Topic: New carb needed with 605cc kit?

[DelbT]

Does anyone have experience with carburetor setups/settings with a 605cc big bore kit on a 550?

I'm also planning on the Web Cams .330/.330 lift, 290/290 duration "hot street" cam and a valve job with mild head porting.

From 544cc to 605cc is an 11% increase in displacement, and considering that the same 22mm carbs were used on the 498cc motor, that's a 21.5% increase in displacement.  I know that bigger isn't always better with carbs, but do the 22mm's properly support the 605cc kit.  Or, will I be breathing through straws?  The 79-80 650's have 26mm's.  Might that be a better option to take advantage of the increase in flow capabilities and displacement?

If this were a car I would use the cfm = rpm x displacement x VE / 3456.  Does anyone know cfm numbers for the various Keihin carbs?

thanks

[moham]

First of all, are you sure the 605cc kit is actually 605cc? The kits I have seen are 61mm pistons which is 592cc. A .75 OS 750 piston would give 606cc but that's a 61.75mm piston. The kit on ebay right now I know is a 61mm piston. That would change your %.

As far as the carbs, somebody else will probably give you more concrete data but from what I've been told carbs from a 750 (70-76) would be the next step up for more fuel delivery on an overbore 550.

[DelbT]

The parts are on their way to the machine shop, so I don't have the pistons to measure them.  However, the kit is the same kit on ebay right now.  (same box anyways, so it's probably the same kit).  So, if the guy on ebay has measured his piston correctly, then they are only 61mm.  Given a 50.6mm stroke that would give 591.5cc's.

That's crazy.  I never figured to measure them, but why call it a 605cc kit?  Even if you consider the true displacement being that of the cylinder bore vs. piston diameter due to clearance allowances, it shouldn't get to 605cc's, right?

[moham]

No it wouldn't. Clearance is next to nothing. I don't know why they call it 605. Maybe somebody else could enlighten us on that. I am boring out to 60mm (573cc) right now and have been told that stock 550 carbs will be ok (time will tell), I have also been told that both 650 and 750 carbs are an option, although rebuild costs on the 650 are higher.  For what it's worth on my build, I am going to try the stock set-up and see what happens. You are obviously going bigger than me so you have a tougher question. What did you spend on the kit?

[DelbT]

$279 buy it now on Ebay

I've been searching the forum.  I've seen some references to recommendations on setting up the stock carbs to work with the "605" kit, but I haven't seen any notes from anyone with their final configurations.

I was hoping someone would have already played with it enough to give me a starting point.  Stock certainly would be cheaper than picking up 650 or 750 carbs.  I might start there myself.