Lotus Elan

Webers leaking at O ring mounts

PostPost by: europatek » Wed Jan 01, 2014 8:20 am

Ok, calling all Weber experts. I've looked through my Weber tuning books and the archives here but cannot find anything conclusive for the problem I have. Recently purchased and rebuilt a pair of 40DCOE27. OE fitment on Alfa's. The carbs look great and I used Webcon service kits. Installed and running great, however after running the front carb starts dripping fuel at the mounting to the head, past the O rings. I've removed the carb twice and checked/replaced everything I can think of and all looks good. I can leave the car sitting with the carbs full and no leaks. Idling and cracking the throttle and no leaks. It seems to only occur after I've been for a drive and after shut off and a few minutes standing it starts to leak - not dripping but quite wet.
So, anyone with any good ideas?
User avatar
europatek
Second Gear
Second Gear
 
Posts: 139
Joined: 26 Mar 2008
Location: Melbourne, Australia

PostPost by: UAB807F » Wed Jan 01, 2014 10:06 am

In the "keep it simple" vein, did you get new O-rings in the kit, and would they stand tightening up a touch ?

As a wild guess, could it be heat soak warming & expanding the static fuel in the bowls and forcing it's way through the jets ? With fuel flow you wouldn't see the same effect, it would only be after you shut off.

My initial thoughts were either excess fuel pressure/shut off valve not seating or float height too high, but I guess if the float height were marginal then the theory might just work ?

Brian
User avatar
UAB807F
Fourth Gear
Fourth Gear
 
Posts: 649
Joined: 20 Dec 2010
Location: Lincolnshire

PostPost by: richardcox_lotus » Wed Jan 01, 2014 10:19 am

A friend of mine has exactly the same issue with his dcoe40's.

Can't work out where the fuel is coming from. Car runs fine. No leaks immediately obvious on running or initial shutdown. 30 minutes later there's a drop.
Richard
'72 Sprint
richardcox_lotus
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1192
Joined: 11 Jul 2004
Location: Kent

PostPost by: types26/36 » Wed Jan 01, 2014 10:45 am

Just a suggestion, could it be dripping from the accelerator pump jet? When an engine has been run hot and then switched off, for the first ten minutes or so the temperature rises as there is no airflow and the water pump is not circulating the coolant.
The fuel can start to "froth" or flood causing a drip although this is more common in an engine with a downdraft carb due to heat rising.
I would suggest you run the engine hot, remove the air box and shine a light into the throat possibly using a mirror to see if the pump jet is dripping.
If it is then check your float level and and set to lower setting, also check and replace the seals on the pump jets.
Brian
64 S2 Roadster
72 Sprint FHC
User avatar
types26/36
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 3655
Joined: 11 Sep 2003
Location: U.K.

PostPost by: europatek » Wed Jan 01, 2014 12:35 pm

Thanks for your thoughts thus far. The float levels have been set as per the spec of 15 and 8mm. The pump jets have new washers under them as supplied in the kits and new O rings used for mounting. No fuel at all running out the throats. I'm puzzled as I've rebuilt and installed several pairs of DCOE's and never had this problem.
I think I'll run the car again and them look down the throats to see if I can see anything. But even if fuel is leaking past the pump jets I'm not sure how I could stop it happening as everything appears to be as it should.
Anyone else with ideas?
User avatar
europatek
Second Gear
Second Gear
 
Posts: 139
Joined: 26 Mar 2008
Location: Melbourne, Australia

PostPost by: Chancer » Wed Jan 01, 2014 5:16 pm

They al do that sir! :lol:

I think its actually a siphoning action from the main jets; the orifice is set just slightly higher than the float level (assuming the floats are correctly set) add a bit of heat soak when parking, perhaps an incline as well.

