Rough idle on my 1971 ford mustang 302?

tundra2000

New member
It started after its been sitting for about 3-4 months, its got a msd distributor and msd box, its got a new holley 500cfm carb. When i took it out of the garage i ran it a bit then i ran some seafoam though it and ran carb cleaner in it too, but it will idle fine but when i put it in drive or reverse and hold the brake it will feel like its about to die and it will idle around 500 rpm. What's wrong?
And should i throw some traction bars on for an almost stock motor?
 
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