Compression testing a 74 70hp

[R F]

I have a 70473-M jet I was thinking on new plugs so I want to do a compression test as long as I'm at it.

Cold or warm?
Pull all plugs and WOT to test?
What numbers should I hope for?
BTW-anyone know what the plug gaps should be?

 

[racerone]

Cold is fine.-----Absolutely no need to open throttle !!------My tester routinely shows 140 + on those.

 

[kevinj]

Cold works fine.
I've always opened the throttle but as Racer said, really no need.

Remove all spark plugs.

DO......Ground the plug boots so the coils aren't sending charge to an open gap.

Spark plugs should be UL77V which I think is a surface gap plug, so there's no gap to set. If it does have an electrode then 0.030" gap should be fine.

http://www.marineengine.com/newparts/part_details.php?pnum=CHAUL77V

KJ

 

[joereeves]

No offense intended to any other member.

There are some engines that, for some reason, perform better with surface gap plugs... BUT... surface gap plugs (UL77V mentioned) really have no heat range regardless of their "77" rating. They're a cold running plug and are prone to fouling.

The better plug (my opinion) is the Champion QL77JC4 with its gap set to either .040 (hot spark) or the revised gap of .030 (long life).

 

[kevinj]

No offense intended to any other member.

The better plug (my opinion) is the Champion QL77JC4 with its gap set to either .040 (hot spark) or the revised gap of .030 (long life).

No offense what so ever. I was just going by the plug spec'd out here at Marineengine.com in the parts diagram for the OP's model.

I had forgotten about using QL77JC4 in these older engines. I used to have a '79 Evinrude that also called for the UL77V but now remember it did run better with the QL77JC4. Good catch.

KJ