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sam 15 Contributor Posts 254 
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06-11-12 06:25 PM - Post#2235990
I have been fighting an overly rich carb (holley 600 cfm with no external float adjustment) and a very erratic vacuum gauge needle flucuation. Based on vacuum gauge readings, I determined that the valves needed adjusting. I finally got around to adjusting the valves (flat hyduralic). The inner and outer springs all looked good. I put on the vacuum gauge back on (at the base of the carb) and it still fluctuated between 8 and 12 Hg. Again based on the reading, I think I have a pertty good vacuum leak. I checked for leaks around the carb base, intake maifold, brake booster hose, vaccum line(s). I could not find any leaks. Doing some research on this, I found an article that when no leaks are found, that the leak could be from the inner part of the intake manifold, basiclly in the lifter valley. I imagine this is possible. The gauge reading info tells me the change the carb gasket (again based on the gauge reading) so I'll do that first just to see if the gauge needle steadys out. I'm planning on rebuilding the carb and putting in a 6.5 power valve. I have never rebuilt a carb so any tips are welcome. I'm thinking of replacing the intake manifold with a duel plane hi-rise, to improve low end torque...suggestions there are welcome i.e. recommended intake gasket...etc. Pervious owner told me "it's got a cam in it" but didn't know the specs. It has a little lope to it so I would say if it has an aftermarket cam, its not to far from stock, in other words, not aggressive. I don't know much about the engine innerds except from casting #'s which tell me 80-85 sbc 350 882 heads (stock I would guess) Thanks Rick
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inline0_0 "10th Year" Silver Supporting Member Posts 1396 |
06-11-12 07:55 PM - Post#2236036
One easy thing to do is remove EVERY vac. hose & plug the port where it was attached. That way, if you have a power brake booster, dist. advance, trans. modulater or whatever leaking, it will eliminate it. Then, you can get down to engine basics. Doug |
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64cv "5th Year" Silver Supporting Member Posts 647 
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06-12-12 05:55 PM - Post#2236404
Rick, First, I agree with everything Doug says. Second, I've been there. If you have a non-stock configuration, it may take quite a bit of advanced tuning to make things right. It may not be a good a good assumption that your car has a mild cam. Rich idle, low vacuum and "a cam" makes me suspect that your idle speed has been adjusted to the point that you've got too much transition slot exposed on your carb. The only way I know to check the transition slot is to remove the carb and check the vertical vs. the horizontal height of the transition slot below the throttle blade. If it's noticably taller than it is wide it needs to be 'fixed.' Ideally is should be square. Ask us what 'fixed' means; it's not entirely obvious. It's easier to remove the carb than the entire intake. What do you see? Brad
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sam 15 Contributor Posts 254
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06-12-12 07:23 PM - Post#2236425
Brad and Doug, I'll remove the vacuum line and see if the shows anything new the weekend when I get some time. With ay luck I'll be able to work on it friday. I'll pull the carb and take some pics of what I got...I think I know what you're talking about the slots Brad...I'll post up again Rick
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sam 15 Contributor Posts 254
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06-17-12 11:35 AM - Post#2238272
Okay, the holley rebuild kit will not be in until Tues. so it will have to wait until next weekend to remove the carb. Today I disconnected all the vacuum lines (700r4 trans no vacuum line) including the PB booster and plugged them. I put the vacuum gauge on the bottom carb plate that normally connects to the Dist vacuum adv. There was no reading at all. I plugged that connection and hooked the gauge to the connection on the side of the carb above the butterflies. Same reading. I reconnected the PB booster hose, with the gauge back at the bottom of the carb...the reading fluctuated between 8-12 Hg as in my first post. I connected the gauge to the side of the carb and at first glance thought it read 0. upon closer look, the gauge was at 2Hg and steady. When working the throttle the reading goes up to about 18 Hg and then back down. Why is this so different from the reading from the bottom carb plate, or is it supposed to be this way? Maybe I'm putting the cart before the horse and my problem is the transfer slots and I need to get that first, but I wasn't expecting to get the readings I did with the booster disconnected and the differences between the carb bottom plate connection and the carb side connection...I know from reading there is controversy regarding these two vacuum ports and which one should be used with the dist. vac. adv. I took a can of carb cleaner (didn't have a propane bottle handy) and sprayed around all the hoses, carb base and intake manifold...no changes in RPM's. My question today is, what is the opinion on the vacuum readings with all hoses plugged and the difference in the bottom and side carb connections. Also is there anything else I should do before I remove the carb. One last thing. If the transfer slots are off, should I adjust them, reinstall the carb and take readings, or just go with rebuilding it.
