The ultimate definitive carbs driveability poll

Hi Bill, Yes indeed a small world, very nice to know where my cars brother resides.
btw, very nice picture with your car in the snow.Rob

 

i put some concave floats in the carbs, it helps a bit.

 

My car displays none of those symptoms. 1981 GTSi converted to carbs. 42 DCNF's, Millermon ignition conversion, MSD ignition and coil, Flowmaster exhaust. Runs great.

 

1978 308 GTS

MY car is hard to start when cold. Several pumps and sometimes the choke helps when it is really cold. It takes about 10 minutes and then purrs like a kitten -basically, once the idle cam lets go. In the summer, one or two pumps and she's fine - still needs to warm up for a while. I have the starvation in the corners...it is real obvious. If the car is cold and I turn it off, it will backfire -LOUD- everytime. If it is warm and I turn it off, no backfire, but a small cough in it's place. I haven't had the fouling be a problem. The ignition is good ol' points, R1 only and work just fine once the dizzys were cleaned and the timing set.

-RJay

 

Most backfiring in the exhaust is due to leaks somewhere, usually at the head where the flange attaches. Many of these cars had air injection, and it could easily be a source of backfiring if its still on the car. Neither of my 77's have ever backfired, excepting that little almost inaudible boom boom boom on overrun that supposedly put's flames out the tail pipes.

 

Mine is exactly the same, except I don't have any backfire. I do have some little exhaust pops and as I was timing it last night a lot more little carb pops than I thought. Timing at 5000 rpm -- that's wild!

 

Just remember to check your at idle timing. If its way off you need your distributor recurved.

Then check your idle jets. I think it was Birdman who said soaking his jets overnight fixed a lot of his idle woes, even though he could see nothing visually fouling the jets.

 

One thing I haven't seen mentioned yet is getting the linkage setup and behaving in a coordinated fashion. In my case need to replace the ball part of linkage as mine are no longer round!
The last major improvement I made in driveability was in the linkage. It is vital that all 4 carbs come off the idle stop at the same time, otherwise the behaviour of progression holes is off kilter and you get stutters, hesitation etc. This applies even when you are already on the road as most of you driving is near idle stop.

Gerrit
http://dino308gt4.com

 

forgive me if this has been stated already, the only way to know for sure if the plates are at the transition ports all at the same time, is to physically look at the ports from the bottom and set the plates accordingly since the holes may not all be in the exact place from carb to carb.

 

No, not me. Mine were just too small!

 

Yes, proper synch is imperative.

 

?????? HUH?

That is not how the carbs are synched.

 

What main jets are you running?

 

I know how to sync carbs. What im saying is dont count on all the carbs being identicle when it comes to port placement below the venturi at the throttle plate. Checking and making sure your carbs were not drilled inaccurately seperates the novices from the pros. Its like blueprinting an engine, blue print the carbs, never assume anything.

 

Sorry, I thought you were suggesting that you adjust the throttle plates to uncover the progression holes at the same rate, which we both know would make the carbs unsynchronizable if the holes were not identical from carb to carb.

So if you find they are not the same, what can you do? I would assume all you can do is replace them.

Birdman

 

my standard saying ..... I HATE POINTS!!!!



i love the dual Crane XR3000s my friend and i installed in my car.

 

HPBooks Weber manual shows several ways of correcting the throttle plate to progression hole interface as well as idle mixture. But you are correct, you would need to set all four up to match each other as close as possible. The other option would be to drill the holes so they all match, by drilling the holes of the carbs with the smallest holes larger,so they match the holes of the carb with the largest ones. Provided of course that the largest one isnt already drilled to much.

 

I love this thread. It really sums up a lot of the issues around carb and ignition tuning. I'm getting a near stall when I take a hard corner with the clutch in. Might be the carb, might be my ignition, might be both.

 

Thanks Stu for finding tread. I would have voted None.

 

That would probably be fuel starvation in a hard corner. A common challenge with these cars. You may consider checking your float height to ensure that it's set properly.

 

I got a strange stuttering today while the car was under load. I'm thinking this is electrical not mechanical as I am still running twin Marellis without electronic ignition.

 

That's on the list as part of the carb rebuild project. I also learned to blip the throttle to keep the revs up. The 308 motor has a lot in common with the 2 stroke dirt bikes I rode in the 70's. It makes power at high revs so it helps to get them up before you engage the clutch. Stomping on the gas at low RPMs gets you bog and a slog too the top end.

Keep the revs up and you are smiling.

 

Once they are rebuilt and setup correctly they are an absolute pleasure!

 

I have no issues with my '79 GTS. I have run with both the hotter cams and the '79 less aggressive cams.

I do have an electronic ignition but that is more about maintenance than performance. The twin distributors with two sets of points each work great but will require more maintenance. Grease hardens, contact foul, and things move.

The other difference is the carbs are jetted differently. Thus, I also run a slightly hotter plug.

I have driven many other cars with carbs and never had any of the issues if the car is properly set up.

The big difference may be in how the car is driven. If you spend much time under 3K rpms, you will likely see some of the plug problems. This is more so if you do not spend any time at 7K+. It is a high performance car and want/needs to rev. It is a rare day when my car and I do not work in a couple of gears.

 

1977 GT/4 with electronic ignition.

The only drivability issue I've seen is a slight stumble on take off. The last time it was in the shop they did a quick carb adjustment and the issue is almost gone entirely. I'm told at there's still improvement to be had with a more comprehensive tune.