Tohatsu M70A2 Stalling- won't start

[Petedacook]

[h=2]Tohatsu M70A2 Stalling- won't start[/h] Today, 10:17 AM


Hello all,

I have a Tohatsu M70A2 that has been dying, hard to start, and dies leaving us stranded for a while.

In general, the motor is hard to start and idles poorly. It has to be turned over many times before it will stay running where I can put it in gear. Once warm and running a bit, it will die if I leave it at an idle for 1 minute or more. These symptoms might give an insight to the community on what is causing the big problem I experience.

On really hot days, after running 30+ minutes or so, the motor will die. This has happened several times. I have trouble shot this down to no fuel getting to the combustion chamber. Fuel enters/leaves the fuel pump at a decent rate, and fuel is in the carburetors when I remove the bowl screw. I have spark at the plugs, and have replaced them during times the motor has cut off on us. And when I pull the plugs, they are bone dry. After I tinker around the engine for a while, the engine will start and run. There is nothing i did to make it start other than mess around with it trouble shooting. I do not find a problem other than fuel not getting to the combustion chambers past the carburetors.

I figure the problem is one of two things:

1. Loose screws on the carb's and/or intake manifold. I checked the screws last night and found them 1/4 or a little more loose. I have tightened them, but have not taken it out for testing.
2. The reeds need replacement.

My questions:

1. any other possibilities I might have missed in this diagnosis, given the symptoms?
2. Should I go ahead and replace the reeds? We all know boating will nickel and dime us to death, so if i can save a few bucks by not replacing something that is not broke, I'm all for it. I don't want to waste money.
3. Am I missing anything overall?

Thank for any advice,

Pete

 

[Sea Rider]

Pete,

Is fuel pump diaphragm in good working order, that's not dried, cracked, ballooned ? Could be an electrical failure, component heats up, shorts and OB misses. To diagnose that type of failure will need to troubleshoot electrically each electrical component with an analog tester that reads DVA volts.

Why do you think reed valves are bad, don?t close tight, are warped ? How old is that OB, was it heavily used ?

Happy Boating

 

[Petedacook]

Fuel diaphragm in good working order. It puts out a good burst of fuel when turning it over.

I wouldn't think it is electrical because it gets good spark at the plug, and there are no signs of fuel in the combustion chamber when it wont start.

OB is 1987 model. It has been heavily used over the years. I've used it heavily over the past year.

I am considering reed valves because it does not like to idle, runs leaner than it did in the past, and I don't see a record of reed valves being serviced, and I suspect the engine was not serviced well because the oil in the bottom half was black and smelled bad indicating neglect.

Thanks, Sea Rider.

 

[Sea Rider]

How about cylinder compression ? when low starting OB is a PITA, does cylinder head gasket been replaced over the years or been retorqued to specs ? if already dried, hardened, compressed, out of correct torque head gaskets gives combustion troubles. Has internal head and pistons been decarboned ?

Happy Boating

 

[Petedacook]

i ran some Seafoam through the engine last year if that is what you mean by head and pistons decarboned. This is a new phrase to me, I found recently it searching for solutions. Please elaborate on decarbonate. How is this accomplished?

Head has been torqued by hand, regularly. Gasket has not been replaced to the best of my knowledge.

Checking cylinder compression is my next step......I was trying to avoid buying a compression tester, but I guess i need to.

I pulled the carbs, intake, reeds, and fuel pump tonight.

All in all, everything seemed to be in decent to very good condition:

• Fuel diaphragm- kind of hard, brittle, and ballooned. I am ordering another.
• carbs- haven't torn them apart, but the throat and choke area is spotless
• reeds- a few of them were not sealing well. I could see a good bit of separation between the reed and reed intake base. Only about 3-4 of the 12 inlets showed this sign.

Thanks,
Pete

 

[Sea Rider]

Pete,

Decarbon is removing carbon build ups on internal cylinder head and head pistons, is only achieveble to perfection mechanically speaking, that's done usually when pulling cylinder head out as to replace worn head gasket. If reed valves are not closing fully, better change complete reed valve assy, comes factory adjsuted.

Compression test is a must do. Would suggest to order a cylinder and base gasket as well. If fuel pump diaphragm is deformed, ballooned, needs be replaced, better yet, order a complete fuel pump kit. Would't worry too much about carbs condition unless OB was sitiing with fuel insdie carb bowl for long time period. That can be checked when all faulty parts have been replaced.

