Help - engine runs only with carb choked. Ideas?

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Model T Ford Forum: Forum 2016: Help - engine runs only with carb choked. Ideas?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Melham on Sunday, September 11, 2016 - 04:10 am:

I've been breaking in a newly-rebuilt engine for my '26 coupe and having trouble keeping the engine running without the carb being more or less fully choked.

The engine was very comprehensively rebuilt last winter. Before reinstalling it this spring, I replaced all the wiring, cleaned the fuel tank, replaced fuel line and sediment bowl, new radiator, rebuilt coils and coil box - the works. The carb is a newly rebuilt Holley NH - the kind with the swivel-type needle valve. (Replacing a vaporiser.)

As advised by my engine rebuilder, the break-in procedure is to run the engine for increasing periods of time, limited by keeping the coolant temperature below 180 F. (Retorquing etc in between.)

A few months ago, we got the engine started and it ran fine the first time. After that, however, we found we could keep the engine running only by having the carb continually choked. I'm returning to the car for another go next week, and wonder if forum members have any advice for what to look for if we have the same problem this time.

As my car and I are 4000 miles apart, and I get to visit only for brief periods, it would be helpful to go armed with ideas to solve this problem.

I think I have checked all the obvious things - fuel in the tank, a good flow into the carb, etc. I believe I know how to operate the throttle and spark advance correctly - though it's been 40 years since I was a regular model T driver.

Any advice?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Alan George Long on Sunday, September 11, 2016 - 07:41 am:

I would recheck your carby mixture screw is one turn or slightly more. Sounds like fuel starvation to me
Alan


Top of pagePrevious messageNext messageBottom of page Link to this message  By Joe Fedullo, Milford MI on Sunday, September 11, 2016 - 08:19 am:

Sounds like a fuel delivery issue. Set your mixture screw like the previous poster mentioned. If you have a fuel filter, it may be plugged. Make sure you have good flow to the carb by taking the line off the carb and opening the valve. If you have good flow it could be dirt in the carb.

-Joe


Top of pagePrevious messageNext messageBottom of page Link to this message  By Peter Claverie, Memphis TN on Sunday, September 11, 2016 - 08:25 am:

I second Alan's suggestion.

Obviously if the engine runs only when choked, the reason is fuel starvation. There are only two possible reasons - the mixture is set incorrectly, or some passage is blocked.

While the "normal" setting for a mixture needle is 1 to 1 1/2 turns open, remember that no two Model T's are alike.

I'd start by closing the mixture needle valve, then opening it 1 1/2 turns. Start the engine on choke, then fiddle with the mixture / choke relationship until you find the sweet spot.

If you can't find a sweet spot, the only reasonable explanation is crud in a passage. It's possible you can dislodge it by opening the needle valve 5 or 6 turns, but not certain. It may require opening up the carb and blowing out passages.

Best of luck!


Top of pagePrevious messageNext messageBottom of page Link to this message  By G.R.Cheshire on Sunday, September 11, 2016 - 08:26 am:

Check for air leaks in the intake (gasket between carburettor and intake, and intake manifold to head) and check the intake manifold for cracks (Sometimes a can of wd40 can help in checking for air leaks although some people prefer an unlit propane torch. just spray or move the nozzle until the engine changes RPM that is where the leak is) :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Sunday, September 11, 2016 - 09:24 am:

Maybe the fuel sediment bowl is plugged?
Maybe someone added an inline fuel filter?
Maybe you have a Grose jet in the carburetor?
Maybe there is not very much gas in the gas tank?


Any of the above and a hundred other reasons could cause a lack of fuel in the carburetor, making it necessary to keep the choke partly closed to compensate for a lean mixture.


Top of pagePrevious messageNext messageBottom of page Link to this message  By john kuehn on Sunday, September 11, 2016 - 09:25 am:

Lack of enough fuel to keep it going sounds like to me. Open the fuel needle about 1 turn more. It should start with 2 turns or even 2 1/2 turns.
Depends on your T. They aren't all alike.

How much gas is in the tank. T's are gravity fed and they do run better with more fuel. Was the fuel tank cleaned out or has it ever been?

I'll bet its something pretty simple.
Good luck!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Eviston on Sunday, September 11, 2016 - 09:43 am:

Greetings, Professor. To the above I will add float level set too low. What part of the world is your T in? If this turns into a conundrum, perhaps there is someone near that can be an extra set of eyes to look things over.


Top of pagePrevious messageNext messageBottom of page Link to this message  By ROBERT BERGSTADT on Sunday, September 11, 2016 - 09:56 am:

Open the drain plug 1st to see if you have a good stream of gas coming out, Bob


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Eviston on Sunday, September 11, 2016 - 09:57 am:

Also, since it ran fine at first, the brass pin that the float pivots on may be bent. As this moves around, it changes your float level. Also causes the float to be unlevel. In other words, the float may be at the proper distance from the carburetor flange directly opposite the pivot and the needle valve.But,the float may be lower on one side. And the side that hits the fuel in the bowl first determines the level. Of course, any of the other suggestions may be the problem, but I have a feeling you are fighting a somewhat unusual situation. Eg:float level variation.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Sunday, September 11, 2016 - 11:01 am:

Well, there are all sorts of things that could be wrong but generally speaking, if it ran well once and then does not there is something restricting the fuel flow.

