Timing!!!!
Drifting
Joined: Aug 2008
Posts: 1,381
Likes: 11
I am sure when I read BarryK's thread a while ago, he said with MSD you should set your initial at 13deg.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
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From: Graceland in a Not Correctly Restored Stingray
As I had suggested earlier, manifold rather than port vacuum can sometimes lead to issues. Since the problem disappeared with the vac adv plugged, I'd reset the initial back up and give port vac a try. If that solves it, you'll have more initial and more total mech advance, than you would by retarding everything to solve a vac advance problem. Agree 13* initial is not a one size fits all setting.
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
Perhaps you can expand on this and educate us all. I just reread Barry's post and particularly on the use of manifold vacuum for vacuum advance. The way he explains it is exactly the way I understand it works - and I gained this knowledge from many sources, on the forum and off.
Thanks,
Tech Contributor
Joined: Jun 2004
Posts: 20,785
Likes: 957
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Reggie,
Perhaps you can expand on this and educate us all. I just reread Barry's post and particularly on the use of manifold vacuum for vacuum advance. The way he explains it is exactly the way I understand it works - and I gained this knowledge from many sources, on the forum and off.
Thanks,
Perhaps you can expand on this and educate us all. I just reread Barry's post and particularly on the use of manifold vacuum for vacuum advance. The way he explains it is exactly the way I understand it works - and I gained this knowledge from many sources, on the forum and off.
Thanks,
I'm curious too. Barry and I have had several conversations over the years, and we've been on the same wavelength. I'm anxiously awaiting Reggie's reply.
Thread Starter
Advanced
Joined: Jun 2006
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From: SHADY SPRING WV
I did get to drive it a bit last night and it ran OK but I didn't get to mess with the timing any more. The balancer is on 0 at TDC so that is good. I have noticed that there is a lot of
vertical movement in the shaft when you manually turn the rotor by hand. Is there a tolerance I should have on that and would that have anything to do with my problem?
vertical movement in the shaft when you manually turn the rotor by hand. Is there a tolerance I should have on that and would that have anything to do with my problem?
Drifting
Joined: Aug 2008
Posts: 1,381
Likes: 11
R
Barry is of the belief that manifold vacuum should always be the source to the vacuum advance. If you believe this you have either not read enough on the subject or do not have experience tuning a diverse variety of engines. Further comments will only turn this into a never ending debate. Use what you want and believe what you like, but there is no one size fits all for timing.
eggie,
Perhaps you can expand on this and educate us all. I just reread Barry's post and particularly on the use of manifold vacuum for vacuum advance. The way he explains it is exactly the way I understand it works - and I gained this knowledge from many sources, on the forum and off.
Thanks,
Perhaps you can expand on this and educate us all. I just reread Barry's post and particularly on the use of manifold vacuum for vacuum advance. The way he explains it is exactly the way I understand it works - and I gained this knowledge from many sources, on the forum and off.
Thanks,
Thread Starter
Advanced
Joined: Jun 2006
Posts: 65
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From: SHADY SPRING WV
Sorry, I have been away from the computor for a few days. It knocks louder under part throttle, but is noticable under load but not as loud. I disconnected vacuum advance again and set the timing to 18 degrees initial and 18 centrifugal and plugged the vacuum. I can still hear the knock, sometimes I'm not even sure it is spark knock, it's not like any spark knock I have ever heard. I have ordered a new distributor to rule out a distributor problem. I know 36 degrees of advance is not too much for this engine. To see engine specs, go to Year one site and look at their CT350PC1 engine.
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Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
"Part throttle" meaning cruise?
If so, you have too much total and you need to reduce either the mechanical or adjust your can down a bit (assuming you have an adjustable vacuum advance can).
What is your coolant's operating temp?
Secondly, are you sure you're not lean?
Lastly, you sure about your compression ratio?
If so, you have too much total and you need to reduce either the mechanical or adjust your can down a bit (assuming you have an adjustable vacuum advance can).
What is your coolant's operating temp?
Secondly, are you sure you're not lean?
Lastly, you sure about your compression ratio?
Thread Starter
Advanced
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From: SHADY SPRING WV
Part throttle meaning under load, but not full throttle. Also I have a 165 degree thermostat in as recommended by manufacturer and it stays right on 165. I am running a Holly 670 street avenger and the plugs don't show lean. Compression ratio is 9.5 to 1 according to the manufacturer spec. In the back of my mind I can't help but think distributor and will try to rule that out when my new one gets here. Thanks
Drifting
Joined: Aug 2008
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The Street Avenger series of carbs are jetted very lean. They provide excellent throttle response and good fuel mileage, but need to be tailored to some applications. If your 670 is factory stock it has #65 jets in the primary and #68s in the secondary - which is way lean even for a nearly stock 350. You should start with 68s in the front and 72s in the back. You can not gauge rich and lean by looking at your plugs, especially with today's gas and an HEI type ignition. I have used several of these carbs and they work great with just a little tuning. I have yet to see one that did not need to be jetted up a tad.
