Johnson Crosslfow 85hp - Intermittent Power Loss - Quick Diagnostics??

[Big6ft6]

Hi All, bought a 78 or 79 85hp Johnson V4 last weekend 15' trihull. Looks very clean and well maintained.

I am having intermittent power issues. I'd like to take the boat out again today, but am worried that if I have a fuel/carb issue I could be causing cylinder-damage from lack of lube (story below). Is there anything I can check/test here at home in an hour or less, to reassure myself that the cylinders are getting enough fuel to stay lubed?

Alternatively, if I do take her this morning, are there specific tests while operating or things I should pay attention to that would help diagnose?

I am an auto mechanic, not a boat mechanic, so I have tools and knowledge, but I'm not very experienced with 2-strokes and I don't want to ruin this engine. My wife is eager to go in the boat, and it is rare that she supports one of my "toy" purchases so if I can the family out today it would be great.


*****Detailed Background****

I was with the seller when he pulled it out of storage, we trailered it to my house, where I slapped on the muffs and fired her up. She started instantly, idled beautifully. I let her run for a minute or two, then did a compression test, 120+ across all cylinders. I handed him the cash.

I put in some fresh gas and took it out last weekend, She ran great, a few times I thought I noticed a very small, almost imperceptible, loss of power and rpm at WOT. I'm a paranoid guy when it comes to engines, sometimes I'm too paranoid. By the end of the day I had dismissed the few times of reduced power/rpm as my imagination and/or just part of the "character" of two-stroke outboards. (I have limited 2-stroke experience, most have been negative)

So I took it out again yesterday, It happened again, this time not my imagination. Definitely some loss of power/rpm, like weeds on the prop. We had just done a long no-wake trip though a weedy canal, so although I didn't see weeds on the engine, I told myself that is likely what it was, as the problem seemed to go away after we stopped and tipped up the motor.

After 5 minutes of WOT cruising, stopped and hooked up a tube. Tried to pull the tube and I had NO power out of the hole, none, couldn't even come close to planing out the boat and rpms were very low. I unhooked the tube, same result...half-power, half rpms at WOT, some funny motor vibration at low throttle position like not all cylinders were firing. I dropped everyone at the pier and headed back to the trailer. As I'm driving back to the trailer, very slowly the bow came down, boat planed out, rpms came up, and for the most part seemed OK. Not quite the speeds I had the first weekend, but it was choppy and I have just a junky old mechanical speedo so I'm not sure if this is dependable diagnostic.

 

[emdsapmgr]

Could be an ignition problem. Weak ignition components tend to work great when the engine is cold, then crap out as it warms to normal operating temps. When it starts to have no power, put a timing light on each plugwire and check the spark. Check for intermittents, weak firing and no fire at all. A cyl drop test is just as good. Just keep in mind that the engine will seem sound normal, running on the trailer, with only 2 or 3 cyls firing. You need all 4 firing when under load and in the water. The 4 plug coils are usually pretty reliable, so look at the timer base, stator and power pack. All are expensive, so some troubleshooting time is worth it. This website has some excellent ignition troubleshooting, specifically for your engine: cdielectronics.com

 

[Big6ft6]

Thanks EMD....I will definitly be prepared with the tools to do a drop test or spark check on the next outing.

Is there a fuel filter anywhere in these engines? Or is it up to the owner to install one in the line from the tank?

 

[emdsapmgr]

~~There is a fuel filter (screen) under the round inlet cap on the fuel pump. The screen does work, but most of us add a round, whitish in-line filter to the fuel supply hose. They work well and really do not restrict fuel flow at all. Get one from your Bombardier dealer. Needs to be 5/16" diameter (398327) inlet and outlet, unless you run 3/8" hose, then get a 3/8" filter (398319).

 

[Big6ft6]

So got out again tonight. Same problem, occurred. Initially seemed strong, drove around a while (10 minutes) shut if off and floated about 20 minutes, two minutes into drive home, rpms and power suddenly drop off. Did a cylinder drop test at slow speed in gear and all 4 cylinders are firing and contributing????

This time things did not improve, I drove the last 10 minutes back to launch without the problem resolving.

The only thing I can think of is that a high-speed jet is clogged, so slow and idle works ok, but can't go fast.....does that make sense?

 

[SigSaurP229]

It does make sense but I would think a clogged high speed jet would be more than intermittent, go to autozone or something and buy a cheap spark tester test the spark on all 4 cylinders it should snap hard be fat blue and jump a 1/2" gap. Also when you lose power have some squeeze the primer bulb to force fuel into the system see if it picks up any at all. Install an inline filter they are like $10 and well worth it.

