Carb jet size markings question

[Aaronhl]

I have a carb main jet, it has a 0 7 2 stamped on it, does that mean it's size is .072? I thought my carb's main jet would be smaller according to the manual... It's 1994 Mercury 200 2.5 FF engine if that helps...

[Glastron1987]

Get an Optimax

[Glastron1987]

I have a micrometer if you want to measure it. Will need to fit something that goes in it first.

If I remember correctly from when I replaced mine a long time ago, the stamping does indicate the size. Maybe somebody replaced them at some time.

I'm no expert on carb jets, but I think when using ethanol fuel your better off with a little bigger jet, especially on the main jet, because ethanol is either less dense or less explosive than real gasoline.

Also, going richer at high speed is less risky than going lean at any speed.

[Aaronhl]

The reason I want to replace the jet is because I striped the head a little bit taking it out with the wrong sized screw driver...
I got a caliper in there and I think I got a pretty good reading at .064 which is what the manual says should be in the WMH39-3 (cylinders 5+6)
Strange that it would be stamped 072 since Mercury does have a .072 jet but maybe the stamping is irrelevant...
I am going to check some other jets to see what they say

[Aaronhl]

Get an Optimax

Well it does have an older Optimax style cover how about that

[racer]

The Merc jets are very close to the stampings, you need a pin gauge to measure it correctly. You also need the serial number to verify correct jets and be careful as different HP are often shown on same page. I looked up 2 different serial ranges and neither had what you mentioned as the main. Did see smaller HP with .072 but the 200's in range I looked called for .080.

[Aaronhl]

The Merc jets are very close to the stampings, you need a pin gauge to measure it correctly. You also need the serial number to verify correct jets and be careful as different HP are often shown on same page. I looked up 2 different serial ranges and neither had what you mentioned as the main. Did see smaller HP with .072 but the 200's in range I looked called for .080.

Thanks for the post - How exactly are you looking at this info based on serial number and comparing to the jets?

I have WMH 39 carbs on a 1994 Mercury 200 2.5L Serial #0G075893

According to the service manual the jets for this engine and carb combo should be:

Main 1,2=.066 3,4,5,6=.064
Progression .050
Idle Air .046
Back Draft Vent .084

Going by the numbers stamped on the jets I see in each of the three carbs the following jet stamps:

Main .072
Progression .040 (except for only #4 cylinder having a .050)
Idle Air .048
Back Draft Vent .072

I am wondering why all three carbs are not the same by having only 1 of the 6 Progression Jets different. Should I replace the .050 Progression Jet on cylinder 4 to a .040 to match the rest of the carbs or should I put in all .050 jets since that's what the manual lists?

Should I be concerned with the differences, specifically of the Back Draft Vent and Progression Jets being smaller than what the manual lists?

Will the Idle Air Jet being slightly larger than the manual suggests make it too lean?

[mach351]

I don’t think those are the original carbs. Pretty sure it should’ve had Whm-21’s stock with a .066 main.

Even the 245’s didn’t run a .072 except for break in.

[Aaronhl]

I don’t think those are the original carbs. Pretty sure it should’ve had Whm-21’s stock with a .066 main.

Even the 245’s didn’t run a .072 except for break in.

Good point... I just check another similar engine I have it's a 1993 200 2.5 FF and it has WHM 21 carbs on it
According to the manual the 93 200 did use the WHM 21
And then under 94/95 it has the WHM 39
The only different Jet between the two is the Back Draft which is smaller on the WMH39

So I want to be able to use the WMH39 on my 200, what advice would you give to run it? Should I get the jets as close to the manual as possible? I guess I am not as concerned about the richer Main Jet as I am about the other Jets like the Progression and Back Draft Vent...

WMH 21


WMH 39

[mach351]

Someone has been in there if there’s .072’s. I’d get new .066’s all the way around that you know haven’t been drilled or messed with and start there. The fine tuning of the other jets may be negligible. Just my opinion.

[Glastron1987]

Yeah looks like those carbs are from another engine, like maybe the 140 jet. In any case maybe what I'd do if your engine is a stock 1994 200, then I would start with the jet sizes listed in the book for that engine (i.e. WMH 34 1A–2–3 jet sizes), unless there is evidence of something being better. Then I would hope there is no significant difference between the Carb 1 you have and Carb 1A that is the correct one. The next thing I would do is get an Optimax

[racer]

Based on your serial number Factory parts catalog says WMH 39 with .066 or .064 depending on cylinder. When you go to serial starting 0G960500 has different carb calling for .078 to .084 depending on cylinder. Thats the reason I go by serial number when looking up parts. Same thing happens on multiple engines, early 245 came with .076 for break in then .072, later ones .072 break in and .068 after or look at a 2.4 mopvp way different again but they had a cross drilled intake.

[Aaronhl]

OK guys thanks for the support, I just put an order in on Boats.net for the 18 jets I need...they are all the sizes listed in the manual for the stock 1994 200 2.5 WMH 39

[Aaronhl]

N just to follow up on my original question... I believe the stampings on the jets are the actual sizes...I checked another engine I have it's a stock 135, every single jet stamping matched the service manual numbers...I also compared some torch tip cleaners in various sizes like 040 050 and 060 on the same size jets and they matched...