2-Stroke Intermittent Bogging During Break-In (25:1 oil mix)

[SeaBisket]

Hello,

Thanks again to everyone. I am on the other side of a powerhead rebuild and 5 hours into a 10-hour break in on a '96 88SPL Evinrude. I am running a 25:1 oil mix.

Over a 10-minute period, I get a bog, where power just drops out when running 3.5k+ and in-gear RPMs won't go above 1.5k. I can clear the bogging by stopping and running at high-idle (4k) for a blip.

Given:

• I'd not started to see this until 5 hours in.
• Runs about 10 mins before presenting.
• Runs great / as-expected when not bogging.
• Break-in started on a new fuel pump, rebuilt carbs, new plugs.
• 6-gal portable filled w/ various 5-gal batches.
• The tank sender is well-submerged during operations.
• Fuel pump / lines tight and not leaking.

Does this simply sound like fouled plugs - from the heavy oil mix, and the high idle burns off fouling? I didn't pull the plugs at the moment when it bogs, but I would maybe do that if I couldn't ask questions here. If it's fouling, then would it really foul when running at WOT? In fairness, I haven't stayed at WOT forever, but I did have it bog at WOT even..

Thoughts?

 

[clemsonfor]

A two stroke will run fine if tuned correctly at 25:1 especially at higher RPM, will not foul out or coke up with modern oils.

Are you sure your not overheating?

 

[SeaBisket]

A two stroke will run fine if tuned correctly at 25:1 especially at higher RPM, will not foul out or coke up with modern oils.

Are you sure your not overheating?

Good to know and good idea.
No buzzer, but let me verify that the temp. sensors are OK.
My official service manual is w/ the boat, a few hours away. Does anyone know the heat crayon temps it calls for, in the service manual? I'd like to order some before the weekend. I got a non-contact thermometer which is reading well, but those crayons are fool-proof.

 

[clemsonfor]

Not sure on the color crayon? But hit it with your IR temp gun in a few spots.

I imagine you did the water pump when the engine work was done? All grommets etc in place for water tube?

 

[SeaBisket]

Not sure on the color crayon? But hit it with your IR temp gun in a few spots.

I imagine you did the water pump when the engine work was done? All grommets etc in place for water tube?

I just grabbed a new IR gun w/ laser. The one I had was not great @ pinpoint stuff.

Replaced water pump when did I did mid-section / lower unit work. Replaced water tube also - it was crushed - see https://forums.iboats.com/threads/water-tube-removal-question-about-flanged-end.751318/
Same w/ thermostats, etc.. Kinda replaced "everything" almost since I had to also replace tiller / steering arm and had it completely disassembled.

Figured if overheat, would have presented in first 4 hours, but still a very good call to verify all things "temp".

 

[flyingscott]

Did you rebuild the carbs? Floats set right? Primer lever in the correct position?

 

[oldboat1]

Use the IR gun -- top of cylinders. Operating temp 120F to 140F or thereabouts (depends a little on lake temp.) 160F is overheating.

 

[SeaBisket]

Did you rebuild the carbs? Floats set right? Primer lever in the correct position?

Ya - I rebuilt the carbs. I remember setting the floats according to something in the manual, or some guide w/ the carb kits.

Primer lever is in correct position.

One variable is that I'm using a portable tank for break in, so I'm not going through my large filter / separator. I grabbed a new fuel pump, just to have a backup anyways, but to also rule out a clog or something in the pump's filter. I figured if something like floats, then I'd not have gotten 4+ hrs w/ no probs?

Thanks so much, all. Getting a good checklist together, thanks to you all. I got spare plugs, but was going to swap out after I am done the 25:1 mix.

 

[oldboat1]

Float looks nice and level. If you mean to check the drop, need to flip the carb top over and measure.

 

[SeaBisket]

Float looks nice and level. If you mean to check the drop, need to flip the carb top over and measure.

Ya I remember doing that adjustment, also. I think the procedure was all in the official service manual (not in front of me).

Edit: another thing to check, though, to make sure something didn't jangle.

Lots of good stuff. Thanks!

 

[oldboat1]

Admit I rarely check the drop --.just set them level with the inverted top most of the time, and go.

 

[SeaBisket]

Arrighty.. I got some good stuff to sweep:

1. Going to pull plugs anyway just to see what's up
2. Compression check while there
3. In the water, idle for a while and watch temp - looking for 120 - 140 F. Halt if hits 160.
4. Keep on the post-rebuild cycle.
5. Check temps periodically if no bog and if bog. Get them quick.
6. If temps check out, likely fuel [something].
7. If temps get whacked, work that angle.

 

[jimmbo]

Check and recheck all the wiring, and connections, including grounds in the Ignition system. Do a Spark test when the engine is hot, to verify that the system can produce a Spark that can jump 3/8" at each Cylinder

 

[clemsonfor]

Check and recheck all the wiring, and connections, including grounds in the Ignition system. Do a Spark test when the engine is hot, to verify that the system can produce a Spark that can jump 3/8" at each Cylinder

Yes good call, he could have a coil that is breaking down when it gets hot. The engine running down a cylinder and then randomly will kick back in and run on all cylinders.

 

[racerone]

Test run with hood / cowling off the motor.

 

[Chris1956]

a 25::1 gas- oil mix should never foul a spark plug. 60 years ago all 2 cycle motors ran that mix or one with more oil, the best we had was magneto systems and non detergent SAE 30 motor oil, and they still didn't foul spark plugs,

 

[SeaBisket]

Check and recheck all the wiring, and connections, including grounds in the Ignition system. Do a Spark test when the engine is hot, to verify that the system can produce a Spark that can jump 3/8" at each Cylinder

I grabbed a spark gap tester and will do that 3/8" gap test also.

Test run with hood / cowling off the motor.

Thank you so much. Your help, for me, and others is immeasurable. When the motor started, after being torn down to nothing, I couldn't stop thinking of the selfless help you and others provide to make things possible.

 

[SeaBisket]

Hey all. Thanks for the info. IR gun showed normal temps idling in water. Ran for very short time and pulled temps and starboard was hitting 160 and port was still no more than 125. I idled back in. Found out that a friend of a friend has tons of experience with this model, so dropped it off to him for a deep dive and to get a chance at hands on troubleshooting.

I did pull head and check water deflectors, so no problem there.

Will report back any info. Thanks again all!

 

[racerone]

Tested with cowling off ?-----Spark is known to short circuit to the latches on these V-4 engines.-----Switching wires around might help.

 

[SeaBisket]

Ya cowling off. Outboard dude said wires were routed terribly, even though I thought I routed as per picture from manual.