Slant Six Problems.

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76Scamp

76Scamp

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Bradenton, Fl
I figured this is the best place for this since it has to do with the engine. I recently re-acquired my 76 Scamp and am having some issues with it. I sold it about a year ago to a kid that was going to use it as his first car, he never did and after it sitting for several months, it apparently wouldn't start. He sold it to a guy that I kinda know that after he couldn't get it started, called me and asked if I wanted a free car. I show up with a trailer and was surprised that it was my car; title was even still in my name. So, I got it running and in ran pretty terrible. It would die at lights and run bad around town, but loved the highway. So because I knew it needed it from a year ago, I pulled the head and put new valves in it which gave me a solid 120 lbs of compression across the board. I also drilled out the broken bolts in the exhaust manifold and fixed the exhaust leak. Put it together and it runs great. Adjusted the valves to 12 intake and 18 exhaust, tuned the idle and set timing at 10 before TDC. Runs and drives excellent. Now here's the problem: if I turn on the A/C, the idle is rough, it will not stay running in gear, will go down the road fine though. When it stalls, it'll fire right up and then die again whether the A/C is on or not. If I give it gas, it'll fire right up, but I have to keep it revved up for a few seconds or else it will stop and actually diesel. Sometimes I can run the A/C no problem, but most of the time I can't. I'm running the original RV2 compressor. I've also put an HEI module on it with a 12V coil and bypassed the ballast resistor. Because of how late it was when I got it back together, I set the idle by ear since I couldn't find my vacuum gauge or tach. I turned the screw all the way in, then out by 2 turns, then adjusted to where it ran the smoothest. Idle sounds like it's around 650-700, but not certain. I'm going to look for my gauges in the morning and see what she's really doing. I didn't put plugs in it since they look great, but I'll check them in the morning. I know that compressor is power hungry, but it never used to do this. The compressor is quiet and it blows 40 degree air from the vents, so it's working properly. I've run several tanks of 87 gas through it, so I don't believe fuel is a problem as it's fresh and the pump has excellent pressure. With the ignition, it should have good spark with the HEI on it, but I haven't checked. I have the module inside of the mopar box and bypassed the ballast and put a 12V coil on it so I could use the factory wiring and not add anything, but only did that recently and it did this before moving it. I'm pretty much at a loss since the last time I drove this car it had nothing wrong with it and now that it sat for a year, it does. Sorry for such a long post, but I wanted to give as much detail as I could to try and answer any questions. I'll post what I see for vacuum in the morning. Thank you for any help, it is greatly appreciated.
 
Is there any electrical solenoid by the carb idle lever to kick up the idle speed when the AC compressor is on? If so, check to the see that 12v is reaching it when the AC compressor kicks on, and that the solenoid is activating and is moving the idle linkage. It may also be stuck in the ON position and not releasing when the compressor is off, and you adjusted the idle around that being too open. Being open all the time would be one explanation for the dieseling.
 
nm9stheham said:
Is there any electrical solenoid by the carb idle lever to kick up the idle speed when the AC compressor is on? If so, check to the see that 12v is reaching it when the AC compressor kicks on, and that the solenoid is activating and is moving the idle linkage. It may also be stuck in the ON position and not releasing when the compressor is off, and you adjusted the idle around that being too open. Being open all the time would be one explanation for the dieseling.
Click to expand...

No, it doesn't have one and doesn't look like it ever did. If it had one or if I could add one, that would probably solve my whole problem. I've been driving it without A/C and it's doing great. But, being in Florida with Summer coming, I'd like to use it.
 
I wonder if you are getting a voltage drop through the bulkhead connector in the ignition circuit. Might try hot wiring the coil to the battery and test drive it. Is your coil an E core setup for straight 12 volts?
 
mguner said:
I wonder if you are getting a voltage drop through the bulkhead connector in the ignition circuit. Might try hot wiring the coil to the battery and test drive it. Is your coil an E core setup for straight 12 volts?
Click to expand...

I'll try that and see what happens. I'm using an Accel canister coil so it would fit in the factory braket. I wanted a stock look with the advantage of the HEI. The Accel coil didn't say it needed a resistor, so I figured it was fine. Plus, it ran great for a few months a year ago before I had sold it and it sat. I put plugs in it and that didn't change anything. I still haven't found my tach or vacuum gauge, but it is running very smooth, just won't take that big load at idle.
 
