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Using carbs from different model years

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I know this is predominately a 4-stroke site, but hopefully someone can help me with this. I recently picked up a 1991 CR250 from a friend who had it sitting in a barn back in Indiana for a good ten years. I was given to me for FREE. It looks a little worse-for-wear (dead rat in the air box), but not a total basket case. Mechanically it seems to be in good shape. It has good compression and spark, so I think it will fire right up once I get a carb on it. The carb that came on it was junk. The slide was frozen inside. After soaking it in parts dip for two months it still wouldn't move, so I tossed it. I just got a replacement off of eBay for it. It is the same 38mm Keihin PJ carb, but it was from a 1988 CR250. I noticed that the serial numbers for this carb are different from year-to-year. Besides the standard jetting being different from year-to-year, I was wondering what else is different. Are there differences in the carb bodies themselves? What I am trying to find out is should I use the standard jetting for the model year of the carb I purchased, or for the bike I'm using it on? I want to use this as a starting point then I can jet up or down for the area I normally ride in. Any help would be greatly appreciated.

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Those two years run different needles. The 88 needle is richer at 1/8 to 1/4 throttle opening. I'd start with the standard 91 jetting. 88 was a weird year jetting wise, the stock main that year is 4 sizes larger than every other year from 86-91 except 89 where it was 3 sizes larger.

Unfortunately I cant find out if different slides were used or not though.

I have an 86-91 Honda manual; if you need pics taken of any sections let me know.

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Thanks James. I think I will go with the '91 jetting as you mentioned. I have a Honda factory manual with all the specs, so I can order the correct sizes. It shows the main jet for an '88 to be #185 and a '91 to be #175. The carb I bought has a #200 in it.

BTW, how did that speedo cable I gave you work out?

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Those jet sizes are assuming you are running a 20:1 mix. You will probably find you need to lean the bike out a ways if you run 32:1.

The cable fit perfectly. Thanks again for that.

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