Nathan Vos

Long time reader, first time thread poster.

I have a 1978 Ford XLT Ranger with a 351M (I am pretty sure it is a 351M, had the truck about 5 years and I believe I had made the determination a few years back). The carburetor is a 2150 Motorcraft as is standard and the transmission C6 auto. I only ever used it seldom, and the longer it sat and then subsequently used, the more the carburetor had begun to develop a dead spot on acceleration (or I believe it is the carb, with an old vehicle it can always be something else). I have been driving it more now at about every or every other day for about a year.

Anyway, with the old carb at idle it would be fine, but would fall flat on its face when the accelerator was depressed moderately until I pumped it again and then it would recuperate and get up to acceleration. It had started to get worse and worse. I didn't want to take the time to rebuild it so I adjusted the accelerator pump diaphragm to squirt sooner (it squirted gas down the venturi when I moved the throttle) and that helped. I believe a few years before I had replaced the accelerator pump diaphragm.

I figured it was time to rebuild or replace so I saw on Amazon they had a Chinese knock off carburetor, Rally 2100 carb, for sale for about $120. It had decent reviews. One guy had said that he put this carb on 1986 460 motorhome with 4 barrel intake with a 2 to 4 barrel adapter and it worked fine. The carburetor was listed as having a venturi size of 1.14 inches and 300 CFM which I knew was smaller than the 2150 at 1.21 and 351 CFM, but I figured if it worked on that 460 it would work on mine. I also had some second thoughts as only the older Autolites had this 1.14 venturi size, but that thought was after I ordered it.

I installed it and all the vacuum lines matched for my hoses and it all hooked up fine.

I started it with the new carb and it seemed to idle great and the motor did not shake like it did with the older carburetor. The only problem is when I goosed the throttle the carburetor spit up. Once it backfired out the carburetor.

In drive, under load down the street, the the engine consistently spits up or backfires out of the carb like the timing is too far advanced, but I have not touched the distributor since it was replaced it two years ago. A mechanic had set the ignition timing (long story on that - the dizzy refused to be removed and had to be removed piece by piece at a shop). It has no power upon acceleration and even backfires while the engine remains a constant speed after acceleration. I have refrained from driving or starting it after these quick experiments.

My question to the group is, what troubleshooting process should I commence from here? Does the ignition timing need to be retarded since I have less CFM for the motor (by the way, is there an easy way to access the dist. bolt? - my truck has A/C - maybe I should just get used to removing the compressor each time I adjust timing)? Should I be looking to adjust the fuel bowl or removing the jets to see what size they are and see if they need to be bigger? I am just looking for advice before I tear into this. Otherwise I would have to wait to rebuild the old Motorcraft rebuilt in a month as I do not have a place to rebuild it until I get a garage next month. I live in the city in an apartment.

I wonder if anyone else had bought these cheap smaller carbs or if someone has had experience putting on a smaller carb or Holly Economaster and see what adjustments they had to make.

Thanks for any help,

Nathan Vos

Braggs

Sounds like you know way more about carbs than me. Since you asked though, my opinion is that the carb overflow meeans the floats need adjusted but the backfire probly blew your powervalve. Time for a rebuild kit.

Nathan Vos

Thanks for the reply. Any idea on the HG for the power valve? It's a stock motor. I've heard you pick the HG of a powervalve by what the engine intake is at idle minus two or engine revved at an rpm I can't remember and halved.

I'll check the float level. I probably won't get to it later this week/weekend. It's pretty hot and humid right now in Iowa.

Also, I forgot to add. When I put the vacuum gauge on, it had said about 14 which indicates late timing, but I always thought too far advanced timing caused this condition. I stupidly did not look at the gauge when the throttle was opened as I was too busy worrying about the carb backfire.

Braggs

Nope, don't know. A new power valve comes in the rebuild kit, and if you take an old carb apart, you probly wanna change the gaskets anyways. 14 seems a little low. Might cap all the ports but the one you're testing and see what you can get it up to by adjusting the idle air screw, then connect everything back and see if it drops alot (meaning a vacuum leak).

GhostriderI

Do you still have your original 2150 carb? I would rebuild it and put it back on that way you are back to the correct cfm flow. Also the gasket under the carb spacer to intake (if equipped) might need replacing (was not in my kit) but I found on on E bay for under $15.00 with shipping

Hope this helps

Nathan Vos

Thanks for the help everyone. I got it figured out. Luckily I didn't blow the power valve, Braggs. GhostriderI, I do still have the 2150, I was planning on rebuilding it in about a month or two and having it on standby when this carb goes out. Luckily, I can still do that.

The ignition timing was too slow. You'd think the mechanic would have set the timing better, and that was over a year ago. The old Motorcraft carburetor still needs a rebuild no doubt, but the slow ignition timing wasn't helping anything.

That distributor bolt was a pain to get loose. I had to go get a 1/2" crowfoot and a socket wrench with three joints in it just to get at the bolt to turn it. Once I got that, the distributor wouldn't go any further clockwise as the advance cone was hitting the cooling hose so I moved the spark plug wires over one to the right in the circle and then moved the distributor counter-clockwise to compensate for the huge advance. It was hard starting and under load pinged and died at idle in gear. I moved it some more counter clockwise and it then really purred and didn't shake anymore. I have it sitting steady at 19" on the vacuum gauge with the idle screws at about 1 1/2" (it stumbled screwed in anymore than that - it isn't a real 2150 so I guess the settings maybe different) and idle at 720-30.

With that new 300 CFM chinese Rally carb, it has pep 1/4 to 1/2 throttle and pretty gutless past 1/2 throttle - but no hesitation anywhere. I can't speak to the longevity of this carb, but I'm pretty thrilled. I will post later as to what gas mileage it gets. Thanks again everyone. I hope this thread helps anyone else.

GhostriderI

Glad you got it figured out, just make a note somewhere about the changes on the distributor so you do not forget you did it and why (I keep a folder in the glove box with these type notes that I can look at when I am tinkering with my old truck)

Phil63146

FYI the power valve has the size stamped on it, (normally) on one of the flats where the wrench is put.