18HP Tohatsu - what compression is "good"

[RRitt]

Re: 18HP Tohatsu - what compression is "good"

i agree with pvanv jerry rigging has no place on an outboard, or in the marine environment at all EVER!! and should only be a last ditch effort to get you home in a bind and should be corrected PROMTLY after it does what it needed to do....not safe.... not smart and if someone were to get hurt by this thing after you rigged it up youd feel pretty bad id like to think ....especially if it was your kid or your wife

it's just a temporary engine. water cooled pos. i hope to finish my john deere by july.

 

[pvanv]

Re: 18HP Tohatsu - what compression is "good"

I already took it apart, cleaned it and put it back together. I'm not familiar with it so I just put it back together exactly as I found it except with new gaskets. maybe it is the plug. it runs like an air passage is plugged. If the briggs doesn't work then I'll look at it next weekend. I like the briggs carb better. It's a more durable design. All things equal I'll take it.

It is surprisingly easy to put a briggs carb onto the tohatsu. the through bolts line up like it was meant to be and the throat is 1/16" larger. It only took about 20 minutes to drill out a small slab of 1/2" aluminum. I already have a spare 13hp 420cc briggs carb laying around. I have not bolted it together yet. I still need to bend some small rod to make a throttle lever.

If you follow along in the Factory service manual, it's surprisingly easy to work on. If you don't at least have an exploded diagram from the parts catalog, you are working in the dark. If you neglect that rubber plug, you will be drowning in fuel.

 

[RRitt]

Re: 18HP Tohatsu - what compression is "good"

If you follow along in the Factory service manual, it's surprisingly easy to work on. If you don't at least have an exploded diagram from the parts catalog, you are working in the dark. If you neglect that rubber plug, you will be drowning in fuel.

yes, it was very easy to work on. everything is there and assembled per exploded parts diagram. i only pipe cleanered the main ject and fuel inlet. It probably has dissolved hose residue in some passageway(s). the fuel is starving. It won't start unless i give it a couple shots from accelerator pump and it runs better for short burst if the pump shoots some gas down throat. I think carb might be a factory defect. the main butterfly is crooked from factory with a 1/64th gap top and bottom.

 

[pvanv]

Re: 18HP Tohatsu - what compression is "good"

Yes, it does sound lean. Typical of low-speed varnishing. Is the Auto-by-starter solenoid operating correctly? As with any 4-stroke OB carb of any brand, the only way to reliably clean the low-speed circuits is to do a complete disassembly of all jets, emulsion tubes, etc., and then give it a 4-hour soak in real carb dip (available at auto parts houses), followed by a liberal blow-out with generic carb spray, then a reassembly, checking float height. Don't use any kind of wire to clear any passages, as it can cause micro-scratches in critical areas, leading to weird flows, with resultant poor mixtures under some conditions.

 

[RRitt]

Re: 18HP Tohatsu - what compression is "good"

Yes, it does sound lean. Typical of low-speed varnishing. Is the Auto-by-starter solenoid operating correctly? As with any 4-stroke OB carb of any brand, the only way to reliably clean the low-speed circuits is to do a complete disassembly of all jets, emulsion tubes, etc., and then give it a 4-hour soak in real carb dip (available at auto parts houses), followed by a liberal blow-out with generic carb spray, then a reassembly, checking float height. Don't use any kind of wire to clear any passages, as it can cause micro-scratches in critical areas, leading to weird flows, with resultant poor mixtures under some conditions.

thanks for tip on wire. I generally avoid the pipe cleaner except on straight shots. It does similar damage in trim systems if you try and force a pipe cleaner to follow a corner or try to shove it down a passage too narrow.

It looks from picturers like carb assy 3V9035002M includes a new choke solenoid. Does your company list on iboats or anywhere? I have deep doubts about this patricular carb because of butterfly gap. I think it is a factory reject that slipped past detection.

If the briggs doesn't work then I'll just go buy a new tohatsu off google or something. I still prefer the briggs. Its a simple design with a 40 year history. When my riding flats tractor is ready then I will still need to have a tohatsu carb for resale value. But - if the briggs works - then I can take my time about finding it.

 

[RRitt]

Re: 18HP Tohatsu - what compression is "good"

Yes, it does sound lean. Typical of low-speed varnishing. Is the Auto-by-starter solenoid operating correctly? As with any 4-stroke OB carb of any brand, the only way to reliably clean the low-speed circuits is to do a complete disassembly of all jets, emulsion tubes, etc., and then give it a 4-hour soak in real carb dip (available at auto parts houses), followed by a liberal blow-out with generic carb spray, then a reassembly, checking float height. Don't use any kind of wire to clear any passages, as it can cause micro-scratches in critical areas, leading to weird flows, with resultant poor mixtures under some conditions.

you were spot-on. auto-by-starter is bad. It sits there and never does anything. I assume it is similar to the auto choke on my mazda pickup. the electrical current heats a coil that retracts slowly as the engine warms up. It does nothing.

The briggs carb fit great and ran well but it had to be choked way down for idle. 320cc at idle just isn't pulling enough air for the venturi. I would have to tear up a working machine to get a smaller throat. Oh well, i was going to have to buy the tohatsu part anyway before I could sell the engine.

 

[pvanv]

Re: 18HP Tohatsu - what compression is "good"

Troubleshooting procedures for the Auto-by-starter are in the Factory service manual.

Yes, the ABS has a heater coil and wax-type actuator, and is similar to an automatic electric choke. The wax does not contract, but rather expands, when heated. Did you test it with 12v? Are you getting 12v to the ABS terminals?

Does the motor run correctly when warmed up? If not, the ABS is not to blame. The ABS unit can fail, but it's rare, and expensive. They are in stock at Tohatsu. 3R3034100M AUTO-BY-STARTER ASSY $144.58.

 

[RRitt]

Re: 18HP Tohatsu - what compression is "good"

i removed it from carb, clamped it gently in bench vice, and hit it with 12v for 3-4 minutes. the plunger did not move. I was going to do a resistance check but then I looked up the price of ABS on a break. Since Tohatsu, nissan, and mercury all charge the same price i think it is gang rape. I just bought a whole new carb off google for $165. Still about double what a small engine carb is worth.