Loss of a cylinder tohatsu 9.8

[dakman]

Just went though my 2006 tohatsu 9.8.
* pulled carborator, cleaned and re installed.
* New plugs
* fresh fuel

OK, hears the issue.... Starts fine, both pull and electric, but sometimes it will rev up just fine, I'll let it idle for a bit and try and rev it again but it seems like it's only firing on one cylendar. I'll pull the kill clip, reinstall it and restart it. Run fine, revs up, idles, revs up, idle, but sometimes after the idle phase, it won't rev up again, that's when it sounds as though it only firing on one cylendar. But, if the kill clip is pulled and restarted, it seems to run on both.

I've pulled the plugs and they look fine.....
Any help, guidance will be greatly appreciated!

Standing by,
Dakman

 

[pvanv]

The 9.8A2 and A3 (you did not mention model -- year is irrelevant) use a siamese coil, so likely not ignition. What method did you use to clean the carb, and what were the symptoms that led you there?

 

[km1125]

Has it done this just since you put the new plugs in, or was it doing it before and you put new plugs in but it is still doing it?

I always try to put new plugs in a GOOD working engine, but then keep the OLD ones as spares. That way you have KNOWN GOOD spares. There's always a chance -albeit small- that a new plug has a problem (like a manufacturing defect or a crack in the insulate during shipment) but if you take plugs out of a good running engine you know they were working OK.

 

[dakman]

pvanv, 9.8 hp electric start and I believe it's A2, not at the boat right now.
The motor had been doing this off and on for while, but the boat hasn't been in the water for a while but planning on a lake sail in a few weeks and thought I'd bucket run the motor just to make sure it was in good shape. When I stored to the boat, the motor was run dry so no gas in the carb.

When I did try and run it, it was running rough and wouldn't idle, alway had to choke it a bit. Once it warmed up, it ran a bit better but rough at idle. That's what prompted the carborator cleaning. Soaked it, cleaned all the port passages with some gauge wire, blew it out with air and reassembled.
Cleaned the old plugs and started it up. Seemed to run a bit better but still ran very rough and would die during idle. So, got some fresh gas, new plugs and it started fine and run pretty well at higher rpm but still very rough at idle. Tat's when this simptom of feeling like it was running on one cylendar; which also happed prior to all the items I've mentioned.

Again, i'll run it for a while at mid rpm and then let it go to idle but when I goose it for higher rpm, it sounds like it's booged down, under a load, and won't go to the higher rpm. I then pull the kill clip, reattach it and start the motor. It run fine for a while but then does the booging thing.

OK, that's my story and I'm sticking to it.
Let the mind meld begin!

Dak out

 

[dakman]

The 9.8A2 and A3 (you did not mention model -- year is irrelevant) use a siamese coil, so likely not ignition. What method did you use to clean the carb, and what were the symptoms that led you there?

pvanv, 9.8 hp electric start and I believe it's A2, not at the boat right now.
The motor had been doing this off and on for while, but the boat hasn't been in the water for a while but planning on a lake sail in a few weeks and thought I'd bucket run the motor just to make sure it was in good shape. When I stored to the boat, the motor was run dry so no gas in the carb.

When I did try and run it, it was running rough and wouldn't idle, alway had to choke it a bit. Once it warmed up, it ran a bit better but rough at idle. That's what prompted the carborator cleaning. Soaked it, cleaned all the port passages with some gauge wire, blew it out with air and reassembled.
Cleaned the old plugs and started it up. Seemed to run a bit better but still ran very rough and would die during idle. So, got some fresh gas, new plugs and it started fine and run pretty well at higher rpm but still very rough at idle. Tat's when this simptom of feeling like it was running on one cylendar; which also happed prior to all the items I've mentioned.

Again, i'll run it for a while at mid rpm and then let it go to idle but when I goose it for higher rpm, it sounds like it's booged down, under a load, and won't go to the higher rpm. I then pull the kill clip, reattach it and start the motor. It run fine for a while but then does the booging thing.

OK, that's my story and I'm sticking to it.
Let the mind meld begin!

Dak out

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[pvanv]

I would re-clean the carburetor.

 

[dakman]

I would re-clean the carburetor.

re-cleaned and it does idle a bit better but while idleing it surges, increased rpm. Then trottle screw seems very sensitive and if it's a tab too much. the rpm increases like I had hit the trottle..... any ideas?

Dak

 

[km1125]

re-cleaned and it does idle a bit better but while idleing it surges, increased rpm. Then trottle screw seems very sensitive and if it's a tab too much. the rpm increases like I had hit the trottle..... any ideas?

Dak

Sounds like you're still running too lean at idle.

When you use the idle speed screw to increase the idle, then the motor starts pulling fuel from the transition ports or from the main jet, causing the mixture to get richer (but closer to normal) along with the slight increase in air causing that bigger RPM increase.

 

[pvanv]

Need to clean the carb more thoroughly. KM is 100% correct.