Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

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Stickinthemud57
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Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Stickinthemud57 » Sat Oct 16, 2021 2:42 pm

I have enjoyed using an older Tohatsu 2-cycle 8-horse outboard motor on my Mac 26S that is, until recently.

For most of this season (starting in March here in North Texas) the motor has started right up, never needing any choke even when "cold". Lately, I have had trouble starting it and found I had to run the starter for quite a while before it would finally catch. Once started, I had to carefully apply throttle to keep from killing it until finally I was able run the excess gas out. Lots of white smoke in the process, so quite obviously flooded.

This morning it would not start at all. I tried disconnecting the fuel line and cranking and cranking, but to no avail. I made several attempts over the course of the next 20 minutes or so. Finally I gave up and we just had our picnic lunch at the marina and went home to put the grandkids down for a nap.

When I came to take the motor off the boat (maybe 2 hours later), I decided to give it another try and it started after a fair amount of cranking, again with careful application of throttle and a big cloud of white smoke. After that it ran fine and would start back up easily. Something I did notice was that if I pumped up the pressure with the fuel line priming bulb that fuel would drip from the bottom of the fuel pump, but it's hard to say if it was leaking from the fuel pump body or from where the fuel line attaches to it.

A friendly expert at the marina suggested that in the future I just unhook the fuel line from the gas tank and let the engine run dry after use. He opined that the ethanol in regular gas wreaks havoc on the fuel line and other components when allowed to sit. I think that stands to reason, so that will be my practice going forward. I intend to replace the fuel lines, fuel pumps gaskets, and fuel pump diaphragms for good measure.

I would welcome opinions and feedback on this, as I missed really nice day for sailing toward the end of the season and wish to avoid a repeat of the experience.

Thanks!

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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by chipveres » Sat Oct 16, 2021 5:00 pm

The "usual suspects" here are the needle valve that shuts off the fuel when the carburetor bowl is full. Or the seat in sits in can gather a speck of dirt. Or the float can sink. Don't bother yourself with hard stuff until you have checked the easy stuff.

Chip V.

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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Stickinthemud57 » Sat Oct 16, 2021 7:58 pm

chipveres wrote:
Sat Oct 16, 2021 5:00 pm
The "usual suspects" here are the needle valve that shuts off the fuel when the carburetor bowl is full. Or the seat in sits in can gather a speck of dirt. Or the float can sink. Don't bother yourself with hard stuff until you have checked the easy stuff.

Chip V.
Thanks for the response!

If the problem is the needle valve or float, how would I determine that and what would be the remedy?

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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Jimmyt » Sun Oct 17, 2021 5:48 am

If you aren't using non-ethanol fuel in all of your small engines, you should be. Also, a storage additive like sta-bil might be a good idea (I use non-ethanol fuel and sta-bil myself in my outboards, mower, edger, etc).

If you can pump your priming bulb until fuel starts pouring out of your engine cover, the float valve and pump diaphragm are good candidates. You have to determine where the fuel is coming out to nail down the cause.

There are different schools of thought on running a 2-stroke out of fuel every trip. They are lubricated by the fuel-oil mixture, so you are running the engine with minimal lubrication for a very brief period. We did it religiously when I was young, and I don't recall any motor failures as a result, though. Also, you are leaving a small puddle in the carb that will evaporate down to just the oil. This may be the more troublesome issue. If you can drain your carb bowl for long term storage, it's probably better. Short term, it's probably fine to leave non-ethanol fuel with a stabilizer in it.

Pump the priming bulb until it gets very firm with the engine cover off. Try to determine where you see fuel leaking or dripping. Under normal circumstances, only pump till the bulb is firm. Don't continue to smash the bulb after it's firm.

One other consideration is over-pressure from the new fuel tanks - which don't vent outwardly. Try disconnecting your fuel hose when you leave the boat. Next trip, vent the tank by loosening the cap before re-connecting the fuel hose. Tank over-pressure due to heat may be sufficient to flood the engine even if your float valve is functioning properly.
Last edited by Jimmyt on Sun Oct 17, 2021 1:39 pm, edited 1 time in total.
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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Jimmyt » Sun Oct 17, 2021 5:58 am

Stickinthemud57 wrote:
Sat Oct 16, 2021 7:58 pm

Thanks for the response!

