Triple Weber stall

[tanny]

I have a 1971 240 engine with triple Weber dcoe 40-18. Engine has standard cam(I was told) and headers. Upon acceleration from idle, the engine stalls momentarily, then will accelerate if I back off somewhat on the accelerator. If I press pedal all the way down, engine will continue to bog down and accelerate quite slowly. I am at 6500 feet altitude

Starter jet = 100 F5

Accelerator pump jet = 45

Int. and discharge valve for accelerator circuit = 35

Main jets = 130

Air correction jets = 185

Idle jet = 45F9

Choke = ?

Any suggestions on what is causing the problem or ways to diagnose the problem? Could a colortune be used to determine whether it is running rich or lean when throttle is manipulated? Thanks.

[carguyinok]

Any suggestions on what is causing the problem or ways to diagnose the problem? Could a colortune be used to determine whether it is running rich or lean when throttle is manipulated? Thanks.

On the colortune. Yes it will help you with the carb tuning for rich or lean. Good tool IMO.

Was the fuel system upgraded for the tripple carbs? It almost sounds like a lack of fuel pressure.

[tanny]

The fuel system was not upgraded. I'm running the stock electric fuel pump only. Mechanical pump is disconnected. I will measure fuel pressure. Thanks.

[HS30-H]

Hi Tanny,

Any advice that you receive will have to be balanced with the fact that you are up there in the stratosphere at 6500ft. That's certainly going to mean that you will have to fine tune for your local barometric conditions, so do remember that the final tuning is up to you or to a local dyno shop that knows Webers.

Having said all of the above, and in light of your request for help in my Gallery pictures ( remember - the car that you saw there runs Mikunis ) - here is what I think regarding Webers on your car;

The good news is that you have the very model that Weber themselves recommended for the L24 engine ( the 40DCOE-18 ). This means that you should have all of the internal circuits and the Accelerator Pump Rod stroke ( 10mm ) that is suited to your engine. HOWEVER - bear in mind that the life of these carbs did not begin on the day you met them. Never take anything for granted when it comes to old carbs, and particularly on old side-draughts. People just cannot resist messing with them, and the lack of local availability for replacement or more suitable parts usually means that people "make do and mend" or use parts that look similar, but aren't suitable. The previous post from carguyinok is very good advice indeed - its very often possible to find jets that have been redrilled ( an old "racer" trick was to solder and redrill them if smaller sizes were needed ). If in doubt -replace. Do you know the history of the carbs? What were they on before you got them? Were they on a running car?

Anyway, you need to check them out THOROUGHLY before you go any further with this. Make sure you know what you have got.

Check out your "Choke" sizes ( its a raised number on the casting ) and they simply slip out after you take off the inlet trumpet and then pull out the Auxiliary Venturi. Either 30mm or 32mm chokes should be sufficient for your engine ( the smaller venturi keeps up the inlet air speed, to promote torque ). I used to run both 32mm, and then 34mm chokes in my old 40DCOE-18's. Both are considered fairly small - but perfectly adequate.

Here are the numbers "from the book" for the 40DCOE-18 on an L24 in normal conditions:

*CHOKE - 30~32mm

*AUX. VENTURI - 4.5

*MAIN JETS - 130 ( 1.30 )

*EMULSION TUBES - F2

*AIR CORRECTOR JETS - 175 ( 1.75 )

*IDLE JETS - 0.50 F9

*ACCEL. PUMP JETS - 0.45

*ACCEL. PUMP INLET & DISCHARGE VALVE - 0.55

*NEEDLE VALVE - 1.75 ( 175 )

*ACCEL. PUMP ROD STROKE - 10mm

Looking at your numbers, I would say that the first thing I noticed was that your Inlet & Discharge valves ( "Bleed Back Valves" ) are small at 0.35 - and you might want to upgrade them whatever happens ( there's only three of them ). In fact, the size you have quoted is a very rare size and I wonder why they were in the carbs in the first place ( 0.55 is stock for the 18-type ).

You do not mention your emulsion tube sizes. F2 should be good for you.

You cannot underestimate the importance of setting the FLOAT LEVELS correctly on these carbs. The float level governs many things in the operation of the carbs. Make sure you do not fudge this issue ( been there - done that - wished I hadn't! ).

You mentioned my throttle linkage in your post on the Gallery pic. and indeed I would recommend that you have the best manifold and linkage that you can find / afford. Carburettors ( and particularly multiple side-draughts ) are basically just precision measuring devices. The precision has to be matched in the linkage, otherwise its all pretty meaningless. You will mainly just need to make sure that each carburettor has the same datum point as the rest ( do this without the linkage attached, and in the idle position ), and then make sure that each carb is pulled the same amount - and at the same time as - the others. I know its just common sense, but here in the UK I have seen manifolds and linkages on L-series engines that would be more at home on Fred Flintstone's car. I hope that yours is better than that.........

And then you have to think about fuel flow and fuel pressure. The Webers like to have about 3 or 4psi AT ALL TIMES ( that means even at full throttle with the engine turning high revs and eating lots of fuel ). Make sure that your pump and lines are able to feed them. I had great success with blocking off the return line to the tank completely, and just running the fuel feed lines into the carbs with no return at all. Some people seem to keep the return lines and still have no problems. Make sure that you have 3 to 4psi at all times and all should be well. You will need to have a proper Fuel Pressure Regulator unit to do this ( very simple ) and I would recommend having it as near to the carbs as possible.

I would forget about the Colourtune for now and start learning how to read the plug colours correctly ( you will get very good at this after a short time ).

If you don't feel up to the job of tackling this, then I would recommend that you find a friendly specialist with Weber / Dell'orto / Solex-Mikuni knowledge ( and a chassis dyno if possible ) and get him to sort it out for you. Once its been "right" once you can eliminate all sorts of possibilities from the equation if it starts running "wrong" again.

At the moment, its difficult to know where to start with advice for you. I'd make sure that the parts are all there and the jet sizes and settings are all near the baseline above, and then start eliminating possibilities. Don't lose heart, as they ought to be great once they are properly dialled-in. The sound alone is worth it.

Good luck,

Alan T.

[tanny]

Thanks much Alan,

Unfortunately there is no history on these carbs. The only info I received from the previous owner was that they had been "adjusted" for this altitude. I am not quite sure why I didn't check the choke size when I was rebuilding and cleaning these carbs. Must have been the carb cleaner fumes. They are a real hassle to get off the manifold because of extremely tight clearance. I would imagine that if the chokes are too large, the air velocity would be too low(especially at low rpm and high altitude-low density air) to create enough vacuum to suck much fuel out. I do have a fuel pressure regulator, but it is on the opposite side of the engine from the carbs. Could move it next to the carbs. I do not have a fuel return line. I capped it off. I will check the fuel pressure today and see if I am in the ballpark. I triple checked the float levels, but not sure how accurate my method was since I used a tape measure, not any kind of float level measuring stick. I couldn't find a size on the emulsion tubes. If nothing else pans out, I think I may order some .55 inlet & discharge valves since there is quite a disparity there. Thanks alot for the detailed analysis. This should at least get me started on dialing these things in. If I am unsuccessful, I will try to find a weber specialist and see what they can do.

[tanny]

Is there anyone out there that has triple Weber DCOE 40-18 carbs on a 240 that lives at higher altitude(above 5000) and knows what jetting has worked well? Thanks, Victor