Carb question

[deputydawg]

I am posting for a friend that is getting his boat ready for spring. He has a merc inline 6, I think about a 145hp. It is a 1974 model with a rochester 2bbl carb. Engine was running rough so at my suggestion he changed cap, rotor, plugs, wires, coil the works. All with new marine parts. Replaced all fuel filters and flushed the tank. <br />Engine will not idle, and is only running on the front 3 cylinders. The back 3 are getting good spark, good compression, removed and replaced head and all is good. But remove plug wires from the back 3 cylinders and the idle won't change. Can't be cap and rotor, these 3 don't fire one after the other plus these parts are new.<br />My question is this.....is this a dual plane type intake? The carb had some junk in it plugging some passages. Will rebuild it or replace it when he gets money. I turn the front idle mixture screw in and the idle changes. I turn the rear set screw in and out all the way and idle won't change. The way the 2bbl sits on the intake, I was wondering if the front venturi fuels the front 3 cylinders, the rear fuels the rear 3 in a dual plane type setup, or if this carb problem could be causing this miss because of the location of everything.

 

[Don S]

Re: Carb question

Have you tried doing a vacuum gauge test? You said the compression was ok, was it tested or assumed it was ok. Did the problem just suddenly start, how long? A little history would help.<br />Have him pull the plugs again and check for water or rust on the plugs. the exhaust could be leaking water into the cylinders.

 

[deputydawg]

Re: Carb question

Compression tested with a guage on a warm engine. Plugs are good, cylinders good, no water intrusion. Ran fine until the owner was deployed for a year. When he came back was not running good. So it sat for a year. There was a lot of old gas in the carb and tank, left deposits in the carb, float bowl and everywhere. The carb definately needs soaked out and rebuilt. The head was taken off shortly after it was run, and no sign of water in any cylinder. No rust or signs of water on old plugs that came out, or new plugs that went in. <br /> I just find it odd that only the rear 3 cylinders are missing. The thing I keep coming back to is the problem started after sitting for a year.<br />Almost forgot, he did not do a vacuum test. Will suggest that to him.