I don't know if this guy is known here or not That block is claimed to be original to an old style #4779 750 DP. I've bought stuff from him before, turned out OK. I'd MUCH rather have that than any overseas imitation. he's got other blocks up too.
Statistics: Posted by tmoble — Fri Apr 02, 2021 5:48 am
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In order to smarten these up, like Mark mentioned above... factory up-high idle feeds should be removed, ideally-sized (0.031" should suffice with your camshaft) idle feed restrictions should be installed down-low, and 0.082" transfer slot restrictions installed in the main body due to the effects of their usual transfer slots being too wide/long... starting with 0.070" IAB's is good...
Additionally, for smartening up of the main circuits, to make it work even better with the above improvements, with 0.028" PMAB's and 0.025" SMAB's... the middle (of the three 0.028"?) booster correction ("emulsion") bleeds should be blocked or have blanks installed... your 7.5"Hg power valve makes oodles more sense than the silly factory 4.5... then, with 0.063" primary-only PVCR's, something like #72 PMJ's and #82 SMJ's could go in...
Less having to fiddle with factory cams/shooters should be the result too...
Statistics: Posted by gntkllr — Sat Mar 27, 2021 4:57 pm
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When the engine is warmed up and at idle and in neutral you can snap the carb. just using the primary's and its all good. If you snap it hard getting into the secondary's there is just a slight hiccup and then it rev's up.
Driving, if you mash it from a stand still it falls on it face and then takes off, if you take off fairly hard but not floored its all good. On the highway, if you mash it at highway speed, (2,900 rpm) it hesitates slightly and then take's off.
When it warms up I will get after pump cams and nozzle's, thanks again
Statistics: Posted by 77k5 — Tue Mar 23, 2021 3:34 pm
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Idle AFR is ok at what you have, stick with highest vac. My apologies, I interpreted your first question of the best way to set the idle on a four corner carb as looking for a stable, consistent idle, not leaner idle. You will likely find that if you change up iab’s and ifr’s to lean transition fuel your engine will still want the 12.5 - 12.9 idle fuel for best vacuum. You may be getting good combustion at idle whereas guys with bigger cams idling in the 14s would likely be being told lies by their gauge and in reality idling richer than indicated. Any little misfire from incomplete combustion at idle will be sensed as lean as the unburned oxygen goes into the exhaust. My 383 likes to idle with the gauge reading 13.2-13.4 but with a cam of 245@ .050” and 28* overlap it would be truly richer than that.
Getting into the secondaries bog, is that flooring it from cruising on the primaries or progressively using part of the secondaries?
If going from closed secondaries to wide open in one hit you are using all of the pump cam. The pink cam gives a bit more total volume. The 31 squirters and pink may work for that situation. Bigger squirter you get all that volume sooner. If your already a little into the secondaries then give it a bit more and it bogs the 28’s and blue cam might do the job. Just remember with a blue in the primaries you have likely spent it before or barely into the secondaries so no help from the primary squirter.
Statistics: Posted by Right hand drive — Tue Mar 23, 2021 7:10 am
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Thanks again, great reading on here
(jmarkaudio),I may tackle the t-slot jet and the ifr lowering as well, I am just a little spooked about doing that on my new carb. Although I do have a carb shop near me so I could have that done there. I talked to him a while back and he is a fan of the upper location for the ifr's but he will do whatever you want.
Statistics: Posted by 77k5 — Mon Mar 22, 2021 2:29 pm
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