You may have to bump up your timing a bit to give it some help....
 
Have you checked for any vacuum leaks?

Try retorquing the intake/exhaust bolts to make sure that they didn't relax any with breaking in new gaskets and initial thermal cycles...
 
Your lash is too tight. Reset it to 14/22;
Remove the idle mixture screws, and gently blow out the low-speed circuit with carb cleaner. Wait a few minutes and repeat. Wait a few minutes and follow with compressed air. Remove the metering rods and polish the tips. Make sure the gas in the carb is fresh.Put a can of seafoam in the tank.If it still dies, search for a vacuum leak.
The two turns out on the mixture screws is a telltale. 1.5 should be enough. The extra 1/2 turn could be supplanting the T-port fuel, which may indicate that the curb idle screw is too far closed, which it would be if the idle-timing is up at 10BTDC.
Or it could just be in response to a vacuum leak.
Or in response to the low speed circuit being gummed up.
Check your timing just before it stalls.

At some later date, after you get it bugged out,in summer, you can tighten up the lash some; like 13/20.
 
My 69 Dart ran like that for decades, slowing down too much in D or w/ AC. I think it was idling lean. It wasn't a vacuum leak. The 4th Holley 1920 carb made it run like a dream, so it was the carb all along, despite what mechanics said. But, your year likely has a Holley 1945, which doesn't clog like that. I suspect you have a vacuum leak, so start by plugging off the main feed from the intake manifold.
 
I took it to a friend of mine that I can call Mr. Mopar because he has so many and knows a lot about them, and he just kept saying it sounds like a vacuum leak to him. I took a can of carburetor cleaner and sprayed over every single hose and the intake gasket and found nothing. I sprayed the carburetor gasket and found nothing. I sprayed the throttle plate, and the throttle shaft bushings are worn out.
 
318willrun said:
Wow! Lucky you, FREE????
Click to expand...

Yeah, never had that kind a luck before. I bought it for 2000, sold it for 3000, and he let it sit for a year and couldn't get it running. He sold it to a friend of mine for 700, which when he couldn't get it running he gave it to me. The title still even had my name on it so I just had to go down and put a new plate on it. The problem it had? It was out of gas.
 
76Scamp said:
I took it to a friend of mine that I can call Mr. Mopar because he has so many and knows a lot about them, and he just kept saying it sounds like a vacuum leak to him. I took a can of carburetor cleaner and sprayed over every single hose and the intake gasket and found nothing. I sprayed the carburetor gasket and found nothing. I sprayed the throttle plate, and the throttle shaft bushings are worn out.
Click to expand...

Are the bushings worn enough to hold the throttle open?If not, then you should easily be able to compensate for the wear. I've had cars with pushing 500,000KMs (300,000mi), and I can still set the carb, worn bushings and all.They always suck carb cleaner through there, I bet even new.You have to remember, the pistons are pulling awfully hard, when the carb is nearly closed.
 
Well, picked up another carburetor and it does the same thing. It will not idle in gear with A/C on, when it dies or sits a few minutes, it'll start and die unless kept revved up for a few seconds. What doesn't really make any sense to me is that a year ago I had no problems with this car and now after it was left to sit, it's doing this. It will idle fine without A/C and go down the road great no matter what. Idle is set at 700 with about 22" of vacuum and 10 degrees of advance. #6 is a hair low on compression, but not by much. 1-5 are at 120, six is at 90ish. I'm just about at a loss. A friend of mine has a four barrel intake and carburetor for sale, I may end up buying it.
 
76Scamp said:
Well, picked up another carburetor and it does the same thing. It will not idle in gear with A/C on, when it dies or sits a few minutes, it'll start and die unless kept revved up for a few seconds. What doesn't really make any sense to me is that a year ago I had no problems with this car and now after it was left to sit, it's doing this. It will idle fine without A/C and go down the road great no matter what. Idle is set at 700 with about 22" of vacuum and 10 degrees of advance. #6 is a hair low on compression, but not by much. 1-5 are at 120, six is at 90ish. I'm just about at a loss. A friend of mine has a four barrel intake and carburetor for sale, I may end up buying it.
Click to expand...

