'94 120 hp will not go above 3000 rpm

[k9hunter]

had idle problems, seem to have gotten them resolved now in gear will not go above 2899 - 3000 rpm. So far, rebuilt all 4 carbs and VRO fuel pump. Checked compression 138 - 142 psi on all 4 cyls. Checked spark all 4 have nice bright blue spark across 7/16" gap. Idle seems really stable at ~800-1000 rpm, even when hot. in neutral motor rev's well, under load (in gear) will not go above 2800- 3000 rpm. boat will not get on plane. removed plugs and looking at motor from rear, right bank looks good, no fouling, left bank both plugs looked fouled, covered in carbon, top cyl is the worst. any suggestions on what to check next?

 

[jonesg]

Re: '94 120 hp will not go above 3000 rpm

Seafoam it,
draw some fuel and check for contamination.
Make sure butterfly valves in the carbs are at 90deg level when throttle is wide open.
Is it link and sync'd?

 

[k9hunter]

Re: '94 120 hp will not go above 3000 rpm

did find water in fuel, pumped out until only gas came out as well topped off with additional gas and stabil marine additive. did add seafoam to cyl's and let soak for over an hr. flushed seafoam out and ran until heavy smoke stopped. after this is when I put it in the lake and tweaked to ge tto idle. did a link and sync last yr, checked butterflies, still @90* at WOT.

 

[ezeke]

Re: '94 120 hp will not go above 3000 rpm

You might be in S.L.O.W. mode if your temperature switches are faulty or if you are running too hot.

Are you over-propped?

 

[kenmyfam]

Re: '94 120 hp will not go above 3000 rpm

Agree ^^^^ S.L.O.W. mode sounds likely.

 

[k9hunter]

Re: '94 120 hp will not go above 3000 rpm

original prop no issues with that in the past, as for temp switches, i did run hot last yr, replaced water pump in march. doesnt appear to be hot now, no alarm and water from pee hole warm but not to terribly bad. Will investigate the switches. would this be the same as the thermostats or other switch. just talked about putting a temp gage instead of alarms. they are good, but i am a visual guy.

Addionally, will motor rev past the 2800-3000 rpm while not under load but still have S.L.O.W. mode active? As mentioned in neautral, motor revs with no problem, only under load in gear i have this issue.

 

[k9hunter]

Re: '94 120 hp will not go above 3000 rpm

checked both temp. sensors, no continuity while "cold" on over temp circuit. 1 sensor has 2 wires, 1tan and 1 white / black wire, believe this is for warm up. when removed from power head contacts were made and had coninuity on white / black wire, after sitting in garage for a few mins, no continuity. (buzzer on fluke meter stopped sounding).

Have to take to lake to test SLOW mode, will do so on next trip, but expect it to be working ok and motor still not reach rpm's above the 2800-3000 range..

ezeke...Back to running hot, last time in water, Thursday afternoon, motor ran at dock for a while to "remove" water from fuel lines. extended high idle time could b a culprit. additionally, exhaust port at bottom of cover, water mist was observed from port. could not enough water be going into cooling system and leaking into seal in lower unit for exhaust? will have to check, but flow from pee hole appears to be "normal".

 

[ezeke]

Re: '94 120 hp will not go above 3000 rpm

The tell tale lets you know that the waterpump is working but tells you nothing about the passage of water through the cooling circuit of the engine.

The thermostats need to be working properly and the cylinder heads should stay around 140 degrees; you should be able to keep your fingers on the cylinder heads for a full three count (no more or you risk third degree burns) any time the engine is running.

The black and white wire controls QuikStart, which advances the tiiming for a cold start. The tan wires that run to the powerpack control S.L.O.W., turning it on when the engine overheats at around 203 degrees. The temperature switches tan wires close to ground when there is an overheat, otherwise they are open.

The switch with the black and white wire closes at 96 degrees, grounds that wire and turns off QuikStart if it is working correctly.

