Idle issues
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Idle issues
I am having trouble getting a smooth idle on my newly rebuilt fuel injection (7014800). It runs fine on the fast idle cam and during normal driving conditions. However, once completely off of the cam, it won't keep an idle and surges between 500 - 800 rpms. Adjusting the air and fuel idle screws seems to have minimal effect.
I have a single point distributor with vacuum advance. I've played with the timing and running it about 20 degrees BTDC.
Any ideas?
I have a single point distributor with vacuum advance. I've played with the timing and running it about 20 degrees BTDC.
Any ideas?
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20 degrees BTDC is a lot. If you are using a '57 distributor, the original spec was in the range of 4 - 8 degrees initial advance (I don't remember the exact value).
Beside re-timing the engine, though, I'd try disconnecting the vacuum advance and noting whether or not the idle stabilizes. My hunch is that the engine idle vacuum is right about at the pull-in threshold of the vacuum can, causing the timing to "hunt" at idle. If the timing is hunting around, so, too, will engine idle speed.
Speaking of engine idle vacuum..... if your engine has an "097" cam or any cam which makes about 14" Hg at idle, your Enrichment Diaphragm should be adjusted to pull the Ratio Lever to the Economy Stop by a vacuum level of 9" Hg. Has it been so adjusted?
One other thought..... 4800 units use a piston-type spill plunger which loves to stick in the bore of the sleeve in which it rides. A good preventative for this is to polish the spill plunger and the interior of the sleeve with 1500 grit paper. Did you do anything like this when the unit was being rebuilt?
Jim
Beside re-timing the engine, though, I'd try disconnecting the vacuum advance and noting whether or not the idle stabilizes. My hunch is that the engine idle vacuum is right about at the pull-in threshold of the vacuum can, causing the timing to "hunt" at idle. If the timing is hunting around, so, too, will engine idle speed.
Speaking of engine idle vacuum..... if your engine has an "097" cam or any cam which makes about 14" Hg at idle, your Enrichment Diaphragm should be adjusted to pull the Ratio Lever to the Economy Stop by a vacuum level of 9" Hg. Has it been so adjusted?
One other thought..... 4800 units use a piston-type spill plunger which loves to stick in the bore of the sleeve in which it rides. A good preventative for this is to polish the spill plunger and the interior of the sleeve with 1500 grit paper. Did you do anything like this when the unit was being rebuilt?
Jim
Last edited by jim lockwood; Nov 5, 2015 at 05:37 PM.
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From: San Clemente CA
Jim,
I dropped the advance to about 8 degrees and disconnected the vacuum advance. If anything, the surging is worse. I noticed when it revs up, the timing advances by 10 degrees or more. Why would it advance when the engine surges if the vacuum is disconnected? I'm also not sure why the idle air and fuel adjustments do very little.
I dropped the advance to about 8 degrees and disconnected the vacuum advance. If anything, the surging is worse. I noticed when it revs up, the timing advances by 10 degrees or more. Why would it advance when the engine surges if the vacuum is disconnected? I'm also not sure why the idle air and fuel adjustments do very little.
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Jim,
I dropped the advance to about 8 degrees and disconnected the vacuum advance. If anything, the surging is worse. I noticed when it revs up, the timing advances by 10 degrees or more. Why would it advance when the engine surges if the vacuum is disconnected? I'm also not sure why the idle air and fuel adjustments do very little.
I dropped the advance to about 8 degrees and disconnected the vacuum advance. If anything, the surging is worse. I noticed when it revs up, the timing advances by 10 degrees or more. Why would it advance when the engine surges if the vacuum is disconnected? I'm also not sure why the idle air and fuel adjustments do very little.
Mechanical advance weights in the distributor kicking in as the rpm increases - they're doing exactly what they are supposed to!
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Jim,
I dropped the advance to about 8 degrees and disconnected the vacuum advance. If anything, the surging is worse. I noticed when it revs up, the timing advances by 10 degrees or more. Why would it advance when the engine surges if the vacuum is disconnected? I'm also not sure why the idle air and fuel adjustments do very little.
