Weber 38/38 Linkage / Off Idle Performance

[Tom H]

Hi all. I'm a relitivley new member. I bought my '73 Bavaria about a year ago and have been slowly making improvments with lots of help from the archives here. The car came with a newly installed new (Spanish) set of Weber 38/38 with the Redline linkage setup. The problem I'm having is that coming off if idle is very difficult to do smoothly. The pedal is very stiff when the car is idling and to get past the stiff point half the time I overshoot and it ends up at maybe 20% into the throttle. It makes for a pretty jerky experiance. When the engine is off, the hard spot is not there. I wonder if I'm pushing against the vacuum pulling the throttle blades closed, that's what it feels like. Last summer as was able to adjust the position of the drop arm off the firewall and the idle postition of the bell crank, so that the bell crank was sitting all the way back on it's stop arm when the car was at idle, and this improved things, but not completely.

I've been told that the Redline linkage is not the best, and that changing the linkage may correct the problem, but all the options that I've heard about seem to be NLA.

If anyone has any ideas or insights, it would be greatly appreciated.

Thanks.

additional details:
-3.0 engine, assumed stock, s/n on block indicates '75 e12
-5sp OD Gettreg trans, possibly also from '75 e12

 

[Coast Motor Werk]

Those (Outlaw) carbs are going to be a challenge. Ideally you want the progressive 32/36 carbs. This will give you much better mid throttle. Like https://www.ebay.com/itm/402743386280

 

[Tom H]

Right. That would be one way to fix it. I see that others have 38s and seem to be happy with them, so hoping to find some less drastic options. But point taken.

 

[Dick Steinkamp]

My Bavaria came to me with the 38/38s. Initially I was leary of them with my all stock 3.0, but after dialing them in, they are quite nice. Good idle. No flat spots. 20 MPG on a corrected odometer on a long highway trip. I'm a believer now.

One of the things I corrected was the linkage. I had the same off idle firm spot. I felt it most after a complete warm up to operating temp. It got so bad that it would chirp the tires when it finally (quickly) made it past the firm spot. Quite frankly, I don't remember what I changed, but no new parts were added and I didn't mess with the stock portions of the linkage (from the pedal to the bellcrank on the block under the intake manifolds). This is how the linkage looks now. I can take more pics if needed. The pedal is now very linear, has full travel, and no firm spots.

 

[Coast Motor Werk]

My Bavaria came to me with the 38/38s. Initially I was leary of them with my all stock 3.0, but after dialing them in, they are quite nice. Good idle. No flat spots. 20 MPG on a corrected odometer on a long highway trip. I'm a believer now.

One of the things I corrected was the linkage. I had the same off idle firm spot. I felt it most after a complete warm up to operating temp. It got so bad that it would chirp the tires when it finally (quickly) made it past the firm spot. Quite frankly, I don't remember what I changed, but no new parts were added and I didn't mess with the stock portions of the linkage (from the pedal to the bellcrank on the block under the intake manifolds). This is how the linkage looks now. I can take more pics if needed. The pedal is now very linear, has full travel, and no firm spots.



View attachment 162917


View attachment 162916


View attachment 162918

View attachment 162919

Yes, your linkage is setup for the least reaction from the pedal. I still believe the 38/38 is too much carb for a 3.0L and the mechanical secondaries come in very quickly, too quick for street use Imo. Even so, the progressives still need re-jetting in every car I have installed them in but not a big deal.

 

[dang]

Great post. I have the exact same problem with my '69 E3. M30B35 3.5L with 38/38 Webers. It is very difficult to drive smoothly with the current linkage setup and I was planning on changing the throw to be less movement, like Dick's setup. I have to dive back into it as soon as I get some time. I don't remember how I thought I could fix it.

 

[Tom H]

My Bavaria came to me with the 38/38s. Initially I was leary of them with my all stock 3.0, but after dialing them in, they are quite nice. Good idle. No flat spots. 20 MPG on a corrected odometer on a long highway trip. I'm a believer now.

One of the things I corrected was the linkage. I had the same off idle firm spot. I felt it most after a complete warm up to operating temp. It got so bad that it would chirp the tires when it finally (quickly) made it past the firm spot. Quite frankly, I don't remember what I changed, but no new parts were added and I didn't mess with the stock portions of the linkage (from the pedal to the bellcrank on the block under the intake manifolds). This is how the linkage looks now. I can take more pics if needed. The pedal is now very linear, has full travel, and no firm spots.



View attachment 162917


View attachment 162916


View attachment 162918

View attachment 162919

Ah, yes. The last linkage arm to the carb; yours is on the closest (least movement), and mine is on the furthest (most movement), as also noted by Coast Motor Werk. This makes a lot of sense to me, and is worth a try. I kept thinking I need longer levers for more leverage, but slowing that last lever down is worth a try.

 

[Tom H]

Great post. I have the exact same problem with my '69 E3. M30B35 3.5L with 38/38 Webers. It is very difficult to drive smoothly with the current linkage setup and I was planning on changing the throw to be less movement, like Dick's setup. I have to dive back into it as soon as I get some time. I don't remember how I thought I could fix it.

dang, Yes I think this could help us. Let us know what you find.

