30hp Tohatsu stalls under load

[bubbasblazer]

I have a 30hp 2 stroke M30a3 that has been giving me trouble for quite some time now. It's my duck boat and occasionally use it for fishing. Last season the boat would run fine then die out similar to letting go of the handle on a push mower. I replaced all the lines , fittings, primer ball, cleaned but not rebuild the carb. The problem was still there. So I emptied my tank and found a piece of foil from a 2 stoke oil bottle in there. I assumed this was my problem. It runs fine in a tank or with muffs. Took it out this year after putting fresh fuel in it and a disassembly and cleaning of the carb, and the problem is Still There. I'm running out of ideas. Any help would be appreciated. Thanks.

 

[Sea Rider]

If fuel lines are clean, fuel pump is in good cond, could be having ignition coil or CD related issues...Heats up, shorts whatever and shuts engine down specially at load & throttle

Happy Boating

 

[bubbasblazer]

Thanks for your quick response. I did forget to mention in my o.p. that. The motor will refire within seconds of it stalling. And I had problem years ago, and kept taking it to a shop and kept getting the "bad gas" explanation. Then I made it out to my spot made a half turn on the mixture screw and all was well. Until years later which is now. I do have a service manual, is there any specific way to test the ignition while under load and underway? Since this problem came back my motor went from a quick turn of the key to cranking for a bit before finally running. I do have a fairly fresh spin on filter, however I did remove the small in line filter between motor fitting and pump due to a cracked sight bowl. And just went straight from motor fitting to pump. I'm leaning towards a rebuild and soak in carb cleaner, but honestly don't see anything visibly wrong with the internal components. The float floats in a glass of water and nothing has made its way into the float. I have my mixture screw 2 turns from seat which seems to be pretty normal.

 

[Sea Rider]

Some issues , general ideas :

Is it a second hand engine you bought from previous owner ? If so, did the engine came with tech issues as described ?

Mixture screw only works at idle, after you pass idle there's nothing to adjust. Adjustment is 1 -1/4 ? 1/4 turns from lightly seated. Readjust to specs if with 2 turns out and check engine behaviour.

When you say engine refires after stalling, you mean engine turns on inmediately after when pulling rope for second re start ?

On electrical parts you can have 3 conditions : (1) works well, (2) part is kaput along dead engine, (3) intermitent failures, the hardest to diagnose. Fastest diagnose, swap each electrical part and test if you happen to have them at hand. I?m a firm believer that you should stock at least a brand Ignition Coil, have saved me twice losing precious boating time troubleshooting the old way as per the service manual method.

Are both plugs firing ok, check on a dark garage, or at night. Are you using correct NGK B7HS-10 or BR7H-10 plugs electrode tight gapped to 1.0 mm ?

Wild guess, someone could have been playing with timing advance, probably out of adjustment. Raise with left hand finger carb's pawl fully untill stops, with right hand full throttle slightly back and fouth, check that high hill of cam bangs lightly the roller. The advance timing marks on timing plate must stop at 25 deg when at full throttle, check, if not you?re out of timing snyc with respect to carb sync.




Check and report back..

Happy Boating

 

[bubbasblazer]

Thanks for the picture. I am right on at the timing mark. I pulled the plugs and noticed one was slightly whiter than the other. I grabbed a timing light and looked at the flashing. The top plug wire outta the electronic box was not flashing as consistently as the bottom wire outta the box. This was also noticeable with the sound of the motor, as it picked up n intermittent miss. I bought a spark tester at work so. It would be easier to verify. Definitely has me thinking power pack now. Just want to go back and re verify.

 

[bubbasblazer]

I also did verify plug gap and number. They are gapped .039 which was close as I was gonna get after converting the spec. previously posted. The spark tester showed consistent spark. I almost liked the timing light better as it seemed more accurate with the flashing of the strobe. Getting "quiet" time to mess with this thing is tough with my 2 yr old "wanting" to help, I may just have to take it to the shop before too long.

 

[Sea Rider]

What's the interior condition of both plug's cap, is the metal hat that makes contac with plug head inmaculate shinny ? check. Does that engine model use a independent Ignition Coil, CD unit, or it's a IC/CD power pack ?

Happy Boating

 

[bubbasblazer]

The boots on the wires are in good condition, no corrosion on the terminals ect. I couldn't duplicate the miss when using the spark indicator for some reason, the miss has been there for years, usually in gear at low throttle. I always assumed it was just a quirk but actually seeing it with the timing light confirmed it was a slight miss. As far as the ign. From the parts diagrams I'm seeing it's listed as old in ( ) . Black box mounted rear of the starter, 2 plug wires coming out, a 3 wire flat with red, blue, and black . Then a small group of 4?? Wires running into the wiring with weatherproof silicone jacketed (factory appearing) butt connectors. I have had this motor for probably 10 yrs and really just performed regular maintenance, with the exception of a new lower unit. Last time I had this problem maybe 4 yrs ago, the carb. Was rebuilt and a new fuel pump. The fact that the problem returned after a few years of trouble free use for fishing and hunting, has me thinking fuel, but at the same time I'm just confused as to which direction to go. I really do appreciate you checking in and giving me ideas. I work auto parts and am starting to feel like some of my customers who may not be familiar.

 

[Sea Rider]

Is the miss still going on when engine is warming up while opening the throtttle ? my horses likes doing so specially when becoming old, but once sufficiently warmed up no issue at any throttle range. My miss is the initial 5 second throthelling from a dead stop (first morning outing)

Happy Boating

 

[bubbasblazer]

The miss is at part throttle, warmed up or just leaving the ramp, higher rpms it isn't noticeable. Next time out I'm going to put the spark indicator on and run till she dies, at least then I'll be able to tell if it's firing after it stalls and loses power. If it's still making fire, I think I'm safe to assume fuel, it not I'll sat electrical. I'll let ya know what I find. Have a great holiday.

 

[bubbasblazer]

Looks like I fixed it. My buddy came over , I unhooked the line from the tank and plugged it back in. When squeezing the ball we noticed fuel coming out of it. I took off the fitting s and used a barbed fitting and hooked the line directly to the barbed fitting in the tank and went to the river , had no issues and ran like she used to. I guess even new fittings don't mean a whole lot lol. Thanks for all your help.

 

[Sea Rider]

Good to read you fixed the problem, small o'rings inside fuel connectors will give you issues on the long run specially when wored out, dried, air is being sucked along fue producing engine missbehaviours which worsens when these o'rings enters a caput condition.

Happy Boating