Hi all,
Small introduction: I am part of a race team from the Netherland and we are racing at the Spa 24h race, classic class.
The car runs great but we are suffering carb problem in the long right corners. It seems the carb is running dry. AF meter is showing very lean, engine power is gone at that moment and only giving half throttle solves the lean mixture. After a few seconds after the corner the power comes back, and the AF meter is showing good numbers again.
Last year the car was the fastest Classic on the straights so the engine itself is very healthy.
Engine specs:
rebuild AM2 2CV6
stock compression
stock cam (new)
stock 26-18 carb with tuned jets
stock exhaust
Things I tried:
Making the carb level higher, there is a small positive effect but its far from gone. I am at 15mm now.
Checked the carb floating leveler (no idea how to call it) with a cut open carb to see if it moves freely and it does.
To make sure the carb does not overflow I put a hose on the overflow tube, led it to a can and found noting in the can after a few fast roundabouts with dropping power.
Filled up the tank to max to be sure the problem is not caused by starvation.
Anyone any tips for us??
A lot of our cars suffered the same problems when the 24hr race went to Snetterton, which has some long right corners. The solutions we used:
1) Put spacers underneath the left side front engine mounting - this stops the engine leaving over too much to the left in corners.
2) Raise the floats a little as you have already done.
Tilting the complete engine? haha, good idea!
I suppose that spacer must be about 1 cm or so?
I think I snapped off the left hand float in my solex.
Quote from: gasklep on August 05, 2016, 05:47:39
Tilting the complete engine? haha, good idea!
I suppose that spacer must be about 1 cm or so?
I feel 1cm is a bit much. Iirc MRB used a thick shockabsorber washer for this. However that was with a weber carb.
We used to chamfer the carb base gasket to till the carb.
That way you don't need to tilt the engine too far and upset the exhaust and gear linkage alignment.
Quote from: Bart van Wijngaarden on August 05, 2016, 08:54:54
Quote from: gasklep on August 05, 2016, 05:47:39
Tilting the complete engine? haha, good idea!
I suppose that spacer must be about 1 cm or so?
I feel 1cm is a bit much. Iirc MRB used a thick shockabsorber washer for this. However that was with a weber carb.
Good memory, yeah we had two thick shocker washers with slots cut to make it easy to alter, but only usually used one. Angling the carb gasket is another option as Nick says.
We use a bit of threaded bar with a nut on it, wind it up or down lock the nuts and job done
If you have an early carb the fuel passage from the primary jet side to the secondary is a 2mm hole 15mm ish from the bottom of the carb,if you have a later carb the fuel hole is 4mm and in the bottom of the float chamber. The older one is best,we used to block the hole in the later one and replicate the early design,or you could try reducing its size,maybe with a primary jet.
If all else fails the below was our solution to the long right hand bend at Mallory park
Remove the float from the secondary jet side of the carb ,reset the float level to 20mm and use a carb spacer machined at an angle too.
Thanks for the tips!
I will definitely look what carb we have. So the one with smaller and higher passage is the one to have?
I was thinking about something else. If I would use 3 gaskets between the lower half and upper half of the carb. The whole fuel level will come up without changing the float. I am at 15mm now and it is not enough. Raising it more can cause closing problems. With extra gaskets I dont take that risk and still have more fuel in the carb.
The one with the smaller higher passage is definitely the easiest to use.
In the primary side there is the round chamber that would hold the dashpot plunger for the trafficlutch fill that in with some plastic tube so the fuel level in the float chamber isn't reduced by filling that area.
Hi all,
I can confirm that the "carb to have" is a 21-24. That one has the small passthrough. The 18-26 has the bigger passthrough. And that is exactly how the carbs react to leaning over. The 18-26 drops down in power dramatically! The 21-24 does this less.
In the last picture you can see the area at the right top what has to be filled with a piece of rubber hose.
Great, now we are getting somewhere!
yep the the place for the rubber hose
Ok, after some testing I came to the following conclusion: It works! Finally I can fly over roundabouts for ten laps without starvation! Also long highway corners to the other direction are no problem anymore. Ok, some people did not liked my exercise but anyhow, it worked. ;D
The float level is at 15mm now but I think it is a bit too high. When I drive a longer period the AF gets richer and richer. Maybe when I set it at 16mm it will be gone, have to test this yet...
We also found a 18-26 carb with the smaller fuel passage so its not only the 21-24 carb you can use. Some 18-26 carbs will do also. Still I prefer the 21-24 because of the way it controls the AF. A 18-26 carb has a lean spot at max torque, a 21-24 has way more steady AF valleus over the rev range.
oh, and I have 1 big tip for everyone: Pull the overflow pipe out of the carb and put a longer 9mm copper pipe in place. It will prevent you from overflowing and saves you a lot of trouble ;)
Which pipe is the overflow pipe?
The large pipe that vents into the second choke,we used to remove it and fill in the hole .
Quote from: Paul on August 21, 2016, 20:45:52
The large pipe that vents into the second choke,we used to remove it and fill in the hole .
And run without air vent? Can you remove it without side effects? Or do you have to make a alternative vent?
Quote from: gasklep on August 21, 2016, 21:20:49
Quote from: Paul on August 21, 2016, 20:45:52
The large pipe that vents into the second choke,we used to remove it and fill in the hole .
And run without air vent? Can you remove it without side effects? Or do you have to make a alternative vent?
Anyone?
No alternative vent,if you remove the choke flap and spindle and carefully blank off the outsides,the float chamber is vented via the holes in the primary choke.