1983 Johnson 25 hp; spark plugs and 'commercial' model Q...

[swelego]

Hi,

Ive been reading this forum for some time but just registered, its was time.

I have a Johnson 25 (J25BACTE), which would need new spark plugs. Ill go with NGK since that is what is on the shelfs around where I live (in Sweden). Ive seen quite a few different recommendations and when I got the motor it had BUHW (either wrong or bad) plugs and the recommendations chart from NGK says BR7HS, or if the commercial version BUHXW1 another source spec BUHW-2. So my question is, which plug is the right plug?

Also, what is different about model listed as commercial?

Regards

 

[Joe Reeves]

Re: 1983 Johnson 25 hp; spark plugs and 'commercial' model Q...

I don't know which NGK plug would be correct BUT if your dealer has a interchange chart... it would be whatever NGK plug interchanges with a Champion QL77JC4.

 

[swelego]

Re: 1983 Johnson 25 hp; spark plugs and 'commercial' model Q...

Thank you for your reply Joe!

I used this NGK guide http://www.ngk.se/docs/Rek_Marin_1.1.pdf and bought a pair of BR7HS and had some luck. However I only got the engine runnig while I was looking for spark with one of the plugs unplugged, that is when I didnt mean to. No luck with em both pluged in. Dont know if it was coincidence or just (bad) luck...

What would be a reason for it start with one plug out but not with both in place?

I had this motor runnin fine (in a bucket) a couple of weeks ago with the BHUW plugs that it had when I bought it, but it was a pain in the #### to start back then too. Ive been building on the boat since then and have had no reason to start it up since.

I will try to get the right NGK plug from the Champion conversion chart!

What else can I do? I have spark, fuel and comp at least feel OK. Motor ran until fuel in it ran out with one plug (no hose connected then). What might be the problem if not the spark plugs?

Thanks

 

[Joe Reeves]

Re: 1983 Johnson 25 hp; spark plugs and 'commercial' model Q...

If the plugs in the engine are the wrong plugs, it's strange that it started at all.

Spark is to be tested with ball spark plugs removed and should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP!

If you have compression and spark, check to make sure you have good fresh fuel, and if so, the carburetor probably needs cleaning.

If someone had the flywheel off and didn't torque it down to factory specifications, the key may be sheared, in which case the engine shouldn't run at all but that area is worth checking.

If the engine is running with one spark plug disconnected (I assume both are installed)... what happens if you connect the other plug while the engine is running?

 

[swelego]

Re: 1983 Johnson 25 hp; spark plugs and 'commercial' model Q...

It's seem strange to me too, but ive had it running with both BUHW and BR7HS plugs in the last couple of days now.

About the one plug start the other day, the engine started with only one plug installed, both connected since I wanted to see if I had spark but didnt think to take em both out. That was strange too!

The carburetor seem to be OK.

Today I put the old plugs in and tried another tank and with a 100:1 mix of fuel. The other fuel is fresh, but mixed 100:2. I mixed it 100:1 because I wanted to try something else after all the trouble. It wasn't the same workout to get it runnin and it seem to run fine on that mix. As far as I know Johnson recommends a 2% mix, would it (or maybe; might it) be safe to run it on this small batch of 1% mix and then go back and try a thicker mix again? Anyone here runnin their 80s Johnson on less than a 2% mix? I use a good quality Marine oil btw.

 

[Joe Reeves]

Re: 1983 Johnson 25 hp; spark plugs and 'commercial' model Q...

DO NOT ever use a 100/1 fuel/oil mix. That setup was a goof on OMC's part that resulted in may powerhead rebuilds. Use a 50/1 mixture.

To repeat myself as apparently it was overlooked (It happens).... What happens if you connect the other plug while the engine is running?

 

[swelego]

Re: 1983 Johnson 25 hp; spark plugs and 'commercial' model Q...

OK, I'll go back to 2%!

I dont know what happens if the other plug is connected while the engine is runnin, didn't try that. Will do if I dont get it runnin as supposed next time.

Thanks!