Two Different Main Jet Sizes

[RIR]

Hi folks. Have a 1984 115 that I bought used last fall. It normally runs good but hard starting especially when very hot and humid out. So anyway last weekend I pulled the carbs to clean and rebuild them as the top one was leaking fuel and we had a backfire which ignited the engine (that was fun). So I figured I better try cleaning them. Anyway as I took them apart today the middle carb has a .076 jet and the top & bottom carbs have .074 jets. Why is this? Should I be at all concerned about this different size jet? Should I stick it back in or order a .074 jet for the midle carb?

Also I did a compression test (except for #6 cause I couldn't get to it) and 1,2,3,5 are around 115-110 #4 is only at 60 could this have anything to do with the different jet size in the middle carb? Looking in the plug holes it looks pretty carboned up. I have added to much oil a few times with the gas. I am going to try seafoam after I get the carbs back on.

Thanks for any help

 

[Chris1956]

Re: Two Different Main Jet Sizes

60PSI is pretty bad. You can try a carbon cleaner, maybe you will get lucky.

The Crowleymarine.com web site shows both of your jets are standard. I would ask a Merc Dealer to see if you can get better info.

 

[corm]

Re: Two Different Main Jet Sizes

Hi,
Someone may have put in a larger one to prevent the #3 cyl from burning.
It looks like they were to late for #4. I'd double check your timing while your working on it. We used to do that to the top carb on some engines to slow down the piston burning when we were running over advanced timing settings.

 

[RIR]

Re: Two Different Main Jet Sizes

I guess I'll just stick the .076 back into the midle carb for now. The Seloc manual shows 2 different sets of serial# ranges for my motor with different jets sizes for each (neither of which show a .076)

I am at sea level here in Rhode Island which shows .074 or .072 jet size

I will check the timing


Thanks guys!