Aisan Decel Fuel Cut Circuit (1 Viewer)

[mwebfj60]

The following lays out the decel fuel cut circuit (Idle Cut Solenoid). Three of the last four carbs I have gone through all had the gasket shown in the pic installed to where the vacuum wasn't getting to the upper left carb vacuum port (decel port). I punched the two holes in this one.

 

[mwebfj60]

The vacuum comes from the little port circled by the butterfly valve.

 

[mwebfj60]

It pulls vacuum through the phenolic? spacer...making it imperitive to use the proper gasket and install it correctly. The vacuum then pulls from the decel port as shown in the pic.

 

[mwebfj60]

The Fuel Cut Solenoid...I think it's a vital part of the carb. When you are decelerating, throttle at idle position, high vacuum, if the decel cut is not working, you are just sucking extra fuel into the chambers.

A look at the primary slow circuit...

 

[mwebfj60]

So when vacuum is high (above 14") and RPMs are above 1800, the cut solenoid closes off this part of the primary slow circuit (idle circuit) keeping fuel from flowing.

 

[CaptClose]

Interesting analysis. Thanks. Do you know if this is usually addressed during a typical rebuild?

 

[NeverGiveUpYota]

The following lays out the decel fuel cut circuit. The three carbs I have gone through all had the gasket shown in the pic installed to where the vacuum wasn't getting to the upper left carb vacuum port.

View attachment 1459670

View attachment 1459671

Ah. Now I understand why you sent me that pix. When I pull mine off and apart, aaaaafxxxingain, I'll check it out.

 

[mwebfj60]

Every rebuild kit I have gotten has come with the two gaskets...the existing ones are normally melded to the spacer and it is a meticulous job to remove them without damaging the spacer.

 

[NeverGiveUpYota]

Every rebuild kit I have gotten has come with the two gaskets...the existing ones are normally melded to the spacer and it is a meticulous job to remove them without damaging the spacer.

Yeah my rebuild kit from outfitters didn't come w/ gaskets, (that I remember) but I can look back at the photos.

 

[mwebfj60]

I would imagine if the gaskets are in good shape and installed correctly they could be reused with no issues.

 

[mwebfj60]

Here's a better pic of the spacer showing the channel through the spacer. If you get confused putting it all back together, notice the different tabs circled, they correspond to the contours of the throttle plate/carb base.

 

[gregnash]

The question is, when installing it, if you were in a rush could you inadvertently install the spacer backwards??? If so, what would the outcome be?

Yeah my rebuild kit from outfitters didn't come w/ gaskets, (that I remember) but I can look back at the photos.

Yeah I got my rebuild kit from Kurt too and I honestly don't remember seeing any gaskets.

 

[mwebfj60]

The question is, when installing it, if you were in a rush could you inadvertently install the spacer backwards??? If so, what would the outcome be?


Yeah I got my rebuild kit from Kurt too and I honestly don't remember seeing any gaskets.

The bolts will line up if it's flipped over so it can be installed upside down. You wouldn't have any vacuum going to the decel switch. I'm not sure if the idle and secondary slow cut holes line up backwards, I will check tonight and update.

 

[gregnash]

Well I finally got around to ordering my rebuild kit and spacers so I can throw @HemiAlex spare JimC rebuilt carb on the truck and take mine apart again. I dont EVER recommend working with a contractor that waits until the last minute to tell you "Oh by the way, you passed that failed inspection so you guys are ready to go. Best get to work if you want to be in before the 1st" (this was last monday EVENING.) hashtag #$*@a$$holebuildingownerswhoarecontractors

 

[mwebfj60]

Update on installing the spacer upside down, the primary slow doesn't line up at all and the secondary slow is about 50% blocked. If it was put on upside down/backwards , you wouldn't have an idle circuit. It would be pretty easy to spot as it doesn't line up very well with the throttle bores or the contour of the carb that way.

 

[mwebfj60]

Just realized I never finished.
Testing the ICS and vacuum switch.

 

[mwebfj60]

This is the way I prefer to test the vacuum switch...by hooking the meter up as usual and using a mighty vac. With no vacuum applied, you should have continuity from the spade terminal to the body (ground).

So with vacuum less than 14" the wire is providing a ground signal to the computer.

As you pull vacuum on the switch, around 10" or so, you will see the ohms increasing and then right at 14" it goes to open.

 

[NeverGiveUpYota]

@Robert Franzke heres how to test your ICS.

 

[mwebfj60]

To check the Cut solenoid, you can turn the key on without starting the motor and disconnect the connector and reconnect it. You should hear the solenoid click each time.

I prefer to pull it off the carb and unplug it. Then apply vacuum with a mighty vac...it should be closed and hold vacuum when unplugged.

Once the connector is hooked back up with the key on...12VDC and a ground is applied, the solenoid should click open and vacuum should release.

 

[mwebfj60]

When the key is on, there should be 12VDC at the yellow wire. The green wire should have continuity to ground. When both the vacuum and tach signal requirements are met at the computer (14" and 1800 RPMs respectively) the computer disrupts the ground and the solenoid closes. This is the principle behind grounding out the solenoid (so the computer can't disrupt ground) but you still need to ensure you have 12V at the yellow wire. Like I have said many times...grounding it out should be a temporary fix to isolate a problem...you can get it to operate correctly!