You think you got problems now? just wait til you get the 4bbl on!
Back to post #9
 
AJ/FormS said:
You think you got problems now? just wait til you get the 4bbl on!
Back to post #9
Click to expand...

Okay, so I won't do that. But back to the valves, the only reason I have not put them where you said is because it is a major pain getting the valve cover off since it's under A/C, heater, fuel, and vacuum lines. But something I just learned, I'm actually standing next to the car now, it is idling in gear with A/C on. It seems like it will do it just fine cold, but not hot. Would this be carburetor or would it be too tight valve lash?
 
When it is cold, is the choke on at all? If so, it should also be kicking up the idle with the fast idle cam, and you should be able to hear this. If so, this is normal.

Just try it again when cold and see if the choke plate is closed down at least part way when you tap the throttle before starting. And you should see the fast idle cam on the side of the carb move into position.

If this is the case, then the choke should go off completely after a few minute of running and the old problem should show up. How long does it take to get 'hot' to where the problem re-appears? And, BTW, you should set curb idle with the car completely warmed up so that the choke is fully off; perhaps you set it incorrectly.
 
Could be either. That's why post #9 covers both.

Here's the thing with valve lash.It's supposed to be done with the engine at running temp. But by the time you get the cover off, the engine has cooled off a lot. And, by the time you get to setting the last one, it has cooled off a very lot. So none of them are gonna be on spec when back to running temp.That's the first error.
Next is this;over time,the valve-stems have a nasty tendency to wear into the rocker arms, a nice narrow slot where the stem rides.And the slot has a curvature/crown to it that is in reverse to the rocker crown, so the slot is deeper in the center of the run, than at the beginning and end.So the clearance is ever changing.
Then: the slot is just a bit wider than the stem. When you stick your 1/2 inch feelers in there they bridge the slot and give you a false "feel" . Your feelers need to be modified to fit the slot.
I always set my lash cold; at between 65 and 75 degrees. That way I can take my time, and get a true,stable,end-to-end adjustment, that will stay where I put it,for many thousands of miles.
By experience I have found that a little loose is waaaay better than a little tight.And at idle is the very first place a too-tight lash, shows up.Your engine is lacking torque as evidenced by it's unwillingness to accept the A/C load. The first line of defense against this is to increase the cylinder pressure (compression).You have already attacked that, and brought the Scr back from the dead, somewhat.Now, the only option you have is the Dcr, and the quickest way to bump that up, is to trap more cylinder pressure by closing the intake valve earlier, and reducing overlap.That is, increasing the valve lash. You can chase the carb to Africa, or crank the timing to the moon, and maybe get it a little better, but you will be introducing other driveability issues.
If increasing the lash solves the problem, the next thing to attack is the cam-timing, starting with the chain-stretch. When the chain stretches, the cam timing goes into retard, and the idle timing along with it, and the engine gets sluggish at low rpm. The first thing a guy does is crank the idle up. Then as time goes by he discovers the idle-timing is out to lunch, so he cranks the dizzy. Eventually the cam, and the ignition, and the carb, stop playing nice together.
So if increasing the lash,produces a better running engine,this may be pointing to chain stretch.
But, when my slanty was fresh, it had 155psi, and I verified the cam timing, and it still responded to increased valve lash. You have got to give the engine what it wants. Factory specs were designed for factory engines. I have read that; out of 10 factory engines, 1 was a good runner, two were slugs, and the rest ran mediocre. I can't say if there is any truth to that, but perhaps yours is not the 1 in 10. Then factor in the years and miles that she has rolled on, and you can see the need for a custom tune . And the tune starts with the cylinder pressure.
-You should be aware of this helpful tip; The engine will run just fine with the valve cover off.......as long as everything else is hooked up.
So put it in a temperature stable environment (something you can repeat at any time of year ), let the engine cool to that environment; then set the lash, with the modded feelers;and cold. Start her up, bring her up to where the stat opens and see if she likes it. If not, let her cool and add .002. Then try again. Stop if/when she gets to 16/24. I don't see any gains after that.
BTW, your slanty should be running over 185*F. Mine is tuned for 195*. The hotter you can run it, in your state, without overheat issues, the better.The stat sets the minimum operating temp, not the max.If you have heat issues, solve those first.
-And finally, your slanty, with the one cylinder at "90ish"psi is no longer a six cylinder. And it's not a 5 either. With 25% leakage, at idle, it is no longer contributing, in fact the other 5, or at least the one next in the firing order, is forced to drag it along.If you care to see this; get the engine up to temp and record the engine vacuum and idle speed; then pull the ignition off the low cylinder, and record the numbers. Finally remove the sparkplug of that low cylinder, and again compare the numbers. Now go repeat the same tests with a known good cylinder.and compare.
Back to #9
 