Happy Boating

 

[Searunner25-414]

Hi,
I have a Tohatsu MFS 3.5L (for sailboat) from 2014, and it would not start at all. I had just acquired it and had no history on the engine. I checked spark and it was good. I sprayed gasoline mist into the carb throat and it would run fine until the fumes were used up. I guessed it was a stuck needle valve for regulating the fuel into the bowl. First I opened the bowl drain screw and yellow liquid came out. Not good, it should have been clear. It must have been rotten gasoline or ...? I turned the carb upside down and secured it in a wood workers wooden vise, and removed the base of the fuel bowl screws and opened the bowl. All mechanisms seemed fine and the fuel passage from the bowl to the venturi exit just prior to the throttle plate passed air when I attached a tube and exhaled into the inlet of the passage, so that was clear. I worked the needle valve manually in and out by swinging the float arm numerous times and put it all back together. I added new gasoline and it started to act as if it wanted to start. After numerous retries it finally ran rough for awhile then smoothed out to run more evenly but the throttle up would fall on it's face at about half-throttle and start to die. After working this for awhile, finally full power started to be realized. I went out in the boat with it the next day and it was 'fussy' on the choke, it barely needs any choke or otherwise it will not start. Once I found the sweet spot for the choke, it was no longer a problem, and once the motor warmed up the choke was returned to zero. The motor ran rough at first and exhibited the strange half-power issue for awhile until it warmed up. The rest of the day I traveled 11.4 miles in 3 hours 8 minutes, with 3.5 miles per hour average and 6.3 mph maximum rate, all with no more fussy behavior. I attribute the failure to start to the previous owner storing it improperly and the gas went rotten over the 2 years it sat in his shed, forming some varnish on the needle valve that still has not fully dissolved due to the new gasoline yet. I will be running some Sea Foam or other varnish treatment soon. I hope any of this information provides some ideas that may end up helpful. Good Luck!

 

[Petedacook]

Thanks Searunner, Searider.

Do you know if I can check compression with the intake manifold off the engine? I have it off now waiting for reeds to come in.

Pete

 

[Petedacook]

Just a side note.....when the engine died and would not start, it was a gradual death, not sudden cut off. As if it was slowly being starved of fuel.

So....I've replaced the reeds, and intake gaskets, and checked for leaks at the intake using cretor. I took the fuel pump out, but had to put it back in because my new one was not here yet, and my kids wanted to go out on the boat.

I completely changed the reeds to Boyesen. The reed cage is still the stock cage.

I warmed the engine on the muffs. It ran fine. I did the compression test. I wasn't sure how the heck i could tell when it was cranked over 5 times. I can't see it spin or anything, it's too fast.

I cranked it over and counted to 5. About 110 PSI both cylinders. If I crank it more, it does not move the needle noticeably.

Took boat out, ran ok at first. Didn't want to idle at first, which is really not a new problem. We went out cruising around about 10 minutes, to a post, stopped the motor and sat there fishing for about an hour,

Motor would not stay running after that. It would start, then die immediately before I could get it in gear. Messed with it doing this for a while, with no success. Changed the spark plugs. Tried a few more times, and got it going in gear.

Cruised around running throughout the throttle band for an hour or so, and it ran fine. No bogging, no hesitation, and a smooth engine sound. Every time we stopped after that, same thing; wouldn't stay running: engine would start then cut off immediately. If I put it in gear, it would cut off with a sound like it was bogging down. Eventually, I was able to get it into gear and the motor would not die, saving us from being stranded. We did this several times during the day.

I'm still waiting for the fuel pump to come, then I'll put the new one on.

Thanks,

Pete

 

[Sea Rider]

Pete,

Is that OB used on fresh or salty water ? hand torque has nothing to do to with wrench torque as won't know how many NM of torque you have adjusted head to and if all head bolts are evenly torqued to.

Happy Boating

 

[Petedacook]

Fresh water, never salt. I'll check the torque in a couple days. Im out of town at the moment.

 

[Petedacook]

Torqued heads. They are OK.

Took carbs off, clean and pristine inside, Like I suspected.

Put carbs back on. Bent Idle set up so screw does not need to go as far down. Set idle on the muffs in my garage. Took boat out next day.

Motor idled noticeably lower than in my garage on the muffs. Stepped idle up a bit on the water. Ran and functioned perfectly for a 6 hour day. No stalling, limited idling problems most likely related to low idle.

So it seems my problem experienced last week was one of setting the idle in my garage, then taking it to the water where the idle set much lower. So far, all is good. I'll know more when I take the boat out again this coming weekend. I still need to step the idle up a bit. Was still too low on the water.

 

[pvanv]

Idle stop and for that matter mixture (when it is adjustable), must be set in the water, on the boat, and verified both in neutral, and in gear.

 

[Petedacook]

Thanks PVANV. I had no idea. Why do you have to set them in the water?

 

[Sea Rider]

Thanks PVANV. I had no idea. Why do you have to set them in the water?

Yep, adjusting idle setting on muffs gives higher rpm readings as exhaust exits freely unrestricted than when combo is floating on water. If not counting with a tach, adjust idle screw at a point that when OB is geraed forward a light clak gearing is heard and OB doesn't die, readjust if needed.

Happy Boating

 

[Petedacook]

In total: new reeds, new fuel filter, new fuel pump, adjusted carburetors. Took the boat out the past two weekends without issue. So far so good.

Thanks for the advice/help everyone.

 

[Sea Rider]

Congrats Pete, it's always good to read that oldie is back and boaters having fun...

Happy Boating