Boiling Fuel

[Voyager]

Entertained my friends at last weekend’s cars & coffee by showing them how the fuel boils in the sight glasses in my carb bowls.

Engine is a KC 408 with a quick fuel HR-750.

Symptoms also include hard starting (when hot) and bucking/lurching under slow/low throttle conditions.

QFT sells a phenolic ½ carb spacer (part # 300-4000) and a quick cool insulator (part # 300-4013).

Anyone tried either? Not sure I like the looks of the quick cool insulator heat shield…

thanks

Bob

[kevins2]

Bob,

I had some fuel boiling going on and installed a 1/4" phenolic spacer - that's all I had room for. Haven't seen it again since but I haven't driven on an extremely hot day. So, I can say it has at least helped. Also, I used to get some backfiring and "crackling" on decel and after installing the spacer, it hasn't done that at all.

Kevin

[vector1]

Edelbrock makes either split plenum or open 1/4" insulator. 9265 or 9266. I don't leave home without it.

[Voyager]

Thanks Kevin,

Talked to 2 different techs at QFT today and both said go with the quick cool insulator (part # 300-4013) over the phenolic ½ carb spacer (part # 300-4000). They said the heat shield really makes a huge difference.

He said if I don’t like the looks of the shield, I can trim it down some.

Guess I’ll give it a try. And I'll probably rebuild the carb while it’s off the engine.

Bob

[lippy]

I don't have the problem with winter gas, but I do with our crappy CA summer gas.

I insulated all the lines and added a 1/4" phenolic spacer from Jegs. I tried the heat shield and it didn't help, plus it was ugly. Not sure I have a complete solution but this is the best I could do.

[vector1]

quikfuel sells the edelbrock setup also.

4150/4160 Style Base Gasket - Quick Fuel Technology

[fastd]

I'd be interested to know how the quick cool insulator works for you. What is it exactly? From the picture and the text it looks like a holley type heat shield and a spacer that "made from a poly-core material sandwiched between two layers of aluminum to reduce heat transfer"...

I had the same problem hot/hard start problems but no bucking when it was hot and already running.

I added the holley heat shield and didn't really help at all. But the 1/2" phenolic spacer really works (I assume it also makes the heat shield work more effectively); don't minimize the potentially benefits.

Interesting I have a big block Pontiac Firebird that was also giving me same problems; I pulled out the fuel system and added:
Aeromotive In tank fuel pump, return line, PTFE fuel lines, insulated taped the fuel lines around the engine heat and still had the same hot/hard start problems!!! (But it helped vapor lock issues).

BUT, adding that silly little phenolic spacer really fixed the hot/hard start...I only recently did it so I haven't had it installed for a humid NC summer day, but so far so good and that spacer was the best $40 I have ever spent.

[fastd]

BTW, the holley heat shield also comes with a pretty cushy gasket similar to the one that vector1 posted.

[Voyager]

My preference is to just add a phenolic spacer so it’s not too visible. Maybe I’ll ask KC tomorrow what they recommend.

[DWRAT]

I added a 1/2" phenolic spacer and it worked great.
No more hard hot starts.

[DanEC]

After following a thread on Corvette Forum about a 67 that had issues with percolation and finally solving 90% of it by insulating the fuel line, I ordered some of this stuff to try out.

[ame="http://www.amazon.com/Heatshield-Products-274012-Thermaflect-Sleeve/dp/B002UH0B3W/ref=sr_1_8?s=automotive&ie=UTF8&qid=1461201445&sr= 1-8&keywords=fuel+line+insulation"]Amazon.com: Heatshield Products 274012 Thermaflect Sleeve 1/2" ID x 3' Heat Shield Sleeve with Velcro: Automotive@@AMEPARAM@@http://ecx.images-amazon.com/images/I/41ZYGgVwENL.@@AMEPARAM@@41ZYGgVwENL[/ame]

Should be easy to install in the summer and remove if desired in the cooler months.

