Steve Warman Posted April 14, 2009 Share Posted April 14, 2009 Hi, I've changed my weber carb in my 90 and the new carb had a 'spare' inlet above where the fuel inlet was compared to the old carb. I'll try an get pictures later on to make it clearer but I connected up the fuel line to one of the inlets and got a short piece of tubing and secured it to the other and clamps it off but I'm now wondering whether that was the best thing to do and what the other inlet is actually for. If anyone has any info on the purpose and the best way to deal with it then please let me know? Thanks Steve Quote Link to comment Share on other sites More sharing options...
markyboy Posted April 15, 2009 Share Posted April 15, 2009 Hi,I've changed my weber carb in my 90 and the new carb had a 'spare' inlet above where the fuel inlet was compared to the old carb. I'll try an get pictures later on to make it clearer but I connected up the fuel line to one of the inlets and got a short piece of tubing and secured it to the other and clamps it off but I'm now wondering whether that was the best thing to do and what the other inlet is actually for. If anyone has any info on the purpose and the best way to deal with it then please let me know? Thanks Steve Are you sure it's not an overflow or a return to the fuel tank? A photo would be a help in diagnosing it. Did the new carb not come with instructions or a diagram? Mark. Quote Link to comment Share on other sites More sharing options...
Steve Warman Posted April 15, 2009 Author Share Posted April 15, 2009 Heres a picture of the inlets/outlets onthe carb. The tubing on the right goes no where and is sealed off. The carb was a second hand one so no manual but it's a weber twin carb. Quote Link to comment Share on other sites More sharing options...
markyboy Posted April 16, 2009 Share Posted April 16, 2009 Heres a picture of the inlets/outlets onthe carb.The tubing on the right goes no where and is sealed off. The carb was a second hand one so no manual but it's a weber twin carb. Hi Steve, Definitely a second inlet. Are they both open with the hoses removed? Sometimes a single casting is used for different installations but they're quite often blanked off internally. IMHO I reckon you can leave it as it is and it won't be detrimental to the operation of the carb. I can't see why you'd have or need two inlets, other than for routing of the supply hose in an installation that's short of space or something like that. Maybe soemone else knows? HTH Mark. Quote Link to comment Share on other sites More sharing options...
Steve Warman Posted April 16, 2009 Author Share Posted April 16, 2009 Cheers Mark, Yes, they're both open. I found that out when I forgot to block it off and petrol quickly dripped out The reason I asked is that I have a smell of petrol coming from under the bonnet and in the investigation of said smell and other performance problems I wondered if this has any effect or any general use. but I think you're right, I'll leave it alone unless anyone has any other reason for it beng there Cheers Steve Quote Link to comment Share on other sites More sharing options...
Aragorn Posted April 16, 2009 Share Posted April 16, 2009 does the carb have a return? It might simply be a return feed, and if you run the carb without one, you'll end up flooding the float chambers and it'll run like carp... Is one hole smaller than the other? Quote Link to comment Share on other sites More sharing options...
Steve Warman Posted April 16, 2009 Author Share Posted April 16, 2009 Without being too technical (I'm away from the truck at the moment) they looked the same and took the same size pipe. Where would a return go to from there? Quote Link to comment Share on other sites More sharing options...
Aragorn Posted April 16, 2009 Share Posted April 16, 2009 Back to the tank... Some carbs are designed to be run with only a feed, others require a feed and return and possibly a pressure regulator too. Usually the return drilling will be a smaller diameter, or will have a restrictor fitted to act as a crude regulator. If you get the model of the carb, you might be able to find some technical details about it online, or from webcon directly. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted April 16, 2009 Share Posted April 16, 2009 Where would a return go to from there? The fuel tank! I'd find the part number and have a google for a manual/spec or a vehicle it was fitted on originally, and go by the Haynes or similar, this info must be out there somewhere. Quote Link to comment Share on other sites More sharing options...
markyboy Posted April 16, 2009 Share Posted April 16, 2009 I suppose it could be a return as Aragorn says. Possibly, when the needle valve closes the fuel still being supplied to the carburettor gets re-routed to the fuel tank via the hose which is blanked off. It depends what type of fuel pump you have I think. IIRC the old SU type fuel pump used to stop running when it "sensed" an increase in fuel pressure. Not all fuel pumps work in that way and they run continually, hence the need for a return. My brother in-law's 2.5 petrol 90 of '86 vintage definitely had a return to the tank. It also had a Webber carb but it wasn't like the one in the picture, his had a separate hose for the return, I think it came off the float chamber somewhere. We've recently converted it to 200 TDi and utilised the fuel tank return for the diesel return. If it is as Aragorn says this could well be the source of the fuel smell you are experiencing. Mark. Quote Link to comment Share on other sites More sharing options...
Steve Warman Posted April 16, 2009 Author Share Posted April 16, 2009 The fuel tank!I'd find the part number and have a google for a manual/spec or a vehicle it was fitted on originally, and go by the Haynes or similar, this info must be out there somewhere. Thanks for the helpful info, I thought it just p**ssed away on the road hence the poor mpg. Quote Link to comment Share on other sites More sharing options...
Steve Warman Posted April 16, 2009 Author Share Posted April 16, 2009 I suppose it could be a return as Aragorn says. Possibly, when the needle valve closes the fuel still being supplied to the carburettor gets re-routed to the fuel tank via the hose which is blanked off. It depends what type of fuel pump you have I think. IIRC the old SU type fuel pump used to stop running when it "sensed" an increase in fuel pressure. Not all fuel pumps work in that way and they run continually, hence the need for a return. My brother in-law's 2.5 petrol 90 of '86 vintage definitely had a return to the tank. It also had a Webber carb but it wasn't like the one in the picture, his had a separate hose for the return, I think it came off the float chamber somewhere. We've recently converted it to 200 TDi and utilised the fuel tank return for the diesel return. If it is as Aragorn says this could well be the source of the fuel smell you are experiencing. Mark. Cheers Mark, I'll see if the in tank pump has a return on it anywhere. Quote Link to comment Share on other sites More sharing options...
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