1990 Johnson 150 gt one plug carbon fouled

[racerone]

I guess some folks are not sure where the term " crossflow " comes from.

 

[Bosunsmate]

Thanks bosons mate and racer one I will rebuild the carbs also how difficult is it to change the reed valves I have never went that far before

Its easy to do but you probably wont have too. just look at them and compare them to the ones that feed cylinder one.
If you notice any big difference then you will then learn that they are easy to fix.
Just shine a torch on them and look for any gaps that are bigger or smaller than on the other side

 

[Bosunsmate]

I wouldnt bother rebuilding the carbs, just get some carb cleaner and poke the little plastic tube down every single tiny hole you see and the ones behind every screw that backs out to reveal a jet inside, and make sure that the carb cleaner blows out another hole, if it doesnt then theres a blockage

 

[V153]

I guess some folks are not sure where the term " crossflow " comes from.

If I'm not mistaken crossflow means what OMC called "cross scavenge". Describing how the fuel & exhaust flowed through the cylinder. As opposed to say a "looper" design?

 

[racerone]

Correct that is the " crossflow " designation.

 

[Gkm70526]

I will pull the carbs and check the reed valves I appreciate all the help

 

[Bosunsmate]

No Title

V153 Heres a crossflow piston. The incoming fuel air mix hits the steep side on the left and goes to the top of the cylinder to be ignited/burnt. The gentle sloping side is where the burnt gases go down and out the exhaust. (So the flow goes across the piston from entry to exit- hence the term crossflow.)
A looper has some kind of swirly thing going on and the pistons have a flattish top and cuts on the bottom of them to open/close/block off exhaust/inlet ports

 

[Bosunsmate]

No Title

Heres a looper

 

[V153]

I would disassemble & thoroughly clean the carb(s). Mebbe soak em in a gal of Berrymans, etc. For a couple days beforehand.

Yes. Blow through the orifices with carb clean but be careful with compressed air. Think they say no more than 25 psi.

Fwiw I've never yet had to remove/replace the 'welch' plug to get em to run?

 

[emdsapmgr]

When you tested for spark on #2, was the engine cold, or was it warmed up to normal operating temps? It can make a difference. Is the engine miss at idle or at speed when the boat is on plane?

 

[Faztbullet]

Only loopers have the X flow intake(opposite side feed) crossflows do not. Index the flywheel and take a timing light and check cylinder timing when running as a double firing pack or SCR in timer base can cause a plug to fire late and produce miss and dry plug...

 

[Gkm70526]

Emdsamgr I ran it on muffs at home and warmed motor up before doing compression check and spark test on #2 cylinder. I haven't put it in the water since changing the plugs

 

[Gkm70526]

Faztbullet would adjusting the flywheel throw my other five cylinders off?

 

[boobie]

How do adjust a flywheel ??

 

[Gkm70526]

Boobie I am not sure.

 

[racerone]

????------Indexing the flywheel refers to the owner marking TDC for each cylinder.---Then using a timing light to check that each cylinder is firing once per revolution and at the correct time !

 

[Gkm70526]

Ok I have an update I pulled the carb off and inspected the reed valves they are all in visible excellent shape I will clean the carbs another day and see if that helps

 

[emdsapmgr]

The reason I asked whether the engine was warmed up-was because weak ignition problems tend to appear once the engine warms up to normal operating temps. May run fine when cold, the drop a cyl when it is warmed up. That engine will seem to run just fine on the trailer when running or 3 or 4 or 5 cyls. It's when it's under load in the lake, that you find one plug is not firing. You may want to run it in the dark and see if you've got a spark jumping to ground from the #2 wire.

 

[V153]

Indexing the flywheel refers to the owner marking TDC for each cylinder.---Then using a timing light to check that each cylinder is firing once per revolution and at the correct time

Correct. And/or not double firing.

Looks like so: (But yours would have numbers 1-6 ...)

If one number superimposes over another you have a double fire condition.