Carburetor Rebuild Help - won't idle after rebuild

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rick3216
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Carburetor Rebuild Help - won't idle after rebuild

Post by rick3216 »

Here's the story on my all stock 1954 M37 which was running just fine. Compression tests recently range from 95 - 102 psi, not great but has run fine.

1. Tune-up done with new cap, condenser, rotor and points was completed and truck ran great - better than before

2. 20 miles post tune-up and I'm driving along and engine starts to sputter - seems like fuel starvation. Stopped engine for a minute and it started right up and ran fine for 20 seconds and then engine sputters again. Got it to my garage and now truck will not start at all. Had to push it into the garage.

3. Checked mechanical fuel pump - pumps well

4. Must be carb, been wanting to rebuild it anyway, so I order rebuild kit and tear into it. I have 40 years experience of rebuilding motorcycle carbs and I have the TM for M37 carb so I felt comfortable. All seemed to go well accept the accelerator leather plunger is very stiff in the bore compared to the old plunger that I removed which had zero resistance. I sanded the leather on the new plunger with fine sandpaper until the resistance was light, re-oiled and installed it.

5. Install newly rebuilt carb - truck won't start at all. Plugs are wet and I smell gas so I check for spark and I have no spark.

6. Re-installed old condenser and truck starts immediately but will not idle unless it is partly choked

7. Go to internet and everyone says vaccum leak. Check everywhere for vaccum leak - nothing. Checked with propane torch and starting fluid - still nothing.

8. Remove carb 6 times and confirmed float level is correct at 5/32 and I verified fuel level by filling carb with top cover off, whole carb spotlessly clean, confirm low speed passage is flowing, replaced low speed fuel jet with old jet, base gasket is not covering the hole in bottom of carb, intermediate gasket is not covering any holes, everything is moving freely. I have run out of things to check and try.

Truck runs fine with 1/2 choke, open the choke beyond 1/2 and it quits. After truck has run a few minutes with partial choke and engine warms-up it will start without the choke but will not stay running longer than 2-3 seconds. This leads me to believe that fuel is getting to the slow speed passages but the delivery is very slow.
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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by just me »

Something is still plugged and or misadjusted. The biggest improper adjustment I see is the float level. There are two different procedures to the same end result depending on solid or spring needle.
When you rebuilt it, did you remove the aluminum core plugs and clean the passages, or just trust to solvent and air?
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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by rick3216 »

I removed and replaced all the aluminum plugs. The new float needle had a needle seat, spring, and solid plunger that hits the floats whereas the old needle did not have the solid plunger. Regardless, I reset the float level to 5/32. I set it by attaching a piece of hose and blowing into the hose to determine when the needle is seated at 5/32. Since my original engine stalling was caused by the bad condenser I don't think I ever had any blocked passages and I doubt my cleaning would have blocked any passages. It has to be something with the way I rebuilt the carb.
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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by rick3216 »

I'm thinking that I don't have the throttle valve arm adjusted correctly and that the throttle valve is not completely closed when the gas pedal is not depressed and therefore not pulling the vaccum through the idle discharge port (and low speed fuel circuit) that is just below the throttle plate. Does that sound possible?
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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by rick3216 »

One more thing, I'm testing the carburetor without the air horn and air cleaner. I did plug the intake manifold hold where the air horn bracket bolts to. I can't imagine testing without the air cleaner makes a difference
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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by NAM VET »

while I have no idea why your truck is not running after your maintenance, I think motor vehicles have a Karma, or a JuJu, and just show their respect or lack of respect for their owners. How many times have I worked on a car, or had someone else work on one of my vehicles, and as soon as the work or maintenance was completed, show me disrespect. Put new brakes on a car, and the horn won't work. Put in a new head light bulb, and the transmission won't shift right. Re-charge the AC, and a wheel bearing starts to grind. Change the oil, and the radio fails. Put in a new cabin air filter, and a dash gage acts up. Put in a new oxygen sensor, and the cars starts to pull to the right. Put on new tires, and the dome light stays on. New shocks, and the door locks fail. It just happens too often to be a simple coincidence. I don't think vehicles have souls, or any spirit, but still, it just happens too often; I can't explain it.

