Slant Six Tuning/Running Issues

[zpsull01]

I have a 75 Valiant more door with a 225 that I recently put back on the road after about 25 years of sitting. Everything on the motor is stock.

I am having an inconsistent issue to where sometimes the car runs and accelerates great. Other times it has noting off of idle and blogs like it is lean. It only does this while under the load of driving. It will rev clean and sounds great in park or neutral. Once I get over 1/2-2/3 throttle it clears up and runs strong. This seems to be an on or off issue, there is no in between. One thing I notice is that the idle rpm changes about 150-200 rpms when this happens. When it runs bad the idle will drop that amount. If I try to re-tune everything and reset the idle to 750 it will jump to about 900-950 once it starts running well again.

I'm thinking that the only two things that would change the idle rpm would be a vacuum leak or the timing changing. I have checked for vacuum leaks around the carb and intake with none found. I also tried to run it without the vacuum canister on the distributor hooked up with no luck. I'm still in the process of removing and plugging the remaining vacuum circuits one at a time while it's running bad to test each. I'm also going to start carrying the timing light in the car with me as well so if it does change to the bad I will check to see if the timing has changed.

I have not been able to pin point when this change happens consistently yet. It will normally do it in the mornings after getting down the road 2-3 miles. It seems to sometimes come and go when the engine is shut off, like it resets. It was running bad once and I gave it a couple of good stabs at the throttle in neutral and it cleared up and started running well again and continued to for the remainder of the drive.

I have the 1945 Holley. It has been rebuilt and back apart many times. Had issues originally that have all been worked through. (Accelerator check ball missing, accelerator pump passage blocked, power valve vacuum piston stuck in bore in extended position, missing fast idle cam). There is a new fuel filter, gas tank, sending unit, and all lines(hard and soft). I thoroughly tested the accelerator pump circuit and check ball system. Everything there is good.

Plugs, wires, dist. cap and rotor were all replaced. All vacuum lines have been replaced. EGR valve, OSAC valve, vacuum solenoid, and vacuum amplifier/canister have been removed.

Timing is set at 1° BTDC at 750 rpm's (17° total). The motor pulls 19.5-20" of vacuum. I have not had a chance to adjust the valves yet.

Am I on the right track with the timing or is something else going on? The only other thing that I could think of would be a sticking valve but I wouldn't think that it would clear up in the upper rpms. Thanks ahead of time for your help.

 

[MarPar]

Check the distributor hold down

 

[zpsull01]

Check the distributor hold down

The hold down bolt is tight. Does the slotted metal bracket have any history with coming lose from the distributer itself?

 

[MarPar]

The hold down bolt is tight. Does the slotted metal bracket have any history with coming lose from the distributer itself?

Not necessarily. To me, it kinda sounds like a timing thing, so I went for the quickest item to check. Next I would check the cap and rotor. Just cuz it's new doesn't always mean it works.

 

[RustyRatRod]

Have you removed and cleaned the gas tank? Getting the entire fuel system clean, clean, CLEAN would be the first thing I would do. Also inspect and or REPLACE all of the rubber fuel hose sections with new and make sure the fuel filter is new. Even if it is, with a nasty fuel system it can and will clog again. Without all that eliminated, you may just chase your tail.

 

[zpsull01]

Not necessarily. To me, it kinda sounds like a timing thing, so I went for the quickest item to check. Next I would check the cap and rotor. Just cuz it's new doesn't always mean it works.

What am I looking for here? The cap fits well and the hold downs are tight. Would pictures of the cap and rotor help with anything?

Have you removed and cleaned the gas tank? Getting the entire fuel system clean, clean, CLEAN would be the first thing I would do. Also inspect and or REPLACE all of the rubber fuel hose sections with new and make sure the fuel filter is new. Even if it is, with a nasty fuel system it can and will clog again. Without all that eliminated, you may just chase your tail.

Tank is new, All lines are new (hard and soft), and a new quality filter. The pump is the only thing in the system prior to the carb being reused. It was flushed before hooking up the the carb.

 

[MarPar]

What am I looking for here? The cap fits well and the hold downs are tight. Would pictures of the cap and rotor help with anything?



Tank is new, All lines are new (hard and soft), and a new quality filter. The pump is the only thing in the system prior to the carb being reused. It was flushed before hooking up the the carb.

Just spitballing here. Could be that the rotor is loose? idk.

 

[zpsull01]

Just spitballing here. Could be that the rotor is loose? idk.

I didn't know. I thought I saw something one time about reading the health of the ignition system by how the inside of the cap looked. As for arc marks, when it was arcing, burns, etc.

 

[MarPar]

I didn't know. I thought I saw something one time about reading the health of the ignition system by how the inside of the cap looked. As for arc marks, when it was arcing, burns, etc.

That too...couldn't hurt to have a look see...

 

[zpsull01]

That too...couldn't hurt to have a look see...

I pulled it off yesterday. It still looked new basically. Pulled all the plugs too. I know this isn't the right way to read plugs but they all look pretty even.

 

[MarPar]

Well sh*t.

