1971 125hp power issue

[Mouse1]

Have a '71 125hp that will throttle up in idle but lags and sometimes stalls under load. Also will not rev up like it should. Fuel pump has been rebuilt and all new hoses. Will work fine on ears out of water. Carbs have not been rebuilt yet, not sure if thats my next step or if it could be electrical.
Looking for some guidance

 

[interalian]

Do you mean it will throttle up in neutral? Not a meaningful test, and possibly dangerous (runaway).

Compression test? Spark test? Spark should jump 3/8" or so with a nice blue spark. Compression should be in the 120/hole range.

 

[Mouse1]

Will check compression. Plugs may be suspect.

 

[interalian]

After you've confirmed compression and spark, carbs would be next. And not a Seafoam clean - they would need full disassembly, soak and blowout, including the idle transition orifice cover plugs.

 

[oldboat1]

When you test for spark as advised, you are checking for ignition output (plugs irrelevant, although they can be a problem as well). You need an adjustable open-air tester to measure spark. Do it with all plugs removed, as you would for a compression test.

 

[Mouse1]

Comp. results: #2 at 80psi, the others at 90 psi. Looks like might be time for rings.

 

[Mouse1]

Before buying rings, pulled head and found the water passages clogged with build up. Noticed what might be start of blow by on the head gasket. Removed bypass cover and the rings don't look bad.
First pics are of the head gasket. Close-up in center i believe is the gasket starting to fail. Last pic is the inside of the head cover with build-up. Engine did run hot once during trying it.
Opinions?

 

[interalian]

Water doesn't flow on the underside of the cylinder head covers. Mineral buildup there is normal and doesn't really affect flow unless it swells the gasket and closes the 'maze' passages cast into the back side of the head. Your head gasket looks like it's been hot but hasn't failed (see pic of failed one). Examine the head itself to see if the sealing areas are even around both cylinders. Check head for warpage (they all do) and if so you'll need to dress it flat before re-fitting.

 

[Mouse1]

Thank you. Could that darker area be the beginning of a failure? Could it also be the reason for lower compression? Haven't pulled the other head yet. #1 & 3 cylinders are the head pulled, no scoring and can see crisscross honing pattern on cyl. walls.
Opinion, should I go ahead and pull pistons to check and/or replace rings or just face heads and rebuild carbs?

 

[interalian]

The failure happens when the gasket material crimped under the metal donut starts to erode, then combustion pressure pushes past the donut as it is no longer supported. Usually caused by loss of clamping pressure on the head - overheating is a factor. Pictures of the head and block between the cylinders might help.

You can inspect rings two ways:

1) Shine a bright light into the gap between the piston and cylinder wall with the piston at top. Move the piston around to make the gap larger. You're looking for a continuous, shiny metal ring. There will be a gap in one place only.

2) Remove bypass covers and turn the motor over to expose the rings in the ports. You're looking for springback on the rings, and presence of rings too.

If the rings look good, new gaskets and head resurface will be required.

Teardown to replace rings is a step for well after more diagnosis is done.

 

[Mouse1]

Removed other head, can see the original hone marks in all cylinders. Included a pick of #2 cylinder. The area circled is what I'm asking about. It looks like it is made into the cyl. Think one of the rings may be stuck on #2.
Opinions?

 

[racerone]

Circlip retainer for wrist pin came out.-----Motor needs to come apart for repairs.----Your location ??

 

[Mouse1]

It just hit me after I posted it, "that's from the wrist pin!"
Located in Alabama, just outside of Birmingham.

 

[racerone]

Depending on the damage you may need to find another block.-----I think I should list my stuff on that auction site.