Carb Tuning

[JaredOSU]

I have a 1989 Mastercraft Pro190 with a 351 Windsor and 4160 Holley carb. I am trying to tune the carb to where it starts easier when the engine is hot. I have adjusted the metering block air screws to about 1.25 turns as per the manual. Now, sometimes the engine wont start when it is cold (hasn't been running). I have adjusted the electric choke but I may not have it set correctly? Any ideas? Oh, I dont have a vacuum guage either.

[thatsmrmastercraft]

With the engine cold, pump the throttle once to set the choke. The choke blade should now be almost completely closed. If not, loosen the three screws securing the choke cap and turn the plastic choke cap until the blade just reaches the almost closed point, and tighten the screws. Once started, the choke blade should open fully within a minute or so. If it doesn't open quickly enough, or too quickly, you need to get a new choke cap.

[JMann]

I set the screws on my metering block to 1 3/4 turns out after a rebuild and it start good warm or cold so I stopped screwing with them. You may need to turn them out a little, try 1.5 turns out and see if it gets better. I think the carb comes factory at 2 turns out and you adjust from there, you may be a little lean.

[thatsmrmastercraft]

It seems 1.5 turns is about the average.

[keith3613]

I have a 1984 that came from the factory super rich. When I had it overhauled it was discovered that the mixture screws needed to be set 3 and ½ turns out. The thing runs perfect and starts like it was brand new. Also the nut on the accelerator pump was set so that no slack was present, not like Holley recommends with a feeler gauge. It took me about 2 hours of adjusting to find out all of the “Experts” were wrong about adjusting the mixture screws. I’ll take rich any day over lean and hard starting. Idling rich hurts nothing.

[thatsmrmastercraft]

Originally Posted by keith3613

I have a 1984 that came from the factory super rich. When I had it overhauled it was discovered that the mixture screws needed to be set 3 and ½ turns out. The thing runs perfect and starts like it was brand new. Also the nut on the accelerator pump was set so that no slack was present, not like Holley recommends with a feeler gauge. It took me about 2 hours of adjusting to find out all of the “Experts” were wrong about adjusting the mixture screws. I’ll take rich any day over lean and hard starting. Idling rich hurts nothing.

Chances are the idle passages on your carb weren't fully drilled from new. I have seen this on two automotive OE carbs from mustangs back in the late 80's. That might explain why you need the increased and immediate accelerator pump stroke. Most importantly, your boat is running properly.

[j.mccreight@hotmail.com]

Originally Posted by JaredOSU

I have a 1989 Mastercraft Pro190 with a 351 Windsor and 4160 Holley carb. I am trying to tune the carb to where it starts easier when the engine is hot. I have adjusted the metering block air screws to about 1.25 turns as per the manual. Now, sometimes the engine wont start when it is cold (hasn't been running). I have adjusted the electric choke but I may not have it set correctly? Any ideas? Oh, I dont have a vacuum guage either.

Only proper way to tune or adjust the carburetor is with a vacuum gauge, too many other variables in play, there are some great tuning tips from holley on youtube...

[thatsmrmastercraft]

Vacuum gauges are cheap and there is no reason not to use one if you are serious about tuning your carb. With that said, I have tuned plenty of carbs by rpm only and while it takes a little more patience, a person can do a fine job. Same thing with timing. A timing light makes it a simple job, but an engine can be timed by ear and cautious runs while getting to the sweet spot.