Webers and power loss. Long

[tranzor_Z]

Hey All,

This isnt really a question so much as an observation.

I have the Weber dgv conversion on my '73 240Z. After a few months of research, I thought I finally unserstood them enough to begin trying to tune them. I had done everything short of a complete rebuild and I still couldnt get the car to run quite right. There was a flat or dead spot at 3500-4500 rpm where the car seemed like it was going to die and then it would " come back to life" and open up. I always figured it was because they were progressive carbs and thats the way they are (this is my first carb'd car by the way). The other problem was the car would loose power at 5500 RPM and you could not accelerate past that.

Today while changing the wheels on the Z, I saw something that a while back hadn't really clicked for me but now did. There was an electric fuel pump in the back of the car by the tank when i bought the car, but it wasnt hooked up. I thought about the problem again of power fall off at 5500 RPM and decided to clean the pump up and try using it.

All I have to say is WOW. The car is completely different now with the addition of the second pump. I think this has something to do with the fact that now there is a constant head of pressure to the fuel manifold that isnt dependent on RPM as the stock mechanical pump is. All hesitation is gone, the car pulls hard well past 5500 RPM and is generally easier to drive.

In retrospect I guess I should have thought about this problem sooner but figured I could take care of the problems with simple carb adjustments. There really is a large lack of information regarding the tuning of these carbs and the Weber books are sometimes hard for someone with limited knowledge on carbureators to understand.

I think the next step I should take is adding a fuel pressure regulator and an MSD style ignition to keep the spark hot at higher RPM's.

If anyone has anymore to add or questions about what i did , post up.

-Thanks

[ZmeFly]

To put a FPR inline before the webers, one thing they dont like is high pressure. Make sure your not supplying more then 4psi to the carbs.

Glad to hear you found a gremlin trying to take away your happiness.

[mtdripo]

Great to here that you fixed your problem.I have also had a terriable time finding information dealing with these carbs. In fact, after searching and searching I've found nothing. What have you been able to find? Some links to some info would be great.

Thanks ,

Dan

[tranzor_Z]

But I have found two books that "help" at least for a tear down and very general trouble shooting step.

1. Weber Carburetors by Haynes, ISBN #1-85010-020-9

This book is ok, good detailed pictures and step by step how to. It doesnt directly cover the DGV but it does cover the DGAV, the auto choke version , which is similar in design and operation.

2. Weber Carburetors by HPbooks, ISBN # 0-89586-377-4 authored by Pat Braden.

This book goes a really indepth on the history of Weber as a company and is an interestng read by itself.

Again this book covers the DGAV but it works for both. Carbs are broken down bit by bit in a diagram provided by Weber along with picture breakdowns.

I think the single most helpful tool for me so far has been the Synchrometer i bought on line at one of the Weber web sites. You also have to buy an adapter but you can tune the carbs very well with it, its very acurate. Right now I have them set at 7 kg/h which gives me a pretty good idle and is not too rich.

Honestly if you want a Carb with a lot of support and can give performance I would just stick with the round top early SU's. This is what i'm going to eventually. If someone can run 12 second quarter miles on them with a little modification , they're good enough for me . Also there is A LOT of support for them.

Good luck with the Webers and keep that Z on the road.

Later ,

-Steve

[mtdripo]

tranzor_z,

Thanks a lot for the info, but I think you are correct about the SU's. They do recieve a lot of praize around here, and I trust the fellow members opinios greatly. In any of those books you researched did they do a comparrison of these two carb options? If so, how did the feel?

Thanks,

Dan

[tranzor_Z]

Those Weber books are just for Weber carbs thats it. As far as a difference in the carbs i'll let you know when i go to the SU's.

-Later

-Steve

[Bleach]

Also, I have found that those Weber carbs come with 140 and 135 jets in them standard. Those carbs are made to run a 2.2-2.4L 4-cyl engine (each) and run a bit rich at that.

Now that your fuel supply is constant, try jetting down the primary's a lot and the secondarys a little. It is hard to tell if you are running too rich because the power loss is not as easy to notice. I got some tips on tuning the Weber carb from www.dimequarterly.com which is aimed at tuning a single Weber DGV on an L20b or L18 engine. The same principles should apply to the 2.4L or 2.8L but really each one should be tuned as though it was running a very small engine of 1.4L or less.

http://www.dimequarterly.tierranet.com/articles/tech_weber_tuning.html