idle drifts down at traffic lights
#16
01-25-2015, 12:02 AM
Does indeed sound like a very productive night. The biggest thing here is you learning your engine, what it likes and how to get the most out of it by giving it what it likes.
It would start at 40 degrees of advance? Wow, ok it's time for you to check to see if your timing marks are right. 40 is way high, I'm not going to take the leap that it's not possible but yeah let's find out. To check your timing marks you'll need two things, a piston stop and an accurate way to mark your balancer. Basically you install the stop, turn the engine one way till it hit the stop, mark the balancer, turn the other way till it hits the stop, mark again, true TDC is right between the two marks. There are a lot of youtube vids and such on doing this, I suggest you look it up.
It's possible even likely from the numbers you just provided that your timing marks are as much as 20 deg off. I didn't want to tell you what numbers to expect in the previous post cause it may have skewed what you found but an engine starting over 20 deg is unusual and if true may indicate other things. Same for idle, over 30 is quite unusual.
Speaking of idle, I should have clarified something, with ideal idle we are looking for the lowest timing where the vacuum and rpm stops climbing. So like idle fuel, advance until idle rpm and vacuum stop climbing, retard until it starts to drop, back up just a touch until the rpm is back to peak. Generally this is in the high 20s.
The snap you lost I have no doubt is due to the lack of advance due to the heavier springs. I suggest picking up a selection of springs and keeping in mind that the two don't have to match, you can put in one heavy and one light. The goal is to have it advance just above idle.
Edit
In the short term the fact that it will start smooth at a reading of 40 says that it's pretty darn safe to bump it up quite high related to that reading. Let me give this example, generally I leave it at that starting timing, I'm going to play it safe and not suggest bumping it up that high, but go to 15 and see, then maybe 20.
It would start at 40 degrees of advance? Wow, ok it's time for you to check to see if your timing marks are right. 40 is way high, I'm not going to take the leap that it's not possible but yeah let's find out. To check your timing marks you'll need two things, a piston stop and an accurate way to mark your balancer. Basically you install the stop, turn the engine one way till it hit the stop, mark the balancer, turn the other way till it hits the stop, mark again, true TDC is right between the two marks. There are a lot of youtube vids and such on doing this, I suggest you look it up.
It's possible even likely from the numbers you just provided that your timing marks are as much as 20 deg off. I didn't want to tell you what numbers to expect in the previous post cause it may have skewed what you found but an engine starting over 20 deg is unusual and if true may indicate other things. Same for idle, over 30 is quite unusual.
Speaking of idle, I should have clarified something, with ideal idle we are looking for the lowest timing where the vacuum and rpm stops climbing. So like idle fuel, advance until idle rpm and vacuum stop climbing, retard until it starts to drop, back up just a touch until the rpm is back to peak. Generally this is in the high 20s.
The snap you lost I have no doubt is due to the lack of advance due to the heavier springs. I suggest picking up a selection of springs and keeping in mind that the two don't have to match, you can put in one heavy and one light. The goal is to have it advance just above idle.
Edit
In the short term the fact that it will start smooth at a reading of 40 says that it's pretty darn safe to bump it up quite high related to that reading. Let me give this example, generally I leave it at that starting timing, I'm going to play it safe and not suggest bumping it up that high, but go to 15 and see, then maybe 20.
#17
01-25-2015, 12:41 AM
Well Brute, got some time to work on the old truck today...here's what happened...
Started the engine. Checked the timing, it was 6 degrees at around 600.
Decided to baseline the distributor by pulling the light springs out of the distributor and put the factory installed heavier ones in. I set the timing again to 6 degrees at 600, and then checked the idle screws, adjusted them for the best idle, highest vacuum, I was chasing my tail for awhile then finally tried to screw one idle mix all the way in, it did not kill the engine, though it was rough, tried the other side, and it was the same. Tried to turn down the primary idle screw all the way, and the engine is still running at about 400 rpm! Ended up I found that the secondary throttle stop was open too far, I closed it some, about 1/8 of a turn open now, and now I find I am having more control with my idle mix screws! I am now getting the highest idle I could around -17 out of gear at 800 RPM, -11 at around 600 in gear. Adjusted idle mix screws again, in gear, at around 600 and gained a little more vacuum at about now -12. Engine seems to be running nice and smooth. Screws ended up being around 2 1/8 to around 2 1/4 out. After many times shutting down and restarting the engine, it seems the hot start stumbling issue is gone, and the engine idle is not drifting down anymore while running in gear and the rear wheels chocked. And it was running for a long time, longer than it would be at any stop light. Next I decided to bump up the timing a little more to about 10 BTDC, engine now runs smoother, and I am liking the exhaust note.
