1971 Merc 800 stalls when put into gear - UPDATE 7/27

[Moody Blue]

Have had this motor going on 4 seasons now and have struggled with this issue since I got it. I've managed to "get by" with it by goosing the throttle as it goes into gear but I can not confidently shift gears while docking etc., without it stalling at the worst times. I'm not prepared to put this boat back into the water until I've fixed this problem.

I have gone thru the link and sync procedures countless times with no success. I'm pretty sure I understand the procedure and I've followed it step by step, over and over again. Motor starts with a touch of the key and will idle reasonably well in neutral at about 800rpm. As soon as it goes into gear it stalls. Compression has been measured at between 130-135 across all cyls. Carbs were torn down, thoroughly cleaned and rebuilt last season. Motor runs very well once it gets past the stalling. Good holeshot and runs at WOT for extended periods of time without issue.

Here is where I'm at. Please, if you can offer any advice or direction I would be ever grateful.

1) TDC verified against timing sticker with dial indicator.

2) With #1 cyl at TDC, flywheel aligned with timing decal, the distributor pulley seems to be off alignment CW 1/2 tooth. Ideally the flywheel, sticker and distrib timing marks should be aligned .

3) If I align the timing marks on the distrib pulley with the flywheel the flywheel timing mark aligns at 5 BTDC on the timing decal.

4) Primary carb pickup is set at 6* BTDC, by sticker.

5) Max advance timing set at 21* BTDC, by sticker.

6) Secondary carb pickup is set to engage at max advance.

7) Carb idle screws initially set 1 1/2 turns out from seated. Have adjusted in AND out 1/4 turn at a time with same stalling results.

8) With the motor running at 800rpm in neutral, timing is between 0 and 2* BTDC.

9) Put the motor into gear (FWD or REV) and it stalls everytime.

10) Touch the key and it starts right back up.

Help please.

 

[schematic]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Could just be a tired engine or too low of a idle speed. Have you tried a higher idle speed?

 

[Texasmark]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

800 in N on muffs is a bit light and probably in the water would be about the same. My manual for a similar HP Merc is 675 in F gear, no fast idle or anything, just plain idle boat in the water and moving. That results in about 1 to 1.2k in N.

Mark

 

[Moody Blue]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Have been running the motor in a large barrel to try and simulate actual operating conditions. In previous years I've used the muffs with no success in trying to set the motor up.

Most posts I've read suggest not setting the neutral idle speed higher than 1000rpm so as to not destroy the lower unit when shifting. I'll try adjusting the idle up to 1000 and see how it behaves.

One thing I did notice is that the carb idle screw adjustments do not make a dramatic/noticeable difference in the engine operation. Not really sure what I am looking for adjusting these idle screws.

 

[Texasmark]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Not really sure what I am looking for adjusting these idle screws.

Taking the throttle in your hole shot. If it takes it fine. If it bogs, you need more gas (ccw on the screw) but just a little at a time and try it....trial and error, trial and error. Sometimes it takes no more than the width of a screw driver blade to solve the problem....BTDT just this year. Everyone has their way of doing it and may chime in. So be it.....this is a Forum. Problem you will have if you get multiple answers is figuring out which one you will use.

I don't remember on the older Mercs, but in todays engines the idle set screw varies timing. Retard or advance for slower or faster idle. What I said is right out of the book and it works.

Mark

 

[Moody Blue]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Thanks Mark. Spent another couple hours at it tonight and went back to double check the basics.

Compression numbers test number one #1-158, #2-164, #3-162, #4 150.
Compression numbers test number two #1-164, #2-167, #3-159, #4 152. Within 10% on a cold engine.

Spark test easily jumps a 1/2"(+) gap with a bright blue snap.

Double checked my timing and it's as originally posted, which I believe to be correct.

Tried squeezing the primer bulb just as I was about to shift into gear but engine still stalled.

Set both idle mixture screws at 1 turn out from seated and adjusted RPM's to about 900. Stalled

Adjusted idle mixture screws out 1/4 turn at a time (all the way to 3 turns out) and tested each time then readjusted RPM's to 900. Stalled each time.

As I'm adjusting the idle mixture screws, I don't notice a big difference in the behavior of the motor other than a change in the RPMs which I then adjusted using the idle speed stop screw, which I believe changes the timing.

I did at one point increase RPM to about 1100 with idle mixture screws 1 3/4 turns out then shifted into gear. Motor stayed running but RPM dropped to between 500 and 600 and idled erratically. That's a big decrease in RPM is it not? No wonder it stalls out with the idle RPM set to 900.

This has really got me baffled and frustrated. Again, thanks for any input you might have.

 

[merc850]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Are you adjusting the idle screws while engine is running in gear then setting the idle stop to 800rpm?
The manual says to set the pulley arrow 1/2 tooth clockwise this should advance the timing sliightly.

 

[Texasmark]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Thanks Mark. Spent another couple hours at it tonight and went back to double check the basics.

