Re jetting 89 rude

[blackbullet175]

I'm about to cut some 200 89 rude heads for aprx.140psi. Should I just read my plugs and get the correct jet size through trial and error or can I just put 225 factory spec jets in it.

[mmassm]

You didn't give enough info!! Where are you starting from?? Stock? 90-95 lb comp. Do you have air box on or off?

[blackbullet175]

It's about 80lbs right now ,all cylinders are really close also ,within 2.5 psi. It seems very low though, cause my old rude ran about 90 lbs. I need to check and see if it has been bored some. The air box is still on ,I would really like to take it off or releive it some.

[Lockjaw]

You need to see if you can get Racer to respond. He will want to know what year carbs you have. He can probably also advise you on head cutting.

I have seen numbers as high as 10 sizes richer, so I would suggest you get some info before doing a trial and error. I suspect being 10 sizes to lean would make your motor into a boat anchor in pretty short order.

He told me not to take my airbox off on my motor without changing to a different carb.

Don't mess around with it, seriously, get the info first. :cool:

[mmassm]

If you take the air box off, you need to put stacks on! That is a least 5 jet sizes. 80 lb compression? you might think about a rebuild or re-ring: It would be cheaper to rebuild before you blow, and then cut your heads. Always jet fat and lean from there,second guessing can be very costly!

[Forkin' Crazy]

80 psi is low... was your battery up? Tried a different compression gauge? Or leak down test?

Plugging with exhaust bleeds will help more than cutting the heads I am told.

[bigbore]

80 psi is low... was your battery up? Tried a different compression gauge? Or leak down test?

Plugging with exhaust bleeds will help more than cutting the heads I am told.
AGREED,he may want to try a different compression guage but,80-90 pds.(on a looper)may not be low,as long as there's not a 10 or more pd. difference in-between em he'll be alright.:cool:

[BenKeith]

Anything you do to an OMC looper will normally require rejetting. Just poking a set of jets in and thinking thats good is gonna cost you. First off, if you just take the air box off you will need #72 mains, minimum. Stock 225 mains are only #68's. Remove air box and boost compression you will probably need #76's but only the pistons and plugs can tell you what size you will really need.

Just cutting a set of heads probably will not get you that much compression. Plug the exhaust relief holes in the cylinders with Marine-Tex and get you a set of 48 - 50 cc heads, (86/87 225 heads work fine, just make sure they have .700" deep chambers or CC them) that should get you to about 145 is the rings are good. 80 - 90 is pretty much normal for a stock motor. When you boost the compression, make sure you run jets two sizes larger in the bottom two (5 and 6) cylinders. With the crap we've gotton for gas now, most people are also backing the timing down to 16 degrees BTDC when they start running that much compression.