 

[Tom H]

Yes, your linkage is setup for the least reaction from the pedal. I still believe the 38/38 is too much carb for a 3.0L and the mechanical secondaries come in very quickly, too quick for street use Imo. Even so, the progressives still need re-jetting in every car I have installed them in but not a big deal.

I've had to rejet these 38s way leaner than out of the box, and also bypassed the power valve to rein the extremely rich running when I got it. But that is another thread

 

[Tom H]

It worked! I first tried the closest (least movement) on the last link, like Dick's, but I wasn't able to get full throttle. I went to the middle position on the last link and can now get full throttle and the hard spot is gone. It's night and day different.

Thanks all!

 

[Coast Motor Werk]

What no vacuum advance?

 

[ricsix]

Hi All,

I'm re-vamping this post as I'm having a similar issue with my 38/38s. That is, there is a stiff spot in the first portion of the accelerator pedal travel. The 38/38s only accentuate this of course, and like @Tom H mentioned above it can give quite a jerk, particularly after the car warms up to operating temp. I have the Redline throttle linkage as shown above in this post (which I really really don't like), and have the carbs located on the middle of the three positions available on the arm. While this is gives less of a jerk than when the the carbs are linked to the outmost position, it still is an issue.

So, I'd like to try the innermost position, but I'm not able to get to full throttle when the carb is linked there. It think I could pull this off if I had a super short linkage arm between the carb and the arm as the photo shows (taken from @Dick Steinkamp 's post above. Dick, do you know where I could purchase two of these short arms? The shortest I can find is about 3x as long.

Also, are there any other options for 38/38 throttle linkages besides the Redline? I did a lot of Googling but didn't see anything.

Thanks All!

Ric

 

[Dick Steinkamp]

Dick, do you know where I could purchase two of these short arms? The shortest I can find is about 3x as long.

Ric,
I don't. The linkage came to me on the car. I only rearranged it somewhat. My guess is that these pieces are not proprietary or unique to Redline. Hopefully someone here has a source for them.

 

[ricsix]

Ric,
I don't. The linkage came to me on the car. I only rearranged it somewhat. My guess is that these pieces are not proprietary or unique to Redline. Hopefully someone here has a source for them.

Thanks Dick, I'll keep digging around the interwebs and post anything I find here as well.

 

[Tom H]

Hi Ric,
I think those short linkages are from the factory linkage set up. Looking at realoem, mine are shown as part 1 and 14 on this drawing: https://www.realoem.com/bmw/enUS/showparts?id=4512-USA-03-1973-E3-BMW-30SBav&diagId=13_0765 The one with the springs is easily adjustable with the center wheel and is used to sync the two carbs, you only need one of them with the springs. Doing a quick search of the part numbers listed for mine on realoem, it looks like they are NLA. I hope you have your factory linkage still. If you don't, you may be able to make some fixed length ones, but I think the adjustable one is pretty important for syncing, but there could be other ways. My two short links are 35-40mm long (about 1.5") from the center of the ball ends, if it helps.

Good luck. Let us know what you figure out.

 

[Coast Motor Werk]

Hi All,

I'm re-vamping this post as I'm having a similar issue with my 38/38s. That is, there is a stiff spot in the first portion of the accelerator pedal travel. The 38/38s only accentuate this of course, and like @Tom H mentioned above it can give quite a jerk, particularly after the car warms up to operating temp. I have the Redline throttle linkage as shown above in this post (which I really really don't like), and have the carbs located on the middle of the three positions available on the arm. While this is gives less of a jerk than when the the carbs are linked to the outmost position, it still is an issue.

So, I'd like to try the innermost position, but I'm not able to get to full throttle when the carb is linked there. It think I could pull this off if I had a super short linkage arm between the carb and the arm as the photo shows (taken from @Dick Steinkamp 's post above. Dick, do you know where I could purchase two of these short arms? The shortest I can find is about 3x as long.

Also, are there any other options for 38/38 throttle linkages besides the Redline? I did a lot of Googling but didn't see anything.

Thanks All!

Ric

Additionally, do you have the 1/2 inch thick base spacers? This helps get the carbs in a slightly better angle for that linkage.

 

[ricsix]

Additionally, do you have the 1/2 inch thick base spacers? This helps get the carbs in a slightly better angle for that linkage.

Interesting, I'd have to go out and look, but I don't feel like they're that thick. I can see show that would help - thanks!

 

[Dick Steinkamp]

@ricsix these throttle linkage pieces just came up on Facebook Marketplace

Log into Facebook

Log into Facebook to start sharing and connecting with your friends, family, and people you know.

www.facebook.com

 

[Tom H]

@ricsix these throttle linkage pieces just came up on Facebook Marketplace

Log into Facebook

Log into Facebook to start sharing and connecting with your friends, family, and people you know.

www.facebook.com

View attachment 171041

You beat me to it, Dick! I was just going to post the same thing.

 

[ricsix]

Thanks guys, I think I just missed out on these!