trouble with 79 70hp merc 5356960

[Tmacular]

im having an issue with this damn mercury and i cant get to the bottom of it.

it was idling and running fine in forward gear for trolling however i come to realize i was down an entire cylinder 2 due to coil. swapped over 3 of the red coils from my mariner 80hp that i have as a parts engine and now my cylinder and all the others are firing again. however i cant troll???? shes running around 900 rpm in forward gear min throttle and yet after a few min its choking and dying out. also runs great on trailer in driveway every time but when i bring it to lake it takes me 50 cranks to get her to run. it runs for 3 seconds dies and does that repeatedly until all of a sudden it fires right up to 1k rpm. when i was down a cylinder once it started it never missed a beat the entire day. i could restart on half a crank and fire right up. but now i have a 3rds cylinder firing and im having issues. could the pump act up at idle but be fine at all other rpms? as long as i keep it 1200 or higher in gear it never misses a beat from there to WOT

things ive done:
compression test 146-148-146
just had carbs cleaned and inspected
brand new plugs l76v champion (per OEM)
swapped out those coils
new fuel filter and i cleaned out the one on the motor.
fuel pump appears to have brand new gaskets on it so i assumed it was replaced prior
im running only rec 89 octane fuel in the tank (new tank)
primer bulb and fuel hoses replaced including the carb hose and ones on motor.
just repropped to a 10 6/8 x 12 pitch from a 12.5 x 8 that was on there.


im starting to wonder if my carb mixtures are off or maybe the new prop thrust is putting more strain on the motor and i need to adjust for it? the issue is the hard starts were a problem before the new prop.

thanks
Tony Mac

 

[Texasmark]

Since you had hard starts before the prop you aren't priming the enough....My experience with Mercs. dating back to the late 70's is that they are thirsty when first started, especially after sitting for awhile unused. On the prop I agree that you have to do some diddling. 4" in prop pitch is a lot of load change on the engine.

Normal idle rpms in the water, boat moving in F gear, turning the idle set screw....which changes the timing arm to advance-retard timing to get the right idle speed which is 650-700 on my range of engines. Fast enough to stay when you shift into gear and slow enough to be able to shift without crunching your gears.

Yes 4" of pitch increase will make more demands on your engine. The manual for my range of engines is open the low speed jets until you can hammer down on the throttle in the hole and the engine will stay with you....all carbs about the same number of turns. Others have mentioned if you get over 2 turns open from a 2 finger closed position (soft seat) you have other problems. I wouldn't be surprised if you won't have problems. Did I miss the reason you made such a drastic change in pitch? Have we been working with you on your 79 70 hp? Haven't we been over the prop swap debacle? Are you still having problems after incorporating our help?

 

[Tmacular]

Since you had hard starts before the prop you aren't priming the enough....My experience with Mercs. dating back to the late 70's is that they are thirsty when first started, especially after sitting for awhile unused. On the prop I agree that you have to do some diddling. 4" in prop pitch is a lot of load change on the engine.

Normal idle rpms in the water, boat moving in F gear, turning the idle set screw....which changes the timing arm to advance-retard timing to get the right idle speed which is 650-700 on my range of engines. Fast enough to stay when you shift into gear and slow enough to be able to shift without crunching your gears.

Yes 4" of pitch increase will make more demands on your engine. The manual for my range of engines is open the low speed jets until you can hammer down on the throttle in the hole and the engine will stay with you....all carbs about the same number of turns. Others have mentioned if you get over 2 turns open from a 2 finger closed position (soft seat) you have other problems. I wouldn't be surprised if you won't have problems. Did I miss the reason you made such a drastic change in pitch? Have we been working with you on your 79 70 hp? Haven't we been over the prop swap debacle? Are you still having problems after incorporating our help?

Yes sir! Texas you helped me over on the prop section! I didn't want to post this new issue in the wrong place so I put it here. We did the prop change bc i had the 8 pitch from a previous pontoon on now an aluminum! The hard start issue is strange. Why would it run and start perfect on trailer but not just sitting in the water at the dock?

In my case it has been ran about 8 times now in the last 2 weeks while I try to hone it in. Its a new motor to me and I've never owned a mercury so I'm scratching my head (came from johnson)

i planned to play with idle screw on the water in the next day or two but was curious if i should just order a pump or rebuild kit for safety?

650-700 rpm in gear at the moment is impossible for me. I can't get it to idle under 1100 ish for long periods.

 

[racerone]

Load test the battery.----Take starter apart for inspection.----Check battery cables and connections.

 

[Tmacular]

Load test the battery.----Take starter apart for inspection.----Check battery cables and connections.

Im not sure I understand how to load test a battery? What would I be looking for?

I put a new rectifier on it when I bought it and my voltage indicator i installed says im getting good voltage and charge. Anywhere from 12.5-14.9 when running and using gear. I should og also stated that I have 2 brand new 4/20/20 batteries both deep cycle 27m series

 

[Tmacular]

Update: took apart the pump today and found the diaphragm slightly warped. Not awful but not good. Repaired with new kit. Aside from having to scrap the gasket off (previous install rtv the gasket to motor and to pump) got it all put together and going to run it on the trailer in a bit! I'll report back. My mechanic claimed when he did the carbs he adjusted them to factory settings (he said 1.25 turns counter from fully closed) so we shall see!

 

[Tmacular]

Update**** seems im not getting spark in cylinder 2 again! I have an extra coil im going to pop into that and if it doesn't work maybe the wires are suspect. Any reason number 2 would keep going out?


Edit: I ohm tested each coil. Got a reading of .04 cylinder 1 .04 cylinder 2 and .03/.04 on cylinder 3!

 

[Tmacular]

Second update. I've now lost spark completely. Wondering if the cdi was starting to go out hence the intermittent issues and loss of spark on cylinder 2. Ive got a new cdi coming tomorrow from the dealer. Hopefully thst solves it. If not on to the stator I guess and triggee?

 

[Texasmark]

Battery load test can be performed at Walmart or Auto Zone for a couple of places. Taking a fully charged battery....charger quits pumping current into it......put a volt meter across the terminals and put a very low resistance load pack across the the terminals also....both contained in the battery tester box. If the battery voltage falls below 11V (my pass fail number) at 300 amperes, it's sulphated up; inside and needs to be replaced.

 

[Tmacular]

Battery load test can be performed at Walmart or Auto Zone for a couple of places. Taking a fully charged battery....charger quits pumping current into it......put a volt meter across the terminals and put a very low resistance load pack across the the terminals also....both contained in the battery tester box. If the battery voltage falls below 11V (my pass fail number) at 300 amperes, it's sulphated up; inside and needs to be replaced.

Would you recommend this if the batter that im using is from 5/20 just got it.

I did a stator resistance test and I'm getting nothing back. I attempted red to blue wire both ways no reading. Went from red wire to powerhead ground and got no reading! I'm guessing this is my spark issue and not the cdi?

 

[Tmacular]

Ok installed new stator, trigger and cdi (all cdi electronics brand) and i still have no spark. I have no idea what to do now. Coils ohm correctly. I grounded coil wires to the new cdi which has a ground and advised me to do so. What else is there???

 

[Tmacular]

Update on stator. Did a resistance test on the new stator and it is not up to OEM specs but it is up to what cdi says it should be. What else could cause no spark? I dont have a main fuse and I believe it was the mercury switch I bypassed and still no spark