1979 7.5hp fuel and spark plug issues

[UtahConrad]

1979 7.5hp model#72H9B having fuel and spark plug issues. It will start with difficulty but stalls as soon as I put er in gear. When I check the plugs, one is wet with black residue and the other seems to be clean and dry.
Bought a repair manual and I've checked and cleaned the following: fuel lines, fuel filter, fuel pump, carb (disassembled, cleaned and reassembled). I'm worried the timing may be off or is it worse...? Thanks for any input.

 

[Fabuloso]

Re: 1979 7.5hp fuel and spark plug issues

Check to see you have the correct spark plugs. I recently bought a 1984 7.5hp sea king that had the wrong plugs with the wrong gap. It was difficult to start and it only run at idle. As soon as I moved the trottle it would die. The manual for the 84 calls for the L86 equivalent to NGK B6HS.

 

[fishrdan]

Re: 1979 7.5hp fuel and spark plug issues

When I check the plugs, one is wet with black residue and the other seems to be clean and dry.

Clean plug? It's probably not firing, check and see if there is spark on that plug wire. If no fire, time to look at the ignition system.

 

[UtahConrad]

Re: 1979 7.5hp fuel and spark plug issues

Thx to both for the good suggestions. I did replace the plugs (NGK B6HS) and confirmed they were gapped per the manual to .30 however, it was happening to the existing plugs as well as the new replacements.
I have also confirmed that both plug wires have spark... so where does that leave me? Is there something I can spray in the spark plug hole (sorry for the improper term) to clean it out? Carb cleaner?

 

[Fabuloso]

Re: 1979 7.5hp fuel and spark plug issues

Is it starting ? not at all? difficult to start? Are you using fresh fuel?
fuel lines air tight? I would't mess around with the timing yet.

 

[jerryjerry05]

Re: 1979 7.5hp fuel and spark plug issues

The main jet in the carb has small holes in it they must be clean.
Do a compression test.Then when you have the carb off check the reeds.Broken/bent?
Diaphram no holes.J

 

[fishrdan]

Re: 1979 7.5hp fuel and spark plug issues

Question, the plug that's clean, is it clean like a new plug or clean like it's been firing good? (I assumed it wasn't firing)

I think rolleyes the fuel pump is ported in common with one of the cylinders and if the fuel pump diaphragm ruptures it can bleed into that cylinder. My 89's fuel pump was hard and rotting out, best to change it out even if it's not the problem. Those old rubber parts were not designed for ethanol.

 

[UtahConrad]

Re: 1979 7.5hp fuel and spark plug issues

It starts pretty normal, then as I let it warm up it changes idle speed a little (up and down) but ultimately settles into a nice idle. There is some white smoke (more as I rev the rpm's manually). As soon as I put er in gear it just stalls out (even when I manually work the throttle). When I say the plug is clean, I mean, I think it is firing correctly. I know it's getting spark and it's gaped correctly. What else do I look for?
I've reconfirmed that both plugs have spark, installed the new (correct) plugs, made sure they are gaped correctly (.03), confirmed that there are no leaks in any of the fuel lines, disassembled the carb and cleaned it (the reeds look good per the manual, the throttle adj valve on the carb is clean - no grooves), disassembled the fuel pump and inspected the rubber diaphragm (there are no pin holes, besides I don't think I can get a replacement for that. Parts are really hard to find). I didn't check the compression because I don't know how nor do I have the tools. I did spray carb cleaner is both plug holes and I haven't tried to start it again since then.
What's next?

 

[jerryjerry05]

Re: 1979 7.5hp fuel and spark plug issues

Check the fuel pump diaphram.Ethanol is messing up a lot of motors.It's delaminating the inside of older hoses causing clogs in the carbs and fuel filter.Check for soft hoses and junk in the filter on the motor.Check the diaphram J

 

[fishrdan]

Re: 1979 7.5hp fuel and spark plug issues

The fuel pump kit is one of the easy to find parts, available here on Iboats when I replaced mine a year back, something like $10.

Even though you said you verified spark on each cylinder, try this. Pull and ground the top plug wire, then start the outboard, did it run? Plug the top wire back in and do the same with the bottom plug wire, did it run? These outboards will run off 1 cylinder and seem kind of normal, other than idling a bit low. This is a quick and easy check, though it might not diagnose your exact problem.

No compression tester? Try putting your thumb over the spark plug hole and pulling the cord. It won't tell you how much comp there is, but will tell you if there is any at all. If it doesn't blow your thumb off (not literally ) you have compression problems.

Ditch the carb cleaner in the cylinders and use some SeaFoam, decarb cleaner or good ol' 2 stroke oil and gas. The carb cleaner will strip off the 2 stroke oil and cause more problems than good. If you have the carb off the engine, then it's OK to use carb cleaner on the carb, just keep it out of the engine.

You said you are "manually" working the throttle. Is this as in, opening the carb with your hand instead of using the twist grip throttle? I bent a couple reeds on my 7.5 Force by doing this (stupid rookie mistake on my part) and had to replace them so the OB would run normal again. Really sucked as these are one of the hard to find NLA parts. I found them by doing a lot of searching on the internet, some outboard shop in CA had them.