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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
| Posts: | 573 |
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By adjusting the idle mixture to max rich was able to drive to a nearby event on Saturday although with a lot of misfiring. (Snip)...
Don't tune for max "rich". Adjust each idle mixture screw as necessary to produce peak manifold vacuum in that inlet tract.
Start with all the Air Bleed screws seated closed. After the first round of peak manifold vacuum adjustments, "IF" the vacuum levels between throats in one carb are not equal, then open the Air Bleed screw in the stronger throat in order to weaken it's vacuum to match the vacuum in the other (weaker) throat. When you're done, only ONE Air Bleed screw should be open per carb.
When both throats on each carb are equal, if the two carbs are not equal, then adjust the balance screw in the linkage coupler between the carbs to bring the two carbs, ie, all four throats) into balance (ie, the same "Peak" manifold vacuum level.
Then screw each Idle Mixture screw in until seated, carefully counting turns as you go so you can put it back where you found it. Record the number of turns, then put the screw back where you found it, carefully adjusting for peak manifold vacuum.
There can be a slight difference in the number of turns out for each screw, but they should be close... in the same ball park. If there is a big spread in the number of turns out, then something is wrong... like twisted throttle shafts.
If the idle mixture screw settings are pretty uniform, then they should be about 3.5-3.75 turns out for a DHLA45E (fine pitch threads and long taper needle), or about 2.0-2.5 turns out for DHAL45 (no letter suffix).
If the Idle Mixture screws are turned out more than that, then the idle circuit is jetted too lean and you're trying to compensate by over-adjusting the mixture screws. Don't. Re-jet richer, then re-adjust the mixture screws for peak manifold vacuum. Repeat until the Idle Mixture Screws are in the ranges given above.
Also, use the 'Deserted Road Dyno' to confirm the Idle Jet size (no stumble approaching 3200 rpm).
Regards,
Tim Engel
Last edited on 03-23-2023 03:58 am by Esprit2