Re: Rochester 2BBL vs. Mercruiser 2BBL on 120 4cyl
the thing to know about the accelerator pump, in any carb, is it's function is to supply the necessary amount of fuel only when the throttle is rapidly opened. The sudden loss of vacuum prevents the carb from metering fuel and maintaining a good air-fuel ratio, and it leans out and bogs when accelerating until rpms come up enough to give the carb a vacuum signal again.<br /><br />If you accelerate slowly and the engine still bogs, it's not because of the acclerator pump!<br />And adjusting the accelerator pump will never fix the bog under a slow and steady throttle opening.<br /><br />If however you are bogging under somewhat hard acceleration, but not jamming the throttle wide open, then an adjustment to make the accelerator pump shoot more fuel may help alleviate the bog but this is more of a band-aid fix and not getting to the root of the problem.<br /><br />What you need to do is make sure the fuel bowl and the idle and transition circuits in the carb are clean. The transition circuit is what is causing the bog by not supplying enough fuel. The most significant adjustment you can make is adjusting the float to raise the fuel level in the bowl. Raise it just a little and run it, if it doesn't help then raise it a little more. If the engine floods on statup or won't start then you raised it too much. Another cause can be a bad power valve or an incorrect power valve where its opening vacuum is too low. So check and make sure you have the correct one. I don't know if different power valves are available for the Rochester 2b, or mercarb, like they are for Holleys but you may also fix the bog by using the next size up power valve where it opens at a higher vacuum.<br /><br />You can try buying a new carb, if it's a mercarb they are set lean for emissions and will most likely give you the same or worse bog. I have a 2002 3L with a mercarb and it bogged from day 1. I fixed mine mostly by raising the float level.<br />I've also gone from 1.55mm to 1.65mm main jets, and there's only 1 power valve available for mine so I'm stuck with that.<br />I don't think a rochester will do anything better or worse since the mercarb is based off the rochester. If you're dead set on getting a new carb, a weber would be the way to go but are expenive. I considered that route but fortunately figured out mine and saved a lot of money.
