351M questions - poor cold start up

[delco1946]

So my motorcraft 2150 carb has been rebuilt and my mechanic had my truck for months to try and getting it running well. Once warmed up it (351m) runs well, but cold its not so happy. Now that the weather its getting even colder, i have to let the engine idle several minutes or else it'll want to stall out once you give it gas. My mechanic said he could adjust the choke so its runs better cold, but that it would negatively impact drivability when warm.

I know the vacuum motor that opens up to suck up hot air from over the exhaust manifold doesn't work. This would help - anyone know where you can get these new? It looks like i'd have to drill out the old one since its riveted in. is there anything else I could do to improve cold operability?

Also, Ive noticed that the engine no longer gets very warm. My gauge barely cracks the left most "backward slant" line on the temp gauge (aka left of the "N"). I temped the engine and after running and driving all over, it was at ~186 right at the thermostat, which I replaced last year (the correct style too and a 195 degree one). the temp at the top of the radiator was ~ 17x, and ~140 at the bottom before going back into the engine. Those temps don't seem terrible, but it seems odd that even after 30 minutes I don't even hit the "N" on normal. The cat was changed and a bigger one installed - would this decreased exhaust pressure and/or rebuild carb cause the engine to run cooler??? Should I ignore this, knowing that come 90 degree days next summer i'll be glad she runs cooler?

[Gary Lewis]

On the temp gauge, don't put much stock in the original gauge. Your test, probably with an IR thermometer, is the best bet. And if you put a 195 degree 'stat in and it is running 186 at the thermostat then the 'stat appears to be stuck open. While it is possible that your IR thermometer isn't reading quite right, I'd still replace the 'stat.

But, that's not the cause of the engine not running well until warm. Nor is the warm air flapper valve. It is surely the choke. And I disagree strongly with your mechanic. If your choke is properly hooked up then all the adjustment does is determine how long it will stay on. But it will still come fully off when the engine is warm unless you go crazy with the adjustment.

There should be three screws that, when loosened, allow you to turn the thermostat housing. And you should have a scale or series of notches on the carb with a single notch on the housing. With the engine cold mark which notch on the carb the index mark on the housing is closest to. Then loosen the screws and with the throttle open just a bit by hand, turn the housing one notch forward/clockwise - I think. That should close the choke plate slightly. If so, tighten the screws and give it a trial spin. If that doesn't close the choke a bit and instead opens it a bit, go the other way.

By going one notch at a time you'll arrive at a setting that works when you first fire it up and yet pulls off completely when the engine is warm. However, if your choke is not properly connected it may not pull off completely. Do you have a metal tube coming from the intake or the exhaust and going into the choke? Do you have a wire connected to the housing?

[ArdWrknTrk]

Christopher,

You might try grounding the temp sensor wire to see if the gauge pegs.

This would show if the instrument is faulty.

Having the flap operating is going to help your truck warm up much quicker.

The part# is Motorcraft 149,

Ford D7AZ-90612-C

or

GP Sorenson 779-3011

They look to be ~$25

[ArdWrknTrk]

On the temp gauge, don't put much stock in the original gauge. Your test, probably with an IR thermometer, is the best bet. And if you put a 195 degree 'stat in and it is running 186 at the thermostat then the 'stat appears to be stuck open. While it is possible that your IR thermometer isn't reading quite right, I'd still replace the 'stat.

But, that's not the cause of the engine not running well until warm. Nor is the warm air flapper valve. It is surely the choke. And I disagree strongly with your mechanic. If your choke is properly hooked up then all the adjustment does is determine how long it will stay on. But it will still come fully off when the engine is warm unless you go crazy with the adjustment.

There should be three screws that, when loosened, allow you to turn the thermostat housing. And you should have a scale or series of notches on the carb with a single notch on the housing. With the engine cold mark which notch on the carb the index mark on the housing is closest to. Then loosen the screws and with the throttle open just a bit by hand, turn the housing one notch forward/clockwise - I think. That should close the choke plate slightly. If so, tighten the screws and give it a trial spin. If that doesn't close the choke a bit and instead opens it a bit, go the other way.

By going one notch at a time you'll arrive at a setting that works when you first fire it up and yet pulls off completely when the engine is warm. However, if your choke is not properly connected it may not pull off completely. Do you have a metal tube coming from the intake or the exhaust and going into the choke? Do you have a wire connected to the housing?

Gary,

Do you feel adjusting for hold open when cold is the best way to adjust the choke?

I usually use a drill bit shank to get that spacing right.

[Gary Lewis]

Gary,

Do you feel adjusting for hold open when cold is the best way to adjust the choke?