Next I look at the ideal start and ideal idle you asked me to check. Advanced the distributor to max idle, ended up at 56 degrees/1480 rpm/at -23 Hg. The start max advance was interesting, it labored just a tiny bit at 56 degrees, but the smoothest start was found around 40 degrees/1200 rpm/at -22 Hg. Put the distributor back to idle at 800 rpm/ but when the transmission engages, the idle drops to about 550, and the engine is sounding labored. I try to trim the idle mix screws a little bit more, but it seemed not to make any difference.
So I ended up with an curb idle of around 900, and the" in gear" idle at around 700. (Maybe the street cam interacting with the stock torque converter).
I wanted to check the distributor curving now since I switched in heavier springs before starting all of this, and with timing set at 10 degrees, there is no advance now til 1500, a little past 15, I am seeing 18 degrees, and it appears all in at 24 degrees at 2000. I drive around the parking lot and I notice that even though the engine seems much smoother, starts better, idle now much more stable, it lacks the punch it had. I am guessing next working on the distributor advance more?
All in all a productive night. With you help I am making progress I think!
Started the engine. Checked the timing, it was 6 degrees at around 600.
Decided to baseline the distributor by pulling the light springs out of the distributor and put the factory installed heavier ones in. I set the timing again to 6 degrees at 600, and then checked the idle screws, adjusted them for the best idle, highest vacuum, I was chasing my tail for awhile then finally tried to screw one idle mix all the way in, it did not kill the engine, though it was rough, tried the other side, and it was the same. Tried to turn down the primary idle screw all the way, and the engine is still running at about 400 rpm! Ended up I found that the secondary throttle stop was open too far, I closed it some, about 1/8 of a turn open now, and now I find I am having more control with my idle mix screws! I am now getting the highest idle I could around -17 out of gear at 800 RPM, -11 at around 600 in gear. Adjusted idle mix screws again, in gear, at around 600 and gained a little more vacuum at about now -12. Engine seems to be running nice and smooth. Screws ended up being around 2 1/8 to around 2 1/4 out. After many times shutting down and restarting the engine, it seems the hot start stumbling issue is gone, and the engine idle is not drifting down anymore while running in gear and the rear wheels chocked. And it was running for a long time, longer than it would be at any stop light. Next I decided to bump up the timing a little more to about 10 BTDC, engine now runs smoother, and I am liking the exhaust note.
Next I look at the ideal start and ideal idle you asked me to check. Advanced the distributor to max idle, ended up at 56 degrees/1480 rpm/at -23 Hg. The start max advance was interesting, it labored just a tiny bit at 56 degrees, but the smoothest start was found around 40 degrees/1200 rpm/at -22 Hg. Put the distributor back to idle at 800 rpm/ but when the transmission engages, the idle drops to about 550, and the engine is sounding labored. I try to trim the idle mix screws a little bit more, but it seemed not to make any difference.
So I ended up with an curb idle of around 900, and the" in gear" idle at around 700. (Maybe the street cam interacting with the stock torque converter).
I wanted to check the distributor curving now since I switched in heavier springs before starting all of this, and with timing set at 10 degrees, there is no advance now til 1500, a little past 15, I am seeing 18 degrees, and it appears all in at 24 degrees at 2000. I drive around the parking lot and I notice that even though the engine seems much smoother, starts better, idle now much more stable, it lacks the punch it had. I am guessing next working on the distributor advance more?
All in all a productive night. With you help I am making progress I think!
The moment your secondaries begin to open you are drawing fuel from the main jets so make sure they are not binding and close freely.
Total timing is coming in WAY too fast, even 2500 is too soon, need to extend the mechanical advance to at least 3k rpm, maybe even 3500 depending on the cam but you don't want the timing fully advanced before the engine starts making power, that's why the engine is sluggish and non responsive.
Idle speed, from what i gather you are running street cam at 700 rpm is too low IMHO, you stand a good chance of flattening the cam lobes because there isn't enough oil pressure and engine rpm to make things operate smoothly, may sound cool but unless it's a roller cam you're asking for problems, some may disagree but that's just my personal opinion.
Search the WWW for SBF timing curves, everything you want to learn is there
#18
01-25-2015, 11:19 PM
Does indeed sound like a very productive night. The biggest thing here is you learning your engine, what it likes and how to get the most out of it by giving it what it likes.