Safety Car
Joined: Oct 2006
Posts: 3,993
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From: Gig Harbor WA
Thread Starter
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Joined: Jun 2006
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From: SHADY SPRING WV
Yes, I knew the 670 carbs were jetted lean from some research I did, so I moved the 68's to the front and put 76's in the rear because I read you needed 8 sizes between the front and rear. Do you think this is enough? As I stated before, I had the same carb and dist. on an identical engine and had no issues. I am hoping the new dist. will cure my ills!
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
I'm not sure about the jet settings on that carb.
Are you running a PCV valve with a hose to the base of the carb? That will lean the charge out a bit since unmetered air is pulled into the intake.
Also, off topic, but don't know of anybody who would recommend an operating temp of 165. You need the coolant and operating temp hot enough that oil can cook out the liquid water (water vaporizes at 212~ degrees). Usually you need an operating temp (coolant) in the 180* range.
Are you running a PCV valve with a hose to the base of the carb? That will lean the charge out a bit since unmetered air is pulled into the intake.
Also, off topic, but don't know of anybody who would recommend an operating temp of 165. You need the coolant and operating temp hot enough that oil can cook out the liquid water (water vaporizes at 212~ degrees). Usually you need an operating temp (coolant) in the 180* range.
Last edited by 73, Dark Blue 454; Jun 2, 2009 at 11:42 PM.
Melting Slicks
Joined: Mar 2008
Posts: 2,989
Likes: 198
From: Meriden CT
I did get to drive it a bit last night and it ran OK but I didn't get to mess with the timing any more. The balancer is on 0 at TDC so that is good. I have noticed that there is a lot of
vertical movement in the shaft when you manually turn the rotor by hand. Is there a tolerance I should have on that and would that have anything to do with my problem?
vertical movement in the shaft when you manually turn the rotor by hand. Is there a tolerance I should have on that and would that have anything to do with my problem?
Thread Starter
Advanced
Joined: Jun 2006
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From: SHADY SPRING WV
The new distributor came in yesterday but all I had time to do was unpack it and check it over. I will try to get it in before the weekend to try it out. Yes, I am running a pcv hooked to the bottom of the carb and the reason i run the 165 thermostat is because that is what they dyno'ed the engine with and I assumed that is what they recommended. I did put in a 180 over the during colder weather to see how it ran with it. That is a good observation SH-60B, I hadn't thought of that, I will look into that further, thanks.
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From: SHADY SPRING WV
Well, I give up! I changed out the distributor and still I can hear spark knock with 12 degrees initial, 18 degrees centrifugal and 8 degrees vacuum advance. That is only 38 degrees of total timing as compared to 52 in Lars and other papers I have read. So I disconnected vacuum advance and set the total timing to 36 and didn't get rid of the knock until I got it down to 32 degrees initial and centrifugal. What gives? I don't know that much about timing and vacuum advance other than what I have read and I have gotten all kinds of answers and solutions from other but I still can't run vacuum advance without retarding timing and affecting performance. What are the disadvantages to running vacuum advance other than worse gas mileage? Thanks for listening to me rant. I'm getting frustrated!
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
The vacuum unit optimizes the timing at light or no load conditions.
For racing and max power applications, you don't really need a system for controlling advance at low or no load conditions
because these engines are operating at maximum power most if not all the time.
The main disadvantages to not running vacuum advance are :
Bad gas mileage.
Tendency to overheat at idle ( gases are still burning in the exhaust pipes at low RPM ).
It could be interesting to watch a video or at least have a sound file to hear the knock you describe...
Do you have the timing specs for your crate engine ? Some of them only take 32° ( initial + centrifugal ).
It is just a question of combustion speed, pressures and temperatures. Some heads burn faster and need less advance.
It is not ONLY a matter of compression ratio.
For racing and max power applications, you don't really need a system for controlling advance at low or no load conditions
because these engines are operating at maximum power most if not all the time.
The main disadvantages to not running vacuum advance are :
Bad gas mileage.
Tendency to overheat at idle ( gases are still burning in the exhaust pipes at low RPM ).
It could be interesting to watch a video or at least have a sound file to hear the knock you describe...
Do you have the timing specs for your crate engine ? Some of them only take 32° ( initial + centrifugal ).
It is just a question of combustion speed, pressures and temperatures. Some heads burn faster and need less advance.
It is not ONLY a matter of compression ratio.
Last edited by 73StreetRace; Jun 9, 2009 at 10:45 AM.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
Well, I give up! I changed out the distributor and still I can hear spark knock with 12 degrees initial, 18 degrees centrifugal and 8 degrees vacuum advance. That is only 38 degrees of total timing as compared to 52 in Lars and other papers I have read. So I disconnected vacuum advance and set the total timing to 36 and didn't get rid of the knock until I got it down to 32 degrees initial and centrifugal. What gives? I don't know that much about timing and vacuum advance other than what I have read and I have gotten all kinds of answers and solutions from other but I still can't run vacuum advance without retarding timing and affecting performance. What are the disadvantages to running vacuum advance other than worse gas mileage? Thanks for listening to me rant. I'm getting frustrated!
Sounds like your vac can is advancing past the engines total advance limit. Has nothing to do with at what vacuum the can comes in. Leave your total mechanical at or lower than 32.
Vacuum advance
There are various ways to do this, but this is a simple bolt on and cheap.
Follow these instructions.
http://69.20.53.62/pdf/254g.pdf
