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Brain Teaser !984 75 hp merc 2 stroke 4 cyl super hard to start

joediv

Member
Once started it runs like a champ,idles smoothly, accelerates fine and once started then shut off it will restart immediately but it seems the longer I wait the harder the restart ??!! New plugs,gas filter, bulbs hard, ect. I give it 1/4-1/2 idle and I choke it and choke it for 5-10 mins and nothing then in frustration I give it a shot of starter fluid and BAM she starts right up and runs smoothly. Obviously there's an issue with it getting gas to start up I think! I did have a problem with another 15 hp motor and it ended up that the butterfly was closed so not enough vacuum to draw in the gas but I don't think that's the problem. It was suggested that I install a 12v fuel pump but I wouldn't know which one or where to put it in the line plus I think that the vacuum to the fuel pump must be working fine or it wouldn't run so good after starting. I'm puzzled !? Any geniuses out there? LOL
 
What do you mean by " choke it for 5 to 10 minutes " ?-----Are you giving it some throttle for cold start , yes , no or do not know how to ?----Are you pushing the key in while cranking it over , yes or no ?
 
What do you mean by " choke it for 5 to 10 minutes " ?-----Are you giving it some throttle for cold start , yes , no or do not know how to ?----Are you pushing the key in while cranking it over , yes or no ?

yes,throttle ( 1/4-1/2) and yes pushing in the key and I hear the elec choke working
 
I just gave it a heavy mixture of Seafoam ( 1 can in 2 gals) and ran it for about 15 mins, let it sit overnight and will start it today to see if that helps !!
 
If that's those carbs that bolt on from the front (long bolts go through them) they have an enrichener circuit that gets plugged up (tiny passages).

The way to cure THAT problem is--after the motor is warmed up and at high idle--hit the 'choke' and hold it until the motor almost stalls, then let it clear up. Do this again a few times to clear out the circuit.

Jeff
 
so I tried that, used the elec choke till it almost quit, did it 4 times then I did it again using the manual choke. I then let the motor sit for about 1/2 hr and NO LUCK, once again it wouldn't start so I decided to remove the carbs. took them apart, they looked clean as a whistle but just in case I blew out all passages with compressed air and also poked into all openings with some fine wire I had around. Reassembled everything,pumped the bulb and she started right up with no choke. Solved you'd think BUT let the motor rest for another 1/2 hour and then squeezed bulb and tried to start at idle, at 1/4 throttle and with or without choking both elec and manual with the same results, it wouldn't start, grrrrrrrrr, so once again a quick shot of starter fluid and bang, she starts right up. My brother who is very knowledgeable about motors seems to think that the needle valve is sticking when it seats, not sure if that makes any sense as I would expect that squeezing the bulb would push the gas through a stuck needle. When I disassembled the carbs the needle fell right out so not so sure about the sticking part. I guess I'll replace the needles and seats in both carbs but I just think it's gotta be something else????? What's your thoughts??? Also, thanks so much for your input, I don't know about you but I love solving a unique problem, this one's got me puzzled, help!!!
 
I've tried every method to start, idle,1/4 to 1/2 throttle , elec choke, manual choke ,no choke. I think the key here is that once I've started it ( with starter fluid) and then shut it off , it'll start right up BUT if I wait 15-30 mins then it's back to not starting. I alway check the bulb for hardness.
 
I would now take your battery in to be load tested.-----Take starter apart for ohm test , possibly new brushes.----Inspect starter cables as well.------If these motors do not crank properly they will not start.----Have your choke / enricher system checked out too.
 
by " enricher" system do you mean the elec choke and if it is closing like it should ? Battery is fairly new but I do notice that the starter kicks out sometimes after a few cranks!!
 
Yes that motor has choke plates.---Are they closing properly ?-----Up to you to do some trouble shooting ( post #10 for one) to determine what is wrong here.----I believe it is easy to figure out what is wrong here.
 
I decided to check out the fuel pump more closely. It's the one with the 2 nickle sized 1 way valves. I removed them and found that they were almost impossible to blow through, I'm thinking that they may be sticking ( tarnish)when you try to start the motor but maybe start working when the rpm's are higher( after starting) ! Thoughts?
 
The fuel pump has nothing to do with starting if carburetors are full.------You should be able to blow through those check valves in one direction.----So maybe replace them, test the new ones the same way to confirm that old ones are possibly bad.
 
Went to merc dealer, they looked at fuel pump valves/gasket and said all was fine.so puzzled. When I blocked the top carb the motor wanted to quit immediately ( much gas could be seen in the carb and on my hand) but when I blocked the bottom carb it took quite a while for it to bog down ( but once again much gas could be seen in the carb and on my hand) I did notice the top carb idle screw is at 2 turns out but the bottom is only 1 1/8 out.My brother insist that the carbs need rebuilding but I did take them apart, cleaned them extensively with air and carb cleaner and inspected them and they look very clean,needle moves easily, all holes seem clear ect. Now once again after running, then shut off, it starts right up without any throttle or choke. I waited about 15 mins,tried restart but this time I had to give it a little more than 1/2 throttle and choke and she started up after several cranks. I'm sure after waiting 1/2 hr I'll try again but most likely will have to use some start fluid. The ONLY thing I haven't done is a compression check, I do suspect the 3rd cylinder may be weak. Thoughts? I'll do the comp test and fill you in!
 
sorry to sound stupid but I'm not sure!!! I see the butterfly that opens when I give it throttle but when I activate the choke( either elec or manually) I don't see any movement ! I wonder if there is another choke plate behind that butterfly but I don't see anything in the diagrams !
 
