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351M questions - poor cold start up

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delco1946

351M questions - poor cold start up

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?

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

Gary Lewis

Re: 351M questions - poor cold start up

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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, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

ArdWrknTrk

Re: 351M questions - poor cold start up

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This post was updated on .

In reply to this post by delco1946

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

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

ArdWrknTrk

Re: 351M questions - poor cold start up

Administrator

In reply to this post by 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,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: 351M questions - poor cold start up

Administrator

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.

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: 351M questions - poor cold start up

Administrator

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"

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: 351M questions - poor cold start up

Administrator

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.

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: 351M questions - poor cold start up

Administrator

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

39 is only a half thou under 0.1

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

85lebaront2

Re: 351M questions - poor cold start up

Administrator

In reply to this post by Gary Lewis

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.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

Frank Wyatt

Re: 351M questions - poor cold start up

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

1981 F 150 Custom 300 ci with a fully rebuilt 1968 240 head Carter YFA T-18 3.25 9" rear 2WD
dual gas tanks
1990 Lincoln Town Car 5.0 AOD
Home town Mc Kenzie, TN

85lebaront2

Re: 351M questions - poor cold start up

Administrator

Frank, the worst ones I used to see were the Chrysler LA 318s, they had a heat riser valve that would stick in the open position resulting in almost no heat, which made the well style choke stay on, which made it run rich creating more carbon. You could get a repair kit from the dealer but the valve had to be welded to the shaft (those and the bushings were CRES). I have my shop guys physically check all Chrysler product heat riser valves. The big blocks, 383, 400, 413, 440 if it was working it would rattle at idle until it warmed up all the way. I told more than a few customers who asked about the noise to be glad it was noisy, it meant it was working.

I pulled many a 318 intake and burned the carbon out of the crossover and ports in the head, guy in the house behind the shop loved us (not) when we were doing those. At least the 351M and 400 are "dry" deck intakes (no coolant passages) so other than the royal PITA of working on it no radiator draining is needed.

Bill AKA "LOBO" Profile

grumpin

Re: 351M questions - poor cold start up

Bill, you ever use Mopar Heat Valve Solvent?

We used to use that on waste gates on aircraft piston engines. If they were stuck, that and a rivet gun and a block of wood. Let it sit fo awhile then hit it with the rivet gun, free them right up!

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

85lebaront2

Re: 351M questions - poor cold start up

Administrator

Yes, but on the 318 it was in the manifold outlet with the shaft parallel to the crank so wasn't easy to get to to bang on. By the time you pulled the right side manifold it was just as easy to replace it as try to free it up and hope it stayed that way.

Bill AKA "LOBO" Profile

delco1946

Re: 351M questions - poor cold start up

Sry for the slow reply, busy week and heading to Palm Springs tomorrow.

Gary- To answer your question I have both a metal tube going from the intake manifold to the choke housing thermostat and it also has a wire going to it as well. I didn’t rotate the choke housing leaner or richer, but it seems like the plate in the air horn is closing too much upon start up. I think I need to watch a couple videos of a correctly working choke to better understand this process. I’m visually oriented and readying about a process doesn’t gel this too well for me.

My gut is telling me that it’s coming off the fast idle too quickly, and maybe not getting enough air when cold. It seemed to run better with a couple vacuum leaks induced via removing the air filter while testing this and leaving the hoses normally connected to the filter open. Only after it warmed up more and the plate opened more fully did it started to run better by plugging those temporary air leaks.

I’ll have to dive back into this week I return from vacation.

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

Gary Lewis

Re: 351M questions - poor cold start up

Administrator

If it ran better with the vacuum "leaks" then rotate the housing one notch leaner. That will open the choke plate up just a little bit, adding more air. But, that will cause the fast idle to come off a bit earlier. However, that is a different adjustment, so let's get the choke right first.

Gary, AKA "Gary fellow": Profile

delco1946

Re: 351M questions - poor cold start up

It’s already rotated quite far forward, prolly around 45-55 degrees forward. Are the other adjustments I can make to recenter/zero the housing such that it is in a more normal position? Ie only 15 degrees leaner / towards the front of truck and while providing more air than what it is currently getting? Or could the spring in the housing be bad/weak?

Christopher in Portland Or. 1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6

ArdWrknTrk

Re: 351M questions - poor cold start up

Administrator

Like Gary said *when the truck is stone cold* adjust it so the choke has a gap of 1/8".
If you want to remove the cap and see where the loop on the end of the spring is, be sure to get it on the choke tab when replacing.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: 351M questions - poor cold start up

Administrator

Yes, Jim is right. But if you are worried about the spring, pull the cap and look. And as Jim says, make sure the loop captures the arm. Then with the cap against the carb turn the cap towards the arm to make sure the choke closes. That way you know things are working properly.

Gary, AKA "Gary fellow": Profile

85lebaront2

Re: 351M questions - poor cold start up

Administrator

If his carburetor has the external pull of diaphragm, either in the air horn or attached to the back of the main body, it needs to be adjusted to properly open the choke initially. Most of these external pull-offs have a two stage operation, first stage is the minimum opening the engine can handle dead cold, then a small spring in the pull-off will exert pressure to open the choke further as it begins to heat up so as not to become over rich. Once this stage is passed, further choke opening is dependent on heat only.

The other factor in cold running is the fast idle speed setting, it is always set with engine warm and on a 2150 is identified by an arrow on the fast idle cam. the screw is placed at the arrow and the fast idle is set with the screw. The reason it is set warm, cold is not an absolute, cold engine at 60° is different from cold engine at 80° or 30°.

Forward on a Ford choke is leaner, they rotate the inside counterclockwise to close as do Holleys. It should be marked on the cover, but may not be. FWIW, Carter AFBs rotate clockwise to close as the rod runs almost horizontally from the choke housing to the choke shaft and the choke shaft rotates counterclockwise to close where the choke housing inside rotates clockwise to pull the rod forward.

Bill AKA "LOBO" Profile

Gary Lewis

Re: 351M questions - poor cold start up

Administrator

85lebaront2 wrote

If his carburetor has the external pull of diaphragm, either in the air horn or attached to the back of the main body, it needs to be adjusted to properly open the choke initially. Most of these external pull-offs have a two stage operation, first stage is the minimum opening the engine can handle dead cold, then a small spring in the pull-off will exert pressure to open the choke further as it begins to heat up so as not to become over rich. Once this stage is passed, further choke opening is dependent on heat only.

The other factor in cold running is the fast idle speed setting, it is always set with engine warm and on a 2150 is identified by an arrow on the fast idle cam. the screw is placed at the arrow and the fast idle is set with the screw. The reason it is set warm, cold is not an absolute, cold engine at 60° is different from cold engine at 80° or 30°.

Forward on a Ford choke is leaner, they rotate the inside counterclockwise to close as do Holleys. It should be marked on the cover, but may not be. FWIW, Carter AFBs rotate clockwise to close as the rod runs almost horizontally from the choke housing to the choke shaft and the choke shaft rotates counterclockwise to close where the choke housing inside rotates clockwise to pull the rod forward.

That's the guy you want to listen to, not me. He ran a carb and ignition shop for decades, and has forgotten more about carbs than I'll ever know.

Gary, AKA "Gary fellow": Profile