1986 6hp Johnson, not much power at full throttle, and other random questions

Howdy all,

You have helped me on a couple issues already with this motor. Here are a few more.

But first--- Carb has been removed, soaked in dip, blowed out with compressed air, and rebuilt with a kit. Seems to be properly adjusted at this point (air screw in front of carb). Fuel lines are new (around the carb), and the fuel screen in the pump looks brand new (it may be, I just bought this motor recently but the owner didn't know if her dad had done anything to it lately).

Keep in mind I'm only just now learning the terminology for these motors. I'm a cabinet maker so I can learn it, but I just don't know some of the terms nor quite how to troubleshoot.

1) The motor will crank and idle just fine, esp. once it's warm. But when I try to run it full throttle (or anything 1/2 throttle or up) it just seems sluggish. The motor sounds "mostly" right--- doesn't sound like it's skipping, but it won't push my 14' Starcraft (1974) any faster than 5mph (GPS) with 300 pounds in the boat total. This is a really light aluminum boat that I know won't plane with a 6hp, but you'd think I could get at least 9-10mph out of it. At 3/4 to full throttle, the sound of the engine changes a little as does power (although it never powers up to what it seems like it should). Randomly it will sound louder and get weaker, and then it will quiet down a little and get stronger, but still not as strong as you'd expect.

2) The carb top is a plastic body that was previously cracked when I got it from someone torquing the screws down too hard. I am not sure if this is effecting it or not, the crack appears to make it's way down into the air jet screw.

Here is the crack. Since this pic, I've covered it with epoxy (cleaned it with lacquer thinner and scuffed gently with sandpaper to make sure it stuck).

This is an obsolete part, any suggestions on where to find one? All the common parts places I've seen online list it as "obsolete".

Is there any chance that spraying WD40 around that crack with it idling at a mid-range RPM possibly tell me if there's air getting into the engine through the crack?

Good info all, thanks.

I will call Seaway tomorrow and see what they can get.

We didn't run a copper wire through the high speed jet, but the carb was actually pretty clean (meaning, we saw no visible build up) before we soaked it. We did air chuck it out but I suppose something in the carb is a possiblity. I can pull it off and see.

If the carb dome is reasonably priced I may just replace it first.

I'll try the vaccum hose trick. Thanks--
Matt

BTW I took the boat out again today. The motor ran marginally better than last week.

It's quite frustrating to get it to crank when cold, it floods very easily. It seems to flood if you pump the fuel bulb too much; seems to me like this shouldn't happen.

Anyhow, got it cranked and ran it. Ran reliably, never stalled, and once warm it idles quite nicely.

When going full throttle (or close to it), if I hold my fingers over the carb intake slightly, it runs with a bit more pep. So I assume this means it either is getting too much air, or not enough fuel (either way seems like it's running lean).


Are there any fuel filters to be found on this engine other than the screen that's in the fuel pump? I can't find any.

The other thing to confirm is that it is running on both cylinders. To confirm this, start it up, warm it up, and at a faster idle, take a pair of insulated plyers and pull one spark plug boot off at a time. It should be able to run on either cylinder alone, so if it dies when one is pulled, you know that the other cylinder was never running or is very weak.

That being said, with a 14' boat and 300 lbs in it, I am not sure she isn't giving you all she's got.

Optsyeagle,

Checked the spark today, both plugs are getting plenty of spark (a good solid 3/8" blue arc) and the engine actually runs almost fine on either piston. So that's ruled out.

On a whim, I ran some Sea-foam through the carb. The carb was cleaned a couple weeks ago but this can (supposedly) also clean out beyond the carb. Anyhow it actually did seem to make a difference in the way it runs, it will run a touch higher RPM (judging by my ear, which I know isn't the most reliable source). I put some in the fuel as well and I'm letting it high-idle in a large barrel of water (with a steady stream of cold water going in).

Perhaps the Seafoam in the fuel lines will help clean out anything that might be restricting it. The carb is already clean but it can't hurt to try. This is all I'm able to do at the moment.

I don't have the tools for a compression test.

What bothers me is that I see guys with heavy 20 foot sailboats that go faster than I'm going with the same HP motor.