NH's are very simple and forgiving of a lot of things so it is easy to overlook reasons why they don't run.

The most common things I find wrong with them when they have been "rebuilt" is:

1. There is some kind of restriction in the inlet valve. Usually that is a little piece of crud or a piece of plastic tape that somebody put on a fuel fitting that has washed down the lines and got stopped by the inlet (float) valve.

2. Grose Jet installed for an inlet valve. Now it is sticking part way closed and will not flow enough fuel. Unfortunately, the new supposedly correct float valves all leak without some work on them so it is a dilemma of how to get them to stop leaking or to keep the Grose jet which doesn't leak but tends to stick.

2B. The inlet valve is sticking partially closed and won't flow enough fuel to run.

3. The main jet -- the one that screws in from the bottom of the stem, is plugged with some little piece of crud; rust, dirt, plastic tape or MOST COMMON, a blob of softened paint from the inside of the bowl or the bottom of the body that was painted with some 49 cent paint from Wally World that has dissolved in the fuel, especially the Ethanol based fuel readily available today.

4. The passage plugs were not cleaned during the rebuild but sprayed with cleaner, blown out and left like that. Now the fuel is dissolving old shellac and varnish and dirt that should have been removed when it was rebuilt and it is settling in the bowl, then sucked up into the main jet plugging it.

My guess would be #3. If it will run with the choke on it has fuel in the bowl, it is just not getting enough in the venturi to run the engine. If you have the adjustment needle open far enough that it should be flowing enough to run you have something in the main jet. Dissolved paint is usually the culprit.

There is another possibility but since it ran well once this is probably not it. Many of the intake and carb flanges are bent enough that they leak considerable air around the gasket. If the carb flange was not checked during the rebuild that can cause the symptoms you are describing. However, since it ran well once, that is not likely.

I laugh at some of the "rebuilds" people sell. I have bought a few just to see what they are actually doing to them. Most of the "rebuilds" I see on ebay or from a few of the people selling them consist of a quick dip in cleaner, a float valve and a coat of paint. I bought three from one guy selling "guaranteed" NH's, basically he was wire brushing the dirt off and painting them, putting in a gasket set and putting them on ebay. I doubt that he even knew they had passages that had to be cleaned. If he knew it, he sure wasn't cleaning them.

Float level on an NH is not very critical, there is a correct level, a little higher fuel level is better than a little lower but it is not all that big a deal on an NH.

Ford was paying around 30 cents per carb for NH's along toward the end. There is a reason there were over 200 accessory carbs made for the Model T. Ford stuck the the NH because they were cheap, reliable and could be cleaned in ten minutes with a Crescent wrench, a screwdriver and a cream tag wire, which every farmer in America had under the seat of his T.

I am not looking for business with this link and do not do a dozen NH's a year so this is not an advertisement but just for fun you might want to look at this. I am still 30 or so carbs behind, headed to the shop this morning again to try to get caught up a little more and I am not accepting any new work until at least the middle of October so I am not soliciting business. However, quality varies, check out who is doing or who did your rebuild.

www.stombergof.com


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Sunday, September 11, 2016 - 11:17 am:

I don't think this has been mentioned; Ethanol blended gas has a short tank life. It absorbs moisture from the atmosphere and is hard on fuel system internals. DRAIN the tank and refill with premium fuel. Scout around to try to buy gas with NO ethanol.
If it was my car I would rev the engine to at least 1500-2000 rpm and then pull the choke on hard for a second and then let off. Do this several times. You will either pull the crap in the carb all the way through or plug it solid. Either way you will have either fixed it or know where to work on it!!!
I had to do this recently on my 33 Ford that had sat for too long. Fixed it right up
One more thing. Sea-Foam fuel treatment has saved me at least 4 carb jobs. Put the whole can in 5 gallons of gas. Get the car started and keep it going for a few minutes. Walk away for a few hours. Try it again. It has dissolved a lot of fuel "varnish" for me. Probably do the Seafoam thing for a day before the full throttle full choke thing!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Sunday, September 11, 2016 - 11:32 am:

Also, Ethanol will dissolve virtually anything in the tank, lines, etc. that has accumulated in there over the years. Old gas would leave a lot of varnish that new gas would not dissolve and it would not cause a problem. As soon as you put anything with ethanol in that tank or system you will dissolve that crap in there and since it is going to be heavier than gas it will head right for the outlet and the line to the carb. If it gets through that it will be in the carb.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Melham on Sunday, September 11, 2016 - 04:14 pm:

Grateful thanks for all these wonderful suggestions - I will approach the car this time with lots of ideas for what to look for. I'm pretty confident that the fuel tank was clean: it was skilfully steam-cleaned by a terrific and experienced guy in Calgary, where the car lives. (One thing is for sure: I don't relish ever again doing the job of removing the fuel tank from under the cowl of a '26 Coupe and putting it back again.) I've been opening the needle valve 1 1/2 turns, but will try other settings. Beyond that, I'll start to take things apart following the suggestions generously made here. The rebuilt carb came from whoever does this for Lang's, so I assume this is good.

