gerg 10,871 Posted March 12, 2014 Hey folks, seems to be a bit of interest in carbys of late, so here's a tech thread where you can ask about them. Note to mod: is there a better choice of section to put this under, or should we create a new one? This thread would apply to all carby-fed engines, not just Clevos. Share this post Link to post Share on other sites
gerg 10,871 Posted March 12, 2014 I have found a few tricks (and problems) with Holleys that you don't read about: • The plastic vac secondary covers are rubbish. I had one warp and gave absolutely no seal on the diaphragm, hence no secondaries. Either toss it for the old metal type or (at a pinch) surface plate it down flat again. • The old style ball check accelerator pumps are pretty rubbish too. Never seal properly, drain back over time and take up too much throttle movement before working. Trouble is, to change to the (much better) umbrella type, you need to change float bowls. • A warped carby body can give a false impression of a blown power valve. The surrounding gasket area near the power valve chamber can suck fuel down from the ports that feed the boosters, giving the idea that the leak is power valve related. A good file-flat finish on the surface that meets the meter block should cure this problem. NEVER file the outside ridge off the meter block where the gasket seals. • Reverse-idle ("emissions" style) 4160 Holleys have a bad rep for lacking tuneability in the idle circuit, but one positive spin-off of having this setup is that adjusting idle mixture adjusts transfer slot mixture as well, much better for dialing in an idle/cruise tune. Normal Holleys adjust idle only, transfer is fixed from factory. Still, didn't help me much though, my carby still drank like a fish. 1 bear351c reacted to this Share this post Link to post Share on other sites
Thom 6,651 Posted March 13, 2014 maybe create a fuel system section 2 gerg and Trev Vaa reacted to this Share this post Link to post Share on other sites
wookie 45 Posted March 13, 2014 heres my handful of change...tune a holley with a quality vacuum gauge [either from the base of the carb or on the manifold, i use the brake booster port on the manifold, for the idle tuning turn your air/air fuel mixture screws out on each side 1/4 of a turn at a time and keep going until you get the highest possible reading. once i cant get the reading any higher and it seems to stumble a bit ill back it off to just before i could get the highest reading. keep both screws wound in/out the same. choose a powervalve that is roughly half your vacuum reading, rounded down, say you get 14hg reading from your manifold vacuum port, you should use a 6.5 power valve.if you have to turn the air/air fuel mix screws out over 2 full turns you may need larger jets, if you have to turn them to one turn or less, you may need smaller jets. 1 gerg reacted to this Share this post Link to post Share on other sites
Trev Vaa 1,185 Posted March 13, 2014 good idea thom. fuel/nitrous/intake section? leave the Forced Induction guys to their own section.... not overly related.... Share this post Link to post Share on other sites
slydog 7,873 Posted March 13, 2014 good idea thom. fuel/nitrous/intake section? leave the Forced Induction guys to their own section.... not overly related.... Full of cocks anyway...LOL Nath,Milan,Danny,Burns,Webby to name a few Share this post Link to post Share on other sites
gerg 10,871 Posted March 13, 2014 <br />if you have to turn the air/air fuel mix screws out over 2 full turns you may need larger jets, if you have to turn them to one turn or less, you may need smaller jets.<br /> I would not have thought that jet size would affect idle at all, but if that's your experience, then duly noted. I had previously compared it to having a hand trigger on your garden hose, turned right down till it's a tiny spray (ie your idle feeds), and turning the tap on full (like your main jets). Turning the tap up or down (ie changing jet size) doesn't affect your flow at the trigger because that's the higher restriction, not the tap. Share this post Link to post Share on other sites
gerg 10,871 Posted March 13, 2014 A table I made using data from Holley on a 350 CID engine, showing secondary opening rpm for all the different springs Note: this is under full load. You will not get your secondaries to open when revving under no-load. /> The two yellow ones are so close together they should hardly have bothered, but maybe they have different curves (only data I could get was start and fully opened). In fact I'm sure the lines would actually look like curves if plotted correctly. Note that when using a black spring, the secondaries don't actually fully open. There is data available for a 402 cid engine and seems exactly the same except everything happens earlier. The black spring doesnt fully open on that one either Share this post Link to post Share on other sites
gerg 10,871 Posted March 13, 2014 My 650 spread bore on my 302 runs a purple and opens at about 2500. I think I might go lighter as you can feel the kick so that means it's opening too late. Share this post Link to post Share on other sites
bear351c 10,272 Posted March 15, 2014 Beavis and Butthead rock................ 1 gerg reacted to this Share this post Link to post Share on other sites
gerg 10,871 Posted March 15, 2014 Beavis and Butthead rock................ YES! Roooock! Huhuhhuh Share this post Link to post Share on other sites
bear351c 10,272 Posted March 16, 2014 I need teepee, for my bunghole.............. Share this post Link to post Share on other sites
gerg 10,871 Posted March 16, 2014 Nachos rule..... They RULE! Huhuhuh Share this post Link to post Share on other sites
