Hey guys, just put a weber carb on my 79 Brat. Found quite a bit on here by searching but no definitive how-to guide for putting a weber on an EA71. Well, I got everything connected and fired it up for the first time and it goes wide open! I have to shut it off immediately. I did some adjustment of the set screws with no luck. The throttle cable is disconnected so that's not causing the problem. I am a novice with carbs, or anything under the hood for that matter. Does anyone know what could be causing the issue? It's fully closed until I turn the key to start.

When you say wide open are you describing what the carb physically does or do you mean the revs shoot to redline?  

 

What rpms does it go up to?  

 

What is your choke doing?  

 

Have you checked for vacuum leaks?  

 

What kind of throttle return spring set-up do you have?

Edited May 10, 201411 yr by ferox

Okay, not necessarily redline, but it goes straight to redline. Theres no tach, so I can't comment on RPMs. The choke is electric and I confirmed it has 12v switched power with a multimeter. I do not know how to check it. I do not know how to check for vacuum leaks, but I have capped off all unused lines from the original setup. Throttle return spring? I left everything on the way it came out of the Weber/redline box for the ea71. Let me know what to look for and ill describe it!

I experienced my throttle stick wide open a few times, then I changed out the old throttle return spring and it's been happy ever since. Basically it does what you think it does. The spring pulls the carburator closed when you take your foot off the gas pedal. If you don't have one, get one asap.

Here is what I'm talking about. 

 

From the look of your attached image you only have the standard weber return spring attached to the carby.

 

I would hazzard a guess that the venturi forces are forcing your main butterfly open (the engine is sucking enough air to open the butterfly)  causing the engine to rev harder causing the butterfly to open futher until it pulls the secondary open causing the WOT.

 

Just a guess, but Ive seen it happen years ago to an old 186 holden motor that ran until it disemboweled itself... funny and sad at the same time.

 

TOONGA

Thanks for the feedback everyone!

 

I don't believe adding a secondary throttle return spring is going to help with this situation.  None of my linkage moves when this issue occurs; only the butterfly opens (I hope I'm getting better with the terminology).  I tried to video what was going on:

 

 

 

Attached are pictures of the vacuum lines I capped off - can anyone tell me if these were correct?  Maybe I capped something I shouldn't have or misconnected a hose?  Please correct me if I'm doing something wrong, unsafe, or dumb.  Part of the reason I bought this awesome Brat is to learn by doing!  I expect to make mistakes along the way.

 

Thanks for all your feedback so far!

 

 

Alright everyone, the issue has been solved and it was a very simple one at that.  The carb tuning instructions that my weber came with skipped a step.  I looked up some generic carb instructions for a different weber model and compared them to mine.  Evidently before starting the vehicle the first time I needed to hold the butterfly completely open with my fingers and then rotate the linkage fully.  This set everything in place.  Now the linkage touches the set screws that its supposed to.  After some slight tuning, the Brat idles normally.  Now I just need to put the air filter back on, reconnect the accelerator cable, and take it for a drive. 

 

I will be adding a throttle return spring for the added benefit based on your feedback though.  Thanks!

Alright everyone, the issue has been solved and it was a very simple one at that.  The carb tuning instructions that my weber came with skipped a step.  I looked up some generic carb instructions for a different weber model and compared them to mine.  Evidently before starting the vehicle the first time I needed to hold the butterfly completely open with my fingers and then rotate the linkage fully.  This set everything in place.  Now the linkage touches the set screws that its supposed to.  After some slight tuning, the Brat idles normally.  Now I just need to put the air filter back on, reconnect the accelerator cable, and take it for a drive. 

 

I will be adding a throttle return spring for the added benefit based on your feedback though.  Thanks!

The throttle return spring is not really optional.  If you had installed one, then you would not have had to manually manipulate the linkage.  Absolutely install a real throttle return spring before you take it for a drive.