84 Evinrude bogging full throttle surge

[Rmillis]

84 Evinrude what I believe to be a 30hp( bought used has johnson 25 hood black engine crankcase with silver/grey carburetor mount) manual start.

Purchased engine with broke shift lever. Fixed that, never heard engine run prior to purchasing. Did the usual after fixing shift lever. Cleaned carburetor ( was already clean) verified float level and orientation, cleaned /checked fuel pump for cracks and debris(all clean), replaced plugs with OE replacements, replaced spark plug wires ( found one bad). Ran ok in tank idle all day, no abvious misfire.
On the water starts fine, upon throttle up about 1/4 throttle boat begins to accelerate and just boggs... like it looses fire on one cylinder or is excessively rich. Forgot to mention if it really matters. Boat is 14ft aluminum jon boat.
After holding full throttle for 5-10 seconds engine seems to have what I think is 1/3 engine power and boat begins to plane off( just one person). After boat planes throttle still wot, engine will sporadically surge, to full engine power, like almost throws me out the boat.( oh crap momment...) during this full power mode engine runs great for however long g it decides to then slows and surges back to full speed again. It's not consistent on how long it runs good at wot, sometimes 1 second sometimes 4 minutes.
Fuel mix is good, checked fuel for water and ethanol Content.
Replaced power pack no change. Replaced cracked charge coil no change. Replaced trigger coil no change. Replaced one ignition coil whi h tested fine with ohm meter but housing had a small crack, no change. All new parts still on engine with bogging surging problem. Carburetor is clean, good fuel pattern in barrel under full throttle, adding full under wot makes it worse. Choke plate is gone. Fuel bulb stays firm, doesn't help if I pump bulb. All fuel hose connections tight.
At idle timing is 8 btdc. It does advance but I can't see to wha t while driving and trying to control this beast as it decides to hit fill power....
Tried watching spark on oscilloscope, looks good as compared to what a known 4 stroke pattern should look like at idle. Pulled plugs after taking it out both relatively dry, not wet..
Stumped.... any suggestions GREATLY APPRECIATED....

 

[tphoyt]

Just for kicks mark your prop and hub take her for run and see if the marks are still aligned. You may have a spun hub that is slipping.

 

[saltchuckmatt]

84 Evinrude what I believe to be a 30hp( bought used has johnson 25 hood black engine crankcase with silver/grey carburetor mount) manual start.

Purchased engine with broke shift lever. Fixed that, never heard engine run prior to purchasing. Did the usual after fixing shift lever. Cleaned carburetor ( was already clean) verified float level and orientation, cleaned /checked fuel pump for cracks and debris(all clean), replaced plugs with OE replacements, replaced spark plug wires ( found one bad). Ran ok in tank idle all day, no abvious misfire.
On the water starts fine, upon throttle up about 1/4 throttle boat begins to accelerate and just boggs... like it looses fire on one cylinder or is excessively rich. Forgot to mention if it really matters. Boat is 14ft aluminum jon boat.
After holding full throttle for 5-10 seconds engine seems to have what I think is 1/3 engine power and boat begins to plane off( just one person). After boat planes throttle still wot, engine will sporadically surge, to full engine power, like almost throws me out the boat.( oh crap momment...) during this full power mode engine runs great for however long g it decides to then slows and surges back to full speed again. It's not consistent on how long it runs good at wot, sometimes 1 second sometimes 4 minutes.
Fuel mix is good, checked fuel for water and ethanol Content.
Replaced power pack no change. Replaced cracked charge coil no change. Replaced trigger coil no change. Replaced one ignition coil whi h tested fine with ohm meter but housing had a small crack, no change. All new parts still on engine with bogging surging problem. Carburetor is clean, good fuel pattern in barrel under full throttle, adding full under wot makes it worse. Choke plate is gone. Fuel bulb stays firm, doesn't help if I pump bulb. All fuel hose connections tight.
At idle timing is 8 btdc. It does advance but I can't see to wha t while driving and trying to control this beast as it decides to hit fill power....
Tried watching spark on oscilloscope, looks good as compared to what a known 4 stroke pattern should look like at idle. Pulled plugs after taking it out both relatively dry, not wet..
Stumped.... any suggestions GREATLY APPRECIATED....

If it's not the prop it's got to be fuel. If your using a boat fuel tank try and use a portable one.

 

[Rmillis]

Using portable tank. I thought about prop but wasn't sure as to the actual symptoms. Engine runs so much better when it runs good as compared to the bogging and surging...
If I add fuel it only makes it worse( bogging)

I'll mark the hub/ prop thenext time I get to get it out.

Thanks!!!!!

 

[saltchuckmatt]

Using portable tank. I thought about prop but wasn't sure as to the actual symptoms. Engine runs so much better when it runs good as compared to the bogging and surging...
If I add fuel it only makes it worse( bogging)

I'll mark the hub/ prop thenext time I get to get it out.

