Mercury 4.5hp 1978

japerritt

Cadet
Joined
Aug 9, 2012
Messages
10
I friend gave me a 1978 4.5hp Mercury. He purchased it new back in 1978. After putting it in storage 5 years ago and said he just couldn't get it running right and ended up getting a yamaha 9.9 4 stroke fall in his lap for 400 bucks. Before I even tired to fire it up I notice that positive wire from the coil to the stator was completely corroded, i barely touched and it broke into. I replaced that wire. I then tried to start and it started fairly quickly, but it only starts at full throttle and it revs up to very high RPMs for a second or three and then it starts to die.. Sometimes it doesn't die, revs up again, repeats this process and then shuts down.

I'm not motor mechanic, but enjoy tinkering so I took the carb apart and cleaned it completely, 100% sure all orfaces were clear, but had one problem thats bothering me. i was not able to remove the main nozzle, part number 29 at this link http://www.crowleymarine.com/mercury-outboard/parts/681_4.cfm , completely as the head where you unscrew it appears to have been damaged. if I had to guess, someone probably tried to remove it by unscrewing and the brass just chipped away on on side. I'm not sure how critical this piece is???? I just cleaned it with a small wire like the other jets, and put the carb back together with gaskets. While i was at it, i replaced all gas hoses, spark plug, impeller (water flows great from tale tell whatever you guys call it), and lower unit lube before attempting to start it again..

After doing all this, the motor still runs exactly the same, maybe a hair bit better, but still only starts at full throttle, revs up and down, and then dies.. It will not start at idle and will not run at idle period. After searching these forums it seemed to be starving of fuel, so I thought maybe the float/needle might have been sticking or the fuel pump was bad. I removed the housing that holds the needle, seat, and filter. The first thing i checked was the needle and seat and it has no issues moving freely, it does not stick. Next i pumped my bulb on the gas tank and gas flowed like crazy thru the needle/seat as i assume it should, so this leads me to believe the fuel pump is good? I then adjusted the levels that the float actuates so allow a bit more gas to stay in the bowl, tried to start it up, and it ran the same as before. I'm positive there is plenty of fuel in the bowl. I'm concerned that my issue may be the main nozzle (part number 29 mentioned above).. Heck, I don't?? Part number 22, i think its called a jet, slides right into the main nozzle/part number 29.Any advice would be appreciated.

I'll add that I have spent days on every forum I can find searching for answers, but this is my first post. In many post I notice folks ask for help, get a lot of great advice, but they never return to the forum to share what they did to get it going. If I get this baby running right, I promise to share the end result! I'm loving the challenge, but I'm getting frustrated at the same time.

P.S.. i'm trying to upload some .jpg photos, but its failing for some reason. jpgs are about 1mg in size.
 

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Fishin Magician

Petty Officer 2nd Class
Joined
Aug 7, 2012
Messages
123
Re: Mercury 4.5hp 1978

I have that motor....too.....good little outboard...

you stated alot of info....I will say this ...you noticed wire from + coil to stater was corrosive..stop..not a stater ..it goes to condencer capacitor and also to ground.
you changed that good....now check the negative from coil to insulator..where points will bolt on..and then screwed down to plateing..any resistance in those two HV wires will throw off the timing to TDC and reduce spank to spark...you said it starts and dies......the rush of RPM's and sudden down fall ..as the amperage is not getting through could be a result of the resistance in those wires...both HV wires need to have no resistance to keep it going..fuel or no fuel..


that's just my experience.....no dis to any one ...hope it helps
FM
 

japerritt

Cadet
Joined
Aug 9, 2012
Messages
10
Re: Mercury 4.5hp 1978

Thanks.. I really appreciate your help. I'll check it out Sunday when I get home. I do recall the + wire going underneath what i thought was called the stator (I'm learning alot quickly), but I now recall it or a jumper wire going to the condeser. the other wires looked good to me, but I can certainly replace them all with ease. I wish I had done that now. Do you or anyone else know what the main nozzle is for I mention? In one post somewhere I read where someone said the couldn't get theirs out without breaking in and a few folks suggested to leave it be and just make sure the tube/passage was clear. My gut tells me not to be concerned, but as you can tell I'm not guru.
 

