Tuning my Slanty

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MarPar

MarPar

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Gents!
I am attempting to tune my Leaning Tower of Power and need advice. It was tuned by the PO and I have never fooled around with it, but my spidey senses are telling me she's not quite right and needs tuning.

Specs:
-225 slant with unknown cam (it's obviously not stock and pretty hot from what it sounds like-see vid)
-Edelbrock 1403 500cfm carb
-Offy intake
-Clifford headers into dual tailpipes
-new black Mopar ignition box from Ray (halifaxhops)
-new ngk ZFR5N gapped at at .030
-initial (just hooking up the light-with advance knob at 0 and pointing) timing at 0
-15 hg of vacuum hooked up to manifold port
-distributor is hooked up to ported port



Now, it has been quite a while since I've tuned a carb (it was my GTX like 10 years ago lol) so im a little rusty. The vacuum is jumping around at idle A LOT and I think that means there is a leak somewheres. Let's start with this and proceed from here.

Thank you for any and all help Gents.
 
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Normally, if there's no leak and the engine is in good physical condition, unstable vacuum indicates retarded ignition timing. That's where I would start. With a hot cam, the vacuum gauge is going to fluctuate a little, no matter what. Mine for example jumps from about 5.9 to 6.1 or so at idle.
 
RustyRatRod said:
Normally, if there's no leak and the engine is in good physical condition, unstable vacuum indicates retarded ignition timing. That's where I would start. With a hot cam, the vacuum gauge is going to fluctuate a little, no matter what. Mine for example jumps from about 5.9 to 6.1 or so at idle.
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Well Rusty, I guess that means no power brakes for you.... That's low! Haha
 
RustyRatRod said:
Normally, if there's no leak and the engine is in good physical condition, unstable vacuum indicates retarded ignition timing. That's where I would start. With a hot cam, the vacuum gauge is going to fluctuate a little, no matter what. Mine for example jumps from about 5.9 to 6.1 or so at idle.
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FWIW, I put my hand over the carb and it does not die. Do I just keep advancing till she pings and back it off 2*? Thank you RRR

RustyRatRod said:
Oh and what video?
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It's a youtube vid. I posted it in my original post.
 
MarPar said:
FWIW, I put my hand over the carb and it does not die. Do I just keep advancing till she pings and back it off 2*? Thank you RRR



It's a youtube vid. I posted it in my original post.
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I would at least put a light on it. Pull it up to 12 initial and drive it. No ping, pull it to 15 and try it again. I have mine on 20 but I have total limited to 32.
 
RustyRatRod said:
I would at least put a light on it. Pull it up to 12 initial and drive it. No ping, pull it to 15 and try it again. I have mine on 20 but I have total limited to 32.
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Do I turn the timing light knob to 12 and turn the distributor until the tape shows 0 then? Sorry Rob, like I says, Im rusty. lol
 
MarPar said:
Do I turn the timing light knob to 12 and turn the distributor until the tape shows 0 then? Sorry Rob, like I says, Im rusty. lol
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Yeah, that'll do it.
 
MarPar said:
Do I turn the timing light knob to 12 and turn the distributor until the tape shows 0 then? Sorry Rob, like I says, Im rusty. lol
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You can do it without the light, but I always like puttin one on it because I want to know exactly where it is.
 
.....and it does have enough cam that it probably needs enough initial to make you end up limiting total. It'll probably like a curve like mine. 20 initial and 30-32 total. To do that, you'll need to pull the distributor and make some changes. I JUST got done rebuilding and modifying an electronic one for Vixen. I'll probably change it over soon.
 
