Twin carbs removal
Discussion
Hi all. I’ve a fuel issue on my car and I think it’s because I’ve tightened up the carbs onto the manifold and potentially trapped something.
So my question is, if I remove the carbs (which looks quite easy) am I going to have issues and need them rebalancing etc? Or should I just loosen off what I tightened before I had issues?
I’d like to take them off if only to look at them and check for issues but if it’s going to cause me problems I won’t. It’s just that to get to the point of getting to these bolts I tightened is a lot of removal of other stuff so I’d rather only have to do it once lol
Or would it be simpler to take the manifold off with the carbs still attached?
So my question is, if I remove the carbs (which looks quite easy) am I going to have issues and need them rebalancing etc? Or should I just loosen off what I tightened before I had issues?
I’d like to take them off if only to look at them and check for issues but if it’s going to cause me problems I won’t. It’s just that to get to the point of getting to these bolts I tightened is a lot of removal of other stuff so I’d rather only have to do it once lol
Or would it be simpler to take the manifold off with the carbs still attached?
Edited by audi321 on Saturday 27th May 12:09
Well I took the carbs off the manifold and then took the manifold off the head.
Can someone tell me should these ports be full of fuel? (Well some are!). If they shouldn’t, what should I do? Let it evaporate or try and soak it up somehow?
I’m probably in over my depth of knowledge already. So please PH, come to my rescue!
Can someone tell me should these ports be full of fuel? (Well some are!). If they shouldn’t, what should I do? Let it evaporate or try and soak it up somehow?
I’m probably in over my depth of knowledge already. So please PH, come to my rescue!
No the ports shouldn’t be full of fuel
It will be either too much fuel pressure causing the float needle to allow a higher level (but if it’s in an oe set up thats less likely)
Or
Float needle tips and or seats are worn - try to buy some viton tipped ones as they seal much better against worn float needle seats
It will be either too much fuel pressure causing the float needle to allow a higher level (but if it’s in an oe set up thats less likely)
Or
Float needle tips and or seats are worn - try to buy some viton tipped ones as they seal much better against worn float needle seats
Have you been pumping the throttle prior to starting? Every time you press the pedal there's a squirt of fuel.
Have you asked on https://lotusexcel.net/
A source of info on everything Excel and 900/912 engines.
Have you asked on https://lotusexcel.net/
A source of info on everything Excel and 900/912 engines.
The purpose of a carburettor is to atomise the liquid petrol coming from the fuel tank and add the aerosol to the airstream being sucked in by the pistons. To get that amount of petrol accumulating in the intake port would suggest that you do indeed have a “fuel issue”, or more precisely a carburettor issue.
It’s only in ports 1,2,3&4 so I think the rear carb was stuck (due to me over tightening the nuts holding it onto the manifold so I possibly trapped the butterfly valves open?
Not quite sure. But either way I’ve soaked up all the fuel from the ports and I’ll leave it overnight to evaporate fully (ports 5,6,7,8 were bone dry).
It’s a lotus 910 engine, with twin delorto 45s. I don’t really want to go messing with the carbs as you’ve probably guessed I’m just a DIYer lol.
Not quite sure. But either way I’ve soaked up all the fuel from the ports and I’ll leave it overnight to evaporate fully (ports 5,6,7,8 were bone dry).
It’s a lotus 910 engine, with twin delorto 45s. I don’t really want to go messing with the carbs as you’ve probably guessed I’m just a DIYer lol.
audi321 said:
It’s a lotus 910 engine, with twin delorto 45s. I don’t really want to go messing with the carbs as you’ve probably guessed I’m just a DIYer lol.
As you may have spotted, the carbs are right above the distributor. Any hint of a fuel leak and it's suddenly bonfire night. Be careful.Starting these cheeky fellows is/was always more art than science. Nonetheless, the science was that they need a couple of stabs on the throttle from a cold start (where the accelerator pump on the carb acts as a choke to enrich the mixture) whereas from a hot start they need no throttle at all. If anything, a difficult hot start needs a s-l-o-w press of throttle to the floor followed by "crank until fires".
