Dirty Carb? Advice needed.

willk · 12 May 2017, 09:28

My 3.5hp Tohatsu 2 stroke has emerged from the winter with a small issue - it won't idle unless it gets a little bit of choke. Running is therefore naturally a bit smoky. There was a bit of fuel leaked from the carb area during setup yesterday - possibly because it was a hot day and tank pressure had built up.

So my question is - does this sound like a "simple" carb clean or should I be planning for something more sinister? (damaged diaphragm, etc). I'm reasonably happy pulling things apart but I'm no mechanic. I have some aerosol carb cleaner and the Clymer manual. I ask all this because currently the engine is largely working and takes me to the mooring - but once I open it and break something......

Fenlander · 12 May 2017, 09:51

>>>once I open it and break something......

In the past when running Citroens and old Discoverys suffering grumbles from others about how unreliable they would be I always said if you bought one thinking it was likely to be unreliable it would be happy to meet your expectations. But as a believer I had total reliability from both makes.

So when you do your carb *believe* and it will be fine.

Personally I would buy the genuine overhaul kit and do it properly so it's good for the next 15yrs+....

TOHATSU CARB KIT 2.5 3.5HP OUTBOARD ENGINE MOTOR 2 STROKE

Or you could get a pattern kit but if it still doesn't run just right you will wonder if the cheap kit was the cause...

Boat Engine Carburetor Repair Kit for Tohatsu Nissan 2.5HP 3.5HP Outboard Motor

jwalker · 12 May 2017, 10:11

Ok, before you pull it apart... If it has an air box, take it off, you're going to put your hand over the carb inlet. If it has an idle mixture screw, speed up the tick-over a fair bit, screw out the mixture screw as far as you can without it stalling. Now you've to give it a good rev up, snap the throttle shut, and simultaneously put your hand over the carb inlet. This will apply full vacuum to the idle fuel system and, hopefully, suck out any crap. Do it a couple of times. Remove the mixture screw completely and check for rubbish on it and inside the screw hole. Refit the screw.

Reset, the mixture and tick-over and cross your fingers.

willk · 12 May 2017, 10:14

Quote:

Originally Posted by Fenlander

>>>So when you do your carb *believe* and it will be fine.

Personally I would buy the genuine overhaul kit and do it properly so it's good for the next 15yrs+....

So you're saying go the whole hog and "rebuild" rather than open and clean?

willk · 12 May 2017, 10:17

Quote:

Originally Posted by jwalker

Ok, before you pull it apart... If it has an air box, take it off, you're going to put your hand over the carb inlet. If it has an idle mixture screw, speed up the tick-over a fair bit, screw out the mixture screw as far as you can without it stalling. Now you've to give it a good rev up, snap the throttle shut, and simultaneously put your hand over the carb inlet. This will apply full vacuum to the idle fuel system and, hopefully, suck out any crap. Do it a couple of times. Remove the mixture screw completely and check for rubbish on it and inside the screw hole. Refit the screw.

Reset, the mixture and tick-over and cross your fingers.

Sounds like fun - worth a try!

paulbrown22 · 12 May 2017, 10:58

On the little 2 strokes pulling the carb and cleaning it is normally a fairly easy job anyway? For various reasons I've ended up pulling the carbs on our 2hp, 5hp and 30hp 2 strokes a number of times over the past couple of years (having never previously looked at one at all), and it tends to be a fairly swift job. Given no electrics or complexity and the ease of handling, the 2hp and 5hp take maybe 10 mins to pull off, and then maybe 20 mins to strip it down and clean. If you have the time, they are so simple and easy to work on that personally I'd just pull the carb, inspect/clean, and decide if you do need to "rebuild" with new diaphragm, etc., or not. You're unlikely to break anything...

Fenlander · 12 May 2017, 11:26

>>>So you're saying go the whole hog and "rebuild" rather than open and clean?

Just my way... do it once with proper parts and do it right. I spent 20yrs with a business where I maintained things for customers and found this the best way as I couldn't afford a call the next day after handing something back that'd I'd only got it *nearly* sorted. I've carried that approach to my own gear and it has paid off.

