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TR6 TR6 Proper vacuum readings?
- Thread starter Norton47
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Poolboy
Mine is set up that way and that is where I connect.
My readings are low when the retard is connected, around 13 inches. When I disconnect the retard which let the timing advance the readings go to 17 inches of vacuum.
I was concerned that retarding was throwing off the readings at idle.
I guess that isn't the case?
Mine is set up that way and that is where I connect.
My readings are low when the retard is connected, around 13 inches. When I disconnect the retard which let the timing advance the readings go to 17 inches of vacuum.
I was concerned that retarding was throwing off the readings at idle.
I guess that isn't the case?
poolboy
Yoda
Offline
Norton, for comparison purpose, I get 18 at idle on my 74 with a 101k mile engine.
Everything connected as I described.
If the gauge needle is pretty steady, then your valves and and rings are decent. You might need a little timing advance and possibly a carb mixture adjustment to get the Vacuum a little higher.
Everything connected as I described.
If the gauge needle is pretty steady, then your valves and and rings are decent. You might need a little timing advance and possibly a carb mixture adjustment to get the Vacuum a little higher.
poolboy
Yoda
Offline
I don't think it will take much of a clockwise rotation of the Dizzy, probably between 1/4 and 1/2 inch. If you watch the gauge, and when you first reach the highest reading, that's probably your sweet spot. Your engine will let you know if it likes it.
It's hard to find that spot with a timing light if the engine has some miles on it.
You have wear in things like the timing chain, the sprockets, the drive gears on the cam and dizzy shaft. All that adds up to the timing marks being not as relevant as they once were. But that Vacuum Gauge will tell the story when you hit the spot.
It's hard to find that spot with a timing light if the engine has some miles on it.
You have wear in things like the timing chain, the sprockets, the drive gears on the cam and dizzy shaft. All that adds up to the timing marks being not as relevant as they once were. But that Vacuum Gauge will tell the story when you hit the spot.
So if found a sweet spot and the vacuum went up to 17 and more or less steady still a little swing from 17 t 17.5 and so did the idle speed. After I adjusted the idle speed down, I lost most of the vacuum gain. I am trying to set the idle to 900-950.
Whats up with that?
Whats up with that?
poolboy
Yoda
Offline
About how high did the idle speed get when you hit 17 ? If it went up a couple hundred, I'd set the speed back down and give a little more Clockwise turn and see if the reading starts to rise again.
I doubt if you will be able to over advance as long as your tach cable is hooked up. It just won't let the dizzy turn that far.. This is one of those kind of things that happens when you adjust the timing. The idle speed changes and chances are you will have a small adjustment to make on the carb mixture.
Just play with it. It's trial and error, a little give and take, but if everything is up to snuff you'll get the right combination.
Also keep an eye on your vacuum line connections on the carbs and dizzy. It's not hard to accidentally knock a connection loose while you're doing all that adjusting.
I doubt if you will be able to over advance as long as your tach cable is hooked up. It just won't let the dizzy turn that far.. This is one of those kind of things that happens when you adjust the timing. The idle speed changes and chances are you will have a small adjustment to make on the carb mixture.
Just play with it. It's trial and error, a little give and take, but if everything is up to snuff you'll get the right combination.
Also keep an eye on your vacuum line connections on the carbs and dizzy. It's not hard to accidentally knock a connection loose while you're doing all that adjusting.
poolboy
Yoda
Offline
Norton, check out "scenerio 11" inthis link;
https://www.secondchancegarage.com/public/186.cfm
https://www.secondchancegarage.com/public/186.cfm
Hi
Long time in working this issue due to many things. I have now returned to it.
I was getting a reading more like scenario 10 on the website.
I then went back, but my number 1 cylinder on TDC watching the intake valve making sure it closed then brought it up to TDC monitoring with a dowel. This appears to match the damper mark.(damper was rebuilt). I reset the dizzy so the tach cable leads over the fuel pump and the dizzy drive gear slot is located just past 12 0'clock position.
