1990 200hp Merc Different main jet sizes

I rebuilt the carbs after buying a boat and found that 2 of the main jets are different then the other 4. There may be a reason. I put the jets back without knowing where they were befor taking them apart. The top carb has .084&.086 ,middle .084/.084, bottom .088/.086 (bottom should have .086/.084) it has WH46 Carbs.

The compression is 132 on 1,2,3,4 cylinders and 124 on the 5,6 the bottom carb. The motor was used by a marina for racing and im wondering if they changed the bottom jets because the compression was lower, if that would make sense to do. I was thinking it would get more gas and combust harder to equal it out, or maybe the .086/.088 should be on the top carb because of the compression and needs more cooling, idk

When I took the carbs apart I didnt check the #'s of the jets so Im just guessing that the larger jets are with the lower compression cylinders. Standard jets for this motor are: 1&2 .080/.082, 3&4 .080/.080, 5&6 .082/.080 So all are really oversized. Im trying to figure out where to put the .088 jet

Re: 1990 200hp Merc Different main jet sizes

If you have those kind of compression numbers and the motor was used for racing I would tend to believe that who ever built the motor knows what they were doing and I would leave it alone. I would also say with those compression numbers your heads have been shaved. Why did you tear into the carbs in the first place? Was there an issue you did not mention?

Re: 1990 200hp Merc Different main jet sizes

The jetting is always staggered on the 200hp's from factory on #2 and #5 as this is a cross induction intake ...looking at the carbs all the throats on left side feed the right side cylinder and vice versa. The jet on the one cylinder thats .088 could be a oversize piston from a rebuild and needs the extra fueling to keep cool. The cylinders are within the 10% range of each other...

Re: 1990 200hp Merc Different main jet sizes

drtyTshrt said:

If you have those kind of compression numbers and the motor was used for racing I would tend to believe that who ever built the motor knows what they were doing and I would leave it alone. I would also say with those compression numbers your heads have been shaved. Why did you tear into the carbs in the first place? Was there an issue you did not mention?

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The guy I bought it from got it from the marina. A Float was stuck, and he didnt want to deal with it. The boat also sat for a few years so I had to clean them out.

Re: 1990 200hp Merc Different main jet sizes

Faztbullet said:

The jetting is always staggered on the 200hp's from factory on #2 and #5 as this is a cross induction intake ...looking at the carbs all the throats on left side feed the right side cylinder and vice versa. The jet on the one cylinder thats .088 could be a oversize piston from a rebuild and needs the extra fueling to keep cool. The cylinders are within the 10% range of each other...

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I have no doubt the guys at he marina knew what they were doing. When I took apart the carbs and broke it down I didnt check all the jet #'s I was thinking they were standard. So I really dont know which over sized ones go where, I was guessing it was the lower compression cylinders, but it could be #1&2. Any thoughts on how to figure out where the oversized jets would go,