1979 Marktwain 165 hp I/O. Dying when hot

[moffitt77]

I have had the boat out twice this week and both times after it gets warmed up it dies when shifted into nuetral. Then it will not start without the throttle pushed up nor go into gear either direction without dying. It was winterized and had the lower unit rebuilt last fall. Any ideas??

thanks

 

[mkast]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

Choke? What RPM does the engine idle at in gear with the engine at operating temperature?

 

[Don S]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

Sounds like a classic case of needing a new lower shift cable. The old one is corroded and stiff to operate and holding the shift interrupt switch engages causing the engine to die when shifting into or out of gear.

 

[moffitt77]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

I got new shifter cables last year, and I am not a boat mechanic so I had it done at the boat shop? But, they might have only replaced the one. Why would the temp of the motor effect that?

thanks

 

[moffitt77]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

No choke. the 2 times that i had it out this year it would idle at very low rpms when it was cold, then once it warmed up it didnt like low rpms at all. I can't give you numbers. Here is what happened after I had the lower unit replaced last fall(not taken out after that). I took it out for the first time last friday, bad trim line leak that it has had for a year. It ran great, started up after sitting and relaxing, then I went to pull into the marina. When I cut the throttle back to dock, it died. Didn't want to start. Motor temp at 140'ish. Throttle cable came off, but wouldnt run at idle speed. I got the throttle cable re-connected and then had the trim line leak fixed. Took it out yesterday and then the same thing happened. Once the motor got warm it wouldnt start or run at idle speed. Each time I would start it without the prop engaged at high rpms it would run, but when I'd cut it back to engage the prop and try to go it would die. I think it has to be temp related not a cable issue, but I am far from a boat mechanic. Does it have a coil?

 

[Don S]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

If you had a mechanic do the job, take it back to them and explain the problem. Probably nothing more than a minor adjustment of the cable. At least they have some idea what is going on and what the problem could be. We are all starting from scratch.

 

[moffitt77]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

Thanks, will do. But I am still curious as to why the temp of the motor would effect that cable. I have worked on car motors quite a bit, but am new to boating.

Mike

 

[ziggy]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

the lower shift cable isn't to hard to check. disconnect it from the shift plate inside the boat. then operate it. don't change anything while the cables off the shift plate (like spin the mounting barrel) or you'll have to go through adj. procedures.. have someone outside the boat spin the prop ccw (fwd) and cw (rev). the cable should move very freely operated with two fingers. if it don't i would think it would be suspect.

whens the last time yer rig had a tune up. it's a good idea to do one ea. spring. ya know, cap, rotor, points, plugs, fuel filters, set dwell, then timing. set idle speed if necessary. the fact that your throttle cable fell off isn't inspiring and would lead me to think your engine has a lack of pm done to it. lack of pm can lead to failures of many kinds. do you have the proper mercruiser service manual for your rig? they generally have some trouble shooting guides in them to help lead you to various problems...

by the way. what is your rig.. a 4cyl. 165 or a 6 cyl. 165... i believe in that year it could have been one or the other. might help for possible diagnosis....

if yer taking it to the shop for repair.. well, let them find the problem as they can feel it, we can't.

imho, temp don't affect the shift cable. to understand how the shift works look at here.

 

[moffitt77]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

Ziggy, thanks for the info. It is a 165 hp 6 cyl. it was supposed to be tuned up middle of last summer when I got it but I am not confident that they did very much. The throttle was worked on last fall and not taken out til this week.

 

[ziggy]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

it was supposed to be tuned up middle of last summer

that's too long ago. it should be tuned up at summerization... a for instance would be my boat wouldn't start the first turn of the key this spring. a little emery cloth on the points and it fired up (points were replaced prior to 1st launch, emery cloth was only to see if i had issues i was unaware of that would need maj. repair, thus not needing points till later). the points were glazed over with tarnish from just sitting. i also clean as many connections as i can take apart prior to the first spring splash. you'd be surprised as to how much tarnish there is from one season of boating. batt. cables are easy to see the difference on. both ends. + and - side.

when I got it but I am not confident that they did very much. The throttle was worked on last fall

well, at least they loosened your throttle cable i guess.... perhaps someone else should be working on it. someone you can trust to do something... i've had similar experiences from various places too. in the end. especially for my boat. i've taken to fixing it myself along with the help from my friends here at iboats and my trusty mercrusier service manual. then i at least know what was done and what wasn't.
here's a place you can get much info on your engine and your drive.. these are the facts and the proper ways to service your rig... has the trouble shooting guides in them too..

 

[Doernuth]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

If you are taking to the shop have them check the choke. The choke on the IL 6 with the Rochester Carb (which yours had when it was new) is a thermal coil spring. If it is not adjusted properly or if it is no longer working your engine could have the choke closed when it is hot. This is not a good thing for a hot engine.

