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Catalina/Capri 25/250 Sailor's Forums

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Tohatsu 9.8 idle question

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SJ
Navigator

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USA
198 Posts

Initially Posted - 07/06/2010 : 09:18:03

Was out yesterday and when I have the motor close to idle it wants to stall. I have to keep the rpms up so it doesn't stall, and thats not so much fun when you are docking etc. Off the top of your heads, does anyone know how to adjust the idle speed on these motors. Remember I know where the gas goes and thats about it...

Thanks!!!!!

Edited by - on

dmpilc
Master Marine Consultant

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USA
4593 Posts

Response Posted - 07/06/2010 : 09:38:43

Are you using fresh gas? Carb may need cleaning.

Edited by - on

Renzo
Admiral

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USA
621 Posts

Response Posted - 07/06/2010 : 12:18:51

There may be many reasons but one possible fix is to change the quick disconnect valve at the end of the gas line where it connects to the engine. The valve has a spring loaded ball that pushes against a pin on the engine portion of the connector to allow gas to flow only when the two parts are connected. Over time the spring gets weak and dosen't open the valve completely so at low flow (like when you are at idle speed there is not enough gas reaching the carb and the engine stalls. I'm not saying that this is definately the cause of your problem but for 5 bucks it's worth a try.

Edited by - on

DaveR
Master Marine Consultant

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USA
2015 Posts

Response Posted - 07/06/2010 : 12:55:16

Probably not the disconnect IMO because that's going to be problem at idle or at top end or in between. Very likely the jet in your carb bowl or one of the various little passageways that create vacuum etc. has a little piece of gunk in it. Take the carb all the way apart, remembering what goes where

and shoot compressed air through every orifice you can find. Past the jet there is usually a jet seat that can shoot out under pressurized air so be careful of that.

Or it might just be old gas

PS~ Renzo I didn't completely read your post before responding, thought you were talking about the connect sucking air. Never heard of what you describe but will keep it in mind next time I have a problem!

Edited by - DaveR on 07/06/2010 13:00:25

Sloop Smitten
Master Marine Consultant

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Response Posted - 07/06/2010 : 12:58:07

Part number 12. Screw it in to increase the idle. Screw it out to decrease the idle.

Edited by - Sloop Smitten on 07/06/2010 13:03:31

SJ
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USA
198 Posts

Response Posted - 07/07/2010 : 09:09:55

Thanks guys! I'll try anything right now....

Edited by - on

tinob
Master Marine Consultant

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1883 Posts

Response Posted - 07/07/2010 : 12:25:06

What you are experiencing now is something that I had occasion to stumble across last season. It cost me a new carboretor with installation @$250. The old carb sits on a bench of my workshop along with other things, listed under, "in case of". Truth of the matter is that my digits trembla to the point that signing my ss checks are the extent of my dexterity, and I persist, for reasons that I'm beginning to question.

The problem was a fouled low speed jet. We tried to dissolve it with a carb- cleaner soak but nada.

Val on Calista,# 3936, Patchogue.

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Renzo
Admiral

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USA
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Response Posted - 07/07/2010 : 14:09:13

<blockquote id="quote">quote:<hr height="1" noshade id="quote">....PS~ Renzo I didn't completely read your post before responding, thought you were talking about the connect sucking air. Never heard of what you describe but will keep it in mind next time [i]I have a problem!
<hr height="1" noshade id="quote"></blockquote id="quote">

It was the last thing I tried when I was having an idle speed problem this spring, and it worked immediately. I know it's not usual and kind of an oddball fix, but I wish I would have tried it first because would have saved me from, trial and error idle adjustments,replacement of gas,and carb cleaning.

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Davy J
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1511 Posts

Response Posted - 07/07/2010 : 17:09:06

<blockquote id="quote">quote:<hr height="1" noshade id="quote">The problem was a fouled low speed jet. We tried to dissolve it with a carb- cleaner soak but nada<hr height="1" noshade id="quote"></blockquote id="quote">

I have run into this problem four times with my Tohatsu. It is just over two years old. After the hassle of taking the motor to the dealer twice, I have just started cleaning the low speed jet myself. A two day soak in carb cleaner has worked for me the last two times. I think I am going to obtain a second jet so I can just change it out when needed. I now also run the fuel out after each trip and change the fuel in the tank as well.

In addition, I started draining the fuel out of the the fuel hose and was suprised how dirty the fuel had become after sitting in the hose for only a few days.

Edited by - Davy J on 07/07/2010 17:13:32

Sloop Smitten
Master Marine Consultant

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1181 Posts

Response Posted - 07/08/2010 : 07:45:14

Looking at the exploded diagram it would appear the idle jet (p/n 1-6) is located inside the carburetor bowl under a plug (p/n 1-2) which requires removing the carburetor to access. Can one of you confirm this? I know on my old Honda 8 it was accessible from the side of the carburetor.

Edited by - on

Davy J
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1511 Posts

Response Posted - 07/08/2010 : 08:44:02

Unfortunately, you must pull the carb off to clean the low speed jet. However, it is not that difficult. All the linkages pop-off and there are two bolts holding carb in place. The most difficult part is to get everything to line up when you re-install it. Also, it is best to run the gas out of the carb before you remove it.

