75 Johnson 15

Ok, I picked this motor up. Guy said he rebuilt it, but got rid of the boat. I pulled the head cover off didn't see issues in pistons. I have spark, but it doesn't seem to be getting gas to the pistons. Now it had been sitting for years and there is moister, but when I pull the spark plugs out, I don't see any fuel coming out. Unless I'm completely off base, there should be fuel coming out. I put on a known good carb off my 6hp and still nothing. There is moister getting to the pistons but it seems to little. I pulled the carb off and squirted some fuel in the intake to try and get fuel into the pistons, but just moist, nothing wet. Anything internal that could be messed up by this guy I need to tear down and check? Thanks a ton in advance.

Re: 75 Johnson 15

if compresion is low(60 psi or less per hole) fuell is not suckng into cylinders,
start with checking compresion
next check if timig/ spark is ok
next is carb should be clean and chocke leave should work

Re: 75 Johnson 15

Don't know if a 6 hp carb. on a 15hp is a good way to start. I would suggest a good cleaning on the right carb. for starters. No need to remove the carb. you can spray fuel mix into the carb. or the plug holes. You should also check for spark on both plugs with a spark tester. Best of luck. Rick.

Re: 75 Johnson 15

Yes, if it was my motor, I would want to know the compression of each cylinder. I would hook up an external spark tester and verify that both sparks can jump a minumum of a 3/8" gap. If both check out, I would prime up some gas into the carb., turn the throttle full on to the neutral stop (ignore the fast, start, shift, and slow readings on the grip for now), pull out the choke and see if it fires up. Make sure it is in a barrel of water with the water level at a minimum, 3 inches above where the lower unit bolts on to the mid-section.

If it has been sitting for a few years, a carb clean with a rebuld kit would not hurt it. Also, those head gaskets are supposed to be a single use gasket so you should think about replacing the old one. If you did put the old one back on, if the compression is good, you could wait until you get it to go, but a new head gasket will last a lot longer.

Re: 75 Johnson 15

+1. Compression test, spark test. Then figure out fuel delivery if those are good.

Re: 75 Johnson 15

Ok, heading down to get a compression tester later today. I pulled off the cover panel on the sides and it didn't have a good seal at all. the tool didn't even clean off all the old gasket before he put the new one on. Do these gaskets need RTV? Still trying to do research on how to set the timing.

Re: 75 Johnson 15

No need to worry about setting timing. You should also make sure the flywheel key has not sheared. But do a compression test first, if that checks out, then check the carb, maybe the float needle is stuck. If still no go then check the flywheel key.

Re: 75 Johnson 15

Got it. already checked the flywheel key. I put the smaller carb on knowing it wouldn't run but rather to see if I am getting fuel to the pistons. I need to find a picture of the carb. I did clean it. It was plugged up with thick black sludge from the old fuel lines, but all my newer carbs have a jet that runs through the entire carb opening. this one only goes half way up and I'm thinking I'm missing a piece there. Thats why put the smaller carb on. Does anyone know about the RTV? It's 10 miles to get parts so I want to make sure I don't need RTV as well. If I understand correctly, the cover on the right side would cause it to not suck fuel in if it was not sealed correctl

Re: 75 Johnson 15

You can find a good view of your carb. here. Just keep drilling down until you find it. Rick.
BRP -- Parts Catalogs

Re: 75 Johnson 15

Here is a picture of your carb's inner pieces. The float and inlet valve are not in the picture. Inside the slow speed jet is a very small plastic piece that looks like a very small funnel, that should be changed during a cleaning. Also, on top of the carb is a welch plug that should be removed and cleaned inside there and then a new plug inserted. No RTV or gasket sealer should be used anywhere near your carburetor.

I would clean up your carb with a rebuild kit. Put it back on and try and start it. If it doesn't start, spray some gas/oil mix through the carb throat and try to start it that way and see if you get a chug or two. If not, put a teaspoon of gas/oil mix in each spark plug hole and try it again.

If you don't get a chug out of that then I doubt it is not a fuel problem. Again, spark and compression tests should be done. Did you set the points to 0.020" gap when you had the flywheel off? Is your carb roller sync'd up with your throttle cam?

Re: 75 Johnson 15

So here is what I see. The part in questions is correct, however, I cannot get the part that goes above the orifice plug #23 to come out. I am guessing those holes on the sides need to be clean to suck up fuel. Is that part supposed to come out?

Re: 75 Johnson 15

The part #23 just unscrews. Anything inside that jet, does not come out. Just spray liberal amounts of carb cleaner in there and blow it out with high pressure compressed air. You can thread some copper wire in there if you want, to try and clean it out, and again, spray some more carb cleaner and blow it out with compressed air.

Re: 75 Johnson 15

Here's an excellent source of info for your motor: OMC outboard related articles