 

[valiantwagonguy]

Put an earlier carb on it ,basically set it up like a 65 with only a PCV and a carter 1 bbl. See what happens then. I had this same thing with my 76 Aspen 6 cyl.This is how I solved it.Mid 70's slants are really dogged out and prone to this sort of crap when left in stock condition.They did everything they could to make them pass emissions tests and totally screwed them up. This woke my Aspen right up.It was downright dangerous getting on the highway before and now it just gets up and goes

 

[Ian McCrimmon]

Well not an expert by any means but the three things I would look at are checking and setting the reluctor gap (assuming its an electronic dizzy by its age), run the valves (hot) then re-set the timing to 10° BTDC.

 

[Ricks70Duster340]

I have a 75 Valiant more door with a 225 that I recently put back on the road after about 25 years of sitting. Everything on the motor is stock.

I am having an inconsistent issue to where sometimes the car runs and accelerates great. Other times it has noting off of idle and blogs like it is lean. It only does this while under the load of driving. It will rev clean and sounds great in park or neutral. Once I get over 1/2-2/3 throttle it clears up and runs strong. This seems to be an on or off issue, there is no in between. One thing I notice is that the idle rpm changes about 150-200 rpms when this happens. When it runs bad the idle will drop that amount. If I try to re-tune everything and reset the idle to 750 it will jump to about 900-950 once it starts running well again.

I'm thinking that the only two things that would change the idle rpm would be a vacuum leak or the timing changing. I have checked for vacuum leaks around the carb and intake with none found. I also tried to run it without the vacuum canister on the distributor hooked up with no luck. I'm still in the process of removing and plugging the remaining vacuum circuits one at a time while it's running bad to test each. I'm also going to start carrying the timing light in the car with me as well so if it does change to the bad I will check to see if the timing has changed.

I have not been able to pin point when this change happens consistently yet. It will normally do it in the mornings after getting down the road 2-3 miles. It seems to sometimes come and go when the engine is shut off, like it resets. It was running bad once and I gave it a couple of good stabs at the throttle in neutral and it cleared up and started running well again and continued to for the remainder of the drive.

I have the 1945 Holley. It has been rebuilt and back apart many times. Had issues originally that have all been worked through. (Accelerator check ball missing, accelerator pump passage blocked, power valve vacuum piston stuck in bore in extended position, missing fast idle cam). There is a new fuel filter, gas tank, sending unit, and all lines(hard and soft). I thoroughly tested the accelerator pump circuit and check ball system. Everything there is good.

Plugs, wires, dist. cap and rotor were all replaced. All vacuum lines have been replaced. EGR valve, OSAC valve, vacuum solenoid, and vacuum amplifier/canister have been removed.

Timing is set at 1° BTDC at 750 rpm's (17° total). The motor pulls 19.5-20" of vacuum. I have not had a chance to adjust the valves yet.

Am I on the right track with the timing or is something else going on? The only other thing that I could think of would be a sticking valve but I wouldn't think that it would clear up in the upper rpms. Thanks ahead of time for your help.

View attachment 1715737299

After 25 years of sitting, strange things can happen. Cars like to be driven! I would pull the distributor cap and look down to the advance springs to see if they look like they are all rusted up. Could be the plate is binding and/or springs are rusty and not allowing things to move consistently.

 

[zpsull01]

Put an earlier carb on it ,basically set it up like a 65 with only a PCV and a carter 1 bbl. See what happens then. I had this same thing with my 76 Aspen 6 cyl.This is how I solved it.

I’m assuming this is the carter bbs carb. I was hoping to avoid spending money on a questionable reman but may have to. Does the kickdown linkage and all bolt right up to this? I have a 66 d300 with an industrial slant 6 with a bbs but it’s a manual choke/trans so I don’t have all the needed linkage. This car had all the emissions timers for the throttle solenoid and catalytic protection systems. I’ve removed all that. I’m only using the idle enrichment valve and the temperature sensor for the heat stove valve.

Well not an expert by any means but the three things I would look at are checking and setting the reluctor gap (assuming its an electronic dizzy by its age), run the valves (hot) then re-set the timing to 10° BTDC.

I’ll check all this. The timing was initially at 10* btdc but I moved it back to match the factory spec. Didn’t think about the detuning at the factory.

After 25 years of sitting, strange things can happen. Cars like to be driven! I would pull the distributor cap and look down to the advance springs to see if they look like they are all rusted up. Could be the plate is binding and/or springs are rusty and not allowing things to move consistently.

Can these items be removed and cleaned with the distributor in the motor or does it need to come out? Also if this is the case how does one go about lubricating these parts? I’m assuming you don’t just spray a lubricant down the distributor. I have some electrical contact cleaner and dielectric grease but I’m not sure I can get it do the right spots with everything together.

 

[zpsull01]

I was able to drive the car about 20 miles on the highway today at much more constant speeds than I have been in the past. There appears to be a surging or bucking that appears at consistent throttle position at nearly any rpm. It is much more prominent from 0 to about 1/3 throttle. The best way I can describe this would be by comparing it to quickly pulsing the throttle.

I’m going to change the coil out and see what that does as well.

