'92 5.8 Pro Boss(Carbed) Intake Vacuum Port

I dont know the size but be sure to use a "T" when hooking up you vacuum gauge. My idle changes on both boats if I block the pcv.

89Martinique wrote: I dont know the size but be sure to use a "T" when hooking up you vacuum gauge. My idle changes on both boats if I block the pcv.

That's good to know. I was curious about that prior to finding out that there is a plugged port towards the rear of the intake manifold that can be used for a gauge. My plan is to use it now and not touch the PCV line.

On my stock manifold it measures out to 5/8.   The port on the plate under the carb isn't the best place from what I've heard, but if you have a new carb there should be a port on the carb itself.

Ah, the 4010. Gotta love em'. Beat any other 600 cfm, or should. But can be real hard to keep consistent. (on the road) Marine conditions vary less than road conditions so its easier to keep them tuned in.

89Martinique wrote: Which side of the carb is the vacuum port on? Obviously the 2 mixture screw control 4 separate cylinders. So, how do get the vacuum of both sides of the carb? I just set the jets by turning in until motor starts to run differently (lean) then back out 1/4 turn. I do this to each side several times. So far, so good.

There is no vacuum port on the carb itself that I see. Since I'm using the port in the intake manifold as shown in the above picture, my understanding is that I'll be able to adjust one side of the carb with the boat in gear (in the water) and then adjust the other side the same amount. After that I'll adjust the idle if needed and re-adjust the mixture screws again until I see the highest vacuum reading at 550-600 RPM with the boat in gear. This is my first carb rebuild and my first time tuning a carb therefore please correct me if I'm going about this wrong!

As for adjusting the mixture screws and listening to the engine, I tried this. The engine didn't start to stumble until the screw was lightly seated (I was adjusting one side at a time). I read on CCF that if the idle is set too high, and the butterfly is open too far, the boat will not be running on the idle circuit. The engine was idling at 600 RPM on the boat tach so I'm purchasing a hand held tach to see if the boat tach is off. My plan is to back the idle off a bit more prior to adjusting the mixture screws again.    

TRBenj wrote: You need to adjust both idle circuits simultaneously- not one and then the other. Start at 1-1/2 turns out on both and adjust them in 1/4 turn increments (both together).

Right there lies my problem. I will bump up the idle as well. Thanks for your input!       

That low of an idle is very hard on your damper... which is why 650rpm is recommended. A 250rpm drop when going from neutral to in gear is also quite excessive... might want to check your alignment to make sure youre not all bound up. A 50rpm drop is more typical if the boat is dialed in.

800-900rpm idle is high. If you cant get it to idle any lower, then you may have a vacuum leak. Or, your butterflies are open. Or, youre idling off the transition circuits (in which case the idle mixture screws wont have much effect). If it only does this when returning to idle after a hard run, also check to make sure the secondaries arent being held open. Its also possible that your dist advance weights arent returning all the way, in which case a shut down and restart will usually reset them. Whatever the case is, something isnt quite right!

Its been that way for a long time. No dizzy weights. Pro Tec takes care of that. The secondaries do close. I will tinker with over 4th of July weekend when it joins the CC in the water. Thats my only grip. Other than that it runs fantastic. I do have to replace my floats. The primary float bowl sunk over winter due ethanol eating the plastic weld seem! My uncle has a pair of after market metal floats waiting for me, just got get em shipped.

Now for the alignment. What thread do I go to again to check my alignment. I have always felt that my CC isn't fully lined up. Has a slight vibration under 1,000 rpm.