Edited by - on

ed_spengeman
1st Mate

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USA
98 Posts

Response Posted - 07/08/2010 : 10:09:55

Did much research on this. Engine comes with idle speed set for normal operation. Problem is, it takes about a month for the engine to breakin. So set the idle up so it doesn't die. It'll be a little bumpy shifting but no big deal. In 30 days try to set it back and see if it works ok.

Also, disconnect fuel line and let it die when you turn it off. If you don't use it for a protracted period, just before it dies, pull out the choke. Use clean gas - try less than a mont old.

GREAT MOTOR (ENGINE)

Good luck.

Edited by - on

SJ
Navigator

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USA
198 Posts

Response Posted - 07/08/2010 : 11:14:47

I will try to adjust the idle speed first and see how that works, then if need be the jets. Not sure I'm up for that challenge. So with that said, when i take off the carb, how much stuff falls off by itself?????? Hopefully not into the water!

Edited by - on

Sloop Smitten
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Response Posted - 07/08/2010 : 13:36:55

No easy answer. You have to assume, when working over the water, that every part and tool has a significant chance of accumulating in Davey Jones locker. Not a lot of parts involved with removing the carb. If your uncomfortable with removing the carb I would suggest raising the idle a bit using the idle screw and adding some fuel injector cleaner or Sea Foam carb/fuel inj cleaner to your gas and taking it for a good run using your engine. If the idle seems high then you can adjust it back down.

Edited by - Sloop Smitten on 07/08/2010 13:37:56

bigelowp
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1757 Posts

Response Posted - 07/09/2010 : 18:59:56

If you are like me you rarely use the engine. By rarely, maybe once a week for short durations and never at full throttle. Add that up and the carb is going to get gunked up between old (one or two tanks a season) gas and lack of use. My engine also started to stall on low rpm. As I am on a mooring it is less critical, but none the less frustrating for an engine that is three years old and has maybe 20 hours on it. I am now trying to run the boat fast for a spell when using the engine and use additive tot he gas mid season on.

Edited by - on

Voyager
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5318 Posts

Response Posted - 07/09/2010 : 21:21:46

With my Honda, I built a fixture out of 2x4s and 2x6s to let me work on the engine in my garage, or down at the boat yard (in a pinch). The fixture includes a tall trash bucket to immerse the engine in water - if I want to run it.

I would never work on my engine hanging off the transom except for an emergency at sea, since I would drop half of the parts in the drink.

I've had both problems: a bad gas connector leaking air and a clogged low speed jet.

For the former, the engine ran fine at high RPMs, but died at low speeds. You could hear the hissing sound, so that was a dead giveaway. I got a $10 part and that was that. If in doubt, just listen to it, and replace the part.

For the latter (low idle jet), I got the shop manual, and bought a carb rebuild kit including gaskets and o-rings. I pulled the carb (there were a few linkages and electrical cables that needed to be removed too). So I labeled them and drew a picture of how it went back together.

I took apart every piece of the carburetor that a screwdriver, wrench or pliers would remove. There was a lot of junk and gunk in the bowl and near the jets. I used carb cleaner and swabs, I used compressed air, but I did not use any thin wires, straight pins, sewing needles or other items that could possibly scratch or damage the sensitive parts.

I changed out all the parts of the rebuild kit, even if they looked OK. It runs great. I will clean it out again at the end of the season and prep it for winter storage.

Now, I only use fresh gas, gas stabilizer, run the bowl dry after use and never let the engine sit more than two weeks during the season without starting it.

So, when the wind is howling, the current is ripping, the breakers are breaking, the water is cold early and late season and the rocks look like they want to take a bite out of your boat -- my life, and the welfare of the boat literally depend on the motor working without fail.

There are lots of things you can let slide. Your engine is not one of them.

Edited by - Voyager on 07/09/2010 21:28:08

tallers
Deckhand

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1 Posts

Response Posted - 06/08/2011 : 17:25:12

Tohatsu 9.8 idle problem. I have a 2007 tohatsu 9.8hp 4stroke. A good friend tried all of the listed solutions with limited or TEMPORARY SUCCESS. He broke down the CARB and was sure there was a GASKET MISSING. I Printed him the PARTS LIST for the 9.8 for 2006 and 2009 FROM TOHATSU website.

HE FOUND THE ENGINE WAS ASSEMBLED MISSING A PAPER GASKET (2 needed one on either side of the PLASTIC GASKET(spacer). This was preventing an AIR TIGHT SEAL.

Hope This Really Solves The Problem, PHIL

Edited by - on

John Russell
Master Marine Consultant

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USA
3444 Posts

Response Posted - 06/09/2011 : 05:45:02

Doesn't "raising the idle speed" just increase the rate of fuel/air flow to the carburetor? How does that differ from simply doing that with the throttle? I don't think it does. You'll still have faster engine speed which translates to faster propeller speed which translates to approaching the dock faster than you are willing to hit it.

Mine died at idle last week as I approached the dock. It turned out that one of my spark plug wires popped off.

Edited by - John Russell on 06/09/2011 05:45:49

dmpilc
Master Marine Consultant

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USA
4593 Posts

Response Posted - 06/09/2011 : 08:58:57

I had the same no idle problem with my Nissan 9.8. I decided to try Seafoam in the gas before pulling the motor and removing the carb to clean the low idle jet. I poured a full bottle of Seafoam into 2 gallons of fresh gas and ran the motor several times over the next 2-3 weeks, actually every time I went to the lake. Just went motor sailing one trip. I must be a little lucky because it cleared up the problem.

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