AJ/FormS said:
Could be either. That's why post #9 covers both.

Here's the thing with valve lash.It's supposed to be done with the engine at running temp. But by the time you get the cover off, the engine has cooled off a lot. And, by the time you get to setting the last one, it has cooled off a very lot. So none of them are gonna be on spec when back to running temp.That's the first error.
Next is this;over time,the valve-stems have a nasty tendency to wear into the rocker arms, a nice narrow slot where the stem rides.And the slot has a curvature/crown to it that is in reverse to the rocker crown, so the slot is deeper in the center of the run, than at the beginning and end.So the clearance is ever changing.
Then: the slot is just a bit wider than the stem. When you stick your 1/2 inch feelers in there they bridge the slot and give you a false "feel" . Your feelers need to be modified to fit the slot.
I always set my lash cold; at between 65 and 75 degrees. That way I can take my time, and get a true,stable,end-to-end adjustment, that will stay where I put it,for many thousands of miles.
By experience I have found that a little loose is waaaay better than a little tight.And at idle is the very first place a too-tight lash, shows up.Your engine is lacking torque as evidenced by it's unwillingness to accept the A/C load. The first line of defense against this is to increase the cylinder pressure (compression).You have already attacked that, and brought the Scr back from the dead, somewhat.Now, the only option you have is the Dcr, and the quickest way to bump that up, is to trap more cylinder pressure by closing the intake valve earlier, and reducing overlap.That is, increasing the valve lash. You can chase the carb to Africa, or crank the timing to the moon, and maybe get it a little better, but you will be introducing other driveability issues.
If increasing the lash solves the problem, the next thing to attack is the cam-timing, starting with the chain-stretch. When the chain stretches, the cam timing goes into retard, and the idle timing along with it, and the engine gets sluggish at low rpm. The first thing a guy does is crank the idle up. Then as time goes by he discovers the idle-timing is out to lunch, so he cranks the dizzy. Eventually the cam, and the ignition, and the carb, stop playing nice together.
So if increasing the lash,produces a better running engine,this may be pointing to chain stretch.
But, when my slanty was fresh, it had 155psi, and I verified the cam timing, and it still responded to increased valve lash. You have got to give the engine what it wants. Factory specs were designed for factory engines. I have read that; out of 10 factory engines, 1 was a good runner, two were slugs, and the rest ran mediocre. I can't say if there is any truth to that, but perhaps yours is not the 1 in 10. Then factor in the years and miles that she has rolled on, and you can see the need for a custom tune . And the tune starts with the cylinder pressure.
-You should be aware of this helpful tip; The engine will run just fine with the valve cover off.......as long as everything else is hooked up.
So put it in a temperature stable environment (something you can repeat at any time of year ), let the engine cool to that environment; then set the lash, with the modded feelers;and cold. Start her up, bring her up to where the stat opens and see if she likes it. If not, let her cool and add .002. Then try again. Stop if/when she gets to 16/24. I don't see any gains after that.
BTW, your slanty should be running over 185*F. Mine is tuned for 195*. The hotter you can run it, in your state, without overheat issues, the better.The stat sets the minimum operating temp, not the max.If you have heat issues, solve those first.
-And finally, your slanty, with the one cylinder at "90ish"psi is no longer a six cylinder. And it's not a 5 either. With 25% leakage, at idle, it is no longer contributing, in fact the other 5, or at least the one next in the firing order, is forced to drag it along.If you care to see this; get the engine up to temp and record the engine vacuum and idle speed; then pull the ignition off the low cylinder, and record the numbers. Finally remove the sparkplug of that low cylinder, and again compare the numbers. Now go repeat the same tests with a known good cylinder.and compare.
Back to #9
Click to expand...

