Hans thats the exact symptoms that I have although like you it feels like the car runs hard.I have the exact same jetting as well and also as you know I also have the X-Ost.My compression is a little higher than yours if it's still stock.I have 10:1 pistons in mine.I still have also the slight hesitation in transition from idle to mains and the research that I have done is to have the progression holes slightly enlarged but I havent found anyone yet to do it.You can go up in idle or up in mains to help mask this but it will still run rich.Going down a size in the A/C will make it even richer.I tried with 190's and it was way to rich on A/F meter.Keep experimenting Hans and let us all know how you go.
The fuel in Europe must be very different than that of what we are subjected to in the states. I could never run 220 ac with 130 mains here without being incredibly lean. My latest variant is 135 mains with 170 a/c and they have been working out very well (last time I drove it anyway, suspension rebuild almost done!).
Little correction to my earlier mail: I've got 205 AC's in there now. Turns out the tuner got these in, rather than the 220's that I had in there before. And yes, I'm at a loss too. I was running 125 mains and 220 AC's and yet produced 208 rwhp with it, albeit a bit on the lean side. Now with 130 mains and 205's, the mixture high up is good (and 213 rwhp). I've asked the tuner to send me a set of 50's idle jets. Let's see how that goes. We're going to Italy next week. Warmer weather and mountain passes up to 7000 feet. last year, I really had to work hard to keep the engine alive. Waaaaaaay rich down low. With it being even richer now, I'd rather sacrifice a bit of low end driveability at sea level than not being able to get up the mountain due to a flooding engine I'll keep you guys posted... Hans
Hans, Maybe on your return from Italy you could go visit Hans Uhlmann in Switzerland. See: http://www.dino246.ch/ He's got a great reputation on tuning carbs. He did the maintainance on my 308 and that engine runs beautifully.
Hans, are you sure that the jets you have are what they say they are ? Many jets have been drilled larger. I am running 160 mains, 55 idle jets and 180 a/c on my Gt4 race car and it runs ok ie not to rich low down. I do however have a problem whereby the car will bog down if I push the accelerator too quick unless the revs are above 4,000. The car does have an agressive cam it it though. I plan to examine the pump jets which have 45 (standard) on them but may have been drilled bigger I think.
Yes, we've measured the jets. Turns out that I was running on 7x 125 and 1x 145 (a drilled 125 with the number not filed off - thank you Italauto for supplying me with these)! That's 8x 130 now. The idle jets are 45's drilled out to 56.... And thanks Peter for the link. BCCP in Gramsbergen is who I am working with now. And I don't think I'll have much time in Switzerland when I'm there. Plus I'd need to get back home in time to deliver my car to Alsa, to park her alongside yours...
John what ET are you using? I have, Carbs 42mm, 36mm venturi, F36 emulsion, 140 main, 55 idle, 170 A/C with P6 cams. As yet have never run on a dyno or AF meter to see where I am at but I want to do that soon to see if I can make any improvements. I have no idea of RWHP etc. The engine goes hard, and yes does have a hestitancy at the transition point around 2600 rpm. Steve
36mm venturis without headwork is a bit radical for the the street (especially w/140 mains), you might do better with 34mm venturis with no high end power loss and better flexibility and response. And while it is my bias, I think that F24 ET (the original pre-emissions fitment) is more sporting than the F36. BUT, speaking of 36mm venturis and P-6s, time to resurrect the 308 GTLM factory specs for comparison: Carburetors: Weber 40 DCNF 35/36/37/38 - Main venturi: 36mm Main jets: 160, Air correctors: 175 Idle jets: 0.60, Idle air correctors: 1.60mm Float level: 48mm, Needle valve: 1.75 Progression holes: 080, 140, 130, 160, 080 Accl. pump discharge: 040, Accl. pump jet: 045, Bleed valve: 050 Emulsion tubes: F6 Remember this engine did not care about below 4500 rpm, was ported for max rpm flow and was all about 9000 rpm on the Mulsanne Straight Since you mentioned you were running 42DCNFs, here is the factory jetting for the 3 liter Jalpa V-8 which also has 42DCNFs: Lamborghini Jalpa 42 DCNF jetting for comparison choke 34 pump 35 main 135 e-tube F27 airs 180 idle 50 Hope this puts some things in perspective and is entertaining.