I used to find there was always one or more barrels that leaked fuel, stripping checking and and rebuilding yielded no clues.
Chancer
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1391
Joined: 20 Mar 2012
Location: Northern France/ Sussex UK

PostPost by: prezoom » Wed Jan 01, 2014 6:26 pm

I have found that fuel can leak from the auxiliary venturi. The DCOE 40 uses a "P" style spring clip to hold the venturi against the body of the carb. These "P" clips are extremely weak and do not offer enough tension to hold the venturi tight enough to prevent fuel from escaping at the transfer port from the emulsion tube well to the venturi. DCOE 40's lack the grub screw of the 45's, therefore additional pressure on the venturi cannot be exerted by tightening the grub screw. Flat music wire can be used to fabricate a new, stronger "P"clip, or by cutting a coil from the appropriately sized coil spring that has stiffer wire than the existing clip. A cut section from a Viton O ring, or a strip cut from flat stock, can be used in the slot in the carb body to prevent fuel from migrating back up into the air box. Since making a stronger "P" clip, and adding the strip of Viton to the slot in the carb body, I no longer have any fuel escaping from the carbs. If you can easily remove the auxiliary venturi from the carb body, then the spring is too weak.

Rob Walker
26-4889
Rob Walker
26-4889
50-0315N
1964 Sabra GT
1964 Elva Mk4T Coupe (awaiting restoration)
1965 Ford Falcon Ranchero, 302,AOD,9",rack and pinion,disc,etc,etc,etc
1954 Nash Healey LeMans Coupe

Owning a Lotus will get you off the couch
prezoom
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1270
Joined: 16 Mar 2009
Location: Escondido, California

PostPost by: Esprit2 » Wed Jan 01, 2014 7:45 pm

The soft mount O-rings are not the problem. There's normally no wet supply of fuel at the soft mounts that the O-rings are failing to seal. The source of the fuel leak is upstream, in the carb body somewhere. After the fuel leaks out, it runs downhill to the first opportune exit from the inlet runner... the soft mount. Focus on fixing the leak source, not the soft mount.

A fuel leak after shut down will usually have something to do with a high fuel level, often as a result of fuel continuing to enter the carb's float bowl. The source motivation would be residual fuel pressure in the pump/ delivery plumbing. Eventually, residual pressure will leak down and the leak stops after a few drops. However, short term, heat soak in a hot engine bay could result in the pressure actually building up immediately after shut down, before leak down catches up.

What's the fuel pressure, measured at the carb inlet? The DCOE likes 1.5 to 2.5 psi 'at the inlet'. If there's a difference between the mounting height of the fuel pump verses the height of the carb inlet, it's likely that the pump pressure will be higher than the inlet pressure. The fuel pressure at the carb inlet is what's important. Inlet pressure higher than 1.5 - 2.5 psi can aggravate leak problems with other components, like marginal inlet shut-off valves. And excessive line pressure just makes any residual pressure/ heat soak expansion issue worse to begin with.

Ideally, the carb's inlet valve should be able to hold any incoming fuel in check once the correct fuel level is reached in the float bowl. However, and old, worn valve may not be providing an effective seal. A leaky inlet valve can result in the fuel level rising in the float bowl after shutdown to the point that fuel spills over into the throat.

Check the float weight, and double check the float height. If a heavier than spec float has been substituted during a rebuild, or if a float has a pin hole leak and has taken on fuel, it will be too heavy and ride low in the fuel pool. The result will be an inlet valve that doesn't shut off at the correct point, and a fuel level that is too high.

The correct fix is a new float. A temporary, get it home fix would be to set the float height lower. Like 9 or 10 mm instead of the 8mm spec.

If a new Viton rubber tipped valve needle has been installed, the float height/ fuel level needs to be checked and re-set shortly after putting the carbs into service... within a couple of days. The Viton will take an initial compression set due to the pressure of being forced against the valve seat. As a result, the float height may drift toward too high (too small of a value, like 7 instead of 8mm), resulting in a fuel level that is too high. Possibly even spilling over into the throats.

The fuel 'level' is what's important, and the float height setting is just a conveninet, indirect way to get there. It works sorta okay when all else is in spec, but can't detect or adjust for something else being wrong. It's more correct to measure the actual fuel level, and adjust the float level as required to achieve the correct value. In other words, the 8mm float height is not gospel, but the fuel level is.