I usually use a drill bit shank to get that spacing right.

Jim - I usually start with a 1/8" drill bit and adjust from there. IOW, if it is too cold-blooded I tighten it up, and if it appears rich I back it off. But 1/8" is usually close.

[ArdWrknTrk]

Jim - I usually start with a 1/8" drill bit and adjust from there. IOW, if it is too cold-blooded I tighten it up, and if it appears rich I back it off. But 1/8" is usually close.

So you do think using a drill bit is the best method (for most of us)???

I usually start around 0.100", but understand that almost everyone has 1/8"

 

[Gary Lewis]

So you do think using a drill bit is the best method (for most of us)???

I usually start around 0.100", but understand that almost everyone has 1/8"

Yes, a drill bit is easy and most people have a 1/8" bit. Each application varies as to the recommended opening, and they are frequently measured in 64ths of an inch, and not everyone has those.

But 1/8" is probably a bit too far open and your .100" is probably closer. However, I find that if I start lean/too far open the engine usually starts but runs poorly, and I know which way to go on the first adjustment.

[ArdWrknTrk]

Yes, a drill bit is easy and most people have a 1/8" bit. Each application varies as to the recommended opening, and they are frequently measured in 64ths of an inch, and not everyone has those.

But 1/8" is probably a bit too far open and your .100" is probably closer. However, I find that if I start lean/too far open the engine usually starts but runs poorly, and I know which way to go on the first adjustment.

I've got a number index from #1-80.

39 is only a half thou under 0.1

[85lebaront2]

On the temp gauge, don't put much stock in the original gauge. Your test, probably with an IR thermometer, is the best bet. And if you put a 195 degree 'stat in and it is running 186 at the thermostat then the 'stat appears to be stuck open. While it is possible that your IR thermometer isn't reading quite right, I'd still replace the 'stat.

But, that's not the cause of the engine not running well until warm. Nor is the warm air flapper valve. It is surely the choke. And I disagree strongly with your mechanic. If your choke is properly hooked up then all the adjustment does is determine how long it will stay on. But it will still come fully off when the engine is warm unless you go crazy with the adjustment.

There should be three screws that, when loosened, allow you to turn the thermostat housing. And you should have a scale or series of notches on the carb with a single notch on the housing. With the engine cold mark which notch on the carb the index mark on the housing is closest to. Then loosen the screws and with the throttle open just a bit by hand, turn the housing one notch forward/clockwise - I think. That should close the choke plate slightly. If so, tighten the screws and give it a trial spin. If that doesn't close the choke a bit and instead opens it a bit, go the other way.

By going one notch at a time you'll arrive at a setting that works when you first fire it up and yet pulls off completely when the engine is warm. However, if your choke is not properly connected it may not pull off completely. Do you have a metal tube coming from the intake or the exhaust and going into the choke? Do you have a wire connected to the housing?

One thing I remember about the 351M/400, primarily the 351M, they were jetted extremely lean (and Ford still got in trouble for fudging the emission readings) and as a result were terrible during warmup, tightening the choke helps, but makes the gas mileage even more abysmal. Not having one in front of me, I can't check, but I think I remember the choke stove on those is in the crossover and if the "mechanic" adjusted the choke to be fully open without proper heat it will be cold natured.

After the engine is warm, actually before it fully warms up, the crossover should be so hot it will almost flash any water put on it to steam, if it does not then that is part of the problem. There were a number of engines I used to see that would load the crossover passage with carbon to the point it wouldn't heat the choke or manifold well enough.

[Frank Wyatt]

One thing I remember about the 351M/400, primarily the 351M, they were jetted extremely lean (and Ford still got in trouble for fudging the emission readings) and as a result were terrible during warmup, tightening the choke helps, but makes the gas mileage even more abysmal. Not having one in front of me, I can't check, but I think I remember the choke stove on those is in the crossover and if the "mechanic" adjusted the choke to be fully open without proper heat it will be cold natured.

After the engine is warm, actually before it fully warms up, the crossover should be so hot it will almost flash any water put on it to steam, if it does not then that is part of the problem. There were a number of engines I used to see that would load the crossover passage with carbon to the point it wouldn't heat the choke or manifold well enough.

I can't remember ever seeing a heat cross-over that wasn't carboned/plugged up my self. That would not be conducive for the proper function of the automatic choke. If that is the case, an electric choke would be a solution for the lack of heat from the choke stove. Mike's carburetor has one with the control block that would work without a functioning choke stove.https://www.carburetor-parts.com/Electric-Choke-Conversion-Kit_p_4165.html