Logo
FULL SITE MENU

Engine revs up and down/stalls. Ready to throw it overboard!

L

labatt

New member
Hi All -

I looked back through a few pages of this forum and couldn't find a similar post although I'm sure others have probably seen this issue. How many problems CAN an outboard have? Unfortunately, the search function on the forum doesn't let you choose a specific engine forum, so please bear with me if this has been asked and answered. This problem started at the end of the last season and we thought the carb replacement mentioned below would fix it, but it didn't - so now we're completely frustrated and ready to cause some harm to the stupid thing.

We have a 2008 (might be 2009) Tohatsu MFS20 four stroke outboard. It started developing issues symptomatic of a gummed up carburetor - without touching the throttle it revs up and down; when it's on the downward rev you have to increase throttle to keep it from stalling; stalls fairly quickly if you don't touch the throttle.

We cleaned the carb - that didn't solve the issue. We verified a good fuel stream from the fuel pump when we disconnected it from the carb. We then REPLACED the carb, the external gas tank, the hose from the gas tank to the engine and the gas. We blew out all of the internal hoses leading from the fuel connector to the fuel pump to the carb. We replaced the spark plugs.

Same problem.

Any ideas of where to look next? We don't have a service manual and aren't overly familiar with outboards (give us a diesel inboard and we'll pull it apart and put it back together) so detailed suggestions (vs. you should look at such and such) would be GREATLY appreciated.

Thanks!

Chris
 
Get ye to a dealer. Use your 3-year warranty. Don't do any more DIY work without the Factory service manual. When you say "We cleaned the carb - that didn't solve the issue.", did that involve a complete disassembly (including jets and emulsion tube "nozzle", followed by a 4-hour soak in real carb dip, followed by a blow-out with generic carb spray)? If not, you did not do a thorough enough job at carb cleaning.
 
labatt said:
Hi All -

I looked back through a few pages of this forum and couldn't find a similar post although I'm sure others have probably seen this issue. How many problems CAN an outboard have? Unfortunately, the search function on the forum doesn't let you choose a specific engine forum, so please bear with me if this has been asked and answered. This problem started at the end of the last season and we thought the carb replacement mentioned below would fix it, but it didn't - so now we're completely frustrated and ready to cause some harm to the stupid thing.

We have a 2008 (might be 2009) Tohatsu MFS20 four stroke outboard. It started developing issues symptomatic of a gummed up carburetor - without touching the throttle it revs up and down; when it's on the downward rev you have to increase throttle to keep it from stalling; stalls fairly quickly if you don't touch the throttle.

We cleaned the carb - that didn't solve the issue. We verified a good fuel stream from the fuel pump when we disconnected it from the carb. We then REPLACED the carb, the external gas tank, the hose from the gas tank to the engine and the gas. We blew out all of the internal hoses leading from the fuel connector to the fuel pump to the carb. We replaced the spark plugs.

Same problem.

Any ideas of where to look next? We don't have a service manual and aren't overly familiar with outboards (give us a diesel inboard and we'll pull it apart and put it back together) so detailed suggestions (vs. you should look at such and such) would be GREATLY appreciated.

Thanks!

Chris
Click to expand...

In the nicest way possible...

You do not know what you are doing so stop and take it into someone who does. Desire to repair your engine does not equal the ability to do so.
 
I do appreciate the comments. We've found, however, that one of the best ways to learn is to do stuff and to get advice from people as to what to look for. We can now strip apart and rebuild most components of a Yanmar diesel and learned this by working with others.

We used to cruise and will be cruising again, so we won't always have access to highly trained resources when we're anchored off a deserted beach in the middle of nowhere - trying to fix our outboard so we don't have to swim in. We do keep a second 6HP Mercury onboard for a spare, but it doesn't get our 11' RIB onto plane so we want to get this 20HP working. In this spirit, we want to learn. We'll pick up the maintenance manual, and we can bring the engine in for warranty repair (without learning anything) but in the meantime if anyone has any suggestions on where to look for more issues I'd appreciate it.

BTW - pvanv - we did pretty much use that procedure to clean the carb, including full disassembly, soaking overnight, compressed air, etc. When we continued to have the issue we had access to a new carb so we replaced the existing one. I'm assuming our issue is probably an adjustment on the carb, throttle, ignition or something else but any suggestions would be appreciated.
 
Looks like it may be an electrical issue. There's a set of wires going from the rear of the throttle linkage area that cause the engine rpms to fluctuate when they are touched. When we get them in just the right position the rpm's are stable. We're going to look at this a little closer.
 
Get the manual, take a local course in outboard repair and you will be fully qualified to...Change a spark plug:) Seriously, I understand your desire to know how to repair your engine. It's not overly complicated, but virtually everything is diagnosed through process of elimination rather than a mechanical magic bullet. Generally, most problems are fuel related, but it could be anything at this point.
 
labatt said:
Looks like it may be an electrical issue. There's a set of wires going from the rear of the throttle linkage area that cause the engine rpms to fluctuate when they are touched. When we get them in just the right position the rpm's are stable. We're going to look at this a little closer.
Click to expand...

You may have problems related to the bullet connectors on the CD. Like Elvin said, grab the Factory service manual (forget the aftermarket ones) and diagnose with the aid of the manual.
 
Back
Top