308 "stumbling" after slow right hand turns

Jonathan,

I've concluded that this is a characteristic of carbed 308s.

Here's some data:
http://ferrarichat.com/forum/showthread.php?t=7218&highlight=hesitation


Mine has always done this, except one time when I had my mechanic do some jet work, it went away for a while. They increased the accelerator pumpt jet size and also the idle jets, but things got too rich.

Not everyone seems to have it. A number of people, including me, have the exact same situation you had.

I had my carbs rebuilt, manually reset float heights PRECISELY to the best spec I could find, tuned, tweaked, and still had the problem.

None of the reviews I've read about the car mention this. There may be a common solution out there but I've NEVER found any solid leads on it.

This is one of the reasons why I decided that, as awesome as they were, I couldn't deal with carbs on a day to day basis; I didn't like having the car basically die on me in slow-speed, part-throttle corners.

Would be very interested in hearing the solution. The problem seems to be losing one or more (maybe up to four or six?) cylinders, could be ignition related or fuel supply related.

Do some searches--there was some good info in the FerrariChat archives, as well.

--Mike

 

I have a '78 308 and mine does the same thing. It did it both before and after its recent major service. I just keep the revs over about 3k on a long right hander and it goes away.

 

Exactly! These cars are known for this problem. The secret is keeping the revs high enough to avoid the problem.

 

From what I have read it is a common characteristic of the carbureted cars. Mine does it too. Has to do with the way the floats swing in the carbs. my Chevy truck does it even worse with the Holley carb on it.

The trick is to pump/feather the gas lightly to compensate with the accelerator pumps and all is well, either that or carry more speed through the corner.

 

Dinos do it too.

Mechanic's advice was, "just stay in the throttle."

Helps, but doesn't make it go completely away. And I've seen it referred to in several road tests for dinos.

 

Fuel injection makes it go completely away.

 

...along with several horsepower!!!! lol!

 

I think these folks didn't read your post. Its NOT characteristic of carbed cars to have backfiring and up to a minute before getting back to normal. If you had the carbs apart and it started doing this after the rebuild, I'd be suspicious. The float level might be too low or you might have a float that is binding. I don't have a trick way to isolate which carb it might be so the only way to tell would be to pull off the air cleaner and inspect each carb. This doesn't take long. You might take two hours to complete the job (including adjusting the float(s) if they need it.

Best wishes,

Andy

 

First of all, yes I did read the post and second I will stick with what I said. The only part that sounds strange is the part about it taking so long to go away. He didn't say he had the carbs apart he said after a recent synching of the carbs, and that he needs to take them apart to check the floats.

He also doesn't mention whether or not this is with the car cold or warmed up? That in itself could make a difference. I have experienced the problem at higher and slower speeds, but the key is the RPM's. If they are kept high enough I don't have the problem at any speed!!

Still could be some other problem but I'm willing to bet it's just one of those little bonuses that we with the carb cars get to enjoy that all the others don't!

 

The carb cars will hestitate like this sometimes in slow speed corners. To the best of my knowledge the solution lies in the ignition. At slow speed in the corners the stock ignition system has its spark plugs 'soaked' by the carbs and the recovery time are the plugs cleaning themselves out. I had the exact same problem with my car and it totally disappeared when I went to an electronic ignition setup. It seems as though the electronic ignition just gives the plugs enough more juice at low revs to keep them from getting soaked. Not highly scientific but this is what happened to me.

 

Carbs don't need to come out to get at the floats.

1. Remove the airbox cover.

2. Remove the air filter.

3. Remove the air horns 4 sets of 4 8mm nuts, don't drop the nuts down the throat. Nut driver or 1/4" socket w/ extension or GearWrenches will make quick work of this.

4. Remove air box cover (additional bolts). Note there are 4 carb gaskets which might have little round metal bushings in them (4 each), don't drop these either.

You're now looking at the tops of the carbs. Each carb has five bolts, flat-head.

5. Remove the tops of the carbs via the five bolts. Keep track of which top is for which carb.

6. Carefully lift up the top of each carb once the bolts are removed. The float will come with it.

Now you can set the float levels. If the needles and seats are not new you'll want to replace them.

Setting the float levels is something I've done once, very patiently and it tooks some time. You'll need a nice set of pliers (I use sears craftsman professional "small" mini pliers, needle nose if I recall). You'll also need a good little tiny metal measuring blade/ruler, or even better a nice vernier caliper.

This is a start...

Archive search should reveal more about how to actually SET the floats.


--Mike

 

If you are running stock coils and want to get a hotter spark, try MSD "blaster" coils. They fit in the stock mounts, are relatively cheap and available, and put out a ton more power than stock. You could go to electronic ignition too but its a matter of how far you want to go. I've been running stock points and caps, with 8mm silicone wires and blaster coils for 18 years. Lots of track time, no high end misfires - but still has a bit of the low end stumble.

Best wishes,

Andy

 

I've got a pair of vernier calipers you can borrow.

 

Birdman,

I have eighteen years and lots of miles on the same set of points I installed with the blasters when I first bought the car. From my experience the coils have produced no negative impact (other than being red in an otherwise dark engine bay)

Andy

 

In theory, the fuel pump is running all the time and applying pressure to the valves simultaneously. Consider that if filling three carbs in a slow speed application is too much for the pump to catch up with, what happens when you are really accelerating and all four are drawing fuel at a more significant rate.

I would put my chips on one or more fuel bowls being low on fuel. I recall adjusting mine many years ago to cure a hard cornering problem at the track. I set the heights 1 mm higher than what the book calls for. No problems and the hard corner starvation got better.

You just might want to set aside a few hours one night to open up the carbs as per Mike's procedure and check the float heights.

Andy