'75 50hp merc miss

[tamarackstyle]

O.k I put her all back together, but I can not get her to run. First off I replaced; coil, rectifier, switch box, plugs, fuel pump diaphram, and rebuilt the carbs.<br /> The problem is I have a very hard sparatic miss. It happens cold or warm. It sometimes happens at idle, sometimes in gear, and sometimes in gear with throttle. she will miss and then stall, or miss a couple times then stall. The longest I have been able to keep her running is a couple of minutes.<br /> Ive tried adjusting the advance, adjusting the idle mixture, priming the bulb, hitting the choke, squirting pre mix in the carbs. Also disconnected the kill wire and merc switch.<br /> I have taken the carbs apart again to double check but beyond that I am at a total loss so any suggestions would be appreciated.

 

[petryshyn]

Re: '75 50hp merc miss

check for spark when she stalls. You must determine a spark or fuel issue.....

 

[tamarackstyle]

Re: '75 50hp merc miss

I checked for spark. no one told me Im running so much juice thru these motors. ouch.<br /> So I tore everything back apart and triple checked everything and this is what I found. My old needle and seat in the carb had the rubber insert in the seat, and the new one from the kit had the rubber needle. No big deal, but just for kicks I reinstalled an old set in one of the bowl covers and left the new set in the other, then blew thru them for comparison. The old ones had a higher flow rate, not much but definately more. Not able to find anything else I went with this I switched out the other set and put everything back together. Turned the key and she idles like a dream.<br /> Thanx schematic. Just a note to anyone rebuilding carbs on old mercs, do not buy them form outboardparts.com. Not only this problem with the needles but from the two kits I had about three or four gaskets from each that did not match up with the other, missing idle tube gasket in both, and not important but inconsistant, two pgs of instructions with one and only one pg in the other.

 

[tamarackstyle]

Re: '75 50hp merc miss

Well I thought I had it. The next morning I Took it to the shop to drop it in the tank and it started to do the same thing. Wouldnt idle because she would miss so bad she would stall out. And if she would idle she would cut out as soon as you gave her gas. Ive replaced everything in the ignition system(because it needed it)besides the high and low speed coils. I tested these per the manual and everything came to specs(ohms). Is it possible for these readings to be o.k but the driver coils still be bad?

 

[boatmanwayne]

Re: '75 50hp merc miss

I recently experienced about the same problem on a merc 500, after replacing driver coils which did pass ohm check with new ones, no help. This one cuts out at high speed (3000 rpms), It almost has to be switchbox which passes ohms & continuity test one time then not the next. I would put your old switchbox back on and try it. Hope this helps.

 

[tamarackstyle]

Re: '75 50hp merc miss

thanx boatmanwayne. I actually have my motor at the motor shop now. they wont do any of the work because "they are not mercury any more" but the have been kind enough to let me keep it in their tank while they look over my shoulder and offer me their experienced advice. One thing they told me to do was pull the drivers and board and check for corrosion underneath. So I did and what I found was salt covering my low speed coil wire feed and where it is soldered to the board. they pointed out to me that with the board installed the corrosion whould be in contact with the metal case and could cause leakage between the coils and/or ground. They also said that the only true way to test the coils is with them apart(disconnected from the board) to avoid any false readings that may be caused by leakage. So I resoldered and cleaned the connections, tested the coils while they were apart and put everything back together. We will find out saturday how we did

 

[boatmanwayne]

Re: '75 50hp merc miss

Hope that corrosion problem was you're problem, It's some chore to replace those coils, I was getting worn out removing and replacing that distributor everytime I needed to check something. I'll check back after saturday, I'm curious about this fix. Later,

 

[tamarackstyle]

Re: '75 50hp merc miss

It wasnt the problem. So we substituded the coil, same problem. Then the switch box and she fired right up. Still the same prob at high speed so I have to exchange the new one for another new one. I wish just once I could order parts and have them be good out of the box. Thanxs for all your help guys, I'll let you know when I get the new box.

 

[boatmanwayne]

Re: '75 50hp merc miss

Hello Tamarackstyle, Did you ever get the new swtichbox? If so what were the results. I'm dieing to know because I've just installed my second box with no better results, I can get 3500rpm with my old box, and barely above idle with the two new ones.

 

[tamarackstyle]

Re: '75 50hp merc miss

I did get the new box and she starts and runs fine untill about mid range and then there it begins to miss. Before we go any further we are trying to locate a high speed driver coil to substitute, being that it is the only thing left to replace, and see how she does after that. Have you put the old one back on since you have had a new one and/or since youve changed the coils? Do you still get to 3500?

 

[boatmanwayne]

Re: '75 50hp merc miss

Tamarackstyle, Yes I installed the second new switchbox, still can't get above idle, re'installed old box, went right back to 3500 rpms Tech from CDI questiions my distributor, I've installed driver coils previously now I'm going to replace cap, I really don't understand how it can be in the distributor but I will try anything. Let you know results soon.

 

[tamarackstyle]

Re: '75 50hp merc miss

boatman heres a few things they told me to do/check. If you have a merc switch (brown wire to box) disconnect it. Also disconnect your kill wire (orange on the blue terminal of box). Your engine will run with these off, your just eliminating possible problems. Try it now. If no luck open up your distributor and check the cap really good for hairline cracks and any carbon. Take the rotor off(be careful its in with loctight and breaks easy if you pry on it to hard, I know $90 for a new rotor) the trick is to put heat to the base. Now remove the shaft assembly(three screws) And spin it to make sure no binding is there. I hope some of this helps. Let me know.

 

[boatmanwayne]

Re: '75 50hp merc miss

Sorry it took so long to get back, I had to put this project on hold for awhile, but was able to install a new dist. cap, rechecked complete dist. & wiring, still no results. Got thought from another merc mechanic, he knows the lighting energizer real well, but he is baffled too. Any other suggestions will be welcomed. Thanks

 

[tamarackstyle]

Re: '75 50hp merc miss

well I had to put mine on hold as well but I think I have discovered the problem. Ive posted a few threads to try to get some info, but cant seem to get a response. i took the distributor apart and discovered that the coils were in there reversed. All of my books show the blue an the right and one went as far as to say "make sure to put the blue on the right". I will let you know when I switch them.

 

[tamarackstyle]

Re: '75 50hp merc miss

yep, that was it. I swithched the coils around and now she runs fine. Thanx all.

 

[tamarackstyle]

Re: '75 50hp merc miss

I'm posting a new thread on the same motor and I was hoping you guys could take a look at it. Thanx