I started it and the vacuum was up, I advanced the dizzy until I got the best vacuum reading just over 17, and adjusted idle speed and advanced and now have a reading over 17" Hg at about 850 RPM, but my timing is way advanced. With a timing light it indicates well past the last markings on the damper.
This engine was rebuilt, and the original cam was rewelded and reground to stock. (supposedly). The machine shop set the cam and crank timing.
Is this indicating retarded cam timing or the possibility of a cam problem?
What else should I check?
I just want as many answers as possible before I talk to my suppliers.
Thanks
Long time in working this issue due to many things. I have now returned to it.
I was getting a reading more like scenario 10 on the website.
I then went back, but my number 1 cylinder on TDC watching the intake valve making sure it closed then brought it up to TDC monitoring with a dowel. This appears to match the damper mark.(damper was rebuilt). I reset the dizzy so the tach cable leads over the fuel pump and the dizzy drive gear slot is located just past 12 0'clock position.
I started it and the vacuum was up, I advanced the dizzy until I got the best vacuum reading just over 17, and adjusted idle speed and advanced and now have a reading over 17" Hg at about 850 RPM, but my timing is way advanced. With a timing light it indicates well past the last markings on the damper.
This engine was rebuilt, and the original cam was rewelded and reground to stock. (supposedly). The machine shop set the cam and crank timing.
Is this indicating retarded cam timing or the possibility of a cam problem?
What else should I check?
I just want as many answers as possible before I talk to my suppliers.
Thanks
AweMan
Jedi Knight
Offline
Norton47:
F.W.I.W.
If you advance your distributor to attain full vacume {as much as you can get} As you have found out ... your timing will be advanced wayyyyyyyyy too far.
Assuming you have a vacume advance distributor. With your timing set the way you have it if you increase your engine rpm to about 2,500 you will notice your engine will start missing like crazy.
You can not set your timing to full vacume on any engine that has either centrifugal or vacume advance mechanisms. I assure you at higher rpm they WILL start missing badly.
To set your timing with a vacume guage. set it to full vacume then back it off 1 to 2 Hg then check with a timing light to see where you are.
Or simpler yet set it with the timing light and forget it. then set the curb idle speed on the carb/carbs then set the idle mixtures then recheck the timing. once you get it all set
drive it like you stole it.
P.S. dont forget to disconnect the vacume advance hose and plug it off to set the initial timing.{either with the vac guage or timing light} re-connect it to set the curb idle speed and idle mixture/s
F.W.I.W.
If you advance your distributor to attain full vacume {as much as you can get} As you have found out ... your timing will be advanced wayyyyyyyyy too far.
Assuming you have a vacume advance distributor. With your timing set the way you have it if you increase your engine rpm to about 2,500 you will notice your engine will start missing like crazy.
You can not set your timing to full vacume on any engine that has either centrifugal or vacume advance mechanisms. I assure you at higher rpm they WILL start missing badly.
To set your timing with a vacume guage. set it to full vacume then back it off 1 to 2 Hg then check with a timing light to see where you are.
Or simpler yet set it with the timing light and forget it. then set the curb idle speed on the carb/carbs then set the idle mixtures then recheck the timing. once you get it all set
drive it like you stole it.
P.S. dont forget to disconnect the vacume advance hose and plug it off to set the initial timing.{either with the vac guage or timing light} re-connect it to set the curb idle speed and idle mixture/s
Kerry
Sorry if I am not clear. If I set the timing with a timing light then my vacuum is around 10" of Hg. It will then run very lean, as it won't suck any fuel in.
I am trying to figure out what has change since the rebuild.
The cam grinder has informed me that since the damper and crank and piston all seem to be true, to check the split overlap as a way to verify the crank and cam timing. on the non-firing stroke coming up to TDC, the exhaust is closing and the intake is opening and they should be equal at TDC.
Thinking back on it, my car has a vacuum retard and I had it connected last night. So that is retarding me about 14 degrees I think.
If I disconnect that and recheck, I'll bet I won't need as much advance to get the vacuum up.
The distributor was also rebuilt and recurved, and I was told to try about 20 -22 degrees of advance and advance it until it pings.