I appreciate there are less expensive/intensive ways that folks find get the result they want too though.

willk · 12 May 2017, 12:20

Quote:

Originally Posted by Fenlander

I appreciate there are less expensive/intensive ways that folks find get the result they want too though.

I'm currently considering all of the options above. I do my own basic servicing but hadn't planned to drop another €75 on this wee pup just yet. If I have to I will. If it was on Herself the RIB I would just buy the kit and get on with it.

Andy C · 12 May 2017, 13:44

My 4hp Mercury (which I think is the same as the Tohatsu?) had exactly the same symptoms earlier this year. The leaking fuel was coming out of the breather on the top of the carb. After a bit of “is it worth messing with as it still runs” pondering, I decided I’d try cleaning the carb, it’s completely sorted the problem. I was pretty surprised at how much crap there was in the float bowl. Total cost in my case was a can of carb cleaner, which you’ve already got!

willk · 12 May 2017, 14:40

Quote:

Originally Posted by Andy C

My 4hp Mercury (which I think is the same as the Tohatsu?) had exactly the same symptoms earlier this year. The leaking fuel was coming out of the breather on the top of the carb. After a bit of “is it worth messing with as it still runs” pondering, I decided I’d try cleaning the carb, it’s completely sorted the problem. I was pretty surprised at how much crap there was in the float bowl. Total cost in my case was a can of carb cleaner, which you’ve already got!

The 4hp is a bit more advanced than the 3.5hp, which is a bit of a dinosaur. The previous owner wasn't overly particular about fuel and I strongly suspect dirt/gum is the issue. The 3.5 doesn't have an inline fuel filter either and seems to rely on the strainer in the tank!

- I might try to squeeze a wee saw filter in there somewhere.

I think I'll have a dig around in this carb as someone has offered me a loaner donk if I b@lls it up...

Rover310 · 12 May 2017, 16:22

Personally, I would just disassembly the carb and clean it, paying particular attention to the small fuel passages that typically become plugged with old fuel residue. Also, once you have it disassembled, access the condition of parts like the bowl gasket, inlet needle & seat, o-rings etc. and if need be, buy an OEM carb rebuild kit as Fenlander suggested.

A small inline fuel would certainly be a good idea, although that won't prevent old gas from gumming up carb passageways in the future... gasoline these days has a pretty short shelf life when it comes to off-season storage. Many suggest that todays gasoline, left untreated, begins to degrade in as little as 30 days.

Davie · 13 May 2017, 18:54

Your engine is running to lean at idle. Take the carb off the inlet manifold. Get a sheet of newspaper on your bench and make sure you keep everything on the paper as the needle valve and float have nothing keeping them on. I would say the main jet will be ok as I assume this runs ok flat out. What you need to do is lift the needle on the throttle slide 1 notch. It's the only adjustment you can make to the mixture. There is a fuel filter in the barbed outlet of fuel tank. There is no fuel pump its gravity fed.

jwalker · 13 May 2017, 22:37

Ok, forget what I said earlier cos when I checked out your carb, I found it was a basic slide valve type and it doesn't have small blockable idle passageways. You can still do the hand over intake trick and it'll draw anything out of the main jet but you do it differently. Put the engine in gear, in water, rev it and without closing the throttle momentarily cover the intake with your hand. This will suck a big gob of fuel in while the main jet is at its largest flow so flushing it through.

However, if it was working nicely last time you used it and since the carb has no small passageways to block up, I'd be looking at where you might have a small leak of air to slightly weaken the tick-over mixture. It would make very little difference to the main running. First stop, there's an o-ring where the carb connects to the engine, I'd check it out.

Apologies for the earlier bum steer.

willk · 13 May 2017, 22:52

Quote:

Originally Posted by jwalker

Apologies for the earlier bum steer.

No worries - I haven't started yet - planned to open it tomoz (clearing the workbench of other clatch today in preparation).

