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> Cursed Bucking!, Fuel injection issue
Gcotton92203
post Mar 11 2015, 03:46 PM
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Hey, here's a stupid question. Anyone know where I can get a "GOOD" 1973 2.0 throttle positioner. I've developed that cursed bucking just off idle during slow acceleration but the rest of the power band is fine. I've cleaned up the circuit board as best I can and a new board may fix my problem but I'm not sure the contacts are all that great either so I'd just as soon replace the whole relay. Yeah, yeah, I know. put a carb on it. Just trying to stay as original as possible.
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monkeyboy
post Mar 11 2015, 04:35 PM
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Look up the number at Summit Racing. I am pretty sure Bosch still sells these.
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914_teener
post Mar 11 2015, 04:55 PM
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Check the alignment of the board "wipers" on the switch.

There is a procedure on the Bird Board and many threads here on it.

Dave Sprinkle is a member vendor and has new boards here.

Also check your fuel pressure and the fuel rail.
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somd914
post Mar 11 2015, 04:56 PM
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Take a look here:

http://www.914world.com/bbs2/index.php?sho...=95583&st=0

I bought one of these kits a few years back - good stuff.

Not sure if he is still around and making them...
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mepstein
post Mar 11 2015, 05:25 PM
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QUOTE(somd914 @ Mar 11 2015, 06:56 PM) *

Take a look here:

http://www.914world.com/bbs2/index.php?sho...=95583&st=0

I bought one of these kits a few years back - good stuff.

Not sure if he is still around and making them...

I think 914rubber has them
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warrenoliver
post Mar 11 2015, 07:44 PM
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I got one from BDStone914 - good guy to deal with. (IMG:style_emoticons/default/beerchug.gif)

Changing the board didn't fix my issues completely. Changing out the whole unit helped a lot.

YMMV

Warrenoliver
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JawjaPorsche
post Mar 11 2015, 07:51 PM
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http://shop.914rubber.com/Porsche-914-Thro...ly-914TPS17.htm
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davesprinkle
post Mar 11 2015, 08:18 PM
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I've got repair kits for the 2.0liter cars and the late 1.7liter cars. The new boards can help if the problem is caused by worn traces on the board.

However, there are other potential source of trouble -- the wipers can get corroded, there are little directional leaf contacts in the stem of the sensor that can corrode, and let's not forget about aged wiring terminals or broken wires.

So, yeah, a new board can help, but everything else needs to be OK.

A replacement board is only $35. If you need one, send me a PM.
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Gcotton92203
post Mar 11 2015, 08:45 PM
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I ordered the board today from 914 rubber. It's the cheapest I found at $48. and I've had good luck with their other products. I would have preferred to change the entire unit just to be sure. I'm sure someone somewhere in the world has a "new old stock" unit but I'm sure I'll never find it. I fully intend to keep this car as it is in great condition, no rust and I have very little money in it. Sooner or later I'm sure I'll switch to carbs but I'll always keep the F.I. parts for the day it's resold.
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914_teener
post Mar 11 2015, 10:13 PM
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QUOTE(Gcotton92203 @ Mar 11 2015, 06:45 PM) *

I ordered the board today from 914 rubber. It's the cheapest I found at $48. and I've had good luck with their other products. I would have preferred to change the entire unit just to be sure. I'm sure someone somewhere in the world has a "new old stock" unit but I'm sure I'll never find it. I fully intend to keep this car as it is in great condition, no rust and I have very little money in it. Sooner or later I'm sure I'll switch to carbs but I'll always keep the F.I. parts for the day it's resold.



Unh hunh. (IMG:style_emoticons/default/WTF.gif)
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dknechtly
post Mar 13 2015, 01:50 PM
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Hope you keep that FI in it. There are so many things to check. Do you have points? As they get closer is will run bad especially when first starting up. Also, check the resistance of the FI points. It should be as low as possible. Don't use emory cloth! Just a piece of note card or a jeweler's cloth. If it runs too lean, all kind of wierd things happen. Check that the mechanical advance is all nice and limber and no springs are broken.
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Gcotton92203
post Mar 13 2015, 02:18 PM
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QUOTE(dknechtly @ Mar 13 2015, 12:50 PM) *

Hope you keep that FI in it. There are so many things to check. Do you have points? As they get closer is will run bad especially when first starting up. Also, check the resistance of the FI points. It should be as low as possible. Don't use emory cloth! Just a piece of note card or a jeweler's cloth. If it runs too lean, all kind of wierd things happen. Check that the mechanical advance is all nice and limber and no springs are broken.