Folks I may have just found one of the problems. As usual it's something dumb, which isn't terribly surprising. I have a Master's degree in theology, not engineering. Pardon my naive nature here, I can learn this but apparently I need hand puppets.

I noticed that every time I'd put the cover on the engine, it seemed to run worse. Yes, just the cover.

Please look at this pic. There are three questions.


1) The line that I marked in orange-- this is the one that seems to be getting bound up on the cover. There are numerous wires coming from it (from the back of the "cam" that surrounds the underside of the flywheel) and they have heatshrink around them, going down to something near the base of the engine block. This wire seems to be obstructed. If I tug on it, the engine revs up VERY nicely (even in gear). I am not sure that this line is "THE" problem, the problem may be on the other side of the engine block where there are some other linkages that may be out of adjustment or something. I apologize for being so vague.

Does this pic look unusual to you? I have no base to compare this old engine too, and it appears that one of the previous owners has spent a lot of time dickering around with it. Either way, it seems to run like a top if I pull on that, so hopefully it's just a matter of getting these linkages straightened out.

A (the red "A")--- A brass looking clip with nothing on it. Looks to me like something should be here, a clip of some sort?

B (the red "B")--- A tapped hole. Not sure what this hole used to have in it. Any suggestions????

kimcrwbr1 said:

Start looking for another prop with less pitch and if you can get your hands on a timing light with a tach on it and see how fast the motor is running at WOT. You want 4900rpm max with a light load in the boat. I still say your over propped your power band will be up above 4500rpm.

Click to expand...

I will keep this in mind. The prop isn't original, it's relatively new, but at the same time I'm not sure that it's anything different than an original prop. I'll snap a pic of it next time I have it out of the water barrel later today and post it here.

However I think I may have found *part* of the problem, see my above post.

Find a local shop that has a " test propeller "----it is used to determine if the engine is running to it's potential.------Hole " B " I believe is used in the factory to put the block in a fixture for all the automatic machining operations.

racerone said:

Find a local shop that has a " test propeller "----it is used to determine if the engine is running to it's potential.------Hole " B " I believe is used in the factory to put the block in a fixture for all the automatic machining operations.

Click to expand...

10/4 on finding the test prop.

And if that's just a mount for the machine shop, then so much the better. Thanks!

kimcrwbr1 said:

You want the armature plate to move smooth from stop to stop with no obstruction. When you first said it runs worse with the cover on there are two likely suspects. A exhaust leak would fill the cowl with exhaust gas cutting off oxygen going into the carb as well as the combustion air intake either under the handle on the top cover or in the bottom cover usually right under the carb. Spiders and mud dobbers make their nests blocking off air supply to the carb. A few more things to look at.

Click to expand...

OK now you are definitely on to something. I do notice a lot of the residual exhaust smoke showing up around the engine block. I assumed it was just boiling up from the barrel of water, but I've seen it a little as well when underway out on the river. I will be looking into this.

I had the breather off, and the carb is clean, so nothing obstructing air to the carb in terms of critters. My truck, however, (which I bought used from a family member a couple months ago) had half eaten acorns in the air filter breather and a pile of dirt dobber nests. Apparently squirrels and dirt dobbers make half decent roommates.

I suspect that my main culprit would be the exhaust housing gasket. This looks like a bear to get to. Is it as complicated as it looks to be on the exploded diagrams?

One final side note about this boat/motor combo.

The motor is a long shaft (20"). I was not aware that having a long shaft could cause performance issues. I don't think it is a "huge" deal on this boat (a 14' Starcraft), but the AC plate does sit WAY below the keel.

I picked up a free mini-jacker plate from a friend (a very generous friend) and installed it tonight. I have a suspicion that this will increase our speed a little. Not much, since I'm not up on plane, but hopefully it will increase my "hull speed".

Curious if you solved this? Might be similar to an issue im having with throttle not going to full speed on my johnson 55hp 1979. Ive noticed a lot of black exhaust marks coming out of the lower engine exhaust vents, i did just put the lower unit back on so wondering if I did something wrong to let exhaust fumes go where they arent wanted somehow?