TOPIC: Merc 1250 High Idle

Hi All,

Had my Merc 1250 out for it's first test and for the most part it ran great except idle was high. Around 900 in the water and in forward gear.

I tried to adjust it down, but carbs are closed and I suspect that it may be a timing issue. I only have a clymer manual and was reviewing the timing procedure and it's pretty intimidating and I don't want to mess up a good running motor. But if it's too far advanced, I'm going to mess it up anyway.

Can anybody shed some light on this?

Thanks,
Mark

use the idle stop screw then readjust the throttle cable.

Thanks Dave. The throttle cable is off and idle screw backed out. Carb butterflies are closed tight.

even when the butterflies are closed you can still retard the dis.which slows it down you are not that far off at 900 should be about 750 in gear.

dave bernard wrote:

even when the butterflies are closed you can still retard the dis.which slows it down you are not that far off at 900 should be about 750 in gear.

I was thinking about that, but I didn't want to adjust the idle with the timing. I would rather time it correctly.

When setting the WOT timing, the book says to "Adjust the spark advance linkage as required until the flywheel timing mark aligns with the specified timing mark on the flywheel"

I have a decal with many marks and when I crank the motor with WOT the timing mark is around 50+ deg. I'm using the timing light on #1 cyl.

Any ideas what I'm doing wrong?

Thanks,

Mark

dave bernard wrote:

even when the butterflies are closed you can still retard the dis.which slows it down you are not that far off at 900 should be about 750 in gear.

I was thinking about that, but I didn't want to adjust the idle with the timing. I would rather time it correctly.

When setting the WOT timing, the book says to "Adjust the spark advance linkage as required until the flywheel timing mark aligns with the specified timing mark on the flywheel"

I have a decal with many marks and when I crank the motor with WOT the timing mark is around 50+ deg. I'm using the timing light on #1 cyl.

Any ideas what I'm doing wrong?

Thanks,

Mark

you are not adjusting with the timing but when you adjust the idle stop it also retards the timing.the butterflies close first.

dave bernard wrote:

you are not adjusting with the timing but when you adjust the idle stop it also retards the timing.the butterflies close first.

Thanks Dave. I have the idle stop backed all the way out and the timing retarded as far as it will go. The WOT timing is at 45 and I can't get it any lower.

Thanks,

Mark

I found the problem. I didn't even think it was possible which is why I skipped the first step of the link 'n sync in the Clymer manual.

The distributor belt was off by one tooth. I don't know how it possibly could jump but I guess it did. The belt doesn't seem damaged and it appears to be tight. What could cause the belt to jump?

After I realigned the belt, I was able to easily adjust the WOT timing and can now use the idle stop to set the idle.

I'm worried now about all the extra advance it had during the full throttle runs.

Thanks,

Mark

Might have been installed wrong last time the belt was changed? (It happens, it's easy to get it off by one tooth!) Does your compression still check out okay?

Hydro Mark wrote:

I'm worried now about all the extra advance it had during the full throttle runs.

Thanks,

Mark

Mark, I recall one of my old 100hp motors slipping timing when I (apparently) didn't lock down the timing stop screw tight enough, I was thinking that day it was really running strong!

When I got home, checking things out, I found the plugs looked like they'd gotten really hot, and the timing stop was backed all the way out!

When I checked the timing it was over 43 deg BTDC!!

After re-timing she ran good with no problems.

Both the 1000 and 1250 motor have the older-style, "crossflow" pistons with a flat on top.

Fortunately the 1000 & 1250 pistons are more tolerant to detonation than the newer "deflector" type, so likely you didn't hurt anything.

You might want to take a compression check just to make sure there aren't any issues.

If just for peace of mind...........ed

Thanks guys...

MarkS wrote:

Might have been installed wrong last time the belt was changed? (It happens, it's easy to get it off by one tooth!) Does your compression still check out okay?

Definitely came to me that way. Idle was high right off the bat and couldn't lower it. I'll check the compression and pray

ed_mc wrote:

After re-timing she ran good with no problems.

Fortunately the 1000 & 1250 pistons are more tolerant to detonation than the newer "deflector" type, so likely you didn't hurt anything.

You might want to take a compression check just to make sure there aren't any issues.

If just for peace of mind...........ed

I'm hoping I have the same experience as you, Ed.

Thanks again guys
Mark