[427Larry]

Get one from Coolcarb, they are the best, available in different thicknesses, it's a different kind of heat spacer, check them out at Coolcarb.com.

[Tom Kirkham]

I have found a bypassing fuel pressure regulator to be a huge help. I also would recommend any fuel lines (such as a fuel log, or fuel filter) bolted onto the engine have some form of insulation installed between the fuel line and engine.

[ScratchBuilder]

A few years ago my GT350 ran into vapor lock and fuel boiling after years of running fine. I tried everything and the only thing that worked was removing the mechanical pump and going to a tank mounted electric.

[steveofiveo]

I had the same thing happen to me with a 66' Mustang (with a block mounted mechanical fuel pump). It left me worried I would get stranded every time I took the car out. Here's what I did:

Any fuel line close to the headers/block/radiator I wrapped it in aluminum foil and then black insulation tape (you really couldn't see it). .I also re-routed the line from the pump to the carb. It was metal but I switched it to rubber.

Later when I swapped the motor and I ran an electric pump. I routed the line along the frame rail (keeping it away from any heat source) then to a regulator on the pass firewall. I then continued the line along the back firewall and sent it into the holley from the back. It's a much cleaner look and is very effective.

I did the same thing on the Cobra. Zero problems. What are the details of your system?

S

[Voyager]

Gentlemen,

Thanks for all the feedback.

Think I’ll start with a 1/2" phenolic spacer.

If that doesn’t work, I’ll look at addressing the block mounted mechanical fuel pump and fuel lines.

Thanks,

Bob

[fastd]

while you are in there, if you have the clearance, i think adding a heat shield might really help deflect some of that nasty heat radiation (despite the fact that I said above that it didn't do much by itself) and allow the phenolic to stop the conductive heat. The Holley heat shield comes with a squishy gasket; and the CoolCarb looks like it comes with a with one that some kind of composite filled material (but it's layered between aluminum for rigidity).

If you don't have the clearance and have the room to only put on thing on I would go with the phenolic spacer...however, it is usually not that kind of choice. If you have only 1/2" of room, personally I would go with a 1/4" phenolic and a heat shield rather than a 1/2" phenolic. I had limited clearance on that pontiac i mentioned and went with a 1/4" and heat shield and it fixed it (again, I haven't tried it in the heat of the summer but I was having hot/hard start issues in the dead of winter - at 35-45 degrees). On my Cobra I have a 1/2" phenolic (with a heat shield) and I don't know that it makes much of a difference. Ideally, heat shield with 1/2" phenolic is obviously the best.

I actually think that the best set up would be 1/4" phenolic sitting on top of the manifold, then the heat shield, then another 1/4 or 1/2" phenolic on top of that.

[fastd]

to me, the worst things about these carbed cars is the hot start issues so you have to get aggressive about dealing with all the issues; like being able to get it started when you go to the grocery store! Other than hot start, I don't really think that drivability is a big issue; if you willing to stick with it, these carbs can be tuned well enough to drive fine (with worse gas mileage and not perfect a/f compared to EFI). My cold starts are easy...

Once the hot start and tuning is taken care of, the other not-too-easily-fixed issue is the warm up (neither of my carbs have a choke; and even carbed cars I have driven with chokes don't come close to a modern engine); but I think we can live with the warm up...

[GBowman]

I bought the Coolcarb spacer, worked perfect.

[Ace23]

I will just post my experience....go figure


*I have a KC 427 with a 112 LSA cam with duration in the 250-260's. I have the idle set at about 1050-1200 and the carb is a QF-750-SS with the choke. I never open my hood when I park and the thing cranks all the time.....even in the middle of summer it handles traffic fine.....haven't ever had it buck, spit ect.

*A local friend of mine has the same fuel pump same fuel line runs ect. He runs a KC 445 Windsor with 108 LSA cam with slightly more duration than me. His carb is a QF-850 no choke, I know he runs a heat shield under the carb and maybe a spacer. The only other difference is he runs a larger oval air clearer. The hood on his car always had to be popped when he parks and he has had the car bucks and spit in warmer weather.