Random Miss at Idle. HELP!!

No sir, it is not possible for your battery (still the 2yr old Deka 24M7?) to have 1000CCA. See East Penn's spec sheet, the 24M7 is right at the top - https://www.eastpennmanufacturing.co...Sheet-0194.pdf

Brand new, that battery had 800CCA, 1000MCA, & 130min RC.

Beg or borrow a gp31 battery with a verified 900+ CCA and see what happens. Your latest reply, IMHO, indicates classic signs of inadequate capacity, something I addressed as a concern in my 4/2/20 reply to your original post in the Mercury Motors forum.

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Originally Posted by SilverFox579

No sir, it is not possible for your battery (still the 2yr old Deka 24M7?) to have 1000CCA. See East Penn's spec sheet, the 24M7 is right at the top - https://www.eastpennmanufacturing.co...Sheet-0194.pdf

Brand new, that battery had 800CCA, 1000MCA, & 130min RC.

Beg or borrow a gp31 battery with a verified 900+ CCA and see what happens. Your latest reply, IMHO, indicates classic signs of inadequate capacity, something I addressed as a concern in my 4/2/20 reply to your original post in the Mercury Motors forum.

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I ran a 31 straight off the shelf. Showed 12.4 volts. Cranked strong. Still stumbling.I do feel like it may be voltage related. It is almost too inconsistent to be a particular cylinder... all plugs look similar too.

Although I agree that those numbers don't make sense. I'll pull it back out and have it tested somewhere else. I am tempted to buy a new one, but am tired of throwing money at this thing lol.

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Originally Posted by Hicktacular

I noticed something tonight that I have not noticed yet. My Lowrance shows 12.4 volts before I start the engine. I started the engine, and it went up to 12.8v and has the stumble while it was idling. When I bring the engine up off of idle, the volts come up to 13.3 ish as the miss goes away (the only time that I have noticed the miss is at idle). After running down the water a little ways and come off of plane and back to an idle, the idle voltage is between 13.8v to 14.1v, and no miss. Sit (with engine off) for 10 minutes or so, and the Lowrance shows 12.4 volts again. When I crank up, it only goes up to 12.8 ish until I come above idle.

I also noticed that when the voltage is showing in the mid 12 range at idle, if I run my trim up or down, my RPMs will drop while the trim motor is running.. that does not seem right. It does not happen when the voltage is in the mid to upper 13v range. I have had the battery tested in two different places and both show over 1000 cca. I also tried a new battery, and it showed similar voltage.

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Didn't know you had already tested with a gp31, and 12.4 off the shelf is low, was it fully charged prior to use?

If possible, retest under the same conditions as above while measuring voltage at the battery with a DMM and post back. If RPM when trimming doesn't drop and stumble goes away when you're seeing 13.3 - 14.1v, problem is somewhere in the electrical system. My boat was originally rigged with a gp24, 800CCA battery by the dealer, and right at two years, I experienced the exact same issues you report. I replaced it with a gp31 AGM rated at 1150CCA and stumble at idle and RPM drop when trimming disappeared.

I'm starting to think it would be a good idea to verify the throttle plate airgap on this one....

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Originally Posted by EuropeanAM

I'm starting to think it would be a good idea to verify the throttle plate airgap on this one....

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From the manual that I have:

"However, should the throttle plate require adjustment, use the throttle plate stop screw
to set the throttle plate clearance @ 0.045 in. (1.143 mm) using a #56 drill."

Am I to take that as a #56 bit is my gauge for the air gap between the butterfly, and the throttle body?
Also, will one of you please double check that spec for a 2008 150 Optimax? The above quote is from the manual that I purchased, but not for my engine.. My correct manual has not came in yet.

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Originally Posted by SilverFox579

Didn't know you had already tested with a gp31, and 12.4 off the shelf is low, was it fully charged prior to use?

If possible, retest under the same conditions as above while measuring voltage at the battery with a DMM and post back. If RPM when trimming doesn't drop and stumble goes away when you're seeing 13.3 - 14.1v, problem is somewhere in the electrical system. My boat was originally rigged with a gp24, 800CCA battery by the dealer, and right at two years, I experienced the exact same issues you report. I replaced it with a gp31 AGM rated at 1150CCA and stumble at idle and RPM drop when trimming disappeared.

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Your making me want to go get another battery, just to make sure... I guess it would rule it out.

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Originally Posted by Hicktacular

From the manual that I have:

"However, should the throttle plate require adjustment, use the throttle plate stop screw
to set the throttle plate clearance @ 0.045 in. (1.143 mm) using a #56 drill."

Am I to take that as a #56 bit is my gauge for the air gap between the butterfly, and the throttle body?
Also, will one of you please double check that spec for a 2008 150 Optimax? The above quote is from the manual that I purchased, but not for my engine.. My correct manual has not came in yet.

