Big Hesitation 512BB

I replace the chokes, main jets. emulsion tubes and air corrector jets with part from
pierce manifolds based on his experience with the boxer and webers ( just so know this is a help question it is not anything against pierce manifolds)

F-8
150 Mains
32mm chokes
tapered idle screws

The result was pretty awful it has a huge hesitation when it comes out of it low speed circuit.
Basically if you get in to it, it seems like it is out of fuel.

I went back to the original in steps but the bog is real bad.

I am now at everything back to the original start point where the original setting made the car run pretty well expect for a rich condition.

The fuel pumps are a couple of years old. The carbs have been rebuilt.

I have been doing this at my office between various project and I guess I should look for some assistance.

Float adjustments?
Gaskets? between the body and the upper section?
Fuel filter, I just had them replaced with the major.

Let me know what you think.

 

The guys at Pierce are definately quite spot on most often. Have you checked that there isn't a vacuum leak through the throttle shafts? This tends to be the problem that most affects a good Weber tune.

Was the car always running rich before or only at idle or at acceleration? A carbureted car always runs slightly rich anyways, it's where the perform the best.

 

Good day 412,

I, too, have a carbed Boxer and surprisingly there were minimal changes to the stock setup necessary for excellent operation. In fact, I found that the stock setup worked very well. I only made one change and I think it was slightly larger main jets?... but I would have to check... But even so, the car ran very well before I made this change.

Although Pierce are indeed the experts and their recommendations are no doubt beneficial, I would check your infrastructure first (possible vacuum leaks as already suggested, fuel pressure, etc) so that you narrow down the issue. Changing too many things all at once introduces too many variables to determine what is causing your problem. If it were my car I would start with fully cleaned carbs, all orifices blown out with air, new gaskets, etc and a stock setup. Next I would ensure that the carbs are all sync'd. Then if the problem was still present, then I would delve deeper... using a methodical approach to determine what is causing the issue and only make small incremental changes and noting the results.

If you find it a bit daunting, then it may be best for you to find a Weber guru locally, as this may save you buckets of time and perhaps $$$ too.

Cheers,

Sam

 

I have had the carbs rebuilt with shafts etc at only about 500 km ago.

I am leaning towards fuel pressure.

By the way, what is the ideal pressure?

 

3.5psi.

 

Have you ever serviced the mechanical advance mechanism of the ignition distributor? This is basically removal, disassembly, cleaning and lubrication of the lower portion of the distributor (weights and spring and all pivots). Since the 512bb has electronic ignition, the distributor often gets ignored. Most of the 512bb/bbi's that I have serviced have never had the distributor apart and there was no grease and significant wear to the mechanical advance mechanism. One car needed to have the distributor replaced because the wear was so bad.

Brian Brown
Patrick Ottis Co.

 

Thanks for the replies.

Distributor has been checked as well as an MSD installed.

I am wondering about a restriction in the fuel lines when the carb tops were removed? I was pretty carfull.The filters are new.

It is funny how it ran great in the morning, I changed the idle screws to the tappered style
from the stepped.

Went to 32mm chokes, F-8 with 150 mains on the new carbs as recommended by Pierce.

I have gone back to the original settings and parts.


It is awful. I used the syn meter with ideal readings on all the carbs as well as pretty clean
at idle.

I picked up a new set of plugs that I will throw in this afternoon because it did start to miss on a couple of cylinders before I put it away.

 

You should get the guys at pierce on the phone again and run this by them. They should be able to recommend a revised setup for you.

 

So I decided to remove the plugs. ( new)

Starting from the drivers side, close to the fire wall, # 12, 11 & 10 plugs were very clean almost if they were being cleaned by fuel. #9, 8 & 7 were black.
The other bank starting from the fire wall, # 1, 2, 3 were black, # 4, 5, & 6 were also clean.

Could it be the MSD is acting up?

It idles fine all the idle screws have the same effect on the running of the motor.
I pulled each plug as it ran and listened to the rpm change.

 

The MSD unit is likely fine...

After 25 years of ownership with a 365bb, here's where I'd start:

-Verify with a timing light that the distributor does indeed advance as it's supposed to
-Pull all of the idle speed/slow running jets and inspect them carefully for debris/obstructions. This is the number one cause of an off-idle stumble.
-These cars will run much better, with less transition stumble with a ,55mm idle jet
-Remove, inspect and ohm test the spark plug extenders
-Ohm test each wire
-Inspect the distributor cap for corrosion
-When synchronizing the carbs, disconnect the primary cross linkage, first
-Then reconnect the cross linkage and verify that the air flow remains the same
-Hold the engine at 2,000 rpm and recheck airflow, side to side and forward and back. Likely it is off "side to side" and you'll need to add some free-play to the linkage rods.

Search for posts by myself on this subject...Much discussion to be found.

Best,
David

[email protected]
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