View single post by Jensen Healey
 Posted: 05-24-2005 01:55 pm
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Jensen Healey

Joined: 03-11-2005
Location: San Anselmo, California USA
Posts: 983
Do you have Des Hammill's book? It was key in my battle with the Dellortos.

You mentioned an Allison ignition. I had a Crane Cams (same as Allison) optical unit on my car. It hit one of the bumps on the inside of the distributor cap and was pushed to the side causing a phasing problem. This means the rotor is not pointed at the tower on the cap when the coil fires. It leaves carbon tracking inside the cap which looks like ferns drawn with a pencil. You need a bright light to see them. You get a weak spark that leaves black crap on the plugs. Start the car after dark and look for a fireworks show. If you have none, ignore this paragraph.

Install new plugs. Trying to tune a car with fouled plugs is a waste of time. I use Autolite 64's because they are cheap and work great.

The Dells adjustment screws are a very fine adjustment and won't change the air-fuel mixture very much. Turn them in until they seat lightly and back off 4 turns. Do not adjust them without a 4 tube manometer. You can get a mercury version at your local motorcycle shop for $40 and it has the correct fittings for the Dells. The less toxic manometers cost more.

Balancing each carb involves making the stronger barrel run worse! Use the manometer to adjust each barrel for maximum vacuum and then open the bypass on the stronger barrel until it matches the weaker one. Do this for each carb and then adjust the linkage until the manometer is even across all four barrels. I tuned mine at idle and then gently increased the rpm to 3000 being careful not to suck the mercury into the engine. I re-adjusted slightly for best average of the two readings, a little worse at idle but a little better at 3000 rpm. I used a dab of silicone so the screws would not rotate due to vibration. There is a good write-up on this procedure by Tim located at:

You have to join Yahoo groups to view the file.

Now take your car to the local smog station and get a pre-test. Use the CO reading to determine if you are weak or rich. Shoot for about 2%.

Installing Dellortos is not for the timid. It took me 6 months to learn, digest and do the tuning. If you stick with it you will be very happy with the results.


P.S. Don't change the idle jets unless you know you are running lean. The emulsion tubes are the fine tune between each jet size.

EDIT It took me a while learn where the bypass (bleed) screws are. Not all carbs have the exact look or configuration. Check the diagram at

Last edited on 05-25-2005 02:32 pm by Jensen Healey