compression question on a 90hp Honda 2003

[stormmnv]

four cylinder 2003 Honda 90hp BBBL 4501214 did a compression test and had 115 cyl #1 , 110 cyl#2 , 70 cyl #3 , 130cyl #4 scared me to death.
Op's I forgot to open the carb throttles when I did the above test.
second test with carbs open..... 185 cyl #1, 182 cyl #2 , 182 cyl #3 , 185 cyl #4..... OK now I'm confused, why such random pressures with carbs closed and even compression with carbs open, and does this indicate a problem.

 

[km1125]

Did you duplicate the test with the carbs closed? I would do that before I got worried at all. The 'carb open' tests all seem good, although they seem a bit high to me... perhaps the gauge reads a bit high.

 

[stormmnv]

I did, a second test > 130 cyl. #1, 125 cyl #2 , 90 cyl #3 and 140 cyl #4.. with the throttles closed. the book says to warm up the motor prior to doing the compression test, but as it is on a engine stand I have not ran the engine.
Did a second test with the throttles open and again 185 + - 4lbs across the board.
Believe I remember reading somewhere that 180 compression + - 14% was acceptable .
norm

 

[km1125]

Sounds like everything is good. I wouldn't worry about the "throttles closed" readings but there could be a lot of reasons why they show up differently.

Warmed up and wide open throttle is the normal way to do a "real" compression test (and on two strokes with exhaust port valves having them in the 'closed' position).

 

[stormmnv]

KM 1125 I did find in the SELOC book where the BF90A series engine was listed at 199-227psi WOT.
Tried to fire it today, sounded like only one cylinder firing. Pulled the carbs and gave them a tear down and cleaned the jets and hard parts in cleaner, some of the jets were plugged, will assemble when the gaskets show up.
Will keep U posted.

 

[km1125]

I don't have a BF90 or the specs handy but I see references from the Honda book specs at 214, which is in the same range as your SELOC book shows. I would not be concerned with 180's, as it is even more important that they are all similar (within 10-15%). The actual gauge used makes for variation in itself from a factory reading.

The one low cylinder reading on the 'closed throttle' test might mean you have a balance variation between the carbs (not necessarily a "problem", perhaps just a variation). Not sure on the procedure to set that for this engine, but as you reassemble the carbs after cleaning you might double check those settings.