talk about carb throttle plates with holes in them

[eli]

would it benefit going to larger hole for clearing up idle somewhat with heavily ported blocks ,I know it will let more air in but it looks to be marginal ,I have to throttle to 2 k to clear it out then let go of throttle when front settles back down then stab it and were off I tried larger idle jet then it will sneeze some times when temps are low 70 ish and off idle but still loads up some ,something i,m pondering

[FORBESAUTO]

It’s a toss up, I’ve found with larger holes you have to run less idle timing to get idle down, which kinda nulls any benefit from extra air. I tend to lean toward better results with smaller holes and more timing, leaning out mixture and adding a larger gap between roller and cam to allow more timing advance present before carbs are picked and just deal with cold start issues and sneezing. JMO

[davemvegas]

On a car motor the hole in butterfly becomes necessary on some motors that have big cam. Aggressive cam causes low vacuum at idle. When you have to turn in idle screw to get motor to idle. The butterfly is open past the transfer slots in throttle bore. The drilled hole allows motor to get air to idle while keeping butterfly closed enough to cover transfer slot. Outboard carbs
may use same setup.

[FORBESAUTO]

Plates should be fully closed, get idle up by raising timing

[FMP]

Different spring rate on the power piston, if it's a quad can help your dial in.

[Merc 2.5]

I member reading a t-rex post and he said hes tried everything possible with a carb and best not messin with and venturies or anything, maybe just drilling holes will help but like forbes said bout air /timin,
I just swapped from a wh22 to 46( I'm sure ur wmh) but 22s had 3 small hole 46 has 2 big holes, 46s run better but dont idle as "clean" with same jets

[eli]

,Idle timing I never messed with it I always set to factory spec in manual,going to look at that ,I always set the roller next to cam then turned idle screw to get idle ,that could be the issue thanks

[FORBESAUTO]

Don’t really worry about idle timing spec on the ported motor. Make sure throttle plates are completely shut. A ported motor usually tends to run a little rich at idle and a richer mixture burns “slower” so to speak and requires a little more timing advance to get good complete burn, thus the need for more advance than normal to achieve good idle. Adjust idle timing to where you get good satisfactory idle on the water, if still get a stumble when stick throttle, widen gap between roller and cam (Usually 1/4 gap or so works well and resync and adjust to make sure throttle reaches wot), to allow the extra timing to burn off the richer fuel mixture before picking up the carbs. Hopefully this helps. T-Rex liked to run em rich and hit them with loads of timing out the hole and then pull timing back once mixture is back right to keep from melt down because a rich mixture with enough timing to take advantage of it makes more torque. But to be able to do this requires some mods and non use of the factory arms and linkages, which isn’t really practical for lake use. I’ve found using factory junk best to lean it down as much as possible without sneezing issues and get as much timing in as I can before carbs are picked up and as much idle timing to keep it clean but not too high of an idle.

[FMP]

Tell us about the air bleeds

[eli]

Good info makes sense

[Captain75]

Don’t really worry about idle timing spec on the ported motor. Make sure throttle plates are completely shut. A ported motor usually tends to run a little rich at idle and a richer mixture burns “slower” so to speak and requires a little more timing advance to get good complete burn, thus the need for more advance than normal to achieve good idle. Adjust idle timing to where you get good satisfactory idle on the water, if still get a stumble when stick throttle, widen gap between roller and cam (Usually 1/4 gap or so works well and resync and adjust to make sure throttle reaches wot), to allow the extra timing to burn off the richer fuel mixture before picking up the carbs. Hopefully this helps. T-Rex liked to run em rich and hit them with loads of timing out the hole and then pull timing back once mixture is back right to keep from melt down because a rich mixture with enough timing to take advantage of it makes more torque. But to be able to do this requires some mods and non use of the factory arms and linkages, which isn’t really practical for lake use. I’ve found using factory junk best to lean it down as much as possible without sneezing issues and get as much timing in as I can before carbs are picked up and as much idle timing to keep it clean but not too high of an idle.

Great discussion!
I use the roughly the same method, although I like the smaller distance btw roller and cam when it comes to manoevering in windy conditions and tight ports, due to faster shift btw fwd and rev.
When pulling a bigger wheel the larger cam-roller gap clearly helps off idle stumbles.

[eli]

Going out sometime after 4 th to try this method