Lotus Elan

S4 No Fuel

PostPost by: nmauduit » Fri May 06, 2022 8:11 am

just to be sure, is the fuel pump operating properly (e.g. when taken off the carbs into a jar and cranking, does it spurt fuel with a bit of pressure)?
S4SE 36/8198
User avatar
nmauduit
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1974
Joined: 02 Sep 2013
Location: France

PostPost by: SENC » Fri May 06, 2022 12:41 pm

Agree with both 2 posts above - recheck fuel pump functionality by pumping into a jar and look for air leaks (when running on starter fluid, can you keep it running by spraying a bit near that joint or other areas of air leak?).

Rereading the thread from the beginning again, I noted your comment about making sure the pistons dropped "slow and steady". They should drop with enough pace to be audible when they hit bottom. Gravity should do that alone with engine off, but the springs for the pistons help them react more quickly to overcome impact of the diaphragm on accel lift. Perhaps the carb itself is an airleak, if the pistons are opened too much or too quickly and not creating enough airflow to pull the fuel?

After fuel pump and air leak checks, you're back to fuel flow within the carbs. Knowing how fiddly it is to remove and reinstall these carbs, I'd first pull the tops and pistons, reinspect the needle orientation in the pistons to confirm they are seated and offset correctly and to see if you see any signs of wear from rubbing inside the jets. With a good light, I'd then reinsert the jets by looking down through the top of the carbs - looking for excessive/unusual wear in the orifices but also for any sign/indication of blockage or buildup within. Maybe remove a needle from a piston and holding it in your fingers slide it up and down within the jets to see if you feel any resistance?

Assuming that all checks out, my next thought would be that possibly the fuel level in the bowl is lower than the bottom of the jet. Perhaps run the pump to fill them, remove the front carb and try to remove the bowl while keeping the carb upright to get a fuel level check? I can't remember how feasible that is, if it all, but if that is possible you can the measure the bottom of the jet and calculate whether it would be in the fuel.
Henry
69 Elan S4
65 Seven S2
SENC
Fourth Gear
Fourth Gear
 
Posts: 977
Joined: 30 Dec 2015
Location: NC

PostPost by: m750rider » Fri May 06, 2022 8:36 pm

look at your fuel pump and make sure you see fuel in the glass bowl. if not you might need to prime the pump
m750rider
Second Gear
Second Gear
 
Posts: 160
Joined: 10 Jan 2010
Location: Asheville area, NC

PostPost by: Temmck » Sat May 07, 2022 2:54 am

Yes, I am missing a nut however, that tube goes to the exhaust manifold and when the engine is not running that manifold is essentially at ambient thus the tubes themselves are a massive air leak. I doubt the missing nut is preventing zero ignition.

I disassembled the carburetors again and didn't find anything out of the ordinary except all of the oil I put in one dashpot leaked out but, that is the topic of another thread.

I thought I was on to something with the large brass screw on the bottom of the float bowl. I had it screwed all the way in and thought that may be choking off fuel from being drawn into the carb throat. I back off the screw a full turn on both carbs but it had no effect.

I have rebuilt Weber's and Delorto's with no issues. These Stromberg's have to be the simplest carburetors I have ever worked on. It has to be something simple.
Temmck
First Gear
First Gear
 
Posts: 37
Joined: 23 Aug 2012

PostPost by: Temmck » Sat May 07, 2022 3:51 pm

Senc,
I'll try to respond to all of your points;
I have rechecked the fuel pump and it is pumping fuel. I have a clear fuel filter between the pump and the carb and can see that it is full of fuel. i also removed the carb and carefully drained the fuel into a container. Removed the bowl from the carb, reinserted the large brass screw and poured the fuel back into the bowl. The level is clearly above the jet pick up and is about right for "full".

When I removed the carbs from the car, I got a bit of spray when removing the fuel line from the carb so there appears to be some pressure build up in the line when the float needle valves are closed.

Pistons fall with a notable thud but slowly enough to show air resistance. Looked like all the videos I found on line.

I would like to look closer at the jet needle itself but I have not been able to remove it from the piston. How does it come out? I can remove the setscrew and I tried pushing and pulling the needle but I don't know which way it comes out so I have not tried to force it. There is some spring force when I pull on it and it has plenty of play, not rigid, when at rest. So it all looks about right. But I would like to remove it to inspect, clean and check for fit in the jet.

