Carb or electrical problem? 7.5HP 1983 Johnson

[merc20076]

Yes I have a problem now with that small outboard. It runs great a low speed and all day long for trolling but when it's time to run it fast it bugs down or sometimes it stalls if giving to much throttle. I did increase the slow speed adjustment and didn't do anything.

It starts this after a while. When I take off for the first time it's ok.

I know my SIB takes alot of power to make it plane but when it runs ok but you can hear that it's not 100% ok.

I run today my spare 7.5HP and it runs faster at WOT.

Since the problems starts when motor warm could it be an electrical problem (CDI powerpack) or it's the high speed jet in the carb blocked? It did run ok before.

 

[ONERCBOATER]

Re: Carb or electrical problem? 7.5HP 1983 Johnson

I gonna go with high speed jet for 100 or fuel pump failing but highspeed jet is my final answer

 

[merc20076]

Re: Carb or electrical problem? 7.5HP 1983 Johnson

I dont think it's the fuel pump because the fuel line primer bulb stays firm but I could be wrong to. I had another 7.5HP that I fixed and sold and I've replaced the fuel pump gaskets .

I also think it's the high speed jet in the carb but why it does run well when motor's not 100% warm. The motor doesn't overheat (brand new impeller and tstat kit) and I can touch the head for a good 5 seconds when warm. It stills has a decent compression equal on both cylinders. (90-95PSI)

At least I have a very good running spare 7.5HP that runs even faster, but is not that nice looking.

 

[dew2]

Re: Carb or electrical problem? 7.5HP 1983 Johnson

I'm with onercboater.easier cheaper fix also

 

[ac0j]

Re: Carb or electrical problem? 7.5HP 1983 Johnson

I am interested in this as well! My friend has an 1985ish envinrude 90 horse that does the same thing. Repaced coil packs, rebiult fuel pump, kitted the carbs, still does it. It runs great when first put in the water, wot accross the lake, after warm up it dies down and wont run. It will start fine, but wont go past idle and often dies when putting into gear. If it stays running after put in gear, it wont throttle up. If you let it cool a couple hours, it will run fine for a short time again. He is at his wits end!

 

[dew2]

Re: Carb or electrical problem? 7.5HP 1983 Johnson

Another thing to check is all the fuel lines for air intrusion leaks, all of then from the tank to motor to fuel pump right on to the carb.If they look brittle cracked replace them with good clamps.

 

[ONERCBOATER]

Re: Carb or electrical problem? 7.5HP 1983 Johnson

do a warm and a cold compression test then, another thought though doubtful....but since you state it is having issues once warm but runs fine cold...it may be electronic but since you cant transition to higher RPM I still going with fuel issue. Just cause the primer bulb stays hard doesnt mean that the fuel pump is working, or that the carb is working correctly. primer bulb primes....then generally under use gets a bit soft as it just functions as part of the fuel line at that point. I would say with some confidence that provided your warm and cold compression are both suitable (i think they will be) that you will be wanting to do a good tear down on the carb and rebuild it. I would also say perhaps prior to this to make sure your fuel filters are nice and clean, make sure you have no kinks in your fuel lines, check for air leaks in system....then clean up carb very well I would wager that like magic the engine will run well after that. Also if your fuel lines either from tank, or inside cowling are older than a few years (3 or so) I would strongly suggest replacing em cause the ethanol does bad things to fuel lines....really bad and you can't see the damage... but your carb gets all these nice lil bits of crud and the high speed jet seems to be the fav spot for this crud to land.

Sean

 

[merc20076]

Re: Carb or electrical problem? 7.5HP 1983 Johnson

I forgot to mention:

-In my boat, I use a Scepter 3 gallons gas tank + a new Seasense fuel line kit, both brand new.

-When I start the motor cold with choke, I have to put it almost at full throttle position to get it started.

-When it does the problem, if I pull the choke, it will die.

The 2 lasts points makes me still think there could be a defect electrical component in my outboard. But like I said, it just does not want to force. Once I get the boat on plane it runs OK. It gets is gas alright. Not as fast as my spare O/B. Think I know what to re-paint this weekend!

 

[levi_tsk]

Re: Carb or electrical problem? 7.5HP 1983 Johnson

doesnt this thing have points??? if so clean em check em and adjust as neccesary ... if no improvement its the coils

ac0j 1st please start another thread but what you have is a power pack going bad they do that very frequently and its a point to note that as ANY ingition component heats up to operating temp everything expands and this is why both of you are having trouble power packs AND coils from these engines are NOTORIOUS for working AWESOME when they are cold and crapping out once they reach operating temp

merc- next time you take it out and it goes to running like that pump the fuel bulband see if it picks up if not its a coil and while your in there replace the points too


-levi

 

[levi_tsk]

Re: Carb or electrical problem? 7.5HP 1983 Johnson

just looked- no points in this one so its either the coil or power pack...

 

[Sixmark]

Re: Carb or electrical problem? 7.5HP 1983 Johnson

just looked- no points in this one so its either the coil or power pack...

Or it could be a stator, poor connection, or other contributing factors as well, do the actual tests to save yourself from throwing parts at it that may not fix the issue.

 

[merc20076]

Re: Carb or electrical problem? 7.5HP 1983 Johnson

This is wierd but my Spare 7.5HP Evinrude started to do the same thing yesterday. Not as bad as the Johnson. Can it be the spark plus wires that are due to change. How can we check them? When I want to accelerate fast, it hesitates for a second. Once it picks up it goes very very good and pushes the boat pretty fast, so can't be a carb issue.