Not sure if this is the right place for this post. (If not please relocate).

I've been driving my '68 (327 ci with Holley 457S) in the heat and very slow weekend traffic last two days. I noticed that when the engine showed higher than normal temp range, I would a feel slight hesitation coming off idle. In one or two instances, the hesitation would be replaced with a backfire...from the carb not the pipes. It scared the cr@#$%^p out of me! As soon as the engine got back down to normal temp levels, the hesitation and backfiring went away.

I assume this is because the fuel in the carb bowls is so hot, it's starting boil. Does that mean the carb is running leaner at that point? Is that why it backfires through the carb? The carb is a Holley 457S which I have spent countess hours tuning. It idles and responds very well once it has warmed up appropriately. So other than the hesitation and popping when hot, the carb works great!

I'm going to replace my old aluminum intake (made by Winter) with an Eldebrock Air Gap..as from what I understand it will cool the passages under the carb. Also, I am going to replace my 1" aluminum carb spacer with a non-metal one...not sure what they are called.

I'm hoping both these changes will help keep the fuel bowls cool and maybe resolve this problem in the heat.

Should I change the idle fuel mixture or the float level to richen the mixture? What about teh main metering jets (since this is really an offidle situation)? My pref is NOT to touch the carb setting as it it actually running pretty good .

Vic

 

I had this problem once with an old Vette, only when it got hot, but that was with a Quadrajet carb. The gas was perking out of the carb faster than it could recover, and the car would buck and jerk something awful. The difference between that and your Holley though, is the Q-jet has the bowl in the body of the carb, getting toasty right above the intake manifold, but the Holley has two bowls front and back hanging out in the open. Because of that, I can't see how you're going to perk out that much gas to starve the engine. How hot is the engine getting anyway? I spose you could do a test, and get the engine up to temp where you get your hesitation, then wrap a flexible ice pack around each bowl (between the bowl and manifold) and see if it still does it. Using a carb spacer with a conventional manifold sure can't hurt, "phenolic" is what you call the non-metallic one. But I'd wait on the spacer and see what the air-gap manifold does for you, and how everything fits under the hood as it's a taller manifold than what you have now. One other thing that comes to mind is if your ignition isn't liking the heat. What ignition are you running?

 

Thanks Chuck.

With regards to the timing, the base timing is 15 degrees, and with the VA attached at idle another 15 for a total of 30. I measured it just after I came back from a drive..so it was nice and hot. My VA is on direct vacuum not ported.

One more thing: after I measured the timing, I shut the car off and left the hood open in my garage...and while I was working around the car I kept hearing an unusual noise coming from the engine...not like the pinging of an engine cooling down...but almost like someone blowing bubbles in water. It was comming from the carb bowls...that is why I think the fuel is boiling when I drive.

I've ordered the AirGap and I do have a "phenolic" spacer on hand. I think the combo should cure this.

Vic

 

Sure sounds like you're perking gas. Just how hot is the engine getting? And oh yeah, I also meant to mention to recheck your float levels to make sure they're not set too low. Even with two carbs, I had one bowl that was low and the engine stumbled bad off the line. I have since put on clear sight plugs so I can always keep an eye on them.

 

Chuck,

It has been unusually hot for my area. And I was in heavy stop and go traffic with passengers. My car (with console gauges) normal runs with the temp gauge one notch below center. The worst I have ever seen it before was 1 notch above center. This week it was getting up to two notches (above) but still not in the "orange" zone of the temp gauge. (Sorry I don't have actual temperatures).

I installed clear site plugs too..but mine are so hazy I can't see anything! With the old standard metal plugs, the fuel level is just at the bottom edge of the hole. If I rock the car, it spills fuel. Is that where it should be (with engine at regular idle)?

Oh, BTW, when you asked about what ignition I'm running..I assumed you meant timing...but just in case you didn't, I use a Pertonix Flame-thrower distributor..with a standard advance curve.

Vic

 

with a holley its no wonder you have spent countless hours tuning it,and with a holley you WILL spend countless more hours. i reccomend a edelbrock carb,they are set it and forget it.otherwise the air gap helps a lot and yes your fuel is probably boiling so your lean idea is right those spacers are called phenolic resin spacers and they are worthy too some people use a electric fan blowing on the carb ala L-69 in extreme cases a pusher fuel pump as well as the mechanical pump with some heat wrap on the line to the carb too good luck

 

Thanks Rusty.

Something tells me you're not fond of Holley Carbs..;-)


One other thing that I am consider is the addition of an axillary fan between my rad and engine fan. (That's for another thread), but I'm hoping this will further cool things down.

The problem is I have way too much invested in the Holley. I probably have a few hundred dollars in parts. In fact, I've had three of them that I tinker with. Sadly, one of them pushed my buttons too many times one day and I introduced it to the garage floor (rapidly). I had a lot of issues with the Hollies..but I have slowly sorted them out ...it would be a shame to give up everything I gained. But you make an excellent point...I would have loved to spend my time tinkering with something other then the smelly carb!

Vic