More things to check.
Sorry if I am not clear. If I set the timing with a timing light then my vacuum is around 10" of Hg. It will then run very lean, as it won't suck any fuel in.
I am trying to figure out what has change since the rebuild.
The cam grinder has informed me that since the damper and crank and piston all seem to be true, to check the split overlap as a way to verify the crank and cam timing. on the non-firing stroke coming up to TDC, the exhaust is closing and the intake is opening and they should be equal at TDC.
Thinking back on it, my car has a vacuum retard and I had it connected last night. So that is retarding me about 14 degrees I think.
If I disconnect that and recheck, I'll bet I won't need as much advance to get the vacuum up.
The distributor was also rebuilt and recurved, and I was told to try about 20 -22 degrees of advance and advance it until it pings.
More things to check.
poolboy
Yoda
Offline
Hey Norton.
When I got my dizzy back from Jeff,he said that timing with a light should be 10--14* BTDC at idle speed with the vacuum retard line disconnected and plugged while making the reading. I have a 74 unmodified engine.
I set it like that, but found it lacked the power that it had when I set the timing with a vacuum gauge.
I needed an advance.
My belief is, in my case, the damper marks did not reflect the REAL timing, because of things like stretching of the timing chain, wear in the sprockets, wear in the dizzy drive gears, well, you get the idea with an engine having 100k miles.
I think a vacuum gauge gives a accurate visual indication of how your engine is operating and whether or not the engine likes what you are doing to it.
When I got my dizzy back from Jeff,he said that timing with a light should be 10--14* BTDC at idle speed with the vacuum retard line disconnected and plugged while making the reading. I have a 74 unmodified engine.
I set it like that, but found it lacked the power that it had when I set the timing with a vacuum gauge.
I needed an advance.
My belief is, in my case, the damper marks did not reflect the REAL timing, because of things like stretching of the timing chain, wear in the sprockets, wear in the dizzy drive gears, well, you get the idea with an engine having 100k miles.
I think a vacuum gauge gives a accurate visual indication of how your engine is operating and whether or not the engine likes what you are doing to it.
vettedog72
Jedi Knight
Offline
Norton47 said:
Look back a Scenario #10; it clearly states your systems are caused by late valve timing.
Vettedog
Sure does, but I can not find any evidence of late valve timing.
I spoke with the cam grinder and he provided this tidbit.
First a recap.
The damper mark for TDC to the pointer appears to be correct as the piston is at TDC (monitored by a dowel in the spark plug hole)ie no more movement of the piston when the mark is reached and moving the crank in either direction moves the piston somewhat as the damper mark moves off.
Now the tidbit.
He told me to move the engine over until #1 cylinder was on the non compression stroke and to monitor the valves, the exhaust will be closing and as the piston comes up to TDC on this stroke the intake valve will start to open and at TDC both the exhaust and intake should be open the same amount as evidenced by the rocker arms being the same.
My engine matched this to a T.
I did advance the timing to about 20 degrees with the vacuum retard disconnected and plugged. This raised the vacuum to 15" of Hg. I also found a small vacuum leak by spraying cleaner around the intake to block gasket at number 3 intake once I had the vacuum up. A slight nip of the nuts seems to have cured that.
The car seems to run better, no pinging, much throatier sounding, no real harsh rumble on the over run, but the plugs are showing what I would call no color. They are not white nor are they brown or black. They are clean.
As they had been this way with stock needles in the carbs, I installed some Jaguar needles which are for a 4 liter engine to make it run richer. I still am getting clean plugs after a run around the 4 mile run I use.
I will take some photos of them. The car seemed to run well.
I am going to recheck the float height, and maybe tweak the advance a little more.
Sure does, but I can not find any evidence of late valve timing.
I spoke with the cam grinder and he provided this tidbit.
First a recap.
The damper mark for TDC to the pointer appears to be correct as the piston is at TDC (monitored by a dowel in the spark plug hole)ie no more movement of the piston when the mark is reached and moving the crank in either direction moves the piston somewhat as the damper mark moves off.