Truth is, it's a completely different world from modern, fuel injected engines. They were built to rev and don't welcome the inconvenient concept of being started, either cold or hot.
audi321 said:
It’s only in ports 1,2,3&4 so I think the rear carb was stuck (due to me over tightening the nuts holding it onto the manifold so I possibly trapped the butterfly valves open?
That seems unlikely to me. I have Dellortos on my Firenza, and they're tightened down hard onto the manifold because it's the only way I could seal the joint properly last time I was messing with it. Tightening them wouldn't trap the butterfly valves open - the difference is only fractions of a millimetre. If it was going to do anything it would be to trap them closed by pushing them against the manifold, but only if the manifold ports are smaller than the ports on the back of the carb body, and even then the butterfly is a little inboard of the back flange so there would still be some movement.Edited by droopsnoot on Sunday 28th May 18:56
When these first came out they would empty the fuel tank into the engine through the carbs if parked on a downhill slope!
An electrical shut off valve was fitted in the fuel line under the car, being Lotus this of course would sometimes fail and the car would stop after a few yards, usually in the most dangerous and embarrassing position.
I wonder if this device has been removed from the OPs vehicle?
An electrical shut off valve was fitted in the fuel line under the car, being Lotus this of course would sometimes fail and the car would stop after a few yards, usually in the most dangerous and embarrassing position.
I wonder if this device has been removed from the OPs vehicle?
Well the initial problem was that it wouldn’t start due to no spark. But then I discovered that the plenum and intake was full of petrol. The coil has positive to both sides so I assumed there was some kind of safety switch which would short the coil to prevent it sparking if there was an excess of petrol (although I’ve found no such sensor).
It’s all back together now and I’m about to try and start it. Fingers crossed I don’t go up in smoke!
It’s all back together now and I’m about to try and start it. Fingers crossed I don’t go up in smoke!
Dellortos annd Webers are very sensitive to fuel pressure, anything more than 3-4 PSI can cause them to flood as can a holed float or dodgy float valve. If you dont already have a fuel pressure regulator consider fitting one and setting to 3-4PSI.
Definitely examine the needle valves on the floats and the floats themselves. When the carbs are mounted they should not be overtightened , you should be able to move them a little on the Misab gasket mounts, this helps them cope with vibration which can also disturb the float valves.
Dave
Definitely examine the needle valves on the floats and the floats themselves. When the carbs are mounted they should not be overtightened , you should be able to move them a little on the Misab gasket mounts, this helps them cope with vibration which can also disturb the float valves.
Dave
DVandrews said:
Dellortos annd Webers are very sensitive to fuel pressure, anything more than 3-4 PSI can cause them to flood as can a holed float or dodgy float valve. If you dont already have a fuel pressure regulator consider fitting one and setting to 3-4PSI.
Definitely examine the needle valves on the floats and the floats themselves. When the carbs are mounted they should not be overtightened , you should be able to move them a little on the Misab gasket mounts, this helps them cope with vibration which can also disturb the float valves.
Dave
I mentioned the float needles earlier - I don't know if the car is new to the OP or just being brought back to life after a period of no use but fuel gets old and stale and tends to get very gummy and carbs don't like thatDefinitely examine the needle valves on the floats and the floats themselves. When the carbs are mounted they should not be overtightened , you should be able to move them a little on the Misab gasket mounts, this helps them cope with vibration which can also disturb the float valves.
Dave
OP needs to get a decent book on the carbs and check them properly (below is a clickable link - hopefully)
Thank you guys, yes the car is new to me, and yes it's been sat for a while so I think a full carb service (x2) is in need.
I'm no mechanic, but I'm handy and can follow instructions. The carbs say DHLA 45 on the top, so can I assume that any service kit for them will be ok? Is it a job which is DIY'able? Carbs rebuilds scare me, but given time and a good youtube search, I can pretty much turn my hand to most things.
Or shall I find a specialist lol.......