Run the engine (or just the electric fuel pump, if so equipped) long enough to ensure the float bowls are full and the inlet valve is seated closed. Switch off. Remove the jet cover (small round cover with thumb wings similar to a wing nut). Remove one idle jet assembly. Then use the depth gauge function of a dial caliper to measure from the top of the jet pedastal down to the fuel level. It should be 25mm. Then carefully measure the current float height, and adjust adjust the height as required to achieve the correct fuel level. For instance, if the fuel level is 1mm high at 26mm, then lower the float height by 1mm... ie, higher number value = lower... like 9mm instead of the spec 8mm.

Fuel can leak into the throats through several paths, but usually through the idle progression holes and idle mixture screw. It can also leak past a loose fitting auxiliary venturi, between the choke and throat, or out the bowl vent into the airbox. But those items won't leak unless full has spilled out of the float bowl and flowed to them. The root cause leak is usually some variation of a high fuel level in the float bowl. Perhaps due to an incorrect float setting or a heavy float. Perhaps due to an inlet valve not sealing, or high fuel pressure at the inlet. Fix the root cause first. If in the course of your investigation, you find some other loose component, fix that too. But don't stop there... jet to the root cause of fuel spilling out of the float bowl.

1) Fuel pressure (higher than 1.5 - 2.5 psi... install inline fuel pressure regulator)
2) Fuel shut off (inlet valve not sealing effectively)
3) Fuel level (should be 25mm down from jet pedestal top)
... Float weight (too heavy?... replace)
... Float height (8mm spec, but not gospel, adjust as required to achieve 25mm)
... Viton inlet valve (check & reset fuel level 1-2 days after install)

The fact that you report only one carb leaking suggests to me that the fuel pressure may not be the issue. One carb seems to be handling it just fine, but one is leaking. Still check the pressure... I'm just sayin'...

I'd start by measuring fuel level...
1) cold, prior to starting the engine. Adjust the float level as required to achieve a correct fuel level 25mm down from the top of the jet pedestal.
2) immediately after hot shut down, and
3) again when wetness shows at the soft mount.
No carb removal or disassembly is required, so this is the easy first step. It's also very telling.

If the fuel level was correct when set cold, but is high after a hot shutdown, then check for high residual fuel pressure and/or a leaking inlet valve. If the inlet valve(s) are new Viton rubber tipped needles, then definitely check and re-set float heights/ fuel levels 1 or 2 days after the new needles are put into service.

Regards,
Tim Engel
Lotus Owners Oftha North (LOON)
Esprit2
Third Gear
Third Gear
 
Posts: 389
Joined: 02 Apr 2008
Location: Twin Cities, Minnesota, USA

PostPost by: fatboyoz » Thu Jan 02, 2014 2:51 am

Hi and Happy New Year,
I had a similar problem that eventually started leaving a puddle of fuel under the engine. It used to manifest itself a few minutes after shutting down the engine after having driven the car.
The following is what was suggested to me. I followed this procedure which cured the leak.
Regards,
Colin.


Throttle lever housing cover plate dribbles:

? The throttle lever housing cover plate is between the two barrels and is fixed with two countersunk screws. (Figure 1 ? item 80)
a) Remove the screws and plate. A full sealing gasket should be in place. Remove it and check if the chamber is wet with fuel or shows signs of this.
b) Fuel can enter the chamber via the pump rod hole or the return spring hole. Yes I realise this should not be the case BUT do you have ANY clearance in the butterfly shaft bearing on either side of the chamber. Of course you do even if it?s only small.
c) When you are pulling 5000 to 6000 + rpm and lift off the throttle you can appreciate many inches of vacuum generated must suck from anywhere it can. Herein lies our problem. Fuel is sloshing around in our float bowl through corners and clearances around pump rod and throttle return spring hole are considerable. The vacuum pulls fuel into the chamber but there it just builds up to gradually dribble over our distributor or hot exhaust as the case may be.

Solution to throttle lever housing cover plate dribbles -

Drill a 1.5 mm ?breather hole? in the cover plate and match drill the gasket. The hole should be level with the top screw and half way to the edge to miss the housing cast edges.
The small hole stops the effect of the vacuum but also keeps the dirt out of the throttle lever chamber. Screw the plate back on for dry, dribble free motoring.

