I recently bought a bass boat with a 150 hp engine. When I run the boat at high speeds it runs perfect. When I am idling, it will make knocking noises and stall. It occurs off and on with the stalls in idle, but it is occuring more frequently. I am just curious what this sounds like to you guys. I am thinking that the carbs may need to be rebuilt. Also, my engine is a 2-cycle.

have you made sure the rpms at idle are ok and not become backed off a bit and not high enough? does it do it all the time or just when its cold?
many things you can check also check all lines for leaks change the fuel filter check idle rpms of course also the knocking doesnt sound good but may be not getting oil at low rpms but not sure how that works with the oil injection and when it kicks on to lubricate unless you have it disconnected and mix your own oil.
plenty of people on here though that know more then i do but will help them more if you tell them the year and make of the engine also
mark

I have a 1995 evenrude 175hp. It has a small box that automatically injects the oil. How do you go about adjusting the idle rpms? It does it quite a bit even if the engine is not cold. Thanks for the help.

You set the idle rpm`s with the timming, not the carb linkage. First I would check all of the hoses for leaks. Carbs may need serviced. Get a manual so you can check and set all. Several things can cause this problem. Good Luck

www.kencook.com will have your OEM service manual, schematics and part catalogue available online at http://epc.brp.com/default.aspx?brands=ej&lang=E

sounds like you might be losing a couple or three cylinders at idle.

what do the spark plugs look like after idling? (wet, dry, black or tan or white, carbon deposits, broken bits, smashed electrodes, that sort of thing, champion or NGK). note if any look different from the others.

cylinder drop test: engine at idle, pull then reconnect the spark plug wires one at time. RPMs should decrease noticeably, if they don't, that cylinder's not making power. (use a plastic spark plug boot tool to avoid getting shocked).

post your results.

I kinda had the same problem one time. Turns out that my reed valves were destroyed. In idle it would drop rpms to about 350-400 and when I would put it in gear, would run rough. high speed it would run fine. Long story short, the pitch on my prop is wrong and at open speed, slowly but surely destroyed the reeds. New ones installed 400 dollars. Could have been worse.

jtexas, I will knock out that check with the spark plugs. I just recently replaced them but I am ddefinitly curious if a cyclinder or two or three is losing power. As soon as the rain and thunder storms stop I will perform the check and post the results.
Thanks TFF

the reason for the spark plug question was not to see if they were worn out, but because their appearance can give you clues about what's going on inside your engine.

You hit this one on the head. Rebuild the carbs. I would imagine that since you have carbs your motor is at least 10 years old. Rebuilding the carbs takes about 30 minutes per carb and is something that you can do yourself, with ease. You will need to buy a service manual for the motor (about $45.00) and rebuild kits for each carb (about $13.00 ea). You may want to install a new fuel filter, as well (about $8.00). When rebuilding the carbs, clean the heck out of them. When you think you have sprayed enough carb cleaner, spray some more. The last thing that you will do and is probably the most important step, is to follow the sync & link procedure in the manual, once the carbs are re-installed. Good luck!

I agree...check the link and sinc...if it is off just a little, the motor will not run right and will die at idle. I had this same problem. The boys at Marine Max are the best and can get it straight if you take it there. They will not overcharge either. It is a quick check and adjustment.

I would check your trim level. If your carb exaust is low on the engine, you may be trimming the motor too far down and choking it out.