1985 Johnson 70hp

[cesandroid]

Hey everyone, new to the forum and have done lots of reading to no avail so far. pulling my hair out as to an idle problem to number 1 cylinder only. idling on the muffs, number 1 misses unless i spray a little fuel in or block some air to the carb than it hits. on the water it will idle very low and go only if i hit the primer. ive went thru everything i can think of with a fine tooth comb! doesnt matter if coils,plugs, carbs, wires, fuel tank, fuel pump hose are switched, problem is number 1. once in mid-high speed, seems fine, goes good. cant seem to find an air leak anywhere either. only thing i want to verify which i think is true to all carbs because ive tested, is on a spare carb i took the large emulsion tube out and noticed the small emulsion tube has a small pinhole inside the throat of the carb where the large emulsion tube blocks it. is that normal? if, when cleaning the carbs you block the low speed ports to create a seal and trickle water in behind the low speed idle jet, it will leak around that small pinhole. anybody ripped one apart to confirm this. other thing is spark jumps 7/16 on all 3 which is visible in daylight but in youtube videos, it seems to be brighter. coils measure good, wires good etc. spark is even.

 

[cesandroid]

Also forgot to mention, compression is good and no visible water leaks in to motor either

 

[Bosunsmate]

you could swap carbs around to see if problem follows otherwise check your inlet reeds

 

[cesandroid]

thanks for the reply Bosanmate, thats been done as well. even a new carb, same problem.

 

[cesandroid]

Bought the boat last spring with this problem as well and dont know the history. motor looks very clean, black painted. a few guys i talk too say i should be running premium. i wouldnt think that would cause the miss. why good a wot i guess with timing being advanced. plugs look fine, all gapped right. Like i say, either restrict air or prime it to get it to go to wot on the lake. this being number 1 cylinder.

 

[Bosunsmate]

Top seal perhaps?

 

[cesandroid]

Today i took the flywheel off as well, key in there and tight and clean. seal on top looks good. measured the timer base 11ohms is what i get. stator output measures 550 ohms. seems to charge fine when running as well. Spins good and strong when trying to start although i alittle hard to start imo probably relating to number one not firing.

 

[cesandroid]

Like i said ive been working on the obvious stuff with both the seloc and oem johnson manuals with no luck. I have learned quite a bit about 2-strokes in the process thats for sure.

 

[Bosunsmate]

Have you tried spraying some fuel around the crankcase seal, perhaps its sucking in air through the join from a worn seal there
Also check any hoses from the choke solenoid to the cylinder/carb

 

[cesandroid]

New hoses from the primer to the carbs. no leaks either, although i could try blocking those bypass ports on the carbs to see if air is getting in. had to change the cap on the primer as well as one nipple was busted. i used starting fluid around the seals and havent noticed anything but i suppose could try fuel in a spray bottle, probably a more accurate diagnosis.

 

[cesandroid]

Now wait a minute, are you referring to a seal between the block where the crank runs thru or the top and bottom seals? in the parts diagram it doesnt show a seal or gasket between the block where the crank runs thru.

 

[cesandroid]

With the flywheel off i put a little oil on that top seal and left it for half a day but didnt appear to be a leak there, if thats what you are reffering to.

 

[racerone]

There are labarynth seals machined in the crankcase to separate the 3 crankcases.----Those are part of the block and therefor not a separate part shown in the book.

 

[cesandroid]

OK gotcha, so if there's a leak, than that's a block problem? Fix is a new block?

 

[racerone]

You need to trouble shoot and figure out a way to check / test for crankcase compression on your motor.----Or perhaps the piston is in upside down ?----I can not do the testing / inspection for you.

 

[cesandroid]

I think I realize I need to test it as you are not here to do that. Are you referring to a leakdown test? I mereley asked if the block is shot if those seals are bad?

 

[Bosunsmate]

If its just the top cylinder playing up, then id just spray on the outside of the number one cylinder crankcase where the case is split, if it was the internal labryinth then id expect your number 2 to be poorly too.
Not sure id take your top seal test as an absolute at all. Sometimes they look ok, maybe even to someone in forensics but if you replace them then the number one cylinder suddenly becomes right again

 

[cesandroid]

OK gotcha on that, thanks for the good reply. How does one get that top seal out? It looks pretty tight in there. Gonna test later here on the muffs to see.

 

[Bosunsmate]

Many people use a pick but i cant speak with experience on that to you unfortunately. Someone else on here may speak up on it. The only other thing i can think of is a worn gasket on the carb face but no doubt you would of noticed any conspicuous rip on that.
You can also try spraying some fluid under flywheel while its running

 

[cesandroid]

Ran it this time in a test tank. still missing on number 1. sprayed fuel up around the flywheel and down the crankcase with no real conclusive evidence. motor i thought sounded like it reved up when i sprayed around the flywheel but it was not instant enough i thought to follow and be conclusive. idle is slowly erratic than it will stall unless you advance the throttle. have to set the timer to about 10btc to keep it idling barely. choking it will help as well. i have a timer base on order as the ohm readings was not to spec and i dont know what else to do with it. At this point im running in circles, i have no clue what to do next! Does a person rip it apart, take the head off, is it worth it, need some insight here please. Im absolutely baffled and frustrated with this motor. Just about ready to throw it in the bush!