This really is an incredibly simple fix for a rather obscure problem. It took a lot of reasoning and close inspection to analyse what was actually happening but investigation is part of the problem solving. It was only after I fixed the problem that a carburetor repair person suggested that this was probably why Weber modified some plates in the 80?s with a 8 ? 10 mm hole in the middle. Unfortunately Messers Weber don?t tell everyone why they did this modification.

NOTE: Obviously all of these fuel checks are better if carried out shortly after a run so wet fuel can be seen when the carburetors are removed.



europatek wrote:Ok, calling all Weber experts. I've looked through my Weber tuning books and the archives here but cannot find anything conclusive for the problem I have. Recently purchased and rebuilt a pair of 40DCOE27. OE fitment on Alfa's. The carbs look great and I used Webcon service kits. Installed and running great, however after running the front carb starts dripping fuel at the mounting to the head, past the O rings. I've removed the carb twice and checked/replaced everything I can think of and all looks good. I can leave the car sitting with the carbs full and no leaks. Idling and cracking the throttle and no leaks. It seems to only occur after I've been for a drive and after shut off and a few minutes standing it starts to leak - not dripping but quite wet.
So, anyone with any good ideas?
'68 S4 DHC
fatboyoz
Fourth Gear
Fourth Gear
 
Posts: 621
Joined: 04 Oct 2003
Location: Gold Coast QLD Australia

PostPost by: types26/36 » Thu Jan 02, 2014 7:30 am

[quote="fatboyoz"]
The following is what was suggested to me. I followed this procedure which cured the leak.
Regards,
Colin.


That's interesting, always wondered why some carbs had the hole and some not, it is mentioned in this thread:
lotus-carbs-f40/weber-hole-return-spring-plate-t24632.html
Brian
64 S2 Roadster
72 Sprint FHC
User avatar
types26/36
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 3655
Joined: 11 Sep 2003
Location: U.K.

PostPost by: miked » Thu Jan 02, 2014 8:50 pm

Well that is interesting, that had bugged me for some while wondering what that hole was all about. :D
I have two sets of 151's on the cars and will be having a look as I can't recall now whether they have the holes.

Mike :D
Mike

Elan S4 Zetec
BSA B33
Suzuki Hustler T250
BMW rninet scrambler
Suzuki TC120R trailcat
Suzuki TC120 trailcat
Suzuki K11 super sport
User avatar
miked
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1198
Joined: 29 Sep 2003
Location: Northwest UK

PostPost by: europatek » Mon Jan 06, 2014 11:01 am

Solved the leak today. Finally timed it to see the leak start and it was from the cover plate on the back not the o-rings as it appeared. So once removed I ran the car and found the leak had ceased to occur so added 5mm holes in the centre of the plates (that match the holes in the gaskets provided) and now all is good. It's a strange one and one I've never seen on many sets of Webers I have had. A first time for everything I guess. My theory is wear on the pump plunger allowing the fuel past the plunger and thus into the chamber below.
Thanks to all those who replied with suggestions and info.
User avatar
europatek
Second Gear
Second Gear
 
Posts: 139
Joined: 26 Mar 2008
Location: Melbourne, Australia

PostPost by: elanner » Fri Jan 01, 2016 5:06 pm

I have been intermittently futzing with my Webers to make them as leak proof as possible (with some PM help from Tim) and they are now pretty good. I still get occasional wetness under the Misab plates and my current theory is that fuel is leaking out of the starter circuit air intake, but this is not yet proven.

Anyway, while searching around in the forum I stumbled across: http://www.lotuselan.net/wiki/Dual_Weber_Tune-up

In this article is the following interesting section:

------
Check the FLOAT LEVEL.
- Remove some fuel from the carbs and let the engine idle for two minutes. Remove the wingnut caps.
- Use the depth gauge end of vernier caliper to measure from the top of the lower shelf to the top of the fuel surface. DCOE spec = 1.14 inch (29mm+4.5mm). If the depth is NOT correct, the top plate of the carburetor must be removed. Carefully bend the tab on the float assembly that touches the needle valve. Reassemble and test the float level as before.
-------

What the heck is "29mm + 4.5mm" trying to say (aside from the obvious 33.5)? This is totally different from the 25mm generally suggested. The note neglects to mention that you need to remove a jet in order to do any measurement, and "Remove some fuel from the carbs" seems bogus too.

