How to monitor for lean or clogged Carbs?

My question is how can I monitor my Carbs to make sure that they are working and not running lean?

I have a 2.0 L 89 Merc 150 with Carbs.
I'll confess that some years I have not winterized my outboard (like I didn't winterize it last year... although I did run the engine in late November, and will fire it up this month). I just didn't get to it.

So, I've since learned that a fouled carb can cause a cylinder to run lean, and your engine will blow if not addressed.

Is there some way to check the carbs to make sure they aren't running lean?

I realize that I could disassemble and clean them, and then I'd *know* that they are good, but I'd rather not, unless that is really the only option.

Is there some other way for me to check and see that the motor isn't running too lean because of a problem with one of the carbs?

-Philip

You can get real good at reading plugs.

I'll have to read up on that. I've seen writeups with color photos, but it never really made sense to me.
I guess I'll get a color printout of a good writeup and follow it step by step. That makes sense.


Thank you, @RSWORDS for the advice on reading plugs. I WILL take that advice.


Any other suggestions that also work? Would an IR thermometer let me tell by checking cylinder temp?

^^^ And piston wash.

Those carbs come off and apart easy for cleaning and inspection. No worries that way, but...

Reading plugs and piston wash will get you info your looking for.

a/f ratio gauge, exhaust temperature gauge

Yep I agree plugs and piston,,Also a gud little test to make sure they doin what they suppose b doin , u can choke out 1 hole at a time with palm of ur hand , if motor rpms dosent change then that carb is stopped up,,

If you are questioning them and not just curious I'd pull them down. Gaskets are cheap compared to a powerhead

There is MUCH info available for this, but imo these types of tuning methods will yield good safe results.
One more thing that is not hard to do and cost nothing but time, that "could" save a motor is to index the flywheel and set WOT tuning on the cylinder that reads the highest timing, all the others might be a fuzz behind this one, but at least All the cylinders will be at or below WOT timing setting.

Forbsauto and Jay Smith did an excellent write up here on S&F just for this.... :cheers:
https://www.screamandfly.com/showthr...index+flywheel

https://www.screamandfly.com/showthr...ston-wash-pics

https://www.screamandfly.com/showthr...71-Piston-wash

http://www.ossaengineering.com/wp-co.../sparkplug.pdf

Quote:

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Originally Posted by W2F a V-King

^^^ And piston wash.
but... Reading plugs and piston wash will get you info your looking for.

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Thanks, I didn't even know about piston wash, but I'll learn.

Quote:

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Originally Posted by SS Minnow

a/f ratio gauge, exhaust temperature gauge

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exhaust temp gauge seems like a good idea, if that would give the info I need.

Quote:

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Originally Posted by Merc 2.5

Yep I agree plugs and piston,,Also a gud little test to make sure they doin what they suppose b doin , u can choke out 1 hole at a time with palm of ur hand , if motor rpms dosent change then that carb is stopped up,,

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Thanks for the palm over the hole trick. That makes sense!

Quote:

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Originally Posted by RSWORDS

If you are questioning them and not just curious I'd pull them down. Gaskets are cheap compared to a powerhead

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Yeah... it's more a how do I know, rather than I think they're plugged... BUT, on the other hand, I'm on my third mota now, and in retrospect, it's possible that the first 2 blew because of a clogged carb making it too lean. I didn't even know that could be an issue back then, much less how to read the plugs or piston wash as a diagnostic.

Quote:

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Originally Posted by W2F a V-King

There is MUCH info available for this, but imo these types of tuning methods will yield good safe results.
One more thing that is not hard to do and cost nothing but time, that "could" save a motor is to index the flywheel and set WOT tuning on the cylinder that reads the highest timing, all the others might be a fuzz behind this one, but at least All the cylinders will be at or below WOT timing setting.

Forbsauto and Jay Smith did an excellent write up here on S&F just for this.... :cheers:
https://www.screamandfly.com/showthr...index+flywheel

https://www.screamandfly.com/showthr...ston-wash-pics

https://www.screamandfly.com/showthr...71-Piston-wash

http://www.ossaengineering.com/wp-co.../sparkplug.pdf

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Thanks for the links! This is just the kind of info that I wanted! I have a long cable with a camera on the end. It plugs into my computer's USB port. I should be able to use it to get good photos of the piston heads to look at the piston wash! :-)

Quote:

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Originally Posted by W2F a V-King

There is MUCH info available for this, but imo these types of tuning methods will yield good safe results.
One more thing that is not hard to do and cost nothing but time, that "could" save a motor is to index the flywheel and set WOT tuning on the cylinder that reads the highest timing, all the others might be a fuzz behind this one, but at least All the cylinders will be at or below WOT timing setting.

