Su carb heat shielding

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NowayPedro

NowayPedro

Active Member
Posts
114
Hello
Has anyone on here made/purchased/fitted heat shields to their su carbs on a 3.5 v8?
Looking at the possibility of doing this but can't find much to go on out there.

Cheers
Paul
 
I bought it with SU'S. The engine is from a range rover classic from the 80's. Yes, it's an on going problem. I have sent the carbs away to Berlen Fuel systems to be looked at. It runs great for about 40mins then starts coughing , farting, spluttering and sucking in air. Eventually coming to a hault. Leave it for 10 mins and it drives again but the process starts again. So heat related. Percolating fuel, evaporation of fuel suspected. I'm just trying to think ahead as when the carbs come back and I fit them again and the symptoms remain i might cry!!
 
Have you got the small fuel pots before the carbs? These are like swirl pots.
Also make sure you have a restricted return so the fuel does not bypass the carbs.
What fuel pump are you using? & where is it

If the fan is still on the engine air flow would prevent the evaporation.
 
No I don't think there are swirl pots. I have after market fans electric thermo switch operated and a new rad and thermostat. Running temperature is good. About 82°. There is a red top (pattern) fuel pump with a return pipe to the tank. Don't know if it has a restrictior on it though. How can I tell?
 
NowayPedro said:
No I don't think there are swirl pots. I have after market fans electric thermo switch operated and a new rad and thermostat. Running temperature is good. About 82°. There is a red top (pattern) fuel pump with a return pipe to the tank. Don't know if it has a restrictior on it though. How can I tell?
Click to expand...
There is a link pipe between the carbs(feed)used to be black pipe with 2 t pieces,on the rear of the carbs
This then returns to the tank & has a smaller hole to make a restriction.
If no restriction fuel flows freely past the carbs & wont fill the bowls.
 
Hicap phill said:
There is a link pipe between the carbs(feed)used to be black pipe with 2 t pieces,on the rear of the carbs
This then returns to the tank & has a smaller hole to make a restriction.
If no restriction fuel flows freely past the carbs & wont fill the bowls.
Click to expand...
Hmmm that's interesting. Please see my photo. The return is wider diameter than the link pipe. Is this correct? Also it runs fine for 40 mins. The horizontal pipe is the link pipe and I'm holding the return.
 

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NowayPedro said:
Hmmm that's interesting. Please see my photo. The return is wider diameter than the link pipe. Is this correct? Also it runs fine for 40 mins. The horizontal pipe is the link pipe and I'm holding the return.
Click to expand...
In that t piece check the hole size, remove that other pipe.

So flow(big hole goes carb)
Small hole return

Make sure both ends of that link pipe has the same size holes
 
Is the fuel pump working properly ? Also is the tank & fuel clean. Doesn't take much debris to block the float valve.

SU carbs are so simple you should be able to strip, clean & rebuild them yourself. Had many non LR cars with them years ago. We used to strip them & then boil for 30-60 mins using old fashioned washing power (not too much so it disolves properly). Then re-assembled using new gaskets & seals & they worked fine.
 
Cheers. They were ultrasonically cleaned and float Chambers and needle valves were spotless. But I'm hoping getting rid of the over run valve thingies will solve the issue. I might get an old one and plau about with it so I can demystify the dark art of these little bleeders!!
 
I've had SU's on my V8 Series for decades an I've never had any issues. Certainly nothing heat related. They're off an SD1 and run on a dead head layout, so there's no return back to the tank, just a feed from the pump.
I've an electric fuel pump bolted to the transfer box with a generic plastic fuel filter fitted both in front and after it. I've removed the original metal mesh filter from the bottom of the tank's pick up tube. Its easier to replace the filter and each one lasts a year or so before they fill with bits of rust etc.
From your described issue after running for 40 mins I doubt it's your carbs themselves, but it could be the fuel supply. You don't mention what type of pump you have but I'll assume its an electric one. I have seen problems before, with electric pumps mounted too high above fuel tank level. Most electric pumps don't have great suction and are designed to be "pushers" i.e. fitted at the rear of the vehicle (unless you fit one from a Morris Minor which is designed as a "sucker".
SU's will run happily on 4 - 5 psi fuel pressure which isn't much, but if your pressure is way down you can run into fuel vaporisation within the float chamber and that will make it run badly.
Next time your Landy starts acting up put your hand on the ignition coil and see if it's very hot. It could be past its best.
 
Rangieman123 said:
I've had SU's on my V8 Series for decades an I've never had any issues. Certainly nothing heat related. They're off an SD1 and run on a dead head layout, so there's no return back to the tank, just a feed from the pump.
I've an electric fuel pump bolted to the transfer box with a generic plastic fuel filter fitted both in front and after it. I've removed the original metal mesh filter from the bottom of the tank's pick up tube. Its easier to replace the filter and each one lasts a year or so before they fill with bits of rust etc.
From your described issue after running for 40 mins I doubt it's your carbs themselves, but it could be the fuel supply. You don't mention what type of pump you have but I'll assume its an electric one. I have seen problems before, with electric pumps mounted too high above fuel tank level. Most electric pumps don't have great suction and are designed to be "pushers" i.e. fitted at the rear of the vehicle (unless you fit one from a Morris Minor which is designed as a "sucker".
SU's will run happily on 4 - 5 psi fuel pressure which isn't much, but if your pressure is way down you can run into fuel vaporisation within the float chamber and that will make it run badly.
Next time your Landy starts acting up put your hand on the ignition coil and see if it's very hot. It could be past its best.
Click to expand...
Thank you for this. The pump is a red top pattern electric pump. It's mounted close to the fuel tank but can't remember exactly where. Ill check it. Carbs are spotless, no crap or gunge anywhere. Changed the coil already.
 
So, for what its worth, I had the same probpem with my Stromberg carbs, extremely pronounced in the Tunesian desert (go figure). Was definietyl heat induced, as the carbs were basically boiling while you could touch the engine block without too much problem. Turned out that it was those temp sensitive auto-jokes the Stromberg carbs have, no idea if SU carbs are similar.

Edit: I thought about isolation as well, came to the conclusion that would only buy time if there is no sufficient air flow, preferably cool air, over the carbs. Having them on top (obviously...) and rather back in the engine bay certainly doesn't help. I am still thinking about cutting some ventilation holes and installing some lines on the beat up, designated expedition hood if I ever have a chanve to go back to the desert with the car. I found several racing-focused sites onlone sellong those bits, incl. FIA certification looking into this... Sometimes I am hopeless...
 
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