New Carb and Low RPMs

[JM3820]

I installed a new 2bbl carb from Guaranteed Carbs. Since installing the RPMs won't get past 4000rpms with WOT. Idles great, starts great and runs good. Could they have installed the wrong jets? Do I need to adjust something?

Boat is 98 Maxum 1800sr (4600-4800rpms is spec at around 42mph) getting 32mph
Carb is a 3304-9565

 

[Scott06]

Is your throttle opening full is choke opening fully? Hopefully they guarantee their carbs. There could be several issues with the rebuild float level, eedle and seat power valve.
the only adjustments u can do are idle speed, idle mixture, and choke.
was this the same issue u had that lead you to replace the carb, also could be fuel supply restriction

 

[JM3820]

Is your throttle opening full is choke opening fully? Hopefully they guarantee their carbs. There could be several issues with the rebuild float level, eedle and seat power valve.
the only adjustments u can do are idle speed, idle mixture, and choke.
was this the same issue u had that lead you to replace the carb, also could be fuel supply restriction.

Yes the choke opens all the way. Not sure about the throttle, I'll look at that. The problem with the old carb was it was hard to start, some of the components were really worn and always smelt heavy on the fuel (most likely float issue). The new carb start great, runs smooth but lacks on top RPM and speed. I'll call the carb place and look at the rest.

 

[Scott06]

Yes the choke opens all the way. Not sure about the throttle, I'll look at that. The problem with the old carb was it was hard to start, some of the components were really worn and always smelt heavy on the fuel (most likely float issue). The new carb start great, runs smooth but lacks on top RPM and speed. I'll call the carb place and look at the rest.

If you have access to the factory manual for you engine or can find it online it will have jet, power valve, and venturi cluster info (part number) on it.

Unfortunately we have seen many times on here where some one buys a carb either rebuilt or new aftermarket, has so many issues they end up going back to the old original carb after rebuilding it.

 

[Lou C]

Franken Carbs
Caveat Emptor

 

[JM3820]

If you have access to the factory manual for you engine or can find it online it will have jet, power valve, and venturi cluster info (part number) on it.

Unfortunately we have seen many times on here where some one buys a carb either rebuilt or new aftermarket, has so many issues they end up going back to the old original carb after rebuilding it

I do have the numbers in a manual. But to check the carb parts, that means I will have to crack the new carb open to look at the jet numbers, right? If I do that will I need a new gasket?

 

[Scott06]

I do have the numbers in a manual. But to check the carb parts, that means I will have to crack the new carb open to look at the jet numbers, right? If I do that will I need a new gasket?

Yes they are inside. would also check the float level and drop. also check the power piston actuator spring moves freely.

Probably will not rip gasket of you are careful.

 

[JM3820]

The throttle plate opens fully and the problem most likely is that one spark plug wire was off making it a 5cyl engine. I will test it on the water in a few days.

 

[Scott06]

The throttle plate opens fully and the problem most likely is that one spark plug wire was off making it a 5cyl engine. I will test it on the water in a few days.

That will do it… buddy of mine has a 3 cylinder 75 hp merc on 16 ft fishing boat, couldnt get on plane … not getting spark on one cylinder, center core of wire is gone last 2” of wire, cut wire reterminated end, works great afterwards. Obviously needed new wires but got him going.