Perculation

[Mad4slalom]

Any body here fitted a phenolic carb spacer. Was surprised how quickly the carb empties if left for just 15/20 minutes, the motor spins over really freely as if no fuel to compress i have to pump som fuel in then she starts.i guess its boiling / evaporating the fuel and emptying the bowls . If I fit a spacer would that mean i would need to retune the carb or should nothing change? Any experiences of fitting a spacer and if it cured the issue of fuel percolation. Any suggestions for make/ thickness of spacers. ( saw some plywood ones ) but that just doesnt feel right . Thanks all

 

[CaptainK]

Yeah, I have a phenolic carb spacer to stop the heat from getting into the carb. Fitted it myself (despite mechanical newbieness). Made a vast difference to the car. I got the Edelbrock spacer - EDL-9266 (it seems the right thing to do as I have an Edelbrock inlet and Edelbrock carb). The issues I was having was the fuel was percolating in the carb and it was making hot starting hard, and it was having issues driving at low speed etc. After a run putting my hand on the carb it felt very hot. After the insulator, it feel "warm", but no where near the hot feeling it was before. Car runs much better now. More importantly, prior to the insulator, whenever I stopped my engine and immediately opened the bonnet, it sounded like a coffe percolator under there - you could hear the fuel bubbling away for quite a long time. It deffo doesn't do that now, even on hot days.

My spacer isn't particularly thick (just over 0.3 inch thick), intentionally, as there isn't much space with my dual plane manifold pushing the carb up towards the hood. You can get much bigger ones if you have the space.

Couple of hints I found:
1) The heat insulator doesn't make a good gasket, so I have carb gaskets on the bottom and top of my heat insulator. This is because in the four corners there are the bolts holes in the gasket that run from the carb to the manifold. They have metal in those holes for the bolts to run through. Those metal bits stop the insulator compressing enough to seal ok. Its not a fault, just the way it is.
2) I took the butterfly nut off the top of the air filter box on top of the carb and replaced it with a standard nut. That saved me precious bits of an inch in space. You laugh - check it out

Dead easy to fit the insulator too

 

[Daytona Vette]

ETHANOL

 

[Roscobbc]

Heat rises......vertical 'path' of rising heat from the engine will rise through rocker covers and ultimately inlet manifold and finally the carb. You used to be able to source a 'stacked' insulator gasket 'set' - effectively 5 or 7 carb gaskets and the same number of ally plates that you would alternate as a heat insulator (much like the phenolic or plywood ones) - which one worked best? - perhaps the 'stacked' one?
Also consider using insulating foil on the fuel line - it runs very close to exhaust on passenger side.....

 

[Daytona Vette]

The Ethanol has a lower boiling point than petrol and so the Ethanol additive causes the fuel to atomise at a lower boiling point, so use the heat insulator under the carb, choose Ethanol free / low Ethanol Fuel and if that becomes a problem a thermostatically controlled cooler fan - check that you have all the Radiator shroud insulation in place and that the under hood temp is not running high

 

[Mad4slalom]

Any body here fitted a phenolic carb spacer. Was surprised how quickly the carb empties if left for just 15/20 minutes, the motor spins over really freely as if no fuel to compress i have to pump som fuel in then she starts.i guess its boiling / evaporating the fuel and emptying the bowls . If I fit a spacer would that mean i would need to retune the carb or should nothing change? Any experiences of fitting a spacer and if it cured the issue of fuel percolation. Any suggestions for make/ thickness of spacers. ( saw some plywood ones ) but that just doesnt feel right . Thanks all

Yeah, I have a phenolic carb spacer to stop the heat from getting into the carb. Fitted it myself (despite mechanical newbieness). Made a vast difference to the car. I got the Edelbrock spacer - EDL-9266 (it seems the right thing to do as I have an Edelbrock inlet and Edelbrock carb). The issues I was having was the fuel was percolating in the carb and it was making hot starting hard, and it was having issues driving at low speed etc. After a run putting my hand on the carb it felt very hot. After the insulator, it feel "warm", but no where near the hot feeling it was before. Car runs much better now. More importantly, prior to the insulator, whenever I stopped my engine and immediately opened the bonnet, it sounded like a coffe percolator under there - you could hear the fuel bubbling away for quite a long time. It deffo doesn't do that now, even on hot days.

