1989 Johnson 20hp surging at mid-high rpms help!

[Abassed]

Ok so i have this 1989 20hp Johnson (TJ20CRLCEM) that surges once i get above about 5mph. Starts up pretty good and idles fine, but as soon as it hits about 5mph (dont know the rpms) the motor starts violently surging. The weird thing about this is, it doesn't happen all the time. It normally will run just fine from the launch to my first spot, but once i decide to crank it up again, the surging normally starts. On the other hand, I can sometimes fix the surging by making it surge, then close throttle so engine almost stalls, open throttle and boom.
I've battled with this problem for quite some time now and I was just hoping someone out there new about these motors and these problems.

I've already cleaned carb and replaced every piece of fuel tubing,
Fuel pump works(Tried pumping bulb and didnt fix anything)
New plugs and wires
Both ignition coils test good
new thermostat

One concern i do have is about the charge coil (i guess stator) wires. When i got the motor there was a toggle switch connected to it just hanging there. Is that how it's supposed to be or not. thanks for any feedback

 

[oldboat1]

Your motor has a power pack located under the flywheel. It may have overheated. I would try to check for spark at the point it wants to act up (might be dropping a cylinder).

 

[boobie]

Do a cylinder drop test on it when it's acting up.

 

[Abassed]

so i should get it to where it acts up then pull the plug wires is what yall are saying?

 

[oldboat1]

That's one way (one boot at a time). If no changes when a boot removed, that plug is likely not firing. Another way is to hook up a timing gun, and attach to one wire at a time -- no flash means no spark.

 

[Abassed]

Okay so I went out today and got a compression tester and inline spark tester. Haven't checked for spark yet b/c it's freezing and raining at the moment but both cylinders were right around 100. If this rain subsides i'll pull the boat out and put some muffs and check for spark. I don't have a timing gun, but should I get one? My dad said something about timing when I talked to him about the problem.

 

[oldboat1]

Sorry, but an inline tester really won't do it. You need to measure spark to be sure the ignition output is proper:

 

[Abassed]

oh wow i literally had that in my hands too. I'll have to run back and get it. So my motor is pull start. Will i need to have someone pull on it while i look?

 

[oldboat1]

Yeah, sorry about that. With plugs out, have a helper pull it over for you after you hook up the tester (keep the other boot away from the plug holes.) Test compression with plugs out as well. Can pull it over yourself after hooking up the tester -- position the gauge where you can see it. Pull it over until the needle stops rising.

I would set the spark tester for about a half inch. If no spark, shorten the gap to see if there is any point where it will spark for you.

If you need to test when underway the repurposed timing gun is helpful -- but could also be a case where an inline tester could be useful just to see if something is happening (assuming you can do that without getting hurt).

 

[Abassed]

I tested the compression and i was getting about 100 on both cylinders. I don't have anybody handy now to pull the motor for the spark test but will post the update as soon as i do. So, just wondering, does the test also tell me if the spark is to weak to support higher rpms?

 

[racerone]

Pull it over at night.----You should be able to see it jump at least 3/8" or more.----You will also be able to hear it.

 

[oldboat1]

Unless bouncing around underway, you should be able to spark test (measure) yourself. Just position the tester where you can see it when pulling over the motor. You might need a jumper wire to add some length to the ground clip. (Dark winter evenings are a good time for this test....)

 

[Abassed]

Good point about the night thing. It's getting dark here now so in about a half hour i'll try it out. Will this hurt my impeller trying to pull it without water connected or should i be okay without?

 

[oldboat1]

I would spark test without water, but wouldn't hurt to hook up muffs or dip it in a bucket over the impeller (gearcase joint).

(nice safe answer.)

Didn't mention a new impeller in your first post, btw. Might be due.

 

[Abassed]

Okay so i tried the spark test and i couldn't see any spark. Maybe i had the gap too far? idk i measured to a 1/2" (no spark) 7/16" (no spark) and even 3/8"(no spark). I may have done it wrong but that was my result.

Also, i got some readings from my multimeter for yall.
(+) multi lead to (+) ignition coil terminal
(-) multi lead to (-) ignition coil terminal
= 0.314 ohms
This if for both coils (think it's measured in ohms at least)

(+) multi lead to primary ignition wire boot from power pack
(-) multi lead to (-) igntion coil terminal
= 170-190 (measured with DC Volts)

I hope these are useful for y'all. And the impeller was replaced this past summer and she pees like a race horse. Sorry forgot to mention that. I have some pics i took of the motor I will post just in case too.

 

[Abassed]

[No message]

 

[oldboat1]

If you had a good ground, your spark test tells the tale on ignition. I believe you should pull the flywheel to get at the power pack underneath (power pack is the likely problem). I can't tell offhand if you are testing resistance correctly with the coils (spark plug wire goes to the secondary winding, btw -- a little counterintuitive, maybe).

You are going to need a flywheel puller (sorry, again -- another trip to the auto parts store). Get a puller used for removing harmonic balancers/steering wheels. It's not too expensive. More on that as you progress ....

 

[Abassed]

I still feel like I did the test wrong... I'll probably try it again soon. However, while I was at it, I decided to replace all the fuel line and pulled my carb again. After doing some reading in a service manual, I saw that the float should be 1 1/8" - 1 5/8" from the carb body when hanging right side up. Mine was just past 1 2/8". Then i measured the depth of the bowl which was only 1 1/8"!

Made adjustments and slapped that puppy back on the motor and decided to try and crank it. Started on first pull super easy and idled good. Gave it a couple of good revs to see if it would surge and it didn't. Didn't give it a lot though since i wasn't in water.

I read that a float set too low will cause hesitation when accelerating and surging when you open up the throttle, but good idle.
Could the float being too low really be the whole reason for this problem?

P.S.
Never once have i adjusted that float on that carb.

SHOUTOUT to OLDBOAT for continually giving feedback. You da bomb man!

 

[oldboat1]

Probably a ground issue with your spark test. Can try it again, but sounds like the motor is up and running. Do not run it without water -- takes only a few seconds to ruin the impeller.

You have a slow speed needle valve, and probably need to readjust after working on the carb. Sounds like it wants to run, so run it at idle in a barrel -- water about half way up the leg. Idle or high idle only, but test shifting into gear -- should do so without stalling or stumbling. Adjust the needle clockwise (lean) until the motor backfires or stalls, then back it out about 1/8 turn richer.

[ed. Thanks for the shoutout!]

 

[Abassed]

Oh yeah I had muffs on when I ran it. I don't have any big barrels or trashcans to put it in, but I'll be at the lake monday morning. Will post update Monday evening when i see how she runs.

I went ahead and just set the needle 1 3/4 turns for now and plan to adjust it on the water.

Oh and btw the motor has had a problem of stalling as soon as i put it in gear if I don't let the motor idle for a minute.