I'm no mechanic, but I'm handy and can follow instructions. The carbs say DHLA 45 on the top, so can I assume that any service kit for them will be ok? Is it a job which is DIY'able? Carbs rebuilds scare me, but given time and a good youtube search, I can pretty much turn my hand to most things.
Or shall I find a specialist lol.......
So near yet so far! I’m close to Skegness so a fair distance away,
I used a Lotus daily as my only car for four years in the 1980s and have probably suffered and repaired every one of the many issues these cars suffer, including replacing a rotten chassis and a complete engine rebuild.
You are welcome to PM me for advice if you wish as I think you might be needing a fair amount of help.
I used a Lotus daily as my only car for four years in the 1980s and have probably suffered and repaired every one of the many issues these cars suffer, including replacing a rotten chassis and a complete engine rebuild.
You are welcome to PM me for advice if you wish as I think you might be needing a fair amount of help.
Hi again all.
So I've removed the carbs, fixed the fuel leak which I think was caused by a mixture of too much pumping the pedal and leaking o rings from the spacer plate between the carbs and inlet manifold. I now have no leaks that I can see. Success and I was really pleased with myself!
However, I think I've maybe created myself a brand new problem as the car won't start whatsoever (just turns over). I have spark and compression, and the plugs are wet so fuel must be getting in there.
Whilst they were off I serviced the carbs basically by meticulously following this video https://www.youtube.com/watch?v=G0jjqcGpTz8
However, since not being able to start it, I have since taken off the carbs and tried to follow the 'setup' video he does here https://www.youtube.com/watch?v=eKEqqimaF3M&t=...
At 34 seconds into the video, he opens the throttle with his hand and fuel squirts forward past the butterflies. When I do that, fuel squirts straight downwards (not forwards) into the venturi and kind of trickles out and presumably down the inlet manifold.
Is that not normal? What is the expected behaviour of a carb when opening the throttle? The carbs on the video are almost identical but not the exact same, and because I didn't do this before I took them apart to service them, I don't know what mine did before.
So........should the fuel squirt forwards and out, or downwards and trickle? If trickling into the inlet manifold, would that potentially cause it not to start?
Thanks for any help guys, I'm at my wits end with the bloody thing right now!
So I've removed the carbs, fixed the fuel leak which I think was caused by a mixture of too much pumping the pedal and leaking o rings from the spacer plate between the carbs and inlet manifold. I now have no leaks that I can see. Success and I was really pleased with myself!
However, I think I've maybe created myself a brand new problem as the car won't start whatsoever (just turns over). I have spark and compression, and the plugs are wet so fuel must be getting in there.
Whilst they were off I serviced the carbs basically by meticulously following this video https://www.youtube.com/watch?v=G0jjqcGpTz8
However, since not being able to start it, I have since taken off the carbs and tried to follow the 'setup' video he does here https://www.youtube.com/watch?v=eKEqqimaF3M&t=...
At 34 seconds into the video, he opens the throttle with his hand and fuel squirts forward past the butterflies. When I do that, fuel squirts straight downwards (not forwards) into the venturi and kind of trickles out and presumably down the inlet manifold.
Is that not normal? What is the expected behaviour of a carb when opening the throttle? The carbs on the video are almost identical but not the exact same, and because I didn't do this before I took them apart to service them, I don't know what mine did before.
So........should the fuel squirt forwards and out, or downwards and trickle? If trickling into the inlet manifold, would that potentially cause it not to start?
Thanks for any help guys, I'm at my wits end with the bloody thing right now!
To think, there are still people who think carbs are better than fuel injection.
I deal with motorcycles for a living, and find anything carbureted now is in trouble due to the ethanol fuel. Motorcycles are worse than cars because the passages are so small,
For myself, If I did still want to have something originally with carbs, i'd be removing the ethanol from the fuel, or more likely converting to EFI
I deal with motorcycles for a living, and find anything carbureted now is in trouble due to the ethanol fuel. Motorcycles are worse than cars because the passages are so small,
For myself, If I did still want to have something originally with carbs, i'd be removing the ethanol from the fuel, or more likely converting to EFI
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