fuel mixture.

Like others said it could of been a head gasket or intake gasket as well.

72HCode,

Roger that on the float bowl. Two days ago I set it to spec dry but I'll have to get her running to check her wet to make sure she's filling up.

Ken