Secondary Diaphragm Affected by Altitude? (1 Viewer)

[LazarusTaxa]

I've so far been unable to get my secondary to open.. I rebuilt my carb ~1,500 miles ago, did a good job, made sure all the vacuum passageways were open, and of course installed a new secondary diaphragm. However, I found that the secondary was not opening beyond the minor amount initiated by the throttle lever.

I know this because I put one of those snake lights under the hood pointing at the secondary lever. I can see it initially open from the throttle lever, but it makes no attempt to go beyond that.

So recently I took the carb apart again to double-check that all the vacuum passageways are open and everything and found it all looks good. The secondary holds vacuum and the passageways are clear. I bent the actuating arm a bit so that it opens sooner and wider and put it all back together.

And yet, it again still does not open past the initial stage initiated by the throttle lever... What gives here? I've read all the threads and can't figure this out. My only thought is that I live at 4,000' and perhaps the altitude is preventing this from working properly. I hope this isn't the case because being able to drive more than 45mph up mountain roads would be very helpful... I got angrily passed by a UPS truck the other day.

 

[OSS]

Take the vehicle down to sea level and test again. 4000 ft elevation air is a lot thinner than sea level air. Maybe that’s all it can do

The FJ60 is the slowest vehicle on the road. Especially at altitude.

 

[micruz60]

6% to 10% sustained grade mountain roads: I can barely maintain 45 mph, and I live at 6200’ asl, driving to 8200’.
HTH

 

[LazarusTaxa]

6% to 10% sustained grade mountain roads: I can barely maintain 45 mph, and I live at 6200’ asl, driving to 8200’.
HTH

Interesting.. Do you know if your secondary is opening??

Out of curiosity, what vacuum are you reading at idle? I'm getting about 17-18" now after adjusting my valves again

 

[CruiserTrash]

Interesting.. Do you know if your secondary is opening??

Out of curiosity, what vacuum are you reading at idle? I'm getting about 17-18" now after adjusting my valves again

I’ve had thoughts about vacuum and the secondary too. I’m at 5000’ with 17inHg idle vac, but I regularly drove to 9000-12000’. I think with less vacuum pulling on the secondary it may open less. Perhaps the diaphragm linkage needs adjusted to account for less vacuum … I don’t see another way that scenario would be accounted for.

To my knowledge the HAC, which activates at 4000’, slightly advances static timing and also leans the mixture out. I don’t think it affects the secondary operation.

 

[OSS]

In my experience having a carb that didn’t have a functioning secondary for years — then it got rebuilt and the secondary became functional....
The secondary fuel circuit only really actuates a WOT. When you’re flooring it. Back off the gas pedal a tad and the secondary becomes inop.

If you’re cruising on a freeway at WOT all the time, then you’ve got bigger problem than an inop secondary.

 

[CruiserTrash]

In my experience having a carb that didn’t have a functioning secondary for years — then it got rebuilt and the secondary became functional....
The secondary fuel circuit only really actuates a WOT. When you’re flooring it. Back off the gas pedal a tad and the secondary becomes inop.

If you’re cruising on a freeway at WOT all the time, then you’ve got bigger problem than an inop secondary.

Bigger problems … like living in Colorado haha. I spend an awful lot of time at WOT on the highway if I’m in the mountains!

 

[LazarusTaxa]

Yeah I use WOT when trying to make it up the hill. Seems crazy to expect a 4.2 liter engine to suck all of its air through a single barrel, but I'm not an engineer..

One more reason I'd like to set up a sniper one day.

Edit: I should also mention that my father in law has a 60 with a freshly rebuilt (but not hot rodded) 2F with a AFI setup. It does not have as if of an issue maintaining a decent speed up these hills.

 

[WartHog73]

I had similar issues. This may not be your issue but may be good to double check: my torque rod somewhere along the line got reversed. I knew something was amiss after vacuum lines were all checked and new rebuilt carb yielded no change.

15 min later it was like having a new rig… Like my 60, I’m a little slow at times lol…