77 75hp johnson wont run out

[morton0904]

have a 77 75hp johnson out of water with muffs on it runs great revs up in forward and reverse but in water with full throttle it seems bogged down wont pick up and take off only runs 5 or 10 mph if that fast.... any suggestions?

 

[txwildhorse]

Re: 77 75hp johnson wont run out

I have a 1978 70HP Johnson that I am having the same problem with, maybe we can compare notes. I have had new Carb Kits put in mine just about two or three months ago and that still has not solved my problem. I have a manual on these Johnson motors and it also spoke of the timing on it as well as the fuel pump

 

[Mas]

Re: 77 75hp johnson wont run out

Check spark and compression on both!

MAS

 

[morton0904]

Re: 77 75hp johnson wont run out

compression in top 2 cylinders 90 bottom 87 not eough diff. to matter and definately getting spark

 

[tashasdaddy]

Re: 77 75hp johnson wont run out

Morton, try another guage for your compresson. easiest way to check it is to leave the key off, and jump the solenoid. you want 3 to 4 good revolutions, and get readings. you present reading are extremely low. if the reading do not come up. i would suggest trying a decarb.

Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck



Both of you, if you did not totally clean and remove the jets, and use rebuild kits, you could still have dirty high speed jets.

http://forums.iboats.com/showthread.php?t=244013

if you are positive your carbs are good, check you spark, if that is good, do the link n sinc procedure, in manual.

 

[rodneyjanssen]

Re: 77 75hp johnson wont run out

I also have a 77 75hp johnson and had basically the same problem. It would only go 7-8 mph unless I hit the choke for a second while giving it throttle and it would jump on plane and be fine until I stopped again. So I cleaned the carbs and checked the plugs a found that I had a milky residue in the middle hole. I replaced the head gasket because the old one had hailine cracks on the fire rings and still didn't fix the problem. I then ordered a powerhead gasket kit for like $85 and replaced the exhaust cover gaskets, powerhead gasket, water cover on the head gasket and replaced the head gasket again. I tested it out and had no more water in the cylinder, so I took it for a test ride and same thing wouldn't go above 7-8 mph. I then checked the carbs again and they were fine and then checked the spark plug gap. Well one of the plugs only had a gap of less then .010, that must of happend when I dropped it while taking the plugs out to remove the head and didn't think about checking the gap when putting together the next day. Anyway changed the gap to .030 and now runs like a champ!!

So I would suggest to check plugs for water and gap, do a decarb and recheck compression. Then clean carbs.

If you have water in the cylinder replace head gasket and exhaust cover gaskets and probably powerhead gasket.

 

[rodneyjanssen]

Re: 77 75hp johnson wont run out

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