I rebuilt the 2100 carb on my 351W the other day and had to retime the dizzy cuz i had to remove it and a flame shot out of the carb and I think the power valve blew out. It sputters until it warms up and then runs purty good. Now when I start it up after its been sittin around just a few minutes its hard to start then puffs white smoke. Also, I took the top cover off and looked in the float bowl right after i was runnin it for a while and bubbles were comin up from the power valve and the fuel level went down about a half inch in a bout a half hour.
Any suggestions?

 

Take it apart and rebuild it. You will probably need a new PV and maybe new gaskets, resetting the float.

 

You mean I need new gaskets to reset the float? Ok, heres what I did this evening after work. I took the carb off and put the old power valve back in from when I rebuilt it last weekend. Nothing changed. Then I fiddled with the idle screws some. Nothing changed, except for it running worse when I screwed 'em in too far (backed them back out). Then I bent the float down some more to lower the fuel level in the float bowl. Nothing changed. Thats all I did. Some more symptoms include: white smoke blowing out after its been revved up to about 2500 rpm then let back down (not held at that rpm). Seems to run a little better when its at max operating temp. Still hard to start after been settin off for 5 or so minutes. Checked the intake passages while the carb was off (they seem purty wet). Checked the plugs on monday (white dusting, but don't make sense with it runnin' rich). I've been fiddling with the timing, seems to be ok. Just timed it to just before it pings. Also ran it with it retarded a few degrees (runs the same, but with less throttle response). Someone told me its messed up cuz I rebuilt it and didnt adjust everything, but by now I have purty much covered all the possible adjustments. Oh, and I played with the choke too. No difference. What also puzzles me is that the motor will run at about 2500 rpm with the accelerator pump arm disconnected from the throttle linkage. And for the fact that when I close the choke butterfly while its idling, it doesnt make any difference. I'm reckon I'm stumped. Remember this started runnin' like crap after I changed the inkake gaskets, valve cover gaskets, cleaned the intake out, cleaned the EGR plate out (which was throroughly clogged with carbon, also left the EGR valve unhooked to any vacuum lines like it was before), and rebuilt the 2100 motorcraft carb. No vacuum leaks here by the way.

 

Update--
While searching through the forums I came across one that caught my eye. Then I suddenly remembered one important step in the rebuild of the carb. The reason gas was flowing out the top of the carb is I forgot to clip the float pivot pin retaining clip to the seat. Fixed that, and it runs better now, but I still think I need to tweak the darn float some more, remedying whenever I bent it to adjust the float bowl. Still kinda sputtering when it idles for a little while. I adjusted the mixture screws to about 6 turns out on both sides. Still need to check the timing with a light and the vacuum with a gauge. Any suggestions?

 

White smoke is usaually an indication of a leaking head gasket.

White=water (steam)
Blue=oil
Black=fuel

 

I suspect a vacuum leak somewhere. I could be wrong, but it sure sounds like it to me. If the intake isn't sealed right, coolant could be getting into the combustion chamber to make that white smoke, too. Usually if a power valve is blown out, too much gas goes through your carb and makes your exhaust black. It would be just like jetting your carb about 15 sizes too rich. Are you familiar on what a power valve actually does?

 

