Weber not opening 100%

rhk109 · 07-08-2005, 08:59 AM

I have a set of Webers on a 3.0. For some reason I cannot get the throttle plates to open 100% with the pedal on the floor. I have all the slack out of the linkages. I have the plastic throttle pedal WITHOUT the adjustable stop. Am I missing something?

Steve@Rennsport · 07-08-2005, 09:10 AM

Hi:

Go ahead and adjust the throttle rod that runs alongside the transmission.

Rich76_911s · Rich76_911s's Garage

You might find some helpful information in this thread. there is a really good write up of rebuilding the carbs halfway down the page. Good luck

Rich

Weber rebuild

kucharskimb · 07-08-2005, 09:17 AM

i had to change the ratio on the bell crank by the #3 cylinder. you can do this by removing the forward ball, drilling a hole maybe 1/4-3/8" lower, and reinserting the ball.

you have to be careful removing the ball, and you have to drill the hole with tight tolerances. after inserting it, you will need to mushroom the backside of the ball post. you can also purchase the balls with threaded posts w/nuts.

it's not the prettiest thing, but it gave me what i needed. this will give you less mechanical advantage with your foot.

another thing you could do is change the offset on the bellcrank that is on the side of the tranny. it is currently about 100 degrees between the two axes. it should be about 70 degrees for maximum efficiency. however, this will change the length of the diagonal rod that runs from the tranny to the carb by about 1" (longer). my diagonal rod doesn't have that much adjustment left.

good luck

rhk109 · 07-08-2005, 01:24 PM

Quote:

Originally posted by Steve@Rennsport
Hi:

Go ahead and adjust the throttle rod that runs alongside the transmission.

Shorter or longer?

silverc4s · silverc4s's Garage

Longer will open the butterflies more at full throttle, also raise your gas pedal a similar level at idle...

rhk109 · 07-09-2005, 06:18 AM

Quote:

Originally posted by silverc4s
Longer will open the butterflies more at full throttle, also raise your gas pedal a similar level at idle...

I took a look last night and I think shorter should be the way to go. In theory going shorter should raise the throttle pedal. But there is a throttle stop on the bell crank that limits the upward travel of the pedal. So I think the only gain in changing the length of this rod is taking slack out of the system and maybe changing the geometry of the bell cranks?

Am I missing something?

silverc4s · silverc4s's Garage

By jove, i think you are correct! It is kind of counter intuitive, at least to my feeble brain...;-))

911pcars · 07-09-2005, 10:53 AM

"Am I missing something?"

Try tackling this from the other direction to better visualize what you have to do.

Disconnect the carb. link at the gearbox bell crank, then block the throttle linkage at the carb(s) so it's WOT. Go back to the gearbox bell crank and see how far it must rotate for WOT. Adjust the length of the throttle cable, gas pedal height and static angle of the gearbox bell crank so the whole system allows the throttle to open at least this amount... and to close. Adjust the pedal stop to limit overstressing the WOT position.

This is one fix that results in at least a couple of thousand more revs and probably 50 HP.

Hope this helps,
Sherwood
http://members.rennlist.org/911pcars