Gas Boiling in Carb Bowls (Percolation)

[at the beach]

To help avoid percolation problems this summer we just installed a Holley heat shield under the carb. It took a little trimming.

I recorded bowl and water temps before I installed it and after. Here’s what I got:

At 200+ the no shield bowl temp was 167 versus 104 with the shield
at 240, no shield 176 versus 159 with the shield
at 250, without the shield the fuel boiled and the engine stopped with the bowl showing 194.
at 250 with the shield the bowl temp was 171.

The shield certainly seems to be doing a good job.

The Holley pn is 108-70. About $36 from Summit.
I had to use longer studs since it comes with a fat (5/16”?) insulating gasket. (actually used regular bolts for now.)

Buck

 

[mr55s]

Heat shield

Hi Buck, the heat shield used, is it like a piece of sheet metal between the carb and intake that deflects the radiant heat or a phenolic spacer that limits the heat transferring from the intake to carburetor? Kind of like the Boss 302 spacer .
Thanks for posting the heat readings.
Brian

 

[at the beach]

The Holley shield kit has both a reflector and an insulator.


As shown in the picture accompanying the earlier post there is an aluminum plate that reflects the heat. There is also a thick (5/16"?) insulating gasket to help block the heat from conducting from the manifold and into the carb.


Buck

 

[Warren]

Sochiro

Honda used insulating blocks on their little bikes. Always a consideration is the outboard edges of the stock air cleaner. I liked Tim R's version from the 90's. Seen a insulator with channels thru it for air flow as well.

 

[hottigr]

I used this little stack of plates and gaskets to accomplish
2 things: insulate from heat and get some ram effect- just
kept adding until the foil squished when I closed the hood:

 

[michael-king]

I would think the pholenic spacer is doing the majority of the work aa it stops the direct hrat transfer from the manifold. While lots of cars used heat sheilds for carbs most are to block radiant heat from exhausts close to a carb like in non cross flow 4 and cylinder motors.

I bough the same kit a few years back.