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Cafe advice

Mheath

CB750 New member
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Going with straight pipes and velocity stacks, what should I change the jets out to? Stock keighan carbs! Also I'm pretty new to Hondas
 
what year 750? also have to change needle clip position and a/f screws. I'm having the same issue. tryin just to get close so I can dial it in. decided 120 mains seem to be where most end up with close to the same setup I got.
 
Why would you want to run straight pipes? It will do nothing for the performance of the engine. All engines need back pressure.
You're turning a good engine into a piece of crap!
 
Four stroke engines dont need back pressure in the exhaust, they actually need low pressure in the exhaust behind the exhaust pressure pulse to fully draw the exhaust out and help pull the intake into the cylinders. If you have a high pressure in the exhaust you are hindering scavanging for the next power cycle. When a cylinder fires it causes a high pressure wave from the combustion, as it leaves the head and travels through the exhaust it creates a low pressure behind it as it travels. The whole down fall to the drag pipes is there is no scavenging effect from the other firing cylinders and often times the drag pipes are to short to create enough of a low pressure area behind the closed exhaust valve. A long drag pipe would work better then the short common aftermarket drag pipes. Thats why 4 into 1 and 4 into 2 exhaust work best on the 750 as the exhaust flow from the previous fired cylinder creates a low pressure area behind the pressure wave which draws the next firing cylinders exhaust charge out. I do agree that drag pipes cut power on the 750, the only reason to do it is for looks and for sound. If you are looking for all out performance 4 into 1 or even a 4 into 2 is far better then drag pipes. The stock honda 4 pipes work so well because of there length and in the HM300 pipes they work better because of the straight through low restriction muffler area.
 
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