Bell crank ratios?

[RichF]

Alright I was having some problems with my carbs not opening all the way up after adjusting all the throttle linkage and a felllow pelican told me about "bell crank ratios" can someone tell me more about this.

Thanks, rich

[RWebb]

recent post:

The CIS tranny bell crank is about 1 cm longer than a corresponding
weber version. The angle between the two arms is also much wider. This
multiplies the movement of the arm and thus the more stiff, on/off
feel of the carbs.

For a better feel, find an early bell crank and then adjust your
linkages to fit it. Its time consuming. You could also just get used
to it. I got used to it for a year and then finally went in and fixed
it. I also think the tunnel rod is longer on the CIS version compared
with the earlier.

- jpnovak

911. 423.018.01 -

Pelican online catalog
911-423-017-01 -- Bell Crank, 911 (1974-86) -- $61.50
- must be for all CIS & DME cars with 915 trans.

911-423-017-02 -- Bell Crank, 911 (1987-89) -- $67.75
- must be for DME cars with G-50 trans.

[RichF]

thanks man

[RWebb]

I'm still not sure what bell crank is supposed to be used with carbs.

Does anyone know if it is the same one as for MFI?

[RichF]

Originally Posted by RWebb

I'm still not sure what bell crank is supposed to be used with carbs.

Does anyone know if it is the same one as for MFI?

x2 any webers experts out there that know whats going on? I did see a guy on there when reading some post that cut his bell crank up to make it work.

[Scott Clarke]

Are you sure that all of the bushings in the linkages are OK? Mine had rotted to the extent that, in one location, there was nothing left of the bushing! The result was 2/3 throttle, max.

[RWebb]

Yes, the bushings should always be examined. Mine are ok.

But I have compared 2 different cranks - and the arms are different lengths.

Here is the result of some perusing of the non-pdf version of PET:
901.423.027.02 1965 up thru 1968
901.423.027.03 for 1969 - 1971

911.423.017.01 for 1972-80 or later (these cars have the 915
trans., and may have MFI or CIS)

No separate p/n's are given for different models (T/E/S/L), suggesting that Webers, Zeniths, and Solex carbs - together with MFI - were all able to use the same bell crank.


The bell crank is called a "reverse lever" in the PET; shown in MG-7 (diagrams on pedals, hand controls)

[RichF]

Originally Posted by Scott Clarke

Are you sure that all of the bushings in the linkages are OK? Mine had rotted to the extent that, in one location, there was nothing left of the bushing! The result was 2/3 throttle, max.

I just replaced the trottle rod bushings about 1 month ago when i found out there wasnt bushing there anymore, my guess is they just fell apart over the years of use.

[Scott Clarke]

I'd check the bushing at the pedal bell crank, and the ones on the stacks/manifold bell crank. ALL of mine were either missing or so badly deteriorated that the linkage couldn't possibly get the throttles open.

[RichF]

I have checked everything and replaced what needs to be replaced soo its got to be the bell crank itself

[RWebb]

so what bell crank is on there now?

[Fishcop]

Working on this problem at the moment. I've got the crank off my original gearbox but I'm using the CIS one from my 915. Problem is that I can't change these cranks without dropping the tranny or the swing arm

[RichF]

why is that it should only be I bolt if i recall right and it slides out.

[RWebb]

The stud the bell crank is mounted on can (at least on some models) be unscrewed. No idea how hard that is...

[RoninLB]

around here shops weld up some of the space of the tranny bell crank slot and use stock CIS throttle cable and bell crank to engine rod.

if you get under there at the tranny bell crank you'll see the slack when activating the cable. From there you'll know how much to close up the slot.

i don't have a a pic of mine available. It's not pretty but a file will clean up the welding.

[Fishcop]

I'm going to d a little more fine tuning of the linkages - I suspect I can live with the "short throw" pedal, but I can't seem to achieve a full throttle without a too high idle when off the gas.

I will see if I can back the stud out that holds the crank ('83 915). If I can, I'll try the original.

[OZCarrera3]

Originally Posted by RWebb

recent post:
For a better feel, find an early bell crank and then adjust your
linkages to fit it.

I'm finalising the install of my PMOs on my C3 which has a 915 gearbox and I am having trouble getting full throttle and have the accelerator 'feel' issues discussed. So, just to clarify this post, I now need to get "an early" bell crank (Part No. 901.423.027.03) and re-adjust my linkages. I assume my car currently has the MFI/CIS Bell Cran (Part No. 911-423-017-01) which is causing the issue?

Conversely I could get another CIS Bell Crank pushrod (that goes the carb linkages through the tinware ) and modify it to close up the loop at the end as mentioned by Ronin?

[OZCarrera3]

Bump

[Mo_Gearhead]

Here's an old-school method and you will need an assistant.

Jack the car up and disconnect both of the throttle rods at the bell crank.

The guy under the car will need a ruler and good lighting. Have the assistant move the throttle rod (engine end) from closed to fully open. Note the "measurement" of movement from ...fully closed- to -WOT.

Now have him move to the throttle pedal and move it through its full movement. Again note the "measurement."

With a piece a graph paper you can draw out the two linear movements of the throttle rods and thus determine the length and angles needed for the bell crank which may need to be cut and re-welded - or new holes drilled. You can factor in the threaded portion of the rods to allow fine adjustments.

[RWebb]

what the world needs is a nice adjustable arm bell crank, made out of titanium