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  '78 Johnson, 70hp surges

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Author Topic:   '78 Johnson, 70hp surges
Cicada posted 08-19-2002 12:27 AM ET (US)   Profile for Cicada   Send Email to Cicada  
Running a '78 70 hp Johnson on 15' Sport.

Engine surges, Seems like a cylinder cuts in and out at all speeds and idle. About 50% of the time bogs down when opened up. When it cuts in acceleration is good. Also the cutting in and out seems to be immediate - either on or off. Either running good or running poor without any transition between.

Replaced the fuel line, tank, fuel and spark plugs. Checked fuel filter - ok. Pumping the bulb while running doesn't have any effect. Pushing in the choke while running makes it bog down. Cleaned up some of the problems but left with the surge.

Suspecting an electrical problem but don't really know where to go first with this.

Purchased the boat used about 6 or 7 years ago. Had to have a Whaler. It's been in "storage" for the past 3 years and only used occasionally. Carbs rebuilt when I purchased the boat. In process of restoring this boat and any thoughts, ideas or comments on engine would be appreciated.

By the way. Great bulletin board / forums. Been wandering around the posts while working on the boat and have found the information invaluable. Made the learning curve alot easier and eliminated some of the frustrations normally found with a project like this. Appreciate it.

Paul Mott

raygun posted 08-19-2002 02:59 AM ET (US)     Profile for raygun  Send Email to raygun     
my 2 cents that certainly can't hurt. check the coil connections for corrosion. the coil packs are the things that the wires to the spark plugs come from. check the other connection on them.look in the boot style connectors. if you find any green/blue corrosion get a wire terminal brush(like a little bottle brush)in there and clean them up till shiny. smear some triple guard grease on the terminals before reconnecting.
Al_A_Buy posted 08-19-2002 09:20 AM ET (US)     Profile for Al_A_Buy  Send Email to Al_A_Buy     
Paul - Sounds like intermittant connection at the power pack. Same thing happened to my Johnson. Typically happens where the wires exit the potting compound on the pack. Only fix is to replace the offending unit. Might not be a bad idea to replace both at the same time to prevent a loss of power at an inopportune moment.
Cicada posted 08-19-2002 10:04 PM ET (US)     Profile for Cicada  Send Email to Cicada     
Thanks for the suggestions.

Took a look at connections and didn't see any signs of corrosion, will clean them up anyway.

Al a buy, when you mention replacing both are you talking about the coils and power pack? Also potting compound - is that on/in the coils? Power pack has screw terminals for connection of coil wires.

Thanks, Paul

dscew posted 08-19-2002 10:15 PM ET (US)     Profile for dscew    
I have the '74 version of your motor; I had the same problem and had to have new carb kits installed. If you haven't done this since you did it 6 or 7 years ago, I'd bet this is the problem, especially if it has been stored for 3 years. Mine now starts, idles, and runs great. Good luck.
shoctor posted 08-21-2002 05:34 PM ET (US)     Profile for shoctor  Send Email to shoctor     
my .02 fuel problem in the carbs regardless if they were rebuilt if they have been sitting for 3 years without being used and have had the same fuel or fuel remnants sitting in there it is a distinct chance that varnishing has occured in the carbs if all of the electrical systems appear to be ok then i would go from here. To check electrical system bring down to a local dealer they can diagnose coils and cdi unit with meters ina matter of minutes. my guess would be the carbs on the motor. My experience is thatintermitent runningproblems turn out to be fuel if an electrical system is broken ie coil chances are you will not get spark at all. I have found a all or none problem on the electrics. Good luck
John O posted 08-21-2002 09:19 PM ET (US)     Profile for John O    
CIRADA ---having same problem w/ 88hp spl 1988. JOHNSON Ran fine at 3500 rpm and then went to excelerate and engine bogged down and began surging. it continued at lower speeds when going slow in a no wake zone. It started the day I kicked the fuel line off my 28gal tempo (by accident) not sure if this is related. I am putting on a spare newer 9 gal tank and fuel line first, then I will check fuel filter, diafram ?(sp) then fuel pump. Plugs looked good

Let me know if the problem has been fixed on your 70hp and what you did --thanks John O

Cicada posted 08-23-2002 08:55 PM ET (US)     Profile for Cicada  Send Email to Cicada     
Took the sport into the mechanic for some diagnostics. He says it's the power pack. Going to pick it up tomorrow and hopefully get out on some water. We'll see what happens.

Thanks
PM

Al_A_Buy posted 08-23-2002 11:02 PM ET (US)     Profile for Al_A_Buy  Send Email to Al_A_Buy     
Cicada - Sorry about not replying sooner - just beamed back down...:-)

The power pack is a circuit board inside a plastic case with some type of rubbery compound poured in to "weatherproof" it. My experience is that engine vibration tends to flex the wires on the back of the P/P where they exit the potting. This is where the problem usually occurs. When I recommended that you replace both units I was refering to the power packs. I assumed that the configuration of your motor was a v-twin - thus dual P/P, sorry if I misspoke.

Am glad to see you got it to the mech....

Al

Cicada posted 08-24-2002 09:12 PM ET (US)     Profile for Cicada  Send Email to Cicada     
Picked up the sport and took it out today. Seems to be running fine now. Power pack.
She's a happy camper now.

Thanks to all.
Paul Mott

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