main fuel jet only difference on 30 and 40hp mercury 2 cyl 1994??

[30mercury]

i have a BIG 30hp mercury, serial og059280, i think its 645cc or something.<br /><br />Having searched the net, it seems that these models are the excact same enigne as the 40hp 1994 model 645cc, can this be right??<br /><br />The only difference i can find in searching part-schemes is that the 30hp have a 0.54mm main fuel jet, and the 40hp has 0.66mm.<br /><br />Can it be this easy?? will my 30hp engine run like a 40hp if i change the fuel jet in the carb??<br /><br />If this is right, are there any other changes or adjustments i have to do??<br /><br />The serial number range my outboard is within,is the same for the 30 and 40hp models. on the timing marks inside the engine, it states 30/40, i guess this means 30/40hp, or?????<br /><br />This is an USA produced mercury, sold innorway. Not produced in belgium as the most of mercury outboards here.

 

[JB]

Re: main fuel jet only difference on 30 and 40hp mercury 2 cyl 1994??

Like all makers, Mercury is not going to answer questions like that. <br /><br />No, the jets are not the only difference.

 

[30mercury]

Re: main fuel jet only difference on 30 and 40hp mercury 2 cyl 1994??

ok, can u please explain what the differences may be then??<br /><br />Have checked all the parts numbers on the 30 and 40 hp mercury, and the only difference is the main fuel jet as i see it. <br /><br />In the parts list for 30hp outboard it shows 2 fuel jets, 1 for 30 hp and 1 for 40 hp. I think there must be a reason for this.<br /><br />Also this 30hp is much bigger than my previous yamaha 30 2 cyl outboard, the mercury weighs 20kg more.<br /><br />All this indicate that the mercury 30 and 40hp engine is the same, except the main fuel jet. <br /><br />Can any1 else explain the differences, or atleast give me the facts why they are not the same.<br /><br />Im not saying that all mercury 30/40hp outboards is the same, but this is a 30 Seapro engine, and as i've understood those are especially big compared to other engines of same hp, i've been told that they are actually just downgraded from 40hp and the engine is basically the same.<br /><br />anyone??

 

[Clams Canino]

Re: main fuel jet only difference on 30 and 40hp mercury 2 cyl 1994??

Get the parts list for both motors and compare them - only way to be SURE<br /><br /> mercruiserparts.com is one way to do this.<br /><br />-W

 

[Zamboni]

Re: main fuel jet only difference on 30 and 40hp mercury 2 cyl 1994??

Are the reed valves and exhaust manifold the same when comparing?.....your saying you checked all the part #'s but I thought that was the dif

 

[kergoat]

Re: main fuel jet only difference on 30 and 40hp mercury 2 cyl 1994??

you also have some restriction on reed valves, on the 30HP you have a piece to limit reed valve opening

 

[WillyBWright]

Re: main fuel jet only difference on 30 and 40hp mercury 2 cyl 1994??

We get the jet thing a lot here. It's never the only difference and usually the weakest link in the chain of differences. Motors run on a very specific gas to air ratio. Changing the jet affects that ratio, usually negatively resulting in the motor running too rich or too lean. Too rich carbons the rings until they break. Too lean and it runs hot and destroys itself that way. One other big factor is usually carb throat size. Dunno if that's the case here. Then there's exhaust tuning, timing, block porting, piston design, and a whole bunch more they do to play with horsepower from the same basic block. Could be a few of the above to all of the above and then some. You'd have to compare ALL of the parts, not just carb parts. Changing the jet alone would make the motor run at LESS than 30Hp. I doubt you'd even get on plane with it that way. A difference of a thousandth or two can make a noticable diffference, .012 is staggering!