BLKMGK Posted October 6, 2001 Share Posted October 6, 2001 Okay, the mystery of the missing horsepower may have an explanation. Tonight I put a wire tie on the vacuum secondary plunger and drove the car around th eblock a few times flooring it in several gears. Ran great! However when I popped th ehood and looked at the plunger the wire tie hadn't moved at all. I've put the weakest spring I can in the can for this test and could feel no secondaries - the wire tie seems to confirm this. How exactly should this be troubleshot further? Brand new carb, linkage moves freely when the throttle is held WOT, when the plunger is pressed I hear escaping air but I'm not sure if it's venting into a throttle bore or not. I'll try to examine the diaphragm tomorrow as that's th eonly thing I can think of - this puppy has a quick change spring thingy and is a Holley Avenger 770. I'll be reading up on any FAQs I can find on the 'net but appreciate any input here. I intend to dyno this sucker again as soon as I get this thing working! Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted October 6, 2001 Share Posted October 6, 2001 Cool! Problems like this are what remind me of how much I hate carbs. I've been a hardcore FI guy for a while now, I'll never go back to carbs. I had a lawn mower carb go bad on me, and I couldn't fix it Bought a new mower instead. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted October 6, 2001 Share Posted October 6, 2001 Maybe the diaphram has a leak in it, theres not much else could be really, they may have pinched it or something when they built the carb.. (Ok, so who was sleeping at Quality control?). Its either the diaphram itself or a leakage in the route to the diaphram somewhere. (How astuit huh? Like you didn't figure that out already... ) I will say that when I got my holley from Summit (and it was packed fine as usual from them) the throttle shaft lever was bent where the throttle wouldn't open. Don't know what they do at the factory, toss em around or something . Anyway, thats actually great news Jim, if your runing 306 hp on the primaries, ya gotta like that. Regards, Lone Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted October 6, 2001 Author Share Posted October 6, 2001 You'd think that Holley troubleshooting stuff would be all over the place - nope! Holley's site mentions how to tell if they're open but not what to do if they aren't Found one site that shows the vac passages - the passage for the secondaries is MUCH higher than what I was blowing air on. It looks much like where Car Craft showed it except that on my Avenger I didn't see it there. Will be looking closer again tomorrow - this is frustrating. I agree that something has to be wrong with the diaphragm or the passage though. Will pull it off tomorrow and check it over. Fun and games! Quote Link to comment Share on other sites More sharing options...
pparaska Posted October 6, 2001 Share Posted October 6, 2001 Jim, try pulling the whole diaphram assembly off. Try blowing air into the carb body port that feeds vacuum to the assembly. YOu should hear air in the carb throats. Then start the car and rev it quickly and see if you get vacuum at that port. Then test the vac secondary diaphram assembly with a vacuum pump that you have and see if it pulls the rod in and if it will hold it in. With the lightest spring, it ought to be opening. Oh yeah, are you sure that the wire tie didn't keep the rod from moving? Good luck! Quote Link to comment Share on other sites More sharing options...
DavyZ Posted October 6, 2001 Share Posted October 6, 2001 Man, 300 hp on primaries alone?!? Whoa, you have got to like that, Baby! I think you'll find your missing 150 hp... Davy Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted October 7, 2001 Author Share Posted October 7, 2001 Okay, looked it over today and FINALLY found the little holes that activate th ething in the carb throat. It was a SuperChevy article that said to blow air past them with the throttle open BTW. Tried this- no joy! Pulled vac can off (PITA), pulled it apart, diaphragm looked fine. Verified linkage moves freely. Haven't retested yet. Pete - the wire tie is on there very lightly, just lightly not to fall down. If my wire tie was blocking th eopening of the secondaries it sure didn't hurt performance one little bit. I've confirmed that a vac secondary carb works on load and NO amount of winging the throttle will open them - my memory is obviously faulty. Managed to dig up my Holley's instructions and will review them to troubleshoot this. Am hoping that having pulled the unit apart, blown out the passages, and reassembled that it will magicly begin working. Didn't think to test with a vac pump today (got rushed) but if this doesn't work I will. Looking this whole part of the carb over I'm struck by just how dirt simply it is - it should work! P.S. Assembled I did try compressing the rod and holding my finger over the hole I confirmed that the unit didn't "leak down". When I pulled it apart I also noted that the rubber was pretty much squashed flat and I popped it back into shape when I put it back together. I hope that indicates that something funky occured during assembly and that I've fixed something. I'm not holding my breath Quote Link to comment Share on other sites More sharing options...
John Scott Posted October 7, 2001 Share Posted October 7, 2001 How 'bout swapping another carb? Surely another gearhead can lend you one for a quick test. JS Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted November 7, 2001 Share Posted November 7, 2001 Jim, Did you ever figure out the scondary problem? Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted November 8, 2001 Author Share Posted November 8, 2001 Actually, no. I put in a lighter spring, tinkered a little, and then pretty much gave up. I hate carbs and my conclusion is that I may have too big a carb and that my vac signal is too low to activate them. I'm not sure about that mind you since I'm pretty ignorant about carbs but I feel pretty certain they aren't opening and that this is why my power is where it was on the dyno. I only installed a carb so that I could debug the drivetrain and I think that's gone well - no weirdo vibes or anything. I wanted EFI from the start and am now working towards that goal now. 300RWHP is plenty right now, I'm breaking parts just fine Why, you having problems too? Quote Link to comment Share on other sites More sharing options...
