Tohatsu 5HP SP Propane won't run...

[ObiQuiet]

video: Untitled_720p.mp4

Getting last-year's new motor ready, and it won't run. In some attempts, it will run rough for 5-10s, then die.
* Spark fires, can hear it in the video
* Propane tank is 1/3 full
* Lever in neutral
* No leaks from the hose (can hear the click in the engine when the valve is opened, and the hose has pressure until disconnected.)
* Choke out, throttle on start. When it is about to die, I can increase throttle and get maybe 10 more secs of run time.
* This motor has started fine before, though it needed ~10 moderate pulls before turning over on a single full/fast pull.
* It would sometimes get into a mode where it would only idle (surging a bit) , and die when increasing the throttle
* 13 hours of run time after the carefully respected break-in

I'm thinking there's a problem with the regulator...

 

[kloudie1]

Yupp, I think you have it.. Ya might try tapping the reg with a hammer.. not whacking but some tapping top, bottom, and sides to see if that may unstick the spring or internal valve.. Some propane can have an oily kinda residue that may be sticking..

 

[Hunter216]

I really don’t have experience with propane fueled motors but your post prompted me to go Googlin

I thought propane was propane turns out I was wrong (happens a lot! ) and it has “grades”

The motor specs calls for a specific grade of propane

This is where I learned about the grades

Propane Grades and Quality - HD5 HD10 and Commercial Propane

Three grades of propane refined in the U.S. are HD-5, HD-10 and commercial propane. HD-5 spec propane is the highest quality grade propane sold by propane companies in the U.S.

www.propane101.com

So it begs the question of are you burning the right grade of propane?

 

[ObiQuiet]

Thanks you for both answers, much appreciated! From the research I did before buying it, all propane available to consumers should be HD5... But I don't know that for certain this tank is. Filled at the local RV park.

Tapping the regulator made a little difference... Runs about 10s then back fires and quits.

(To think I switched to propane to get away from carbs and fuel gunk

Repair options, anyone?

 

[Rich Stidger]

If you are unsure about the propane grade, I would do one of two things- First I would visit or call the propane dealer from who you purchased the propane, explain your issue and ask what grade he is/was selling when you bought. If that is not possible, or if he gives an answer that shows the propane is the wrong grade or doesn't know, go and buy the right grade. Although I never knew there were different grades of propane, and I have never checked the label on a 16.4oz disposable can, I would try that first before starting a warrantee claim.

 

[SoSound]

You might try cleaning or replacing the spark plug, also check to make sure that it's getting enough air (obstructions, covers, clean filter?). Most of my recent small engine experience comes from an old chainsaw. I finally replaced the air filter last year, and it ran great. You need the proper balance of both propane and air for it to run properly. I googled "cause of backfire" for small engine. FWIW, I have a Lehr propane motor, and it has a procedure to prime the fuel system if it has not started for a while.

 

[SycloneDriver]

Liquid propane is a good solvent. Try turning your supply tank upside down and press the primer button on the carb, if so equipped, until liquid propane sprays out. This should flush out the system. You will now have to turn the tank right side up and turn off the valve, now bleed the system down. Now make everything normal, wait several minuets or so for the propane vapors to dissipate. Now try to start it. Worth a try.

I've had a propane hose/safety valve gummed up with a thick green liquid. It was very frustrating when I couldn't get the heat working in the cold on my RV. I took the hose apart and used carb cleaner on it. It's been fine for years now.

 

[ObiQuiet]

I'll try the plug and air filter tomorrow. Was pondering the problem today, and thought maybe the cause was liquid propane getting into the regulator and damaging the seal -- it's an idea to treat the liquid as a solvent... hmm. Is the regulator all-metal, or is there rubber in there?

 

[GSBNY]

I have the same outboard and had a similar issue last season. In the end, there wasn’t enough propane in the tank despite it not being empty.

I thought I had about 1/4 tank left, so I motored for about 45 seconds and then it cut out. It would turn over but only for a few seconds before dying again. I got a tow and when I got to the boat yard I found a bbq tank that was full (and warm) and hooked it up, outboard started up right away and ran fine.

It was cold out so the volume in the tank went way down and the propane wasn’t reaching the outboard.

 

[ObiQuiet]

Well, it's not the spark plug nor air filter. There's some merit in the gas pressure idea -- I put the tank in the sun for a few hours, and it ran a bit longer.

Can't find the regulator part (Walbro PTG 1a 723) at the Tohatsu nor Walbro parts lookup. (Looking at possibly replacing it if the liquid propane idea doesn't work out). The hose clamps are special high-pressure and no doubt require a special crimping tool. Mayhave to buy the service manual supplement.

So, I'm still open to other ideas or advice.

