Motor Problem Please Help!!!

I have a 1975 70 hp Evinrude outboard, for some reason the 3rd carb(the lowest) will not run, the other 2 are fine. it has fire on all cylinders and good compression last i checked, I just had the carbs cleaned, fuel lines replaced and it still only runs the top 2. I tried everything i can think of and im still stuck. Right now my top speed is 6.5 and it should be 35. why is it not running, someone told me it was fuel not getting to it and i believe him i just cant figure out how to fix it. the fuel pump looks only a year or two old. The last thing is why the bottom one, why doesn't gravity help out any?
Thanks for the help

Were the carbs taken apart, cleaned and reassembled with new gaskets, needle and seats?

The carbs were taken apart and cleaned by a professional and he said the gaskets were fine, as well as the needles and such.

Pull the fuel line that Goes to bottom carb and pump bulb on tank. Should have some fuel coming through it. If not back track to see where it is getting stopped. If getting fuel through line then something in carb is stopped up. Good luck.

already tried it, pumps through just fine

you can also try spraying wd 40 into the carb to see if picks up.if it doesnt you have spark problems

didnt spray wd 40 in but i checked, spark plugs are fine

Checking spark without a spark tester is not satisfactory. Will the spark jump at LEAST a 1/4" air gap on the tester with a hot blue spark? If not, it's not enough. The conditions of non-conductive hydrocarbons and high pressure inside the cylinder won't let it fire if there isn't enough voltage. I suspect bad spark, but one thing you can do is spray some fuel/oil mix with a spray bottle into the carb throat. If it's fuel related, it will pick up rpm's and smooth out; if not, it's spark. As a last resort, if spark checks good and there still seems to be a fuel problem, you can check the reeds. It's VERY rare to have a reed go bad, but any kind of foreign object such as a bug (happened to me once) or other object that blocks a reed open enough, can prevent the cylinder from getting fuel if the motor is designed such that the intake bypass runners are only controlled by one set of reeds which is separated from the others. I don't know if that's even possible but.......
Lastly, check your bottom plug and see if it's coming out really clean. If so, swap it out with one of the other plugs and see if one of the other dirtier plugs comes out clean after a short run. If so, you may have water intrusion into that cylinder steam cleaning the plugs and preventing much combustion, which could be caused by a leaky head gasket, crack in a water jacket (unlikely), or bad exhaust cover gasket. Milky stuff on the plug is an obvious sign of H20 intrusion as well.
Good luck,
BTW a simple spark tester can be had at autozone for about $6.00. It has an adjustable air gap and fits between the plug and the boot. Very handy.
JBJ

Coil pack

Another hint would be to take a propane torch and without lighting it, let the gas flow into the carb that's not working. If the engine picks up speed, you know it's a fuel problem.

Word of caution on this one. Sounds like you already have a few minutes of run time on this motor with a problem. If it is indeed a fuel starvation issue, you have also been running the motor without the oil that would normally be supplied to the bottom cylinder. Despite the original problem that causes you to have the carbs worked on, there is always the possibility that the "rebuild" of the bottom carb was not correct. Damage to the bottom cylinder and all associated moving parts, due to lack of oil coming through with the fuel will become a far greater issue than simply a bad carb job.

Disassembly and inspection of the bottom carb is essential prior to any more run time on the motor in my opinion. If it is an ignition problem, you can deal with that separately. Just make sure that if the motor is running, that it is also getting lubrication. My 2 cents.

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Originally Posted by boatstall

Word of caution on this one. Sounds like you already have a few minutes of run time on this motor with a problem. If it is indeed a fuel starvation issue, you have also been running the motor without the oil that would normally be supplied to the bottom cylinder. Despite the original problem that causes you to have the carbs worked on, there is always the possibility that the "rebuild" of the bottom carb was not correct. Damage to the bottom cylinder and all associated moving parts, due to lack of oil coming through with the fuel will become a far greater issue than simply a bad carb job.

Disassembly and inspection of the bottom carb is essential prior to any more run time on the motor in my opinion. If it is an ignition problem, you can deal with that separately. Just make sure that if the motor is running, that it is also getting lubrication. My 2 cents.

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I started in on that one myself but had something come up. I'll call your 2 cents and raise you 2 cents.

I had a mechanic rebuild my carbs and they didn't run right. Turned out he didn't replace the gaskets even though I supposedly paid for kits. Would suggest you get someone to rebuild the carbs right and use the new gaskets like they should and you'll probably run like you are suppose to. I would insist they make sure it runs properly. My second mechanic found that several things had been re adjusted trying to make the engine run correctly and after he set things to specks it runs great. Good Luck, Ferdi aka Fred

Thanks for all the advice guys, but I found the problem, while I was running it yesterday it threw a rod, bearing, or something through the crankcase. So I doubt I'll worry about the carbs.

dang, that hurts. i know it's not funny but i couldn't keep from laughing at the way you "found the problem." sounds like a new motor is in order.

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Originally Posted by olduckhunter

dang, that hurts. i know it's not funny but i couldn't keep from laughing at the way you "found the problem." sounds like a new motor is in order.

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OUCH, x2 We outta make a sticky out of this experience. NO FUEL-NO LUBRICATION
Go back to your mechanic and "thank him" or better yet post his business or name so that we can all avoid him.

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Originally Posted by crappiedoc

OUCH, x2 We outta make a sticky out of this experience. NO FUEL-NO LUBRICATION
Go back to your mechanic and "thank him" or better yet post his business or name so that we can all avoid him.

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No it wasn't him, he is actually one of the best mechanics I've known, fair, honest and knows more about motors than anyone. and it wasn't a lube problem, it had fuel and oil I was spraying a mix in when it did it, just very low compression I found out, not sure if it broke a ring to do that or not. Maybe a valve, I dont know but im gonna tear it apart just to see exactly what happened.
old duck, yeah its funny now, but still a little depressing, now i gotta look for a 60 to 80 horse motor if anyone in NC knows anything

rap, if you had the motor since new it was like an old friend dying on you. at 35 years old the motor had lived it's normal life i would say. shop around for a good looking older ski boat that might have the size you are looking for and you might get a good motor cheaper buying both than just a motor somewhere. then try to sell the ski boat and trailer to someone to re-coop some of the money. just a thought. there's lots of ski boats up for sale now and with gas prices headed no telling where there will be more. if you aren't in a big hurry you could get a good motor at a good price. and i wasn't laughing at your bad luck either. i would never do that.

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Originally Posted by olduckhunter

rap, if you had the motor since new it was like an old friend dying on you. at 35 years old the motor had lived it's normal life i would say. shop around for a good looking older ski boat that might have the size you are looking for and you might get a good motor cheaper buying both than just a motor somewhere. then try to sell the ski boat and trailer to someone to re-coop some of the money. just a thought. there's lots of ski boats up for sale now and with gas prices headed no telling where there will be more. if you aren't in a big hurry you could get a good motor at a good price. and i wasn't laughing at your bad luck either. i would never do that.

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Haven't had the boat long, 8 months maybe, and yes its had a good life, its done better than me, since i'm only 17. Yeah the ski boat isnt a bad idea though, problem is I want a motor in a hurry, with spring coming fast I don't want to miss the best time to fish.

Thats a bummer! My mech always runs a compression test first, kinda upsets me having to pay for it, but I guess its cheaper than your predictament. I've learned short-cuts to save money only cost more later, at least for me

Sorry to hear about that. Unfortunately this is a very good example why it is important to find out why a cylinder is not firing. If it is due to not getting enough or no fuel, the cylinder is running very lean (or dry) and it will cause problems like this. Good luck with your search for a replacement.