 

[k9hunter]

Re: '94 120 hp will not go above 3000 rpm

Thermostats seem to be working properly. Tested with an ohm meter, boiling water and a thermometer.

my details about the tell tale were not intended to assume everything was ok with water passages, but my question was regarding the water mist coming from the exhaust port at the bottom of the cover. I do not remember water misting from there also, when hooked to muffs, I get a lot of water leaking from lower unit and it takes time to get water flowing from the tell tale. I do not believe I have good seals from pump to tube to power head and wondered could this cause motor to run hotter. Next time out, I will use a temperature gun to check temp of top of power head. So far everything checked comes up working as should. Any more possibilities?

 

[k9hunter]

Re: '94 120 hp will not go above 3000 rpm

Problems continue.... Got back to the water Thursday. Took a little while to start, when did smoked a lot and sputter for several mins. Finally cleared up and engine smoothed out. Idle appears a little high (~900 - 1000 rpm in neutral) but smooth. Let motor get to temperature. Head on port side running much cooler then starboard. Could touch and leave hand on pretty much indefinitely, however starboard head very hot and could only touch for a few secs. FYI plugs on port side carboned up bad where starboard plugs clean. Disabled temp. Sensors and left dock. Same problem, motor would not get above ~2800 rpm (still smooth). Came back to dock and looked into testing power pack. Check connections, everything seems ok. After an hr or so of investigating, decided to call it quits for the day. Went to start and get back on trailer. Motor would not start at all. Checked spark had none on all 4 cyls. Friday, in the yard, checked spark again initially had none on port and weak inconsistent on starboard. Checked all 4 several times, spark was very erratic and appears weak. Sunday will check in more detail power pack, trigger and stator.

Anyone got a clue what might be happening? Please suggest.....

 

[ezeke]

Re: '94 120 hp will not go above 3000 rpm

Thermostats seem to be working properly. Tested with an ohm meter, boiling water and a thermometer.

my details about the tell tale were not intended to assume everything was ok with water passages, but my question was regarding the water mist coming from the exhaust port at the bottom of the cover. I do not remember water misting from there also, when hooked to muffs, I get a lot of water leaking from lower unit and it takes time to get water flowing from the tell tale. I do not believe I have good seals from pump to tube to power head and wondered could this cause motor to run hotter. Next time out, I will use a temperature gun to check temp of top of power head. So far everything checked comes up working as should. Any more possibilities?

Thermostats are not temperature switches; the thermostats are under the covers with the four screws at the tops of the cylinder heads. Those need to be checked and tested.

 

[k9hunter]

Re: '94 120 hp will not go above 3000 rpm

I check and tested the temperature sending units or temp. sensors as others call them. I also checked the thermostats 2 different items. I know this. I have ruled out the electrical problem being related to temperature. Appears to be in either stator, trigger or powerpack. Thought someone might have some suggestions related to that.

 

[ezeke]

Re: '94 120 hp will not go above 3000 rpm

If you have removed and cleaned all of the connections with no improvement, test the powerpack; it's probably bad. You need a peak reading voltmeter. See the "power pack test" instructions in your service manual's ignition system section.

You might also want to check the flywheel to be sure that the sensor magnets have not moved.

 

[k9hunter]

Re: '94 120 hp will not go above 3000 rpm

Tested power pack and had no voltage on port side, erratic on starboard. ordered new power pack and installed. fired right up with no hesitation and idled fine although a little high. going to water tomorrow to test and may have to tweak the timing. at high idle on muffs (~1100 rpm which was as low as it would go) timing at 4ATDC, specs say 8 in forward gear. didnt want to run too long on muffs and motor has no load on it. will post results after test run. so far so good

 

[kenmyfam]

Re: '94 120 hp will not go above 3000 rpm

Sounds promising. Good Luck.

 

[ezeke]

Re: '94 120 hp will not go above 3000 rpm

Tested power pack and had no voltage on port side, erratic on starboard. ordered new power pack and installed. fired right up with no hesitation and idled fine although a little high. going to water tomorrow to test and may have to tweak the timing. at high idle on muffs (~1100 rpm which was as low as it would go) timing at 4ATDC, specs say 8 in forward gear. didnt want to run too long on muffs and motor has no load on it. will post results after test run. so far so good

It's probably not the timing but that QuikStart is not releasing the timing advance. Test the the temperature switch with the black and white wire and make sure that the balck and white wire goes to ground at 96 degrees. Also check that there is no voltage on the red and yellow wire except when the starter is engaged.

