Engine Stalls When Shifting into Gear - Maxum Boat Owners Club

jrsick · 07-05-2019, 08:30 PM

2006 Mercruiser 5.0 with zero hours on newly rebuilt carb. Electric choke.
Complete the carb checklist in the manual; accel pump squirts fuel through discharge holes, idle mixture screw set to 1.5 turns out, idle speed screw at 2 turns.
Engine starts and idles fine on the hard. Took it to the lake to set the carb and test.
Engine started fine coming off of the trailer. Good idle at 800 rpm. Engine stalled when put in gear. Restarted, idled fine, revved fine out of gear. Put it in gear and immediate stall. This happened 6 times then engine would not restart.
Starter working good and battery is strong. Choke was open.
Tach was jumping around occasionally, but I don't think it's related to engine problem. Not sure about that though.
Service manual lists several potential causes for engine stalling. My most likely causes are accel pump problem, dirt in carb, or leaky gaskets.
I'm going to replace the base gasket and put a thin layer of RTV on each side to get a good seal.
If new gasket doesn't fix problem, that leaves taking carb back to shop.
Anyone have similar issue or any suggestions on potential causes?

mmwjr · 07-05-2019, 08:45 PM

While the shift interrupt switch is supposed to only short the ignition coming out of gear I have seen misadjusted or bad cables cause issues going into gear. Try disconnecting it just to see if that resolves the issue.

jrsick · 07-06-2019, 02:36 AM

Thanks for the reply. I removed and reinstalled the throttle bracket when I replaced my carb. Do you think I could have affected the cable adjustment in the process?

jparsons121 · 07-06-2019, 01:06 PM

Yes. Go thru the procedure to set the cable adjustments. Also, no RTV. It doesn't do well around gas.

mmwjr · 07-06-2019, 01:52 PM

Quote:

Originally Posted by jrsick

Thanks for the reply. I removed and reinstalled the throttle bracket when I replaced my carb. Do you think I could have affected the cable adjustment in the process?

It doesn’t take much to knock the alignment out for the interrupt switch.

jrsick · 07-16-2019, 12:20 AM

I'm ready to fix my stalling problem. Merc manual has little info on lower shift cable in the MCM section, but decent discussion in the MIE which probably applies to my setup. SEI has some good videos also.
Attached is pic of my shift bracket before I tear into it. My understanding is that I need to get exactly 6 inches of space between the center of the forward mounting hole and the center of the adjustment barrel. If that doesn't fix problem then I need a new lower shift cable. Does that sound right?
So if I can't shift into gear without stalling the engine then I should disconnect the shift interrupt switch and see if problem goes away. If problem goes away then cause is still likely the lower shift cable, but I can be fairly certain that it is either cable or switch. Correct?
I have read some discussion boards that say adjusting the lower shift cable must be done with boat in the water and a load on the prop. That doesn't sound right to me and I am interested in experience anyone has in installing a lower shift cable. Thank you.

mmwjr · 07-16-2019, 01:27 AM

While you may get it adjusted right out of the water the proper procedure is to do it in the water as the load on the prop is transferred to the clutch which intern puts load in the shift compartments including the cable.

For the most part the switch either works or not, although they can get sticky but this doesn’t happen too often.

jrsick · 07-16-2019, 12:22 PM

Thanks for the reply. In the picture I think the shift lever is in neutral The shift interrupt switch is the gray switch with two wires in the lower third of the picture. The shift interrupt switch is sitting on the high part of the cam and depressed. Which likely means the switch is activated and not where it should be. I'm going to the boat this afternoon and working on this.
Do you know a test for the shift interrupt switch? It is either open circuit when depressed, or open circuit when not depressed.
I see what you mean about the cables, they may stretch slightly under load.

mmwjr · 07-16-2019, 12:43 PM

When in neutral the switch should be in the valley of the cam. The contacts are closed when the switch is depressed.

jrsick · 07-16-2019, 11:44 PM

The problem was a sticky lower cable. The shift interrupt switch moved into the valley of the cam as soon as I removed the lower shift cable.
I'm going to order a new lower cable. I want to get out this weekend though so I'm going to try and lube the existing cable. I know not recommended procedure.
I will probably put some 20W oil down the cable and see if that loosens it up enough for a couple days on the water. Let me know if anyone has other ways to lube cables.

mmwjr · 07-17-2019, 02:51 AM

Best of luck and I would do the same.

jsum · 07-17-2019, 09:54 PM

Hi I just had similar issue although it wasn’t the cable for me. While docking and trying to go from drive to neutral or reverse to neutral it would stall. After a few times of that happening it wouldn’t start at all. I had no fire. The coil on top of the distributor had gone bad, I replaced the cap, rotor button and installed a performance coil for corvette into the cap and fixed my issue., all of these parts were purchased in stock at advanced auto parts.

jrsick · 07-18-2019, 12:37 AM

thank you jsum. I replaced those items as part of a tune up this season. My problem was definitely the shift interrupt because I could see the switch depressed when the shift lever was in neutral. Removed the lower shift cable and switch sprung to the correct position on the cam.

rwc · 07-30-2019, 01:39 AM

Good to see you found the problem.

Since I just rebuilt my carb as well, I'm curious as to how you will tune it as you have to do it as I understand you have to do it with a hot engine in gear. I got my wife to steer in gear at idle, cranked the idle mixture in until the engine stuttered from too lean, then counted the turns out until it stuttered from being too rich, then split the difference.

I know this is probably the poor man's method and it should be done with the proper tools, but I don't have them, don't know how to use them, and this seemed to work. What is your plan?

jrsick · 07-30-2019, 11:41 AM

rwc, your approach is as good as any. The manual calls for putting engine in base timing mode then setting idle rpm, 600 for my engine, with the carb set slightly rich. Lean carb out to get max rpm, then set idle to 600 again using idle adjustment screw.
I haven't had chance to do an underway adjustment yet. I set my idle rpm initially as per the carburetor checklist. The idle mixture screw didn't seem to have any effect with unloaded engine running on muffs.

rwc · 07-30-2019, 05:01 PM

Quote:

Originally Posted by jrsick

The idle mixture screw didn't seem to have any effect with unloaded engine running on muffs.

I was 6.5 turns from lean stutter to rich stutter. No particularly noticeable effect from about 1/2 turn in either direction of the stutter, so that's 5.5 turns where not much happens. I went back 3 turns from rich, so based on mmwjr's advice in the other thread, I'm probably at least one turn too rich.