I hope you can get your truck running well soon.

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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by sturmtyger380 »

That's funny! I have thought the same thing. I call it Machine Karma. I do regular maintenance on stuff and things do go bad, but my Son he is always having things break. His stuff goes bad faster than mine. I don't know if he is just harder on things or has bad, 'Machine Karma'! :lol:
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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by jim lee »

There's two schools of thought.

A) Working on your machine & using it. One tends to get "in tune" with the machine. You get used to its noises, typical behaviors and condition of most of the bits. This makes you subconsciously use it in such a way that you don't hurt it. I see this more with my Sailboat. I don't enjoy sailing until I've sailed enough to get back in tune with the machine and get a running feel for its condition.

B) Second school of thought is described by Terry Pratchett in the Diskworld novels. Basically it says "Everything strives". Meaning everything is a little alive. The more complex the mechanism, the more alive it becomes. In that model, your truck IS a little bit alive.

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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by RMS »

my vehicles always work better after a good cleaning. my buddy had a m37 and he suffered through three cracked blocks( all in the same place behind the starter). I told him that he needed to finish the truck and install the few missing bits, splash pans, side covers and driver side mirror. he said I was crazy and that those pieces would never contribute to the problems he was having. another buddy bought the truck we installed the missing parts and it has worked well ever since.

as far as your carb goes....... I will assume you got a kit with a white plunger and that's why it needed to be sanded. that being sait I have noticed some inconsistency's with the springs in that kit. could be worth comparing the old and new springs.
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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by MSeriesRebuild »

rick3216 wrote:Here's the story on my all stock 1954 M37 which was running just fine. Compression tests recently range from 95 - 102 psi, not great but has run fine.

1. Tune-up done with new cap, condenser, rotor and points was completed and truck ran great - better than before

2. 20 miles post tune-up and I'm driving along and engine starts to sputter - seems like fuel starvation. Stopped engine for a minute and it started right up and ran fine for 20 seconds and then engine sputters again. Got it to my garage and now truck will not start at all. Had to push it into the garage.

3. Checked mechanical fuel pump - pumps well

4. Must be carb, been wanting to rebuild it anyway, so I order rebuild kit and tear into it. I have 40 years experience of rebuilding motorcycle carbs and I have the TM for M37 carb so I felt comfortable. All seemed to go well accept the accelerator leather plunger is very stiff in the bore compared to the old plunger that I removed which had zero resistance. I sanded the leather on the new plunger with fine sandpaper until the resistance was light, re-oiled and installed it.

5. Install newly rebuilt carb - truck won't start at all. Plugs are wet and I smell gas so I check for spark and I have no spark.

6. Re-installed old condenser and truck starts immediately but will not idle unless it is partly choked

7. Go to internet and everyone says vaccum leak. Check everywhere for vaccum leak - nothing. Checked with propane torch and starting fluid - still nothing.

8. Remove carb 6 times and confirmed float level is correct at 5/32 and I verified fuel level by filling carb with top cover off, whole carb spotlessly clean, confirm low speed passage is flowing, replaced low speed fuel jet with old jet, base gasket is not covering the hole in bottom of carb, intermediate gasket is not covering any holes, everything is moving freely. I have run out of things to check and try.

