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Discussion Starter · #1 ·
I have read in the forums about having carbs bored with engine mods.
I have 92 Wildcat carb'd, 790cc bigbore kit, PSI Pipes, Boyeson reeds,
major porting. Still have stock carbs, no airbox- pods.

1) Will boring the carbs really make a significant difference?

2) I have heard 2mm over (to 42mm). Is this common overbore?

3) If I strip the carbs, can local machinist just bore them out, or
are there other specific skilled internal mods that need to be made by
snowmobile specialist?

Thanks in advance for any help.
 

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journeyman sled/motorhead
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You can have your 40's bored to 44 mil.
A milling machine is the best machine for the job.[/b]
I have access to a nice bar hone that works good as well. makes the straitest hole I ever seen.
 

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Discussion Starter · #4 ·
I have access to a nice bar hone that works good as well. makes the straitest hole I ever seen.[/b]
Ok, I took a close look inside a spare carb. See that you can bore it until there is just enough
curve left in intersecting slide bore so that slide seals on the sides. In other words, the
slide bore is slightly larger than the venturi bore, and has to stay that way in order for the
slide to seal on the sides where the 2 bores intersect.

So do you just use an automotive break cylinder bar hone on a drill to hone it out?
Does that type of hone really have the grit to take off a couple of mm's? How many
hours and liters of honing oil does this take?
 

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The other option is Oval boring (more CFM and drive-ability)and rifle boring (supposed to augment turbulence). Personally, unless your trying to build a screamer, going to the largest aperture in carb size usually hurts bottom and mid range power delivery. Most times, porting the inlet system to maximize the carbs that you have pays bigger dividends. Yamaha has been able to get excellent results using smaller carbs than the competition (CC wise) and still remained competitive and economical. Just my $0.02
 

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its nice machine not a drill. my buddy has it to do carbs for karts. we also use it to do 5 hp briggs blocks. have 3 differant grit of stones for it. not speedy by any means. it makes the straitest holes though. I wonder if it is worth it on a sled. when we do carbs for karts it is because we can only use their carbs and the bore has to be x size max. I think doc hit on something the velocity of the smaller carbs is hard to beat. you always give to get. question is what are you giving and what are you getting? is it worth it?
 

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The other option is Oval boring (more CFM and drive-ability)and rifle boring (supposed to augment turbulence). Personally, unless your trying to build a screamer, going to the largest aperture in carb size usually hurts bottom and mid range power delivery. Most times, porting the inlet system to maximize the carbs that you have pays bigger dividends. Yamaha has been able to get excellent results using smaller carbs than the competition (CC wise) and still remained competitive and economical. Just my $0.02[/b]
T doctor:
Is oval boaring elongating the aperature to take advantage of the cutaway in the slide?
 

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Not really, Oval boring allows good vacuum signal and low end properties of the stock sizing and adds more flow potential at WOT.
 

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Is it done on the horizontal plane (airflow passage)? Isn't regular boring done in the vertical plane (piston valve opening)?
 

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It's done vertically, the floor and the roof of the mixing chamber are cut. The needle jet protrudes more after the machining which creates even more of a hood.
 
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