Exhaust tube leaked. Poor idle now

[jdklein001]

So on my shakedown run the rubber tube between the exhaust elbow and y pipe spring a leak. This is on a 1998 4.3 vortek with Rochester 2 jet carb.
I found out what happened by looking at the engine while running and seeing exhaust water/gas spurting out of the tube. I had probably run it this way at cruising speed for an hour. I had not other way home. Lots of white dust caked the flame arrestor and other areas in the engine compartment. I’ve cleaned the arrestor but it still stalls at idle. My theory is that salt water crud has caked the inside of the carb a bit. I turned both idle mixture screws clockwise 1/4 turn and increased the idle speed with the screw on the throttle linkage. It runs well now and I think it’ll all burn out soon.
Does the idle mixture screw on these carbs adjust the gas or air (I’m not sure what my adjustment actually did)
Does anyone think I’m off target in my thinking here?

 

[alldodge]

The mixer screws adjust fuel flow. The more the screw goes IN, the less fuel the motor gets.

The throttle set screw opens or closes the throttle plate. It this screw is adjusted, also need to remove the throttle cable and adjust it to help close the plate. This is done because the carb has no throttle return spring, the throttle cable is what does it

 

[Scott06]

A couple of thoughts here

this engine was overheated, the rubber connector will only burn through if it gets hot. As you saw the cooling water is sent overboard after it mixes with exhaust. I’d double check that the water pump impeller is in good working order and you are not getting hot. Would check that the exhaust shutters are still there as they get fried from a overheat with no water flow.

second the carb if it has two idle mixture screws is a Rochester two jet vs the mercarb your boat would have come with which has a single mixture screw. Only means someone replaced it at some point, the two carbs share a common lineage. The screws turning in will lean the idle mixture. These screws are out = more gas, in is leaner = less gas. Check what your plugs look like, if ok it’s probably fine as is. If you got salt all over the engine compartment you will want to wash this off so it doesn’t corrode things, especially off soft metal parts like linkages and the carb. I can see salt sprat making it run richer, only a clogged flame arresting effectively chokes it. Is the choke fully open when warm ?

 

[jdklein001]

The engines are from 1998 with really low hours on them. I suspect the Rochester carbs came with or were ordered with them when the boat was repowered (in 1998). The tube that burst was aftermarket, Barr, that came with the kit I used to replace the single piece manifolds with the two piece plus elbow on three of the four in the boat. The fourth I did last season after a piece of metal broke loose and messed up the impeller.
that was on the port engine as is this current issue, different sides of the port engine though.
I had the drives off this winter and did the full impellers plus ran through them looking for debris and wear. All of the manifolds and thermostats were replaced.
during the shakedown run the temps on both engines were equal to each other as was oil pressure. I have no reason to think they were overheating but wouldn’t rule it out. The exhaust flapper was in perfect condition when I replaced the tube and the inside of the tube didn’t show any metal debris or melting. It actually looked pretty good. The tube burst right next to a seam on it but it wasn’t the seam failing per say.
I will say the oem tubes are noticeably thicker than the Barr’s.
Does this info change any thinking?

Thanks for the info on the carb screws

 

[jdklein001]

All of that said I am curious and concerned about what cause it to burst. The boats gotta be safe to have the wife and kids out on. I’ll check the temp of all for

 

[alldodge]

All of that said I am curious and concerned about what cause it to burst. The boats gotta be safe to have the wife and kids out on. I’ll check the temp of all for

When you work with after market there can be issues. Not everything that Merc does is better then others, just need to note what the differences are. Manufacture like Gates make quality hoses, and would not surprise me if Merc uses Gates without the label

Barr makes good enough exhaust, but just they go cheap on hoses.

Being in salt water will be harder on things like belts and hoses then another in fresh water. Your going to need to do more inspection maintenance then another in fresh. Will need to feel and visual hoses for soft spots and such.

 

[jdklein001]

When you work with after market there can be issues. Not everything that Merc does is better then others, just need to note what the differences are. Manufacture like Gates make quality hoses, and would not surprise me if Merc uses Gates without the label

Barr makes good enough exhaust, but just they go cheap on hoses.

Being in salt water will be harder on things like belts and hoses then another in fresh water. Your going to need to do more inspection maintenance then another in fresh. Will need to feel and visual hoses for soft spots and such.

Thanks for the input. I’ll be on my maintenance game.