'69 merc 1250 outboard troubles

[madMANskoot]

i just recently bought an old larson runabout with a merc 1250. it runs pretty well for what it is except for a few issues. the first one is the stalling out when throttling down which i would assume is carb problems. i looked into rebuild kits for these carbs but they are close to non-existant for full kits. i am very new to boats so i am still hesitant to pull the carbs off because im told the timing is very difficult to cue in once put back together. i tried running seafoam in the fuel along with a fuel stabilizer in case there was any water in the fuel, i replaced the spark plugs, did a gear box oild change, new primer bulb, some new fuel lines, and fuel filters; but stalling is still an issue.
im open to any pointers for other things to check before i tackle the intimidating task of carb removal and cleaning. i still have yet to replace the impeller propeller but i wouldnt imagine that would cause stalling. i do plan to replace it this week either way though.
i am also wondering what other things to look for in general with this motor, i would really hate to damage it because of something that could have been avoided. any help would be greatly appreciated.

 

[steelespike]

Re: '69 merc 1250 outboard troubles

Idle mixture adjustment from generic service manual, you should find a factory manual.
With the motor warm idling in gear confirm idle speed (probably about 700)slowly turn out (counter clockwise)idle mix screw till motor begins to load up then turn in screw until motor speeds up continue until motor stumbles Ideal setting is between these positions.
Clockwise leans mixture.slightly rich idle setting is more desirable than too lean.

 

[madMANskoot]

Re: '69 merc 1250 outboard troubles

thank you for the reply. i greatly appreciate it. is there a method to getting all three carbs in sync or does it matter if they are all at the same adjustments? im sorry if it sounds like a dumb question, i just dont want to mess anything up. i would assume i just count the turns on one and put the other two to the same number of turns?

 

[steelespike]

Re: '69 merc 1250 outboard troubles

There is nothing mentioned about syncing the carbs but at least need to be eyeballed to be opening together.
I think mixture for each carb should be done to their best setting not necessarily the same number of turns.
Don't mess with the Thunder bolt ignition without a factory service manual. There should be info about syncing the carbs
and getting it timed right.

 

[madMANskoot]

Re: '69 merc 1250 outboard troubles

i got the carbs all adjusted and it is running a lot better. thank you so much for your help. i have unfortunately discovered that cylinder number six is no longer firing and the plug wire seems fine. would that be an indicator that the distributor is messed up, or could it be a timing issue?

 

[steelespike]

Re: '69 merc 1250 outboard troubles

Could be as simple as carbon deposits inside the cap shorting the path to the plug could be going to ground or even to neighboring
cap contact. Look for a carbon track inside the cap or on the rotor. indicating evidence of a short.
Also a chance of a bad plug you could swap plugs see if the problem follows. I Don't know know about parts but cap and rotor could be both hard to find and expensive. Would be a good idea to confirm the plug wire. Again be careful trouble shooting the ignition
as you could disable it.

 

[madMANskoot]

Re: '69 merc 1250 outboard troubles

i went through and didnt find anything visibly wrong with the cap and plug wires, although i did find that the guy that had the boat before me had taped the wires for the engine harness together and there were cracks in the wire insulation on a few wires. i replaced the cracked wires with new ones and the spark returned to cylinder 6 again. the motor still idles rough though, so im kind of at a loss at this point. i compression tested the motor and there was about a 13 psi difference in cylinder 1, but from what i can find in the service manuals and other forums, they can supposedly have a difference of up to 20 psi. is there other things that could potentially cause the rough idle?

 

[michaud500]

Re: '69 merc 1250 outboard troubles

Check for air leaks in the fuel lines. First look for leaking gas at cracks in the line or at clamp connected fittings. I had great luck replacing the primer bulb with a Mercury part. Dont go cheep!!! I had a after market one that was as bad as the 10 year old one!!!!

 

[madMANskoot]

Re: '69 merc 1250 outboard troubles

Good call. i'm going to have to change all that out. i found cracks in a few of the lines in the engine. i did put a walmart primer bulb on it but i will make sure to change that out to a better one. i will reply with the results as soon as i finish with the changes. thanks for the advice, you guys are awesome.

 

[madMANskoot]

Re: '69 merc 1250 outboard troubles

i put a mercury primer bulb on, mercury specific fuel filters, and replaced the dry/cracked fuel lines. the guy that had the boat before me had put a 3/8 fuel line on the motor just after the fuel line hook-up from the tank,and the line is actually suppose to be a 1/4 inch line. the motor ran great and idled like it was new, so i thank you for that great advice. after running for about an hour, it started losing power and was spraying a lot of water out of the back of the motor just below the upper housing right at the top of the shaft. i have no clue where to even begin looking or if that is a bad sign. i was worried because the small pee stream prior to this looked weak but i assumed it was fine because it was running so well. any ideas? i appologize for being such a noob.

 

[michaud500]

Re: '69 merc 1250 outboard troubles

Try rebuilding the pump! do a complete rebuild with housing and all. Its a pain to remove the lower housing so be patient


It could also be the water hose in the engine compartment

 

[madMANskoot]

Re: '69 merc 1250 outboard troubles

thanks for the reply, i will give it a try. this thing was pretty neglected so i was almost tempted to do a complete engine rebuild this winter but finding parts is pretty difficult. i almost lost hope until i saw what this motor was selling for at a few places. i will post results when i finish. thank you for your help, this boat thing is pretty new to me.