Went to merc dealer, they looked at fuel pump valves/gasket and said all was fine.so puzzled. When I blocked the top carb the motor wanted to quit immediately ( much gas could be seen in the carb and on my hand) but when I blocked the bottom carb it took quite a while for it to bog down ( but once again much gas could be seen in the carb and on my hand) I did notice the top carb idle screw is at 2 turns out but the bottom is only 1 1/8 out.My brother insist that the carbs need rebuilding but I did take them apart, cleaned them extensively with air and carb cleaner and inspected them and they look very clean,needle moves easily, all holes seem clear ect. Now once again after running, then shut off, it starts right up without any throttle or choke. I waited about 15 mins,tried restart but this time I had to give it a little more than 1/2 throttle and choke and she started up after several cranks. I'm sure after waiting 1/2 hr I'll try again but most likely will have to use some start fluid. The ONLY thing I haven't done is a compression check, I do suspect the 3rd cylinder may be weak. Thoughts? I'll do the comp test and fill you in!
 
So I go out about 40 mins later and she starts right up with no throttle or choke!!!!!! WTF is going on here? The only difference is that I have the plate that bolts on over the 2 carbs off !! I wonder if that plate is somehow cocking those carbs so they're not seated but would it still run so good on the water if that was so? Maybe I should just leave that big air intake plate off???? Replies??!!!
 
Those carbs use an enrichener circuit for cold starting. Work the choke and you should see the little levers on the left side of the carb rotate. If they don't move, the solenoid is not operating properly (electrically, or it's burnt out).

IF there's also a manual choke as well, pull the knob, watch those levers rotate, and start it that way next time.

Jeff
 
I have used the manual choke to no avail. I did notice something today!! After waiting about 45 mins I went out and she started right up, at idle with no choke!!!! The only difference is that I had removed the plate that goes over both carbs for the air intake manifold thing. When I've put this back on it seemed as thought it was hard to start one of the 2 bolts that hold it on so consequently I think it put pressure on those long bolts/carbs and may have been causing a vacuum leak where they meet the engine ( maybe) I'm gonna investigate further tomorrow by reassembling all and the spraying some starter fluid around the base of the carbs to see if the engine races!but I really am wondering about that choke as I see the levers rotate but do not see the butterfly close or any other choke type plate moving inside! I have looked and looked at the diagram of the carbs but only see that one butterfly plate. Do you have a different diagram? I'm almost positive we are talking about the same carbs.
 
Hi Jeff, I'm ready to give up ! I finally realized those enricher valves were and removed them along with both carbs, I blew out everything, used a fine wire to see if there were any blockages and there were non, I rechecked both carbs to make sure everything was in working order, reassembled everything , charged battery to be sure and it started right up with no throttle and just a tweak of the elec choke!!! However this is the same results as before and if it sits for a while or overnight it will then again not start without the starter fluid !! So what other possible problems do you think could be present. 1) I'm using 89 oct but the dealer did say to use 93-not sure that is an issue as it did start this time without the starter fluid. 2) there are no reed valves so that's not it 3) bad cylinder- could be but why did it start and also why does it start right up if I shut it's off and immediately restarted ? Any other ideas or thoughts, also thanks for your time and input. I'm stubborn but this things got me beat!!!
 
I'm ready to give up ! I finally realized those enricher valves were and removed them along with both carbs, I blew out everything, used a fine wire to see if there were any blockages and there were non, I rechecked both carbs to make sure everything was in working order, reassembled everything , charged battery to be sure and it started right up with no throttle and just a tweak of the elec choke!!! However this is the same results as before and if it sits for a while or overnight it will then again not start without the starter fluid !! So what other possible problems do you think could be present. 1) I'm using 89 oct but the dealer did say to use 93-not sure that is an issue as it did start this time without the starter fluid. 2) there are no reed valves so that's not it 3) bad cylinder- could be but why did it start and also why does it start right up if I shut it's off and immediately restarted ? Any other ideas or thoughts, also thanks for your time and input. I'm stubborn but this things got me beat!!!
 
apparently the previous owner replaced the starter solenoid and when doing so disconnected a very small hose (http://www.marineengine.com/parts/m...-up-usa/cylinder-block-and-crankcase-assembly) item 22 on this diagram, I'm wondering if that has anything to do with priming the motor ?? It comes from the lower cowel where the gas connects from the tank and seems to eventually go in right next to each carb so would that have an effect on start up ? I'll find out tomorrow !!!!
 
apparently the previous owner replaced the starter solenoid and when doing so disconnected a very small hose (http://www.marineengine.com/parts/me...kcase-assembly) item 22 on this diagram, I'm wondering if that has anything to do with priming the motor ?? It comes from the lower cowel where the gas connects from the tank and seems to eventually go in right next to each carb so would that have an effect on start up ? I'll find out tomorrow !!!!
 
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