Pull the flash suppressor with the engine hatch open. Start the engine and watch the choke plate. As the engine heats up the plate should open. If it doesn't and you have to move the throttle to open then you need the choke worked on or replaced. There is a piece of metal from the choke to the manifold that transmits temp make sure it is touching the manifold.

 

[Fordiesel69]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

Has anyone thought of a idle mixture & speed setting problem? When cold the choke is closed or half closed bumping the idle up very slightly, if choke opens when warm, the idle is now going off the speed screw. You will need to make a carb adjustment OUT OF GEAR first. Get it about 700-800, then when you get it idling smooth put in gear IN THE WATER and make the final minor speed adjustment.

Two mixture screws you will screw in until they stop then back out 1-1/4 turns. Adjust idle to 700-800, then if engine idles rough but maintains speed turn each screw in 1/4 turn until the engine gets smooth. Then go back and adjust the speed scew.

I just went thru all this with my glastron 165HP L6 and it idles perfect and smooth all the time. I give it 1-2 min warmup and it idles right down smooth, and contiinues to when warm.

Service manual #2 will detail the carb adjustment procedure better than I just described if you are not sure how to do it.

 

[moffitt77]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

Wow, tons of great advice. My mechanic checked it out Friday morning and found nothing wrong with it. I have changed the plugs, cleaned the carbs and breather, adjusted the idle up, but not in the water. Took it out yesterday same thing happened. Ran great cruising short periods and then fairly long ones. Never had had any trouble starting or getting into gear. Then Cruised for about 20 minutes, pulled into the dock and died. Then would start, but die when shifting into gear. We watched the choke and it wasn't choking out he didnt think, but if it was already closed he wouldnt have noticed, but that is what it seemed like. Already thought about the coils but we ran 3k rpms+ 5 minutes, then 10 minutes, then 20 minutes, and it had no trouble starting or shifting into gear. It was on the last longer run that it just wouldnt go back into gear. I could start it in nuetral and rev it up and down, but not in gear. Doesnt that have to be connected to the kill switch?

 

[haulnazz15]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

It does sound like a shift-interrupter issue, but again it may be related to the shift cable. It could also be one of the contacts sticking closed causing it to hold the interruptor switch too long.

 

[moffitt77]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

Mechanic ordered a new shift switch this morning. He also doesn't think it is the coil becuse it would just die and not start when it got hot.

 

[moffitt77]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

Latest update. Replaced the shift switch and adjusted the idle speed and carbs while in the water. The boat ran great at the dock in nuetral for 20 minutes, then would still die when engaging the prop. Then noticed the amp guage reading 0 for the first time, it hadn't been before. Took off the battery cable and sure enough the alternator/generator had crapped. Is it possible that it, in the process of going bad, was the problem all along? I have to get it rebuilt since we couldn't find a new one available.

 

[haulnazz15]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

I'm not sure if they are related. While the voltage from the alternator is needed to keep the engine running, it shouldn't die merely by putting it in gear. Normally if the engine dies from an alternator failure, it has already drained the battery and won't be easy to restart without a jump start or another battery.

 

[Don S]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

Hate to say this, but I think your biggest problem is your mechanic.
The fact that he replaced the shift interrupt switch tells me he has no clue how the system works. He is just throwing parts at it because he has no clue what the problem is.
With the boat in the water, it's very easy to watch the shift plate while someone shifts the boat and see if the shift interrupt switch is being held engaged or not.

I got new shifter cables last year, and I am not a boat mechanic so I had it done at the boat shop?

1. Did they use an OEM cable, or aftermarket?
2. Was the old style cable used, or was the new style installed. If the new style, was the threads tapped out properly from the bellows side of the bellhousing?
3. Was the shift slide on the drive end of the cable able to spin easily and not catch? or the set screw too tight.

 

[schalmat]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

Hey Moffitt,
I noticed on my 73 165 6cyl, when i had the first start this year it ran well,once it warmed up the idle got rough and was wanting to die.This led to pulling the plugs which were a little damp..soooo ,i get it statrted back up and look in the carb,low and behold the gasket between the venturi booster and the carb body was leeking,causing it to flood .you could see it still dropping fuel even when the motor died.this caused a really hard start.as long as i throttled up it was ok because it would burn it and run okay,but at idle when hot.no dice.so had to rebuild carb,..actually replaced the gasket and its fine now.it' was the worst once heated up because parts can expand a little which makes it worse.so when it dies look down the carb throat and see if its fairly wet.could be dropping fuel from the bowl through that gasket.hope ya get her fixed.
Matt

 

[moffitt77]

Re: 1979 Marktwain 165 hp I/O. Dying when hot

I have used my secondary onboard battery twice to get it started after running for 30 minutes or so, but then disconnected the jumpers and it was fine. This last time, however, the battery was getting weak from starting and restarting.