M3A1 White Scout Car Zenith Model 29 Carburettor questions

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M3A1 White Scout Car Zenith Model 29 Carburettor questions

Post by Big D » Mon Feb 09, 2015 1:46 pm

Hi all,

I am after a bit of advice and photographs on the rebuild of my Zenith Model 29 carburettor for my White Scout Car.

I have finally got around to working on the carburettor as part of the restoration of my scout car. It was in a bit of a sorry state internally with a bit of rust through the bowl area. I’ve cleaned it up a fair bit and now just need to seal the bowl with a metal cleaner and conditioner.

I bought a carb overhaul kit for it, knowing that the kit was for the Zenith on the M8/M20 but I figured I would be able to use most of the gaskets etc, even if it wasn’t fully compatible. I hadn't seen a source specifically for a kit for the scout car.

I need a bit of advice on a couple of the bits and a photograph of the inside of the Zenith from the Scout Car would be real handy if someone has one. I have the Zenith model 29 carburettor manual which has been very useful.

This is what I have done so far.

• I replaced the idling jet from the kit. My one was bent and the one from the kit looked identical anyway.

• I removed the metering well and cleaned it and replaced it.

• I replaced the fuel valve seat but left the existing fuel needle valve. The one in the carb kit was slightly different.

• I cleaned the main jet and put it back in the carb. It is marked as ‘33’ which I understand is correct for the Scout car.

• cleaned out the other orifices as best I could.

• I tried to remove the pump assembly but it appears to be stuck (a little rust I’d say) in the top of the carb. It is different in appearance to the pump in the carb kit anyway.


I have attached a picture of the inside of my carburettor, top and bottom. I have also attached a screenshot of the parts manual which shows these items in an exploded view. Also attached are the parts that came with the carb kit that I haven’t used yet.


My queries are around these items:

• pump refill check valves. This is described as a pump refill check valve in the Zenith manual but called ‘disc’ in the Scout Car parts manual, with a part number of WI- 404846.


• power jet valve. This is described as a power jet valve in the manual but called ‘valve assembly’ in the Scout Car parts manual. Its part number is WI- 411230.


• pump assembly. This is called the pump assembly in both manual and Scout car parts manual and has a part number of WI-404844.

My questions are:

• Are the pump refill check valves and power jet valves the same between scout car and M8/M20? If so, how does one remove them without the tool specified in the manual? Alternatively, will I lose anything by not replacing them?

• The threaded valve in the carb kit; what is it, and is it compatible with this carburettor at all? I don’t see where it would go anyway.

• Is the pump assembly from the kit compatible with the scout car Zenith? Looking at the top of the carburettor I am wondering if part of the pump assembly has pulled away and is actually frozen in the top. Should the pump assembly be a loose fit in top and bottom?

Any advice would be appreciated.
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Darryl Lennane
NZ

1943 Willys MB
1941 LP2A MG Carrier
1943 White M3A1 AOP
1942 Willys MBT
1944 Ford M8 Armoured Car
1945 Ford M20 Armoured Car


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Re: M3A1 White Scout Car Zenith Model 29 Carburettor questio

Post by TopKick » Wed Feb 11, 2015 4:50 am

There appears to be a lot of dirt and rust residue in the bowl. I would make it as clean as possible. I would also replace every part that I could if I had the replacement parts in the kit. In the event something is held by rust, I tend to use PB Blaster to get it free. It may require a good soaking. Best of luck to you. 8)
"Keep 'Em Rolling"
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"Until it's melted down and turned into something else, or blown to Smitherines, it's restorable"!

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Re: M3A1 White Scout Car Zenith Model 29 Carburettor questio

Post by Big D » Wed Feb 11, 2015 10:49 pm

Hi Topkick,

Thanks for the reply. Yes, the flash on the camera probably makes the insides look worse than it is but I agree, it could be cleaned a little more. I'll tidy it up a bit more before sealing it.

I have not heard of that PB Blaster before. I had a solvent soaking for several days in the bore where the pump assembly should go though but in the end I got no further and took the bull by the horns. It turned out that the end of the pump assembly had come away and was stuck in there. It refused to budge and in the end I had to carefully drill a hole in it, tap it and then put a bolt in it so I could extract it.

I've attached a picture showing the power jet valve in the bottom of that channel now. Despite the way the end of the pump assembly was stuck, the bore that the pump runs in looks in good shape. I still have to clean out bore of the brass shavings from the drilling of the end of the pump assembly.

I will try to extract the top part of the pump assembly from the top of the carburettor next. The pump assembly in the carb kit looks exactly the same size although the ends have a slightly different shape so hopefully this will work.

