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Runs rough under 2000rpm and only runs too rich

 
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WildP1  



Joined: 25 Dec 2020
Posts: 18
Location: Switzerland

PostPosted: Fri Nov 12, 2021 5:52 pm    Post subject: Runs rough under 2000rpm and only runs too rich Reply with quote

My 2.0 NA 1976 924 has a really rough idle and runs rough below 2000rpm. It gets better when warm but still is nowhere near perfect. The whole engine is shaking. As soon as I go over 2000 RPM it is really smooth and when driving it doesn't stutter or anything bove 2000 RPM.

Another problem is that it's running too rich. When I adjust the air fuel mixture screw to make it run leaner it just runs a lot rougher.
Before I changed the fuel pump, accumulator and fuel filters it was at like 9% CO value. The lowest I got it to before it died was 3%. The pump and filters have made it run a lot better when driving. It used to stutter randomly but now it only does it below 2000rpm.

I have also replaced the ignition coil, spark plugs, plug wires, rotor and cap, points and breakers, condenser.
Could the injectors cause a problem like this?

Many thanks in advance
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924RACR  



Joined: 29 Jul 2001
Posts: 8794
Location: Royal Oak, MI, USA

PostPosted: Fri Nov 12, 2021 11:39 pm    Post subject: Reply with quote

Moved to General - you put this in 931, and you have an NA - get a lot more responses here!

Certainly the injectors should be checked for spray pattern, but I'm guessing you haven't checked your control pressure?
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WildP1  



Joined: 25 Dec 2020
Posts: 18
Location: Switzerland

PostPosted: Tue Nov 23, 2021 7:18 am    Post subject: Reply with quote

Thanks!
The spray patter didn't look too bad. I'm thinking it might just be timing related.
What is the control pressure supposed to be? I measured it once but didn't exactly know if the values were any good or not.
Thanks again.
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BTRacing  



Joined: 31 May 2014
Posts: 434
Location: Nortbrook,IL

PostPosted: Tue Nov 23, 2021 3:42 pm    Post subject: Reply with quote

I would start with connecting CIS gauges and monitoring fuel pressures. Most likely warm up regulator issue. It controls system pressure.
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WildP1  



Joined: 25 Dec 2020
Posts: 18
Location: Switzerland

PostPosted: Wed Nov 24, 2021 9:18 am    Post subject: Reply with quote

BTRacing wrote:
I would start with connecting CIS gauges and monitoring fuel pressures. Most likely warm up regulator issue. It controls system pressure.


Will have a look at this, thanks!
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scm924s  



Joined: 22 Oct 2010
Posts: 261
Location: Gloucester UK

PostPosted: Fri Nov 26, 2021 2:36 am    Post subject: Reply with quote

There are 2 screws governing idle and mixture, the idle is controlled by a screw on the throttle body and mixture controlled by a screw on the fuel distributor, both should ideally be adjusted by using an exhaust gas analyser getting it to around 2.5%.

Always a good idea to have a fuel pressure test kit when monitoring the Kjet system.
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WildP1  



Joined: 25 Dec 2020
Posts: 18
Location: Switzerland

PostPosted: Fri Nov 26, 2021 7:01 am    Post subject: Reply with quote

scm924s wrote:
There are 2 screws governing idle and mixture, the idle is controlled by a screw on the throttle body and mixture controlled by a screw on the fuel distributor, both should ideally be adjusted by using an exhaust gas analyser getting it to around 2.5%.

Always a good idea to have a fuel pressure test kit when monitoring the Kjet system.


I had it on a gas analyser and the lowest I got it to was 3.5% and everything below would make it die. It drove the best at around 9% which is waaay too much. I suspect timing or some leak in the intake system might be the problem.
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