Weber 40DCOE - Crossflow Engine (Lotus Seven)
16 posts
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Hi everyone,
I got my weber carbs rebuilt and having an issue with the idle. When I start the car, it revs up to over 3000rpm's, it runs smooth though, no back fire through the exhaust or the carbs.
Current jettings:
120 Main
150 Air
45 Idle
30mm Venturi
F15 Emulsion Tube
40 Pump Jet
My Lotus Seven S4 has been bored out. 1700cc crossflow kent engine 135HP-140HP. My father and I are lost, we have called Ray at RD, Ken at Dave Bean and everyone we know to try and help us. Have any of you experinced this with webers on the Twin Cam or other engines?
I got my weber carbs rebuilt and having an issue with the idle. When I start the car, it revs up to over 3000rpm's, it runs smooth though, no back fire through the exhaust or the carbs.
Current jettings:
120 Main
150 Air
45 Idle
30mm Venturi
F15 Emulsion Tube
40 Pump Jet
My Lotus Seven S4 has been bored out. 1700cc crossflow kent engine 135HP-140HP. My father and I are lost, we have called Ray at RD, Ken at Dave Bean and everyone we know to try and help us. Have any of you experinced this with webers on the Twin Cam or other engines?
74 Europa 3675R
70 Elan S4 0036K
72 Lotus Seven S4 LS4/2927
70 Elan S4 0036K
72 Lotus Seven S4 LS4/2927
- TheKid#99
- First Gear
- Posts: 24
- Joined: 12 May 2020
viewtopic.php?f=40&t=47507&start=15
https://240260280.com/Tech/Carbs/Weber/ ... uning.html
g search Keith Frank White Paper but its in the above link
https://240260280.com/Tech/Carbs/Weber/ ... uning.html
g search Keith Frank White Paper but its in the above link
Born, and brought home from the hospital (no seat belt (wtf)) in a baby!
Find out where the limits are, and start from there
Love your Mother
Earth
Find out where the limits are, and start from there
Love your Mother
Earth
-
h20hamelan - Coveted Fifth Gear
- Posts: 2060
- Joined: 25 Sep 2010
I tried the new metal mounts with the o ring and I tried my old plastic mounts. I'm using cup washers and cushions. Same result, 3000 rpm.
Their isn't any leaks as far as I know around the manifold. It may be the timing...? I'll check that tomorrow.
Their isn't any leaks as far as I know around the manifold. It may be the timing...? I'll check that tomorrow.
74 Europa 3675R
70 Elan S4 0036K
72 Lotus Seven S4 LS4/2927
70 Elan S4 0036K
72 Lotus Seven S4 LS4/2927
- TheKid#99
- First Gear
- Posts: 24
- Joined: 12 May 2020
TheKid#99 wrote:I tried the new metal mounts with the o ring and I tried my old plastic mounts. I'm using cup washers and cushions. Same result, 3000 rpm.
Their isn't any leaks as far as I know around the manifold. It may be the timing...? I'll check that tomorrow.
before messing with the timing (esp. if running correctly before) I would spend some time looking for leaks (e.g. using a spray can of starter fluid) or if both butterflies of each carb is actually closing fully and symetrically.
Last edited by nmauduit on Fri Nov 10, 2023 2:43 pm, edited 1 time in total.
S4SE 36/8198
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nmauduit - Coveted Fifth Gear
- Posts: 2074
- Joined: 02 Sep 2013
^^^^^ I agree. Are these carbs the 151 type? If so, make sure each throat's air bleed is fully seated.
Check this thread:
viewtopic.php?f=40&t=49536
Check this thread:
viewtopic.php?f=40&t=49536
Greg Z
45/0243K Sprint
45/7286 S3 SE DHC
45/0243K Sprint
45/7286 S3 SE DHC
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gjz30075 - Coveted Fifth Gear
- Posts: 3575
- Joined: 12 Sep 2003
First things first:
Set both carb butterflys to be open exactly the same amount as each other.
