Mariner 91 150hp idle/shift problem

[larrydm]

My 91 Mariner 150hp mariner (ser# ODO320093) suddenly starting idleing high and throughout the day the idle increased.. This made it difficult to put the engine back in neutral. When I kill the motor it goes easily into neutral. Once I have it in gear and increase rpms, it runs great all the way up to wide open throttle. I searched the various forums and found the suggestions on kinked shifter cable but it appears to be fine. The idle adjustment is sitting against the stop but when I start it up it immediately revs so high I'm scared to let it run to trouble shoot. I read an old thread about a very similar problem with a 97 Mariner 150hp where the owner reset the idle setting but mine was fine where it's set so I can;t help but think that if I try readjusting it, I would just be working around the real problem. Can anyone point me in the right direction to start troubleshooting?

Thank you.

 

[GA_Boater]

You shouldn't start adjusting anything before doing some troubleshooting. I take it that it was working OK and this just started to happen?

You can remove the throttle cable at the motor end and make sure the carb butterflies are closed. Start the motor on muffs or in a barrel and see if the speed increases with the throttle cable disconnected.

One more thing - If you have a warm-up lever on the control, make sure it is staying fully down as the throttle lever is moved fore and aft.

Oh - Check to make sure the carbs are tight on the motor. An air leak between the carb body and mounting flange can cause a condition similar to this.

 

[Chris1956]

My '93 Merc V6 has a thermostatically controlled air valve. When the engine is cold, more air is allowed into the motor to raise the idle. It shuts off when the motor warms up. You might have the same device. Look for a valve on the starboard head, with an open port, and a hose that runs to the carbs. Maybe the hose broke off the valve, or the valve is bad.

 

[larrydm]

Hey guys, thanks for the tips. I really appreciate the advice. I checked for the air valve and there is a electric valve on the starboard side that has a hose to carb#1 and a second hose to the back of the block. There is a black push button top. Is this what I am looking for? Is this what my manual refers to as the enrichment valve? I check every hose I could find and all look good. I checked that the carb butterflys stay shut through the entire throttle range and they do. The carbs are securely bolted on. Nothing loose. I disconnected the throttle cable and I started the motor. It immediately revs to over 2000 rpm. Both the shift cable and throttle cable work smoothly from the control. Any more advice on what to check next? I see the Selco manual refers to an idle stabilizer. Could this have anything to do with my problem?

 

[Dukedog]

first get yaself an OEM manual then put tha other one in tha "outhouse".....

Hey guys, thanks for the tips. I really appreciate the advice. I checked for the air valve and there is a electric valve on the starboard side that has a hose to carb#1 and a second hose to the back of the block. /QUOTE]

this is wrong.. top hose on tha enrichner should go to tha "bottom of tha top carb".. bottom hose on tha enrichner should go to tha "top of tha middle carb"....

tha "thermal valve" is right below tha middle spark plug (cyl. number 3) starboard side.... there should be ONE small hose from tha outside bib on tha valve going up to bottom of a "T" fitting on tha side of tha bottom carb.....

check trigger linkage and movement

 

[Faztbullet]

My '93 Merc V6 has a thermostatically controlled air valve. When the engine is cold, more air is allowed into the motor to raise the idle. It shuts off when the motor warms up.

No... when cold its closed and shuts air off to carb idle circuit making fuel mixture richer, as engine warms up it slowly opens and when engine get to 100degrees it is fully open

 

[larrydm]

I can find a Clymer manual. Are they any good? Any recommendations on a website that sells oem manuals. I can find manuals for every year and hp but mine.

 

[larrydm]

Hey guys, I finally was able to double check things today. The enrichment valve is connected as advised and I found the thermal valve which is where you described. The hose is hooked up and in perfect condition. Will either one of these cause my idle problem if bad and if so, is there an easy way to test them to see if they are bad? I checked the trigger linkage and it is connected and appears to move freely. I have been searching for an OEM manual for my motor but the only ones I have found are downloads. Do you have any experience with these and are they any good? Any more advice on what to check next?

One question from you that I failed to answer is that the boat was running fine when I put it on the water and for the few hours I ran it. When I slowed to an idle when pulling into the marina, it wouldn't idle as low as normal. The next day it got progressively worse. The idle kept getting faster.Once I would out it gear it ran fine all the way to wide open throttle..

Thank you for your help