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1976 924 Idle gets rough after a short time

 
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WildP1  



Joined: 25 Dec 2020
Posts: 6
Location: Switzerland

PostPosted: Sun Feb 21, 2021 11:31 am    Post subject: 1976 924 Idle gets rough after a short time Reply with quote

Hello all,

My 1976 NA 2.0 924 has a rough idle. Compression is good. After I found and fixed a bad vacuum leak it ran okay in all RPM, though the idle was never below 1000RPM and when adjusting the air/fuel mixture screw it didn't run as smoothly at 800-900RPM. After standing for a week the cold starts were still quite good but after a minute or so it gets really rough but throttle repsonse isn't suspiciously bad. The idle on a warm-ish engine is bad straight away.
I bought it after it has been standing for at least a year with a disassembled engine.

Link to a short clip of it after a cold start: https://youtu.be/L_iCS8Nj_1w

Any suggestions on what it could be?

Thank you very much in advance!
Cheers.
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Harm  



Joined: 02 Apr 2009
Posts: 1373
Location: Holland

PostPosted: Sun Feb 28, 2021 1:13 am    Post subject: Re: 1976 924 Idle gets rough after a short time Reply with quote

Please do post in General Discussions.

First question:

— The OLDer engines use old fashioned Spark Distribution by 'Points'. Did you look into the Spark Distributor's housing and measure/set gap?

Then

— See if enough fuel is able to reach the Fuel distributor (probably is, since it clearly starts running by the Cold Start Valve and/or WUR).

— Check if every single injector gives an even amount of fuel in a good cone. Hot start problems will happen when injectors don't hold pressure and leak after shutdown.

— Did you use a timing light and check the dot on the back of the cam wheel? There is a difference between front and rear dot. Use the right one: check TDC.

Document/fotograph your current setup of fuel/timing/mixture before you take it all over the place .

When running almost perfect: Check AFR and CO2 for verification exhaust fumes are in spec and the engine isn't running to lean (and burning your rings).
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WildP1  



Joined: 25 Dec 2020
Posts: 6
Location: Switzerland

PostPosted: Mon Mar 01, 2021 6:23 pm    Post subject: Reply with quote

Thank you for the reply! Will put it in general discussion next time.

The timing and the distributor gap should be set correctly. I double
checked the timing with a timing gun too.
I will check the fuel flow to the distributor and also check the injectors. Shall I crank the engine when I've pulled out all injectors and see what the spray pattern/ amount of fuel coming out looks like?

I took it for a drive (about 50km) and it idles better now but doesn't idle nicely below 1000rpm. I think I will have to drive it more and it might clear up a bit. I think the mass air flow sensor might be stuck a little and it could get better if I drive it for a while. Under full throttle it runs really smoothly but at like 3-4k rpm it stutters a bit.

Thanks.
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anthonimartini  



Joined: 17 Feb 2020
Posts: 115
Location: portland oregon

PostPosted: Sun Mar 21, 2021 7:35 am    Post subject: Reply with quote

your warm up regulator is out of spec causing lean running on a warm engine. you need a fuel gauge set to check and remedy. you may need to find a good one or try to rebuild yours.
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WildP1  



Joined: 25 Dec 2020
Posts: 6
Location: Switzerland

PostPosted: Sun Mar 21, 2021 11:48 pm    Post subject: Reply with quote

Thanks a lot for the advice, will definitely take a closer look at the WUR.
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