I say it was working properly last season, but I only used it to run to and fro moorings, so I guess I could have missed something. It did stop occasionally for no obvious reason (and restart first go) which I put down to being a piddly one cylinder engine. There's deffo something amiss now though...

gpsguru · 15 May 2017, 23:20

Quote:

Originally Posted by willk

My 3.5hp Tohatsu 2 stroke has emerged from the winter with a small issue - it won't idle unless it gets a little bit of choke. Running is therefore naturally a bit smoky. There was a bit of fuel leaked from the carb area during setup yesterday - possibly because it was a hot day and tank pressure had built up.

You dont mention the year, but I assume pre 2006 ............

The carb is the same as the Mercury 3.3 and pretty simple to work on.

It is basically a needle carb, and therefore easy to clean .......... drop the float bowl (2 screws) and you will probably find its full of sediment. and not allowing the float to rise and fall correctly, also there maybe an issue with the float needle valve..............

Once cleaned, run the engine in a tank ......... put it in gear for a bit of load and blip it to 3/4 throttle a few times, this tends to clear out any sediment that may have found its way around the carb body .......

I am just fixing up a 1998 Mercury 3.3 for my daughters dingy. It had been stood for 3 years and declared a non runner as fuel was leaking from the carb, and would not start, but after a carb clean, a quick fix on the stop switch and a new water pump kit, it runs like a dream.

This might help ...... 3.5hp Tohatsu ........... 2004 M3.5A2 Tohatsu Outboard CARBURETOR Diagram and Parts

willk · 15 May 2017, 23:35

Quote:

Originally Posted by gpsguru

You dont mention the year, but I assume pre 2006 ............

Cheers - she's a 2003 IIRC. I've just reassembled the carb tonight and waiting for some daylight to run* up in a tank tomorrow and reset idle etc. Rather annoyingly, the interior of the carb was immaculate - but here's hoping...

* assuming it will start now

gpsguru · 15 May 2017, 23:51

O ye of little faith ..............

Of course it will start ............... they are good little engines with very few known faults.

The stop switch can go intermittent .......... on some you can pull it apart and clean it.

spartacus · 16 May 2017, 08:44

They're cracking little engines. Used to have a 3.5hp Twatsoo as an auxilliary on my last RIB. Given the fuel and oil mix is in these engines over a prolonged period of time - as they are relatively frugal, and depending on actual use, it's no big deal to drain the fuel and start from scratch. I use the 2-stroke fuel in a 4-stroke Honda lawnmower - which is a bit of a treat for it!

I'd also check out the spark-plug, pull it, dry off and check the gap. Just wondering if the carb has a drain hex nut? I'd always remove this rather than pull the carb off.

I sometimes loosen the filler cap right up to get it started, then tighten the fuel cap and vent it open. Good luck - hope you get it sorted.

willk · 16 May 2017, 09:48

I prolly should have mentioned at the start that I'd tried a couple of the less complicated tweeks - so I had used fresh mix with some petrol cleaning additive in it, checked the plug (good) and sprayed a bit of carb cleaner into the intake. Anything to stave off stripping my first carb!

I still haven't gone out to try to start it - the Coffee of Procrastination beckons

I suspect however that even if it starts, the problem will persist. If it does, I'll order up a kit - even though the parts look good it could be a poor seal on a gasket or o-ring, or anything I guess...

willk · 16 May 2017, 12:14

Quote:

Originally Posted by Davie

Your engine is running to lean at idle. Take the carb off the inlet manifold. Get a sheet of newspaper on your bench and make sure you keep everything on the paper as the needle valve and float have nothing keeping them on. I would say the main jet will be ok as I assume this runs ok flat out. What you need to do is lift the needle on the throttle slide 1 notch. It's the only adjustment you can make to the mixture.

So this all means something to me now that I've had them in my hand

The engine ran - but exactly as before (see below). I didn't change any of the settings as described above but am considering doing so now.

The engine still starts and runs - but will only idle with a VERY little choke, even when warm - no choke and it dies. When throttle is applied, it will die out unless MORE choke is applied (about a third) - then it will run happily.

Does this sound like a mixture issue? I'll lift the throttle slide if it sounds like it is...