engine will not idle

hello,
this is my first boat.i've had it for a few months and it has been running great until today. it is a 1974 glastron with a 165hp gm 6 cylinder engine.
it will not idle. it will start if you put the throttle to anything over about 1000rpms. does not matter if it is hot or cold. and it seems to run fine at 1000rpms.
plugs and wires have been changed, i think it may be fuel related, just not sure where to start, i have not worked on many carburated engine.
any help would be great thanks.

 

Your carburetor is leaking air or fuel into engine. Check idle valve/screw or choke. Carb may need rebuilding. Check vacuum hoses.

 

You're correct, it is fuel related.
Because you own the boat for just a few months and it is pretty 'ancient', you should do a little more than just find the cause and go boating. The cause probably is a clogged idle jet or an air leak under the carb.

Make sure the tank contains no sludge or very old fuel, otherwise the problem keeps reappearing. Replace fuel filter, check for fuel line leaks, take the carb apart, thoroughly clean and reassemble it using new gaskets. Also check the fuel pump and the plastic hose between the pump and the carb, replace it when it seems to be brittle.

 

An ultrasonic cleaner is ideal for this, it will clean inaccessible parts and not risk damaging jets by poking wires through them.

 

took the pump and filter all apart this morning and also took the carb all apart checked the idle jets, everything looks pretty clean did not find anything gummed up took some air and blew it out. so decided to put it back together and try it and it seems to be working fine now. maybe there some small piece of debris in there that i couldn't see, but so far i took it out at about for about 3 hours stopping and starting multiple times and so far so good.
thanks

 

Often a good cleaning is all they need, but CDK makes a valid point, in that you should just bite the bullet and put a "level playing field" on this old puppy. By this I mean, change out all of the consumables, such as oil, water and fuel filters, replace the belts, hoses and distributor parts (rotor, cap, condenser and points if there), R&R the spark plugs, spark plug wires, raw water pump impeller, etc. Then put everything to factory spec in regards to timing, idle speeds, etc.

Now you'll have a level playing field, so you know the age and condition of the usual things, that might leave you paddling for the launch ramp, come some mid afternoon. Changing out these parts will also familiarize yourself with the way things fit, work and need to be handled, so if something does happen, you don't open the engine cover and stand there with a deer in the headlights look on your face. In fact, because of this new found familiarity, you'll probably know where to look and possably fix it too (always have spare spark plugs, fuel filters, etc., just in case). This is the old school approach, but you have an old school boat, so have the wrenches along to change out things, if something wants to take a dump on you 5 miles from the nearest shore.

The first tool to buy is a manual for your engine/drive assembly. It's the best 30 bucks you'll spend. Read the first few chapters well, as it'll nurse maid you through the tuneup and evaluation process, so you don't have to preform the classic novice routine of "hunt and peck" replacing part after part, until you've solved the problem. Before long, your boat will become reliable, because you know the parts are good or "fresh" and you'll have a new found understanding of things that most everyone else pays $85 to $150 and hour to have done for them.

 

the other thing that will kill idle is a distributor that is rusted worn so it is advancing at idle meaning if the engine slows a few rpm then it retards further slowing till it stops
You will need a timing light to check that