Number of carb bypass ports?

[jimmaki]

1998 SPX dual Mikunis on a 787. I think they are BN38s. How many bypass ports are there supposed to be. On one carb I see three but only getting fuel out of two. On the other carb I see two bypass holes and getting fuel out of both. I tried to push a camel's hair brush hair through the third hole but it won't go. No amount squirting carb cleaner or compressed air will open that third hole. Strange how can carb have three holes and the other only two.

 

[soccerdad]

Should have 3 on both. I bet it is there, just plugged up with gray stuff so you don't see it. At least that is what is in a 96 carb.

 

[Dr Honda]

Should be 3.

Use spray carb cleaner, and compressed air, back and forth. You will get it open. BUT... DO NOT poke it out. If you change the size of the port, it won't run right.

 

[jimmaki]

Thanks, does your carb have an accelerator pump? If not, I think the 98 carb might be different. I'm pretty sure there are only two bypass ports. I've soaked, blown and run compressed air so many times any dirt obscuring a port should be gone by now.

 

[jimmaki]

I used a hair from a camel's hair paint brush for poking which I didn't think would harm anything. I've come to the conclusion the third "hole" in one carb is just a pit in the metal, not a hole. Maybe a defect in the metal or something. Or possibly, since it's located right where the throttle plate closes against the wall of the outer venturi, maybe something got caught between them at one time.

On carbs with three bypass holes, what does the hole patter look like so I know where to look for the third hole if it exists? Are they all inline or do they form a triangle? My two bypass holes that I see fuel coming out of are inline up and down parallel to the airflow. What I originally thought was the third hole is off to the left about a half inch forming a triangle from the other two. Do you happen to know if any SPX carbs were made with just two bypass holes?

 

[soccerdad]

They are in a line on a 96

 

[jimmaki]

Thank you for the picture, now I know what I'm looking for.

Here are pics of my carb throats and it appears I have two inline. On the PTO carb what I thought was a third hole is way off to the left and I'm pretty sure it's just a pit in the metal, not a hole that I can pass anything through plus it's not anywhere near where a third hole would be thanks to your picture. I appreciate your help!

This is the PTO carb, what I thought was a clogged third hole is off the larger low speed port at its 7 o'clock.


This is the MAG carb with two inline bypass ports and no other potential bypass ports, nicks, etc. A couple scratches but no pits like the PTO carb has.