One lung FM Z 1 1/2 HP

[Geo46]

Good morning, I am new to the forum and not sure where to post this , anyway we have a Fairbanks Morse 1 1/2 HP Z , someone has removed the original mixer and installed a Flo Jet carburetor, apparently it did run at some point, we are looking for a substitute for this carb as it is prone to leaking, any thoughts?
Thanks
Geo46🇺🇸

[cnr6400]

Welcome to the forum. Have you looked at all on Smokstak.com? Plenty of info there on FM 'Z's , and a sales / want ad bulletin board too. You might try a rebuild kit for the FloJet carb in the meantime, it might help fix the leaks. 

[Geo46]

Hi, yes I am a member of that forum, just looking for other inputs, carb has been rebuilt, they are prone to leaking.
Geo46🇺🇸

[gipetto]

If it were me i think i'd try adapt a motorbike carb to it. Honda 50cc are about the smallest that i know of, they are 4 hp, so they should be a good match.

[Geo46]

Thanks, looking at all options, any idea on Honda P/N?
Geo 46🇺🇸

[Bluechip]

If it were me i think i'd try adapt a motorbike carb to it. Honda 50cc are about the smallest that i know of, they are 4 hp, so they should be a good match.

My Mantis cultivator has a Honda 22cc OHC engine.  Maybe too small ?


https://www.ebay.co.uk/itm/175659641621?chn=ps&norover=1&mkevt=1&mkrid=710-153316-527457-8&mkcid=2&itemid=175659641621&targetid=4584757337008490&device=c&mktype=&googleloc=&poi=&campaignid=431353847&mkgroupid=1298523655396099&rlsatarget=pla-4584757337008490&abcId=9301942&merchantid=87779&msclkid=b28ce512d43017a91e818044e67cec4f

D.

[Geo46]

Thanks, I’ll check it out
Geo46🇺🇸

[Alyn Foundry]

Hi.
I rallied several of these engines years ago. One of which was missing the carburettor. I made patterns and castings for it.

Please see attached.

Cheers Graham.

[Alyn Foundry]

Not sure whether you missed my previous post….

Originally these engines were dual fuel. The carburettor has a small chamber that is filled with Petrol/Gasoline and an inbuilt needle valve to adjust the mixture. Once running the engine would start to get hot enough to transfer to the main fuel, Paraffin/Kerosene which was stored in a large rectangular tank carried between the skids. The Venturi area has a front cover that has a spring loaded valve, effectively acting as a choke device.

I have a set of Iron castings, unmachined, but I don’t think the original style carburettor would be suitable for what appears to be a mobile unit.

   Graham.

[Geo46]

Thanks for the reply, I am well aware of the original mixers, seems like you are more capable then we are, someone retro fitted this with a Flo Jet, I believe it was to get better throttle control as this was used on a small locomotive, my main goal now is to find a carb other than Flo Jet even if it means making a new manifold, not sure how to size a carb.

[Vixen]

It would help if you were to tell us the engines capacity and required operating speed. It should then be possible to recommend a suitable commercial  carb
Mike

[Geo46]

Well it’s a 1 1/2 HP about 450 RPM, open crankcase , 5” piston, intake valve controlled by an external spring.

[gipetto]

I suggested a honda 50 carb before, but given your figures it would be way to small. I would suggest a mikuni vm clone. they are flange mount, sold on aliexpress. I love them as they are more reliable than the pz series. I'm just guessing as to a size, but i had one on a 220cc honda fourtrax and it ran great. to be more accurate, you would have to calculate the horsepower of a motorbike/atv engine at the same 450rpm, not especially difficult since horsepower doubles with rpm.
for instance, a honda recon 250cc generates 15.6hp at 6500 rpm, therefore the same engine will generate 1.08hp at 450rpm because 6500/450=14.4 and 15.6/14.4= 1.08hp
I fitted a mikuni vm22 to my honda fourtrax, so it will run, but you might want a larger model such as vm24.

[Vixen]

 A honda recon 250cc generates 15.6hp at 6500 rpm, therefore the same engine will generate 1.08hp at 450rpm because 6500/450=14.4 and 15.6/14.4= 1.08hp
I fitted a mikuni vm22 to my honda fourtrax, so it will run, but you might want a larger model such as vm24.

If the vm22 can deliver enough air/fuel to run a 250cc engine at 6500RPM then it will be capable of passing about 15 times too much air/fuel for a 450 RPM engine. IMHO, a much smaller carb than a vm22 is required, not larger.

Mike

3mm (correction 6mm) diameter is about 1/15 the area of 22mm diameter. Therefore, the carb from Bluechip's Mantis cultivator, which has a Honda 22cc OHC engine would be much closer to the mark


https://www.ebay.co.uk/itm/175659641621?chn=ps&norover=1&mkevt=1&mkrid=710-153316-527457-8&mkcid=2&itemid=175659641621&targetid=4584757337008490&device=c&mktype=&googleloc=&poi=&campaignid=431353847&mkgroupid=1298523655396099&rlsatarget=pla-4584757337008490&abcId=9301942&merchantid=87779&msclkid=b28ce512d43017a91e818044e67cec4f

[gipetto]

Well I could be wrong, but I think my math is correct, since it's not especially difficult to calculate. The only issue i can see is that a vm22 may not allow the engine to idle at that slow a speed, the pilot jet could rev higher than the max rpm of the engine. from a quick search, polaris atv idle at 1200 rpm.
I guess to avoid the idle issue it would be better to go small. It may run, but the power it produces will be abysmal.