Topic: '74 main jets.

[Dusthawk]

Press in or screw in?

[Soos]

screw in unless you have non stock carbs.
Keihins are stock for '74 cb750.

If yuu have Mikunis or something else, then i don't know.


l8r

[Dusthawk]

Rita is a '71, but I got a set of '74's off E-bay last year. I am doing an engine rebuild and taking the engine up to 850 cc's so I need a set of larger jets. Along with the larger displacement, I'll be using drag pipes and pods, so I am trying to figure out what size to go with.

[dusterdude]

sorry for the hijack,how ya hangin dusthawk?

[Dusthawk]

One day at a time, you know... Just trying to get my ankle healed up but things aren't looking good. Might need another surgery soon. Other than that, trying to get the last of the parts I need to finish off Rita. My biggest worry is the springer, its going to run me over $600, so I am saving a little bit each month til I can get it.

I moved to a new place out in the boonies and waste a lot of time doing nothing every day, lol. God I miss going to work everyday, I am so bored!!

[TwoTired]

Rita is a '71, but I got a set of '74's off E-bay last year. I am doing an engine rebuild and taking the engine up to 850 cc's so I need a set of larger jets. Along with the larger displacement, I'll be using drag pipes and pods, so I am trying to figure out what size to go with.

If you increase engine displacement, it draws more air through a carb of the same venturi size as a smaller displacement engine would.  This deepens the pressure drop in the carb throat which would draw more volume of fuel through the fuel jets.  You may find that a smaller Main jet is required for a displacement increase.
Score one for smaller jets.

The pods ostensibly have less air restriction than the stock paper filter.  Less restriction means higher carb throat pressure relative to atmopheric.  Thsi is the force that pushes fuel through the fuel jets.  The less differential, the less fuel moves through the jet orifice.  Pods usually mean an increase in jet size.
Score one for larger.

The point is, the model for prediction of fuel jet requirements is complex and non-intuitive.  Be prepared for disappointment, trial and error jet substitution, and plug chops before you arrive at the correct jetting for your specific design of engine parts configuration.

Cheers,