Thanks!!!!!

I don't think it's the prop with what your saying. When the prop slips your engine over revs and your boat slows. Is that happening? Doesn't sound like it. In the past others here have stated that you should look for a damaged wire, probably one under the flywheel that is shorting out when you move the throttle/timing. I have the same engine on a 16 ft lund and it goes like a bat out of hell, so yours should too.

 

[saltchuckmatt]

Using portable tank. I thought about prop but wasn't sure as to the actual symptoms. Engine runs so much better when it runs good as compared to the bogging and surging...
If I add fuel it only makes it worse( bogging)

I'll mark the hub/ prop thenext time I get to get it out.

Thanks!!!!!

I was going to add this and I forgot.

 

[tphoyt]

Yea if bogging is more a problem than the surging then it may not be the hub.
But it’s a free test and you can check it off your trouble shooting list when your done.
Best of luck

 

[racerone]

Test run with another tank and hose.-----Inspect fuel pump diaphragm, a new diaphragm is cheap.----Inspect primer pump on motor.-----Replace sparkplug boots.

 

[Rmillis]

I don't think it's the prop with what your saying. When the prop slips your engine over revs and your boat slows. Is that happening? Doesn't sound like it. In the past others here have stated that you should look for a damaged wire, probably one under the flywheel that is shorting out when you move the throttle/timing. I have the same engine on a 16 ft lund and it goes like a bat out of hell, so yours should too.

That's kinda what ibwas thinking about the prop, but.. was gonna atleast rule it out.
Engine does not rev when it bogs.. when it does go to full power.. yes you better hang on. Wires under flywheel all new and good. Not shorted anywhere.

 

[Rmillis]

Yea if bogging is more a problem than the surging then it may not be the hub.
But it’s a free test and you can check it off your trouble shooting list when your done.
Best of luck

They seem to be equal. But atleast I can check it off after the test...

Thanks

 

[Rmillis]

Test run with another tank and hose.-----Inspect fuel pump diaphragm, a new diaphragm is cheap.----Inspect primer pump on motor.-----Replace sparkplug boots.

If it was lack of fuel it wouldn't bogg more when I add fuel to the carb while under way. Adding fuel makes it die and sometimes cutoff. Sparkplug boots and wires good/new. No spark leakage can be seen at night either.
Thanks

 

[tphoyt]

I can’t remember if it was mentioned but have you tried running with a running light hooked up to see if your dropping a cylinder from time to time?

 

[racerone]

Some simple trouble shooting needs to be done.

 

[Culpy14]

It’s your stator.

 

[jimmbo]

Start with a Compression Test
As for timing, there is no Spec for Timing at Idle speeds. Only Specs for maximum Advance, and another Spec for when the Carb just starts to open the slightest bit.
Have you verified that the Spark is not dropping out on one Cylinder as the Throttle is increased?
Is the Carb opening up Fully, at Full Throttle?

 

[Rmillis]

I can’t remember if it was mentioned but have you tried running with a running light hooked up to see if your dropping a cylinder from time to time?

Used a timing light while underway and problem present, didn't see any change.
Would using a running light be different? If so how would that work..

 

[Rmillis]

Some simple trouble shooting needs to be done.

Advice appreciated...where do I start

 

[Rmillis]

It’s your stator.

I may be confused but I thought the charge coil/trigger coil was used in place of the stator on a manual start engine. Ni battery charging capabilities..

 

[Rmillis]

Start with a Compression Test
As for timing, there is no Spec for Timing at Idle speeds. Only Specs for maximum Advance, and another Spec for when the Carb just starts to open the slightest bit.
Have you verified that the Spark is not dropping out on one Cylinder as the Throttle is increased?
Is the Carb opening up Fully, at Full Throttle?

Compression good(did cranking compression test). Spark doesn't seem to be dropping, used timing light whole underway didn't see a loss of spark or change. Carb is fully open at wot, clear view of what looks like a good fuel spray into the engine.

 

[Culpy14]

I may be confused but I thought the charge coil/trigger coil was used in place of the stator on a manual start engine. Ni battery charging capabilities..

Something still needs to produce the voltage. There’s likely a stator somewhere, and magnets inside your flywheel.

What I had one my outboard was an idle problem, but fine while at mid throttle, and reduced power at WOT. It is pretty hard to diagnose without a Peak Voltage Meter, and you’ll end up assuming it’s everything else in the ignition system.

When I used a timing light I would see the misfires happening in all cylinders. By that point I had replaced everything else in the ignition system and tested resistance. My mistake was testing resistance when the engine was hot. That gave me a false reading and kept overlooking the stator.

On my engine it will charge the battery and provide ignition voltage separately. Looks like it’s all in one system for yours.

I could be wrong if the battery is charging, but the symptoms sound as fickle as a stator issue, and very few people will likely mention that on here.