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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
| Posts: | 572 |
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Which DHLA carbs (40, 40E, 45 or 45E ?), what choke size, and how are they jetted?
Are the carbs mounted to the manifold with proper soft mounts, O-rings, and either springs (Thackeray washers) or rubber grommets under the Nyloc nuts? Are they correctly tightened 'just enough', or cranked down hard (metal-to-metal)? There should be a 'uniform' 1.0mm/ 0.040" gap between either side of the softmounts' sandwich plate and the carb & manifold mounting flanges (a 0.89–1.27mm/ 0.035-0.050" range works).
Have you accurately balanced the carbs? If so, how? 4-tube manometer, Synchrometer, Uni-Syn, by ear?
How are the Idle Mixture Screws adjusted... how many turns out from fully seated? Four screws, four answers.
How are the Air Bleed Screws adjusted? Ideally, all should be closed and seated. In the event of an imbalance within one carb (like, just #4 is lean), only the one Air Bleed on the stronger throat should be cracked open, and only the minimum amount required to weaken the stronger throat's manifold vacuum to match the weaker throat's.
In the videos you emailed to me, the spitting sounds like a lean mis-fire. That could be because the carbs are jetted & adjusted too lean, or there's an air leak somewhere in the #4 inlet tract, or the soft mounts are tightened down too tight (ie, metal-to-metal, and no longer 'soft').
With the engine running, slowly pull the enrichment device ('choke') on. Does the situation improve? If yes, then the choke's richer mixture is compensating for a too lean mixture. That's not a 'fix'. It only confirms that too-lean is the problem, but the question is still 'why'.
With the engine running, spray a combustable liquid (aerosol carb cleaner or brake cleaner, etc) around each soft mount's joint perimeter. If the lean-miss goes away, and/or if the idle rpm increases, that indicates an air leak. Similarly, spray around the joint perimeter between the intake manifold and the head. If you find any leaks, fix them before going any further.
Answer the above before we start throwing a lot of blind guesses at the wall.
Regards,
Tim Engel
Last edited on 11-18-2021 06:32 pm by Esprit2