Inigo Posted January 9, 2014 Share Posted January 9, 2014 I have a 1987 110 V8 that has been fitted with an Edelbrock carb and an LPG system. It ran OK on LPG, but not very well on petrol. On investigation, the carb floats had been crushed so it was running way too rich and flooding. Current state: new floats, carb fettled, new leads, dizzy cap, coil and spark plugs. Static timing done. It now runs fine on petrol at low revs. At high revs, or under load it starts to stumble after a while eg I can give it some welly up a hill in third and it runs great for about 20 seconds then starts to stumble and miss. If I back off and give it a minute or two I can again accelerate hard, if briefly. Similarly on the motorway, it is OK until about 65 in fifth when it starts to stumble if I try and get it going faster. It previously ran well up to 90 on lpg. My initial feeling is a fuel issue. I replaced unknown fuel filter in line in the engine bay with what I thought was the correct Land Rover part (STC1677) that is a metal canister with tube stubs coming out of each end. I have since found out that for the low pressure carb pump, the plastic fuel filter may have less resistance. I then traced fuel lines back to under seat fuel tank (rear tank removed to add LPG tanks) and found an additional filter housing (NRC9786)- I replaced filter or rather fitted filter as filter housing was empty. Still the same issues. Would using two sequential filters slow down the flow of fuel? Is my fuel pump shot? Fuel appears to be reaching the carb, but I'm not sure what the flow rate needs to be or how to test? Checking parts manuals, originally the vehicle would have had a vapour separator and a fuel return line - I have neither. Would the lack of these cause a problem? Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted January 9, 2014 Share Posted January 9, 2014 Does certainly sound like you have a weak fuel pump -I don't see the need for two filters, it will only harm the fuel pumps efforts for sure. Quote Link to comment Share on other sites More sharing options...
Rangy35 Posted January 9, 2014 Share Posted January 9, 2014 Yes does sound like the fuel pump can not keep up, the two fuel filters is over kill but should not cause to much of a concern if the pump was good, you could have some restriction in the fuel tank around the pump pick up. There could also be a filter in the banjo bolt where the fuel enters the carb, or it could be a separate filter in side where the banjo bolt screws into the carb. Fuel pressure should be around the 6-7psi and if the previous guy removed the return line he must have put some restriction in somewhere to try and maintain the fuel pressure, that could also be a factor. Quote Link to comment Share on other sites More sharing options...
Team Idris Posted January 9, 2014 Share Posted January 9, 2014 I bought a fuel pressure gauge for my SU carbed V8. It sounds like a daft thing to have seing as they are rare, but for modified stuff it is very useful and has already saved our ass with a super quick diagnosis half way through an event ! I'm with everyone else with the weak pump though. It sounds a lot like our old pump did, except it was steep hills that left us floundering. Anything under 30 degrees good, anything over that and we had a limp 4 banger. I fitted a Facet red top pump, (7psi) but had to fit a return line tap to reduce my pressure at the float needles on the SU. (3-5psi). No idea what the Edelbrock carb would like? Might be happy at seven? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 9, 2014 Share Posted January 9, 2014 If it's a facet-type external pump (I think some were as standard) it will have an internal filter which may never have been changed/cleaned. Quote Link to comment Share on other sites More sharing options...
smallfry Posted January 9, 2014 Share Posted January 9, 2014 The Edelbrock/Weber.........assume its a 500 ? Will like to have 6 to7 psi If you have the in tank pump, it only gives about 3 to 4 (well mine does) might be the problem ? Dont know the history of the carb, but did it run OK on petrol at any time ? Wrong main jets maybe ? If this had points ignition, I would look at the condenser ? Quote Link to comment Share on other sites More sharing options...
Inigo Posted January 9, 2014 Author Share Posted January 9, 2014 Thanks everyone. It is an in tank fuel pump, which I have just ordered a replacement for (Allmakes as the Land Rover one is £250). Before I replace it, I have found (on the pilgrim sumo site) a description of how to test if it is pumping enough (disconnect fuel line at carb, let pump run for 1 minute, measure volume of fuel collected.) Amount required relates to the BHP of the engine thus: CC per minute = BHP X 4.7. Might have to get a fuel pressure gauge to test the pump pressure of old and new - I guess a cheapy ebay job temporarily fitted in the engine bay would do? Lucas 35DLM8 dizzy, so I'm not sure it has a condenser, but does have an external amplifier. If none of this solves it, my plan was to take it to the local rolling road tuner to get him to play with jets, etc. I just wanted to get the obvious things and things he can't do anything about out of the way first - he was the one who discovered the crushed carb floats last time. Quote Link to comment Share on other sites More sharing options...
Inigo Posted January 11, 2014 Author Share Posted January 11, 2014 OK. Volume output from pump appears to be 280ml per minute, which would be enough to feed a 58 BHP engine. Also pressure, when pumping appears to be around 1 psi. I'll fit the new fuel pump (when I get a gasket) and see what figures I get then. Quote Link to comment Share on other sites More sharing options...
Inigo Posted January 11, 2014 Author Share Posted January 11, 2014 As an aside, I previously noticed a strong smell of petrol while driving and then noticed that fuel was actually running out of the filter bowl underneath the car. It seems that the cheapy ebay filter housing I bought, the seal was not fuel resistant and appears to have swollen over a couple of days and now will not go back in the recess, maybe 2cm too long. Replaced with genuine item. Quote Link to comment Share on other sites More sharing options...
Inigo Posted January 21, 2014 Author Share Posted January 21, 2014 New fuel pump fitted - gives a pressure reading of around 5 psi, engine now runs well and for as long as I like at high revs. Can now do the timing and carb tuning properly. Thanks everyone. I have a new issue. The old fuel gauge read either massively overfilled (equal to fuel tank full) or just overfilled (fuel tank empty). I replaced gauge with a VDO version and now gauge reads half full (when fuel tank 3/4 full), but this varies wildly with RPM. Not terribly useful. Should I investigate the in tank sender, the wiring in between or any earths? I have the paperwork for the VDO gauge and can investigate what signal it expects, what signal is being sent from the original sender? Should I be able to just swap these over - or is that where my problem lies? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted January 21, 2014 Share Posted January 21, 2014 Sounds like voltage regulation problem to me, assuming the sender is matched to the gauge. Quote Link to comment Share on other sites More sharing options...
smallfry Posted January 22, 2014 Share Posted January 22, 2014 Sounds like voltage regulation problem to me, assuming the sender is matched to the gauge. What he said............. VDO gauges work on a different voltage I seem to remember reading somewhere, maybe even unregulated ? I cant even remember if 90/110 Defenders even have a regulator ? Quote Link to comment Share on other sites More sharing options...
paulnb57 Posted January 22, 2014 Share Posted January 22, 2014 Im pretty sure they dont have a regulator, I had a recent fuel gauge issue, reading full most of the time and then threequarters occasionally.....turned out to be a duff gauge...... Paul Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.