Jump to content
Panda FREE Antivirus for Personal Use (affiliate link)
Pete McCrary

Tohatsu 3.5 hp longshaft . .

Recommended Posts

Some may know that the Suzuki 2.5 cavitated excessively as "Chessie's'" OBM on her maiden voyage [empty ballast tank & solo crew].  So I replaced the OBM with a Tohatsu 3.5 hp longshaft which was hard to start, wouldn't idle properly, and ran poorly and was generally unreliable to the point that I didn't dare join in the water events at the MASCF.  We think the selling dealer's mechanic has discovered the problem.  A small hole in the fuel pump's diaphragm.

 

The pump gets its energy from the negative pressure in the intake side of the carborator-- which [hole] allows some extra gas to enrich the mixture beyond what it should be causing unburnt fuel to exit thru the exhaust and generally poor running.  This diagnosis will be confirmed after installing a new fuel pump.  A trial run on the water will be proof.  The mechanic says that some OBMs power the fuel pump with exhaust pressure -- which wouldn't have any effect on the mixture, but [probably] would cause other problems.

 

Has anyone else had a similar problem with a new small OBM?  

Share this post


Link to post
Share on other sites

I'm all ears.  Anxiously waiting for your report.  My 3.5 is cranky as heck.  It's been "ok" with a new carb, but still has a flat spot when accelerating. Using nothing but Truefuel now.  

 

 

Share this post


Link to post
Share on other sites

All engines have application specific issues. Known weak or poorly designed parts. Find a real Suzuki mechanic and have them look up the common idiosyncrasies. Again ALL engines have them and the good mechanics, know what they are and likely how to best address them.

Share this post


Link to post
Share on other sites

I noticed you had the Suzuki back on board at the messabout and meant to ask.  Suzuki seemed to do ok? 

 

I know it's a different issue, but my Suzuki ran almost like a different engine after I ran it through the first gallon or so, i.e., after it was broken in.  The manual advised a break-in period, but I was surprised at the difference it made.   After that initial period, it now idles like it should, including running at low speed to allow shifting without a big thump.  Also starts reliably and predictably, like it should, without undo fussing back and forth with choke and throttle.  Basically a one-pull engine now.  So, maybe after you get your new fuel pump on the Tohatsu, then get a chance to run it for a few hours, everything and everyone will be happy.

Share this post


Link to post
Share on other sites

The Suzuki ran just fine at the Messabout.  Turns out that both engines suffered from some bad gas (water!).  Wanting to avoid the ethanol problems, I bought several gallons of ethanol-free 93 octagon gas from a Steil dealer.  At the MASCF when the Tohatsu wouldn't run right, I took it to a marina mechanic [who] discovered water in the gas.  But he still couldn't get it to run properly.  It took the dealer to find the hole in the fuel pump diaphragm.  So, I got rid of all the ethanol-free gas and am now using regulars gas with a stabilizer additive.  That made the Suzuki run like a charm.  Also, its short shaft didn't cause any cavitation -- maybe because I always had the ballast tank full and at least a crew of two adults (myself included).  In that configuration the hull speed was almost 5 knots.  If there is little or no cavitation when I'm solo with full BT, then I'll keep the Suzuki and sell the Tohatsu.

Share this post


Link to post
Share on other sites

We rent out a couple skiffs with 9.9s on them at work.  My first 2 years we had constant problems with fuel. It was always the fuel.

 

If you can get ethanol free, do so!  If not, treat it with something that combats the absorption of moisture.  Don't store more fuel than you can use in a short time.  I will pour month old fuel into my truck so I can get new. What ever it takes, be anal about fuel.

I never had to deal with laying an outboard down between uses.  Apparently that is another issue.

Share this post


Link to post
Share on other sites

Fuel stabilizers work, get some. I have lots of small gas engines, all run the same fuel, which is jug stored with a stabilizer. 

Share this post


Link to post
Share on other sites

I'm fortunate to get non-ethanol gas at the yacht club, where we have it in the fuel pump specifically for the marine engines in use there.  It does seem to make a difference.  I know I'm tempting fate, but I put some stabilizer in last fall (both in the fuel tank and ran it through the engine when I ran the engine dry) and everything worked this spring.  Fingers crossed.

  • Like 1

Share this post


Link to post
Share on other sites

I've used stabilized fuel that was over a year in storage and had no issues. You don't need to purchase non-ethanol fuels or worse the old leaded stuff, which is also still available and not desirable on modern engines. In marine applications not as much of a problem, but will screw your O2 sensors and catalytic converter in a car. Once stabilized the fuel isn't hygroscopic any more and it ties the few other additives together a lot longer, so corrosion isn't an issue. The real problem with ethanol laced fuel is the break down of the additives in the presence of moisture, which eats stuff, like gaskets and seals, plus the corrosion.

Share this post


Link to post
Share on other sites

I bought my ethanol-free 93 octagon fuel from a Steil dealer whose customer base is mostly rural.  Their tank is above ground and about 500 gallons in size.  It turned out to be contaminated with water.  That can happen if you happen to be getting your fuel load from near the bottom of the tank.  Especially if the dealer has a fairly low sales volume of that gas.  The tank can be half empty for multiple cycles of temperature & humidity variations -- causing condensation.  And the tank was not under cover, which would exacerbate the temperature daily highs and lows.  I got rid of all the e-free gas that I had.

  • Like 1

Share this post


Link to post
Share on other sites

For several years now, I've run my 2.5 hp 4 stroke 'Zuki with non ethanol fuel and Sta-bil. I always have some left in my gas can that sits over winter. I use it in my outboards as well as other small engines. Since doing this, I've had no fuel related problems. I buy the gas from a station that seems to have a fairly high turnover, so the gas doesn't have problems with water, or sits in the underground tank too long.

Share this post


Link to post
Share on other sites

I'm with Chick. I have had good luck with this web site https://www.pure-gas.org/

 

I also would add that on my Honda 2, there is a little drain screw on the fuel bowl that gets the last half teaspoon of gas out after you run it dry, which I do for really long term storage. I think draining the gas by running it out and then leaving that little bit is not good without getting rid of this. I haven't checked my Suzuki to see if it has such a drain.

 

I have a few old motorcycles, antique tractors, chain saw, weed wacker, etc. One thing overlooked which can wreak havoc on these small machines when not used is insects. Make sure when you store them they are out of the way of mud daubers and the like. A tiny passage is all they are looking for. I have resurrected more machines that suffer from this. I keep all of mine in a garage with a tight fitting door and they still find a way in. Just this summer I had a Stihl 2-cycle weedwacker that wouldn't start and it had spark, gas, etc. I took that tiny carb off and it was clean. I put in a new diaphram and it still wouldn't even fire. It was then that I grabbed an air hose and blew a big bunch of mud out of the exhaust port (mud dauber nest or something) and she ran perfect.

 

On my little Honda I have a cover for that I shoot with bug spray, let dry and then put on. I had the vent for the float bowl get plugged once this exact way. 

 

A friend says stress can be measured by how many internal combustion engines you own.

 

 

 

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


×