I have a feeling you are running pretty lean with that setup. I use the identical arrangement for my stock '76 GTB and I am still lean over 5k rpm. I am changing to F24 emulsion tubes, but 135mains and 200 air correctors to start. I have a good feeling the F24 tubes will take care of this situation pretty easily.
Steve, I am using the F36 Emulsion tubes. My engine has 10.5 compression ratio 82mm pistons and a hot cam but really does pull higher up ie above 4500 rpm. It has the standard carbs. I recon I could up the mains to 165 or even 170. I will try to find what jetting the 1974 lemans entry ran. Hans, are you sure that your ignition ie plug extenders/plug wires are all ok with no crud on the connections? This (on another of my carbed f cars) led to poor fuel burn at tickover for me. Image Unavailable, Please Login
BUT, speaking of 36mm venturis and P-6s, time to resurrect the 308 GTLM factory specs for comparison: Carburetors: Weber 40 DCNF 35/36/37/38 - Main venturi: 36mm Main jets: 160, Air correctors: 175 Idle jets: 0.60, Idle air correctors: 1.60mm Float level: 48mm, Needle valve: 1.75 Progression holes: 080, 140, 130, 160, 080 Accl. pump discharge: 040, Accl. pump jet: 045, Bleed valve: 050 Emulsion tubes: F6 Russ what's a F6 ET? I have never heard of that? I have been pondering the F24 tubes as a start to see what changes I can make. Yet to dyno the car but will soon to see where I stand. Keeping in mind that my main aim is to have this car optimum for the track. If its a bit cranky down low I don't mind as long as it flys up top. Thanks for the info.
Yep it will be interesting to see what the dyno says. I am running the larger mains and A/C but certainly don't want it running lean at the top end.
You will find this useful. Looks like 34 degrees at 5k rpm is recommended, but the distributor is listed as only advancing 13 (26 on the flywheel) degrees as opposed to our stock cars which advance 16 degrees (32 on the flywheel). The idle on the Lemans arrangement must be set to 10-12+ Image Unavailable, Please Login Image Unavailable, Please Login
Just to let you know I've change the mains to 130, ET F24 and a/c 190. eliminated a tiny stumble when going from idles to mains. mixtures etc stayed the same as before. still running 50 idles.
until then I am runnign 140 mains F36 and 170 a/c with good top end results. I still have a slight low-end stumble but the top end has definitely smoothed out.
wow that is rich with 140s. what lead me to move to 140 from 135 was the color of my plugs and the small stumble at low rpm. the plugs were bone white with 135s! there is a small amount of brown color with the 140s. I really need to get a a/f meter hooked up so I can really see what is going on. how did your plugs look or did you not read them after the runs?
Hi Guys, What plug gap are you running and with what ign system? I am running MSD6-AL with a blaster coil, msd wires, AC 63 plugs, (iirc) with a 45 gap, pulls strong at high rpm. The carbs are 135 mains & 200 ACs and i have a big stumble off of the idle circuit at 3500rpm, on hard acceleration. I will have my wife bring her mac to the next track day, (7-17), so i can record a few laps and can take a look at the top end performance under hard use. I haven't been staying up on the LM-1 with the rpm signal sender. Has anyone found a way to make it work with an MSD??? thanks, chris If Pierce has finally received a set of F24s, i will order a set. Does anyone else have a source for them???
I posted this before in another thread but I thought it'd be useful to have it here for reference. Here is my graph with 140/190 in the carbs. I'm running cranes ignition, BPR7EIX gapped at .25. Power delivery feels very smooth. No noticeable stumble at low rpm. Image Unavailable, Please Login
