Oscillating idle when hot

[MKS427]

I'd start with the phenolic spacer previously mentioned. If clearance is an issue, solid engine mounts or a drop down air cleaner base may be the solution.

[Tom Wells]

SB,

Been down the "try to make the carb stop percolating" rabbit hole.

Insulators, heat shields, return lines for continuous fuel recirculation, drop base filters (made it worse by shrouding the float bowls), you name it.

Nothing worked.

Depending on the chemical makeup, gasoline can boil at as low as 100 degrees F. The petroleum companies seem to like to hide their facts, so we may never know exactly. At elevated altitudes the problem is aggravated.

What I'm certain of is that it boils at a relatively low temperature; way lower than the leaded gasoline that was standard when these carbureted cars were originally produced. Even then they had some problems...

I've driven one of my carbureted cars with the hood and air filter removed. After it warmed up, the geysers coming out of the float bowl vents were an impressive sight. Right before they made tight u-turns and got sucked into the venturis - then everything shut off until the gas could evaporate. All's well now with EFI.

Just saying...

Tom

[NROTOXIN]

Tom,
No "root cause analysis" has really been done here, only internet troubleshooting. What has worked for some does not always work for others. At the same time, these are low cost things to try. Maybe it's not boiling at all and it is something else.......nothing here so far has this been identified 100% fuel boil, only symptoms. Let's treat the symptoms with a couple of low cost parts and then take it from there. YMMV

[patrickt]

Originally Posted by NROTOXIN

TLet's treat the symptoms with a couple of low cost parts and then take it from there. YMMV

I agree with that. You could do a pretty quick test with just aluminum foil and ice packs around the carburetor. If doing that will temporarily make the problem vanish then you're on the right track.

[Tom Wells]

NRO and Patrick,

You guys are probably right

My experience is only with my two cars.

Tom