I dropped the advance to about 8 degrees and disconnected the vacuum advance. If anything, the surging is worse. I noticed when it revs up, the timing advances by 10 degrees or more. Why would it advance when the engine surges if the vacuum is disconnected? I'm also not sure why the idle air and fuel adjustments do very little.
http://www.lbfun.com/warehouse/tech_...101Article.pdf
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Why would it advance when the engine surges if the vacuum is disconnected?
I'm also not sure why the idle air and fuel adjustments do very little.
Jim
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From: San Clemente CA
There are TWO advance systems in your distributor - the vacuum advance responds only to engine load conditions, and the centrifugal advance responds only to engine rpm, regardless of load.
http://www.lbfun.com/warehouse/tech_...101Article.pdf
http://www.lbfun.com/warehouse/tech_...101Article.pdf
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Hmmmm..... that makes me wonder if your mechanical advance is starting too soon. Let's circle back to this a little later.
What Tux and John said explains this.
You should be able to stall the engine if you turn either the idle fuel or the idle air screws all the way clockwise. Can you?
Jim
What Tux and John said explains this.
You should be able to stall the engine if you turn either the idle fuel or the idle air screws all the way clockwise. Can you?
Jim
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From: San Clemente CA
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OK, this is a Real Good Thing. Many things inside the FI unit have to be working properly and there almost certainly aren't any vacuum leaks.
I previously asked how your Enrichment Diaphragm was adjusted. I didn't get an answer, so let me try a different approach:
Remove the fuel meter shield, if your FI unit has one, and reinstall the two main diaphragm screws.
Start the engine and let it warm up to the point that cold enrichment turns off.
The picture below shows the Ratio Lever. At engine idle, it should be resting solidly against the left-hand set screw (the one labled Economy). Is it? Or is it moving back and forth between the two set screws?
Jim
I previously asked how your Enrichment Diaphragm was adjusted. I didn't get an answer, so let me try a different approach:
Remove the fuel meter shield, if your FI unit has one, and reinstall the two main diaphragm screws.
Start the engine and let it warm up to the point that cold enrichment turns off.
The picture below shows the Ratio Lever. At engine idle, it should be resting solidly against the left-hand set screw (the one labled Economy). Is it? Or is it moving back and forth between the two set screws?
Jim
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Joined: May 2014
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From: San Clemente CA
OK, this is a Real Good Thing. Many things inside the FI unit have to be working properly and there almost certainly aren't any vacuum leaks.
I previously asked how your Enrichment Diaphragm was adjusted. I didn't get an answer, so let me try a different approach:
Remove the fuel meter shield, if your FI unit has one, and reinstall the two main diaphragm screws.
Start the engine and let it warm up to the point that cold enrichment turns off.
The picture below shows the Ratio Lever. At engine idle, it should be resting solidly against the left-hand set screw (the one labled Economy). Is it? Or is it moving back and forth between the two set screws?
Jim
I previously asked how your Enrichment Diaphragm was adjusted. I didn't get an answer, so let me try a different approach:
Remove the fuel meter shield, if your FI unit has one, and reinstall the two main diaphragm screws.
Start the engine and let it warm up to the point that cold enrichment turns off.
The picture below shows the Ratio Lever. At engine idle, it should be resting solidly against the left-hand set screw (the one labled Economy). Is it? Or is it moving back and forth between the two set screws?
Jim
Thanks for the above photo. I'll look at the ratio lever and get back to you today.
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Joined: May 2014
Posts: 530
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From: San Clemente CA
OK, this is a Real Good Thing. Many things inside the FI unit have to be working properly and there almost certainly aren't any vacuum leaks.
I previously asked how your Enrichment Diaphragm was adjusted. I didn't get an answer, so let me try a different approach:
Remove the fuel meter shield, if your FI unit has one, and reinstall the two main diaphragm screws.
Start the engine and let it warm up to the point that cold enrichment turns off.
The picture below shows the Ratio Lever. At engine idle, it should be resting solidly against the left-hand set screw (the one labled Economy). Is it? Or is it moving back and forth between the two set screws?
Jim
I previously asked how your Enrichment Diaphragm was adjusted. I didn't get an answer, so let me try a different approach:
Remove the fuel meter shield, if your FI unit has one, and reinstall the two main diaphragm screws.
Start the engine and let it warm up to the point that cold enrichment turns off.
