Got a couple of questions about a Holley carb. In the attached photos the number 1 is pointing to the port and hose that I think should provide "ported" vacuum to the advance can. Can anyone confirm my guess, I don't want to hookup to manifold vacuum. On the base of carb, toward the front of the engine is another port with an orange vacuum cap on it, I think this is a manifold vacuum source, right? wrong? Next question, I want to fill the float bowls with fuel prior to fire-up to hopefully avoid prolonged cranking before the engine fires. In the photos the numbers 2 and 3 point to two possibilities for filling the bowl chambers, can anyone confirm my guess or point me in the right direction
Use the lower port for vacuum to your distributor. Use #2 to fill for gas. #3 is the float adjustment which you need to adjust to have correct fuel level. The ful should just trickle out #2 when the bowl is full. Hope this helps. Good luck
Fill it at the vents in the top. Old musturd or ketchup squeeze bottles work for that. The ported vaccum is correct #1 use if vac only dist. And the other port orange cap if it comes out below the butterflies on the venturi side it is manifold vaccum which I believe it does. It goes on mechanical advance dist which you should have if not a pre 56 ford. Number 2 is used to set float level. Take out, can fill bowl there also, and loosen nut on #3 and turn screw clockwise to lower fuel level and counter to raise fuel level. Just get it to trickle out of #2 at idle or just even with bottom. Should leak out more when rpm are raised..
#1 is correct connection for your vacuum advance. #2 is a plug to check float level and you could squirt fuel into this opening for starting, although I've never done that. #3 is the float level adjustment which you would adjust with the #2 plug out. Not with engine running, could start a fire. Good luck.
The two tubes sticking straight up, one in front and one in back, are the bowl vents. Pour gas down them...easy way to prime just about any carb. I cut a soda can in half, use the bottom half, bend a little spout into it.
Ok I need to add some info, distributor is an hei. So far as I know an hei is mechanical and vacuum advance. I think I understand to fill the bowls through the vents. Seems to be some disagreement about ported vacuum source or if I should use ported or manifold vacuum. anyone else have an opinion? In the attached photos, are the vents we're talking about the parts I've placed a red dot on? All of this is on a 350 chevy.
You could try both the ported and unported, and see which works out best. Don't cost nothin to move the vacuum hose.
I would use the orange capped one for the HEI. Set timing with light with it unplugged. Then plug in vac line. Like Squirrel said can try it in the other one. And yes those are the bowl vents
Everyone that says the gas should just trickle out ,There wrong ,Should only trickle out when you bump fender ,Down and 2 adjust fuel sqirter at 15 thousandths at wide open throttle
Ported vacuum provides no vacuum and hence no vacuum advance at idle. It will provide vacuum advance at part throttle/cruise rpm. Ported vacuum and manifold vacuum pretty much go to zero when you floor the throttle but there are exceptions to that. Sooo, if you want/need advance at idle, then manifold vacuum. If you don't want advance at idle then ported vacuum. I try to set up engines with ported vacuum and use the initial advance and tune the carb for a nice idle. If that just won't work then the additional advance from vacuum advance connected to manifold vacuum can cover up a lot of sins in idle quality. To further answer your question, the upper port is ported vacuum and the lower is manifold vacuum. They are easy enough to test as well, just check for suction at idle. Be aware that if your throttle blades are open too far at idle then you might start to get some vacuum at the ported vacuum nipples at idle.
Cam is as follows: Comp cam Dual-pattern 255DEH. Specs are Gross lift Intake - .421, exhaust - .451 Duration @ .006 Intake - 255, exhaust - 261 Duration @ .050 Intake - 203, exhaust - 212 ----Lift Intake - .2810, Exhaust - .3010 Lobe seperation 110'
Simple way to prime carbs is to put the shop vac on "blow" and stick the hose wrapped with a rag in the fuel tank opening. It will push fuel up through the fuel system. Bill
Seems like a lot of different opinions on the subject of port versus manifold vacuum for an hei. I was hoping for a strong consensus on the subject, but it looks like some experimenting will be necessary.