Thanks again.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Sunday, September 11, 2016 - 05:33 pm:

Tom
Ethanol has caused me a lot of grief in the last couple of years. And Sea Foam has saved me some grief (or at least helped me get out of some trouble)
I live at Calgary


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Sunday, September 11, 2016 - 06:15 pm:

OK, I'm going to phrase this as carefully as I can to try to solve your problem without sounding like I am bad mouthing some car rebuilder.

NO fuel bowl on any carburetor should be painted with any kind of paint or coating except possibly good quality powder coating. Ethanol will dissolve virtually any paint including epoxy to the point with will shed some "slugs" of paint which will suck up into the main jet and partially plug it. Sea Foam will dissolve just about any paint ethanol won't and will cause even more of the paint to slough off.

Knowing where your carb came from and who most likely rebuilt it my suggestion to you remains to remove the bowl, bead blast, sand or whatever you have to do to the inside of the bowl to get rid of the paint that is most likely in there.

It takes 30 seconds to remove the bowl on an NH. If I were you, I would order a new bowl for it, remove the old one and replace it with a new bowl. Do not paint or coat the inside of the bowl with anything. If you don't want to remove the carb, which is what should be done, get a chunk of G string off a guitar, while you have the plug out of the bottom of the bowl, screw the adjustment needle out a dozen turns and run the guitar string up through the jet. That should solve your problem unless the underside of the body was painted. Then that paint will also slough off and work its way into the main jet.

In any event, that is most likely the cause of the problem with your carburetor. If it is not paint it is something else blocking the main jet but I'd put a couple bucks on the line for it being paint.

By the way, here is the correct link. www.strombergof.com


Top of pagePrevious messageNext messageBottom of page Link to this message  By bob middleton on Sunday, September 11, 2016 - 06:23 pm:

Intake leak


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Coiro on Sunday, September 11, 2016 - 07:00 pm:

If your engine will only run while choked, it may be telling you that it needs a richer mixture—that's what choking does; it enriches the mixture.

Why might it need the mixture enriched? -Well, if it's a new carburetor, the mixture might simply need to be properly adjusted. -When a piece of dirt gets stuck in my carburetor, as will occasionally happen, the answer is to give the mixture knob enough counter-clockwise twist to richen up the flow and smooth out the engine. -After the dirt or debris or whatever gets swallowed by the engine and blown out, the engine will start to run sloppy and that's when it's time to lean it out again. -Over the course of six years, that has happened maybe four times.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Sunday, September 11, 2016 - 08:04 pm:

The rebuilt carbs from Langs have a Grose jet that causes problems.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Lloid on Sunday, September 11, 2016 - 08:11 pm:

Sounds like not get to g fuel. Just my guess. Tim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Melham on Sunday, September 11, 2016 - 08:47 pm:

Thanks for the suggestion, Stan. I will order a new bowl and (I guess) some gaskets prior to my trip to Calgary - in case this is the problem. One of the exciting things about working on a car 4300 miles from home is you need to order all the parts you think you might require, well before you get on that plane.

The intake leak suggestion is also a good one to follow up. After all, this is a rebuilt engine run-in and maybe there are loose bolts after the first few minutes of running. I'll also drain and refill with ample gas before starting. All it had last time was a gallon or so. . .

I have to confess, looking at the diagrams I have found of the NH, I am a little baffled about all these "passages" people speak of. Not to mention the "low speed inlet". I guess I have to take one apart and see it with my own eyes.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Monday, September 12, 2016 - 01:41 am:

The low speed inlet is the hole under the ID tag on the side of the carb. There are three passages that are plugged with brass plugs. They are what feeds the fuel to the idle jet in the inlet near the butterfly valve. They have to be clean or it won't idle.

There are 50+ guys in the Foothills T club in Calgary, I'm about 300 miles south of Calgary in Helena, Montana. There is a lot of T expertise in the club.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Melham on Tuesday, September 20, 2016 - 02:20 pm:

Since I have just opened another carb-related thread, I figured I should close this one off by reporting back on the advice taken.

Following Stan's advice, I sourced and installed a new bowl. Drained the old gasoline - there was only 2/3 gallon - and replaced it with plenty of high-octane, ethanol-free fuel. Checked the flow upstream of the carb, which was strong. I noticed the spray needle had a groove in it from over-tightening; replaced that too. Finally, tightened the intake manifold.

Basically, I took everyone's advice. Thanks to all!

The effect was that the engine started and ran beautifully, purring contentedly at an idle on 7/8 or a turn of the mixture knob.

Incidentally, when I removed the old bowl, there was some chocolate-brown goo at the bottom - lending credence to Stan's suggestion about the paint. Or else my gas tank cleaning left something to be desired.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Tuesday, September 20, 2016 - 02:33 pm:

Paint


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Melham on Tuesday, September 20, 2016 - 06:32 pm:

I think that's right. By the way, I also exercised a guitar G-string through the jet. It came out with a wee bit of black crud stuck to it. More evidence. . .


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