 

[Big6ft6]

What if there is something floating around in the float bowl? Is there a bowl drain plug on these carbs? I want to check the fuel filter/screen, but it looks like I have to remove a bunch of pieces on the air horn cleaner/shroud assembly to easily get to that screen cap....any hints?

It is much tougher now with kids to deal with these things....I get about 4 minutes and 30 seconds of free time on a given night. The garbage disposal needs replacing and you can imagine which one the wife feels is more important. I'm nervous to take it to a shop because I have such low confidence, too many times on boats and cars for these types of "intermittent" problems, I take it in and pay $300 for some part or adjustment, only to have the problem come back on my next outing. When you only pay $1,500 for the whole boat it is hard to swallow investing hundreds of more dollars on a gamble that it will fix the problem.

 

[Big6ft6]

What if there is something floating around in the float bowl? Is there a bowl drain plug on these carbs? I want to check the fuel filter/screen, but it looks like I have to remove a bunch of pieces on the air horn cleaner/shroud assembly to easily get to that screen cap....any hints?

 

[Big6ft6]

OK, after watching this video...I'm just going to pull these carbs off and look inside. As the video says, getting the carbs off the motor is the harder part. Any tips?
http://youtu.be/o5cxBMDezuU

 

[itsaboattime]

Not a bad idea to check the carbs, but like emdsapmgr said, it sounds electrical to me. Those parts will work fine when cool but can develop issues after they warm up. There is a wealth of info here in the forums and at CDI for checking your electronics. If you are an auto mechanic you should be able to relate eventually to a two stroke outboard. Not trying to insult you, but they aren't rocket science. If you can change the plugs in a Ford 3 valve V8 without breaking them all off, you can fix your outboard. A factory repair Manual is a sound investment that will pay for itself in a short time.
On a side note, not related to your problem, if that boat had been sitting in storage for over a year, you may want to invest in a water pump assembly. The rubber impeller tends to not age gracefully and can reek all kinds of havoc in your power head if it comes apart. It's a less than $50.00 investment that can save you a lot of money in the future.

 

[Big6ft6]

Thanks IABT...I was misleading...I am not an auto mechanic, that is giving me WAY too much credit, I should have said "All my experience is on car engines".

I started the process of taking off the carbs tonight. Only thing I've noticed so far is
1) filter screen is perfectly clean (now that I can reach the fuel pump I checked it)
2) When I took off the black plastic air intake, it was wet on the inside with fuel???? (normal?)
2) Looking into the carb throats they look very clean
3) Linkages....what do I do with the linkages?? I can't see how to disconnect them. What do most people do?

 

[Big6ft6]

Deleted duplicate post

 

[SigSaurP229]

Start with spark test and have someone squeeze the primer bulb if its idling well the culprit is more likely the fuel pump/weak ignition. When it loses power do a cylinder drop test are any of the ignition coils cracked

 

[Big6ft6]

Thanks Sig...I did do a cylinder drop test under load on the lake during the problem. It seemed to pass. Removing any one of the 4 plug wires caused the engine to stumble. I could also hear the *tick*tick*tick* of the spark jumping to all four plugs when I pulled the boot but held it near the plug, it seemed to be jumping a healthy gap.


I know there have been two votes for electrical due to the fact symptoms appear after running, and electrical problem occur when things get hot. But what doesn't fit that theory is both times the problem occurred only after shutting off the engine and sitting:

1) The first time boat was running great, we stopped the engine for 5 - 10 minutes while I hooked up a tow rope and tube, it started right up but when I tried a hole-shot to pull the tube It had no power. After unhooking tube and rope, still had no power but slowly seemed to resolve itself on way back to launch.

2) The second time, the engine was off at least 20 minutes while we ate dinner. After dinner she started right up, we were underway at part throttle with no problem for a couple minutes when suddenly the rpms dropped and we lost power. (this is when I performed the drop test)

In both cases it doesn't seem the engine could have been that hot after spending time off and sitting? Right? (or not necessarily?)

 

[Big6ft6]

Problem solved: Not sure what the issue was, but I replaced all the fuel lines under the cowl and replaced the main supply hose to the engine (the one with the primer bulb. (it was possible kinked or collapsed at the the little clip on the outboard). I did a light reuiblt of carbs, used compressed air to blow out jets, and then finally did a sea-foam decarb treatment.

From a visual inspection all of this looked really clean, carbs were imacculate with no blockage, I could've eaten off of them. Hoses were hard, but appeared clear. Not sure what helped, but the problem is gone and have had many good boat outings with much better power and higher top speed.