It would start at 40 degrees of advance? Wow, ok it's time for you to check to see if your timing marks are right. 40 is way high, I'm not going to take the leap that it's not possible but yeah let's find out. To check your timing marks you'll need two things, a piston stop and an accurate way to mark your balancer. Basically you install the stop, turn the engine one way till it hit the stop, mark the balancer, turn the other way till it hits the stop, mark again, true TDC is right between the two marks. There are a lot of youtube vids and such on doing this, I suggest you look it up.
It's possible even likely from the numbers you just provided that your timing marks are as much as 20 deg off. I didn't want to tell you what numbers to expect in the previous post cause it may have skewed what you found but an engine starting over 20 deg is unusual and if true may indicate other things. Same for idle, over 30 is quite unusual.
Speaking of idle, I should have clarified something, with ideal idle we are looking for the lowest timing where the vacuum and rpm stops climbing. So like idle fuel, advance until idle rpm and vacuum stop climbing, retard until it starts to drop, back up just a touch until the rpm is back to peak. Generally this is in the high 20s.
The snap you lost I have no doubt is due to the lack of advance due to the heavier springs. I suggest picking up a selection of springs and keeping in mind that the two don't have to match, you can put in one heavy and one light. The goal is to have it advance just above idle.
Edit
In the short term the fact that it will start smooth at a reading of 40 says that it's pretty darn safe to bump it up quite high related to that reading. Let me give this example, generally I leave it at that starting timing, I'm going to play it safe and not suggest bumping it up that high, but go to 15 and see, then maybe 20.
It would start at 40 degrees of advance? Wow, ok it's time for you to check to see if your timing marks are right. 40 is way high, I'm not going to take the leap that it's not possible but yeah let's find out. To check your timing marks you'll need two things, a piston stop and an accurate way to mark your balancer. Basically you install the stop, turn the engine one way till it hit the stop, mark the balancer, turn the other way till it hits the stop, mark again, true TDC is right between the two marks. There are a lot of youtube vids and such on doing this, I suggest you look it up.
It's possible even likely from the numbers you just provided that your timing marks are as much as 20 deg off. I didn't want to tell you what numbers to expect in the previous post cause it may have skewed what you found but an engine starting over 20 deg is unusual and if true may indicate other things. Same for idle, over 30 is quite unusual.
Speaking of idle, I should have clarified something, with ideal idle we are looking for the lowest timing where the vacuum and rpm stops climbing. So like idle fuel, advance until idle rpm and vacuum stop climbing, retard until it starts to drop, back up just a touch until the rpm is back to peak. Generally this is in the high 20s.
The snap you lost I have no doubt is due to the lack of advance due to the heavier springs. I suggest picking up a selection of springs and keeping in mind that the two don't have to match, you can put in one heavy and one light. The goal is to have it advance just above idle.
Edit
In the short term the fact that it will start smooth at a reading of 40 says that it's pretty darn safe to bump it up quite high related to that reading. Let me give this example, generally I leave it at that starting timing, I'm going to play it safe and not suggest bumping it up that high, but go to 15 and see, then maybe 20.
#19
01-25-2015, 11:47 PM
The secondary throttle stop functions to keep the secondary throttle blades from opening too far at WOT, it can only be adjusted when the throttle is WFO. It has nothing to do with if the secondary throttle blades are fully closed, which they MUST be at idle.
The moment your secondaries begin to open you are drawing fuel from the main jets so make sure they are not binding and close freely.
Total timing is coming in WAY too fast, even 2500 is too soon, need to extend the mechanical advance to at least 3k rpm, maybe even 3500 depending on the cam but you don't want the timing fully advanced before the engine starts making power, that's why the engine is sluggish and non responsive.
Idle speed, from what i gather you are running street cam at 700 rpm is too low IMHO, you stand a good chance of flattening the cam lobes because there isn't enough oil pressure and engine rpm to make things operate smoothly, may sound cool but unless it's a roller cam you're asking for problems, some may disagree but that's just my personal opinion.
Search the WWW for SBF timing curves, everything you want to learn is there
The moment your secondaries begin to open you are drawing fuel from the main jets so make sure they are not binding and close freely.
Total timing is coming in WAY too fast, even 2500 is too soon, need to extend the mechanical advance to at least 3k rpm, maybe even 3500 depending on the cam but you don't want the timing fully advanced before the engine starts making power, that's why the engine is sluggish and non responsive.
Idle speed, from what i gather you are running street cam at 700 rpm is too low IMHO, you stand a good chance of flattening the cam lobes because there isn't enough oil pressure and engine rpm to make things operate smoothly, may sound cool but unless it's a roller cam you're asking for problems, some may disagree but that's just my personal opinion.
Search the WWW for SBF timing curves, everything you want to learn is there
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