I should probably have started a new thread as this is a new problem...

My Longchamp now idles fine, and I had it idling for ½ hour without problems today. But then I looked at the plugs, they were all black and dry.

So I started the engine again to adjust idle mixture screws. Nothing happened, I could turn the idle screws all the way in without any effect, I've never seen that before. So the carb must give fuel from somewhere else?

I changed the PV (still 6.5) even though the old one seemed OK, and traced the vacuum path from the PV to the bottom of the carb. And I made sure the secondary throttles close fully (bent the linkage and adjusted the screw from beneath). Same result, perfect idle, but black plugs and absolutely no effect of adjusting the idle screws.

I tried putting my finger on each of the 4 idle bleeds, each time the engine started to stumble. (By the way, there are 2 small holes beneath the secondary throttles, is there an entire idle system there, I thought it was only non vacuum carbs?)

Any suggestions??? If I have the world's only car that can idle wihtout using gas, I'm impressed Wink
Original Post
I think you have solved the riddle of perpetual motion. Take it out for a drive and see if you can go for a month without filling up. Then you will know you have it. Congrats, people have been working on this for years. Razzer As for your problem I cant help. Dont have much carb experience. Give me a fluid diagram and im all over it.

I found out that due to the mixing of parts when I assembled it, there's was no passage from the idle screws to the throttle bores. No wonder the idle screws had no effect. I drilled passages, thinking that was it. But no! It idled better, and the idle screws now had an effect, but small. And the carb was too rich still.

I browsed the web, googled, got on hotrodders.com and there was advice. To get proper idle I had to turn the primary throttle plates up so much they showed the transition slots, this gives too rich idle. I tried to remedy by first increasing secondary throttle plate gap, after that by drilling holes in primary throttle plates, bigger and bigger. No decent idle and black plugs! Mad

At this time I realised I must have had that carb on and off 15 times and spent 2½ days. And one of the gas tanks was on empty, so I've spent $100 on gas idling in my garage. roll on floor

That combined with the fact that the similar carb from my Pantera worked perfectly, I decided to buy a new Holley 600 vacuum, on it's way from Summit. It better be good.

Embarrassing having to give up, but life's (and Danish summers are) too short...
Finally got my Summit parts yesterday. Danish post office decided to keep it a secret that there was a big package for me...

Well, the good news is that the new 1850C works fine, idles fine, takes the gas fine, and the new plugs I put in at the same time look decent.

So now I could drive the car, so I discovered my next issue, if you know about Ford C6s, please see my next post, in the Longchamp/Deauville forum.
Last edited by noquarter
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