Hmm, its not steam, although I haven't checked with a piece of glass at the tailpipe. The coolant level is doing some funny things though. I'll take the cap off while its cold, and its a couple inches from the neck, and when it warms up it surges up and down. Also, I took the radiator cap off after runnin' it for a while and it was real foamy. I've also considered it to be the new intake gaskets not sealing correctly and allowing water in the cylinders. I'm going to pull the plugs tomorrow and take another look at them. Last time I did this they had a white dusting on the electrodes. I have a basic idea on how a power valve works. I think it draws on intake vacuum to add more gas to the motor directly from the float bowl. I also know the symptoms of a blown power valve. Checked the valve (wasn't blown). Last night, I was reading on the net and came across a forum where someone was havin a similar problem that I had when I first rebuilt the carb and then put it back on. I forgot to clip the little float pivot pin retaining clip to the seat. Well, last night I did this and didn't really notice any difference when it was driven. Today I started it up and it ran like crap like usual (sputtering at all rpm ranges, especially at idle) and I drove it around then put some gas in it. After I filled up I fired it back up and surprisingly it caught on the first turn of the key. Then drove it back to the barracks and for about 2 minutes from after I filled up with gas it was running good. Usually if I let it sit for about 10 minutes or so it will never fire up on the first crank and I have to crank it for quite a while for it to catch. Seems like it wants to run, just can't. Then I usually end up holding the gas pedal to the floor then cranking it for about 10 seconds and it catches, but runs real rough for a few seconds. Now I'm seeing how this could be a water leak issue. Too bad the only way to find out really is to either pressurize the system and listen for leaks through the intake or just pull the intake manifold and check it out firsthand. Any more suggestions? I think I'm going to have to adjust the float some more but I thought the float level only really affected higher rpms, not idling. Appreciate any assistance.

 

If you can get access to a cooling system pressure checker you can rule out the coolant leak. It goes on like a radiator cap then you use a hand pump and pump it up to around 30 psi and it should hold that pressure for 5-10min at least if it does not you have a leak in something.

Your rough running at start is sounding like a wet plug then when it runs long enough it heats up the plug and dries it off.

Also a leaking head gasket will cause a foaming or bubbling radiator when running.

 

Check the vacuum line fron the tranny, the smoke could be from a bad modulator valve. This would cause white type smoke too.
The foam in the radiator could or could not be from a head gasket. Does it build up excessive pressure in the cooling system and boil over? If not, it probably isn't a head gasket.

 

If I didn't mention the model and equipment my truck has here goes. Its an 84 F 150 4x4 w/ 351W, 2100 motorcraft carb, NP435 tranny, NP208 t-case. I dont see how it could be a head gasket considering this problem started after I changed the intake gaskets to stop an oil leak on the intake end seals. Yeah, Brian460, I am planning to do the coolant pressure thing. I'll try it tomorrow. I cant check the tranny line cuz I got a NP435 4 speed manual, but good thought LxMan. Today I checked the intake manifold bolts and more than half of em were finger loose. So I gave em a good wrenching, but not too tight. I think I'm just gonna have to pull the intake manifold again and look for a leak between the coolant passages and intake ports. While I'm at the base auto shop I'm gonna check the timing with a light and vacuum gauge and also do the pressure test. That'll reveal anything cuz I now know it aint the carb. I've already fiddled with that enough. Boy I love my 351W. Appreciate y'alls assistance in this problem.

 

Well shucky darn, no modulator valve on the manual tranny. I too would suspect a leaky intake gasket since you blew my theory out of the water

 

Ok y'all, problem solved. Performed the pressure test-no leaks. Timed it to 10 degrees BTC so thats good. I took the carb off and re-rebuilt it so I know thats good. Then I was checkin the EGR plate. Looked kinda funny considering the EGR valve's been disconnected long ago. The passages showed new carbon deposits on both sides which meant that exhaust gas was flowing through in spite of the EGR valve being disconnected. I then knew what my problem was. So I took that darn EGR valve off and cut out a plate of 1/4 inch metal, made a new gasket, and bolted it on in place of the valve. Problem solved. I guess the exhaust gas was flowing unrestricted into the intake now since I cleaned out the clog in the EGR plate. That was messin' me up the whole time. No more EGR and a good runnin' truck. I just need to adjust the idle and I'm all set. Appreciate y'alls assistance in this matter.

 

Glad you got it fixed. Thanks for letting us know what you found

 

I can't wait to get home tonight and remove my EGR because your symptoms sound just like mine and I've done everything you did about 40 times and nothing helped. Because my truck had been running for several years with the restrictor/one-valve in the vacuum line from the thermo valve to the
EGR valve was installed backwards, i.e. no vacuum to EGR, the EGR valve hadn't worked for a long time so I'll bet it is clogged up. At any rate I want to eliminate one possible source of a problem and clean up the engine compartment a little too.