just another merc. losing power

[Bill Adkins]

I have an 1971 1350 tower that starts, idles, pumps water out the telltale like it was a happy camper. Put it in the lake and for about 30-40 minutes it does everything really well. The boat just flies as it were, it should as its a bit small for that engine but after the described running time it will stall if you bring it back to idle. It will restart without too much difficulty but it wont take throttle after the event starts, it will just die with throttle. After it cools for a while it will start the cycle again.The fuel primer bulb is firm and seems to be ok. Could it be carbon on a reed valve? I had it dyno'ed and it is at spec for being at 7000 feet altitude. Perhaps there is someone on the board that remembers some old pain in the backside, anyway I hope so.
Bill Adkins

 

[BR]

Re: just another merc. losing power

Sounds like it could be a carb mixture adjustment problem.

You won't get carbon on a reed valve w/o a catastrophic event like a holed piston. Reeds are in the crankcase on 2 strokes, not in the combustion chamber so they normally do not see any byproducts of combustion. If it were a reed problem you'd likely experience the problem right off the bat, not after 30-40 minutes running as you say. My guess is that you may be running a little too rich and that when you idle back down it's too much fuel. A waiting period may be allowing that fuel to evaporate? Try leaning it up a little and check to be sure you still have a decent hole shot. If you don't, you went too far lean. Also, when's the last time the carbs were cleaned?

Good Luck!

 

[Bill Adkins]

Re: just another merc. losing power

Thanks for the response BR, to be honest I havn't had the carbs worked with other than the local repair shop tried a couple of times to resolve the issue to no avail. The main jets are sized for sea level which is .078,the recommended size for the altitude is .074. .004 doesn't seem a large amount, at least I wasn't feeling it was a bunch. I ran a dyno for 11 yrs. some years ago but never with a 2 stroke and never such a small displacement engine. Do you think that amount of difference could be noteworthy? I think the jets are still available or are there some other possible methods? I suppose the floats could be set high also. I have had ignition control modules act like that in past years with early transistorized ignitions. Thanks again for any and all ideas.
The wife is seeing a ETEC in the future if I don't resolve this darned thing.
Bill Adkins

 

[BR]

Re: just another merc. losing power

My Merc manual says the following for the 1350 carb jet sizes:
.078" is good up to elevation 4000'
.076" good from 4000-7000'
.074" good from 7000-10000'

Doesn't seem like a significant difference but they wouldn't put it in a service manual if it was inconsequential, right? If you're at elevation 7000' you're right at the threshold of the two smaller jets. Maybe look around for the .074" jets and experiment. They are simple enough to swap out, especially if you're into the carbs for a clean & rebuild.

 

[Bill Adkins]

Re: just another merc. losing power

So who knows where one might find .074 main jets that fit a 1971 1350? It is equipped with three single throat carbs. It has .078 mains fit currently. Theory has lowering the float level another method of leaning the fuel delivery. Any ideas on that line? I have searched the web for early vintage parts supply and havn't been successful.
Bill Adkins

 

[BR]

Re: just another merc. losing power

Bill,

I just looked up the jets on Crowley Marine's website which has a good online parts reference section. The mercury part # for the .074 jets is 3794. They are listed as still available from your Mercury dealer and cost $4.17 ea.

Good Luck.

 

[Bill Adkins]

Re: just another merc. losing power

BR, thanks for the info on the parts availability. I have ordered the jets, carb kits, both fuel pump diaphrams and the check valves for the pumps. I figured I'd just hit the whole thing and see what happens. I'll post the results when it's done.
Bill Adkins

 

[gcleehusker]

Re: just another merc. losing power

If you're still looking at these replies, I've got another idea. You see, mine did the same thing. While running, the motor was able to stay cooler and not act up, but when you idled or stopped, heat built up inside the distributor and caused the trigger to act up. Mine was severe and needed to be run with the cover off--some sputtering when throttling-up, but smooth after that until I idled or stopped. The engine begins to act like it's being starved for fuel, and throttle up only produces a bog. Bet she would run with the cover off, but only a bit better. My guess is that you also have some trouble starting it and need to crank several more times than most? Anyway, heat build up could easily be the cause here and could be the sign of a failing trigger (distributor body in this case). If so, also look to replace the top rotor shaft bearing. Careful, the Merc part is 47 bucks, but take the number off the bearing and get it at a local BDI bearing distributor for 5-11 dollars.

 

[Bill Adkins]

Re: just another merc. losing power

GC, thanks for the response. That was what I was hoping for. I have ordered some fuel supply pieces but they havn't shown up yet. I ran a dyno during the seventies with MB, thats when they came out with cd ignitions and they acted exactly the same. The usual cause was in the control module but when the ignition failed the symptom was exactly the same. I probably fixed over a hundred of them for that issue. I looked at the distributer this weekend and it is a cd unit with a chopped and light reciever module the chopper travels through. The wiring is also frayed in the distrbutor. Does anyone have or know of a distributer body that can be had. Or does anyone have an earlier distributer that still used ignition points and a standard coil set up. I am looking far a functional replacement for the distributer body with pickup for a capacitive discharge system or a standard ignition replacement. I wasn;t aware that this motor used a cd system or I would have looked into it earlier.
Thanks again. The motor is a 1971 1350 serial 2840310.
Bill Adkins

 

[gcleehusker]

Re: just another merc. losing power

Bill,

Yep. What you are looking for is the distributor body that has the white, black and brown wire coming out of it.
Look at this site or at boat fix dot com for (no spaces) for part number 134-3736 Mercury Trigger Rapair CDI: $206.74...or just google the part number.
That part comes with the Trigger (in this case, our distributor body with the sensor) and I THINK it comes with new upper and lower bearings, the new steel disk and I don't know what else... In any case, there are some .pdf files available for the exact install instructions and those can be had from CDI. If you run across needing a top bearing, don't pay 47 bucks for it, just take the number from it and buy from your local bearing distributor for about eleven bucks, or five for the cheaper one since this does not carry a load. You will also need the flywheel removal tool for about 30 bucks off ebay, or just have your local marine shop remove the flywheel for you - free or a couple of bucks. Last thing you'll need is the link and sync instructions for our motors from this forum and a timing light to make it happen. Good luck. Bill, do double check the part number, as mine does not have points and the trigger or distributor housing (same thing) may be slightly different? Greg