"Very stuck" throttle question

[Markos]

'71 - Weber Carbs. This is my first carbed car, first BMW, and the first time I've spent looking at fuel delivery on this thing. I noticed this problem when I bought my car, which was the last time (and only time) I drove it. The gas pedal sticks to the floor. I originally thought it was hanging on the carpet, as it does interfere.

I searched around this site and there are several threads on the subject, mainly referring to idle issues. I read about an extra spring near the A arm on the block, but I don't see any spring that attaches to a thin bracket on the oil filter mount. The pedal return spring feels like it is a bit worn out as well.

Should there be any spring attached here? What is that extra hole for?

No spring bracket here:

I disconnected the main rod that goes from the pivot point on the firewall to the A arm on the block, as seen in the first pic. When I turn the arm to move the carbs into full throttle, the A arm locks into place. There is no visible way to unlock it, other than the weak pedal return spring under the dash. I searched through www.realoem.com and can't find any of the throttle linkage info.

Second question, much less important right now. At full throttle, should the butterflies be at 90 degrees? Mine are close to 45 degrees, but you can manually open them to 90 if you push on the butterflies. I noticed that I have slight interference with one of the dog bones and the choke, maybe a mm or two reduction in travel. It looks like I can move the main throttle rod a few millimeters back towards the firewall.

Interference between dog bone and choke. This clears the choke on the carb closest to the firewall.

As you can see, my WOT isn't very wide open...

 

[Honolulu]

you'll need to go into this yourself a bit more. Webers can get to a situation where the linkage goes "over center" or past the point it's supposed to stop, and locks there. This has been discussed before, so the Search function should bring it up. I don't have webs myself but we certainly read of them here.

Additionally, anything could have gone wrong with the linkage, the way it's installed, ... one can never know.

If visual inspection shows nothing obviously wrong, I'd suggest disconnecting the linkage and starting by examining the movement(s) of the carbs by themselves.

Butterflies should go vertical at maximum travel.

 

[Markos]

Great thanks. I'll still post up the pics in a bit. I ran out of time last night and was tied up today. I have Haynes Webber manual also. I'm not looking to tune the carbs now, but I don't want the throttle to stick. If it does I can put the clutch and and pray the pedal up with my foot. I just need to move the car down the street to a friend's garage while I put up new drywall.

 

[Markos]

you'll need to go into this yourself a bit more. Webers can get to a situation where the linkage goes "over center" or past the point it's supposed to stop, and locks there. This has been discussed before, so the Search function should bring it up.

Thanks for the lead. I haven't adjusted anything yet, but here is a thread warning of the getting stuck at wot.

http://e9coupe.com/forum/showthread.php?t=4558

 

[Stevehose]

Yes that happened to me on my first coupe when I replaced the Zeniths with downdraft Webers (mistake) back in the day. The linkage goes over center and locks open. Definitely an underwear changer.

Thanks for the lead. I haven't adjusted anything yet, but here is a thread warning of the getting stuck at wot.

http://e9coupe.com/forum/showthread.php?t=4558

 

[Sven]

Yes, you are missing a spring. There should be one around the pivot shaft of the linkage on the block. See photo.

 

[Markos]

Yes, you are missing a spring. There should be one around the pivot shaft of the linkage on the block. See photo.

Fantastic, thanks Sven! Hopefully they are still available.

 

[jmackro]

Yes, you are missing a spring. There should be one around the pivot shaft of the linkage on the block.

I'm not disagreeing that Markos' coupe may be missing that spring. But, as Stevehose wrote: "The linkage goes over center and locks open." Adding that missing spring to the bellcrank on the block isn't going to fix the over-center problem. If that is the cause of your stuck throttle, you'll need to adjust the linkage up near the carburetors - that can involve using a thicker heat isolator between the carbs and manifold, or adding a stop to limit rotation of the shaft between the carbs.

 

[Markos]

I'm not disagreeing that Markos' coupe may be missing that spring. But, as Stevehose wrote: "The linkage goes over center and locks open." Adding that missing spring to the bellcrank on the block isn't going to fix the over-center problem. If that is the cause of your stuck throttle, you'll need to adjust the linkage up near the carburetors - that can involve using a thicker heat isolator between the carbs and manifold, or adding a stop to limit rotation of the shaft between the carbs.