You should hear and feel the engine slow down when the 96 degree temperature is reached.

 

[k9hunter]

Re: '94 120 hp will not go above 3000 rpm

Well took her to the water and would not start. After several attempts and finally just removing and wiping plugs off, got her to fire up. ran fair at the dock but did have a miss or skip. Took out on the water and same problem....~2800 rpm no more. After cruising around like that for a few mins, she kinda coughed and rpm's increased slightly. It did this cough a few times until finally we were up on plane and around 5500ish rpm. shut down and restarted several times went right back to running fine. unfortunately it was dark so didn?t run very long. going back tomorrow for a second try and keeping fingers crossed.

looked at quick start circuit again and found nothing out of the ordinary. here in SC we have been having many days in the high 90's to low 100's. just sitting in the yard with the sun beating on her, the temp on the heads is above the 96 degree threshold so even cold the quick start circuit should be bypassed.

will post next results

 

[ezeke]

Re: '94 120 hp will not go above 3000 rpm

It's water temp, not air temp, but QuikStart engages every time you restart the engine, hot or not. If the system is not working correctly, QuikStart will not disengage no matter how hot the engine gets.

S.L.O.W. is controlled by the same wires that control the warning horn when the engine overheats.

Anyway, run the powerpack tests.

If you have an inductive timing light, it's easy to "read" the spark through the range of RPM so that you can see when it's breaking down.

 

[k9hunter]

Re: '94 120 hp will not go above 3000 rpm

saga continues..... Still starting and running through rpms fine with no load. in forward gear did the same as last post. coughed and rpms would slightly increase until it would get to ~5500 rpm. could shut down, re-start and no problems reach 5500 rpm again. idle would be low (~500 RPM) and had an obvious miss. would not stay running. Adjusted idle by advancing idle 1 to 2 degrees as manual describes, but nothing. set back to 7 degrees where it seemed most stable. went to run, again would not get above ~2800 rpm. tested temp sensors again by disabling. nothing, grounded quickstart, nothing. Back at dock checked spark again. it was getting dark so spark with gap tester easy to see. 3 cyl's bright blue spark and very consistant. 1 cyl spark not as bright and erratic. occasionally would get bright but still erratic (miss). When home checked trigger or sensor coil. on low side cranking volts seem low on all 4 and different on 1 w/ erratic low spark. resistance in the middle of spec on all 4 and no apparent short to ground.

next thought, which I mentioned early on in post, from exhaust port in lower motor cover there is a mist of water, I don?t believe there is a head gasket leak since all compression was within 4 psi of each other (138 - 142) but not sure where its coming from or if it is contributing to.

Next steps / thoughts anyone?

 

[k9hunter]

Re: '94 120 hp will not go above 3000 rpm

Well things have improved. Found powerpak to be faulty. replaced with new and things were much better, Still had very weak spark on #3 cyl. tested timer base (looked good) and stator (resistance out of spec low). Went ahead adn replaced both stator and timer base. engine smoothed out and idle great (~750 rpm out of water on muffs, ~650 - 700 in water). left dock and same problem engine would not get above ~ 3000 rpm. After a few mins at full throttle, but 3000 rpm, it once again acted liek it coughed adn rpms picked up to 5500 adn stayed this way the rest of the trip (~3.5 to 4 hrs). Would stop engine and let cool, would start right back up and always went to high rpms. Will try again tomorrow. hope things go well.

1 question for all, what could make the engine at initial start up and for maybe 10 - 15 mins, restrict the rpms to 3000 and then all of a sudden go through the full rpm range with no problem up to 5500? It acts as if a switch is all of a sudden made "good". I have checked the quickstart and found it to be working correct as well tested teh over temp sensors which also seem ok. kinda ruled out over temp. sensors since it does the total opposite of what this circuit is designe to do. Next steps look in carb bowls fro "debris" and at the recirculation valves. Not sure where to go from there.