If the problem is the needle valve or float, how would I determine that and what would be the remedy?
Pump bulb and see where fuel is leaking with the engine tilted slightly. You want fuel to run out of the carb, not into the engine. If it's pouring out of the carb, (or you can tell that fuel is being pumped into the intake, voila. Disassemble carb. Place float in bowl of fuel to make sure it floats - first. Engine manual usually has procedure for setting float height. To crude check, place a small length of clean tubing on the disassembled carb and blow on it while lightly raising and lowering the float with your finger. It should vent and stop the air from blowing through as you lower and raise the float. Remove the float and needle and inspect the needle and seat for pitting, scoring, etc. if the needle and/or seat show damage, replace both with new.
Last edited by Jimmyt on Sun Oct 17, 2021 1:41 pm, edited 1 time in total.
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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Tomfoolery » Sun Oct 17, 2021 8:32 am

Stickinthemud57 wrote:
Sat Oct 16, 2021 2:42 pm
Lots of white smoke in the process, so quite obviously flooded.
White smoke usually means water. Black usually means rich mixture/flooded cylinders, and blue means oil. My old 2-strokes would burn bluish black smoke when flooded.

Are you sure it’s flooded, and doesn’t have a blown head gasket? Might want to pull the plugs and see what’s on them.
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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Jimmyt » Sun Oct 17, 2021 9:15 am

Tomfoolery wrote:
Sun Oct 17, 2021 8:32 am
White smoke usually means water. Black usually means rich mixture/flooded cylinders, and blue means oil. My old 2-strokes would burn bluish black smoke when flooded.

Are you sure it’s flooded, and doesn’t have a blown head gasket? Might want to pull the plugs and see what’s on them.
Excellent point (as always).

If you've got a compression tester, or a buddy with one, you can check that while you are doing the visual inspection of the plugs.

Have you run the motor hot? Water pump failure that you didn't notice immediately, maybe? Has anyone been into the powerhead? Is there any reason you can think of for head warpage or gasket failure?
Last edited by Jimmyt on Sun Oct 17, 2021 1:42 pm, edited 1 time in total.
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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by chipveres » Sun Oct 17, 2021 1:04 pm

JimmyT nailed the test procedure for the needle valve and float.
Chip V.

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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Jimmyt » Sun Oct 17, 2021 1:26 pm

Tomfoolery wrote:
Sun Oct 17, 2021 8:32 am
Stickinthemud57 wrote:
Sat Oct 16, 2021 2:42 pm
Lots of white smoke in the process, so quite obviously flooded.
White smoke usually means water. Black usually means rich mixture/flooded cylinders, and blue means oil. My old 2-strokes would burn bluish black smoke when flooded.

Are you sure it’s flooded, and doesn’t have a blown head gasket? Might want to pull the plugs and see what’s on them.
After cogitating on this awhile, per Tom's comment, it is critical that you be able to differentiate between steam in the exhaust and the light blue smoke caused by the low ash, 2-stroke oil burning. A head gasket and a carb rebuild are two entirely different days...
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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Jimmyt » Sun Oct 17, 2021 1:36 pm

chipveres wrote:
Sun Oct 17, 2021 1:04 pm
JimmyT nailed the test procedure for the needle valve and float.
Chip V.
Thanks Chip. Sounds like you've been down this rabbit hole a time or two. When you're wrong as much as I am, the odds eventually work out for me to get one right once in awhile. :D

The cool thing about this format is, you put a problem out there (usually without much support data), and you get back a lot of possible causes/solutions to mull over. Sometimes you get an idea that you may not have thought of. Of course, you can wind up with 50 different wild goose chases. Under optimal conditions, it's still pretty difficult to diagnose engine issues over the Internet. If you have video, audio, multiple photos, and the shop manual, it is a bit better. Best case is a good tech savvy guy (or gal) on the other end with a pile of test equipment so you can get at what is actually going on. Of course, that person would probably not need help anyway. :wink:
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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Stickinthemud57 » Sun Oct 17, 2021 4:20 pm

I greatly appreciate all the responses!

