Propane problems

[muskeg]

 I recently installed a JD gasoline (chinese) 15 hp engine on my autostart battery charging system.

 A U.S carburation propane adapter from the old Honda bolted on perfectly.

 It was running perfectly when I left for work....

 A call from home said it was backfiring through the caburator , had to be started on gasoline and switched back to propane.

After witnesssing the nice blue flame popping out of the carb when trying to start

 Heres what I found..

 1. needed a minor valve adjustment. (The manual gives no valve clearances.)

     I used  0.006intake and 0.008 ex

 2. The Sparkplug had to have the GAP Reduced to .015in from the recommended 0.28in.

    ( strange enough this is what stopped the backfire)

  3. Leaned out the propane mixture a tiny bit.

  4. The start primer adjustment is only open a tiny bit.

 Timing light is broken , unable to check

  I am running Wal-Mart tech 2000 0w30 oil ( for gasoline/propane/natural gas)

  It starts and runs just fine now...

Sparkplug is a nice tan color.

Hopefully this experieance helps someone who is considering this engine..

 muskeg.

[dnix71]

Some gasoline engines have intake valves that don't completely seat so that they are easier to spin and start. I found out the hard way with a free riding mower from a coworker.

It just would not start. After trying everything I could think of, I started a tear down. That's when I noticed the intake valve didn't completely seat. After putting it all back together, I held down the manual choke and it started immmediately.

If you did a propane conversion on that, you might have a problem. The pulsing backflow through the intake side would probably mess with the propane diaphram.

I briefly considered removing the intake valve and shaving 10 thou off the stem so it would seat, but that was more work than I wanted to do in the heat of the summer.

[muskeg]

 A burned valve was my first thought too...

 Watching the valve opening /closing showed this brand uses a decompressor on the exhaust valve...

 Good thing...the compression on this engine would really hurt on backfire when pulling it over.

  I did have some problems with the caburator diaphram... Leaf cutter bees found the vent hoses for the diaphram and plugged them up...

 good for another head scratching moment...

 I may condsider this engine for use with a wood gas producer. (on my lis tof projects)

muskeg

 

[tecker]

Wood gaas looks really good .It takes some monitoring .So It may well be only good for wash days weekends or high current charging for a battery bank , A down draft gassifier is well documented on the net and you tube  .I have spent a lot of time this winter with it and have an updraft unit set up now and a few things to wrap it up with a generator and small blast furnace . Here's the carb adapter I plan to use .It's very simple and can be fashioned fast. The pipe size should be slightly larger than the carb throat.http://www.youtube.com/watch?v=F258s13UxfY

[sk windpirate]

A propane conversion makes the engine run "much" hotter. So you "must" retard the timming.

You did that by closing the spark plug gap. That works, but the engine will not run as efficent as it could. An engine will run a lot cleaner on propane. Oil changes will be less freqrent. But be sure to use a good quality oil to make up for the extra time.

[tanner0441]

Hi

I used to convert cars to run on propane for a living, and had to present training courses. It has a slower flame front but a higher ignition voltage which is the reason for closing the plug gap, closing the gap actually advances the engine because the spark develops earlier, there will also be a higher primary ignition loading, so if the engine has points keep your eye on them.  If you retard the engine too far you will loose your exhaust valve, especialy if it is high carbon steel, propane is carbon defficient in combustion, which is why the oil stays clean so long between changes. Propane has a calorific value of 19,500 Btu per lb, petrol is about 23,000 so you will loose some 15% on economy.

If the engine is running hot check the mixture. The stoichcometric mixture for propane is beween 14% and 17% but it is virtually impossible to flood the engine, pull the plug and crank it a few seconds to purge any excess fuel. Hope this is useful.

Brian.

[muskeg]

 

  It would be nice to use a exausht analyzer . So far I have been using the mixture adjuster and setting it where it runs the best.

 Does anybody know what the exhaust temp should be with propane on a small engine?

 I am guessing the reason that my JD engine on propane needs a smaller gap is the head design.

 It has a Wasted spark which is igniting on the valve overlap.

The small gap makes it harder to ignite uless there is some compression.

 

[tanner0441]

Hi

How I would go about it would be to part load the engine, and monitor the voltage with a meter, tweek for the highest reading.  You don't want full load, and no load may hunt on the regulator. On the plug gap we used to close the gap from 25 thou on Leyland 30 on Ford down to 20 thou for both of them.  If you left them at stock gaps the voltage would sometimes track on the ignition coil.  One advantage with propane is because of the slower flame front, the engines produced more torque on long stroke engines.  If it is not out in the weather you will probably never have to replace the exhaust, lower acidic products of combustion, mainly CO2 and water vapour.

Have fun

Brian.

[tecker]

What they don't say about propane is they don't really analize the mix they send out . The gas varies  form tank to tank that wouldn't mater if you flame it but the 4 stroke has a hard time with the occasional really lean or rich mix that come out of the tank.

[Yyrkoon]

Just a FYI for all of you:

Backfiring through the carburetor is always a timing issue. Since most if not all small engines do not have a distributor, this means it is almost always valves out of adjustment. The only other thing that can go wrong is your crank and cam shaft not being aligned correctly, and if it worked previously the chances of you knowing this happened would probably be obvious ( rod through the block ).

To be perfectly honest I am not familiar with JD small engines. But if they're a Honda knock off ( sounds like it is possible ) Valve clearances should probably be around .002/.003 intake/exhaust respectively. This of course is going by memory , and assuming the 15HP JD engine is similar to the Honda 13HP GX390. These specs are of course for gasoline/ tri-fuel models.

Anyways, just remember that on most small engines if you blow flame out the intake, the chances the valves need adjustment are nearly 100%. If it is just a pop( which is not a backfire ), it can be a few things, and the carburetor is usually where I start.

By the way, a burnt valve will most likely just cause low compression, and the engine will run either very badly under a load, or not at all period. Also I am curious about the "propane runs hotter, and needs to be retarded" comment. I definitely do not know everything, but this does not sound right. What about tri-fuel setups ? Having the valves that far out of alignment can mean a 3-5 pull start/ not running correctly/efficiently vs a 1 pull start every time, hot or cold.

[Yyrkoon]

Err ooops,

I neglected to mention that another timing issue can be caused by the keyway on the crank, holding the flywheel in the correct position. BUT, I have had this happen personally, and what happens is your engine will not run period, giving the occasional pop. I suppose different makes/models could behave differently . . . but I have seen this happen on a Briggs, and a couple of Honda's( through no fault of the manufactures ).