400SBC/300A choking questions

Propane, Butane, LPG, GPL, C3H8, C4H10
kuchen
Posts: 79
Joined: Tue Oct 25, 2011 12:38 pm
Location: Stuttgart/Germany

Re: 400SBC/300A choking questions

Post by kuchen » Sun Jul 10, 2016 1:18 pm

The spring setting is very sensitive, and misadjustment leads to the fault which gave that carby its nickname: Quadrabog.
Only a small sping tension change is needed here. Sorry for not pointing that out earlier.


Billhilly
Posts: 27
Joined: Sun Apr 17, 2011 4:11 am
Location: New Zealand

Re: 400SBC/300A choking questions

Post by Billhilly » Tue Jul 12, 2016 4:23 pm

kuchen wrote:there is a depression caused by that mixer that does interfere with the Quadrajets secondary air flaps. Tweaking the spring load did the job for me.

Still going back and forth on this....Spring is now nearly back to where I started with no change. Just to clarify that I am interpreting this correctly, the mixer 'reduces' vacuum so I need to reduce spring pressure to compensate? I'm assuming......

kuchen
Posts: 79
Joined: Tue Oct 25, 2011 12:38 pm
Location: Stuttgart/Germany

Re: 400SBC/300A choking questions

Post by kuchen » Wed Jul 13, 2016 4:51 am

Yes, that's the theory behind it. Discussed that a few month ago:

viewtopic.php?f=5&t=1663&hilit=spring+quadrajet

Billhilly
Posts: 27
Joined: Sun Apr 17, 2011 4:11 am
Location: New Zealand

Re: 400SBC/300A choking questions

Post by Billhilly » Mon Jun 05, 2017 3:43 am

Man I know how to drag out a simple job huh!... Nearly eleven months mucking with this. I apologise for not updating sooner.
I never did win with adjusting the springs on the air flap. I went back and forth (tighter/looser) twice but couldn't get any improvement. Obviously, in some situations it works. As usual, for me, not so much! I also tried attaching a tube to the carb breather, and then actually drilling a hole in the adapter adjacent to the breather, but still no luck. After more deliberating (procrastinating) I bought an offset adapter and modified it to work. I offset the adapter over the primaries and did get an improvement! Still a little rich under hard acceleration but it took the collapse from 12 to 10 (on the O2 gauge) away and eliminated the stutter. Finally some progress! Pic of adapter installed....

Then, just a couple of weeks ago I actually got the LPG system filled! Way to drag that job out too! Got it starting and running good, but am struggling with tuning/O2 levels, and (excessive) fuel consumption. If I could direct you gentlemen over here - viewtopic.php?f=5&t=1719 What are your thoughts on this?
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