 

[zpsull01]

Update: I checked each vacuum circuit with no found issues. The internals of the distributor look great, almost new. Set the reluctor gap. I have not been able to hot lash the valves yet. Reset the timing to 10° BTDC. Since I have reset the timing I have yet to have any major issues with drivability. I have driven the car about 200 miles on about 8 different occasions.

With that being said, how far can you push the timing on these? I see that people are running 14+° on some. What is the best way to go about finding this threshold?

 

[AJ/FormS]

What is the best way to go about finding this threshold?

My slanty likes lots of Idle-timing. But if you give it too much you will have problems at idle because the throttle will end up being too far closed. and the mixture too lean. So then, you will crank open the mixture screws and then it will idle just fine.
But, as soon as you open the throttle, you will get a hesitation or a bog, until the transfers come back on line. The transfers are your low-speed circuit, and the mixture screws are just the idle-trimmers. Now, still set this way, your entire low-speed circuit will be rich, because the trimmers are open too far.
And to think this all started because the timing was too far advanced.
But if the timing is too far retarded, the exact opposite will occur. Your throttle will need to be set too far open to obtain a decent idle speed. And the mixture will be rich. So then you will close the trimmers and it will idle fine. But as before when you step on the gas, the entire slow-speed system will be lean because the trimmers have been shut off.
Ok so, by this, you can know where to set the trimmers and the idle speed, and then use the timing to set the idle speed. When you do it this way, you will not have any low-speed and or driveability issues.
However, this all assumes your slow-speed circuit is actually functioning as designed. and that means you start with the correct fuel level, and that the fuel level stays correct. Next up are the Idle air bleeds at the top of the idle wells, and finally are the emulsion tubes.
Now add a bit of a vacuum leak or too tight intake valves, and things can go sour in a hurry.
In comparison, the timing is no big thing, a slanty will run on just about any timing until it is too much.
Mine likes about 8* at idle, and 28* by 2800, slowing to 32 at 3400. And easy on the V-can. And for lash, mine likes no less than .013 on the intakes and no more than .023 on the exhaust.

 

[Inertia]

Kinda sounds like the trouble begins when the choke comes totally off.
jmo

 

[Bewy]

If you find more idle timing helps [ & it often does ], you should cut back the centri curve in the dist so that you maintain the same WOT timing.

 

[DMC_78]

I have a 75 Valiant more door with a 225 that I recently put back on the road after about 25 years of sitting. Everything on the motor is stock.

I am having an inconsistent issue to where sometimes the car runs and accelerates great. Other times it has noting off of idle and blogs like it is lean. It only does this while under the load of driving. It will rev clean and sounds great in park or neutral. Once I get over 1/2-2/3 throttle it clears up and runs strong. This seems to be an on or off issue, there is no in between. One thing I notice is that the idle rpm changes about 150-200 rpms when this happens. When it runs bad the idle will drop that amount. If I try to re-tune everything and reset the idle to 750 it will jump to about 900-950 once it starts running well again.

I'm thinking that the only two things that would change the idle rpm would be a vacuum leak or the timing changing. I have checked for vacuum leaks around the carb and intake with none found. I also tried to run it without the vacuum canister on the distributor hooked up with no luck. I'm still in the process of removing and plugging the remaining vacuum circuits one at a time while it's running bad to test each. I'm also going to start carrying the timing light in the car with me as well so if it does change to the bad I will check to see if the timing has changed.

I have not been able to pin point when this change happens consistently yet. It will normally do it in the mornings after getting down the road 2-3 miles. It seems to sometimes come and go when the engine is shut off, like it resets. It was running bad once and I gave it a couple of good stabs at the throttle in neutral and it cleared up and started running well again and continued to for the remainder of the drive.

I have the 1945 Holley. It has been rebuilt and back apart many times. Had issues originally that have all been worked through. (Accelerator check ball missing, accelerator pump passage blocked, power valve vacuum piston stuck in bore in extended position, missing fast idle cam). There is a new fuel filter, gas tank, sending unit, and all lines(hard and soft). I thoroughly tested the accelerator pump circuit and check ball system. Everything there is good.

Plugs, wires, dist. cap and rotor were all replaced. All vacuum lines have been replaced. EGR valve, OSAC valve, vacuum solenoid, and vacuum amplifier/canister have been removed.

Timing is set at 1° BTDC at 750 rpm's (17° total). The motor pulls 19.5-20" of vacuum. I have not had a chance to adjust the valves yet.

Am I on the right track with the timing or is something else going on? The only other thing that I could think of would be a sticking valve but I wouldn't think that it would clear up in the upper rpms. Thanks ahead of time for your help.

View attachment 1715737299

Long time lurker here....saw this post and had to reply. I honestly had the exact same symptoms before in a slant that had been sitting over the winter. Motor had all the recommended maintenance stuff completed including valve lash and timing chain. I verified just about everything I could like you have done before I went on a hunch and went after the ignition module. Changed out the module for a Napa stock replacement and a new ballast resistor while I was there ....problem solved, been running like a champ since.
Might be worth a shot. My engine was a 78 for reference.