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1985 Johnson 25hp surging high idle

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Xtyfighterx

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I'm new here got my first boat two days ago 1985. Lund 14ft aluminum with a 25hp Johnson believe it's the original motor from 1985 owner said it was running couple months ago. So yesterday I put new fuel line on new tank new mixed gas and got it started took it to the lake and wouldn't stay running in gear kept surging and dieing on and off so took it home cleaned the carb checked the gaskets used pressurized air checked my plugs. Took back out today it stays running now but still surges. I've been reading a lot and thinking it may be my power pack? Any help here thanks
 
Sounds like a nice setup take some time and get to know the motor and do a thorough diagnostic. We need numbers what is the compression engine cold? Do a spark gap test with a open air spark gap tester. It must jump a gap of at least 7/16 inch crisp blue snap. Exactly how were you adjusting the slow needle? After running about five minutes put your hand on the head can you hold it there for a slow count to six? Adjust the slow speed needle on the water in forward gear after the engine is up to temp at idle speed. Slowly turn it in 1/8 turn at a time until the engine stumbles, wait at least five seconds for the crankcase to respond. Then turn it out slow for a smooth idle. The quickly go to full throttle if it hesitates add 1/8 turn rich and try again. Once you get a nice clean hole shot just leave it alone.
 
kimcrwbr1 said:
Sounds like a nice setup take some time and get to know the motor and do a thorough diagnostic. We need numbers what is the compression engine cold? Do a spark gap test with a open air spark gap tester. It must jump a gap of at least 7/16 inch crisp blue snap. Exactly how were you adjusting the slow needle? After running about five minutes put your hand on the head can you hold it there for a slow count to six? Adjust the slow speed needle on the water in forward gear after the engine is up to temp at idle speed. Slowly turn it in 1/8 turn at a time until the engine stumbles, wait at least five seconds for the crankcase to respond. Then turn it out slow for a smooth idle. The quickly go to full throttle if it hesitates add 1/8 turn rich and try again. Once you get a nice clean hole shot just leave it alone.
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i adjusted the needle till it stayed running at idle and didn't die. 1 and a quarter turn I believe. I'll do a compression test to day and measure the plugs. It seems ok at low and somewhat half throttle it still wants to surge tho. Full throttle it surges pretty bad. I ran it for maybe 15min on the water last night like that then turned it off fished for half hour then it wouldn't start again. Had to row back.
 
It could be a restriction in the fuel system or a fuel pump diaphram getting old and stiff. Do you have a service manual? Do you know the history of the motor? Confirm the compression and spark gap are up to snuff is allways the first thing to confirm.
 
Update.

so went down got new plugs for it idk how old they were started up first pull. But same issue. I then pulled the plug wire off top plug and it kept running. Did the bottom and it died. I than swapped plug wires same issue. So top cylinder is dead. I don't have a compression tester. Any way I can go about this thanks
 
Ya float looks and is set right from my knowledge my father In law looked it over to he does a lot of dirt bike carbs he said it looked good to.
 
The ignition coils are normally a go no-go test. When it happens again and only fires on one coil just swap the coils and see if it follows the coil. If it stays the same both coils are likely good and you have issues with the power pack or trigger. The first step is to clean all the connections good with electrical cleaner and put back together with delectric grease and sand all the grounds. Disconnect the kill wire at the pack to take it out of the loop. A DVA adaptor for your multimeter will pinpoint the faulty component.
http://www.cdielectronics.com/wp-content/uploads/2013/09/IS-113-2285.pdf
http://www.cdielectronics.com/wp-content/uploads/2013/09/IS-133-3387.pdf
http://www.cdielectronics.com/wp-content/uploads/2014/04/IS-183-2508.pdf
 
That means it is only firing on the bottom cylinder. swap the coils around and if it stays the same then both coils are good. Pull both spark plugs and swap the two wires from the trigger and see if the spark is still on the bottom plug. If not the trigger is likely bad if so the powerpack likely is bad.
 
Did you test the compression three times 1-2 1-2 1-2 and take the high number for each cylinder? That accounts for any mistest. Did you use a spark gap tester? Hold each plug about 7/16 inch from a good ground and see if it jumps the gap. Chip a little paint off the corner of a bolt or housing if necessary. You dont want to see more than 10% between the high and low compression numbers your sitting just over 14% 103.5 is 10 %.
 
Re tested 100 in top and 100 for the bottom.
notnsure why I got that 115 last time. I tested each cylinder 5 times each time it was 100.
 
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Get a can of seafoam spray take it out on the water and bring the engine up to temp. Run it at high idle speed and spray seafoam in the carb until it starts smoking real good and quickly shut it down. Wait half an hour then start it up and point it toward the big part of the lake and open it up for at least 5 minutes WOT. Then go back to idle speed and dial in the slow needle. You may have fixed the erratic spark just messing with the wires does it run on both cylinders now?
 
Put some fuel mix in the upper cylinder and disconnect the bottom spark plug and see if it fires? If so your losing crankcase pressure for the upper cylinder.
http://www.marineengine.com/newparts/part_details.php?pnum=OMC0330549
Pull the bypass cover or tighten the bolts if loose two other possibilities would be the upper crank seal or a bad reed. Do not over tighten the bolts, if your good at making gaskets just make a new gasket and put a light coat of permatex aviation on both sides of the gasket.
 
Yes for now just make the upper cylinder fire after adding fuel. I just use a length of vacuum tube and dip it in the fuel tank and hold your finger on the end then stick it in the upper cylinder releas your finger put the plug in and see if the upper cylinder fires. disconnect the bottom plug you know it is firing.
 
I forgot another possibility is the fuel pump diaphram could have a hole causing the upper cylinder to flood out it is mounted on the upper bypass cover does your primer bulb get hard after you fill the carb float bowl?
 
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