Zenith carburetor, it never ends :(

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Horst
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Zenith carburetor, it never ends :(

Unread post by Horst » June 17th, 2017, 9:11 am

My truck has now 4620 miles on the clock since new, pretty much all with me (got it with 72mi). So not very much use over all the years, there had been years with a lot of driving and years with mainly in storage. This year I decided to take out the little jeep a bit more for driving around town. And it annoyed me again. At light loads, driving 30mph in 4th gear, the power distribution is "uneven". The engine does not make smooth and constant low power but jerks back and forth a little bit, not much, but enough to not feel right. It always has been like this. Pulling a little choke makes things better.

So I tried the following:
1. removed the stock, non-emission carb
2.installed a 13660A emission carb with Milplus modified venturi (Rick knows what I am talking about). Pretty much similar, slightly better but also does not feel right, needs more throttle to do the same thing.
3. So I yanked it out again and replaced the venturi with a stock one. Made sure that the float was correctly adjusted. Idling very well in the drive way but terrible on the road, accelerating it would sputter and backfire.
4. Next adjusted the choke so that the choke blade would no longer sit horizontally with the choke knob pushed in but 20°slanted. Now the jeep would run ok, somehow similar stock configuration. I am surprised how much difference that little choke adjustment made, from non drivable to almost ok.
5. not sure what to do, probably replace the stock carb and do a similar adjustment on the choke
6. I have not played with the mixture screw yet, but will do this. Experience on the stock carb was that it would not affect the light load driving situation.

So I am a little lost what the issue could be, pulling a bit choke is what a lot of 151 drivers have seen, but somehow I don't like it.

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Horst

1972 USMC M151A2 w/ROPS (ex Barstow) and M416
1962 M201 and trailer
1966 GTO,1982 E350 Skoolie, 1987 SJ413, 1987 911
Gone: 2xM35A2c, Unimog 404S, Hanomag AL28, DKW Munga

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Horst
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Re: Zenith carburetor, it never ends :(

Unread post by Horst » June 17th, 2017, 2:51 pm

update:

I drove around today with that emission carb and the choke setting. Wasn't to happy with it, so I switched back this evening to the stock carb
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I could not do another test drive but it should be as before, right?

I did however a BIG rookie mistake: I don't know how many times we said on this board that before you start adjusting/messing with the carb, check everything else. Well, before I pushed the jeep back in the garage, I thought why not checking timing. I have an electronic ignition, checked some time before, as such it should not be an issue. Well, wrong. Timing was off, not very much, but when I advanced it to the correct position at idle, the idle speed at least changed (increased). Now will this affect or even solve my problem? Not very likely, but it sure made most of the carburetor testing of today obsolete. Having changed the carb so often now, I can do it now blindfolded with one hand behind my back...
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Horst

1972 USMC M151A2 w/ROPS (ex Barstow) and M416
1962 M201 and trailer
1966 GTO,1982 E350 Skoolie, 1987 SJ413, 1987 911
Gone: 2xM35A2c, Unimog 404S, Hanomag AL28, DKW Munga

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Re: Zenith carburetor, it never ends :(

Unread post by Hambone » June 17th, 2017, 4:32 pm

A correctly timed engine produces the most horsepower. An engine with timing too late (retarded) will have a low idle vacuum, have slow throttle response, feel like a turd at low RPMs and will run hotter than normal. An engine with the timing too soon (advanced) will have a high and erratic vacuum signal. It might have a snappy throttle response but it won't pull very well under a load, and it will have pre-ignition (detonation) problems, sometimes called "pinging", which will certainly lead to either a blown head gasket and/or serious piston damage, It will also idle rough. Hambone

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rickf
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Re: Zenith carburetor, it never ends :(

Unread post by rickf » June 17th, 2017, 5:06 pm

Normally I would say to adjust the idle mixture just a little to the rich side but I have a question. How are you getting that venturi in and out past the emulsion tube? That tube sticks up into the air stream and will make all the difference in the world with exactly what you are talking about. And to get it in and out is quite tricky since it is very thing copper and it is pressed in there. There is a specification for how high that is supposed to be in the venturi, it is buried in the -34 I believe. That is one thing I do not play with on my rebuilds. Try adjusting the idle as you normally would for the best idle and then turn it a little out and try that.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Horst
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Re: Zenith carburetor, it never ends :(

Unread post by Horst » June 17th, 2017, 5:12 pm

yes, you need to pull that emulsion tube out to get the venturi out. It did not get better doing it. I actually destroyed one in the process and took one out of another carb. Removing it will always put very little dents in it. I would want to buy new ones if they are ever available (which I doubt).
Horst

1972 USMC M151A2 w/ROPS (ex Barstow) and M416
1962 M201 and trailer
1966 GTO,1982 E350 Skoolie, 1987 SJ413, 1987 911
Gone: 2xM35A2c, Unimog 404S, Hanomag AL28, DKW Munga

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Re: Zenith carburetor, it never ends :(

Unread post by rickf » June 17th, 2017, 5:40 pm

If you get one of those drill bit sets with like a hundred plus bits in it then you can find one that is a perfect fit down that tube and then you can grab it with pliers and a soft cloth. But that measurement hast to be right and the contour on the tip and position of the tip have to be perfect. Try richening up the idle mixture and see how that works, and be sure the idle passages are all perfectly clean and blown out from the manifold side.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Horst
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Re: Zenith carburetor, it never ends :(

Unread post by Horst » June 18th, 2017, 3:10 pm

further update:

I did a test drive with the stock, non-emission carb, choke plate at around 20° and now correct timing. Doing today a 50mi trip it did everything it should. Almost pleased. I want to get rid of the presetting of the choke, a board member recommended to lower the fuel level in the bowl, I will try that. I wonder what setting a little bit of choke does, I am assuming it just changes the airflow to the better when it is set a few degrees into the air stream, I don't think it will considerably change the mixture.