blueovalz Posted November 8, 2001 Share Posted November 8, 2001 When you take the diaphram housing off, suck on the hole that goes to the chamber. The rod will or should move with very little vacuum. Unless you are running something in the order of 900cfm, you should, on a good run get this to open, especially with the lighter springs. Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted November 8, 2001 Share Posted November 8, 2001 The carb you have should be just fine on a 350. Chevrolet used a 780 on the Z28 (302). I had a Holley 780 on my 351 CJ Mustang before going to a 700 double pumper. Hd tried a 600 to start but like the 780 MUCH better up top. I had all the springs and cams for the accelerator pump at one time...this was back in '70's and 80's - wish I'd never sold that car.... Something is Definitely wrong with the carb if the secondaries don't open. Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted November 9, 2001 Author Share Posted November 9, 2001 Whew, where to start! MotorCam specs posted here somewhere. Cam isn't super high lift (under .500) but the lobe centers are a bit wide if memory serves - hydraulic flat tappet. Vac at idle is less than 15 at 1K I think. Victor Jr single plane, Edelbrock RPM heads. I've got a white spring in there now, no noticable bog ANYWHERE nor do I hear the secondaries opening - on my first Mustang the secondaries were VERY loud, not this car. If I hold the throttle open and move the vac can's arm it swings through it's full throw without hitting anything. When I pulled the can off to check things and pressed against the spring then covered the hole it held until I let off, no leaks. Carb gunk sprayed through the passage came out fine on both primary and secondary sides. Engine has seen 7K no problem, still pulling hard. Only vac connections were to the PCV using the correct connection. No vac to the distributor right now. (shrug) If the secondaries ARE opening they're darned smooth. Putting a wire tie lightly on the vac arm and looking after a hard run shows no movement down the arm and thus I believe no movement of the arm.... Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted November 9, 2001 Share Posted November 9, 2001 Jimbo, My Holley books (I have three of them) indicate possible Vacuum Sec. problems as follows: 1) As you already mentioned "Over Carburation" AKA:Too large of a carb 2) Improper Vacuum routing/port choices 3) Too Heavy of a Vac.Sec. Spring 4) Vac.Sec. Throttle Linkage binding 5) The Secondary Butterflies are binding against your Intake to Carb Gaskets & therefore even tho you may be getting vacuum to the diaphram the butterflies are jammed against the base gaskets & wont move..thus you think you have diaphram prob's when you actually have base gasket to butterfly problems. 6) On some Holley's the Vac.Sec. has a bleed off venturi w/a check ball inside the bleed off passage; if this check ball is stuck on its seat (from the carb sitting on the shelf in the warehouse for too long: or for whatever reason) then your diaphram will just bleed off its vacuum & never open...even tho it's getting the vacuum signal as designed. Questions: 1) What Vacuum ports on the carb did your route to what ports on the engine/distributor? 2)When you installed it; did you manually work the linkage including the Secondaries w/your fingers as you slowly torqued down the carb bolts...if you only work the linkage-the primaries will only open as there is no vacuum to the secondaries w/out the engine running-therefore-as you're initially setting up the carb you've assumed that both primary & secondary butterflies are not binding...but you have to manually open the primaries w/one hand while manually open the secondaries w/the other hand..then & only then have you confirmed that neither primaries & secondaries are free of any binding....hope this was said half way inteligently. 3) When you changed the Vac.Sec. Springs what color spring did you install; my books indicate that the [white] spring is the lightest. If you install the [white] spring & still dont feel the secondaries are opening then IMHO your Vac.Diaphram is not the problem, rather, a restriction to the linkage or the vac.signal to the diaphram is the problem. 4) When you test drive your car & floor it; does your car bog/hesitate in any way, as rpm's build? 5) As you accelerate-what rpm do you accelerate to? 6) What intake manifold did you choose/along w/the specs of your camshaft & cylinder heads! If you're running a large cam, Single Plane Intake, Large CFM Heads w/a large carb that is improperly tuned...you may not be getting the vacuum signal that your carb requires to open at lower rpms! You may have to accelerate to 5000/6000 rpms before your Vac.Sec's get the signal they require inorder to open: dont do this on a new engine "WE DONT WANT ANY SPUN BEARINGS". Bigger is not always better. 6b) Even w/a high Static Comp.Ratio-things look fine...but Dynamic Comp.Ratio may be bleeding off to such a degree that your Vacuum Signal isnt strong enough to open the Vac.Sec.Diaphram at a lower rpm: You'ld have to gauge the signal below your carb to prove "what signal" is actually being fed to the base of your carb. Easiest sollution would be to do what someone on this thread mentioned earlier....borrow someone else's carb that is known to work & see if you get the same results as your carb. If you get that feel of monstrous power & its obvious the borrowed carb's secondaries do open...then it should be obvious that your carb was either defective or improperly tuned to your engine. Hope some of this helps. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted November 23, 2001 Share Posted November 23, 2001 That's definately a mystery to me? I agree that when the secondaries open under a WOT that not only should you hear them opening but you should also "feel" them opening (butto'dynometer). Either they are not opening or as you said the transition from primaries to secondaries are smooth/quiet (Hmmm?). All I can say is 300 RWHP is nothing to sneeze at(!) with a moderate cam profile. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
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