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64cv "5th Year" Silver Supporting Member Posts 647
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06-17-12 12:47 PM - Post#2238295
Your vacuum readings are as expected. The bottom port is manifold vaccum below the throttles. The top port is vacuum inside the metering block above the throttles. When the throttles are nearly closed, there shouldn't be much vacuum above the plates. One thing to check is your PCV valve. With low vacuum you might be letting too much air in at the wrong time. It's cheap and easy to try a Fram FV178 (made for a 1969 Z28;) it should have a "F" on bottom of the piston. Some equivalents aren't actually equivalents and might have a "D" or "E" on the piston. Install that and readjust idle speed and idle mixture. If you're still not satisfied move on to checking the transition slots. The transition slot showing below the throttle plates should be just about square (.045 - .060 tall). If it's much taller than it is wide, it's too tall. The way to adjust it is to close the throttle. That's done with the idle speed screw obviously. (BTW, once the carb is off the car, count and keep track of the turns on the you make of the idle speed screw.) Of course, the idle speed will slow; maybe even too much to keep running. The engine needs more air. The first thing to try is opening up the secondary throttles with the secondary throttle stop. When looking throught the carb into a light, the primary and secondary should be open just about the same. Play with it a bit to see how many turns of the primary idle speed screw equate to turns on the secondary throttle screw. Try to get the transition slot square with the primaries and secondaries open about the same. You then have to put the carb back on an run the engine. If it idles too slow you can try opening the primary and secondary throttles equally until you get the desired idle speed. Every time you adjust, you'll have to adjust idle mixture too. It may turn out that you'll still go way beyond a square transition slot just by messing with the primary and secondary throttle set screws. If so, the next thing to try to get more air in, but keep a square transition slot, is drill small holes in the throttle plates on the side opposite from the idle feed hole. You'll have to take the carb off again again to do this, remove the baseplate from the throttle body and do some masking so that all drill shavings can be removed and none get into the carb or the engine. Start with 3/32" holes, put everything back together, adjust idle mixture and see where you're at. You might have to take it off again and drill bigger holes, 1/32" at a time. If you go too far, you can always fill them with JB Weld and start over. It's a long process getting this right. That's basically what I did and I'm really pleased with the results. Brad
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sam 15 Contributor Posts 254
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06-21-12 08:04 AM - Post#2239772
I took the carb off today. the transfer slot was looong...so I adjusted it to eyeball square..see photos this is how it was [image]  [/image] This is after I adjusted it square [image]  [/image] Looking at the float..held up side down as in the instructions...the float is supposed to be flat...I dont know if it can be seen in the picture, but the float leans a bit lower on the left side as you look at the picture...no much but just a bit...should I adjust it to (eyeball) level..or is it good the way it is. If yes...what do I have to do...bend the tang? [image]  [/image] Also, the power valve is good 6.5 the jets in front are 64 (I have some 70"s I can put in) and the squirter is 31...how does this sound?