I am getting a little unsure if I really have an electronic ignition installed. I know it had points to begin with and I had bought an electronic ignitor later on as a spare. Not sure which one is which, so I need to open the spare one to check what is inside. I still don't understand how the ignition timing retarded but certainly, given it can be done in 5 minutes, I will now check timing every 500miles or so.

After the drive I checked a plug, surprised to see that it is actually on the lean side now. This was however after driving it the last minutes through town, I need to repeat directly from a full load run to compare.
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Horst

1972 USMC M151A2 w/ROPS (ex Barstow) and M416
1962 M201 and trailer
1966 GTO,1982 E350 Skoolie, 1987 SJ413, 1987 911
Gone: 2xM35A2c, Unimog 404S, Hanomag AL28, DKW Munga

PPanagakos
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Re: Zenith carburetor, it never ends :(

Unread post by PPanagakos » June 19th, 2017, 10:13 am

I just had to comment on this topic. I have two of the Zennith carbs ( I assume these are aftermarket as they don't say Zennith on them). I fought with these for months, rebuilt them both, adjusted per instrcutions, tried everything and all failed. Had the flat spot when accelerating, got them to idle, but that was it. I'm not meaning to advertise for anyone, but someone here said send it to Billy Brooks. I did and when I got it back, put it in, adjusted nothing and it has worked fine ever since. Don't know what he did, but he obviously understands this carb and I don't. So if all else fails. And I still have the other carb left. I may send him that one for a spare.

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Re: Zenith carburetor, it never ends :(

Unread post by Grasshopper » June 19th, 2017, 10:33 am

PPanagakos, can I assume that Billy Brookes is based in the US? I have one of those crummy copy carbs on my machine and everything I try on it is a compromise.

Vince (London(ish), UK)

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Re: Zenith carburetor, it never ends :(

Unread post by rickf » June 19th, 2017, 11:28 am

Grasshopper, Does this carb have one number on top of the carb instead of several? If so I am running one on mine and have been for 6 years with no issues and there have been many guys with M151's at Aberdeen who have found that they cannot even come close to catching me pulling the long hill from the beer store. One of our other members set our unofficial speed record, 71 mph on the GPS in a photo with one, Pulling a trailer! And I know of many others out there. There is absolutely nothing wrong with those carbs. They are exactly the same as the 13660, just made on a different contract. There is no magic to eliminating the flat spot, I do it all the time and have posted how on here so many times I can't count them. I guess nobody listens. I am also rebuilding carburetors but I do not profess to make them look nice and shiny new. You send me your carb and I will clean it and rebuild it so that it runs correctly. If you want one that looks like brand new then go to Brooks. Mine are serviceable carbs.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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m75
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Re: Zenith carburetor, it never ends :(

Unread post by m75 » June 19th, 2017, 11:54 am

Grasshopper,

https://www.youtube.com/watch?v=AdP-qHbsPeI

The company is located in Florida. I have yet to hear anything bad about his work. Price was about 250 USD, using your carburetor as a core.
Jim Peterson
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1961 M151 -Sold
1974 M151A2, Working It!

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rickf
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Re: Zenith carburetor, it never ends :(

Unread post by rickf » June 19th, 2017, 12:07 pm

I do not get in the habit of putting other business's down but that first video is a piece of work. He has the damn choke on the whole time and is choking the engine to the point of stalling. I could do the very same exact thing with his brandy new shiny carburetor. This is called marketing and it is not very good marketing at that. Just look at the choke position in the first part of the video, granted they make sure the video is blurred but you can still see the choke is almost completely closed and he is keeping it right at the stalling point. If the carb was in that bad of condition it would not accelerate as fast as it does. Hey, It is his business and if people want to pay that kind of money for a rebuild then go for it. I can still buy new ones from Zenith for 330.00.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Horst
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Re: Zenith carburetor, it never ends :(

Unread post by Horst » June 19th, 2017, 4:07 pm

he specifically says that the engine would not run without the choke almost closed. With would mean that carb is really shot.

Everybody seems to be quite happy with his work, I actually wonder what he modifies besides a normal rebuild. These carbs are so simple that there is not a lot of room for mods..
Horst

1972 USMC M151A2 w/ROPS (ex Barstow) and M416
1962 M201 and trailer
1966 GTO,1982 E350 Skoolie, 1987 SJ413, 1987 911
Gone: 2xM35A2c, Unimog 404S, Hanomag AL28, DKW Munga

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Re: Zenith carburetor, it never ends :(

Unread post by rickf » June 19th, 2017, 6:04 pm

Horst, While we are talking about Zeniths, a while ago didn't you say you could not use the inlet fitting with the filter in it in a late 13660 carburetor? The one that screws in from the top that has the bypass on the later carbs. I just did some testing while rebuilding some carbs an swapped them back and forth between each other with no problems. There is no difference on the inside of the fitting other than the late model has no filter and it does have a small hole for vapor return. Apparently this is one of his mods, he grinds a spiral cut in the thread for some unknown reason. All that will do is allow gas into the unused chamber above the threads, it goes nowhere from there. I would like to see one in person.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Re: Zenith carburetor, it never ends :(

Unread post by m3a1 » June 19th, 2017, 7:41 pm

I think you are thinking of me. I actually did that with my A2 after swapping in the Brooks Rebuild that had originally hung on the Alley Cat. He told me to make the angle cuts saying that the fuel wouldn't flow through in sufficient quantity. It was actually quite an easy modification.

http://www.g838.org/viewtopic.php?f=27&t=10252&start=30

Cheers,
TJ

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