I a$$ume that you've performed a compression check of all cylinders (what were the psi readings of those individual cylinders? Also a$$uming that you did a spark test to see that the spark was jumping across a 7/16" gap with a strong blue lightning like flame... a real SNAP!.... If not, do so as these two areas are the very beginning of the trouble shooting procedure.

Spark plugs should be Champion QL77JC4 plugs gaped at either .030 (long life) or .040 (strong spark)

NOTE that on that 1987 model, as you're probably already aware... the spark plugs must be left in during a compression check, removing only the spark plug of the cylinder you're testing, otherwise the starter bendix will kick out on every revolution.

Have "all" of the spark plugs removed for the spark test.

The carburetor(s) rebuild job you did earlier this year.... did the engine run normally for a time after that job... OR... did this 3400 rpm condition exist immediately thereafter?

In a tight turn as you describe (I used to do that test myself)... the only change that is being made to the engine is the level/angle of the fuel within the float chamber and the float itself........ making a bit of clogging debris move around possibly, unblocking a small high speed jet? (it happens)

Make sure that the compression is as it should be... perfect would be 95 psi on the starboard bank with 90 psi on the port bank... then do the spark test using the 7/16" air gap.

Air gap spark testers can usually be fount at any auto parts store... or you can build the following, modifying for any number of cylinders.

(Spark Tester - Home Made)
(J. Reeves)

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

..........X1..........X2

.................X..(grd)

..........X3..........X4

Let me know what you find.

225 johnson won't go over 3400 rpm

Thanks for your reply joe. The rpm problem started from the first day I put the boat in this year. I had cleaned the carbs a few years ago and had no problem. Maybe I missed something, I soaked the carbs in a strong solution of dawn dish soap and water and used compressed air to dry them. Can I use an automotive compression tester? Should I disconnect the coils to run the test? I will also check the spark as you reccomended. I might not be able to run all the tests until the weekend. I'll let you know how I made out.

Any compression gauge will do.

On the compression test, have the key turned to OFF.

Crank the engine by using a small jumper wire from the battery cable terminal of the starter solenoid to the small 3/8" nut terminal that engages it.. NOT the 3/8" nut terminal that leads to ground....... no need to be disconnecting coils or whatnot.

Dawn is a good detergent (I use it) BUT it won't clean those carburetors. Many auto parts stores have carburetor cleaner in a one gallon can complete with a small basket. I tried one... works great but too small to handle more than one carburetor at a time... about $20 or so.

The high speed jets (6 of them)... carefully clean them with a piece of single strand steel wire. They're located horizontally in the bottom center of the float chambers... way in back of the drain screws. They unscrew if need be... 1/4x20 threads. When installing, snug them tight.

Shape a jet screwdriver tip like this special tool that has a shank just the right fit to go inside those 1/4x20 threads of the drain screws.

hey joe i was afraid to use a solvent base cleaner with plastic carbs, didn't know if it would affect them in some way. Is the reason not to use the ignition switch to turn the motor during the comp. test to keep the ignition system off?

Oh geeze yeah... plastic carburetors. I forgot about that, sorry.

And yes... it's best NOT to have the ignition engaged.

joe i just did the compression and spark tests. port side from the top cylinder down 92, 90, 90. starboard side top cylinder down 85, 85, 86. spark was good on all cylinders. engine was warm and throttle about 1/2 open on compression test. also cleaned and rechecked gap on spark plugs, .035. let me know what you think, thanks joe.

Compression psi varies from gauge to gauge and also the speed upon which the engine is cranked over... the readings you gave are average for the V6 Looper. You say that the spark was "good" but not whether it jumped a 7/16" gap or not... I will assume that it did...... That leaves the carburetors.

I'd suspect that at least one high speed jet is fouled.... Horizontal, in the bottom center of the float chambers, in back of the drain screws. They are secured via 1/4x20 threads and can be removed via a tool as shown above (post #4). Clean carefully with a piece if single strand steel wire. When installing, snug tight.

Usually a difference in appearance of a spark plug will reveal which carburetor might have that fouled jet.

joe, the plugs were all consistant in color . no signs of fouling. you think i would remember where the high speed jets are i just had them apart a month ago. this getting old stuff is for the birds. do i have to remove the carbs to get at them?

When the throttle (control box) is set to full throttle, are "all" of the throttle butterflies wide open?

Yeah...getting old... I agree. The "Go*den Years" sucks!... 85 on Aug 6th.

No need to remove the carburetors. You can get at the HS jets via the drain screw hole... location - horizontal, bottom center of the float chamber.

If the HS jets were okay a month ago, they should still be okay. However, that's what your explanation of the problem points to, and the first thing I'd be looking at if it were me.

Take notice of the fuel that runs out of the carburetors when you remove the drain screw..... wondering if possibly (if the HS jets are okay) debris in the fuel line could have jammed at the float needle valve resulting in very little or no fuel being supplied to one carburetor.
************************
Check the continuity of the coils:
(Magneto Capacitance Discharge Coils - Continuity Test))
(J. Reeves)

Check the continuity of the ignition coils. Remove the primary orange wire from whatever it's connected to. It may be connected to a powerpack screw type terminal, a rubber plug connector, or it may simply plug onto a small boss terminal of the coil itself.

Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground of the coil or the powerhead itself if the coil is still installed.

Then touch (still with the red lead) the orange wire if it's attached to the coil, or if it's not attached, touch the primary stud of the coil. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire. Poor or no continuity of a coil is one reason for s/plug fouling.

1987 johnson won't go over 3400 rpm

joe been meaning to get back here since the first week of july. I used the boat for three days in a row on the holiday weekend. the engine fixed itself, i get full throttle and good low speed without misfires. the only issue i get is at low rpm around 1000 to about 2100 is what i'll call a surge in the rpms. for a second the tach will move a little and you can feel the boat speed up. this happens for only a second. seems to be more prevalent when the boat sits for a couple of days.we have about a fifteen minute ride out of the harbor at low rpms and this surge seems to go away about 10 mins. into the ride and sometimes sooner.I also smacked a rock on the third day of the holiday weekend, we boat in the thimble islands here in ct. and the rocks here like to move around. no damage just the skeg got roughed up a little.