Wow! lots of good info. I just converted to a Pertronix but it still did the same bucking just off idle. I'm pretty sure it's a worn circuit board. I just hoped I could find a new complete replacement but I guess people in Hell want ice water too. I also believe I'll be facing the vapor lock issue as I sometimes hear gurgling in the gas tank when starting warm after several minutes rest. Other than that I have no other issues with the way it runs and intend to keep it injected as long as humanly possible
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marksteinhilber
post Mar 13 2015, 02:53 PM
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QUOTE(Gcotton92203 @ Mar 13 2015, 01:18 PM) *

QUOTE(dknechtly @ Mar 13 2015, 12:50 PM) *

Hope you keep that FI in it. There are so many things to check. Do you have points? As they get closer is will run bad especially when first starting up. Also, check the resistance of the FI points. It should be as low as possible. Don't use emory cloth! Just a piece of note card or a jeweler's cloth. If it runs too lean, all kind of wierd things happen. Check that the mechanical advance is all nice and limber and no springs are broken.

Wow! lots of good info. I just converted to a Pertronix but it still did the same bucking just off idle. I'm pretty sure it's a worn circuit board. I just hoped I could find a new complete replacement but I guess people in Hell want ice water too. I also believe I'll be facing the vapor lock issue as I sometimes hear gurgling in the gas tank when starting warm after several minutes rest. Other than that I have no other issues with the way it runs and intend to keep it injected as long as humanly possible

Try the suggested repair where you clean the contacts and /or move the finger to run on a new groove!
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Amphicar770
post Mar 13 2015, 05:48 PM
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Circuit board from 914 rubber had my 914 purring like a kitten.
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TheCabinetmaker
post Mar 13 2015, 05:56 PM
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Gently clean up the board with some 2000 grit wet/dry sandpaper then some lacquer thinner or alcohol.
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DRPHIL914
post Mar 13 2015, 10:41 PM
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QUOTE(warrenoliver @ Mar 11 2015, 09:44 PM) *

I got one from BDStone914 - good guy to deal with. (IMG:style_emoticons/default/beerchug.gif)

Changing the board didn't fix my issues completely. Changing out the whole unit helped a lot.

YMMV

Warrenoliver

(IMG:style_emoticons/default/agree.gif)
This is exactly what I saw too. The very slightly used one i got from bruce
Has worked flawlessly. Absolutely no bucking! Drove it 250 miles this week and didn't happen once.
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Gcotton92203
post Mar 27 2015, 10:50 AM
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Replaced the circuit board. Seems better but still bucks. Improved greatly when fully warm. I have a sneaky suspicion there's a loose ground somewhere.
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PancakePorsche
post Mar 28 2015, 12:17 AM
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Identical to my car a year ago. A NOS TPS did not help.
I went through the distributor by removing breaker plate and precisely setting trigger point opening, set timing, set ECU, and fuel pressure to 34 PSI.
Now has power everywhere, milage 30+ MPG highway, no bucking. Remember modern fuels are at least 10% methanol so you need to increase volume accordingly. Bucking=lean.
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TheCabinetmaker
post Mar 28 2015, 08:30 AM
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Tps does not typically cause bucking at off idle, but at cruise. 3200-3600rpm. I would look at dwell and timing.
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Bleyseng
post Mar 28 2015, 08:59 AM
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QUOTE(PancakePorsche @ Mar 27 2015, 11:17 PM) *

Identical to my car a year ago. A NOS TPS did not help.
I went through the distributor by removing breaker plate and precisely setting trigger point opening, set timing, set ECU, and fuel pressure to 34 PSI.
Now has power everywhere, milage 30+ MPG highway, no bucking. Remember modern fuels are at least 10% methanol so you need to increase volume accordingly. Bucking=lean.


yes, off idle is usually caused by sticking advance plates in the dizzy. TPS bucking occurs at 3000 rpm.
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