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Old 18-09-2005, 06:26 PM   #1
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Question Xr2 Carbs

Does anyone know how much revs or power i might lose by going from .068 main jets to .070 on my xr2?
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Old 18-09-2005, 06:36 PM   #2
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Re: Xr2 Carbs

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Originally posted by scottyboy
Does anyone know how much revs or power i might lose by going from .068 main jets to .070 on my xr2?
i thought XR2's ran .8 sommat for mains but i aint sure
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Old 18-09-2005, 06:47 PM   #3
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Jay Smith on the subject of correctly jetting a motor


The plugs should be a "paper bag" color to be the ultimate in correct jetting. I don't read plugs as there are too many varibles involved, I have had good luck only reading the piston itself. I make a high speed pass and if the hull will allow it without back washing over the splash well kill it clean. Then I roll # 5 piston ( as generally # 5 is the hot hole on a Mercury and prone to burn if the mixture is too lean ) to bottom dead center and look at the piston crown on the intake side ( that will be the side toward the outside of the block ) with a bend o lite , the intake side of the piston at the intake port should be wet and look moist about the size of a quarter out toward the middle from the port. If the wettness is over across half of the crown your too rich and can lean down a bit. If it is dry and ashy in color your too lean and you need to richen up in a hurry. Maybe other people have different methods but this has always been the ticket for me. Some rely on pyros , I have found that when a motor is too lean a pyro will be too late in its report and the piston is already smoked ( a 2.5 Merc with stock stroke comes to top dead center@ 10,000 rpms at a rate of 120 times a second I'm an old man and I can't react that fast maybe some of the younger ones can but my incounters with a lean motor things just happen too fast ) also on MANY occations I have had customers motors be STUPID rich and the pryos are reading flame not egt and they continue to richen even more chasing thier tails. Also if a pyro is "coked" up" it will also read incorrectly . This is why I haven't alot of faith in the pyro system of jetting. I always tell my customers when I build modified motors to start off very rich and SLOWLY work your way to dialing in your jetting. And by ALL means don't listen to JOE BLOW as to where his motor runs best on jetting as EVERY MOTOR is different and what might run great on one jetting curve might cost you another trip to the machine shop and bank !
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Old 18-09-2005, 06:50 PM   #4
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not much, why would you want to though?
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Old 18-09-2005, 06:54 PM   #5
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Think There supposed to be .068 (Well im assumong there supposed to be .068)but mine have been changed to .070 by little pete coz he wanted to run it slightly rich to reduce the risk of blowing it up! Im gonna put it back to standard and just wondered wot rpm or power i might gain
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Old 18-09-2005, 06:57 PM   #6
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A lil bit but not much get a carb plate or stacks and go upto 72's
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Old 18-09-2005, 06:58 PM   #7
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carb plate??
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Old 18-09-2005, 06:59 PM   #8
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it says here http://www.mercruiserparts.com/Show_...RETOR+ASSEMBLY

that they are .80's standard. what year is your XR2 dude
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Old 18-09-2005, 07:01 PM   #9
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Dunno? Think its a 97 But its been rebuilt by ocean racing since then! Think its done about 10hours since then?
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Old 18-09-2005, 07:01 PM   #10
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Quote:
Originally posted by scottyboy
carb plate??
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Old 18-09-2005, 07:26 PM   #11
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So do ya ditch the air filter? wot sort of rpm do ya gain from fitting these and where ya get em from?
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Old 18-09-2005, 07:29 PM   #12
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I think it depends on what carbs are on the xr2. Duel bowl or single bowl pumper.

Being a newer motor yours would have had the single bowl pumper carbs from the factory but that doesn't mean someone didn't fit the older dual bowl carbs at some point. Some people dont like the pumper carbs as they can make the motor bog down when you stamp on the throttle.
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Old 18-09-2005, 07:51 PM   #13
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Mine has one acceloration pump per carb but theyve been disconected!
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Old 18-09-2005, 08:07 PM   #14
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Quote:
Originally posted by scottyboy
So do ya ditch the air filter? wot sort of rpm do ya gain from fitting these and where ya get em from?
i think you gain 2 to 300 rpm. you can make one yourself and its over to JBD to explain how
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Old 18-09-2005, 08:08 PM   #15
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Burty's link showing 80's is on the older 150 XR2 motor with dual bowl carbs so dont worry about it.
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Old 18-09-2005, 08:20 PM   #16
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Come on then JBD how'd ya make em or where ya buy the proper ones?
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Old 18-09-2005, 08:31 PM   #17
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Quote:
Originally posted by scottyboy
Come on then JBD how'd ya make em or where ya buy the proper ones?
check this thread out, what you are looking for is on page 2. and yes you did start the thread
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Old 18-09-2005, 08:37 PM   #18
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No thread rob?
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Old 18-09-2005, 08:42 PM   #19
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Quote:
Originally posted by scottyboy
No thread rob?
O Bollox i forgot to put it in

i'll try again

http://www.boatmadforum.co.uk/showth...b&pagenumber=2
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Old 18-09-2005, 08:47 PM   #20
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I think that 13443 on the plate in the photo is the merc part no.

Or you could cut an airbox up or buy some velocity stacks from anyone who does race motor bits.
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