Author Topic: 550 Jetting Advice for Velocity Stacks  (Read 1588 times)

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Offline syverter

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550 Jetting Advice for Velocity Stacks
« on: April 14, 2013, 06:14:02 PM »
Hello, Does anyone have any jetting advice for a 75 CB550 with velocity stacks and a MAC 4-1 exhaust?  I'm looking for a good place to start with jet sizes/needle height etc...  Any help is greatly appreciated!

Offline Bankerdanny

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Re: 550 Jetting Advice for Velocity Stacks
« Reply #1 on: April 15, 2013, 08:13:38 AM »
You might post this over at the regular SOHC4 board too. I think you will get a few more views.
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Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline luceja

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Re: 550 Jetting Advice for Velocity Stacks
« Reply #2 on: April 15, 2013, 02:45:32 PM »
I was running stacks on a 550 with a mac muffler and it was livable but I didn't get it ideal. I had the stock 38 pilots in, seemed to like the screws out, and was experimenting with mains up and down around 115's. The mid and top were excellent, so I didn't play with the needle. It basically acted both lean and rich around idle, was hard to figure out. It was a little weak down low, it didn't like/need choke to start, had black plugs, and ran worse with 40 pilots, so it was acting too rich at idle with 38s even with the idle screws leaned all the way out. Also, it was getting backfires out the carbs when cold, which I think is a lean sign, and the throttle stop would have to be turned in quite a bit at first to hold idle when cold, and you'd have to back that screw off bit by bit for the first 5 or 10 miles. I went back to the airbox, and it resolved the severity of the idle climbing and the popping out the carbs, and is stronger down low, as expected.
'75 cb400f, '77 cb550f , CB160 road racer, '88 Hawk GT track bike, FZR400 race bike, and a bunch of old hondas in boxes.

Offline syverter

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Re: 550 Jetting Advice for Velocity Stacks
« Reply #3 on: April 16, 2013, 05:29:56 PM »
Thanks guys, the replies are much appreciated.  I was also experiencing climbing revs at idle and a lot of inconsistency down low.  I'll be sure to post what works if things get more dialed in.