So if I went down to 14 degrees (and fixed the vac leak), and the t slot was at .040 and still too slow an idle, but I don’t want to change timing, then I’d open the secondaries slightly in this context correct?
Proper Transfer Slot Position
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So if I went down to 14 degrees (and fixed the vac leak), and the t slot was at .040 and still too slow an idle, but I don’t want to change timing, then I’d open the secondaries slightly in this context correct?
jmanhoff, I presume Hysteric is referring to me in post #57. That post & his others just show how ignorant he is.
Think about these comments from Hysteric:
[1] I did not, nor would I, recommend 50*of initial with such a mild cam.
[2] Then he says lean mixtures burn slower. Yes they do. Increasing cam duration increases overlap, which causes exh dilution & LEANNESS, so more timing is needed to get the most HP out of the engine.
[3] A common sense question for you. If you increase the idle timing and the engine rpm increases, do you think the engine is 'fighting itself'. Wouldn't you expect the rpm to decrease if that was the case.
[4] Rich mixtures burn fast, post #57. No they burn slow like lean mixtures.
[5] Post #59. A lot of timing is reqd for cruise, but NOT because of high vacuum. Using that logic, a stock engine that idles with 20" of vac would require 45-55* of advance. At cruise, the engine is 'throttled' because of the small throttle opening. The air is less dense because the air is being stretched. That means the molecules are further apart & the mixture takes longer to burn. So the burn needs to start earlier [ more advance ] to complete the burn at the optimum crank angle for fuel & engine efficiency.
[a] GM cars used MVA for many years. My GTO left the showroom idling at 26*. 6* init + 20* MVA. Below is from the 1967 manual, noting VA at idle. The factory cam was about 10* shorter than your cam.
Vacuum at idle is a measure of how well the mixture is being burned. More vac, more efficient. Below, idle vac increased by 2" with more idle timing.
[c] Below also are some success stories with MVA.
[4] Even the LS engines in stock form with high comp ratios & stock cam had over 20* of idle timing.
Think about these comments from Hysteric:
[1] I did not, nor would I, recommend 50*of initial with such a mild cam.
[2] Then he says lean mixtures burn slower. Yes they do. Increasing cam duration increases overlap, which causes exh dilution & LEANNESS, so more timing is needed to get the most HP out of the engine.
[3] A common sense question for you. If you increase the idle timing and the engine rpm increases, do you think the engine is 'fighting itself'. Wouldn't you expect the rpm to decrease if that was the case.
[4] Rich mixtures burn fast, post #57. No they burn slow like lean mixtures.
[5] Post #59. A lot of timing is reqd for cruise, but NOT because of high vacuum. Using that logic, a stock engine that idles with 20" of vac would require 45-55* of advance. At cruise, the engine is 'throttled' because of the small throttle opening. The air is less dense because the air is being stretched. That means the molecules are further apart & the mixture takes longer to burn. So the burn needs to start earlier [ more advance ] to complete the burn at the optimum crank angle for fuel & engine efficiency.
[a] GM cars used MVA for many years. My GTO left the showroom idling at 26*. 6* init + 20* MVA. Below is from the 1967 manual, noting VA at idle. The factory cam was about 10* shorter than your cam.
Vacuum at idle is a measure of how well the mixture is being burned. More vac, more efficient. Below, idle vac increased by 2" with more idle timing.
[c] Below also are some success stories with MVA.
[4] Even the LS engines in stock form with high comp ratios & stock cam had over 20* of idle timing.
jmanoff,
This is how you determine what the beast timing is for your engine. You do this FIRST, before changing anything on the carb or the ign curve.
- Start with factory init timing.
- adjust idle for best idle
- chock wheels if auto
- engine idling, slowly turn dist. Idle rpm will INCREASE [ how did I know that?]. Keep turning dist until you get the highest rpm; toggle dist to make sure highest rpm. Now check what the timing is. That is what YOUR engine needs for best idle. Modify your dist curve accordingly.
This is how you determine what the beast timing is for your engine. You do this FIRST, before changing anything on the carb or the ign curve.
- Start with factory init timing.
- adjust idle for best idle
- chock wheels if auto
- engine idling, slowly turn dist. Idle rpm will INCREASE [ how did I know that?]. Keep turning dist until you get the highest rpm; toggle dist to make sure highest rpm. Now check what the timing is. That is what YOUR engine needs for best idle. Modify your dist curve accordingly.
TT5.9mag
Two atmospheres are better than one
Exactly. Timing and carburetor adjustments must be made together and their relationship cannot be overstated.
Alright, it’s going to be a few days before I can actually take the carb/dizzy off and modify things, but I am going to try to map out my curve tomorrow as well as change out the pcv grommet. I’m going on a trip across state this weekend and I don’t want to change things and have issues during said trip, so I’m going to wait until I’m back home to muck around
Am I right in thinking that you believe that you have a vacuum leak that is related to the pcv grommet?