Fishin Magician

Petty Officer 2nd Class
Joined
Aug 7, 2012
Messages
123
Re: Mercury 4.5hp 1978

if it's getting fuel to start and rev..than I would investigate that other wire and all connections....use a multi meter and look for resistance set on ohms....
I think a stater and what I call the pickups are the same thing..both are on in the flywheel magnets path..da juice.. hehe
I changed my HV wires and it's like right out of the box........
run SeaFoam thru ur gas too....
FM
 

River Boy

Petty Officer 3rd Class
Joined
Apr 18, 2009
Messages
92
Re: Mercury 4.5hp 1978

You sound serious about getting this motor running. I've got one just like it. In fact, I've got two. When you find something you like, buy two. Right?
Leroy Wisner, (a guy who hangs around this site some), brought one of these motors back to life and was good enough to chronicle the findings on his web site at: http://www.leeroysramblings.com/mercury_4.5.htm

Here's another link for checking the phasemaker ignition and hi and low speed alternator coils:http://ocmmarketing.com/onlinemercuryoutboardmanual.com/Mercury_Outboard_Manual_2_Cyl_1971-1975.html I know it says 71 to 75 but it's the same ignition as on a 78 4.5.


You need,
A flywheer puller,
a VOM with diode check (volt ohm meter)
A manual for the motor.
Basic mechanic hand tools up to 5/8".
A 50 gallon barrel.
You say if hasn't been ran for 5 years or so, it almost certainly needs a new water pump impeller. 78 4.5 Merc takes the .456 shaft diameter impeller. 1978 vintage gas hose is not ethenol friendly so you'll eventually need to replace that. I imagine all the wiring under the flywheel except the two alternator coils has the insulation cracked, you'll need to replace that. Have fun! River Boy
 

japerritt

Cadet
Joined
Aug 9, 2012
Messages
10
Re: Mercury 4.5hp 1978

Thanks all.. I have a multimeter and can check for resistance, but I'll probably just go ahead and replace every wire I see, which is only 3 wires.. The spark plug wire, the -wire coming from the coil, and I recall a short 4" jumper wire under stator. I've already replaced the + wire and wish I would have replaced all wires at once. Before even attempting to work on this motor I found 'leeroys ramblings' and his mighty fine article on this 4.5hp motor. To be honest, it was his article that gave me the 'i can do this' attitude. Frankly, I don't have the money to have a pro look it and I know the only marine service center where i live in Waycross, Georgia has steep service prices, not to mention I went there on 2 different occassions looking for a fly wheel key and then and impeller and they told me both times that parts were no longer available/obsolete and I wouldn't be able to find them anywhere. Needless to say, they arrived on my doorstep 3 days after placing an on-line order. So far I've got $70 bucks into it.
 

japerritt

Cadet
Joined
Aug 9, 2012
Messages
10
Re: Mercury 4.5hp 1978

update.. i replaced all wires and all hoses in addition to the other items mentioned. it still on starts at full throttle, runs at full throttle, but i wouldn't say it 'runs' well. it revs up, then starts to shut down like its starving for full. i dont have a meter with a diode checker. I've mentioned my concern about the main nozzle being broken badly at the base where you screw/unscrew it in (its hollow there too), so i have a used coming. I found it on ebay for 20 bucks shipped! My gut tells me the nozzle is a serious problem and for 20 bucks i get to see.

I will also add that i checked the contact set, they seemed good. is there and adjustment on the contact set?
 

River Boy

Petty Officer 3rd Class
Joined
Apr 18, 2009
Messages
92
Re: Mercury 4.5hp 1978

.020 on the points, (contacts). Don't worry if they're a little burnt. Sounds like you're getting fire. Diode check is just handy if you think the diodes might be bad in the ignition assembly. VOM is the main thing, hard to do any electricial troubleshooting without one. Main nozzle, what's that?
 

mrteeman

Cadet
Joined
Aug 7, 2012
Messages
14
Re: Mercury 4.5hp 1978

The main nozzle supplies the fuel to the venturi where air get's mixed with the fuel. This is the fuel flow when the throtlle valve opens a bit. For idle (throttle valve closed) there is the idle tube that supplies the fuel for the mixture.

Be sure the main nozzle isn't clogged. Either spray some carb cleaner though it and clean afterwards with a solvent to prevent damage to your rubber parts or try removing it with some wd40 (did that once succesfully). Next method according to seloc manual i think is to heat the carb body so it will expand.... haven't tried that one though.
Be carefull with the screw driver on the brass(?), you can easily ruin it.
 

japerritt

Cadet
Joined
Aug 9, 2012
Messages
10
Re: Mercury 4.5hp 1978

Thanks River boy and Mrteeman... The the main nozzle, part number 29 at this link http://www.crowleymarine.com/mercury...arts/681_4.cfm. Again, its really messed up, one side is torn away on the stem end where someone clearly tried to remove it.. My grammar stunk on my last update, to be clear, i found a used carb on ebay for 20 bucks and its on its way.
 

rdrguru

Recruit
Joined
Jul 21, 2013
Messages
1
Re: Mercury 4.5hp 1978

Did you ever get the motor fixed, and if so what fixed it? I am having the same issue.
 
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