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115 Johnson top carb running dry

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greghennings

New member
Hello, i've been having a major headache trying to get my 78 115 johnson to run. i bought it last fall, and it did start and run. Over the winter i fixed everything i could within the limits of my abilities, one being rebuild the carbs. Really isnt much rebuild as much as cleaning out and replacing a gasket and o-rings. But now i can't get the thing to start, on gas, it will start on starting fluid and i can get it to run but when it runs i can tell gas is coming out of the bottom carb but not the top carb. I rebuilt the fuel pump also, and if i disconnect the top carb and crank the motor, the fuel pump is pumping gas.

compression, #1 95 2,3,4 105.

i have spark on all four and have brand new plug firing really good. if i had an ignition problem, and/or compression problem, at some point when cranking over this motor i should get some kind of pop or bang and i don't get anything.

i took the motor to a local marine mechanic and was told because the compression was low i'd need a new powerhead to the tune of over $4k installed. I just think he didn't want to waste his time with me.

Any ideas would be great, getting a little depressed and upset with myself about this, we're supposed to be going to MN in a couple weeks fishing, because of the long winter and busy schedule i couldn't get the motor outside to start it up until last week.
 
Remove drain plug on top carburetor.----------Then squeeze the bulb.----Does fuel run out ?------------Do the same with bottom carburetor.---Does choke operate properly and do choke flappers close completely.---------Do a proper test for spark !-Does the spark jump a gap of 7/16" or more , no other test is acceptable.-----Are the starter / battery / cables in good condition ? ------Slow cranking means that there will be no spark to start the motor !!!
 
Whether you're filling the float chambers or not can be easily found by removing the bottom side drain plug screw from the float chamber(s).

There are four (4) brass high speed jets (2 to a carb), located horizontally near the bottom center of the float chambers... way in back of the drain plug screws you see on each side of the carburetor float chambers. Clean them with a piece of single strand steel wire as cleaning solvent just doesn't do that job properly.

NOTE: Fuel must flow thru those high speed jets before the fuel can gain access to any other fuel passageway. If the jets are clogged, the engine will not start or run!

Make sure that the electric choke setup is functioning properly.

The fact that you have 105 psi on three cylinders and 95 psi on one... a drop of 15 psi, that does spell trouble. However, it may simply be a head gasket problem... BUT... you do not want to run the engine in that condition without knowing the facts.

Remove the cylinder head from the starboard bank (#1/#3) in order to inspect the head gasket, the sealing surfaces of the head and block, the piston and cylinder walls. Hopefully a new gasket is all you need. If the piston is failing, cylinder walls scored, whatever, at least you know what you're up against and that running the engine is simply leading to further problems.... knowledge that is to be used to prevent one from extending the engine's limits.
 
joereeves said:
The fact that you have 105 psi on three cylinders and 95 psi on one... a drop of 15 psi
Click to expand...

10 psi actually but thats ok, drop is a drop.

I neglected to say that the float bowls are full. I'll take the top carb apart again this afternoon and see what i can do. I'l see if i can round up a spark tester too.

Its just weird (to me any) that this thing doesn't even try to start, at some point while cranking you'd think i'd get something like a pop or cough but absolutely nothing...
 
someone will also have to help me with the spark testing, i've been told by a few people to get a tester but all the testers i've found are just an inline unit that flashes a light when a spark is made, not really telling me how strong the spark is. How do i go about testing the strength of the spark?
 
Often times folks post information about these outboards.-----Information based on assumptions.----Only by doing simple tests can you move forward.-----Check to see if you have spark that will jump a gap of 7/16" with all plugs out.-Then test the same thing with all plugs in.----Many folks can not grasp the conceopt of slow cranking.----If one of these motors cranks slow there will be no spark !!
 
Well, guess i'm gaining. Couldn't find any help getting a spark tester that was more than a light so i found a picture of a home made tester using a block of wood and two screws. Crude, but sure works. All 4 will jump a 7/16 gap, poor starter's gonna go out next with all this cranking :(.

top carb out and recleaned sprayed every orifice and made sure cleaner came out, even the little idle holes. What made me think its running dry is the bottom carb the two brass vertical tubes (don't know their specific name) when running spray gas, where the top one does not.

Put it all back together, primed, cranked and cranked and cranked and nothing. Cranked once more and with one shot of ether she took off and stayed on. Like i said about the two brass vertical tubes, still applies, bottom one is spraying, top one is not. But, it stays running now, and i can shut it down and start it back up. Idles like before, like crap. With that, i can go along with an ignition problem, though i might have good spark, i can hear it missing, rev up and cough, rev up and cough.

Still don't think those carbs are quite right yet either...

I'd like to just buy all new coils and plug wires and cdi but i'm still worried about spending any more cash on it if that #1 cylinder is going to junk out on me.
 
Sounds like you need to find the time and look for the high speed jets.---- These are found in the float bowl of the carburetor.----They are screwed in behind that drain plug.--------------They are brass and about 5/8" long.
 
racerone said:
Sounds like you need to find the time and look for the high speed jets.---- These are found in the float bowl of the carburetor.----They are screwed in behind that drain plug.--------------They are brass and about 5/8" long.
Click to expand...


alright, took the the both carbs apart for good measure, again, took my flash light and inspected the high speed jets, bottom one was fine, cleaned it anyway. Top one i could see light through it but obviously not as good as the bottom, cleaned them out. Reassembled. Runs ok. Definitely fuel coming up now, but more so on the 1&3 cylinder side of carb on both top and bottom. There's fuel coming up on the 2&4 side, but i can hold my finger over the 1&3 side and my finger gets soaked, the other side its probably half as good.

maybe now its running would be a good time for some sea-foam and a decarb.

Still won't start on its own, took a couple shots of ether to get fired. Maybe since the carbs were empty it just needed something to get it going? Or probably the ignition system not working properly...

Maybe tonight i'll order new power packs, i'd have them and get them installed before next weekend. Worst case scenario the engine conks out on me and i just have to transfer my new parts to a new powerhead i guess.
 
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