Johnson 150 WOT issue, maybe??

[jaxdad]

Re: Johnson 150 WOT issue, maybe??

A 22 pitch 4 blade is not an unusual prop pitch for an XP/GT. Maybe you have the engine mounted too low on the transom. If it is the correct height, you may want to try a 21 (or even a 19) to get the rpm's up a little. To me, you are lugging the engine at 5000. You gain 150 rpm when you go down in prop pitch, like from a 22 to a 21. When you say you are replacing the ignition module, I am assuming you mean the power pack. Likely that will cure your problem.

the motor is on a 6" jackplate, and the seam where the lower unit meets the mid section is level with bottom of boat.. I was afraid to get it to high and transom block any water flow to water intake area as it is not a tunnel hull...the boat is a 19' long, 80" wide bottom (96"wide at top of rails) aluminum custom flat bottom boat (3/16" thickness hull)..

 

[wilde1j]

Re: Johnson 150 WOT issue, maybe??

It's likely way too deep. The AV plate should just ride dry on top when height is right.

 

[emdsapmgr]

Re: Johnson 150 WOT issue, maybe??

Follow Wilde's recommendation on engine height mounting. If the engine is mounted too low, you will have excess water spray from the lower unit. The significant excess drag from the water can slow your rpm's down to the 5100 figure you cited. Is your jackplate a fixed height model, or electronically variable?

 

[jaxdad]

Re: Johnson 150 WOT issue, maybe??

another update..

another on water test and again right off trailer nothing above 3000 RPM.. rechecked all wires and all appear to be tight, good connections and no pins "backing out" of any boot connection. did the "jiggle" test of kill switch laynard/connection point and no change. At ignition packs i disconnected the single Black/Yellow wire (kill switch wire) and NO change. Shut off and unhooked wiring harness and installed test harness/key switch and still no change.. Checked Spark plug wires with inductive timing light again and found same bottom cylinder very intermittent along with top and middle cylinders sparking but had some misses to it according to the flash pattern of timing light. With Spark Gap tester set on 7/16" top and middle cylinder appeared ok, but not great, then the bottom cylinder was weak but would hit occasionally. These issues were all on left side as facing the motor from back, the right side was great all around,no issues..

have not installed new ignition pack, but about to and retest.. again it still starts right up and no issues or hard starts, and throttles quickly to the 3000 RPM without a sound of a miss by ear.. got fingers crossed on the pack working..

(emdsapmgr) jackplate is a manual lift style, not hydraulic, and not single position style..so there is some room for adjustment, and as soon as i can get this motor running good again i'll see how much i can raise the motor to "un"bury it...

 

[jaxdad]

Re: Johnson 150 WOT issue, maybe??

ok so today used the multiple spark gap tester to see all 3 cylinders per side fire at same time, versus the single unit i have.. here is what i found.. Cylinders 2,4,6 - 2,4 seemed weak, unless 6 failed to fire then they seemed better.. 6 seemed weak when firing and also had times where it would not fire for several cycles. Moved #6 ignition wire from pack to #4 and vice versa.. Then #4 would fall out and #6 would stay constant but weak.. Cylinders 1,3,5 all fired great and spark was bright blue/white and strong, no apparent misses seen..

Switched ignition packs to opposite sides.. 2,4,6 now strong and no apparent misses.. 1,3,5 now had spark falling out and missing and appeared much weaker than 2,4,6 side was now.. Multiple tester i had has 4 locations so i hooked #6 up while 1,3,5 were hooked up and could really see the difference as #6 was much stronger spark than any on 1,3,5...

Changed Ignition Pack out and all cylinders had strong spark and no apparent misses on either side... So now for the on water testing and see how it does.. got my fingers crossed..

thanks again everybody..

 

[emdsapmgr]

Re: Johnson 150 WOT issue, maybe??

I noted on your earlier post that you may have adjusted the idle when on the trailer. Now that you are running on all 6 cyls again, you may need to readjust it when you go out on the water. That engine should idle between 650 and 750, set when floating normally in the lake, in forward gear. You can't set it on the trailer.

