mercruiser 3L sterndrive wont idle at low revs

[robR]

I just bought a 93 bayliner with a 3L Mercruiser sterndrive. Yesterday was the maiden voyage. First, it was hard to start until we held the choke open manually. Once we were able to start it, it reved up to 3000 rpm and wouldn't go back down. We had to bring the revs back down by closing off the choke. Afterwards, it was easy to restart, but still reved high. <br />I disconnected the throttle linkage to see if it was the linkage causing the problem, but the same thing happened. However, with the throttle linkage off, I looked down the carb and found the throttle baffles were closed. Why is it reving so high?<br />Another weird thing I found was the throttle cable did not seem to engage the carb linkage until the throttle handle was pushed forward approx. 40 degrees. The throttle linkage should start to engage the carb as soon as it is pushed forward from the vertical position, shouldn't it?<br />Anyone's opinion would be much appreciated.

 

[DJ]

Re: mercruiser 3L sterndrive wont idle at low revs

robr,<br /><br />I suspect two things.<br /><br />1. Timing is way advanced.<br /><br />2. A vacuum leak.

 

[trevorcday]

Re: mercruiser 3L sterndrive wont idle at low revs

The first portion of the throttle lever travel operates the shift cable. The throttle cable does not move until the shift cable has gone full stroke.

 

[Boatist]

Re: mercruiser 3L sterndrive wont idle at low revs

If you have a single lever for throlle and gear shift it is normal. This is to allow you to shift into gear without reving the engine. Think about it if you did not have this room to shift and you were coming into the dock and you took it out of gear to glide in then had to put it back in gear you would have to hit it perfect to get it back in gear without adding power. This way you can shift into gear then slowly speed up or come back to idel without taking it out of gear.<br />My guess on engine RPMS is automatic choke. When it is cold choke will close and also adjust engine idel up for warm up. As engine warms up choke should open but RPM will stay up until you give it a little gas and then come back to idel. What offten happends either choke sticks or cam that brings idel up sticks. I know you said throddle plate was closed but remember at idel out of gear moving plate a very small amount you will get a big gain in rpms. There is also an idel speed adjustment screw that adjust to the same cam that choke moves. This screw could be set adjusted too far in. I would make sure that cam is not gummed up. After that I would start up and make sure choke opens fully then give it a little gas and see if engine slow down. if it does your fine. If the choke does not open all the way could be gummed up, adjusted war too rich, or heat tube to choke could be stopped up or missing. Also if it is a new boat to you could be someone was useing it at high altitude and adjusted idel for that location so may just need to turn the screw. As far as hard starting at first in many cases gas in carb after sitting for a long time has leak or evaporated out of carb so have to pump fuel up first and that can take a while. Good luck and let us know what you find.