Truck runs fine with 1/2 choke, open the choke beyond 1/2 and it quits. After truck has run a few minutes with partial choke and engine warms-up it will start without the choke but will not stay running longer than 2-3 seconds. This leads me to believe that fuel is getting to the slow speed passages but the delivery is very slow.
First mistake, sanding on the leather pump boot, chances of ending up with a boot that fits the bore well without flat spots as a result of sanding is less than slim to none. Pumping action is lost because of extremely poor fit in the bore, simply could not work well. Don't know where you got your rebuild kit, sounds like you may have used either NOS, (total junk) or one that has been on someone's shelf for years. I say this because in a fresh production kit the leather would have been soft and pliable. Trying to oil the leather is not worth anything as gas is a solvent that will wash away all oil in a second flat. Kits that are available today do not have all the necessary components to build an ETW1 carb the best it can be. We source parts from several sources to get all the best stuff to build these carbs. All the proper parts needed for a successful carb build are not available from any single source that I know of. The proper workmanship ethic is also extremely important, and based on what we hear is not available from many builders these days. Simply opening a kit and installing the parts included there WILL NOT build a top quality ETW1 carb. While some kits are better than others, all I have seen in recent years fall short. You would simply not believe all the times I have had people call saying exactly what you have described. We have built MANY of these carbs, learned a few tricks along the way. Almost always the reason the engine will not run smooth or sometimes not at all is a vacuum leak, however most do not look in the most obvious of places to find it. If torch testing proves nothing around the intake etc., most say ok vacuum leak is not the deal. Most never check on the carb itself. The most common place to find a leak is where the carb center section attaches to the cast lower section of the carb and where the cast base mates with the intake manifold. The surfaces on the cast top and bottom are almost always never flat, so much so that the gasket can not seal it. We have lots of carbs come in for rebuild, many with the complaint they have to be run with the choke partially out. It is standard procedure practice for us to surface both top and bottom surfaces of the casting on a precision surface grinder so they are perfectly flat. Good track record, feed back has turned out 100% positive for the carbs we have built that came in with the line attached, "will not run without partial choke". When they were put back into service, the problem of having to run with partial choke was cured. Certainly other issues can cause the problem, CHECK EVERYTHING, however based on what we have seen after building MANY, this is by far and away the most common cause of not running well without choke. You have talked about carb float level setting, 5/32" is not correct, it should be 5/64". Being a professional rebuilder, we do not use the original cone needle / concave seat assembly. We incorporate a flat face assembly that works much better and cures fuel starvation issues 100%. Short explanation; the float must drop way down with a pointed needle installed before MAX fuel flow can enter into the carb bowl. This is almost always the issue with sluggish acceleration, running out of fuel when operating on steep terrain, etc., because the bowl is not allowed to fill completely until the need for additional fuel in the bowl passes. The flat face assembly allows full open fuel entry into the bowl with a very small drop of the float, keeping the fuel level high in the bowl during peak demand. Our feedback from customers whom we have built carbs for has been better than 100% since we have started incorporating these improvements into ETW1 carburetor rebuilds. We offer full rebuild services if we can help you.

Other issues you have described such as running a short time then shutting down point to totally separate issues. #1, is the distributor ventilation system hooked up and functioning correctly? Don't say yes because you see the tubing in place! Many times we have discovered incorrect brass fittings at the carb elbow. Without the correct fittings, everything can appear great, BUT there is no forced air circulation which renders the vent system totally useless. Also check for plugged tubing, fittings, etc. Tubing is only 3/16" diameter on the outside, so obviously it does not take a lot to plug a line or elbow fitting. No ventilation means dead coils quickly as well as corrosion issues, etc. Running for a short time and shutting down is a classic symptom of coil break down. Typical scenario is after it cools a bit it will start and run for a short time, then shut down again. This will keep repeating. There are other distributor issues that can cause less than 100% efficiency as well. If your distributor has never been rebuilt professionally, there is a good chance we could vastly improve the unit for you, BUT before going further on carb and distributor issues, carefully read my next paragraph.

Now to the bigger problem we see that causes this, and we see it often. LOW ENGINE COMPRESSION. The next question I ask AFTER it is established that the distributor vent system is 100% is have you performed a compression test? Most often the answer is no and why should I? This usually comes after people have spent several hundred dollars working on the carb and distributor to no avail. Common sense here; it takes only a few minutes to perform a compression test, the test kit is cheap, and many auto parts stores loan them to customers. I strongly suggest this, perform a compression test in accordance with instructions included with the test kit BEFORE spending $$ on accessory component (carb and distributor) rebuilds. An engine with low compression will exhibit the same warm up / shut down symptoms as a bad coil. A common complaint I hear often is "I stopped for fuel and the engine either won't restart or is really hard to start." CLASSIC SYMPTOM OF LOW COMPRESSION. First rule out internal issues, low readings are most often the result of ring/cylinder wall wear, however there can be other things in play such as broken rings, cracked or slipped sleeves, valve issues along with a few other things. If you have a reading as low as 100 PSI, that is border line problems. Any reading of less than 100 PSI, you definitely have things that are not good going on and need to perform follow up testing to pin point the exact issue. If you find you have a low reading on 1 or more cylinders, post the test result here, I'm happy to advise you on follow up testing to find out exactly what is going on. If the test results show good, 105 PSI - 130 PSI, with no more than 5 PSI variation from 1 cylinder to another, then you can feel good about focusing all your attention toward carb and distributor. Obviously readings on the lower end of the "good" scale indicate not a lot of life left in the engine until rebuild time, we can discuss those issues if needed after we see the test results.
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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by keyslammer »