When rebuilding the carbs I ran a clean out brush through all of the passages so I know they are not blocked. I did double check the jet passage again last night when I took them off again, inspecting from the top and all is clear.

I will try to identify any air leaks while running on starter fluid/fuel.

If this were a worn needle or clogged port, I could understand one carb running differently then the other but for neither carb to draw fuel at all seems to point to something more fundamental. I think the carbs are fine. I don't think I'm getting enough vacuum to pull the fuel.

Next Steps:
- Retrace the air flow path from the manifold and make sure all passages are clear.
- Make sure the float bowl vents are clear.
- Make sure that by bypass valves are closed (I did disassemble these).
- Make sure temperature compensating valve is closed. I reset these to open from 40-60 deg.C
Temmck
First Gear
First Gear
 
Posts: 37
Joined: 23 Aug 2012

PostPost by: Donels » Sat May 07, 2022 4:17 pm

It sounds like a fuel pump diaphragm failure. Split small enough for suction to fill the bowl but not enough to fill the carbs.
Elan +2
Elise mk 1
Donels
Third Gear
Third Gear
 
Posts: 498
Joined: 10 Sep 2016
Location: Tamworth

PostPost by: SENC » Sat May 07, 2022 6:00 pm

There are 2 types of pistons, as I recall (not with my spare now, can check them Monday). Look into the piston tube from the top - from recollection, you may see a star washer holding it in (friction fit) in which case I think you need to press the needle and washer up from the bottom. Or you may see a hex socket and then use an Allen wrench to unscrew it. The other piston type is sealed and you pull the needle out from the bottom. Again, this is my recollection, I may be remembering incorrectly.
Henry
69 Elan S4
65 Seven S2
SENC
Fourth Gear
Fourth Gear
 
Posts: 977
Joined: 30 Dec 2015
Location: NC

PostPost by: Temmck » Sat May 07, 2022 6:09 pm

Fuel pump diaphragm is new and the carb bowls are full of fuel.

These Strombergs are not the adjustable type. All documentation I have found on-line on how to remove the needles is for the adjustable type. I can't see a darn thing down that long dark tube. They are not sealed as all of the oil I put in one of the carbs drained into the air passage.
Temmck
First Gear
First Gear
 
Posts: 37
Joined: 23 Aug 2012

PostPost by: Temmck » Sat May 07, 2022 6:20 pm

Perhaps someone can educate me on this emission system. From what I can see, when cranking the car with no accelerator pressed, the secondary butterfly's are closed. The two crossover pipes are routed such that one pipe has its intake manifold opening on up-stream side of the secondary butterfly and the second is down-stream of the secondary butterfly. Thus all of the suction from the intake stroke of the cylinders, and corresponding vacuum on the down-stream side of the secondary buttery, is pulling air from the exhaust manifold. These secondary butterfly's are hard closed with nearly no gaps compared to the very large passage going to the exhaust manifold. I can't see where the carburetor is going to see much vacuum to pull fuel from the bowl.
Temmck
First Gear
First Gear
 
Posts: 37
Joined: 23 Aug 2012

PostPost by: oldelanman » Sat May 07, 2022 6:58 pm

Temmck wrote:These Strombergs are not the adjustable type. All documentation I have found on-line on how to remove the needles is for the adjustable type. I can't see a darn thing down that long dark tube. They are not sealed as all of the oil I put in one of the carbs drained into the air passage.


SENC is correct.
Fixed needles are mounted in a blind pocket in the bottom of the air valve and retained by a grub screw, there is no drilling between the top and bottom of the air valve for the damper oil to escape. Are you 100% sure you don't have adjustable needles - maybe a previous owner has changed to adjustables? Maybe try inserting a 1/8" (3mm) allan key and feeling for the adjuster screw.

Temmck wrote:Perhaps someone can educate me on this emission system.


At idle and low throttle openings the fuel/air mixture does not pass directly from the carburettor into the engine, it is diverted by the closed secondary throttle through the crossover pipe to a chamber in the exhaust manifold where it is heated and then returned via the second crossover pipe to the downstream side of the secondary throttle and thus to the engine. At higher throttle openings the linkage opens the secondary throttle and the mixture passes directly from carburettor into the engine.