I'll post some more pictures when I get the other piece out as it might help someone else.
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Darryl Lennane
NZ

1943 Willys MB
1941 LP2A MG Carrier
1943 White M3A1 AOP
1942 Willys MBT
1944 Ford M8 Armoured Car
1945 Ford M20 Armoured Car

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Re: M3A1 White Scout Car Zenith Model 29 Carburettor questio

Post by TopKick » Thu Feb 12, 2015 3:37 am

BigDm
Remember that once everything is disassembled all parts have to be clean, rust and dirt free, and set properly to get the best performance. When you put the outer housing back together be sure there are no leaks of air or fuel. Be sure the floats move freely. Have fun and good luck with it. 8)
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"Until it's melted down and turned into something else, or blown to Smitherines, it's restorable"!

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Re: M3A1 White Scout Car Zenith Model 29 Carburettor questio

Post by motto » Thu Feb 12, 2015 5:55 pm

Hi Darryl,
The threaded valve in the photos, as you've probably discovered, is the power valve. 'U' in the exploded view.
Both pistons on the accelerator pump assembly should be a neat sliding fit in their respective bores with minimum clearance. It works by manifold vacuum lifting it up against spring pressure, this draws fuel into the well below the lower piston. When you open the throttle, vacuum is dumped and the spring pushes the piston assembly down which squirts the fuel into the throat. Without this feature the engine would falter due to the fuel/air mixture being too lean momentarily until fuel flow catches up with air flow.

David

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Re: M3A1 White Scout Car Zenith Model 29 Carburettor questio

Post by Big D » Fri Feb 13, 2015 10:31 pm

Hi Topkick and David,

Thanks for the replies.

As you can see by the photos, I managed to get the other end of the pump assembly out. It was also stubborn and rusted in the bore. After a bit of cleaning the bores look not too bad but I will still need to clean the remnants of the rust off before reusing.

I note that the end of the pump assembly is slightly different to the one in the kit for the Zenith on the M8/M20. The pump in my carb has a chamfer on the end to match the end of the bore in the carb top.

What are your thoughts on how the flat end of the replacement vacuum pump assembly will work? I guess it may be a case of trying it and seeing if there are any issues.

I won’t be removing the power valve. It is marked ‘25’ but the one in the kit is marked ‘18’ so I will leave well enough alone and just make sure it is clear which it is.

Dave – do you know much about a product called Deoxidine? I was reading on a forum the other day that it is available in aussie and one guy in Victoria raved about its properties. I thought that this might be quite useful to clean the metal in the bowl and seal it. It is a phosphoric acid and solvent type metal cleaner and conditioner which removes rust and leaves the metal surface chemically clean.

I am not familiar with the product PB Blaster recommended by Topkick. The other thing that was recommended to me to try in the bowl to clean away any remaining residue was citric acid.

I’m just wary of using anything too harsh in around the brass valves in the carb.

Any other ideas?
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Darryl Lennane
NZ

1943 Willys MB
1941 LP2A MG Carrier
1943 White M3A1 AOP
1942 Willys MBT
1944 Ford M8 Armoured Car
1945 Ford M20 Armoured Car

motto
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Re: M3A1 White Scout Car Zenith Model 29 Carburettor questio

Post by motto » Sat Feb 14, 2015 9:31 am

Darryl
I don't believe the flat end on the vacuum piston would have any adverse effect on its operation.
I am not that familiar with deoxidine. I seem to remember using it in the airline workshop many years ago and that it was brush applied. It may be the answer. I don't imagine it would bother the brass components at all.
Most of my experience with chemical de-rusting has been in the use of phosphoric acid which is probably the active ingredient in deoxidine. I've been using it for around 40 years in the form of immersion baths which I would not recommend for such a complex, precision item.
I would be inclined in your case to follow the advice of the fellow who suggested deoxidine. Question him closely about application and possible adverse effects. I would be mindful of any very light springs if any are present. There is one in the power jet.
You may be better to tolerate a little unsightly surface rust which won't do any harm than risk complications by treatment. Continue as you are, tread lightly and take your time.

David

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Re: M3A1 White Scout Car Zenith Model 29 Carburettor questio

Post by Big D » Sat Feb 14, 2015 9:37 am

Morning David

You are up early.

Thanks for the replies. That was my other idea, that I would clean the bowl up a little more and just run with it as it is. As I said in one of the other posts, the flash on the camera probably makes it look a little worse than it does in natural light. There is no loose material and all the jets are now clear. I figure if all the degreaser and carb cleaner that I have used so far won't move what is left of the rust, then petrol in the carb is unlikely to as well.

I'll progress as you suggest. Cheers.

By the way - hope your projects are progressing.
Darryl Lennane
NZ

1943 Willys MB
1941 LP2A MG Carrier
1943 White M3A1 AOP
1942 Willys MBT
1944 Ford M8 Armoured Car
1945 Ford M20 Armoured Car

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Re: M3A1 White Scout Car Zenith Model 29 Carburettor questions

Post by RCASSIN » Thu Nov 02, 2017 2:32 pm

Hi, How did your rebuild go? I am about to start on mine... Just got my Scout car 2 days ago! Rob
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