Trim and Idle

[CaptainDucky]

I have a Mercruiser Sterndrive 140 1977 and last time we took it to lake the trim would not trim up as I approached the trailer. It will trim up after getting out of the water, but as you are aware that is a little scary for my taste. Many ramps won't allow this. I think I was lucky that time. I did not have boat going when I trimmed up so something leads me to believe that it is when there is a load on it that the trim does not work going up. It works fine trimming in and with a load. Any ideas?

Also, At idle with muffs on it idles/chugs at about 1000 to 2000 rpm. However, when a little throttle is given it runs fine and sounds great, but then when I back off the throttle it goes back to chug/idle at the numbers above. Any ideas?

I replaced the shift cable, impeller, lower unit seals, shift shaft etc a year ago. So overall it is running but with the problems above.

Thank you for your help in advance.
CaptainDucky
Proud Owner of '77 Mark Twain
Mercruiser Sterndrive

 

[Don S]

Re: Trim and Idle

Engine sounds like it needs a full tuneup including a compression test. The points need to be set using a dwell meter, then the timing checked, and the advance timing checked. Then the idle mixture needs adjusted. The turns out for the idle mixture screws stated in the manual are prliminary adjustments only.

On your trim, assuming you have the 3 button panel, does it go up if you use the center and up buttons?

 

[CaptainDucky]

Re: Trim and Idle

That is how I have always trimmed up. When my grandfather gave me this boat that is how he said to use the trim up. I don't believe it works with just the top button.

As for the tuneup, I will get to that.

Thanks will let you know how it goes.

CaptainDucky
Proud Owner of '77 Mark Twain
Mercruiser Sterndrive

 

[CaptainDucky]

Re: Trim and Idle

I will check into the compression test and I plan on getting a dwell meter.

Advanced Timing I am not sure of. I have done the timing, but can you steer me to the advanced timing?

Thanks DonS

CaptainDucky
Proud Owner of '77 Mark Twain
Mercruiser Sterndrive

 

[Don S]

Re: Trim and Idle

Below is the tuneup specs for your engine, on the last page is the advance timing chart. When you get your timing set to 6? BTDC at 700 rpm, as you speed the engine up, the timing steadily increase. At 2000 rpm, you should see in the range of around 32? to 38? with your timing light. If it doesn't move, the weights in the distributor are probably frozen.

On the trim pump, do you have one or two solenoids?

 

[CaptainDucky]

Re: Trim and Idle

Don, I have 1 solenoid on trim pump.

I am enlcosing a picture of a compression tester that I found that apparently my grandfather gave me with all the boat stuff. I am a little clueless to the tubing that is there next to part I put into the spark cylinder housing. Any suggestions?

Also, the service manual says to remove and ground coil high tension lead from distributor cap tower. What actually does that mean? Remove flame arrestor and block throttle and choke in wide open position, how to do that? Everywhere I have read how to do this does not say anything about these. Most say to remove all plugs and lead wire off rotor cap and then insert the guage (hand tight) then crank a few times making sure to right down numbers of each cylinder. If I know what the book means and how they are saying it then I can run test. Also, does the drive need to be in the down or up position?

I am headed to get a feeler guage and a dwell meter today so I can run the other tests.

 

[CaptainDucky]

Re: Trim and Idle

Ok so I went to get a dwell meter and ended up with an automotive multimeter that says on it that it does dwell angles. Will that be alright?

Thanks for your help.

 

[haulnazz15]

Re: Trim and Idle

Definitely too high of an idle set at the moment. Should be below 800rpm and steady. You should be able to trim up just using the "up" button, but it will stop once it gets to the upper trim limit. The "up/out" button is help simultaneously with the "up" button in oder to bypass the trim limit sensor in order to trailer the boat. You shouldn't run the engine while the unit is in the trailer position. If the trim limit switch is messed up, or the wiring has been altered to bypass it, you may have to hold both buttons to get it to move up at all. Nice to see another 'Twain on the water.

 

[CaptainDucky]

Re: Trim and Idle

Ok so compression test is this:
Cyl 1 test 1 125. Test 2 125
Cyl 2 test 1 155. Test 2 155
Cyl 3 test 1 140. Test 2 140
Cyl 4 test 1 120. Test 2 120

Wet test on 1 and 4
Test 1 no change. Test 2 no change

Book only says something about them being adjacent which they aren't. Book says if no change then they are sticking or seating poorly now what? That explains the bad idling. How to fix this?

Thanks for advice
CaptainDucky
Proud owner of '77 Mark Twain

 

[Bondo]

Re: Trim and Idle

Ayuh,.... Do a Leak-down test on the low cylinders, 'n see if it's the valves...

If so,... Have the Head rebuilt at a Machine Shop...

 

[Don S]

Re: Trim and Idle

Follow this procedure for doing the compression test. The oil will eliminate the rings. And disregard the 30% difference the bulletin allows. That may be fine for GM warranty, but not for having a good running engine. You shouldn't have more than 15% from lowest to highest. With 155, you shouldn't have less than 130.

View attachment 97-25 Compression Test.pdf