The picture below shows the Ratio Lever. At engine idle, it should be resting solidly against the left-hand set screw (the one labled Economy). Is it? Or is it moving back and forth between the two set screws?
Jim
When the engine is warmed up and off the idle cam, it idles poorly, surging between 400 - 900 rpms, almost stalling. In this state, the lever fluctuates between the economy stop and the power stop. As the engine approaches stall, the lever comes off the economy stop, then returns when rpms pick up.
Incidentally, the motor also was newly rebuilt. It supposedly has a 097 cam, and I am double checking with the builder on this. Hope this helps.
Last edited by Ktholin; Nov 6, 2015 at 03:35 PM.
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Hi Jim,
When the engine is warmed up and off the idle cam, it idles poorly, surging between 400 - 900 rpms, almost stalling. In this state, the lever fluctuates between the economy stop and the power stop. As the engine approaches stall, the lever comes off the economy stop, then returns when rpms pick up.
Incidentally, the motor also was newly rebuilt. It supposedly has a 097 cam, and I am double checking with the builder on this. Hope this helps.
When the engine is warmed up and off the idle cam, it idles poorly, surging between 400 - 900 rpms, almost stalling. In this state, the lever fluctuates between the economy stop and the power stop. As the engine approaches stall, the lever comes off the economy stop, then returns when rpms pick up.
Incidentally, the motor also was newly rebuilt. It supposedly has a 097 cam, and I am double checking with the builder on this. Hope this helps.
At 900-ish RPM, the engine starts to free fall towards cut off until the ratio lever swings to the Power Stop. At that instant, the mixture suddenly becomes significantly richer and engine speed picks up again. Once the engine is back up to speed, the ratio lever swings back to the Economy Stop, sending a leaner mixture to the engine. Rinse and repeat.
And, you say the Idle Fuel screw has little influence, except that you can turn it all the way in and stall the engine.
Well, this makes me wonder how the Economy and Power Stop adjustments were done because it sounds like the engine is getting a mixture which is way too lean. Did you use a manometer? A wide band air/fuel gauge? Seat-of-the-pants-o-meter? Other?
Just for grins, disconnect either end of the 1/4" steel tube which conects the Enrichment Diaphragm to the Cold Enrichment mechanism. Run the engine until its fully warmed up and note whether the surging still happens.
Jim
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Well, hmmmmm, OK, let's review:
At 900-ish RPM, the engine starts to free fall towards cut off until the ratio lever swings to the Power Stop. At that instant, the mixture suddenly becomes significantly richer and engine speed picks up again. Once the engine is back up to speed, the ratio lever swings back to the Economy Stop, sending a leaner mixture to the engine. Rinse and repeat.
And, you say the Idle Fuel screw has little influence, except that you can turn it all the way in and stall the engine.
Well, this makes me wonder how the Economy and Power Stop adjustments were done because it sounds like the engine is getting a mixture which is way too lean. Did you use a manometer? A wide band air/fuel gauge? Seat-of-the-pants-o-meter? Other?
Just for grins, disconnect either end of the 1/4" steel tube which conects the Enrichment Diaphragm to the Cold Enrichment mechanism. Run the engine until its fully warmed up and note whether the surging still happens.
Jim
At 900-ish RPM, the engine starts to free fall towards cut off until the ratio lever swings to the Power Stop. At that instant, the mixture suddenly becomes significantly richer and engine speed picks up again. Once the engine is back up to speed, the ratio lever swings back to the Economy Stop, sending a leaner mixture to the engine. Rinse and repeat.
And, you say the Idle Fuel screw has little influence, except that you can turn it all the way in and stall the engine.
Well, this makes me wonder how the Economy and Power Stop adjustments were done because it sounds like the engine is getting a mixture which is way too lean. Did you use a manometer? A wide band air/fuel gauge? Seat-of-the-pants-o-meter? Other?
Just for grins, disconnect either end of the 1/4" steel tube which conects the Enrichment Diaphragm to the Cold Enrichment mechanism. Run the engine until its fully warmed up and note whether the surging still happens.
Jim
I'm not sure he ratio lever swings are causing the up and down revs or are a result of the vacuum changes caused by the up and down surges. You probably have more insight into the causes and effects of this. I will disconnect the tube tomorrow and let you know. With respect to the stop adjustments, I'll send you a PM.
