Johnson 40, excessive smoking

[Ardjan]

Hello Everyone,

Hope I can ask my question here;

I've had my Johnson 40 (MDL: BJ40TLENJ, S/N: G03108531) for just about a year now, and all the sudden (3 days ago) I was cruising along the river when, when I reduced speed from cruise to near-idle, it started smoking badly (something it hasn't done before); lots of white/lightblue-ish smoke coming out of the upper exhaust (is it called "idle exhaust"?) from the smell, it is definately smoke and not steam.

After playing around a bit, and scratching my head a lot, it appears that when I trimmed up with the prop just under water, after +/- 30 seconds 90% of the smoke is gone, but the moment I trim down, it's back again.

I am inclined to say that smoke-production reduces slightly at higher speeds, although I haven't been able to test at WOT due to speedrestrictions close to home.

I can't think of anything obvious; I have checked and cleaned the sparkplugs, which were not extremely polluted or anything, just "used" (QL78C, they're about 6 months old) and I cannot yet tell if she's using excessive amounts of oil as I have only run the engine for about 2-3 hours since this started. Oil used is XD30 which the dealer who serviced it last winter provided me with, it has been running on it for about 20 hours since service. With this service, a new fuelpump has been fitted as well.

Would any of you be able to give me any suggestions; things I would best check to try and trace back to the cause of this sudden change?

All advice would be much appreciated.

Thank you,

Ardjan Stam
Holland

[Edit] Sorry; I forgot to add, just reading through all these forums I realise I probably don't exactly "fit the crowd" equipmentwise, but from all the site's I've come across this one definately contains a lot of valuable information; I'm hoping someone could spare a minute for me..


Modified by Ardjan at 1:40 PM 7/20/2006

[rudetech1]

Welcome to the site. Are you premixing or are you using the OMS pump? What is the water temp there, have they changed the fuel at the stations? Does it run better or worse when you trim it up?

[Ardjan]

>Welcome to the site.
Thanks

>Are you premixing or are you using the OMS pump?
OMS Pump, I myself premixed only once which was after the new fuelpump was fitted. Can't say about previous owner.

>What is the water temp there,
I'd have to check, don't have engine instrumentation, the cooling water exits at low temp, you couldn't even call it warm really, even after long cruise the water temp remains low.

>have they changed the fuel at the stations?
Now that you mention it, problems started +/- an hour after I topped up the 6 gal tank which was still about 40% full at that time. Engine started running badly (stutters, slow stalls at idle when motor was perfectly warm, things it never did before) for about 1-2 hours. This is where the smoking started as well. The problems suddenly disappeared after +/- 30 minutes, except for the excessive smoking.
I'd have to ask if they changed fuel, although I've been refilling both OB and car at this station for year(s) without any problems (or at least, as far as I noticed).

>Does it run better or worse when you trim it up?
Better. When Idling in up position it's ok, little smoke and constant RPM, but when I then trim it down, RPM drops noticably and smoke clouds start to form.

Best Regards,
Ardjan

[rudetech1]

If trimming it up lets the engine run better, you may need a little idle adjustment. The engine is more than likely running rich on fuel. Trimming the engine down richens the carb setting, fuel flows easily down hill. Trimming the engine up leans the engine out, fuel flows less effectively uphill. Make sure the cam roller on the carb is not touching the cam when adjusting the carb. If you have had any recent work done, ask the tech if he/she enrichened the carb setting. If the water is staying very cool, check the thermostat, if it is stuck open, the engine will run too cool at idle to about 1800 rpm, this allows less effective fuel burn. Check the primer solenoid on the right hand side of the engine to make sure it is not leaking. It's the device that has the red lever on it. Check the fuel lines and the tank for an air leak, any air that gets into the fuel system will make the engine pump more oil. If you have quick connects, replace them, the o-ring get dry and cracked. The new pump will pump more oil at idle than the original, it is designed this way to improve oiling thru the midrange. I run a 91' model of this engine, I have to trim up a little to maintain a good idle if I idle for a long period but the engine has a lot of time on it and needs a rebuild. Check these items, then let us know the results.

[Ardjan]

Okay, Yesterday I have checked for any leaks in the fuel/oil lines, but found no bad parts yet. I haven't been able to check for air in the fuel yet.
I did take off the air intake cover and found that it was wet on the inside, and fuel/oil mixture was leaking out from the carburator back into the air intake, and slowly dripping out into the base of the motor where I found a few drops of fuel. Though not much, I am surprised to see fuel leaking out of the air intake. I cleaned it all, put it back, let engine run for 5 minutes and took it apart again, and it clearly shows that the mixture (vapor) is "spayed" back in the intake cover in minuscule drops.
I am guessing it shouldnt be doing this?

I then I left it running without fuel line connected until it died, Rechecked the plugs, which were the same as 2 days ago; clean apart from some unburnt fuel, connected a different fuel tank, and all the sudden the problem was gone; some smoke at startup, like all 2-stroke cold engines, but after a 5 minute ride on various speeds, all smoke was gone and it now runs perfectly clean again, on the original fueltank(!)

Apart maybe from that I drained the fuelsystem from all fuel when I left it running without supply, I have no idea what it was that (seems to have) fixed it...

Thanks a buch for all the advice rudetech,

Regards,
Ardjan

[rudetech1]

There may be an air leak inside the fuel tank that caused the problem. Glad it's running good.