I just rebuilt my ETW1 carb on my 1953 M37. I had a bad float valve and decided to go thru it. After reassembly, I used a marine priming bulb to fill the carb and bench test it. I discovered that my carb is leaking fuel between the top and bottom halves. All the fasteners are tight and the carb body is not cracked. Is there a BETTER gasket then the rigid Grey one found in the rebuild kits?? Is there a reasonable sealant that can be used?

Thanks for any advice!

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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by MSeriesRebuild »

keyslammer wrote:I just rebuilt my ETW1 carb on my 1953 M37. I had a bad float valve and decided to go thru it. After reassembly, I used a marine priming bulb to fill the carb and bench test it. I discovered that my carb is leaking fuel between the top and bottom halves. All the fasteners are tight and the carb body is not cracked. Is there a BETTER gasket then the rigid Grey one found in the rebuild kits?? Is there a reasonable sealant that can be used?

Thanks for any advice!

Keyslammer
We see this all the time, check both the casting surfaces (top and bottom), we surface this on our surface grinder on each carb we build, it's never true on any we see. This is something most people never even give a thought, yet it's an issue every time. This one issue is the MAIN reason why engines won't run without partial choke. If you have gas escaping, I highly suspect you have other issues in play as well, maybe a crack or some other internal problem that you can't see easily.
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Carburetor Rebuild Question

Post by keyslammer »

I've resolved my fuel leaking problem...MSeriesRebuild was correct...the two halves were not flat. After surfacing them, and replacing the paper gasket with a Viton Flouroelastomer gasket...no leaks. I do have a question after my "pump up leak test" (no leaks):

How does the accelerator pump actually work?

On past carbs I've worked on...there is a mechanical linkage to the pump...so when the throttle is advanced, fuel is squirted into the barrel of the carb. On the ETW1, this is plunger/piston combination that appears to be hydraulically actuated. However, after filling the carb with fuel and actuating the throttle plate...no fuel is being squirted into the throat of the carb. I just want to be sure I'm not missing anything else (is there a special priming or bleeding needed to finish the carburetor rebuild)?

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Re: Carburetor Rebuild Help - won't idle after rebuild

Post by Elwood »

The accelerator pump on an ETW-1 is activated by a drop in intake manifold vacuum. No mechanical linkage. So you won't see any fuel squirt unless the engine is running (or you have a source of vacuum if you're bench testing the carb).

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A copy of TM9-1826A Carter Carburetors is helpful when rebuilding or diagnosing these carbs; the illustration above is on p. 157. Chapter 12 covers the ETW-1, and Chapter 13 covers the governor.

You might be able to find this manual online to download, or it is available from the usual military parts suppliers, ebay sellers, etc.
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Re: Carburetor Rebuild Question

Post by jim lee »

keyslammer wrote:I've resolved my fuel leaking problem...MSeriesRebuild was correct...the two halves were not flat. After surfacing them, and replacing the paper gasket with a Viton Flouroelastomer gasket...no leaks. I do have a question after my "pump up leak test" (no leaks):

How does the accelerator pump actually work?

On past carbs I've worked on...there is a mechanical linkage to the pump...so when the throttle is advanced, fuel is squirted into the barrel of the carb. On the ETW1, this is plunger/piston combination that appears to be hydraulically actuated. However, after filling the carb with fuel and actuating the throttle plate...no fuel is being squirted into the throat of the carb. I just want to be sure I'm not missing anything else (is there a special priming or bleeding needed to finish the carburetor rebuild)?

Keyslammer
Did you make those gaskets? If so, how'd you cut them out?

Thanks

-jim lee
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