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8 & 10 cyl Bristol cars Type 407 onwards - restoration, repair, maintenance etc

412 Series 1 Vapour Lock

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Old 13-01-21, 04:43 AM
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Default 412 Series 1 Vapour Lock

My 412 series 1 ( 400ci motor ) when the weather hots up suffers vapour lock , the fuel in the carbie boils and the car wont start after a run . The motor does not run hot at all but after a recent trip in 35 degree heat I stopped for a brief period and it took 20 minutes to get it running.
ebay and the web have lots of answers

1/ Heat block below the carbie ( not enough room )
2/ Redirect the fuel line away from the motor. ( This has been done by previous owner
3/ Add an electric fuel pump ( already fitted )
4/ Block the exhaust gases flowing through the inlet manifold.
5/ Replace the inlet manifold with an alloy unit ( reduces the heat soak )
6/ Fit a return line back to the tank and have the fuel circulating to keep the fuel cool.

My first thought is to replace the manifold.

My question is has any one done this and managed to fit the original air cleaner with the limited space available ?

Please note the series 2 cars had a completely different motor.

Any other ideas
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Old 13-01-21, 07:03 AM
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Hi Peter,
I have an alloy mainfold on my (your old) 411 S5, which has the same engine as your 412. However, what we don't know is if the space between the bonnet and the inlet manifold is the same between the 411 and 412. I'll see if I can work out some meaningful measurements so you can make comparisons.

What carburettor does your 412 have?

Kevin
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Old 14-01-21, 06:33 AM
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Kevin thanks for that.

I have a Hollie manifold on my 411 (unknown what model) and even without a heat block the new edelbrock carbie causes the standard air cleaner to touch the bonnet. To overcome this problem I had an engineer machine as much as he could off the top of the manifold. The air cleaner now just fits.

Its hard to take measurements but I believe there is less room under the bonnet of the 412. I would be interested to know what manifold you have. My limited knowledge leads me to an Edelbrock low rise Performance manifold but short of buying one its hard to get retailers to give you a meaningful measurement.

I have just had my new air conditioning system in the 411 gassed up, the garage tells me it works well . I guess time and a few hot days will tell a story.
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Old 14-01-21, 03:33 PM
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Default Vapour Lock

Hi. My son had the same problem on his 65 Gordon Keeble powered by a Corvette V8. I cured this by installing an anti perc fan from a Renault 5 GT Turbo. This took cold air from the front of the car and blew this over the fuel line and around the carb. Completely solved the problem.I am going to do the same on my 69 411 as it is difficult to start when hot -- fitted with a Thermoquad carb.
I shall use a 3 inch 12 volt bilge fan and a reducer to a 1 inch pipe to the hose to the carb.Will adapt some de-mist vents-- probably from a mini to introduce the air around the carb with a switch in the cabin.
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Old 15-01-21, 06:43 AM
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Peter,
My alloy intake manifold is a Weiand 8008 Action +Plus.
Carby is an Edelbrock 800CFM AVS Thunder Series 1812

I measured between the valley cover just in front of where it is bolted to the rear of the engine block to the top surface of the carb where the air cleaner sits (with gasket removed). It 203 mm and I am assuming that the top of the carby is parallel with the top of the block.

I have attached photos showing how I took the measurement and a close up of the valley cover showing where I positioned the bottom end of one of the rulers.

The height of the carby from the base to the top rim where the air cleaners sits is 83mm and the carby is sitting on a double gasket totalling 5mm thickness. So the intake manifold is 115mm high.
.
Attached Images
File Type: jpg measuring carby height.jpg (409.8 KB, 16 views)
File Type: jpg top of block measuring point.jpg (162.9 KB, 15 views)
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Old 16-01-21, 07:13 AM
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Kevin
Thats great info for me. The manifold you have is the same as my brother Geoffrey had on his 411 Mk1 ( which has returned to England) . Unfortunately Geoff never tried the original air cleaner on the car. My next question to you is have you ever fitted your original air cleaner?

I noted 2 things about your set up 1 you dont have a heat block below the carbie and 2 Most people fit 650 cfm carbies on standard motors . How do you find the big carbie performs in normal road conditions ?
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Old 16-01-21, 03:22 PM
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Peter,
I still use the standard air cleaner. I suspect there isn't much room between the air cleaner and the bonnet, but it does fit.

Although the phenolic resin heat block below the carby is missing, the double gasket totalling 5mm probably has a similar effect in terms of heat insulation.

I didn't specify the 800 CFM carby, nor did i approve the purchase and fitting by the guy who was working on my car at the time - long story. Personallly I would have thought a 650 CFM would be adequate, however the 800 CFM works fine. That said, I should mention that the main jets in the carby have been changed, also my engine is not standard and has a higher capacity and volumetric efficiency that the standard 400 CID engine.
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