Lost with new carburetor

[andrewterri]

Still fighting with the old boat. I have a 89 mercruiser 3.0. The old carb would run great at speed but would not idle and was hard to start. I ordered a new carb from i5 and now it idles better but bogs at high speed. There is no high speed jet to adjust. The boat is smoking which leads to to think it is flooding. I have changed plugs and fuel filter but still have the same problem. Do you guys have any thoughts? Really don't want to rebuild a new carb. The boat is still hard to start with the new carb after it has been ran. Starts good when cold. Idle is still not great but better than before. I even thought maybe a stuck valve. Thank you in advance guys.

 

[Bondo]

I ordered a new carb from i5 and now it idles better but bogs at high speed.

Ayuh,...... I just put 2 of those carbs, from them, on a pair of I-6s, twins,....

Starboard motor won't make over 3000 rpms, port-side is much better, but wasn't there,...

Goin' up tomorrow to see if I can figure out what's goin' on,...

Whole new fuel system, right from the tank,....

This 1 on the starboard motor has been fightin' me all the way,...
The port motor it was pretty much plug, 'n play,....

 

[andrewterri]

This is the second carb I got from them. The first had the same problem and was replaced under warranty with this one. Problem is I rebuilt the old one while I was waiting. That was a year ago and now it's to late to send back

 

[Jmunk]

Sounds like main jets are incorrect or float height is off.

 

[NHGuy]

First thing is to look up the jet size and float height and how to set the float and where the jet(s) is/are. You check jet size with tiny drill bits, just don't ream out the holes. You can get a set of the small bits at HF. Just gently put the heel of the smaller bits in the jet and work your way up til it fits. That's your jet size.
Check or reset the float height. You will posssibly need a gasket too.
Avoid changing the low speed & choke settings since they are working.
But truthfully it's wrong float setting usually.
Also, get a can of carb spray, with the engine running shoot bursts of it around the carb base, the throttle shaft, choke shaft intake manifold edges, anywhere air can leak into the engine.

 

[achris]

ok. Start from the beginning. Did you do a compression test? Leakdown test, check valve adjustments and fully and completely check all parts of the ignition system before condemning the carb? Do you have the correct flow and pressure from the fuel pump? Have you checked and confirmed you don't have an air leak between the tank and the fuel pump? What leads you to think it's the carb?

Chris.......

 

[andrewterri]

I think it is the carb because with the old run it was running great at high speed then bad idle. Changed to new carb, plugs, fuel filter. prior to the problem stkrting I Kept poinst but changed out cap, rotors, and wires. When it first started it was idling rougher as time went on with the old carb until to would not hold an idle at all. Then changed carbs and had opposite problem. that is why I think it is carb related. compression test was done 2 years ago and was great. I will do another one. I believe the carb is getting the correct pressure to the carb . I do not think there is an air leak as that would constrict fuel. it is acting like it is running way to rich by the sight of black smoke while on the trailer.

 

[andrewterri]

I do not have high speed jets that I can adjust from the outside. I am trying to find a scamatic of the carb, but finding a diagram for i5 carbs is not easy

 

[Scott Danforth]

take the new carb and send it back, its new and should have been plug and play. take the old carb and get a carb rebuild kit. you have a bit of dirt in the fuel passages. a few hours of soaking, followed by a few minutes of running a fine wire thru the passages then 15 minutes putting the carb back together and you would be good to go. not sure why anyone would replace a carb when you can rebuild them so easily.

 

[andrewterri]

I bought the new one because I was missing the choke linkage and the piece of metal the throttle stops against where you adjust the idle screw was broken off by somebody. I completely agree with you though, they are every easy to rebuild. I can not send it back it has been to long they said.