Former owner of a carbed 308 which I regrettably sold a number of years ago. However, I still have my Jalpa, which runs on 4-42DCNF carbs. I rebuilt the carbs completely before storing the car for 4 years. Recently, pulled/cleaned all jets and ET's and pulled the top covers off and everything looked really clean. I also put in a new fuel pump which puts out 6psi, which is too high. the #7 and #8 cylinders (shared by one carb) are soaked and fouled immediately. I am thinking its a stuck needle valve, or too much pressure from the fuel pump. any thoughts are welcome.
I’ve seen your vids. I’m sure you will figure it out. Your diagnosis sounds correct to me. But it should be checked. Along with floats. Good luck
7-8 are at the end of the line. If it was the fuel pump, you would think it would be 5-6 that would have the issue, as that's where the fuel line comes up from the pump? 7 psi is the Facet pump you can buy as a replacement. I'd open that one back up and check the needle valve. Sounds like your float may not be closing it.
everything seems to be running rich, I haven't driven it and loaded it up really hard, so that might be contributing, but all the plugs are too sooty, with 7/8 being wet.
I can tell you - I just got a couple 14 mm colortune plugs - I'm going to try and fix my mixture issues with those.
I had very similar issue on my car shortly after buying. Previous owner had rebuilt carbs. The issue was that the needle valve hadn’t been tightened into the top cover and gradually worked loose; moving itself lower down toward the float. As a result in no longer worked as a valve and effectively flooded the float chamber. Car ran very rich on one cylinder and the plugs were ‘wet’ like you say. I would clean them up; everything would be fine for a bit then it would stop firing on that cylinder, again. (what also interested me was that the engine temperature would rise when that happened; not sure why?) anyway; i couldn’t trace down the problem; thinking it was ignition. it was only when I noticed a fuel leak from the carb; and evidence of a small fire where fuel had collected on the cylinder head and burnt out that I took the carb apart. Such an easy fix once I found the problem
Have a look at my blog (Derek’s 308) as I tested the float levels without taking the carbs apart. You might have the one float level too high or something stopping the valve from sealing (try squirting carb cleaner into the fuel inlet, might clean the seat.) I wish I’d bought the white Jalpa parked next to my 308– less wrong with it and worth much more due to the few made.
Thanks all - will report back on results. On the fuel pump pressure, my Jalpa WSM says 4psi, and I have read a lot that Webers generally like 3psi. Is there a problem with running higher, like at 6psi? I understand the problem could be over pressurizing the carbs, flooding the float bowl, and introducing too much gas into the carbs. Has anyone really experienced this?
Another possibility is a float than is no longer a float (so confirming that it is still sealed is as important as the mechanical adjustment). Also, are you saying that you can make a reasonable idle A/F adjustment on those two cylinders (i.e., you can swing it from lean miss to rich miss with good running in between)?
Steve, good to see your name! I didn't do any playing with idle screws, just turned it off when it was running on 6 cylinders, pull the plugs, saw they were wet, and didn't do anything (yet) after that. Do you have a point of view on the fuel pump pressure?
Enough carb 308s are running OKish with the 7 psi Facet pump installed that I wouldn't say that being at 6 psi is an instant serious problem for DCNF, but it probably does needlessly increase the needle valve wear and shorten life. You've just got to get in and see what's what. It's way more concerning when everything checks out as OK, and you still have a problem Don't know if you use the choke (nor know the exact mechanics of it on your Jalpa), but another possibility could be something like the 7-8 choke being stuck "on" for some choke linkage problem -- just another thought...
Just sitting there running (or not running but pump on) is fuel visibly dripping in the 7/8 carb? If so, from the pump jets or main discharge or? If no it isn't a pump pressure or needle and seat issue. Conversely if yes it is not automatically a pressure or needle and seat issue. I agree with Steve but if pressure concerns you an inline regulator isn't expensive.
I can share a video of where the fuel dripped from my carb, which was a needle valve issue, but not sure how to upload videos?
I bet the pump you have now is outputting 7 psi or so. Pump is at the bottom of the car, and it's got to push 6 pound/gallon gas up about 2-3 feet to get to the carbs - so you are losing about 1/2 to 1 psi just getting the fuel to the carbs. Ya - I agree with the above posts - either your floats aren't floating, or you have a needle valve issue.
Facet makes two pumps, the carbed Ferraris want the lower 4 -5PSI. Higher one makes 7 -9 PSI I guess you could use the higher pump if you had an adjustable regulater, buy why??
Never....ever....use the choke... As Steve mentions, sticking "on" is the worst possible thing to happen!! Well , my Tech broke the console cable off, I guess that might be worse!!! Wankers.....
Facet make around 20 different pumps and Webers dont like much above 4psi although they do seem to tolerate the higher pump on some cars, perhaps due to the return line? The 477060E is a suitable pump for Webers at 4 to 2.75psi range. With a little resistance in the circuits etc they normally settle at about 3.5psi which is good. Rated at 34 GPH. Regulators go wrong and not needed if you fit the correct pump imho. As for wet plugs, obviously you have checked that the plugs are firing, Follow same firing sequence ie 1,5,4,8,7,2.6.3, if not got to be floats, valves etc. Pull the top off and check floats for piece of mind, Ethanol loves eating solder on brass floats if sitting for too long. Tony