Low Engine RPM

[Lawrence71]

So another day, another problem ... 🙂

Got my distributor/voltage issues sorted out, and the previous owner (from hereon referred to as "blockhead") had had a broken kickdown cable, which is on the list.  In the short term, blockhead's fix had been to have the throttle return spring attached to the kickdown cable, and the attachment to the carb itself isn't a nice pice, but a couple'a nuts attached to a bolt. I suspect previous stuck throttle issues could be related to the kickdown slide piece catching on the threads of the bolt being used.

Regardless, trying to sort through the mess and get things working.

Engine will start, but without any throttle applied it lopes and runs at a level of almost dying (doesn't *quite* get there, but still is very close). I am ultimately trying to set the timing on new distributor but seems like without a steady idle this is a fool's errand.

So dumb question time:

- what should I be looking at for getting a "normal" idle? is this adjusting some of the carb screws?

- could fuel flow have anything to do with this, since I need to hold (slightly) on the accelerator to get things running normal? I did buy a new fuel filter for the pre-carb line (some sort of one with a return, no idea if it's "right", but looks the same as what I'd be replacing).

- any other general tips? Had originally wondered if this was related to the timing on the engine being off, but now I'm not sure.

Thanks,

David

[jft69z]

Idle speed screw on the carb can be adjusted to bring the idle up. But, there are too many unknowns right now to diagnose from here. First place I'd start is a good tune up, things like new spark plugs, ignition wires, fuel filter, etc. Maybe some of that stuff is new already, but if the guy was a 'blockhead', I'd start fresh.

The timing also needs to be set properly, but that will probably interact with the idle speed, so you may need to check them both a couple of times until they're right. Idle mixture screws on the carb will also have an effect on the idle speed as well. If it has an idle stop solenoid, that'll figure in as well. They all sort of work together..  I'd check for vacuum leaks, cracked hoses, etc, and if all that doesn't help, maybe a carb rebuild down the road. Start with the simple things first though.

I'm sure someone else will add to this to steer you in the right direction.

[Lawrence71]

Hi, thanks for the response. Redid the spark plugs, wires and coil already (basically a whole ignition rebuild). New distributor (traded out points for electric). Oil change/filter. New alternator.  New air cleaner filter.  Ignition converted to 12V. Very possible the timing of the distributor is off, set to match TDC and as a new guy don’t know if I should move clockwise or counter to speed it up. 

The vehicle had been running decent before, low rpm ish but not like this, so likely something I did, most likely the timing if I had to guess. 

[jft69z]

Counter clockwise to increase timing, but you really need a timing light to check this properly. With that, you'll also see what direction to turn the distributor.

[MC1of80]

Counterclockwise to advance the timing. 

[jft69z]

1 minute ago, MC1of80 said:

Counterclockwise to advance the timing. 

increase...advance....I knew what I meant, 😁

[MC1of80]

Lol your answered him seconds before mine posted. Tomatoe, tomato lolol

[Lawrence71]

Ok, and as I understand it I want 30 degrees. Is that literally turning it 30 degrees counterclockwise (assuming 0 for TDC)? I just need it to stay a reasonable rpm so I can get out and use the gun.

[MC1of80]

No! Lol. With the vacuum advance disconnected start at 12 to 14 degrees advance. 

[Dtret]

How did the car run before you changed the distributor? What was the reason for the change?

[jft69z]

10 minutes ago, Lawrence71 said:

Ok, and as I understand it I want 30 degrees. Is that literally turning it 30 degrees counterclockwise (assuming 0 for TDC)? I just need it to stay a reasonable rpm so I can get out and use the gun.

No, you need to get the timing set on the harmonic balancer timing tab, not how many degrees you turn the distributor. I'll eyeball it a little when setting it up from scratch, but you need a timing light to get it right. 30 degrees is quite a bit for initial/idle timing. Where did you get that number? (Don't forget, the camshaft spins half the speed of the crankshaft, if you're trying to eyeball the distributor 30 degrees at the rotor, you may be way off, if I'm understanding you correctly)

Bump the idle speed screw up a bit to keep the engine running if needed. Adjust it down accordingly as you zero in on the timing. 

I have to get to work now, I'll check back later. My next to last shift before retiring 

[Lawrence71]

38 minutes ago, Dtret said:

How did the car run before you changed the distributor? What was the reason for the change?

It ran fine for about 9 months; the idle started getting a lot lower towards the end of that cycle.

The reason for the new distributor was twofold:

1) some play in the shaft of the original

2) desire to switch away from points

[Lawrence71]

40 minutes ago, jft69z said:

No, you need to get the timing set on the harmonic balancer timing tab, not how many degrees you turn the distributor. I'll eyeball it a little when setting it up from scratch, but you need a timing light to get it right. 30 degrees is quite a bit for initial/idle timing. Where did you get that number? (Don't forget, the camshaft spins half the speed of the crankshaft, if you're trying to eyeball the distributor 30 degrees at the rotor, you may be way off, if I'm understanding you correctly)

Bump the idle speed screw up a bit to keep the engine running if needed. Adjust it down accordingly as you zero in on the timing. 

I have to get to work now, I'll check back later. My next to last shift before retiring 

So I did a slight twist of ~ 5-10 degrees (on the distributor) and the engine will run consistently enough for me to test with the timing light, will report back with any developments.

[jft69z]

37 minutes ago, Lawrence71 said:

So I did a slight twist of ~ 5-10 degrees (on the distributor) and the engine will run consistently enough for me to test with the timing light, will report back with any developments.

Slight twist is perfect. 