Nick
User avatar
elanner
Fourth Gear
Fourth Gear
 
Posts: 532
Joined: 14 Sep 2010
Location: Boston, MA, USA

PostPost by: mbell » Fri Jan 01, 2016 6:59 pm

The removing fuel is fine, you want to make sure the carbs refill to break level and haven't assume how gotten over filled. So letting the level and refill is ok.

I wouldn't use this method thou as for it to be accurate you need to take account fit the displacement of the floats. Which will be different based on type and fuel density.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
mbell
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1778
Joined: 07 Jun 2013
Location: Austin, TX (UK Ex-pat)

PostPost by: Esprit2 » Fri Jan 01, 2016 8:37 pm

elanner wrote:What the heck is "29mm + 4.5mm" trying to say (aside from the obvious 33.5)? This is totally different from the 25mm generally suggested. The note neglects to mention that you need to remove a jet in order to do any measurement, and "Remove some fuel from the carbs" seems bogus too.
Nick,
The correct fuel level for a DCOE is either
29mm +/- 0.5 mm (1.142 +/- .02 in.) with the top cover OFF, or...
27mm +/- 0.5 mm (1.063 +/- .02 in.) with the top cover ON
...... (+ or -)

Remove the top cover, then notice that the top of the carb body, and the top of the jet pedestal in the middle of the float bowl were both machined in one pass to one flat plane. The fuel level is measured from that plane down to the surface of the liquid pool.

If the carb is mounted at anything other than dead level (most are at some angle), then the fuel level measurement will vary with where around the bowl you take the measurement. Therefore, the measuring point is standardized as close to the center as possible. The Jet pedestal is in the center, mostly blocking that measuring point. But in top-view, the pedestal is not straight-sided, and one side dips inward between the jets. So either measure in the center of that dip, or remove one main jet assembly and measure down in the empty bore.

The engine will start and run on the idle jets, so having one main jet assembly removed will not prevent the engine from running.

Scooping out some fuel first lowers the fuel level, ensuring that it wasn't artificially too high for any reason. Then, with the top cover in place, running the electric fuel pump, or running the engine to operate the mechanical fuel pump, let the fuel level rise until the float turns off the fuel inlet valve. That procedure ensures the fuel level is now correct for measuring.

Remove the small round jet cover from the top of the large top cover, and use the depth gage feature of a caliper to measure down from the top of the jet pedestal, through the empty jet bore, do the surface of the fluid pool. With the top cover in place, and the floats in the fuel pool, the correct level will be 27mm +/- 0.5 mm (1.063 +/- .02 in.) down with the top cover ON.

If for any reason you cannot make a measurement through the small round jet cover opening, then remove the carb's top cover for better access. However, note that as the cover is lifted off, the floats will droop, the inlet valve will open, and any residual pressure in the fuel line will squirt some additional fuel into the bowl, giving a bogus measurement. So before removing the top cover, first disconnect the fuel line, venting any residual pressure and draining the inlet port.

When the top cover is removed, the floats will be withdrawn from the fuel pool, and the level will drop accordingly. So fuel level is now further down with the top cover (and floats) off, and the measurement is 29mm +/- 0.5 mm (1.142 +/- .02 in.).

Bend the tabs on the float assembly as required to raise or lower the fuel to the correct 27mm with cover ON, or 29mm with cover off.

The cover-OFF dimension is correct for the old style round, brass floats that were used in Lotus TC applications. The later plastic floats will require a different dimension for when the top cover (and floats) is removed. The 27mm cover-ON dimension is the same for both types of floats.

*~*~*
The stock Weber Inlet valve pin is all brass with a solid metal point. Some aftermarket valve pins have a rubber tip The rubber will take a compression-set after a few days, allowing the pin to seat a little deeper, the float to rise, and the fuel level to become too high.

If you use an all metal inlet valve pin, you can set the fuel level and forget it.

If you use a rubber-tipped pin, then go back in and re-set the fuel level after a few days.

Regards,
Tim Engel
Esprit2
Third Gear
Third Gear
 
Posts: 389
Joined: 02 Apr 2008
Location: Twin Cities, Minnesota, USA
Next

Total Online:

Users browsing this forum: No registered users and 7 guests