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360: timing/mixture/vac help needed.

I think it's running way too fast, that's the big problem here.
Just as a test try 20- 25 Degrees BTDC and slow down the idle as much as possible and tune it at idle in gear when warm with the air cleaner attached.
You may need to drill 1/8" holes in the throttle plates so they are closed more at idle.
If that helps then you'll need to cut down the amount of mechanical advance to get your maximum advance in the 35 degree range.
But that's a separate project.

Thanks. I'll have another go at the car tomorrow or Sunday.

Some excellent advice on the past few posts. You may not know, but is the cam set up straight, retarded, advanced ? As a prior posted noted, setting ignition timing backwards is something I routinely did. Set total, then adjust advance & initial to suit.

I agree. Some very helpful and much appreciated advice. I'm afraid I don't know the answer to your question about the cam.

David
 
I think things are getting close to done. I reset the idle mixture in case it was off spec., reduced the idle to 950rpm with the vac advance detached and the port on the carb capped and then I redid the timing working back from 34BTDC @2800rpm. I revved it up a few times to 3500- 4000 rpm and the timing did not advance further. When dropped back to idle, the initial advance sits at 11BTDC. Now, the idle: I did set it to 950rpm in neutral as best I could and it drops to 700-750 when I put the car in drive. It idles a bit rough there but doesn't stall. Also, on shutdown, there's no run-on and no spitting from the top of the carb and the car hot starts are ok.

So far, all good and perfectly drivable I think (I have a binding rear brake to fix before I can test on the road) but the idle is odd. It changes. It flutters a bit but nothing major. The change that I mean is that sometimes when I rev it up and then release the throttle, it settles around 1000rpm and other times it settles as low as 860rpm and anywhere in between. I pushed the throttle closed on the lever on carb and it makes no difference that I can tell but I will go through the linkages to see if anything is binding. Meanwhile, any thoughts on that?

Thanks to all for the help. As you can tell, I really need it!

David
PS, I am going to change the thread title again as the spitting seems to be cured.
 
Total timing at *** RPM is a horrible method to time a street car engine. Here's why. Two distributors, one with 18* advance the other with 28* advance. Those distributors will have VASTLY different performance characteristics, especially at idle and off idle into transition circuits. IMO, Yours has more mechanical timing in it than it should, which is not what you want with that camshaft. Even 5* more initial timing can make a huge difference in how the engine runs at idle in park and in gear.

I agree with @Don Frelier
Get the idle timing set correctly, then worry about total timing. Idle timing is the foundation on which other timing event is built.

Some of the issues you mention are caused by lack of initial timing.

IMO, it will want 18-20 initial timing if that is the [email protected] cam and .450ish lift.
 
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Total timing at *** RPM is a horrible method to time a street car engine. Here's why. Two distributors, one with 18* advance the other with 28* advance. Those distributors will have VASTLY different performance characteristics, especially at idle and off idle into transition circuits. IMO, Yours has more mechanical timing in it than it should, which is not what you want with that camshaft. Even 5* more initial timing can make a huge difference in how the engine runs at idle in park and in gear.

I agree with @Don Frelier
Get the idle timing set correctly, then worry about total timing. Idle timing is the foundation on which other timing event is built.

Some of the issues you mention are caused by lack of initial timing.

IMO, it will want 18-20 initial timing if that is the [email protected] cam and .450ish lift.

Thank you. Yes, the cam spec is 228@050 and 0.450in intake lift.

I believe the 'work down from total timing' approach was to prevent me ending up with too much total mechanical advance. Before I go try setting initial timing in the range you suggest to see how it then idles, am I right in assuming that my distributor seems to have about 24 degrees of mechanical advance? If so, does that mean if I end up with initial timing at, say, 18BTDC then my total timing will be 42BTDC and is that is too high? So would I then need to change the advance limiters in the distributor to keep the max. mechanical advance to approx 34BTDC?

Thanks again. I appreciate all help.

David
 
Thank you. Yes, the cam spec is 228@050 and 0.450in intake lift.

I believe the 'work down from total timing' approach was to prevent me ending up with too much total mechanical advance. Before I go try setting initial timing in the range you suggest to see how it then idles, am I right in assuming that my distributor seems to have about 24 degrees of mechanical advance? If so, does that mean if I end up with initial timing at, say, 18BTDC then my total timing will be 42BTDC and is that is too high? So would I then need to change the advance limiters in the distributor to keep the max. mechanical advance to approx 34BTDC?

Thanks again. I appreciate all help.

David

Correct, you would need to limit mechanical advance in the distributor. weld slots, JB weld, FBO limiter plate, adjust stops.n Don't know internals of the petronix distributor. Could be very easy to do.

I would find the point that the engine likes at idle. Then you can adjust to hit total and curve.. Tune vac adv is next if you are running it.
 
Correct, you would need to limit mechanical advance in the distributor. weld slots, JB weld, FBO limiter plate, adjust stops.n Don't know internals of the petronix distributor. Could be very easy to do.

I would find the point that the engine likes at idle. Then you can adjust to hit total and curve.. Tune vac adv is next if you are running it.

Thank you. Adjusting the mechanical advance in this distributor seems easy enough. I'll have to order some parts though.

David
 
A little rule that I live by:

Carb doesn't effects timing settings, timing ALWAYS effects carb settings.

