Tohatsu 50D2 carb

[K9Kampers]

Made it to the lake yesterday for final sync. All carbs same on gauge. Fiddled with pilot screws but ended with no discernable difference, so I put the settings back to factory specs. Idles great- no sputters, runs great ... 17.9 mph on GPS in wind and chop at 4600 rpm WOT. Still outside of manf. range. Don't recall if I've ever been in the range in the past...

[kmclemore]

WRT to optimizing your fuel mix, mileage and performance, try this procedure... lower your idle to as low as it will reliably (smoothly) run using the main idle speed screw (i.e. the one that opens the throttle plates)... then adjust the fuel pilot screws in small increments, looking for the RPM's to pick up - if you turn them clockwise you're reducing the amount of fuel and vice versa. Blip the throttle from time to time to clear the intake whilst you're doing this. If the RPM's rise after adjusting fuel flow, then lower them back down using the main idle speed screw again and keep repeating this process until you get the engine idling smoothly at the minimum fuel flow (clockwise pilot screw positions) and minimum idle screw depth (anti-clockwise idle screw position). This procedure will give you your best fuel efficiency.

Notes on the process:
Listen for stumbling (misfires) and if they start to appear then back off a bit until they go away. If you're already getting misfires, then back off until it smooths out. If you turn too far counter-clockwise (too much fuel) you'll get a kind of 'fluffy' puffing from the exhaust and you may smell gas as well - if so, then simply reverse and tighten the screw until smooth running is resumed. The object is to be able to supply only enough fuel for the engine to run smoothly, and no more.

[WASP18]

Need help.

I have a 1999 Tohatsu M50D2 serial # 62709 I purchased recently.

I just installed new throttle and shift cables and when I started the engine (on ear muffs) and ran it for five or so minutes to warm it up, it sounded ok. Backed the throttle/shifter to neutral and it would drop below 800 rpm and then stall. I tried this a few times and still the same. In order to shift it in gear, I have to add a little power with the "idle" throttle and then quickly shift into gear. The throttle clevis was installed with no tension on the throttle arm (my own terminology).

Reason for changing the cables was the engine started in gear. Troubleshooting: I found the gear shift cable was severed and decided to change both. The engine idled quite well before I worked on the cabe replacements.

[K9Kampers]

From your description, the original cable had slightly more preload than the replacement has now. If your engine was properly tuned beforehand, you can turn in the new cable end a half-turn at a time til you get the desired results, or leave the cable at zero preload and adjust the nuetral idle RPM at the throttle stop screw.

[restless]

A little side question.
I'm looking at getting a balancing kit, 4 guage type for our club to use. Now, do these old strokers have a little point to attach the hoses to?
I'm only asking as I can't get to my boat without a 2300mile trip, which too is coming up soon
While we're at it, same question re yam 4strokes, as there are heaps of these fuel efficient sneakily quiet engines gliding around our rallies. I'm not at all jealous I was told the new tohat injection stroker does 2l/hour, as opposed to our 11l/hr

[kmclemore]

I'm looking at getting a balancing kit, 4 guage type for our club to use. Now, do these old strokers have a little point to attach the hoses to?

Not that I know of. The most popular and easiest to use is a single manometer that fits on the face of the carb, and move it from carb to carb as you adjust them. That being said, it's likely you'll need to make an adapter/extension to fit a standard manometer to the face of a Tohatsu carburetor... easy and cheap to make. I made mine out of a simple piece of PVC tube.

[restless]

Hi Kev
I saw the photos. Trouble is, boaty is in the middle of nowhere, so I need to get everything right in theory AND practice. Also, been sooo long since I played with these sorts of toys that I'm not confident that I can just intuit it all through.
Will have another look at your set up.. be prepared for further interogation...

[restless]

ok.. this is my headache.
I would have thought one would be looking at the pressure on the engine side of the butterlfy, that'll be where the true action is. Sat on the outside like the thingy on this thread would work in a different way.. guessing that there is an air inlet so the carb can breathe somehow with a little pitot tube poking in somewhere?
I've got to sort this or peachies is gonna refuse to take the helm on mooring operations

[Catigale]

You are measuring airflow on the opposite of the engine with the Unisyn tool... You aren't tRying to measure the actual flow, you just want to equalize them

[133bhp]

ok.. this is my headache.
I would have thought one would be looking at the pressure on the engine side of the butterlfy, that'll be where the true action is. Sat on the outside like the thingy on this thread would work in a different way.. guessing that there is an air inlet so the carb can breathe somehow with a little pitot tube poking in somewhere?
I've got to sort this or peachies is gonna refuse to take the helm on mooring operations

If I remeber (from the late 70's) with twin stromberg days on Rover V8's and triumph stags, the single meter mesures the airflow entering the carb. hence vacumm, as opposed to messuring vacuum after it. Unless you need an accurate number, either wuld work. Can even use a tube to your ear, listening to air if desperate.

There appears to be what I assume are vacuum balance pipe spigots on the inlet manifold, so shold be easy to attaching there. I have a twin bike balancer which I intend to try one day. but given the close proimity to the reed valves it might be difficlut to get a stable reading. Upping the gauge damping and idle speed might be in order.

If after the usual carbs checks etc, be worth checkingte reed valaves themselves if still unstable idle? Also the butterfly sync? - On motobeike engines I have used thin cigarettte paper bent in a L shape. held by the buttflies, then set to drop in unison. Gives pretty much spot on results. (L shape prevents falling into inlet)

[kmclemore]

If I remeber (from the late 70's) with twin stromberg days on Rover V8's and triumph stags, the single meter mesures the airflow entering the carb. hence vacumm, as opposed to messuring vacuum after it.

Yes, you're partially right. The UniSyn and other similar tools are called 'manometers' and they measure airflow through an orifice, and the way they do that is to force the air to go through a venturi (narrowed hole) and then, using a tiny pilot hole off that venturi they measure the vacuum over that orifice. So, you're *not* measuring the vacuum in the engine, you're measuring the vacuum created by the manometer.

Most of these manometers have an adjustable orifice - in the case of the UniSyn you twirl the inner hub to increase or decrease the size of the venturi and thereby controlling the vacuum over the UniSyn's orifice. This allows you to adjust the height of the ball in the sightglass so that it's not stuck at the top or bottom of the glass tube.