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1973 Honda B75 converted to propane power

Honda_B75

New member
Hello all honda lover's

I recently acquired a honda b75 ser # b75-1003075 and it had some top end carb issues. The main jet needs an 0 ring and fuel shut off needs a new rubber stopper.

So I decided to remove the dirty gas carb (gasoline is a dirty fuel with all the carbon, and gas souring in 60 days due to ethanol, carb is very clean), and build a very simple propane carb for the motor. Just some copper tube and a good regulator.

So if have carb trouble with a 4 stroke honda this maybe an option for you

Have the idle now down from spec 1200 to 575 and purrs like a kitten, a top end is same at 5000 rpm

Use a $13.00 20 lb bottle of propane in 50 hours at trolling speed

And more worries about storing the fuel, and my brother can not steel the gas for his car

just a thought for anyone with an old 4 stroke that the parts are obsolete
 
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Great post! Just saw my first commercially produced propane outboard the other day (5 Hp) ---nice to know you can do your own conversion.
 
I just want to know where you're buying you're fuel!! I'd love me some $0.60 a gallon steaks for me barbi!

Gday mate!
 
Honda_B75 - It would be neat if you posted more detail on exactly how you did that and what parts you used.


How i converted to propane

For most 4 strokes simple putting propane into the air mix will make it run, however i had carb issues

So i completely removed all fuel systems (carb and fuel pump)

I then put a propane torch into the intake manifold to see what would happen, and to my delight the motor started right up at a low chug

Then i started looking for stuff to Canibalize , and found the turkey deep fryer to have a nice variable pressure regulator on it, so stole that

I then found an water hook up kit for an ice maker (the plastic tubing and a saddle back valve) unscrewed saddle and to my luck was the same npt thread as the regulator

So i now i have the 20 lb propane tank hooked up with the 1/4 plastic tubing at the end (tank, variable regulator, the saddle back needle valve - the saddle removed, compression fitting to plastic 1/4 inch hose

"Carb making" Made a template of intake out of 1/2 inch uhmw (plasic cutting board) x 2 , drilled a 1/2 inch hole put a 3 inch 1/2 inch piece of copper between them
and made a carb.

bolted it on to motor with oem bolt and then applied propane and engine ran,

Ok well this is a start i will need to find out how to link pictures for this to make sense, but is a start
 
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Honda B-75  Boat view.jpgo on boat, the deck screws keep it from sliding down shaft, (just simply screwed in to plastic then threw copper pipe) high heat silicone to seal up.

NOTE: never put propane inside boat, propane if leaks or vents will pool at lowest point danger danger explosive whenever

will try to post a video of motor start and running
 
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Hello, can you help me find the parts that I need from Ace Hardware's website and/or Home Depot so that I can buy what I need from the stores for this conversion? Here's what I would need to find:

1. water hook up kit for an ice maker (the plastic tubing and a saddle back valve)
2. variable pressure regulator

The rest of the supplies I can figure out. My challenge has been not being able to locate a main jet for my newly rebuilt 1975 B75 Honda 7.5 Outboard. She's ready to go, otherwise. So, I'm guessing the propane conversion is the way to go.
 
Welcome to the forum.
It is my opinion that the system described above would not be very economical to operate in that there is no regulation of the fuel for ON DEMAND delivery. You would simply be "fogging" the fuel in on a "guesstimation" schedule and the possibility for waste is evident. Will it work? Yes, absolutely. Is it efficient or cost effective? I doubt it. There is also a bit of safety to consider with a project like this and that may or may not concern you. Do you boat with your family?

If it were me, I would continue to solve the jet problem. Have you tried the local "speed" or hot rod shops in your area? There are usually many jet options in those types of stores and you might find something you could use.
If you have the old jet but it is worn and oversize, you could simply braze in the hole and re-drill. If undersize for your altitude, drill baby, drill!

You may find that propane (LPG) will present you with some unique problems, especially if you live in a colder climate. Cold start enrichment can be problematic in cool weather with LPG and, sometimes, preheating the engine (ironically by running it on gasoline) could be necessary to get the old girl going.

Valve icing can be another issue as the drop in pressure as the fuel leaves the tank can cause a "refrigeration" effect and in places of high humidity, icing will easily occur.

I've worked on many engineered commercial LPG systems and have experienced all of the above. There is much info out there on the net about LPG conversion from gasoline and I suggest you do some reading before you jump in with both boots. Impco is a company that probably makes something that you could utilize to achieve an efficient, economical to operate and SAFE conversion. The initial cost is high, I realize, but the fuel savings and performance, in the long run, should offset that outlay.

Whichever way you go, may the seas be calm and the winds be fair.
Good luck.
 
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