Technical & General Discussion Area > Tech Torque Pre 1973

67 Running Issues

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Azz67:
Hey all,
I'm needing some advice on an issue that cropped up several weeks ago.
Car starting running weird with occasional stutters and hesitation and poor low speed acceleration, which worsened to backfiring. 
I checked the carb over the weekend (Holley 600) and it appeared to be jetting fuel ok from the front 2 nosels. The idle seems to be ok with no noticeable rpm drops or hesitancy that I can detect.
I pulled 6 spark plugs to check for condition and gapping - photos attached. They all appeared generally like this and uniformly gapped at 0.040".

They look fairly carbon fouled which is a sign of running rich am I right?
Am I also right in saying these carbs are sensitive to drops in air temps, I live in Qld but it has been cold so I'm wondering if some adjustment of air/fuel is required?

Motor is late model 5.0.
Would appreciate any assistance to try and fix the issue.

Cheers
Aaron.

unilec5544:
It looks like your Holly needs a rebuild and also an engine timing check.You can buy rebuild kits for the holly, where by you can rebuild it yourself, or take it to a carb shop and have it rebuild.

Bucks:
Could be as simple as bad fuel, blocked filters/jets/stuck float valve or timing.

GLENN 70:
Just put a new set in . NGK only and a 5 heat range . Might need a good hwy run to clean it out .

minipete:
What fuel do you use?

I took my car to a carburettor specialist when I first got it because it would blow black smoke on acceleration and was fouling plugs.

Problem was mostly oversized jets but he suggested I not run 98 in my 289.  He said the 98 was too dense and old cars struggle to burn it properly.

I thought I was doing the right thing.  He suggested 95 octane and now the car runs much better with no black smoke on acceleration.

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