My spacer isn't particularly thick (just over 0.3 inch thick), intentionally, as there isn't much space with my dual plane manifold pushing the carb up towards the hood. You can get much bigger ones if you have the space.

Couple of hints I found:
1) The heat insulator doesn't make a good gasket, so I have carb gaskets on the bottom and top of my heat insulator. This is because in the four corners there are the bolts holes in the gasket that run from the carb to the manifold. They have metal in those holes for the bolts to run through. Those metal bits stop the insulator compressing enough to seal ok. Its not a fault, just the way it is.
2) I took the butterfly nut off the top of the air filter box on top of the carb and replaced it with a standard nut. That saved me precious bits of an inch in space. You laugh - check it out

Dead easy to fit the insulator too

Thanks for the info all

 

[Chuffer]

I also fitted a titanium fibreglass weave heat shield sleeve over the fuel pipe that rises from the fuel pump to join the carb feeder pipe . The pipe passes very close to the front of the block and up past the water pump so there is a lot of radiated heat down there .

 

[CaptainK]

Thanks for the info all

You're welcome. Putting that insulator on mine helped massively. I couldn't believe the distance. Like Chuffer says, insulating the fuel pipe is another thing you might want to look at. I was considering it too, read some bits about it, including that it can also keep the fuel "warm" in that pipe when the engine is off (not so good) as the pipe is now insulated. So pros and cons really. Ultimately I never bothered with it due to the fact the carb insulator solved my problem.

 

[Roscobbc]

Having the OEM fuel 'return' system on the car is a help (if your car has one) as any fuel not required by the engine is effectively circulated back to the fuel tank. This helps to keep the fuel cooler (or at least closer to ambinent temperatures)

 

[Chuffer]

You're welcome. Putting that insulator on mine helped massively. I couldn't believe the distance. Like Chuffer says, insulating the fuel pipe is another thing you might want to look at. I was considering it too, read some bits about it, including that it can also keep the fuel "warm" in that pipe when the engine is off (not so good) as the pipe is now insulated. So pros and cons really. Ultimately I never bothered with it due to the fact the carb insulator solved my problem.

I take on board what you are saying but at least the fuel will not be getting nearly as hot in the first place . The guy who prepares and builds the race cars where I rent storage for the C3 gave the length of the insulation he uses to me when I was doing a lot of work on the car a couple of years ago suggesting it would be a good idea . I have also always made a habit of opening the hood for a while to disipate heat build up after getting back from a quick blast or a long drive .

 

[Mad4slalom]

I take on board what you are saying but at least the fuel will not be getting nearly as hot in the first place . The guy who prepares and builds the race cars where I rent storage for the C3 gave the length of the insulation he uses to me when I was doing a lot of work on the car a couple of years ago suggesting it would be a good idea . I have also always made a habit of opening the hood for a while to disipate heat build up after getting back from a quick blast or a long drive .

I must feel how hot the carb gets to the touch, you’d think it would have to feel untouchable to boil the fuel, not sure it is but will check next run out

 

[Chuffer]

I must feel how hot the carb gets to the touch, you’d think it would have to feel untouchable to boil the fuel, not sure it is but will check next run out

Boiling point of petrol is 95 degrees C . Water as we all know is 100 degrees C so that`s still a tad warm . I think it more to do with vaporisation as petrol will sit there and steadily vaporise at atmospheric pressure at ambient temperature very easily .

 

[Roscobbc]

Many years ago I used to do wedding work with a RR Shadow - summer weddings were a major worry because of percolation - all that stop/start stuff. Usually time between 'dropping off' the bride and then waiting for the 'happy couple' to re-emerge was generally an hour or so and percolation wasn't an issue - nevertheless I would open the hood to 'ventilate' things......which drew many amused remarks. Some people thong that RR's don't break down....lol!