Thank you.

 

[Captain Larry-DH]

Tapping the regulator made a little difference... Runs about 10s then back fires and quits.

If that made a difference, replace the regulator. Any two-stage regulator made for cooking will probably work just fine. Also, you mentioned your tank is not empty- is it a fiberglass see-through tank so you have a visual? If so that would be accurate. If you’re going by one of those dial gauges, it’s probably empty. Those gauges are garbage.

 

[ObiQuiet]

Yes, it's one of the Viking composite tanks, see-through. I understand the pressure doesn't vary much by fluid volume, but some by temperature.

 

[rgranger]

Regulators can do strange things. I'm an analytical chemist and do a lot of work with compressed gasses and work with several different regulator types and they all have their idiosyncrasies but for something closer to home take a BBQ LP tank regulator as an example. I find that if I have the burner valves open when I open my tank, I never get a good flame. Something in the regulator gets stuck at about half open. So I have to shut down, bleed the lines, close the burner valves... and THEN open the valve on the LP tank. Everything works fine then and it is time to put the burgers on.

If your OB were mine the first thing I would try is to disconnecting the thank... shake it a bit. Tap the regulator. Then close all of the upstream valves, throttle etc., reconnect the tank and then open the tank valve. Then try firing it up using your normal procedure. If that didn't work, I'd change the plug and and the tank and try again.

Also, .... have you tried blowing out the air intake? It could be something as simple as a spider nest or a dauber in the line.

 

[ObiQuiet]

It's purring again, which is awesome.

I did these things today:
* Tried the liquid propane as solvent, suggested by SycloneDriver
* Replaces the new sparkplug with an even newer one.
* Blew out all the air lines and intake again, for good measure
* Blew compressed air into the two holes on either side of the regulator housing... no idea if that would make any sense, but did it anyway.

Not sure which of these did the final trick. Did rule out fuel pressure issues with the tank, though.

Thank you all for the advice! If it runs fine tomorrow, it goes back on the boat.

 

[Captain Larry-DH]

It's purring again, which is awesome.

I did these things today:
* Tried the liquid propane as solvent, suggested by SycloneDriver
* Replaces the new sparkplug with an even newer one.
* Blew out all the air lines and intake again, for good measure
* Blew compressed air into the two holes on either side of the regulator housing... no idea if that would make any sense, but did it anyway.

Not sure which of these did the final trick. Did rule out fuel pressure issues with the tank, though.

Thank you all for the advice! If it runs fine tomorrow, it goes back on the boat.

I love it when something works, hate it when I don’t know what did the trick.

 

[Pandragon]

It's purring again, which is awesome.

I did these things today:
* Tried the liquid propane as solvent, suggested by SycloneDriver
* Replaces the new sparkplug with an even newer one.
* Blew out all the air lines and intake again, for good measure
* Blew compressed air into the two holes on either side of the regulator housing... no idea if that would make any sense, but did it anyway.

Not sure which of these did the final trick. Did rule out fuel pressure issues with the tank, though.

Thank you all for the advice! If it runs fine tomorrow, it goes back on the boat.

How is your outboard running now? I'm now in the same situation with my 2020 Tohatsu 5hp propane outboard. Seems to be doing the same thing yours did. Do you have any new insight since you fixed it a few years ago? I was really hoping my outboard problems would go away by switching to propane.

 

[john6206]

@pendragon me too!

So far I haven’t had any problems with my Mercury 5hp propane sailpro, but this thread makes me nervous. The ancient gas motor was reliable most of the time, if this is not any better it was a waste of money!

 

[Pandragon]

I dropped mine off at the local dealer this morning. We will see what they can do.

 

[seaward22]

It's purring again, which is awesome.

I did these things today:
* Tried the liquid propane as solvent, suggested by SycloneDriver
* Replaces the new sparkplug with an even newer one.
* Blew out all the air lines and intake again, for good measure
* Blew compressed air into the two holes on either side of the regulator housing... no idea if that would make any sense, but did it anyway.

Not sure which of these did the final trick. Did rule out fuel pressure issues with the tank, though.

if anyone comes across this like I did via Google, I had the same issue with it cutting out after a few seconds.

what definitively fixed it for me was replacing the spark plug!

 

[patbratton]

I have had my Mercury Propane Sailpro for about a year and a half. I have noticed that if I sail once or more a week (required to motor out of the harbor) it starts fine (five pulls). If I go longer, it takes as many as 10 to 15 pulls. I wiggle the shifter to make sure the neutral switch is made but it acts like it just wants a little attention before it fires up. It is quite easy to pull compared to my old Honda 8 hp. It has never failed to start. I will start referring to her as she.

I have a '98 Hunter 240.