Compression numbers test number one #1-158, #2-164, #3-162, #4 150.
Compression numbers test number two #1-164, #2-167, #3-159, #4 152. Within 10% on a cold engine.

Spark test easily jumps a 1/2"(+) gap with a bright blue snap.

Double checked my timing and it's as originally posted, which I believe to be correct.

Tried squeezing the primer bulb just as I was about to shift into gear but engine still stalled.

Set both idle mixture screws at 1 turn out from seated and adjusted RPM's to about 900. Stalled

Adjusted idle mixture screws out 1/4 turn at a time (all the way to 3 turns out) and tested each time then readjusted RPM's to 900. Stalled each time.

As I'm adjusting the idle mixture screws, I don't notice a big difference in the behavior of the motor other than a change in the RPMs which I then adjusted using the idle speed stop screw, which I believe changes the timing.

I did at one point increase RPM to about 1100 with idle mixture screws 1 3/4 turns out then shifted into gear. Motor stayed running but RPM dropped to between 500 and 600 and idled erratically. That's a big decrease in RPM is it not? No wonder it stalls out with the idle RPM set to 900.

This has really got me baffled and frustrated. Again, thanks for any input you might have.

Squeezing the bulb just fills your bowls. You are onto the solution. When you had the screws 1 3/4 turn out, which by the way is not all that much, and the idle set to 1100 you were getting there.

I'd open the jets some more and if you get to 2 turns and no help, I'd put carb kits in. Your compression numbers are great.

Mark

 

[Moody Blue]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Are you adjusting the idle screws while engine is running in gear then setting the idle stop to 800rpm?
The manual says to set the pulley arrow 1/2 tooth clockwise this should advance the timing sliightly.

You might have something there. I've been adjusting the idle in neutral. I'll give this approach a try when I get a chance. Heavy rains expected over the next 2-3 days here.

From my first post you can see from the photos that in fact the dist pulley is set about 1/2 tooth CW of "ideal" alignment. I wasn't sure if that was right or not.

 

[Moody Blue]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Squeezing the bulb just fills your bowls. You are onto the solution. When you had the screws 1 3/4 turn out, which by the way is not all that much, and the idle set to 1100 you were getting there.

I'd open the jets some more and if you get to 2 turns and no help, I'd put carb kits in. Your compression numbers are great.

Mark

I'm convinced that the motor is starved of fuel for a brief time when shifted into gear, SOOOOO, what if I were to set it up so that the carbs open up just a bit sooner than what is described in the manuals. Primary carb pickup should occur at 5-7* BTDC. What if the butterflies start to open sooner so that at that timing event there is more fuel feeding the motor? Any downside to doing that?

As for the carbs, I pulled them last season (after enduring two previous seasons with the same stalling problem), cleaned and rebuilt them completely. They carbs were spotless when I torn them down and I have no reason to believe they should be fouled so soon. If all else fails, I will be forced to pull them (a real PITA) and tear them apart again. Hope it doesn't come to that.

 

[Moody Blue]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Going back to my first post for a minute. Help me understand the CORRECT alignment of the flywheel and distrib pulley please AND their relationship to the timing decal.

My understanding is that if you were to draw a straight line between the crankshaft center and distrib shaft center points, then the flywheel timing mark should align with the arrow on the distrib pulley AND should align with the TDC mark on the timing decal AND the #1 piston should physically be at TDC. Is this correct? If so, then something is amiss with my setup as seen in the photos.

 

[merc850]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Here are 2 pages from different manualsthe 800 one is what you're probably using but note the 850 method, it might work for you.
If you have this type of carb the filter may be plugged - you can take the top off without removing carbs to check them for crud and I would suggest removing the screens and throwing them away.

 

[Moody Blue]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Thanks, that is the setup I have currently. The distrib pulley arrow is aligned with the flywheel timing mark but the resulting timing indicator position ends up at about the 6* BTDC as is also shown in one of your manual pages. So it must be correct.

One less thing to consider as a problem.

 

[Moody Blue]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Hope to get back at this Friday, so if there are any other ideas or suggestions, would love to hear them.

 

[Moody Blue]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Upon further investigation I've discovered I'm getting water into cyl #4. That would probably explain the lower compression number for that cyl and possibly a cause of the stall problems I've been battling.

I pulled the plugs today and found the face of plug #4 completely rusted. It was like new when I installed it prior to my testing earlier this week. Looking into the cyl with a bright like I can see the top of the piston is nice and shiny.

Pulling the powerhead and going to replace the lower crankshaft seals and o-ring. No sense pursuing my stalling problem until this leak is fixed. Wish me luck.

 

[Texasmark]

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Re: 1971 Merc 800 stalls when put into gear .... grrrrrrr

Looking into the cyl with a bright like I can see the top of the piston is nice and shiny.

That's what water does in a combustion chamber. I never had it happen on a boat but used to happen on the old "rent-a-wrecks" I used to fix up for the kids to have transportation.

Mark