Checking jet sizes.

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Gavin
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Checking jet sizes.

Unread post by Gavin » September 13th, 2021, 1:53 am

I have a box of sundry jets that I have collected over the years and someone recently asked me for one, but I haven't got a clue as to what sizes they are and I cannot see any markings and have no gauges.

Any assistance much appreciated.
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rickf
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Re: Checking jet sizes.

Unread post by rickf » September 13th, 2021, 9:02 am

There are only two sizes, 28 and 30. They are usually marked on either the face of the jet or on the side. I have seen some where you cannot see the marking. I do not remember the drill sizes right off but if you have some welding tip cleaners find one that will fit one of the jets and see if it fits the other one. If it is much looser in the other one then you have a 28 and the other is a 30. You get the idea.
I just enlarged the pic and I notice you have power valves, needle seats, idle jets, accelerator jets. This all looks like it is from later 13660 carbs so all of the other jets other than the main jets I mentioned will be the same.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

Gavin
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Re: Checking jet sizes.

Unread post by Gavin » September 14th, 2021, 1:51 pm

Thank you Rick, that's a great way to sort them out.

Which model carbs took the larger jet and why please?

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Horst
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Re: Checking jet sizes.

Unread post by Horst » September 14th, 2021, 2:56 pm

The smaller jets where used in the later emission carbs to provide better emission values. Apart from the main jet, they use also an entirely different accelerating jet assembly (not interchangeable to older carbs) and a different spring rate for the accelerator pump.
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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rickf
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Re: Checking jet sizes.

Unread post by rickf » September 14th, 2021, 5:22 pm

According to the blueprints the 13660 and the 13660A used the #28 main jet and the 13660B used the #30 main jet. But I can tell you that in real life after taking apart and rebuilding over a hundred of these carbs this simply does not hold water. Most of the 13660 series of carbs used the #30 main jet but I have found the #28 in all three of the models. And as far as the size of the main jet vs. power......... this engine will never reach the top of the power band to fully utilize even the #28 main jet due to the restrictive design of the exhaust manifold.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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rickf
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Re: Checking jet sizes.

Unread post by rickf » September 14th, 2021, 5:23 pm

Horst, I have seen the two sizes of pump springs but I have seen very few of the heavy springs. I don't know what the application was or if it was a mistake but I have not seen enough of them to say it was a design change. There is nothing in the prints about a spring change.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

Gavin
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Re: Checking jet sizes.

Unread post by Gavin » January 30th, 2022, 2:23 am

So definitely two spring sizes then?

It's been nearly 15 years since I did a full strip and I can remember finding springs of different lengths, but not much different and I assumed that was an age difference.

Do you have any pics of the two types, by any chance?

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rickf
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Re: Checking jet sizes.

Unread post by rickf » January 30th, 2022, 10:22 am

I have a can full of parts from old cores, I will look through them but I have to ask, what are you looking to accomplish? A stronger spring will give you a little more gas on the accelerator pump push but all that is going to accomplish is a rich situation for that one second it is working. All the accelerator pump is doing is preventing a bog, it is throwing in extra gas to fill in the space made by the opening of the throttle. A standard spring works just fine so a stronger spring will probably cause you to actually lose a bit of power for the second it takes to burn off the extra fuel. Every part of a carburetor is designed around all the other parts so if you want to change one part you need to change the rest of the parts. And with todays tech, Just throw a Holley injection unit on it and call it done. You will have any power setting you want at the tap of a key on a laptop. And the parts will be a lot easier to find than old Zenith parts.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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rickf
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Re: Checking jet sizes.

Unread post by rickf » January 30th, 2022, 10:34 am

I see a guy on one of the 151 Facebook pages doing all kinds of stuff with a carb, grinding the ends of the jets, porting( not very cleanly) the inlet, Changing main jets and drilling jets, putting washers behind the accelerator pump springs. And what do you think he has gained? I would bet anything if you put that vehicle on a dyno it would still have no more than 75 horsepower but now instead of a nice smooth torque curve the torque curve would be about 600 rpm wide and mostly upper RPM. In stock form the torque curve on these engines is amazing, It starts right off of idle and stay level all the way up. Put a stock 151 in fist gear at idle and slowly start putting on the brakes and you will be surprised at how much it takes to stall it even at idle.

You want more power? You have to start going this way.
IMG_20201206_131156626.jpg
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1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

Gavin
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Re: Checking jet sizes.

Unread post by Gavin » January 30th, 2022, 1:23 pm

I believe we saw the same post Rick and that's what sparked my question. I truly have no idea what his objective is, or what he expects.

There seem to be a number of owners who seem to see these trucks as sports cars and want to tweak them up.

Not to forget the other poster who keeps telling people that Amsoil will improve their MPG and make it go faster.

The snag is that a lot of people hit FB for quick answers and get fed all sorts of myths and legends.

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Horst
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Re: Checking jet sizes.

Unread post by Horst » January 30th, 2022, 1:45 pm

I looked through my carb parts but for whatever reason did not find the two different accelerator pump springs. I’m 90% sure that they were quite different. But maybe just a mistake of the manufacturer. With NOS parts you never know if the reason why they are available was producing not to spec.

I ran into a part which I almost forgot. The next best thing after snake oil. Was supposed to remove the flat spot:
9AAB33DB-E2F3-4BFF-BF51-A0CA447AF3CF.jpeg
A different venturi build by some Italian guy. Was super expensive but sometimes you have to go the hard way to learn.
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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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rickf
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Re: Checking jet sizes.

Unread post by rickf » January 30th, 2022, 2:10 pm

Oh I remember those quite well! Remember he was going to sue me for even looking at that and wanting evaluate it. I told him to go ahead and sue away, from Italy. Vittorio is his name. He did make some nice lockers but that was about the only useful part he made. All that modification did was screw up the venturi effect of the original part and you ended up with a lean mixture because of poor atomization.

And everything he did was super expensive. That way the few parts he sold made the money before people realized they were a scam. Or just so expensive that it was simply no worth it.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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