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120hp v4 evinrude will not exceed 2800 rpm's under load

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mypuchyo321

New member
Hi guys,

Im at a loss. I own a 1992 Evinrude 120hp V4 VRO. The engine revs fine in neutral and reverse however while going forward the RPM's will not exceed 2800 rpms....and this is constant....from cold to hot hour to hour it never planes out or goes past 2800. I have checked while the boat is running and verified the butterfly valves are wide open and the ignition is advanced. I have replaced all the fuel and oil lines, the plugs, rebulit all the carbs, the primer bulb. I have good spark on all four cylinder as well as good compression ranging between 115-135. I have tried ditching the onboard tank and went with a portable tank today and it made no difference. My next step will be to eliminate my vro I feel like it may be choking my engine with excessive oil. what scares me is people talking about S.L.O.W mode and a bad power pack.

So my questions are any advice on getting my boat to go fast? Also, how can I test too see if I am in slow mode and if the power pack is bad?

Thanks,
Bryan
 
Look into issues with crankcase compression.------Check flywheel key.---Check flywheel magnets.
 
Last edited:
Docksidemarineservices said:
You will need an analog volt meter or a Digital Meter with a Peak reading adapter for testing.

This will help you.

https://issuu.com/cdielectronics/docs/practical_ouboard_ignition_troubles
Click to expand...


Thanks, thats a good guide. I checked the flywheel key and magnets are good. Ive replaced the power pack and all ignition coils. Compression is between 115-135....also a cheap tester could be better then that reading. How do you test crankcase compression? The bottom right cylinder has had no spark in the past intermittently. Seems fine now with new coil and power pack. Ohm reading on timer base seems good. Stator has continuity, its charging the battery and I have spark.(didn't have ohm specs) Carb bowls rechecked, good, no pinched fuel lines, ran portable and onboard tank. VRO rebuilt and verified no tears....pumps hard enough to implode the portable tank. Reeds verified not stuck. I don't know how to lync and sync however, the timer base advances first then the butterfly valves open to 90degrees, cam roller replaced. Idles and runs smooth to 2800rpms looks like 2900-3000 now. One weird thing that made me think fuel issue is at WOT (and its stuck at the usual 2900), if I push in the key too activate the electric primer the rpms surge too 3800 then the ignition starts skipping and retards the motor too keep it from accelerating past 3800rpms. but cranking the primer bulb dosent help either. Also theres no adjustments too make the carbs spray richer if it is starved. My new idea is too have my buddy drive the boat while I advance the timing further....can I over advance and cause damage? oh and I've seen the slow mode videos where the ignition acts like a rev limiter I am def not in slow mode...just no power. I'm running low on ideas thanks for your help guys.
 
mypuchyo321 said:
replaced the power pack and all ignition coils
Compression is between 115-135.
Ohm reading on timer base seems good.
Stator has continuity
Carb bowls rechecked, good, no pinched fuel lines, ran portable and onboard tank.
VRO rebuilt and verified no tears....pumps hard enough to implode the portable tank.
Reeds verified not stuck.
....at WOT if I push in the key too activate the electric primer the rpms surge too 3800 then the ignition starts skipping and retards the motor
Click to expand...

Do you get any warning sounds when the skip and retard happens? The fact that a squirt of the choke primer bumps RPM to 3800 tells me this could be a fuel delivery issue.

When you say the bulb "pumps hard enough to implode the portable tank" has me very curious. When you're running that WOT 2800RPM, does your primer bulb collapse? If you can make the portable tank implode, that means you're pulling a vacuum on the tank. Any fuel tank, portable or permanent, should NEVER pull a vacuum.

I would go through the entire fuel system and looks for restrictions at any point.

KJ
 
kevinj said:
Do you get any warning sounds when the skip and retard happens? The fact that a squirt of the choke primer bumps RPM to 3800 tells me this could be a fuel delivery issue.

When you say the bulb "pumps hard enough to implode the portable tank" has me very curious. When you're running that WOT 2800RPM, does your primer bulb collapse? If you can make the portable tank implode, that means you're pulling a vacuum on the tank. Any fuel tank, portable or permanent, should NEVER pull a vacuum.

I would go through the entire fuel system and looks for restrictions at any point.

KJ
Click to expand...

The alarm did not sound when I hit the primer. I didn't collapse the portable tank with the primer bulb. The VRO did it because I didn't open the vent on the tank. The primer bulb goes soft when its running but it dosent implode. I figured since the pump was able to implode the portable that it was safe to say the pump was strong. I feel like its fuel delivery too ever since the primer squirt gave it a boost but I've done all the lines new, got a new primer bulb, ran my own 50:1 mix, rebuilt the carbs three times to be sure I didn't miss anything, rebuilt the VRO for no reason just to be sure, I pushed on all the reeds to make sure they weren't stuck. I almost feel like the engine has got something going on that it won't suck hard enough to draw in enough fuel. Ive ran it with the air box off and it wasn't drawing in full fuel, Ive seen a video of one at full throttle and you could see how much gas it draws in....mine is not drawing in maximum gas from the carbs. Is there part of the fuel system I am missing? Also I was thinking if I advance the ignition and get the rpms up a little it will draw more fuel and go.

-Bryan
 
So I figured out the problem. One of the carbs had a 38D high speed jet (too small). Put in a 63D and she finally went fast. Did 30 something at about 4800rpms. So I was happy and pumped and second time out it died out and became a 2800 rpm 3cylinder again.... So carb jets check ignition check....do a compression test and one of my cylinders has dropped from 125psi to 98psi so 28psi lost. Pull the head and the cylinder is tore up a bit. So I'm taking some pics and will post a new thread tomorrow asking 1. can I hone it and do rings? 2. is it too far gone? 3. why did it happen? FML this is my first boat/outboard
 
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