RustyRatRod said:
.....and it does have enough cam that it probably needs enough initial to make you end up limiting total. It'll probably like a curve like mine. 20 initial and 30-32 total. To do that, you'll need to pull the distributor and make some changes. I JUST got done rebuilding and modifying an electronic one for Vixen. I'll probably change it over soon.
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I did peep yer distributor thread, but I need much more research before I understand exactly what the hell you did. lol
 
MarPar said:
I have a light and mostly know how to use it! lol
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It'll tell you how much initial it wants. When it stops idling up as you add timing, that's where it wants to be. The thing is, that's usually too much total and that's why you need to limit it either by welding and refiling the governor slots or using an FBO limiter plate.
 
MarPar said:
I did peep yer distributor thread, but I need much more research before I understand exactly what the hell you did. lol
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Have you gotta extra one? Send it to me I'll do it for you.
 
RustyRatRod said:
It'll tell you how much initial it wants. When it stops idling up as you add timing, that's where it wants to be. The thing is, that's usually too much total and that's why you need to limit it either by welding and refiling the governor slots or using an FBO limiter plate.
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Ill start with getting her to 12 and go from there. Not guna be able to take her out for a few days yet.
 
MarPar said:
Ill start with getting her to 12 and go from there. Not guna be able to take her out for a few days yet.
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At 12 initial it will probably have 34-36 total.....which is too much for a slant, but it'll never ping unless it's had some internal work like a heavy head or block mill or different pistons. So it'll probably be ok.
 
You can test the theory easily. With the light on it, pull the timing up until the engine stops gaining idle RPM. It'll reach the point where it really starts to get a deep rough rumble at idle.....I always put my hand on the valve cover. You can really feel it when it gets there. Then, back off until that "extra" roughness goes away and look with the light where the timing is. Just play around with it until you pick up on that extra roughness. You'll spot it. It's not hard. It's a lot easier to spot with your hand on it. Of course, without limiting total, you'll not leave it there. This is just to see "how much" initial only the engine will like. I bet with stock compression and that big cam it'll be "around" 20.
 
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RustyRatRod said:
You can test the theory easily. With the light on it, pull the timing up until the engine stops gaining idle RPM. It'll reach the point where it really starts to get a deep rough rumble at idle.....I always put my hand on the valve cover. You can really feel it when it gets there. Then, back off until that "extra" roughness goes away and look with the light where the timing is. Just play around with it until you pick up on that extra roughness. You'll spot it. It's not hard. It's a lot easier to spot with your hand on it. Of course, without limiting total, you'll not leave it there. This is just to see "how much" initial only the engine will like. I bet with stock compression and that big cam it'll be "around" 20.
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Ok, now it's all coming back to me. :D

I consulted the FSM and it says to pull the vac advance off of the distributor and plug it. Do I still do this? Im not sure cuz of dat cam. The cam in the GTXer is very stock-ish and I have never dealt with a hot cam.
 
Are you sure you have the valves adjusted properly to the cam card (unknown. Start at .020/.020)? I'd start there if it has a shaky vacuum needle. it all starts there......
 
MarPar said:
Ok, now it's all coming back to me. :D

I consulted the FSM and it says to pull the vac advance off of the distributor and plug it. Do I still do this? Im not sure cuz of dat cam. The cam in the GTXer is very stock-ish and I have never dealt with a hot cam.
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It's really not necessary, since the vacuum can doesn't have vacuum at idle, but to appease the forum guys, yeah take the vacuum hose off and plug it.
 
Should I re-gap the plugs to .035 before I do anything else? I cant member why I put em at .030.
 
MarPar said:
Should I re-gap the plugs to .035 before I do anything else? I cant member why I put em at .030.
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2 things jumped out at me while reading your initial post.
Plug gap only. 030. Chrysler spec with their electronic ignition was .035.
Timing at zero, or TEC. Try 12 to start with vac advance disconnected and plugged. See post 10 and others.
You'll have to readjust idle

If this car is new to you, assume nothing. Pishta is right, run the valves.
 
I also agree about the valve adjustment. If you think the engine is a stock compression engine, I would adjust them loose. Maybe like .018 intake and .020 exhaust. That will help build more cylinder pressure than tight lashing them.
 
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