Forbsauto and Jay Smith did an excellent write up here on S&F just for this.... :cheers:
https://www.screamandfly.com/showthr...index+flywheel

https://www.screamandfly.com/showthr...ston-wash-pics

https://www.screamandfly.com/showthr...71-Piston-wash

http://www.ossaengineering.com/wp-co.../sparkplug.pdf

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I didn't know about the deviations in timing advance from one port to another. That's great to know. I think I'll get it running right first, and maybe back off a tad on the max high speed timing advance, just as a precaution. Then, when I have the time (and the right gauge), I'll go back to figure out which piston on my engine has the most advance, so I can set the high speed advance accordingly.

I suppose the "lazy" way seems to be to assume that piston 6 is the most advanced, and tune the engine off of that, but I'd still need a gauge to measure properly, so I might as well check 'em all and just do the job correctly!

For $75, I guess I'll buy the gauge from supporting vendor Jay Smith. Being a fishin' and pleasure boat guy (rather than a racer or speed hound), I really don't wanna pull the power head covers, except for those times when I really HAVE TO do it!

Quote:

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Originally Posted by SS Minnow

a/f ratio gauge, exhaust temperature gauge

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It sounds like an exhaust temp gauge is also in my future. I think I get it now. I want a baseline of what exhaust temps are normal when she's runnin' correctly. Then, when I'm runnin', if it seems hotter than usual, that tells me that it's likely runnin' lean, so there is a problem!

How much of a deviation in temp do you tend to see when it leans out?

Does the exhaust temp vary much (or at all) based on the outside air temp, changes in barometric pressure or humidity?

I always run in the same waters, so changes in elevation aren't a factor for me.

Thanks again for all of this great info! :cheers:
Once I get the this baby tuned and running properly, hopefully y'all have taught me enough that I can keep it running trouble free for many, many years!

Quote:

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Originally Posted by SS Minnow

a/f ratio gauge, exhaust temperature gauge

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OK. I've done some reading on a/f ratio gauges, and it seems that this could be the ticket.

So far, I've only found info on a/f ratio gauges for automobiles.

Does anyone have info on marine a/f ratio gauges, and info on how and where to install one?

Would the gauge be sensitive enough so that I could tell if one of the cyclinders is too lean (even though it wouldn't tell me which one),
or would that info get lost if the other 5 were OK?

as somebody who is crazy on this stuff i would also like to mention you can spend a lot of money on it
like you said in you first post your,e just a pleasure boater
you can buy a lot of fuel for these gauges
if your carburators are in good order and you use factory jets you should be on the safe/rich side of jetting
you can try to put a number on a 1 cylinder rebuild and have a cost number and see how much you are willing to spend on all these gauges
do you want live monitoring or just a check once in a while ?

maybe with a budget in mind go with those 750p 8mm endo phone camera units they have become very cheap
second would be an EGT setup still won,t give you a particular cylinder indication but at least an indication one side is deviating
http://thesensorconnection.com/categ.../multi-channel
these bolt into you bottom exhaust chest bolt holes
possible you could use these same bolts for an AF sensor
something similar as the yamaha OX system
or add sparkplug temperature to you your gauge
http://thesensorconnection.com/cht-s...e-12-and-14-mm
don,t know how precise it will be but it could give you a cylinder by cylinder number
but all this stuff adds up
at some point you should just go boating and enjoy

1. You've said that your boat is for fishing and not really speed.
2. You've blown 2 other motors already? Same Carburetors?

Dont over complicate what youre trying to accomplish. You just want a relioable motor for your fishing boat. You do not need an EGT

First thing you MUST do is take the money that youre willing to spend on an EGT or A/F ratio gauge and instead, have your carbs cleaned,rebuilt, and checked for proper factory jetting and. While your at it have your timing checked and all your fuel hoses checked or replaced.

Most Hi performance pleasure boaters dont even have EGTS's. Actual racers typically do but they've usually logged enough data to have a reference temperature. They found that reference temp by carefully jetting the motor to their conditions.
You do not have that reference point and could quickly melt another piston trying to find it with an EGT. 2 stroke outboards wont run long if they're too lean

if in doubt?.. get ya a nice clean table with clean table cloth.. a little brake kleen.. compressed air, new gasket kits for each carb.. spend a lazy afternoon (no hurry) CLEANIN' and installin' ALL new gaskets, inside and out on carbs.. do a link n synk and put it on tha water..

sure learnin' tha "read this n that" is good but ya can't beat a good cleanin' ta start...……… jmo