V8_DatZun Posted February 9, 2007 Share Posted February 9, 2007 i have a holley 750 DP on my 383. when i ordered the carb it was rebuilt and came with no instructions. there are 3 vacuum ports. 1 on the back. 1 on the passanger side and one in the front. what connects to these 3? the one on the passanger side has a red vac. cap and so does my distributor so i assume those two get connected to each other? if so do i come off the intake to the one on the front.. then the brake booster to the back of the carb? am i correct or no? Quote Link to comment Share on other sites More sharing options...
Teekass Posted February 9, 2007 Share Posted February 9, 2007 i have a holley 750 DP on my 383. when i ordered the carb it was rebuilt and came with no instructions. there are 3 vacuum ports. 1 on the back. 1 on the passanger side and one in the front. what connects to these 3? the one on the passanger side has a red vac. cap and so does my distributor so i assume those two get connected to each other? if so do i come off the intake to the one on the front.. then the brake booster to the back of the carb? am i correct or no? The one on the passenger side (about half way up the metering block) is for metered vacuum. Use this one for the vacuum advance on the HEI. The other two ports are ported vacuum, so they would be used for brake booster, and other items that required a ported vacuum source. I've always used the rear one for the brake booster, and plugged the front one. Hope this helps, Chris Quote Link to comment Share on other sites More sharing options...
V8_DatZun Posted February 9, 2007 Author Share Posted February 9, 2007 so... i get no intake to carb vac?? Quote Link to comment Share on other sites More sharing options...
Teekass Posted February 9, 2007 Share Posted February 9, 2007 do i come off the intake to the one on the front.. then the brake booster to the back of the carb? am i correct or no? Sorry to answer your question twice, but I think it will make more sense if I say this. All of the ports on the carb CREATE vacuum (not USE vacuum). So if the only items on your car that need vacuum are your distributor (which NEEDS to be connected to the metered source on the metering block) and your brake booster (take your pick between the one on the front of the carb, and the one on the back), then you have to plug the other one (and any other ones on your intake), so they don't suck air. Quote Link to comment Share on other sites More sharing options...
Teekass Posted February 9, 2007 Share Posted February 9, 2007 so... i get no intake to carb vac?? correct....they are both vacuum sources, so they would just be sucking against one another. Kinda reminds me of a date I was once on . Quote Link to comment Share on other sites More sharing options...
V8_DatZun Posted February 9, 2007 Author Share Posted February 9, 2007 ok THANKS! that really makes me mad tho... lol i went through ALOT to find a piece to put in that back hole on the intake where i broke the vacuum port lol. i could have just put a plug in it... i have to run vac to my fuel pressure regulator so that will work good w/the front vacuum port on the carb.. thanks for explaining that. makes sense to me now! lol i need to go on the kind of dates you go on! sounds kinky hah. Quote Link to comment Share on other sites More sharing options...
Teekass Posted February 9, 2007 Share Posted February 9, 2007 I think the other port on the base plate of the carb was connected to a pcv valve on one of the valve covers. Theres something about sucking piston blow-by back into the intake that gives me the creeps. Quote Link to comment Share on other sites More sharing options...
V8_DatZun Posted February 9, 2007 Author Share Posted February 9, 2007 my air breather came with a piece to run the pcv to the air filter guess so it sucks clean air? lol its weird to me how you can have oil pressure with all this stuff sucking air into the engine. seems like it would be blowing pressure out of the holes instead of sucking in vacuum Quote Link to comment Share on other sites More sharing options...
Teekass Posted February 9, 2007 Share Posted February 9, 2007 ok THANKS! that really makes me mad tho... lol i went through ALOT to find a piece to put in that back hole on the intake where i broke the vacuum port lol. i could have just put a plug in it... i have to run vac to my fuel pressure regulator so that will work good w/the front vacuum port on the carb.. thanks for explaining that. makes sense to me now! lol i need to go on the kind of dates you go on! sounds kinky hah. LOL....everything was kinky back in high school:flamedevi . As far as the vacuum for your fuel pressure regulator goes, don't take my word for the gospel. Maybe someone like grumpyvette will respond because honestly, I don't know if all the vacuum sources are all the same quality. Example: intake vacuum may be a better source than the ones on the base of the carb?.....I honestly don't know. I'm sure your fuel pressure gauge will work on both the intake and the carb, but is one a better choice?......I'm not sure. Quote Link to comment Share on other sites More sharing options...
Teekass Posted February 9, 2007 Share Posted February 9, 2007 my air breather came with a piece to run the pcv to the air filter guess so it sucks clean air? lol its weird to me how you can have oil pressure with all this stuff sucking air into the engine. seems like it would be blowing pressure out of the holes instead of sucking in vacuum This isn't my area of expertise, but I tell you what little amount I know. All of the vacuum is created between the throat of the carb and the intake valve (after the intake valve opens, and the piston is travelling down the cylinder). As far as oil pressure, I'm not going to even act like I know the exact route, but it starts at the oil pump and eventully goes through the crank, oil galley, lifters, up through the push rods onto the rocker arms, and then drains back down (and it obviously runs across the cam, timing chain, etc also). So if you think about it that way, the vacuum system, and the pressurized areas of the oil system are never connected. So as far as oil pressure blowing out the holes, it shouldn't happen....famous last words, right, lol. Also, as the pistons go down, they create positive pressure below them due to the compression of the air below them (and blow-by from the top side of the piston). This pressure builds in the crankcase (oil pan), then works its way up the inside of the block and is vented through the valve covers (along with exhaust gases that work their way between the exhaust valve stem and a worn out valve guide). If this pressure isn't vented quicky enough, I've heard you can have gaskets start to leak (oil pan, front or rear intake seal, etc.) The pcv valve uses vacuum to suck the pressure from the crankcase to prevent this (along with being environmentally friendly). Quote Link to comment Share on other sites More sharing options...
Guest rat454 Posted February 11, 2007 Share Posted February 11, 2007 my air breather came with a piece to run the pcv to the air filter guess so it sucks clean air? lol its weird to me how you can have oil pressure with all this stuff sucking air into the engine. seems like it would be blowing pressure out of the holes instead of sucking in vacuum Here is how the PCV (Positive Crankcase Ventilation) should be connected. There should be a hose or tube running from the air cleaner to one of the valve covers. This provides the filtered fresh air for the PCV to work. The other connection is the vacuum source. So the PCV valve is hooked to the other valve cover then to a large vacuum source. The vacuum source sucks air through the valve cover removing the combustion blow by that gets into the inside of the engine. Sometimes instead of the fresh air side going to the air cleaner, folks use a push in type breather. either way you need the fresh air for the PCV to do it's job. I prefer to hook up the vacuum for the PCV to the intake manifold. Just my preference. What kind of intake maniforld are you running? Also is the 750 DP a standard flange (all four of the barrels the same size) or is it a Spread bore (2 small barrels and 2 large barrels). How many fuel connections are on the carb (just one in the front) or (is there one in the front and one in the back) G Quote Link to comment Share on other sites More sharing options...
V8_DatZun Posted February 12, 2007 Author Share Posted February 12, 2007 they are both the same size... and i have 2 fuel connections.. thanks for the info on the pcv i was wondering about it too a little. Quote Link to comment Share on other sites More sharing options...
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