Post the list number of the carb and someone can probably give you a lot better indication of which tube is ported and which is manifold vacuum. Borders or one of the other bookstores usually has one of those how to work on your Holley books that covers current models. I have one somewhere in the reference pile but am not able to dig it out right now.
Hear is some info on ported vs manifold vacuum Quotation thanks to JohnZ As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word document if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative. TIMING AND VACUUM ADVANCE 101 The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency. The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation. At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph). When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean. The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic. Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it. If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more. What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone. Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam. For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.
Your right on the ported vac ,Use that one ,Get yourslf a distributor spring kit while your at it ,Try the medium springs and weights first .Also if its a factory holley 600 ,You will need to change the rear spring to the vacumn secondaries ,Please post motor, head, carb specs and rear and stahl converter .
The carb is a mystery to me, I purchased it a long time ago as a carb/intake package from Thermodyne. The intake is a Thermodyne Driver. The list number on the air horn is 80504 and the build date is 0305. I've never found 80504 on any Holley list so I'm unsure of the cfm rating etc. At the time I purchased the carb/intake I also purchased a brand new HEI and sent it to Thermodyne to have it curved per their specs. Their specs are: in the mechanical advance 28 degrees, 15 degrees in the can, initial 12-15 and all in by 3000rpm. I'm assuming that since those are their recommended specs that they curved the distributor to match. The engine is a .030 over 350, with the Comp Cam mentioned earlier in the thread. It's running Crane gold roller rockers and has been balanced. The transmission is a 350th w/a stock converter. Don't know the rearend ratio at the moment. All of this is in a 41 woodie that'll never get hammered but I'd like it to pass easily and hold it's own getting up an on-ramp to the interstate. I really appreciate all of the information being given thanks
themoose, thanks for the cut and paste. That was a really clear cut description and I learned a thing or three. I might use manifold vacuum more often now. 41woodie, even by the standards of the quote by JohnZ, you have a lot of advance. Initial, plus centrifugal plus vacuum equals 55-58 degrees. That sure seems like a lot.
Triggerman, When I added up all of the advance numbers it seemed like a lot to me. What are the dangers or potential problems that too much advance can cause.
Some engines like that much total advance (vacuum + initial + centrifugal). Usually you'll hear the engine ping or knock (sounds like a hammer striking cast iron, because that's what's happening inside the engine). Or you might have detonation you can't hear. The usual result of way too advanced timing is a hole in a piston. Again, 50+ degrees is typical for full vacuum (lightly loaded) high rpm operation.
Having read back through John Z's quote, I assume that the three numbers (static,vacuum and mechanical advance) are not added together. That the total would be only the static and mechanical as the vacuum would be a non-factor under load. So the total timing would be 40-43 degrees, yes?? No??
[I] and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the[/I] vacuum advance) 41woodie, as you can see from the quote above, JohnZ was clearly referring to all three advances added in total. Either way, as squirrel states if there is no pre-ignition then it is commonly thought that you are okay. Here is the catch...you can often no hear mild pre-ignition. You can either see it on the plugs or a knock sensor can sense it. To answer your question, the dangers of too much advance are reduced life of the pistons and rings plus the rod bearings. That is ONLY if you are experiencing pre-ignition. Otherwise, the only disadvantage of too much advance is that you go beyond the point of increased power and mileage.
Triggerman, Squirrel, Moose and others, If an engine is going to suffer from pre-ignition wouldn't it occur when under load, such as pulling a grade or heavy acceleration when vacuum is low and little if any vacuum advance is present? Please understand I'm not questioning anything being said, if I knew anything about the subject I wouldn't have asked the question. I'm just trying to reason my way through all of the info presented.
Not necessarily so Mr Wood. Pre-ignition usually happens under the conditions you stated because of the higher cylinder pressures but it can happen anytime with the right ingredients. You seem to have most of the info you need so far. I would run initial advance around 8-10. and let the rest go as it is with the vacuum advance connected to manifold vacuum based upon John Z's advice. Go do that and let us know how it runs.
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