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64cv "5th Year" Silver Supporting Member Posts 647
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06-21-12 05:46 PM - Post#2239936
Rick, Bingo! That transition slot is the issue. You'll also want to check the secondary transition slot. Unless it's been moved from the spec, it's probably ok. In a previous post I'd suggested opening up the secondary plates a bit to even things out. (the screw is on the passenger side to the rear, up side down; easy to see with the carb off but sometimes adjustable even with the carb on.) My personal experience though is that with that much slot exposed now, you're never going to make things right monkeying with the secondary. You've started on the right path by adjusting the idle screw so that the slot is of the 'correct' size. Of course, the car won't idle just like that, it needs more air. The best way to get more air from here is to drill the throttle plates (all four) with 3/32" holes OPPOSITE the transition slots, put the carb back on, warm up and adjust the idle mixture and idle speed. Before you drill the holes, remove the base plate and mask things off so you can remove the shavings and NOTHING goes into the carb or engine. I wouldn't recommend drilling if I hadn't done it myself. With things put back together, you may still find you have to adjust the idle speed screw to raise the idle speed to get the car to run. While you have the carb off, see what a half turn does. If you have to adjust more than a half turn with the drilled throttle plates and your experiment showed that that's too much, you may have to take the carb off and drill bigger holes. No problem; just suck it up and do it. Don't go up more than another 1/32" hole size at a time. If you go too far, you'll have to pull the carb off again, fill the holes and start over; too much work. Saw your note about the float and haven't analyzed it. It's easy enough to adjust the float level with the carb installed so if you don't detect a problem now then no, don't adjust it. In fact, don't make more than one adjustment a time. Drill holes now do float later. Same principle with jets and power valve. One thing at a time; don't adjust them now. Get the transition slot, idle speed and idle mixture right then move on. The only good way I know of to adjust jets and power valve is by reading the plugs. So, get the idle transition behind you, pull the plugs, clean them off with brake cleaner and a soft tooth brush and start fresh. Brad
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busterrm Contributor Posts 999 
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06-21-12 07:40 PM - Post#2239991
Rick, Good advice, one thing at a time. Do each process then evaluate results. Then move on to the next. Agree on the jets and powervalve. With the power valve once you get the idle set, running good at idle. Get a vaccum gauge, get the best vacuum reading, write it down. That is your secret to powervalve. Once you get it jetted right on primaries(lean = light color almost white, good = tan color on plugs) then check the powervalve for size. If its correct it should be half your idle vac reading plus 1. Bingo! That transition slot is the issue. You'll also want to check the secondary transition slot. Unless it's been moved from the spec, it's probably ok. In a previous post I'd suggested opening up the secondary plates a bit to even things out. (the screw is on the passenger side to the rear, up side down; easy to see with the carb off but sometimes adjustable even with the carb on.) My personal experience though is that with that much slot exposed now, you're never going to make things right monkeying with the secondary. You've started on the right path by adjusting the idle screw so that the slot is of the 'correct' size. Of course, the car won't idle just like that, it needs more air. The best way to get more air from here is to drill the throttle plates (all four) with 3/32" holes OPPOSITE the transition slots, put the carb back on, warm up and adjust the idle mixture and idle speed. Before you drill the holes, remove the base plate and mask things off so you can remove the shavings and NOTHING goes into the carb or engine. I wouldn't recommend drilling if I hadn't done it myself. With things put back together, you may still find you have to adjust the idle speed screw to raise the idle speed to get the car to run. While you have the carb off, see what a half turn does. If you have to adjust more than a half turn with the drilled throttle plates and your experiment showed that that's too much, you may have to take the carb off and drill bigger holes. No problem; just suck it up and do it. Don't go up more than another 1/32" hole size at a time. If you go too far, you'll have to pull the carb off again, fill the holes and start over; too much work. Saw your note about the float and haven't analyzed it. It's easy enough to adjust the float level with the carb installed so if you don't detect a problem now then no, don't adjust it. In fact, don't make more than one adjustment a time. Drill holes now do float later. Same principle with jets and power valve. One thing at a time; don't adjust them now. Get the transition slot, idle speed and idle mixture right then move on. The only good way I know of to adjust jets and power valve is by reading the plugs. So, get the idle transition behind you, pull the plugs, clean them off with brake cleaner and a soft tooth brush and start fresh. Brad Example: My nova runs like 12 in of vac, 1/2 is 6 plus 1, in my engine a 7 for powervalve will be where I start.
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sam 15 Contributor Posts 254
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06-21-12 09:25 PM - Post#2240027
Brad, thanks for all the help with this problem. I still have some twinking do do to get everything dialed in, but clearly I have made more progress so far following your suggestions and things are looking up. I'll take it slow one step at a time as you suggest. Thanks again Rick
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