Evinrude 6hp power issues

[crxess]

1973 Evinrude 6hp 6302
Only running 2-2.5MPH WOT

Things done so far.
Water pump replaced
L/U oil changed
Head Gasket replaced - compression 60/60
T-stat replaced
Fuel Pump tested - no leaks
Carb rebuilt
Points Set .020
New Plugs .030
Tiller arm replaced - Old arm gears slipping
Filed Prop - Decent condition - Stock 2 blade

Barrel test - running smooth idle to wide open.
Shift -F/N/R all smooth
Throttle response in gear quick and smooth
Starts/restarts easily
Verified Both cylinders firing strong

On water - loaded - Full throttle - Balanced so Bow rises about 4" on acceleration. Stern only squats an inch or so. Starts to go and just stays at this attitude.
2.5 miles up river=1 hour ride
Motor never reaches full RPM

Boat - BassTender 10.2 165lbs

Length 10'2"
Width 55"
Depth 16"
Capacity 474
Rated Hp 7HP

Weight
Motor- 50?
Fuel - 24
Battery 45
Troll motor 6
Paddle 2
Tackle 10
2-persons 330
----------------
Total 467

I understand it is a Trihedral hull and won't plane but it should at least go. Sadly my 24lb thrust trolling motor is almost as fast.
I have no clue what to try next.

 

[tx1961whaler]

Re: Evinrude 6hp power issues

I would say you're running on one cylinder, but you already verified that it is running on both......
60 psi is marginal compression, but it's difficult to get really good readings with a pull-start motor.

 

[Chinewalker]

Re: Evinrude 6hp power issues

How do you know you're firing on both cylinders? Have you run it on either cylinder with the other wire pulled? I agree - sounds like a classic running on one cylinder...

- Scott

 

[crxess]

Re: Evinrude 6hp power issues

How do you know you're firing on both cylinders? Have you run it on either cylinder with the other wire pulled? I agree - sounds like a classic running on one cylinder...

- Scott

Yes, I did the wire pull test in the tank.
Set at high idle. Pulled lower wire first. RPM dropped steeply. Reconnected and motor smoothed back out.
Same response/results on top wire.

If no other suggestions, I'm thinking about pulling the carb just to be sure nothing settled causing a restriction.

Shouldn't it miss at high rpm if it is starving for fuel?

 

[film495]

Re: Evinrude 6hp power issues

what fuel mix are you running? too much oil can cause a ton of carbon build up and I guess it causes the rings to not really work so good and compression/power is lost from the moter. get a can of sea foam deep creep and spray some into the carb while running or engine tuner from OMC is a good decarb also - just follow the instructions on the can. in that year motor if you are running at 24:1 mix, I'd wonder if that is not the root of your problem. Do the plugs look clean after run for a while or do they turn black pretty fast from carbon stuck to them?

 

[crxess]

Re: Evinrude 6hp power issues

mixed up 2 gal @ 50:1 Before trip. Didn't seem to make a difference from original fuel. PB Blast soaked the pistons while head was off. Will try the Sea Foam if carb check reveals nothing.
Can't check (look at)the bottom plug again without replacing head. Helicoil for plug has just about had it. Was hoping to get a few days use before replacing.

 

[crxess]

Re: Evinrude 6hp power issues

Side stepped pulling the carb for now.
Went ahead and did a decarb with Sea Foam. What a smokey job that was.
Had to run it in the tank. No time to run to the river.

Noticed an odd intermittent sound while running with the hood off. Kind of a buzzing vibration or rattle. Not a metallic noise. Almost as if the reeds are vibrating. Whole injecting the Sea Foam, no buzz at all. Then as it clears the sound starts to show up again.