Carbs - achieving WOT

[toddu]

Former CIS car changes to carbs. I have an "early" bell crank on the granny, and an early rod from granny bell crank to bell crank on intake manifold. But, I'm still a little shy of WOT.

What do.I change next? 300hp 3.2ss on an engine dyno, I know I'm leaving a few of those ponies on the table.

Todd

[joefrantz]

Don't know if all is equal, because i went from 73 cis to 83 3.0l carbs.

I was about 25% short of full throttle with the original '73 cis rod and bell crank.
Kept the original bell crank; went to the early rod, and all is well.

I know there were different bell cranks, and somewhere there is a thread comparing them. I also suspect that the 901vs 915 mount location may be a variable. Is it possible that your early crank could be for a 901 car?

I'm speculating a bit here, and I don't have part numbers, but glad to take some measurements if it would help.

I would definitely compare your old and new bell cranks for difference in stroke.

[VFR750]

You can adjust the link to the pedal. Inside the tunnel.

Plus you may need to lengthen the link between the carb mounted bellcrank and the cross- shaft.

All of the links can be tweaked. It takes some time to get it right.

[Gordo2]

Todd,

I dread adjusting linkage to balance my carbs or trying to adjust the throw to get WOT while still getting full closure for idle.

It seems no matter how many linkage adjusters I play with - I find it very difficult to get to a near perfect set up.

In my case, I've found that the rod that goes from the bell crank (on top of the engine / attached to the intake manifold) to the cross bar (that connects the 2 banks of carbs), is simply too short and could stand to offer additional length adjustment.

I've been looking at extending this rod - either by cutting it in half, tapping the ends and adding a threaded coupler, or just replacing the original rod with a threaded rod that I cut to the required length.

Not sure your config is similar - but mine's a challenge as well...

Good luck,

Gordo

[chris_seven]

If you have the 'large' plastic throttle pedal you may find you need to shorten the 'blade' on the back of the pedal which works as a stop.

This will tend to hit the board a little too early when you move to carbs. It needs around 1/2" removing and then the throttles should fully open.

[VFR750]

I have a modified link that has a small threaded aluminum spacer. Same thing, that being longer helps the proportionality.

I also cut some of that plastic blade off.

Interesting difference comes from the type of manifold used. My Porsche original magnesium manifold was less of a problem. Got it all set up. When I went to the taller aluminum PMO intake, all the adjustments were affected, and I had to doors tweaks to get it to got to wot.

[zedsn]

The stop on the plywood board is gone from my 1977 and I was able to adjust the ball end behind the gas pedal to get the other 1/4 travel to fully open my weber IDA carbs.

[Geneman]

todd, i had same problem after switching to PMOs and it took me forever to get it figured out. included shortening long linkage rod from tranny to bc. ugh.. most of the vintage racers i run with, just bag the whole stock linkage and run a throttle cable from pedal to the motor. they mount it on top of the tunnel between the seats . pretty nifty . i will see if i can find pics. cheers frank

[chris_seven]

I just realised that the bell crank fitted to the manifold is quite a bit longer on the Solex 40PI carbs and changing this part will provide more throttle opening for a given travel.

I have all the blanks laser cut to make some of these quadrants and should have them finished in a few weeks.

[toddu]

I guess I need to spend a day tinkering. Should have mentioned that I have Rennline pedals, so all kinds of adjustment there.

Cable sounds interesting Frank!

Todd

[Farrell]

is this the correct piece you need for WOT to be achieved when using PMOs?

The part number is 901-423-026-02

[KTL]

Throw $550 at 901 Shop and they'll give you this Throttle Pedals

[LJ851]

Originally Posted by Geneman

todd, i had same problem after switching to PMOs and it took me forever to get it figured out. included shortening long linkage rod from tranny to bc. ugh.. most of the vintage racers i run with, just bag the whole stock linkage and run a throttle cable from pedal to the motor. they mount it on top of the tunnel between the seats . pretty nifty . i will see if i can find pics. cheers frank

Please do, i am interested in this. Any idea where they source a high quality, long throttle cable?

[toddu]

Farrell, that is the piece I have. I think the tunnel rod might be part of the issue.

Todd

[KTL]

Pegasus is a good source for throttle cables & hardware. https://www.pegasusautoracing.com/advcat.asp?CategoryID=CABLES

[Lapkritis]

Aren't there plastic spacer segments inside the tunnel that fall apart and lead to slack in the stock throttle system? I have an old set of PMO's in my car and similar adjustment is maxxed, some throttle left on the table.

[KTL]

Those plastic spacers are just guide bushings to support the rod as it runs thru the tunnel. But, yes, if those spacers have crumbled to pieces from gear oil contamination? There will be a considerable amount of slop in the rod due to flex or lack of support

The typical approach here is to shorten the rod that comes out of the tunnel. Doing so puts more "throw" into the gas pedal.

[LJ851]

Originally Posted by KTL

Pegasus is a good source for throttle cables & hardware. https://www.pegasusautoracing.com/advcat.asp?CategoryID=CABLES

Perfect, thank you Kevin.

[Farrell]

do you have to have the older 901 linkage to work with PMOs?

[Geneman]

kevin that 901 shop cable linkage is what is was seeing in those vintage cars. pretty nifty . but seems way overpriced for what you get. i have set up a similar system with a cable from pegasus