This extract from the workshop manual may help.

scan_20220507_193725.jpg and


There's more info here....
http://obswww.unige.ch/~wildif/cars/doc ... tuning.pdf
Roger
S4 DHC
oldelanman
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1867
Joined: 02 Jan 2008
Location: Dorset UK

PostPost by: snowyelan » Sun May 08, 2022 12:19 am

It appears you have the, for lack of a better term, overrun valves. These are just downstream of the temperature compensator valves. Rebuid kits sometimes have 2 different gaskets. One has a peanut shaped opening and the other 2 separate holes. The peanut one will dump air past the butterfly, bypassing the overrun valve, and lowering vacuum at the fuel needle. I have no idea what carb version the peanut is for. My non emissions carbs require the 2 hole version as well.
Scott
45/9011
Hawkestone, On, Ca
snowyelan
Third Gear
Third Gear
 
Posts: 355
Joined: 14 Sep 2003
Location: Hawkestone, Ontario, Canada

PostPost by: Temmck » Sun May 08, 2022 2:27 am

Needle Valves: The top of the tube does not have notches for the tool to prevent rotation so i assumed they were not adjustable. I will check with an Allen wrench tomorrow.

Air Flow: Wow. the mixture goes from the carbs through the exhaust manifold then back to the intake! I'm not sure if I should be impressed or horrified. I can now see why any air leak in the crossover pipes could be a death blow for cold start. Maybe I'll just block these passages and remove the secondary butterfly's.

Bypass vales: Interesting comment. The gaskets that I removed were the peanut shaped ones that are open to both ports. So, I installed the same. When looking at the circuit more carefully I see that this peanut shaped gasket also has the internal vacuum passage blocked. There is a brass tube coming out of the housing that activates the valve under vacuum however on my car there are no hoses on these tubes, they are just left open to atmosphere. Are these tubes supposed to be attached to something? I re-checked my rebuild kit and see there are a number of gasket configurations for this bypass valve. Which is right for our cars?
Temmck
First Gear
First Gear
 
Posts: 37
Joined: 23 Aug 2012

PostPost by: Temmck » Sun May 08, 2022 3:01 am

Some improvement today. I got the engine started on staring fluid and sprayed around the flanges as the engine started to stumble. There was definitely an air leak on both carbs. I needed to tighten the carb/manifold nuts far past the spring washer recommendation (fully collapsed) in order to stop the air leak. It seems like it was running half on fuel and half on starter fluid. But, it was running!
Temmck
First Gear
First Gear
 
Posts: 37
Joined: 23 Aug 2012

PostPost by: oldelanman » Sun May 08, 2022 6:01 am

Temmck wrote: There was definitely an air leak on both carbs. I needed to tighten the carb/manifold nuts far past the spring washer recommendation (fully collapsed) in order to stop the air leak.


It shouldn't be necessary to overtighten those mounting nuts to get the joint to seal and doing so may distort the adapter plate and make the problem worse - perhaps that's been done in the past and is the cause of the leak now - worth checking if you have to remove the carbs again.
It's also important to use the correct sized O ring in that joint to achieve the 'flexible' mounting and to seal properly, it's not a standard size...I think it should be 47 x 3.5mm but maybe someone else can confirm that. It's also tricky to ensure the O ring stays in place in it's recess when you fit the carbs and it can get damaged as a result.
Roger
S4 DHC
oldelanman
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1867
Joined: 02 Jan 2008
Location: Dorset UK

PostPost by: Temmck » Mon May 09, 2022 2:18 am

I checked and tightened all flanges. No change.
I made and installed blanking plates for the crossover tubes and held the secondary butterflies open. No change.
I ran an electric fuel pump from a gas can directly to the carburetors. No change.
I replaced the coil as the car was not starting even on starter fluid. New coil had no overall effect - car starts on starter fluid but not from its own fuel.
Pistons are not adjustable. No hex head down the tube. But there is something that looks like a rivet.

There does not appear to be a smoking gun here. I'll go back and check everything; timing, points, plugs, HT leads, replace jets and needles, etc. How to remove the needles? Pull from the bottom? I assume the jets are a press fit from the bottom.
Temmck
First Gear
First Gear
 
Posts: 37
Joined: 23 Aug 2012
PreviousNext

Total Online:

Users browsing this forum: No registered users and 9 guests