The white smoke/blue smoke distinction is one I may not be making correctly, and I see it may be the source of some confusion as to the cause of my engine troubles.

Perhaps this information will help...

After I have managed to get the engine started, it runs like a top, and restarts with a single pull of the rope. When running, it does not appear to be producing a significant amount of smoke of any color. If it were a bad head gasket, shouldn't I be seeing whitish smoke when running the engine?

Pressure from the gas tank is a prime suspect (or over-prime suspect as the case may be). I am using one of the newer ones that does not vent properly, so it's not unusual to find it distended from pressure after a warm day. It has been my intention to disconnect the fuel line from the motor after use, but I keep forgetting.

I plan to be be going out tomorrow and possibly the day after, so I might have a chance to see if simply disconnecting the fuel tank helps alleviate the problem.

Tomfoolery, in your post you recommended examining the spark plugs. What should I look for?

JimmyT, Impeller was replaced recently and I frequently check to make sure water is flowing. No one has been into the powerhead, and nothing leads me to suspect head warpage or gasket failure. I will be taking a closer look for any tell-tale signs.

A compression gauge is only 30 bucks, and although I can't find any specs in the manual, it seems it would be simple enough to test each cylinder for equal compression. Chances that head gasket is leaking at both cylinders (and to an equal degree) seems pretty slim.

As mentioned before, I plan to replace the fuel lines and pump diaphragms. Beyond that, I make put the motor in the shop for a check-up over the off-season. It may make sense to do a carb re-build just on general principal.

Thanks again, everyone!

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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Jimmyt » Sun Oct 17, 2021 5:10 pm

Based on your additional information, I'm betting fuel tank pressure is the culprit. I wouldn't put a wrench on it until you have tested the fuel tank theory. This is based on the fact that it starts and runs fine IF you get it started - and doesn't smoke excessively, and you aren't sure that it's steam or oil smoke you're seeing. All of the other problems would probably cause you grief continually. New tanks are a known problem for carburetor engines.

The bad part about the new tanks is they can inhale, but they can't exhale. So, if you have several hot days where the temperature changes significantly between daily high and low, you could push a good amount of fuel into the engine between uses.

That's what I'm betting on anyway. Have you started a pool to see who wins the all expenses paid trip to drink Scotch with Highlander? :D
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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Tomfoolery » Mon Oct 18, 2021 5:13 am

What Jimmyt said - that pressurized fuel tank is a strong suspect. I've never had one, and don't want one, but residual constant pressure in the fuel line may be enough to overcome the float valve in the carbs, and/or sneak past the engine's fuel pump.

As to checking the plugs, I would pop them out and look and sniff for fuel on them. Having messed with antique lawn mower engines as a kid, that was the go-to move for checking for fuel in the cylinder, excessive or otherwise, as well as a spark. :D

Blown head gasket has moved to near the bottom of the list at this point.
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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Dougiestyle » Mon Oct 18, 2021 8:12 am

My Nissan 50 WILL push fuel through the carbs and drip if I do not disconnect the fuel line, due to the new type tanks :( .
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Re: Help troubleshooting a flooding Tohatsu 8 HP 2-stroke

Post by Stickinthemud57 » Mon Oct 18, 2021 8:51 pm

Update:

After disconnecting the fuel line and running the motor dry on Saturday, today I connected the fuel line, gave the bulb a few pumps and the motor started up, no trouble. I am beginning to think the problem lies at least to some extent with the fuel tank creating pressure that causes the carb to flood. After sailing for a few hours, it did take a several tries to get it started again - acting like it was a bit flooded. This was not a problem in the past, so something has happened over the course of the summer aside from just pressure in the fuel tank, I think. My plan is still to replace fuel lines and fuel pump diaphragms (winter project), but in the meantime I think I will install a petcock in the fuel line just upstream of the coupling at the engine. That way I can just shut it off rather than having to disconnect the fuel line.

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