Some people don't tighten the distributor hold down clamp enough either, and the distributor will rotate out of adjustment. Never had good luck with the chrome/aftermarket clamps. OEM works good and keeps it tight....just a thought.

[420ponies]

Here is how I get it done. Find TDC with #1 spark plug out, turn starter (or turn engine at crankshaft pulley 5/8"  socket) ,plug spark plug hole with thumb until you feel pressure from cylinder. When you feel that ,look at timing tab and see where crankshaft balancer timing mark is. Bring the balancer mark to 8° mark on timing tab( should be on upper side of tab).Now take distributor cap off and turn distributor ,so #1 plug lines up with cap. Install cap back on distributor. Now it should start on this initial setting. Adjust idle to get to 850 rpm (to where it sounds good) or where it runs ,and not to high where it jumps into gear. Now, if you don't have any vacuum leaks, try pulling a vacuum hose off to see/hear rpm rise. If it rises with hose off, good ,now you can set your timing with a gun. About 1/4 above idle,not half throttle, should be around 3,000rpm,you will notice mark on balancer disappears ( to the top of timing tab), now turn distributor until it gets to 0° on timing tab... Go back to idle,might have to adjust, bring it back to the song, check it again. Remember, this is with vacuum advance hose installed on carb. It's a process, I know but should get you close enough for your timing light. Let us know how you make out .

 

[stangeba]

Talking about vacuum hoses reminded me to ask if the vacuum advance hose is off and plugged, when you are setting the timing?

Perhaps the fancy new dist doesn't have this option.

 

[Scott S.]

Did yo replace the fuel filter ??

Could be a partial blockage, or dirty jets in the carb.

[Lawrence71]

17 hours ago, stangeba said:

Talking about vacuum hoses reminded me to ask if the vacuum advance hose is off and plugged, when you are setting the timing?

Perhaps the fancy new dist doesn't have this option.

 

tested with the vacuum advance off but just used a rag to block, no plug. (Bought some, can’t find ‘em. 😂)

 

1 hour ago, Scott S. said:

Did yo replace the fuel filter ??

Could be a partial blockage, or dirty jets in the carb.

Haven’t replaced fuel filter yet. I *think* there might be two, one closer to the fuel tank and one is in the carb fuel line with a return. I have a replacement for that one but just visually bought one that looked similar so there may be specs I’m not aware of. 
 

So the timing tab only goes to 10ish; how do you measure beyond that? I think my timing gun may have a tare option, just tare and sum them if trying to get to 14?

[Lawrence71]

17 hours ago, 420ponies said:

Here is how I get it done. Find TDC with #1 spark plug out, turn starter (or turn engine at crankshaft pulley 5/8"  socket) ,plug spark plug hole with thumb until you feel pressure from cylinder. When you feel that ,look at timing tab and see where crankshaft balancer timing mark is. Bring the balancer mark to 8° mark on timing tab( should be on upper side of tab).Now take distributor cap off and turn distributor ,so #1 plug lines up with cap. Install cap back on distributor. Now it should start on this initial setting. Adjust idle to get to 850 rpm (to where it sounds good) or where it runs ,and not to high where it jumps into gear. Now, if you don't have any vacuum leaks, try pulling a vacuum hose off to see/hear rpm rise. If it rises with hose off, good ,now you can set your timing with a gun. About 1/4 above idle,not half throttle, should be around 3,000rpm,you will notice mark on balancer disappears ( to the top of timing tab), now turn distributor until it gets to 0° on timing tab... Go back to idle,might have to adjust, bring it back to the song, check it again. Remember, this is with vacuum advance hose installed on carb. It's a process, I know but should get you close enough for your timing light. Let us know how you make out .

 

So you turn back to 0 degrees while it’s at still at 3000? Just hold the throttle somehow?

[Scott S.]

2 hours ago, Lawrence71 said:

tested with the vacuum advance off but just used a rag to block, no plug. (Bought some, can’t find ‘em. 😂)

 

Haven’t replaced fuel filter yet. I *think* there might be two, one closer to the fuel tank and one is in the carb fuel line with a return. I have a replacement for that one but just visually bought one that looked similar so there may be specs I’m not aware of. 
 

So the timing tab only goes to 10ish; how do you measure beyond that? I think my timing gun may have a tare option, just tare and sum them if trying to get to 14?

If you still have the quadrajet, there's one built into the carb body..... Anything else is aftermarket.

[420ponies]

Just turn distributor counter clock wise to advance timing,clock wise to retard timing. If advancing ,mark will move closer to timing tab 0° vice versa if moving opposite way.You can turn distributor while running engine, you can check ,then let idle,adjust distributor,re - check at 1\4 throttle.... Until that mark is on 0° ,when you have it there,fights down distributor hold down and then recheck at 1/4 throttle again. Actually you will hear motor smooth out when you're close.

[Lawrence71]

Just following up; thanks for all the help, things are working great. Also adjusted carb idle mixtures, idle speed, etc, so that's a new thing learned as well.  Final initial advance ended up around 18; seemed a little higher than expected, but based on the engine sound and everything, that was the right value for me.

David

 

 

[cny first gen 71]

7 minutes ago, Lawrence71 said:

Just following up; thanks for all the help, things are working great. Also adjusted carb idle mixtures, idle speed, etc, so that's a new thing learned as well.  Final initial advance ended up around 18; seemed a little higher than expected, but based on the engine sound and everything, that was the right value for me.

David

 

 

It's great learning new stuff 👌 you'll learn a lot working on your car yourself and there's always people here to help.