Hope I can find some help with a little problem thats driving me crazy. I have 74 26' with a chev 454 conventional ignition dual fuel (gas/propane). Have replaced plugs, points, coil, wires etc but I can't set the timing correctly. The timing marks are on the drivers side but can't be seen due to the AC compressor etc and can't even see them through the wheel well either. Have tried adjusting by guess and prayer and can get close but I still get backfiring through the carb. Even had a small fire in the carb.. not the first time as I had replaced the carb before due to melted jets etc. Seemes to run smoother on propane than gas but I still get the odd cough and hack from it... any ideas ?????

Five cent answer:

Use your light on #5 or #8 lead and time from underneath. Pointer is on driver's side.

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Five dollar answer:

From the Chevrolet Motor Home Chassis Service Guide;

Set the ignition timing by following these instructions:

1. Refer to the Vehicle Emission Control Information Label located on the radiator support panel. Follow all instructions on the label.

2. With the ignition off, connect the pickup lead of the timing light to the number one spark plug wire (engines with the timing pointer mounted over the upper side of the damper), or to the number 5 or number 8 plug wire (engines with the timing pointer mounted at the lower left side of the damper). Use a jumper lead between the wire and plug or an inductive-type pickup. DO NOT pierce the wire or attempt to insert a wire between the boot and the wire. Connect the timing light power leads according to manufacturer's instructions.

3. Disconnect and plug the vacuum line at the distributor.

4. Start the engine and aim the timing light at the timing mark. The line of the balancer or pulley will line up at the timing mark. If a change is necessary, loosen the distributor hold-down clamp bolt at the base of the distributor. While observing the mark with the timing light, slightly rotate the distributor until the line indicates the correct timing. Tighten the hold-down bolt and recheck the timing.

On a motor home chassis with the engine having the timing pointer mounted at the lower left side of the damper, the timing light must be aimed up from beneath the vehicle. This procedure requires two people, one to observe the mark with the timing light while the second person makes any required adjustments at the distributor.

5. Turn off the engine and remove the timing light. Reconnect the spark plug wire. (Unplug and reattach the vacuum line at the distributor.)

Explanation:

The camshaft operates at half crankshaft speed. The distributor is driven by the camshaft at a 1:1 ratio, so also operates at half crankshaft speed. That means that the timing mark on the harmonic dampener goes around twice for one complete distributor revolution. So, one time you line up the marks, the distributor is firing #5 cylinder and the next time it is firing #8 cylinder. This can be observed by removing the distributor cap and watching the balancer as the crank is rotated slowly by an assistant who is also watching the rotor.

The firing order is 18436572, so the same situation exists for four pairs of cylinders. 1 and 6, 8 and 5, 4 and 7, and 3 and 2. You will observe that these plug wires are opposite each other on the distributor cap.

Thanks for the info.. I'll have to give it a try.

Bill:

Thank you very much. You are a gifted tech writer.

Timothy

Well, the bulk of that was lifted from the GM manual, so I can't take too much credit.

DGTilley, if you get it figured out I would like to hear about it. In my '73 the only way I could figure out how to see the timing mark is with a mirror and flashlight :~) I found having a co-pilot turn the distributor while I drive it down the highway gets it pretty close.

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Bill & Diane
1973 25'
454 CID P-30 Chassis
German Shepard Dog