Decel fuel cut vaccum switch

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I'm working with Paul at SOR...they're very receptive and helpful but want to rule out some things before I send the carb back. They'll take it back and put it on a truck to see if it works. If it checks out, they just send it back to me. If it fails then they rebuild.
 
I don't think it is the accel pump. PS the noise is the carb fan on its last legs...
 
So, we have the problem about 80-85% resolved. I put some washers on top of the accelerator pump arm so that the pump engages a bit sooner. After futzing around with a combination of washers, six seems the right amount and, as I said, problem is mostly gone. There is still a slight stumble when backing off of the throttle after reaching cruising speed around 2500RPM. Paul suspects carb float because the glass is low when at idle. I'll try adjusting that to see if I can knock out the last 15%.
 
So here is an update. The folks at SOR suspect that the float needs to be adjusted. I'm putting that off because I don't want to pull the carb apart until I have backup transpo. AND, I'm not super convinced that is the problem, especially since the truck runs fine under load.

I do have some additional data...when the choke lever is pulled out, the hesitation is gone. I don't believe the choke is actually being closed because of the choke opener & breaker stuff.
 
Yeah, the choke is only keeping the throttle open a bit while driving (because like you said of the choke opener). So there's no choking or richening of the a/f mixture. It's essentially the same as having a very fast idle or keeping your foot always slightly depressed on the gas pedal.
 
Output Shaft said:
Yeah, the choke is only keeping the throttle open a bit while driving (because like you said of the choke opener). So there's no choking or richening of the a/f mixture. It's essentially the same as having a very fast idle or keeping your foot always slightly depressed on the gas pedal.
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I'm stumped. I can't figure what is being changed by pulling the choke lever...it is quite obvious when driving though. Much, much smoother acceleration up to cruising speed....
 
Check the operation of the Choke Opener as detailed in the FSM. If it isn't working correctly (bad BVSV, faulty vacuum diaphragm) the when the choke knob gets pulled it WOULD richen (choke) the A/F mixture which would help if the carb is starving the engine of fuel.
 
CurtB said:
So here is an update. The folks at SOR suspect that the float needs to be adjusted. I'm putting that off because I don't want to pull the carb apart until I have backup transpo.
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It should take less than an hour to remove the air cleaner assembly to expose the carburetor, disconnect things and remove the top of the carburetor, adjust the float level, and put everything back together.
 
Output Shaft said:
Check the operation of the Choke Opener as detailed in the FSM. If it isn't working correctly (bad BVSV, faulty vacuum diaphragm) the when the choke knob gets pulled it WOULD richen (choke) the A/F mixture which would help if the carb is starving the engine of fuel.
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Good call. The pink BVSV is inop. That put me back on the trail of vacuum leaks and I found another. The little pipe that runs through the insulator is a leak source. It only happens when I wiggle it around but I'm assuming that is happening when driving. I'll get a new one ordered but am trying some fuel resistant permatex in the mean time. It only serves the EVAP so, if the permatex doesn't help, I might just pull the pipe out and put in a slightly larger bolt until I can get to the new insulator.
 
Are you talking about the PCV port out the front of the insulator? If it's loose, use some JB Weld liquid. Let it cure at least 24 hrs before heat cycle.
 
Spike Strip said:
Are you talking about the PCV port out the front of the insulator? If it's loose, use some JB Weld liquid. Let it cure at least 24 hrs before heat cycle.
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No, I'm talking about the port in the insulator below the carb that exits towards the left fender. It goes to the EVAP VCV Port Y.

It is the pipe at the bottom of the photo

IMG_20170413_141151.webp
 
@CurtB whatever was the conclusion here? Is your 2k-2500k hiccup resolved?
 
NeverGiveUpYota said:
@CurtB whatever was the conclusion here? Is your 2k-2500k hiccup resolved?
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The problem is finally resolved, but I'm not sure there was one primary cause. I spent a bunch of time chipping away at vacuum leaks but the stumble persisted, even if diminished. I didn't suspect the distributor because it was a fresh rebuild. When I came back around to the distributor, cleaned up the sticky advance mechanism, the stumble went away.
 
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