springs on throttle bodies

[Johan123m]

I guess the returnsprings on my throttle bodies ('73 mfi) are worn.

the throttle plates don't return to a full stop so the micro switch isn't engaged and the car starts running way to rich

Last weekend the engine even died on me from to much fuel when I stopped at a traffic light (and I couldn't get it started again)

Is it an easy fix to change these springs? are they still available at porsche?

or is their another cause...i read in some treads the throttle valve bushings could be worn?

I don't want to spend to much on a rebuild of the throttle bodies because I'm building a new engine, so a temporary solution will work. Put an extra spring on the throttle linkage perhaps?
Thanks
Johan

[Flieger]

First, always remember the proper sequence to tune MFI from the Bosh "Check, Measure, Adjust" manual.

The way to fix this is to send the throttle bodies, crossover linkage, and everything to a place like Eurometrix but you say you don't want to. They will refresh bushings, bearings, and ball-cups. The throttle return spring is on the MFI pump and you should get a replacement.

The throttle bodies themselves are magnesium and the butterflies will wear grooves in the metal as the intake reversion pulses hit them from the S cam timing at low RPMs. This will allow air to bypass at low revs and cause noise and less power. The way to combat this is to set up the butterfly stop screws so that the butterflies are just barely open when on the stops so that they do not contact the inside of the magnesium bore. If yours are old and have a groove worn, they will need a pro to help them.

If your concern is to get the microswitch to close, just use the adjustment screw on the arm on the crossover tube/rod. Much like adjusting a valve, tighten the adjustment screw to get more throw on the arm and get more force from the throttle spring.

The microswitch only operates above 1500rpm, though. The RPM transducer/speed switch sends the signal that the engine is above 1500rpm, allowing the microswitch into the loop. When the microswitch closes at that speed, it cuts off all fuel until the RPM drops to 1300, where the speed switch deactivates the microswitch and signals idle fuel flow to keep the engine from dying.

Maybe your MFI injection pump is set too rich on the idle end for your climate and driving style?

Remember to CMA before adjusting the pump, though.

[Mr9146]

Originally Posted by Flieger

First, always remember the proper sequence to tune MFI from the Bosh "Check, Measure, Adjust" manual.

The way to fix this is to send the throttle bodies, crossover linkage, and everything to a place like Eurometrix but you say you don't want to. They will refresh bushings, bearings, and ball-cups. The throttle return spring is on the MFI pump and you should get a replacement.

The throttle bodies themselves are magnesium and the butterflies will wear grooves in the metal as the intake reversion pulses hit them from the S cam timing at low RPMs. This will allow air to bypass at low revs and cause noise and less power. The way to combat this is to set up the butterfly stop screws so that the butterflies are just barely open when on the stops so that they do not contact the inside of the magnesium bore. If yours are old and have a groove worn, they will need a pro to help them.

If your concern is to get the microswitch to close, just use the adjustment screw on the arm on the crossover tube/rod. Much like adjusting a valve, tighten the adjustment screw to get more throw on the arm and get more force from the throttle spring.

The microswitch only operates above 1500rpm, though. The RPM transducer/speed switch sends the signal that the engine is above 1500rpm, allowing the microswitch into the loop. When the microswitch closes at that speed, it cuts off all fuel until the RPM drops to 1300, where the speed switch deactivates the microswitch and signals idle fuel flow to keep the engine from dying.

Maybe your MFI injection pump is set too rich on the idle end for your climate and driving style?

Remember to CMA before adjusting the pump, though.

Sorry, Max, but you just gave him a whole lot of unnecessary information.

Johan, just try some WD-40 on the springs/shafts and a little grease on the ball sockets. DO NOT MAKE ANY ADJUSTMENTS!!!

If you continue to have problems, and you just want to band-aid the issue, then add another return spring - preferably on the crossbar or on the bell crank on the side of the transmission. However, that will only serve as a band-aid and the "problem" will still need to be addressed.

[Flieger]

I'm just saying that the microswitch is probably not the problem if his car is stalling while idling at a stoplight. The idle speed should not be high enough to allow the microswitch to cut off fuel.

He is probably correct in his thinking that his system is worn out in more ways than just the spring.

[Johan123m]

Thanks for your responses!

I know the right way to solve this isue would be to have the throttle bodies rebuild (by eurometrix f.e.)

This is the way I will go with the 2.4S-engine I'm rebuidling that will replace the tired 2.4T that is currently in the car

I've tried the WD40 and grease-routine, but it didn't make a difference....

So, just to be able to drive this summer, I installed an extra spring on the crossbar and it works great! Car idle 's lower and microswitch is actived properly.

Btw. what's the best place in us or europe to send out my s-mfi-pump for an overhaul? are there a lot of price-differences?

[Flieger]

From the Pelican MFI Resources page:

Pacific Fuel Injection (Gus Pfister)

Suite B, 153 Utah Av
South San Francisco, CA

Tel. 650-588 8880


Jerry Fairchild Industries (Robert Turner)

5242 Westside Rd
Redding, CA 96001

Tel. 530-241 1592


Walz Diesel Fuel Injection (Norbert Schuller)

Sydney (expensive)

Tel. 02-9755 1422


Eurometrix (throttle body rebuilder)

228 Boston Rd

Groton, MA 01450
Tel. 978- 448 2557 (Matt Blast )


Phil Sumich (throttle body rebuilder)

Brisbane

Tel. 07-3390 8133


Super Tec (throttle body rebuilder)
Tel. 714-429 1863

[Jim727]

And: http://www.koller.de/

[jtsilverfox]

Hi Johan123m,
I realize it's been a while (!) but I just found this old thread and was wondering if you might recall what kind of spring you used on the crossbar (per your 6/22/08 post), and where you mounted it? I've got a '69 911E with similar issues.
Thanks,
cheers, jt (jtsilverfox)

[shadowjack1]

Last time Johan was on was May 2014

[jtsilverfox]

Thanks shadow,
That's what I was afraid of, but thought I'd give it a shot anyway...
cheers,
jt

[Jeff Higgins]

Any auto parts store that caters to the hot rod set will have a selection of carburetor return springs. Here is one idea, but I don't think it will work as well if the microswitch is still there.

[jtsilverfox]

Thanks Jeff,
Yeah, I've still got the microswitch, so this config wouldn't work for me, but I'll look for a workable location for the spring. And, Ive got an ACE hardware store with an excellent selection of springs. And if you google for "springs", there's lots of websites with tons of info & selection criteria. But an auto store might have a more appropriate spring (e.g., "carb return springs", etc).
cheers,
jt