Thanks again for your help with this.
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Interesting finding
Jim,
In the process of doing your recommended test by removing the Enrichment Vacuum line, before I did so, I disconnected the Main Vent tube which is connected from the air cleaner to the Fuel Meter.
Lo a Behold, the idle smoothed out at 950-1000 rpms with the enrichment lever solidly against the Economy Stop. My wife even came into the garage because she noticed it was running better!
Reconnecting the vent tube brings us back to the poor idle. While I understand this still is not correct, perhaps it leads us to a little more insight into the problem? Could plunger valve be sticking?
Keith
In the process of doing your recommended test by removing the Enrichment Vacuum line, before I did so, I disconnected the Main Vent tube which is connected from the air cleaner to the Fuel Meter.
Lo a Behold, the idle smoothed out at 950-1000 rpms with the enrichment lever solidly against the Economy Stop. My wife even came into the garage because she noticed it was running better!
Reconnecting the vent tube brings us back to the poor idle. While I understand this still is not correct, perhaps it leads us to a little more insight into the problem? Could plunger valve be sticking?
Keith
Last edited by Ktholin; Nov 8, 2015 at 05:40 PM.
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Jim,
In the process of doing your recommended test by removing the Enrichment Vacuum line, before I did so, I disconnected the Main Vent tube which is connected from the air cleaner to the Fuel Meter.
Lo a Behold, the idle smoothed out at 950-1000 rpms with the enrichment lever solidly against the Economy Stop. My wife even came into the garage because she noticed it was running better!
Reconnecting the vent tube brings us back to the poor idle. While I understand this still is not correct, perhaps it leads us to a little more insight into the problem? Could plunger valve be sticking?
Keith
In the process of doing your recommended test by removing the Enrichment Vacuum line, before I did so, I disconnected the Main Vent tube which is connected from the air cleaner to the Fuel Meter.
Lo a Behold, the idle smoothed out at 950-1000 rpms with the enrichment lever solidly against the Economy Stop. My wife even came into the garage because she noticed it was running better!
Reconnecting the vent tube brings us back to the poor idle. While I understand this still is not correct, perhaps it leads us to a little more insight into the problem? Could plunger valve be sticking?
Keith
That is an "interesting" piece of information.
That large diameter tube (the Balance Tube) exists to ensure stationary air at atmospheric pressure under the Main Diaphragm. Disrupt either of these conditions and air/fuel metering accuracy suffers significantly.
I've never, ever encountered a situation where engine behavior improved with the Balance Tube disconnected, so you've got me scratching my head at the moment.
Is there *any* chance the balance tube or any part of the tubing between the air cleaner and the Fuel Meter is plugged up?
Regarding a spill plunger which might be sticking..... it very well could be, especially given what you told me in a PM, but I can't relate this new development to a sticking plunger.
Jim
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Keith,
That is an "interesting" piece of information.
That large diameter tube (the Balance Tube) exists to ensure stationary air at atmospheric pressure under the Main Diaphragm. Disrupt either of these conditions and air/fuel metering accuracy suffers significantly.
I've never, ever encountered a situation where engine behavior improved with the Balance Tube disconnected, so you've got me scratching my head at the moment.
Is there *any* chance the balance tube or any part of the tubing between the air cleaner and the Fuel Meter is plugged up?
Regarding a spill plunger which might be sticking..... it very well could be, especially given what you told me in a PM, but I can't relate this new development to a sticking plunger.
Jim
That is an "interesting" piece of information.
That large diameter tube (the Balance Tube) exists to ensure stationary air at atmospheric pressure under the Main Diaphragm. Disrupt either of these conditions and air/fuel metering accuracy suffers significantly.
I've never, ever encountered a situation where engine behavior improved with the Balance Tube disconnected, so you've got me scratching my head at the moment.
Is there *any* chance the balance tube or any part of the tubing between the air cleaner and the Fuel Meter is plugged up?
Regarding a spill plunger which might be sticking..... it very well could be, especially given what you told me in a PM, but I can't relate this new development to a sticking plunger.
Jim
Last edited by Ktholin; Nov 8, 2015 at 09:43 PM.