Motorcycle Forum banner

1 - 8 of 8 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
Hi everyone,

I recently purchased a honda sl100 to convert to propane fuel. We tried starting it when it was gasoline powered and had no luck. There was good spark and fuel running to the carburetor, but it wouldn't turn over. We sprayed some starter fluid in the carb and the engine would run for a few seconds and then stop when the throttle was pulled. I decided to go ahead and do the conversion and found the gasoline carb float seemed to need adjusting. After I went through with the conversion I thought these carb issues would be solved and that that was my problem, but the engine still would not turn over. I checked the spark again and it looked fine. I tried the choke in multiple positions and held the throttle wide open a couple times too. I have not checked ignition timing or compression yet, but this is my first motorcycle so I wouldn not know how to go about that.

Thanks in advance,
tutz15
 

·
Registered
Joined
·
3,162 Posts
OK, I'll bite. Does the propane conversion depend on the carburetor unmodified as original to run the bike? Does it require the bike to start on gasoline to warm up and then run on propane? Why do you want to run on propane,anyway?
 

·
Registered
Joined
·
6 Posts
Discussion Starter #3
OK, I'll bite. Does the propane conversion depend on the carburetor unmodified as original to run the bike? Does it require the bike to start on gasoline to warm up and then run on propane? Why do you want to run on propane,anyway?
This conversion is for a senior project for highschool about alternative fuels and is my way to get a motorcycle without my parents' disapproval ;). I bought an aftermarket carb for $15 and made sure it fit on the bike. I then did a spud-in conversion in which I drill out the existing venturi and create a new one with copper pipe (this works, I promise). This runs 100% on propane and I removed the gas tank completely. I just really need some help right now to get it started because I have to present it to a group of people.:confused:
 

·
Registered
Joined
·
3,162 Posts
You have to give decent information if you want help. Actually,I do know a bit about running propane because i had a dual fuel conversion kit on a 350 Chevy.

It was liquid draw in that liquid L-P gas entered a unit that was plumbed to the carburetor and HEATED with water from the engine block. The truck was started on gasoline and that allowed the water to heat and thus heat up the carburetor. Propane expands to 256 times its original volume once released from the tank. Expanding liquid has a potent cooling effect and will freeze your carburetor [in my opinion] You can see why I have to guess as to the advice you want and that is simply because you have given us no useful information.

Now if you were to post some set of plans on how to do the conversion from someone who has done it before,that would be a start. Did you see such plans on a website? If so,post up the website.
Also,please note that even with a manufactured unit put together by engineers and all that, the truck would not start on propane even in the summertime. If you did not have that bike start and run on gasoline as a starting point before your conversion, you have no baseline with which to ask us for advice on how to get the bike to run

Not trying to be mean about this, but just realistic
 

·
ZAMM Fanatic
Joined
·
2,730 Posts
Having worked with a propane-powered lawnmower engine....

If you were able to start the motorcycle with starter fluid then there's nothing wrong with compression, spark, timing, etc.

My FIRST guess is you don't have the ignition turned on on the bike; perhaps you have the kill switch off.

The carburetor is irrelevant at this point; you are feeding this thing gaseous propane, not liquid propane. Chances are, without a LOT of design, you've created a single-speed engine. It will run at a single speed, or in a narrow range, UNLESS you figure a way to meter BOTH the air AND the propane flow.

As for starting, it should start right up UNLESS you are lacking spark OR have air in your propane lines that needs to be bled off.

No reason you can't cheat and use starter fluid, again, to get it running, and then adjust your propane flow to KEEP it running. Lock the throttle at mid-rpm.

No reason you can't use the throttle cable to ALSO operate some sort of variable orfice / jet to meter propane, although I have no idea how large or small it needs to be.

So in short, you're missing something simple, propane SHOULD act very similar TO starting fluid and unless youre WAAY too rich or WAAY too lean should fire right off. Are you using a BBQ regulator on your propane tank?

If you are INDEED attempting to use the carburetor to feed the engine LIQUID propane, well, as the previous post mentioned, that 256x expansion means your probably getting NO air/oxygen in your intake manifold/cylinder.

If so, suggest you backtrack to a BBQ regulator AND off/low/medium/high knob and feed THAT, mixed with air, into intake manifold.

I salute your efforts and am glad, at least so far, you have not blown yourself up. Please keep a fire estinguisher (or two) handy WHENEVER you play with fuels.

Cheers.
 

·
Premium Member
Joined
·
7,595 Posts
Fire

I would like to know this engine will run as it was supposed to, on gas and air, and spark and compression. All at the right time and in the right ratios.
Then convert it to propane, for which I am no help.
If it will not run as it was supposed to, how will it ever run on propane?
Buying another carburetor that maybe fits, does not tell us much about what size jets are in it, or whether the fuel and air passages are clear, or whether it has an air leak around the butterfly shaft. Like my Rochester on my 350.

Unkle Crusty*
 

·
Registered
Joined
·
6 Posts
Discussion Starter #7
The system is set up so that the propane comes from 2 1 pound cylinders, mounted vertically to only get vapor, into a manual lock off, then into a primary regulator. From there it goes into a zero pressure regulator, also called a demand regulator or zero governor, which has a priming button on it to force the propane through the system. After that it goes through a needle valve into the new venturi in the carburetor. I left the needle on the throttle on to also vary the volume of propane entering the carb so the bike will operate on more than one speed. I know there is typically an idle jet on a carburetor and I thought I could overcome this by using the priming button on the secondary regulator.

Also, the bike itself is very basic. There is no kill switch, no light switch, just a a clutch lever, throttle, and brake lever. There is a key on it that has two positions but I tried both and it doesn't seem to make a difference, so the bike may have had an electric starter at one point but has since been removed.

Again I REALLY need to get it started within the next week or so to be ready for my presentation.
 

·
Premium Member
Joined
·
7,595 Posts
Electric start

There was never an electric starter on a 71 SL100. With the propane at a safe distance remove the spark plug. Connect the plug wyre, lay the spark plug on the cylinder and kick it over a few times. No spark, turn the key. Nothing in the for of vroom vroom will ever happen if you do not have spark. You also need compression of at least 110 pounds. 90 will do but that is pushing it. If you only have 90, go up one heat range on the spark plug.

Unkle Crusty* My 41 Ford tractor has 112 pounds.
 
1 - 8 of 8 Posts
Top