TOPIC: 77 Johnson 115 carb problem

Hi working on a 77 115 with a perplexing problem . carbs are clean , good spark all 4 , top 2 cylinders only fire when I choke it , does pick up when I squirt gas into the carb , float needles free and float level looks correct , what might I be missing here ?

Maybe a weak fuel pump. The top carb takes more pressure to get the gas up there, but the bottom carb is "downhill" from the pump. Does it have the old style, or the newer HP pump? Have you checked the diaphram in whichever pump you do have?

Only run when you choke it at idle or when the carbs are open?

Assuming at idle:

1st, if the carb linkages are not synced, then if the bottom carbs are open & tops are closed, the idle RPM will be produced by the bottom 2. Remember, all 4 carbs (in this case 2 shafts equals 4 carbs) are to be fully closed at idle & idle rpm is controlled via timing. The maladjusting of the carb linkages would require a mal adjustment of the idle timing to get the idle RPM near normal.

If both carb shafts are fully closed & both top cyls are dead at idle I would look for an intake leak, top crank seal leak or that both idle pilot jets are clogged which would be unlikely because you've cleaned the carbs.

To check for an intake leak, spray carb cleaner around the carb flange & reed plate. For a top crank seal, you can try to spray carb cleaner up under the flywheel. I don't know if it will work.

took the fuel pump apart and diapram LOOKED ok , not sure which pump it has , pumping the primer bulb didnt seam to help and I did spray carb cleaner around the upper carb again with no results , if idle jets were pluged it should pick up when its reved up and it doesnt ...sporadickly it will pick up and die again , choking is the only thing that helps ... Im suspecting the fuel pump myself but hopng to pin point it closer .. trying to get this motor going asa favor to a old guy who wants to go fishing so thanks to all for your ideas and help !

some more info , fuel pump looked to be original and motors been sitting at least 2 years and possibly longer

kingdve, don't know if it will help or not, but here's the thread where I went through my 72 Johnson 115 carbs and fuel pump. I found a lot of black rtv silicone in mine, but not sure what's causing your problem here. The FP on mine is the HP version, previous owner had already changed it out....I put the kit in it anyway.

www.fiberglassics.com/glassic-forums/j-e-g-o-s-place/1973-johnson-115esl73m-revival

New fuel pump showed up today and I dont see any difference after changing it in how it runs ... good spark , 125-127 #s compression on all cylinders , top 2 cylinders pop on occasion , choking it briefly gets those cylinders to fire , sprayed carb cleaner around the carb flanges and tried to get it up under the flywheel , made no difference , dont see any spit back out of the top carb like a reed problem , carbs are in sync ... Im stumped ...

Im stumped

Me too! Even after rebuilding the carbs and f/p on mine, it "popped back" at idle once in a while and died. I adjusted the idle speed up just a tad, ran several tanks of gas through it and it cleared up. Then I was able to adjust the idle back down to where it should be. Hasn't given me any trouble since, I wrote it off to gunk on the reed valves or something else I know nothing about. (From sitting up so long without being run dry, I guess.)

If you're not getting any gas to (Thru) the top carb, running it probably wouldn't be advisable though, don't wanna do any engine damage trying to figure this out. I don't know........wish I could help.

well now heres a strange thing the plugs come out almost wet on the top cylinders , when I advance the throttle it trys to fire on those 2 plugs just popping but if I blip the choke it picks up and runs on all 4 till it runs out of the choke fuel , didnt rebuild the carbs just checked them out and they LOOK clean nothing in the bowls , spraying carb cleaner thru the jets they seamed clear ... history on this beast is unknown , been sitting several years and a little tid bit about the preveous owner not getting it to run so ... Im wondering about sticky reeds , bad crank seals , evil gremlins ? going back to Mercs !

going back to Mercs !

If you're throwing it out, strap it to a pallet and I'll have a truck line come by and pick it up!
Seriously, tho, I'd try pulling the carbs for a thorough rebuild with kits and try that. There could be some junk in there you're not seeing, like up under the welch plugs or something. There are also several minute little passages that require soaking in carb cleaner, running small diameter wire thru, and blowing compressed air thru to make sure they're open.

The top plugs looking different from the bottom sounds like a link & synch issue. Has that been done yet?

MarkS has it right. If you didn't pull those carbs and do a complete rebuild, then you didn't clean them.
This is a must on any engine sitting that long.

Would not have been the fuel pump as manually squeezing the primer bulb by-passes the fuel pump and fills the carbs. Remember, the only job the fuel pump does is try to keep the needle and seat closed in the carburetor. Primer bulb will do the same thing.
There is a piece of linkage on the starboard side of the carbs. It goes from the lower carb to the upper carb. Remove it from the upper carb and let the throttle blade snap shut. Try the engine now. If that works then adjust your "sync & link". If not, try bringing two fingers into the airflow into one of the venturis, if this brings that cylinder back then that is further indication that the carb is not clean. If this is the case then you will have to go back into the upper carb and completely go through it. Try running a piece of tag wire through all passages. You only have an idle circuit and a high speed circuit on that carb, no intermediate circuit. Remove all jets, clean as necessary and run tag wire every place it will go. Make sure the brass tubes are not blocked and the large brass emulsion tube is not cracked.

Thanks all for the ideas ... carbs are in sync , carbs are clean , manualy choking the problem carb didnt help ... let it run on the muffs for a couple of hours it started clearing up , Im thinking the reeds are sticky and running it is loosening them up ... Im a Merc man and working on this junk to help a old guy who wants to go fishing , changed the impeller on sunday , what a hatefull ignorant setup this thing is ! I could do half a dozen Mercs in the time it took to change this one ! Almost had to take the bottom carb off to get that link off and back on ... I hear people grumble about Merc Auot Trannys changing the impeller , there a pleasure by comparison ! oh well my lesson no more V4 johnnyrudes for me !

????dve wrote

working on this junk..................what a hatefull ignorant setup this thing is !

Probably best if I don't comment on the statement(s) you made, I promised a friend I'd try harder not to "flameout" on anybody.

You need more practice on the OMCs. Then you will realize they are the superior product. A mechanical fingers is helpful.

There Mark, I said it.

The crossflow V4s are great motors. I have a 1983 90hp on my 18-foot Starcraft and it is a sweet runner. With what you've given us, it has to be something fairly simple causing your issue. Very likely the reeds are NOT stuck. Most likely the top carb is gummed up somewhere.

Is it possible this motor came from an area of significantly different altitude? That might mean it could need rejetting to work properly in the current altitude.

Alternatively, is there ANY side-to-side play in the flywheel? That might be evidence of the upper main bearing going, which would in turn make the upper seal wear faster.

- Scott