Simple test. At idle, if you twist the distributor CCW and the engine picks up RPM, it wants the timing. As long as the car can start when hot without kicking back on your starter, you can run timing up quite a bit. Another that is a symptom, long crank times and having to mat the pedal to fire up. Usually low initial timing situations. Engine should want to fire at the flick of the key. I've fixed tons of cars, all makes over the years, from the total timing crew. Most were quite impressed with the snappiness of the engine and how the cars didn't smell like a fuel truck dumping raw gas out the tailpipes any longer.

There are other things that happen with a high idle, mechanical timing bleeding in slightly. Pull engine in gear, RPM drops, timing (mechanical) gets pulled exacerbating the idle tune issue.

You should be able to get that idling at 700-800 rpm with minimal RPM drop in gear. It should not require any drilling of the carb butterflies. It's not a large camshaft. Similar to an XE268H or voodoo 603 which are mild.
 
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I wish I had a "totally agree" button.
I'll bet it will run way better at 20-25 deg. BTDC at idle and you should be able to get it to idle in the 650 RPM range without the huge drop in RPM going into gear.
 
Parts for distributor (springs and limiters) won't be here until the weekend but I'll try to set idle at higher advance tomorrow. I won't rev her up though.

I'll let you gents know what happens.

David
 
A little rule that I live by:

Carb doesn't effects timing settings, timing ALWAYS effects carb settings.

Simple test. At idle, if you twist the distributor CCW and the engine picks up RPM, it wants the timing. As long as the car can start when hot without kicking back on your starter, you can run timing up quite a bit. Another that is a symptom, long crank times and having to mat the pedal to fire up. Usually low initial timing situations. Engine should want to fire at the flick of the key. I've fixed tons of cars, all makes over the years, from the total timing crew. Most were quite impressed with the snappiness of the engine and how the cars didn't smell like a fuel truck dumping raw gas out the tailpipes any longer.

There are other things that happen with a high idle, mechanical timing bleeding in slightly. Pull engine in gear, RPM drops, timing (mechanical) gets pulled exacerbating the idle tune issue.

You should be able to get that idling at 700-800 rpm with minimal RPM drop in gear. It should not require any drilling of the carb butterflies. It's not a large camshaft. Similar to an XE268H or voodoo 603 which are mild.


I wish I had a "totally agree" button.
I'll bet it will run way better at 20-25 deg. BTDC at idle and you should be able to get it to idle in the 650 RPM range without the huge drop in RPM going into gear.


Again, I was on my own and the set of alternate springs and limiters won't be here until the weekend but I thought I'd try a bit of advance today.

Firstly, a total basic goof, I found the erratic idle was due to vacuum leak around the carb-to-manifold gasket. The nuts holding the carb down were a loose. Idle is now is fluttering between 870 and 910 rpm which seems ok. So I set the initial timing to 18BTDC and gradually upped it. In the end, the idle seemed smoothest and the timing mark most stationary at 21BTDC at idle with the vac advance disconnected and plugged at carb. At this initial advance, when changed from neutral to drive, the idle drops to 700-750rpm but sounds steady and doesn't produce as much of a thump as the transmission engages. I can't see what that does to timing being on my own. The engine shuts down cleanly and restarts hot easily. I forgot that you recommended an even lower idle than that so I plan trying a lower idle this weekend.

I did rev the engine a little using the linkage on the carb and it looks like the ignition advances almost immediately - certainly by 1000rpm. If that persists when I've lowered idle and set initial timing again, will that mean I need to adjust the distributor springs to slow the start of the advance?

My choices of limiters in the set are 12, 16 and 20 degrees. So if my final initial timing plus one of those isn't exactly 34BTDC (e.g. if initial ends up at 20, do I use 20+12=32 or 20+16=36?)

Thanks again for all the help.

David
 
As you increase the advance you can usually lean out the mixture a bit since it's burning better.
Keep going try and slow it down, lean it out a little and head towards 25 degrees.
Then a rough tune warm in nuetral and finally try the mixture screws in gear.
With an Edelbrock/Carter style carb I usually go just a bit leaner than max RPM at idle.
I think you will see improvement.
You can drive it moderately like that but next work on maximum advance.
 
I also always disconnect everything from the intake that draw vacuum to eliminate it as an issue. Power Brakes plenty of times can cause idle issues with a leaky booster or lines. Reconnect one at a time and wait a minute to see if the idle changes.

Good on fixing the vacuum leak. Have to have that right as well.

If I had a choice, I'd back down a little on initial to get the total number I want. I think you can mix the limiters on the distributor. See if you can get a 14* set up and go with 20 initial. Hard to know exactly what it wants for total other than track times or pinging under load. 34 is likely fairly safe.
 
I haven't had a chance to get back to this and fit the limiters yet but I have a question: If the limiters stop the weights from moving as far out as the max. advance limit (hits limit of 24 degrees@2800rpm), does that mean that I should expect the new, lower advance limit to be reached at lower rpm than that? If the weights can't spin out as far, surely the limits will be met earlier?

David
 
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Yes unless you change the weights or springs the advance curve will be the same only you cut off the maximum mechanical amount.
 
Thanks for the help, guys. Today I redid the timing and fitted limiters to the distributor. With vac plugged the car idles well in neutral at 900rpm with20BTDC timing and at about 750rpm in drive. The limiters are set to 14degrees. The mechanical advance starts at about 1100rpm and reaches 34 (the limiters hold it there, of course) at just before 3000rpm. The car drives well, pulls easily from a standing start, responds well to throttle including enough to kickdown. it also fires right up when restarting the hot engine which has been a problem before.

I may continue to experiment a little more but I think this can be considered job done. Thank you.

David
 
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