1974 1.8L engine fast idle then stalls, Fuel injection issues Options

[tshih914]

My 1.8L 914-4 with stock Bosch L?-Jetronic FI after being stored several years started to develop a hard to start problem. When finally started would stall when I give the gas pedal any input to raise the revs. I suspect there was some kind of intake air leak and while fiddling around had a backfire which blew the AF meter which I had Pelicanparts repaired. After replacing the fuel lines with the stainless ones from Tangerine Racing and flushing out the fuel system with Techron the engine started to run normally for a short time. Now the engine can be started and fast idles at 3000 rpm but again any input to rev up the engine results in stalling. The idle adjustment screw at the base of the throttle housing is fully closed. Any suggestions on how to fix?

[Van B]

See the little hole near the front right off the AFM? That's your air bypass screw.

[tshih914]

See the little hole near the front right off the AFM? That's your air bypass screw.

Thanks, now for my case is there any point in messing with that screw when it appears I already have some air bypassing the AFM?

Also since my decel valve appears to be farked up and there are no replacements has anyone opened one up to see if they can repair the damage?

[wonkipop]

See the little hole near the front right off the AFM? That's your air bypass screw.

Thanks, now for my case is there any point in messing with that screw when it appears I already have some air bypassing the AFM?

Also since my decel valve appears to be farked up and there are no replacements has anyone opened one up to see if they can repair the damage?

i probably wouldn't play with it at this stage.
its a new rebuilt AFM and theoretically should be about right.
but then again @Van B might have something to say.

i have never had to fool with mine.

i don't think you can open a decel.
its the sort of thing i would do of course.
attacking a fuel pump was a lot of fun.
but only with a spare to replace it.
i take the attitude destruction is likely.
i kind of looks like it would be pretty hard to get back together.
however there is a guy in australia who apparently rebuilds these things and other vac devices and has proper equipment to open up the crimping seams etc.
if it is farked up and won't respond to adjustment it will very likely be the diaphragm that is rat sh#t. so its pretty hard to fix unless you feel like becoming one of those kinds of experts.

[tshih914]

See the little hole near the front right off the AFM? That's your air bypass screw.

Thanks, now for my case is there any point in messing with that screw when it appears I already have some air bypassing the AFM?

Also since my decel valve appears to be farked up and there are no replacements has anyone opened one up to see if they can repair the damage?

i probably wouldn't play with it at this stage.
its a new rebuilt AFM and theoretically should be about right.
but then again @Van B might have something to say.

i have never had to fool with mine.

i don't think you can open a decel.
its the sort of thing i would do of course.
attacking a fuel pump was a lot of fun.
but only with a spare to replace it.
i take the attitude destruction is likely.
i kind of looks like it would be pretty hard to get back together.
however there is a guy in australia who apparently rebuilds these things and other vac devices and has proper equipment to open up the crimping seams etc.
if it is farked up and won't respond to adjustment it will very likely be the diaphragm that is rat sh#t. so its pretty hard to fix unless you feel like becoming one of those kinds of experts.

Just for the hell of it I google search " schematic of Bosch L-Jetronic decel valve" and came up with hit on last years' 914world post

http://www.914world.com/bbs2/index.php?showtopic=342479

Read all 3 pages and it appears that a 911 decel valve may be usable as a last resort. but the tests for proper function is given by GregAmy:

Testing the decel valve is fairly straightforward. With no vacuum on the port, the valve should be closed and you can't blow through it. Adding a vacuum via a Mity-Vac and the valve should open and you can blow through it. As I recall the desired setting for that cutover is 17mmHg?

If you can blow through it when it's off the car, and/or cannot blow through it with vacuum on it, then it's bad and/or out of adjustment. I wouln'dt be surprised if a prior owner danked around with the adjustment...

If it works fine but the cutover vacuum is either too high or too low, then it can be adjusted via that locknut and screw to ~17mmHg.

What are your current symptoms when testing in this manner?

[tshih914]

See the little hole near the front right off the AFM? That's your air bypass screw.

Thanks, now for my case is there any point in messing with that screw when it appears I already have some air bypassing the AFM?

Also since my decel valve appears to be farked up and there are no replacements has anyone opened one up to see if they can repair the damage?

i probably wouldn't play with it at this stage.
its a new rebuilt AFM and theoretically should be about right.
but then again @Van B might have something to say.

i have never had to fool with mine.

i don't think you can open a decel.
its the sort of thing i would do of course.
attacking a fuel pump was a lot of fun.
but only with a spare to replace it.
i take the attitude destruction is likely.
i kind of looks like it would be pretty hard to get back together.
however there is a guy in australia who apparently rebuilds these things and other vac devices and has proper equipment to open up the crimping seams etc.
if it is farked up and won't respond to adjustment it will very likely be the diaphragm that is rat sh#t. so its pretty hard to fix unless you feel like becoming one of those kinds of experts.

Just for the hell of it I google search " schematic of Bosch L-Jetronic decel valve" and came up with hit on last years' 914world post

http://www.914world.com/bbs2/index.php?showtopic=342479

Read all 3 pages and it appears that a 911 decel valve may be usable as a last resort. but the tests for proper function is given by GregAmy:

Testing the decel valve is fairly straightforward. With no vacuum on the port, the valve should be closed and you can't blow through it. Adding a vacuum via a Mity-Vac and the valve should open and you can blow through it. As I recall the desired setting for that cutover is 17mmHg?

If you can blow through it when it's off the car, and/or cannot blow through it with vacuum on it, then it's bad and/or out of adjustment. I wouln'dt be surprised if a prior owner danked around with the adjustment...

If it works fine but the cutover vacuum is either too high or too low, then it can be adjusted via that locknut and screw to ~17mmHg.

What are your current symptoms when testing in this manner?

I wonder what is the diaphram (redline in schematic) made of rubber or metal? If rubber then age will lead to hardening and cracking