20hp running right?

[gnarbrah]

Alright, I just got back in from my first lake run with my 1988 20hp Johnson. It's on the back of a 12' Carolina Skiff. It started and ran "fine" the whole time but I think it's either missing slightly or may be a dirty carb? It took quite a bit longer to get on plane than I expected and never seemed to really "tach out" to where it sounded right. I just moved up from a 9.9 to this motor which is a totally different animal so I might just not know what to expect.

Whether I'm idling or running wot it just seems like it's a little rough. It never seems to smooth out if you know what I'm saying. I'll try and get a video posted for reference.

In the meantime any suggestions? I'm thinking a good carb overhaul won't hurt. It seems pretty accessible on this motor which is nice but I'm hoping someone can point me in the direction of a post outlining the process (I know there's some good ones here and I'm fairly new at the carb rebuild thing)

Thanks

 

[Mas]

Re: 20hp running right?

It may very well be a dirty carb and a carb rebuild may be needed...but what about new fresh gas??

Try squeezing your fuel line primer bulb while it's running...if rpms increase, look to the fuel pump.

Do you have a strong blue spark?

MAS

 

[tashasdaddy]

Re: 20hp running right?

new motor to you. i would start with compression and spark check on both cylinders. clean and rebuild the carb with a kit. the only difference in is your carb has the adjustable slow speed needle http://forums.iboats.com/showthread.php?t=244013


(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

Note: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

 

[gnarbrah]

Re: 20hp running right?

Thanks for the replies!

The gas is good, I just filled it this past weekend and compression is at 118 and 119 so I'm thinking ok as well. I haven't checked the spark yet but I'll do that today. I'll most likely look into the carb rebuild kit today too. From my past experience (carb on a 6 horse) the kit seems to come with everything under the kitchen sink, do I need to replace every item or are there some that stay good over time (plugs etc.)? Also what is the best stuff to use to clean it? Soak or spray?

Thanks

 

[ryanmitton]

Re: 20hp running right?

Hey guys I'm so stoked I just bought a 20 johnson myself for 500 dollars and it runs but runs a bit rough so I am following this thread as I will also be doing the Carb overhaul. Thanks for starting the thread Gnarbrah.

I beleive the answer to your question about soaking or spraying is covered in the the 3rd step of the carb overhaul link provided by tashasdaddy.

 

[kybill66]

Re: 20hp running right?

If you think it is a fuel problem a quick and easy test is start the motor up on the trailer in the water and pull the choke. If the rpms pick up your idle port is dirty, if it dies that means it is ok then try mid range and then wot just remember that at wot it wants gas so you may have to pull the choke a few times to see if it dies or picks up. Plus the whole shot are you sure about the right prop.

 

[Tinman57]

Re: 20hp running right?

Alright, I just got back in from my first lake run with my 1988 20hp Johnson. It's on the back of a 12' Carolina Skiff.

That 20 hp should make a little 12 foot run very fast and peppy. It definitely sounds like the engine has a problem, probably dirty carb as others have said.

 

[gnarbrah]

Re: 20hp running right?

Hi all - It's been a while since I've been on the site. Mostly because it's been too f-n cold to even think about boating! Anyway now that Florida is trying to get back to some sort of normalcy I've been back on the water the past 2 weekends. Last weekend the motor ran absolutely perfect - this weekend completely different story. I changed absolutely nothing (except the gas - both weekends). I can get it started up and it idles just fine but once I give it any throttle it just dies. I did replace the fuel pump over the winter (even though it didn't change anything). I'm guessing the first thing I need to do is go through the carb again. I just did it last year - and it really hasn't been sitting all that long. Could it really be that fouled up already? I'm also curious as to if it may be a timing issue. The pull cord broke on me again so I fixed that. The only thing I'm wondering about there is once you have the recoil off and upside down on the bench, hand wound tight and let it recoil and pull the rope in it there's a little mark or arrow that says "align arrow here" or something to that effect. What's the point of that? Does that have anything to do with timing or something else?

Thanks and as usual I really appreciate all the insight!

 

[gnarbrah]

Re: 20hp running right?

Update - Well it's Sunday afternoon, rain is looming and wife won't be home till 5:30 so of course I'm sitting in te shed drinking a few cans of beer just looking at the motor - what else am I going to do?

Anyway - I noticed a "drip" of black sludge coming out near the prop (unburnt fuel through the exhaust I presume). Obviously running rich so I start looking at the carb. I'm definitely not a professional marine mechaninc but I do remember that when the throttle is wide open the butterfly should be horizontal (correct?). For some reason it wasn't even close. I've adjusted the linkage and tightened the screw as hard as I dare. I'm assuming this could definitely cause my problem????

Why would that setting change? Did I just not tighten it down enough last time? Sound right - wrong?

Thanks

 

[rjezuit]

Re: 20hp running right?

What you did is part of a link and sync. Correct in saying when fully advanced, the throttle butterfly should be wide open (horizontal). The sync part relates to when and where this happens. Rick

 

[gnarbrah]

Re: 20hp running right?

Thanks for the re-assurance. Can you elaborate on where the sync part of it comes into play? I believe I read in my book that the butterfly should start moving as soon as (I have no idea what it's called) the thing above the carb, has a roller thingy that sits between two marks starts to pull off towards the front of the motor. Sorry I know I'm being vague...