Wow. Very informative. I'll run through it this week and see what I can do to it. I will say, that I did set the lash with the engine hot and idling, but I guess a little tight. I'll work on it after work and tell what happens. Thank you.
 
nm9stheham said:
When it is cold, is the choke on at all? If so, it should also be kicking up the idle with the fast idle cam, and you should be able to hear this. If so, this is normal.

Just try it again when cold and see if the choke plate is closed down at least part way when you tap the throttle before starting. And you should see the fast idle cam on the side of the carb move into position.

If this is the case, then the choke should go off completely after a few minute of running and the old problem should show up. How long does it take to get 'hot' to where the problem re-appears? And, BTW, you should set curb idle with the car completely warmed up so that the choke is fully off; perhaps you set it incorrectly.
Click to expand...

The choke does come on when pedal is pressed, but the moment the car starts, I tap the gas and it goes to low idle. On low idle with a cold engine, it's fine. After about 10-15 minutes, it's not.
 
Carb's messed up.
Depending on outside air temp, and temp of engine the Choke pull-off, will pull the t-blades open from, usually, the second highest step,to the next lower step,and so on as the engine warms up. If she has electric assist, it still can take a few to several minutes, again depending on the temps, to allow the fast idle to drop out.
If yours works as you describe, and the engine temp is about 60*F , and it remains running, well then, the low-speed circuit is very rich; cuz really it should stall or nearly so.
In my experience,after 73 or so, slantys were pretty lean and wanted to stall, as soon as something wasn't just right. I guess thye 10* initial is helping it run...
But, if she really is rich, then that could be contributing to the stalling with A/C. Of course that takes me back to post #9, and the T-port sync.It was #9, wasn't it?
Yup #9
 
AJ/FormS said:
Carb's messed up.
Depending on outside air temp, and temp of engine the Choke pull-off, will pull the t-blades open from, usually, the second highest step,to the next lower step,and so on as the engine warms up. If she has electric assist, it still can take a few to several minutes, again depending on the temps, to allow the fast idle to drop out.
If yours works as you describe, and the engine temp is about 60*F , and it remains running, well then, the low-speed circuit is very rich; cuz really it should stall or nearly so.
In my experience,after 73 or so, slantys were pretty lean and wanted to stall, as soon as something wasn't just right. I guess thye 10* initial is helping it run...
But, if she really is rich, then that could be contributing to the stalling with A/C. Of course that takes me back to post #9, and the T-port sync.It was #9, wasn't it?
Yup #9
Click to expand...

Lash is set as described, runs better and number six is performing like the other five. Not sure why six was so much tighter than the others, but it was too tight to get a .010 in there. All six are now at 120 like they should be. First start of the morning, the engine is probably in the mid 70's as far as temperature, but it always did that. Pump it once to set the choke and prime it, bump the starter and it goes to high idle. Let it run for a couple of seconds, tap the gas for low idle, put it in gear and take off down the road. I was over at a friends place setting the lash because he wanted some help with his Mustang (not sure if one can be helped) but he asked me something that made me feel mighty stupid. He asked how easy the compressor spun by hand. It doesn't. It's nearly impossible to turn the compressor by hand. I put that compressor on it a few months before I had sold the car, it had maybe 200 miles of run time on it, and it's very difficult to turn. Being it has been awhile and I don't remember, should the RV2 be difficult to spin by hand or should it turn smoothly?
 
That takes me back to what you said earlier, about the discharge air temp being 40* . I assumed that was correct for a 70* day. Cuz in my experience if the system is adjusted correctly,the discharge air is rarely more than about 30 degrees cooler than ambient.
So at 75* less 30* , being 45*, as compared to your 40*; your system may have too much refrigerant in it.If your compressor is a piston type compressor, this may have damaged the compressor.
But if the system was just running,and fully warmed up, this may be normal. You will have to recheck it after it has set overnight, and the pressures have equalized. If it is still hard or impossible to turn over by hand, that would not be right.
If your compressor is other than a piston type, I have no experience with those.

Congrats on getting the lash set right! Now the engine's idle-torque should remain the same or actually improve as it warms up.
 
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