1969 427/400 backfires on startup

[Roger G.]

My 69 427 has a fresh rebuild, with about 600 miles, and had been doing pretty good until the weather got cold. She is getting hard to start, especially after setting awhile. This morning it took about 5 minutes to get her up an going. Also, I am getting a loud backfire every now and then when trying to start her up. It is a pretty loud pop. Could this be an issue with the choke, or maybe the timing?

[Terry M.]

Re: 1969 427/400 backfires on startup

Don't you love those three Holleys? Be careful -- backfires through the carburetor have the potential of damaging your power valve. Bad news that!

[Roger G.]

Re: 1969 427/400 backfires on startup

Don't you love those three Holleys? Be careful -- backfires through the carburetor have the potential of damaging your power valve. Bad news that!

Its a love/hate relationship

[Timothy B.]

Re: 1969 427/400 backfires on startup

Roger,

Sounds like the choke is not set correctly, probably best to get a service book and go through all the choke adjustments on the middle carburetor. After the car warms does it run ok.

[Roger G.]

Re: 1969 427/400 backfires on startup

Roger,

Sounds like the choke is not set correctly, probably best to get a service book and go through all the choke adjustments on the middle carburetor. After the car warms does it run ok.

Thanks, yes it runs great after it starts.

Usually on the first crank it will run for a couple of seconds then sputter out. I have been trying to pump the pedal a couple of times, then it seems to flood out.

[Timothy B.]

Re: 1969 427/400 backfires on startup

Roger,

Refer the service manual but on cold initial start the foot application should set the choke blade completely shut and when cranking the low pressure area created by this blade being shut pulls fuel from the venturi nozzle. After the engine starts the blade opens only far enough to keep the engine from loading up with fuel but maintains a rich mixture because there is poor fuel vaporization in a cold intake manifold. As the intake manifold warms the choke coil relaxes and opens the choke because the heat vaporizes the fuel load for proper combustion.

[Terry M.]

Re: 1969 427/400 backfires on startup

My 69 427 has a fresh rebuild, with about 600 miles, and had been doing pretty good until the weather got cold. She is getting hard to start, especially after setting awhile. This morning it took about 5 minutes to get her up an going. Also, I am getting a loud backfire every now and then when trying to start her up. It is a pretty loud pop. Could this be an issue with the choke, or maybe the timing?

One of the more difficult adjustments with the three duces is the throttle linkage. The end carburetors must close completely on shut-down/start-up or the center carb will be fighting the excess air from the end carb(s). There is an extensive set of instructions for this adjustment in both the FSM (Factory Service Manual) and the AIM (Assembly Instruction Manual). IIRC there is a TSB (Technical Service Bulletin) on this subject and one or the other of the sources I first mentioned is either not complete or not accurate. The TSBs are reprinted in the most recent edition of the 1968-69 TIM&JG (Technical Information Manual & Judging Guide). I would look for that TSB and follow those adjustments to the letter.