Our Mikuni throttle body model #? Vac ports issue.

[ateick]

Anyone know the Mikuni manufacturer part number (if there is one) for our throttle bodies?

The reason I am looking is that each throttle as 2 capped vacuum ports (the clutch side actually 3). They look very different however. The one furthest from the block has a large open inside diameter. The one closest to the block has a much smaller ID and actually looks like it might be one way or checkvalved.

Trying to understand how they differ. Thanks

 

[cannondale27]

I remember running into that when I synced mine. Is a thread here somewhere. If you blow into themdoes one have air come out before butterfly and one after?

 

[ClutchMaster]

Both ports are engine vacuum, the restricted one is for map sensor common rail.

 

[ateick]

The restricted one seems to have no vacuum at idle. Likely ported vacuum vs. manifold. Ran out of time yesterday mid tear down. I'll report more later.

 

[ClutchMaster]

The restricted one seems to have no vacuum at idle. Likely ported vacuum vs. manifold. Ran out of time yesterday mid tear down. I'll report more later.

You have a leak somewhere

 

[ateick]

I remember running into that when I synced mine. Is a thread here somewhere. If you blow into themdoes one have air come out before butterfly and one after?

To confirm -- both ports are after the butterfly. Very very limited flow out of the small port at idle.

 

[74Nitro]

To confirm -- both ports are after the butterfly. Very very limited flow out of the small port at idle.

Isn't that the entire point of the smaller opening? If a vacuum guage was put on either port they should read exactly the same regardless of hole size. The smaller one won't fluctuate as much and won't move volume, by design.

 

[ateick]

Isn't that the entire point of the smaller opening? If a vacuum guage was put on either port they should read exactly the same regardless of hole size. The smaller one won't fluctuate as much and won't move volume, by design.

Yes. Sorry the context to my question about the differences in the two ports is that I am having some issues with a turbo kit. I was trying to understand the ports abit better. My experience is that the map sensor, bov and boost gauge are reacting differently to the small vs. larger diameter ports so they may be sensitive to the volume movement differences between the two.

 

[ClutchMaster]

Yes. Sorry the context to my question about the differences in the two ports is that I am having some issues with a turbo kit. I was trying to understand the ports abit better. My experience is that the map sensor, bov and boost gauge are reacting differently to the small vs. larger diameter ports so they may be sensitive to the volume movement differences between the two.

Or you have a leak somewhere?

 

[ateick]

Or you have a leak somewhere?

I know, I know. Lol. I'm not ignoring your insight. I fixed the leak with a new BOV. My propane torch tells me there should be no other leaks.

Once the leak was taken care of I again tried using the small diameter ports with the standard 3 tube manifold that Hurricane suggests and supplies and it didn't like it. Still ran like sh$t. High AFR and when I did a diagnositic through the gauges it showed ISC at 134 cold, 120 start and then quickly dropped to 90 then back up to 105-108 and hovered there even after fully warm. So I temporary tapped into just the one clutch side larger diameter port (only one I can reach without taking everything apart) instead of the three small diameter ports and boom AFR dropped down and ISC dropped to 70ish (which from what I've read is normal). I don't think the MAP likes so little of volume of movement (if that makes sense) from the small ports. Just my thoughts out loud. I'm no expert by any means but I love to learn.

Anyway, I took it all apart again last night to connect to all 3 larger diameter ports and make sure again that there are again no leaks and everything is ziptied and tight. Tonight it goes back together and I hope that does it. Fingers crossed.

 

[ClutchMaster]

I think ya got it. The old machines used the small restricted ports for the map sensor, my 2015 uses the larger port, but only one? Most older machines have all the cylinders tubed to a common tee then to the sensor. Either way it sounds like you have it ciphered out!

 

[cannondale27]

I think ya got it. The old machines used the small restricted ports for the map sensor, my 2015 uses the larger port, but only one? Most older machines have all the cylinders tubed to a common tee then to the sensor. Either way it sounds like you have it ciphered out!

I always wondered why the viper throttle bodies have different vacuum tube routing than Nytro.