 

[jaxdad]

Re: Johnson 150 WOT issue, maybe??

on water test today..

It ran pretty good and response to throttle seemed better than ever. Ran approximately 4 gallons of fuel through it. Initially set idle at 900-1000 in neutral. Once away from dock and floating, shut motor off and restarted, placed into gear, but no gas and checked RPM then - right at 700 RPM. Then came the testing under various loads, Tried WOT for couple miles, Idled for a few minutes, got on plane and cut throttle back a ways and ran a while, numerous starts and stops from still position, a few WOT from slower moving speed. ALL seemed well and no issues..

Did notice 2 things with test however, initially on startup (before idle set) it was a little hard to start (cranked longer than usual) and was running rough when it started.. after it warmed up it smoothed out and no issues at all.. Could this have been from all the testing/cranking out of water testing the compression and spark? it was almost as if it wasn't getting fuel or something, when it did it started but briefly acted as if if had an air pocket or something.

2nd item was it still would not get above 5000 RPM, which has been normal for this motor even before issues with bogging down to 3000 RPM... I still have not adjusted motor up or verified the depth of AV plate. will test again tuesday with fishing partner and verify depth etc to see about moving up and how far, maybe this will cure the 5000 RPM max to the 5500 RPM we need..
thanks for everyone's help, so far with new Ignition Pack it's good, will know more after tuesday's on water test..

 

[jaxdad]

Re: Johnson 150 WOT issue, maybe??

another water test today, about 4 gallons of fuel run through it today.. started and ran fine... had one time where it seemed to "bog" for a split second but never dropped down to 3000 RPM like before.. and it was only just long enough to realize something changed.. we also noticed once at start up a "sneeze" sound from motor, it only did it once, after warmed up, and probably around the 7 or 8 time we started it during test..
It did only max out at 5000 rpm again, but did check the AV plate depth and it is buried under water, not near top as needed.. when on plane and pretty much trimmed where needed the water was right at or just below the "pinstriping" line just above small edge, probably 2-3inches above AV plate.. maybe this accounts for the 5000 RPM max??? will be raising 2" tonight and retest tomorrow.

With GPS in hand (actually on console) we were running 5000 RPM, trimmed as best we could get it (water choppy with some white caps on Ohio River) and GPS read 47.6 MPH.. not bad we thought for a 19' 80"wide flat bottom/Flat nose aluminum "barge" with a 4 blade stainless prop.... might be able to swing 50 mph if we get motor a little higher with jackplate and can turn 500 more rpm..

we'll keep ya'll updated as to any changes, or advancements..

 

[wilde1j]

Re: Johnson 150 WOT issue, maybe??

Your motor should turn ~5800 @ WOT when motor height is right and propped right. Getting the height right will pick up some speed and RPM, but I doubt anywhere near 800 RPM. Probably a three bladed prop would work better than what you've got. (four bladed props are usually used on heavy boats, not light aluminum ones.

 

[jaxdad]

Re: Johnson 150 WOT issue, maybe??

wilde1j, thanks for the advice.. as soon as we get the motor moved up some we are gonna try to see if the rpm comes up any at all.. like i said it is buried right now, because the pinstripe line is actually a little above the split where the lower unit and midsection area come together.. so we got somewhere between 2-3 inches we can raise motor safely..

we are hoping that between the depth of motor and 4 blade prop that they are cause of 5000rpm issue, and not something else.. we however like the 4 blade prop for its ability to get us out of the hole and on plane with the large loads we have sometimes of fish (over 1000 pounds).. we were afraid a 3 blade would create so much more work to get a load like that on plane.. but then again we have never tried a 3 blade, so maybe the right pitch and diameter three blade would work well also.. the other reason for 4 blade was that's what we had around to fit the motor without having to buy another one..so its all a work in progress.. i think a buddy has a 3 blade spare to fit this motor, i may look at specs and take with us this weekend to tournament and if we "load" the boat, may switch props out and try to see how it does with everything..

thanks again everyone!