Now the tidbit.
He told me to move the engine over until #1 cylinder was on the non compression stroke and to monitor the valves, the exhaust will be closing and as the piston comes up to TDC on this stroke the intake valve will start to open and at TDC both the exhaust and intake should be open the same amount as evidenced by the rocker arms being the same.
My engine matched this to a T.
I did advance the timing to about 20 degrees with the vacuum retard disconnected and plugged. This raised the vacuum to 15" of Hg. I also found a small vacuum leak by spraying cleaner around the intake to block gasket at number 3 intake once I had the vacuum up. A slight nip of the nuts seems to have cured that.
The car seems to run better, no pinging, much throatier sounding, no real harsh rumble on the over run, but the plugs are showing what I would call no color. They are not white nor are they brown or black. They are clean.
As they had been this way with stock needles in the carbs, I installed some Jaguar needles which are for a 4 liter engine to make it run richer. I still am getting clean plugs after a run around the 4 mile run I use.
I will take some photos of them. The car seemed to run well.
I am going to recheck the float height, and maybe tweak the advance a little more.
poolboy
Yoda
Offline
Norton, so the complaint is that your plugs are still clean looking after a 4 mile circuit ?
You know who you're sounding like ?
Use copper electrode spark plugs and drive 20 to 50 miles, the last few miles with as few of stops as you can.
Kill the engine and coast to a stop when you get home. Be aware of the steering wheel lock if you have it, you may have to turn the key to on for a second if you need to manuever.
Getting back to checking the Mixture. Do it the time honored way of lifting the air valve about 1/8 of an inch.
Pulling the plugs and trying to read them is OK after you give them some time to develop color or to differentiate if a plug is fouled due to a rich mixture or from oil burning.
Playing with the timing and mixture is something that is trial and error; for each engine has a little different response to those adjustments.
Once you get to just an "acceptable" point, minor adjustments will let you hone in on a sweet spot for your engine, under current conditions such as your fuel, outside temperatures, etc.
Once you find a sweet spot, you'll have a pretty good feeling for how your engine responds to changes.
You know who you're sounding like ?
Use copper electrode spark plugs and drive 20 to 50 miles, the last few miles with as few of stops as you can.
Kill the engine and coast to a stop when you get home. Be aware of the steering wheel lock if you have it, you may have to turn the key to on for a second if you need to manuever.
Getting back to checking the Mixture. Do it the time honored way of lifting the air valve about 1/8 of an inch.
Pulling the plugs and trying to read them is OK after you give them some time to develop color or to differentiate if a plug is fouled due to a rich mixture or from oil burning.
Playing with the timing and mixture is something that is trial and error; for each engine has a little different response to those adjustments.
Once you get to just an "acceptable" point, minor adjustments will let you hone in on a sweet spot for your engine, under current conditions such as your fuel, outside temperatures, etc.
Once you find a sweet spot, you'll have a pretty good feeling for how your engine responds to changes.
Car is running well. Plugs seem to be getting some color the rear 3 are getting more than the front 3 but none are white.
I did get the carbs to respond to lifting the whatca callit and not stumble all though they did at first but by turning clock wise to richen that stopped.
I left the timing at 20 degrees advanced without vacuum for now. What a relief.
Thanks for the help and support.
I did get the carbs to respond to lifting the whatca callit and not stumble all though they did at first but by turning clock wise to richen that stopped.
I left the timing at 20 degrees advanced without vacuum for now. What a relief.
Thanks for the help and support.
charlie74
Jedi Warrior
Offline
not to hijack norton's thread, but i recently did a vacuum test on my 74 '6 and found the needle to read about 17". the instruction sheet for the guage said that some needle pulse was normal on 4 and 6 cylinder engines. would this pulse look like a rapid and steady fluctuation of about 1/2 to 1" of vacuum? or should the needle be rock steady?
i'm trying to figure out if i have a bad valve seal as i am getting some smoke when coasting down hills in gear.
thanks
c74
i'm trying to figure out if i have a bad valve seal as i am getting some smoke when coasting down hills in gear.
thanks
c74