I’m curious what else could be causing it. I’ll be transparent that I’m not entirely sure how the PCV system itself doesn’t cause a leak, but in my case specifically:
If I pinch the line, idle speed goes down. If I pull out the valve and put my finger over the bottom of it, same thing. The grommet that came with my valve covers seems a little large for the PCV that I have, even though they’re LA covers and it’s an LA PCV valve. But I could be wrong
I’ve replaced it a couple times in the past, and this one was recently changed and still rattles. But they’re cheap, so why not
Your pcv valve might be bad and allowing too much vacuum to bleed by the valve at idle. A little bit of vacuum passing through the valve is normal. The vacuum is there to prevent pressure that is caused by blow by from venting gasses to the atmosphere. The pcv is part of your emissions control system. if the pcv doesn't fit the valve cover seal correctly it could cause an oil leak and or cause your pcv system to not work correctly. I don't see the pcv seal itself causing a vacuum leak.
Jmanhoff.
The PCV. Hotted-up engines have low vacuum & will not work with stock PCVs. You can buy expensive aftermarket PCVs that will work. When I build an engine that has low idle vacuum, I do this: I get a short length of 3/8" diam alum or steel [ old bolt? ] & drill a 1/8" diam hole through it. This approximates the orifice size of the PCV. I push this piece into the PCV hose & I now have a working PCV. The original PCV can be left in place. Make sure you have a separate breather. You could try this & reduce the hole size if rpm is too high.
The PCV. Hotted-up engines have low vacuum & will not work with stock PCVs. You can buy expensive aftermarket PCVs that will work. When I build an engine that has low idle vacuum, I do this: I get a short length of 3/8" diam alum or steel [ old bolt? ] & drill a 1/8" diam hole through it. This approximates the orifice size of the PCV. I push this piece into the PCV hose & I now have a working PCV. The original PCV can be left in place. Make sure you have a separate breather. You could try this & reduce the hole size if rpm is too high.
So there’s two styles of PCV valves I’ve seen as well. The first one is what I see a lot when you see PCV kits for SBMs, the second is the one that I currently have. The style I have is the same one that was in the magnums, and it went into the smaller pcv grommet that the magnums have and it seals on the small end. The new covers I have the small end is way too small to seal, so it presses in with the larger end if that makes any sense.
PCV is a controlled vacuum leak. You need a valve that is more restrictive to passing the gas... 
There are or were adjustable PCV's on the market.
There are or were adjustable PCV's on the market.
So even though the engine makes about the same vacuum a stock one does, I need a different PCV?PCV is a controlled vacuum leak. You need a valve that is more restrictive to passing the gas...
There are or were adjustable PCV's on the market.
TT5.9mag
Two atmospheres are better than one
Mine is the same way.
TT5.9mag
Two atmospheres are better than one
Me Wagner pcv valves.
M/E Wagner Performance Products – High Performance Crankcase Ventilation Systems
They work awesome. I don’t think this build will benefit though, as he has 20” or so of vacuum at idle. Plenty to operate a stock valve.
Yeah that was my thought process, basically stock engine should be able to use stock PCV stuff
TT5.9mag
Two atmospheres are better than one
As long as it seals.
Alright, so been MIA for the past few days but I’m back now and have been monkeying around. I pulled the carb off again and noticed the gasket between the main body and the throttle plates (I’m not sure what the proper terminology is) is squished out and it’s wet with fuel around there. It is possible it’s leaking from the bowl screws but I’ve replaced those gaskets twice, once just recently when I had the carb off so I’m going to keep an eye on it. If that was leaking fuel, would that cause a vacuum leak as well? Could that be why my low speed tuning has been so goofy? It could be nothing too, I’m just not familiar so I figured I’d ask
Yeah that’s what I figured. It could be leaking from somewhere else but I have no idea, need to take a deeper look. I have never taken the carb apart fully, only the metering blocks. Is it possible the plate is warped?
Here’s a crappy image, but you can see where the gasket pokes out, and the color difference from where the fuel was. Since been cleaned, but I’ve only driven it maybe 10 miles since then.
It’s similar on the other side as well, just no obvious leakage
It’s similar on the other side as well, just no obvious leakage
TT5.9mag
Two atmospheres are better than one
That is always a possibility but the base plate is small and held on with enough fasteners that it shouldn’t be an issue. When I put a carb together I hit all machined flat surfaces with a file and if anything is noticeable they go on a sheet of glass with some 600 grit.
Alright. Does it look like the gasket is squishing out too much? I haven’t seen enough carbs to know what’s normal, and this carb is stamped 0225 on the choke horn so I’d imagine that’s its date stamp. Is it possible it’s just lazy production?
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