Mercruiser 140 won't idle, backfires while starting

[RonLLeffert]

I have a 1985 Mercruiser 140 that has been stored for the last 20 months. Fuel was stabilized, engine was oil fogged, and alternator belt was loosened when stored. I tried to start it yesterday after tightening the alternator belt. It took a lot of cranking, and several backfires, but it finally started. Seems to run fine, but won't idle. It ran fine when stored. Is this an ignition timing problem, a stuck valve, or a fuel problem?

 

[cosander]

Re: Mercruiser 140 won't idle, backfires while starting

was the fuel tank full when it was stored?

 

[RubberFrog]

Re: Mercruiser 140 won't idle, backfires while starting

How long is fuel stabilizer actually effective? 20 months seems like a long time.

 

[tommays]

Re: Mercruiser 140 won't idle, backfires while starting

points dont usally store well for what ever reason and its and easy and cheep thing to change<br /><br />only a compression test will tell you the motor is healthy<br /><br />it doesent take much to gunk up the idle circut on the carb<br /><br />10% blend gas does not do well in storage compared to the real stuff<br /><br /><br />tommays

 

[RonLLeffert]

Re: Mercruiser 140 won't idle, backfires while starting

Fuel tank was full when stored. Fuel stabilizer is stated to be good for 12 months, but I have had sucess with it up to 7 years in an outboard 2 cycle engine. Will check ignition and points.

 

[Don S]

Re: Mercruiser 140 won't idle, backfires while starting

A full tuneup after being winterized is almost manditory on engines with points.<br />Like tommays mentioned, points don't store well.<br />The tuneup should include, points, condenser, cap, rotor. Also set the points by dwell, not gap, reset timing, and adust carb mixture.<br />Check timing advance is working also.

 

[Richard Petersen]

Re: Mercruiser 140 won't idle, backfires while starting

Rotor caps and rotors can condansate badly and cause a arcing path, which sounds like you.

 

[RonLLeffert]

Re: Mercruiser 140 won't idle, backfires while starting

I have rebuilt the carburator, using a kit. Replaced accelerator pump and needle valve. Cleaned using carb cleaner and compressed air. Also changed points and plugs. Dwell set at 28 degrees (spec is 26-32). Checked compression. All cylinders range from 144 to 148 psi. Engine starts and runs, but won't idle below 1500 rpm. If I try to go lower, it starts shaking badly and then dies. Checked timing, but it is advanced due to engine speed. Can't check idle timing. Did I miss something in the carb. Seems like the idle circuit is not working. Carb and ignition seem to be in good shape visually (no gunk, carbon traces, cracks etc.)

 

[tommays]

Re: Mercruiser 140 won't idle, backfires while starting

i would go back over the timeing and be sure its in spec you need to get down to 650 RPM<br /><br />its hard to hook up a vacume guage but this would let you know if theres a problem with a leaking intake and other stuff <br /><br />tommays

 

[olbuddyjack]

Re: Mercruiser 140 won't idle, backfires while starting

The "shaking badly" make me thinks like cyclops, check the cap.<br />A sticky valve would show up on the compression test.

 

[RonLLeffert]

Re: Mercruiser 140 won't idle, backfires while starting

Inspected recently installed plugs after running for a few minutes. Found no. 3 plug was still shiny. Other plugs were blackened from firing. Checked all cylinders for spark plug fire and found that all were firing. Yesterday, I took your advice and replaced the rotor and cap. It worked!!!!! Engine now running fine. Cylinder no. 3 must have been crossfiring somehow. Inspected cap, but can see no cracks or carbon tracks. Interesting. Thanks for all of your info.

 

[Uncle Dave]

Re: Mercruiser 140 won't idle, backfires while starting

RonL,<br /><br />Thanks for posting back your "fix". Lots never post their fix back to the forum.<br />Glad you problem is over.<br />Uncle Dave