Balance throttle linkages so that the carbs match each other in terms of synchronised opening.
Check throttle stop screw - carb butterflys may be open more than needed causing high-speed running.
Check idle mixture screws.
Check ignition timing.
Set both carb butterflys to be open exactly the same amount as each other.
Balance throttle linkages so that the carbs match each other in terms of synchronised opening.
Check throttle stop screw - carb butterflys may be open more than needed causing high-speed running.
Check idle mixture screws.
Check ignition timing.
-
promotor - Fourth Gear
- Posts: 824
- Joined: 16 Mar 2012
As above, sounds like a balancing & throttle stop issue. One carb's butterflies are opening more than the others, ie two on one carb slightly open at idle. Even if you remove a pair of carbs, and i minute later put them back on without touching anything, they'll need rebalancing , due to re-tightening of the mounts, and not being able to get them exactly the same tightness as they were.
Current :- Elan S3 DHC SE S/S 1968,
1963 Alfa Giulia Ti Super Rep.
Previous :-
Elan S3 DHC SE SS 1968,
Elan S3 DHC S/E 1966
Elan S3 FHC Pre-Airflow 1966
1963 Alfa Giulia Ti Super Rep.
Previous :-
Elan S3 DHC SE SS 1968,
Elan S3 DHC S/E 1966
Elan S3 FHC Pre-Airflow 1966
- elans3
- Third Gear
- Posts: 490
- Joined: 12 Sep 2003
They are real Italian made webers. I took them off and took them down to a friend of mine who is the expert weber guy at a restoration shop about 30min away from my house. He said he would look at them this weekend for us.
74 Europa 3675R
70 Elan S4 0036K
72 Lotus Seven S4 LS4/2927
70 Elan S4 0036K
72 Lotus Seven S4 LS4/2927
- TheKid#99
- First Gear
- Posts: 24
- Joined: 12 May 2020
I've also found the idle mixture screws can be a source of air leaks. First, confirm all 4 are the same shape (differences occurred over the years). Then, use some fuel lube (like EZTurn) on the threads. I also use a light smear of EZTurn on the mounting o-rings
Henry
69 Elan S4
65 Seven S2
69 Elan S4
65 Seven S2
- SENC
- Coveted Fifth Gear
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- Joined: 30 Dec 2015
According to my mechanic who is very familiar with webers. The throttle stops were holding it open and they had to modify them to make them close. Not exactly sure what they did since I haven't picked them up yet, but I knew something wasn't correct.
74 Europa 3675R
70 Elan S4 0036K
72 Lotus Seven S4 LS4/2927
70 Elan S4 0036K
72 Lotus Seven S4 LS4/2927
- TheKid#99
- First Gear
- Posts: 24
- Joined: 12 May 2020
TheKid#99 wrote:My mechanic trimmed the throttle stops in order to have the carbs close all the way. Problem solved, just need to get the mixture correct now.
Can you post photos of what was done as I'm confused why the throttle stops needed to be trimmed, rather than the throttle stop screw just being adjusted/backed off, as should be the case?
My initial thought: it seems like there may be a mismatch of parts somewhere.
Otherwise, if not, perhaps there is an opportunity for me to learn something!
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promotor - Fourth Gear
- Posts: 824
- Joined: 16 Mar 2012
Yes, I do believe that the company I used to rebuild them used their own throttle stops and not the ones we had on it.
My mechanic just shaved off the top of the throttle stops to make them close, that’s it.
My mechanic just shaved off the top of the throttle stops to make them close, that’s it.
74 Europa 3675R
70 Elan S4 0036K
72 Lotus Seven S4 LS4/2927
70 Elan S4 0036K
72 Lotus Seven S4 LS4/2927
- TheKid#99
- First Gear
- Posts: 24
- Joined: 12 May 2020
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