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I think Don may be on to something. I am going to Lowes now to see if they have the #56 bit. I Found something here that mics under the 1.1mm that the manual calls for, and it tight. So either I misunderstood the manual, my mics are off, or the air gap is too tight. I wont adjust until I hear back from you guys though. I am attaching a pic. Probably can't tell much from it.Attachment 405413

I may have missed it but has this mtr always done this or did it start this after comp fail or another item failure

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Originally Posted by JOE54

I may have missed it but has this mtr always done this or did it start this after comp fail or another item failure

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I don't think it has ever been perfect, but I don't remember it being this bad. It is not as noticeable with my smaller 21P prop. The bigger 23P Tempset that I put on about a year ago seems to magnify it.

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Originally Posted by Hicktacular

I think Don may be on to something. I am going to Lowes now to see if they have the #56 bit. I Found something here that mics under the 1.1mm that the manual calls for, and it tight. So either I misunderstood the manual, my mics are off, or the air gap is too tight. I wont adjust until I hear back from you guys though. I am attaching a pic. Probably can't tell much from it.Attachment 405413

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Most of the manuals no longer contain that info. What part number is on your manual (and what page)?

Traditionally you use a wire gauge or bit at the highest point of the butterfly (90 degrees from the throttle shaft). It should be snug but the plate should NOT jump when it is pulled straight up/out of the gap.

This is one of those items that must be done VERY carefully and critically. Just a few thousandths of an inch can make a BIG difference in the air flow (at idle).

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Originally Posted by EuropeanAM

Most of the manuals no longer contain that info. What part number is on your manual (and what page)?

Traditionally you use a wire gauge or bit at the highest point of the butterfly (90 degrees from the throttle shaft). It should be snug but the plate should NOT jump when it is pulled straight up/out of the gap.

This is one of those items that must be done VERY carefully and critically. Just a few thousandths of an inch can make a BIG difference in the air flow (at idle).

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I believe this is the part number.. it is at the bottom of the page.

90-859494R1 JUNE 2000

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Originally Posted by EuropeanAM

Most of the manuals no longer contain that info. What part number is on your manual (and what page)?

Traditionally you use a wire gauge or bit at the highest point of the butterfly (90 degrees from the throttle shaft). It should be snug but the plate should NOT jump when it is pulled straight up/out of the gap.

This is one of those items that must be done VERY carefully and critically. Just a few thousandths of an inch can make a BIG difference in the air flow (at idle).

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Would you look at that! .045 wire. I will mic the wire tomorrow, but believe it definitely needs adjusting if the .045 spec is correct. What do y'all think?

IF I need to adjust, I assume I need to adjust the rolled and cam ALONG with the idle stop screw on the big arm. My manual explains how to do that. Do any of you know what size the security screw is on the arm that the roller is attached to? I may not have to adjust that, but seems that I would to keep the correct geometry (with the roller sitting in the saddle part of the cam).

https://youtu.be/9Y8sjuwrFfs

Attachment 405466

Due to the nature of this adjustment- I'm going to suggest some direct guidance rather than posting. My phone number is in my signature (below).

You also have a PM.

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Originally Posted by Riccochet

My '14 150 ProXS does the same thing at idle, mostly when warm. Has done it since new. It's been back to the dealer numerous times for it. They never found anything wrong. My buddy I fish with is a Mercury tech, even he said it's odd. And he's checked the motor three times over, never found anything. It hasn't gotten worse or better in 6 years, and the motor still runs perfect at anything over idle. So I just chalked it up to a nature of the beast.

I hope you find your answer, as I'm genuinely curious.

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Same here. My '04 175 Opti makes the exact same little sputter now and again at idle in gear, like when I'm graphing. In fact, I don't recall ever being in a 2-stroke that didn't do that.
Did it with the stainless reeds which were all in spec; then I purchased TDR reeds from Don, all in spec after lapping the cages, and it still does it here and there. Nature of the beast to me, BUT if there is something to look into I certainly will.

Please let us know what you find.

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Originally Posted by djb750

Same here. My '04 175 Opti makes the exact same little sputter now and again at idle in gear, like when I'm graphing. In fact, I don't recall ever being in a 2-stroke that didn't do that.
Did it with the stainless reeds which were all in spec; then I purchased TDR reeds from Don, all in spec after lapping the cages, and it still does it here and there. Nature of the beast to me, BUT if there is something to look into I certainly will.

Please let us know what you find.

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Mine is bad though. Like to the point that it dies at times. I can live with a little spitting and sputtering.

Hey guys, just an update. I have the throttle body properly adjusted. It has helped a lot!! At first, I thought it fixed it completely. I took my 21 pitch laser 2 off, and put my 23 Tempest back on. After a tank of fuel it seems worse again.. I am looking for a good 21 pitch now. I believe it was a combination of over propped, and the air gap being off. I'll update after I get the new prop and run a tank of gas through it. I also replaced the battery with a 31gp.

This is probably my last post on this thread. I just wanted to make sure i closed it with an update. Try as I may, I still can not get the idle 100% correct. I may call Don to see when he can fit it in, but may try a local first. Correcting the butterfly on the air handler helped a lot. Before, when I put it in gear, the engine would die down and idle lower. Now it does not. That alone has made it good enough to live with. Usually after a long run, it idles great. After sitting a little while, it will have a pretty rough idle and may die. I just make sure that when I crank it, and put it in gear, I bring the rpms up a little. Seems to help. I appreciate all of the help, and hope I can help others one day. If I eventually do find the fix, I'll post it.