Lunge and hesitation at 3000 rpm

[terykely]

I have a 1993 Evinrude Intruder 150 Spitfire. Idles a little rough, runs fairly smooth up until 3500 rpm, then lunges and surges, and dips back and forth in rpm. I can back off to 2800 rpm and smooths out. New Champion plugs, new impeller, new fuel filter. I can only put it about half throttle, then it starts acting screwy. Am I looking at carbs or power pack trouble?

 

[Bosunsmate]

Have you tried manually priming the fuel bulb while running her to act as a fuel pump

 

[racerone]

How long have you owned it ?----Did this problem develop suddenly ?-----Looked into possible warped carburetor float bowls ?

 

[terykely]

I've owned it about 3 months, been doing it since I had it. I will try priming the bulb while running and look into the float bowl issue. Thanks!

 

[terykely]

Carbs cleaned, changed out fuel lines and primer bulb. Tried it today. Primed it with the bulb when it acted up. It runs great as long as its primed. But now it boggs down and eventually stops running if it's not continually pumped up. I will let it idle for a minute, then WOT, runs great for about 8 seconds and starts bogging down. Fuel pump or pickup hose in tank possibly? Any suggestions would be appreciated.

 

[boobie]

Fuel pump..…...

 

[oldboat1]

Sounds like a fuel pump issue to me too. Might check the fuel supply, though, for water contamination. Tilting of the tank when throttling up might be a factor, but easy to check the fuel. Pump some into a glass jar and let it separate (water will settle at the bottom).

 

[terykely]

Well... back again... Changed fuel pump, changed fuel lines, changed primer bulb and location of it, removed screen in fuel tank. Runs fine at 1600 rpm, or 3000 rpm for about 1 or 2 minutes, then boggs down and dies. While that's happening, primer bulb can be pumped and the motor picks back up. Without pumping bulb, it will die. What am I missing?

 

[oldboat1]

Geez. Maybe an undersized fuel pump or undersized fuel line or lines somewhere, or fuel line collapsing, or....

Fuel tank screen removal would not avoid water issue, so still might suck up some fuel from the bottom of the tank and test it for water.

 

[flyingscott]

are you running the VRO pump or a double pump conversion? Or are you running a single pump which won't work at all. There can be issues with the double pump on the looper motors also. If.you are running anyrhing other than the VRO pump did you remove the pulse limiter?

 

[terykely]

Running VRO pump. oil side plugged. Mixing oil and gas in tank. Will drain tank and see if there's still water in it.

 

[oldboat1]

Unplugged the VRO harness? And might look into a water separating fuel filter (Racor style filter). But get any water out of the tank, as planned.

Also, check for dropped cylinder at 3500 rpm. Can do this with a repurposed timing gun, one plug wire at a time. Enlist a helper, or place the gun where you can see the flash. (no flash means no spark)

 

[terykely]

Yes, unplugged the vro harness. Does the same at 1500 rpm as well as 3000 rpm.

 

[oldboat1]

Check compression and measure spark -- post numbers. Need an open air adjustable spark tester (verifies whether there is an ignition issue). Get the spark measurement at idle. If in the neighborhood of 1/2 inch, do the drop test. Do compression test and initial spark test with all plugs removed.

Need a screw-in style compression tester, with a compression release button. Crank engine until needle stops, and record result before moving to next cylinder.

 

[flyingscott]

Look at your optical sensor.

 

[oldboat1]

https://www.maxrules.com/fixomcoisignition.html

some simple stuff too -- proper plug and plug wires, tension washer, correct power pack, etc

 

[Faztbullet]

Sounds like VST top leaking or VRO is failing...if you can pump bulb and engine picks up it not electrical,

 

[Bosunsmate]

Check vacuum/ compression values to VRO from engine. Maybe something failing there

 

[terykely]

Cleaned out fuel tank. Brown stuff in the bottom of it. Got it all cleaned out, new fuel, new oil. Primed the motor, cranked it up and within 2 or 3 minutes it went dead again. As long as I pump the bulb fast, the motor will catch up and not die. I changed all fuel lines and bulb from tank to motor. However, I used automotive 3/8" hose. Could it be collapsing and causing the issues? Seems that the old hose had a stiffer, thicker wall. I can pinch the automotive fuel hose closed with my fingers.

 

[oldboat1]

Old hose was probably just, well, old -- less flexible. I think with what you discovered in your fuel tank, the carbs need to be cleaned (disassembled, idle circuit opened, soaked in something like lacquer thinner, sprayed out with carb cleaner, and reassembled with kits.) Not as bad as it sounds.