 

[Corvetteville]

My fuel disappears when the car is cold. I can fill the fuel chambers via the breather & next day it's gone? I know this, by operating the throttle & see the 2 power pumps working. If I refill & do 2 presses on the pedal, it's fires almost instantly.If I start in the normal way, it takes about 5+ seconds to fire. (Quadrajet)

 

[Roscobbc]

Even a 'moderately' tired engine will suffer more from percolation than a 'fresh', new engine with tight piston ring gaps. The heat that causes percolation also can also effect other parts of the engine in extreme situations (starter motor?). My original stock 427 engine would have percolation to a mild degree and if left for a few days wouldn't start untill fresh fuel had been drawn from the tank and filled the carb. I'm sure many engines when left 'hot' and observe the carb throat after a few minutes will be 'welling-over' with fuel from the 'squirters' and other areas. That fuel can be seen 'puddling' in the base of the inlet manifold. Not generally an issue as it will evaporate over the next couple of hours (and probably why you'll get that petrol smell in the csr or engine compartment)

 

[Chuffer]

I think it is worth pointing out that percolation was always commonly known as `vapour lock ` and nothing to do coffee makers or fluid filtration through a porous medium . It was / is a common issue on carb fed cars . My mates 4.2 litre E Type did it regularly after a good hard drive or if the weather was hot .

 

[Mad4slalom]

Boiling point of petrol is 95 degrees C . Water as we all know is 100 degrees C so that`s still a tad warm . I think it more to do with vaporisation as petrol will sit there and steadily vaporise at atmospheric pressure at ambient temperature very easily .

Yes, I think you are right Chuffer, went to see a guy locally building the L88 racing vette replica this afternoon, We were talking about the fuel disappearing from the carb when hot, he asked if it smelt of fuel when parked up in the garage, I hadnt noticed this but when I went back to open up the air chamber to get my phone 45mins after i put vette away the chamber was smelling hot and fuelie. So like you say possibly evaporating away. He did say that on his 76 back in the day he thought his had some sort of none return valve in the fuel pipe up to the carb as standard ??
Feeling privileged this week to have been able to get out for 5 or 6 little blasts in the car. Loving it more and more each run, soooo worth the 30 year wait

 

[Oneball]

Yes, I think you are right Chuffer, went to see a guy locally building the L88 racing vette replica this afternoon, We were talking about the fuel disappearing from the carb when hot, he asked if it smelt of fuel when parked up in the garage, I hadnt noticed this but when I went back to open up the air chamber to get my phone 45mins after i put vette away the chamber was smelling hot and fuelie. So like you say possibly evaporating away. He did say that on his 76 back in the day he thought his had some sort of none return valve in the fuel pipe up to the carb as standard ??
Feeling privileged this week to have been able to get out for 5 or 6 little blasts in the car. Loving it more and more each run, soooo worth the 30 year wait

Was that Oli you went to see?

 

[Chuffer]

Yes, I think you are right Chuffer, went to see a guy locally building the L88 racing vette replica this afternoon, We were talking about the fuel disappearing from the carb when hot, he asked if it smelt of fuel when parked up in the garage, I hadnt noticed this but when I went back to open up the air chamber to get my phone 45mins after i put vette away the chamber was smelling hot and fuelie. So like you say possibly evaporating away. He did say that on his 76 back in the day he thought his had some sort of none return valve in the fuel pipe up to the carb as standard ??
Feeling privileged this week to have been able to get out for 5 or 6 little blasts in the car. Loving it more and more each run, soooo worth the 30 year wait

My car always pongs of fuel when I first park it up . Next day the pongs gone . It pales into insignificance compared with my Marcos Mantara . It had a fuel injected V8 so the engine didn`t smell of petrol but the boot did constantly . I spent a lot of time when i first had it having the tank out looking for cracks or pin holes , leaks in the filler pipe etc etc , only learn from guys in the club that they all did it . Some sort of design fault in breather set up as tank was long , thin and mounted vertically behind the rear bulk head in the boot Any clothing I put in the boot was wrapped in a big plastic sack or you walked around in a cloud of fumes . Club guys joked that you always new a Marcos Owner by his smelly luggage !
Glad you are enjoying get out for a few spins .

 

[Mad4slalom]

No ,

Was that Oli you went to see?

he is called Alex and lives six miles from me , he was thrilled to see another local stingray on the road , gave it the once over and was impressed how good it is inside , outside and underneath and how sweet the motor sounds