I agree completely. I have three identifiable issues. The throttle return is very stiff, due to what appears to be a missing spring. The second is the over cam situation, which creates the "very stuck" problem. Lastly, my butterflies don't open all the way, which seems to be unrelated.

It wasn't going past center after I hooked everything up. I drove the car offsite this morning so I am good until my garage project is done.

I'll dig into it next month

 

[jmackro]

Lastly, my butterflies don't open all the way, which seems to be unrelated.

In your first post, you make the statement "As you can see, my WOT isn't very wide open..." and then you posted a photo of the choke butterflies. Assuming the car was fully warmed up when you took that picture, you have a problem with the choke not fully opening. But have you looked down into the carbs to see whether the throttle butterflies are fully opening? My guess would be that they are.

 

[Markos]

In your first post, you make the statement "As you can see, my WOT isn't very wide open..." and then you posted a photo of the choke butterflies. Assuming the car was fully warmed up when you took that picture, you have a problem with the choke not fully opening. But have you looked down into the carbs to see whether the throttle butterflies are fully opening? My guess would be that they are.

Well there you have it! Like I said I know nothing about carbs! Does the vacuum generate at full throttle fully open up the choke butterflies? My WOT test was with the engine off.

Carbs sure are neat! I'm sure once I drive the thing more than a mile I'll long for fuel injection.

 

[Stevehose]

No you should have water or electric chokes that fully open them up when the engine is warm regardless of throttle position or vacuum. You can start the engine when cold and watch them progress from closed to fully open, usually about 5 min or so. If they don't fully open then you have an adjustment issue or faulty bi-metallic choke module(s). I suspect that having sat for so long, these carbs will need rebuilding.

The Weber book is good to get.

Well there you have it! Like I said I know nothing about carbs! Does the vacuum generate at full throttle fully open up the choke butterflies? My WOT test was with the engine off.

Carbs sure are neat! I'm sure once I drive the thing more than a mile I'll long for fuel injection.

 

[Markos]

No you should have water or electric chokes that fully open them up when the engine is warm regardless of throttle position or vacuum. You can start the engine when cold and watch them progress from closed to fully open, usually about 5 min or so. If they don't fully open then you have an adjustment issue or faulty bi-metallic choke module(s). I suspect that having sat for so long, these carbs will need rebuilding.

The Weber book is good to get.

Thanks! I actually have the weber book so I'll be educating myself soon. Too bad you can't get the audio version for my daily commute. I have water chokes. You can see the coolant line running to one in the second pic. Rebuilding them should be fun. I'm confident that I can do that, just don't ask me to adjust them when I'm done!

 

[Honolulu]

Markos, see if you can adjust the choke plate opening by rotating the choke element, before you get into the carbs. Although those Webers are a lot simpler than the original/stock Zenith carbs, there are still opportunities to get good and lost if this will be your first time.

It's common to assume that when something goes wrong, it's something drastic. Actually, many problems start with some simple thing. Worst of it is, Mechanic's Rule dictates that when you have a problem, carefully review whatever it was that you did last. Many of my "problems" have been self-inflicted, and I've been futzing around (technical term, you have to earn it) with my cars since 1970 or so.

All BMW models have a few quirks, some weak points, some "I wish they didn't do that" or "I wish they did that differently" items. And that's putting it nicely. Hanging around here will instruct you as to those elements that apply to our coupes.

 

[Markos]

From what I've read so far the torsion spring that Sven displayed is NLA. If anyone knows otherwise please let me know. I'll be measuring the shaft that it sits in and seeing what I can come up with below. I'm not sure how well I'll be able to add a hook to spring steel. I may need to search for something with hooked ends.

http://www.mcmaster.com/#torsion-springs/=z5ewiz

 

[Markos]

Update: The torsion spring is available. Carl carries them. I ordered a new torsion spring and a new fuel line tee from him today.

He asked if I had Webers, and mentioned that he has seen very few weber linkages setup properly. He mentioned the over center scenario and I confirmed that I had this issue. The spring will help my return but I'll need to adjust the linkages. He also discussed how the pedal return spring is on an adjustable slide so the pedal feel can be tweaked. I'll search the set for more info. I won't be touching the car for at least 30 days so that is it for now.