Smaller diameter primary tube on exhaust manifold

Road-race engines and ancillaries - general discussion
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Brit01
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Joined: June 28th, 2011, 4:54 pm
Location: Uruguay

Smaller diameter primary tube on exhaust manifold

Post by Brit01 »

One of my exhaust manifold primary pipes has had a bump on it for some time now. Must have gotten hit by a high bump on the road, maybe a speed bump.

On that particular cylinder, the vacuum of the carb barrel at idle is 10-15% stronger than the others and I have to compensate for this by opening the air bypass screw a little on the dellorto carb.

Not sure if that is just coincidence or anything to do with the slight collapse of the inner diameter of the primary reducing the escape of the gases from that valve..

Just curious.

Regards

Chris
Guy Croft
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Re: Smaller diameter primary tube on exhaust manifold

Post by Guy Croft »

the vacuum would be weaker not stronger if it was the pipe...

Throttle plates need clearance around them -that is one reason for differences barrel-barrel. Also the depression in cylinder on the intake stroke (affected by rings valves etc...).

Just balance it out with the air bleed and don't worry about it.

G
Guy Croft, owner
Brit01
Posts: 825
Joined: June 28th, 2011, 4:54 pm
Location: Uruguay

Re: Smaller diameter primary tube on exhaust manifold

Post by Brit01 »

ok thanks Guy for the info.

Yes it is balanced out with the airbypass screw. No plans to change any throttle plates.
Idling nicely, just an occasional tweak here and there with the idle mixture screws.
Looking forward to see the MSD arrive and hooking it up.

Chris
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