99 merc 90 hp 2 stroke minimum compression and wrong spark plugs

[amoler821]

what is the minimum compression on a 1999 merc 90hp 3cyl? i cant find anything in the seloc book other than 15% of each other. also, if a compression test is done "cold" how far off would they be?

when i bought the boat used, i had it taken to a marina and checked over. every spring since, i replace the plugs with what was in it... i just got the seloc book and found the 90hp takes a Gapable plug. p/n bp8h-n-10. and what was in it and i replaced it with...(i mean, a merc dealer wouldnt put the wrong plug int...would they).....a surface effect, no gap plug for a 75hp, pn buhw-2..

how much affect would this have? i suspect loss of power? carbon build up?

 

[QBhoy]

Hi you ideally want over 100 psi on all three. But make sure your gauge is good. I dread to think how many guys think the worst of their engines after using a cheap and un calibrated gauge.

 

[amoler821]

ok thanks. im getting 90 on all three, but thats "cold" too.i gues ill have to get it running up to temp and and
again

 

[Sea Rider]

Would be cool to know what's the PSI difference reading between a cold and a warm compression test...

Happy Boating

 

[amoler821]

see

 

[Texasmark]

The manual for that engine up through the 200X model (of which I had a 2002) year states: "For compression pressures below 120 PSIG, you can expect problems.

 

[Texasmark]

what is the minimum compression on a 1999 merc 90hp 3cyl? i cant find anything in the seloc book other than 15% of each other. also, if a compression test is done "cold" how far off would they be?

when i bought the boat used, i had it taken to a marina and checked over. every spring since, i replace the plugs with what was in it... i just got the seloc book and found the 90hp takes a Gapable plug. p/n bp8h-n-10. and what was in it and i replaced it with...(i mean, a merc dealer wouldnt put the wrong plug int...would they).....a surface effect, no gap plug for a 75hp, pn buhw-2..

how much affect would this have? i suspect loss of power? carbon build up?

The engine is produced with surface gap plugs. The serv. manual lists a standard gapped plug for certain circumstances. I don't remember the reasons why nor the numbers for each but industry went to surface gaps for production engines for that reason and it's been since the '70's in the practice....mist be something to it. I had them in my 1972 Newly purchased Johnson 124 V4. I tried the gapped plugs in my 90 Merc for awhile and went back to the SG.

I never had carbon buldup with that 90 on the piston crowns nor plugs nor rings.....I kept Sea Foam in the fuel!

 

[amoler821]

thank you for the replies. i called 3 dealers and 2 or 3 said the plugs i have r what it calls for.
if its 120 then im really screwed. the paperwork from the dealer i had inspect it before i bought it says 118, 116, 118...ENGINE COMPRESSION WITHIN SPEC.i did a cold compression test and found 90 across all cyl. a dealer told me thats ok cold? i think i have a float problem. everytime i pull the carbs and recheck and reinstalll...the boat starts idles fine. start 5 min later....same starts idles, revs etc..leave i the down position....1 hr later crank, no start....smokes like hell and i full throttle it to keep running but spitting and sputtering, id i bring it down off full idle it dies. ? any idea?

 

[Texasmark]

thank you for the replies. i called 3 dealers and 2 or 3 said the plugs i have r what it calls for.
if its 120 then im really screwed. the paperwork from the dealer i had inspect it before i bought it says 118, 116, 118...ENGINE COMPRESSION WITHIN SPEC.i did a cold compression test and found 90 across all cyl. a dealer told me thats ok cold? i think i have a float problem. everytime i pull the carbs and recheck and reinstalll...the boat starts idles fine. start 5 min later....same starts idles, revs etc..leave i the down position....1 hr later crank, no start....smokes like hell and i full throttle it to keep running but spitting and sputtering, id i bring it down off full idle it dies. ? any idea?

Do a search either herein or google the word: Decarb! Basically it's a quick "engine enema" and is designed to flush the carbon out of your combustion chambers and in the process loosen wedge shaped rings that are popular with today's loop charged engines.....the wedge ring has to be loose in the piston such that combustion pressures can cause it to expand against the cylinder wall and seal off the gasses. It will be messy so if you live in town, do it during the week when everybody else is at work. Then keep it in your fuel.

They sell manuals herein or rent computer time for the Seloc manual. The OEM can be purchased used on ebay. I just bought one for my newly acquired....going to pick it up tomorrow, 2002 115 and boat-trailer......22 bucks, free shipping. Get your engine serial number when ordering to ensure it covers yours.

 

[QBhoy]

Always question the gauge before writing it off I’d suggest. Try a couple of them and defo a warm or engine with some 2 stroke oil defo still present to help seal the rings.
Like I say. Some gauges will give you wild readings

 

[amoler821]

thanks for the replies. i went back to the SG plugs. i questioned the plugs because of my rough idle problem (another thread) . im not sure how to combine threads, or if it should be on its own...but on the 90hp 3cyl is the bowl jet vent supposed to be installed?