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Topic Review (Newest First)
03-09-2013 10:00 AM
ggevaert
Bad dizzy

Looks like the Dizzy went bad; dropped in another one I had sitting around and it ran again. Had to clean plugs as they were absolutely black; likely from the constant stop/starts in testing the dizzy. jeez.

Ordered a pertronix unit to replace bad dizzy.
02-24-2013 12:08 AM
ggevaert
Bad tidings

Ok, got some problems, something went south and not sure what that is yet. Need some help here.

Started up the engine today to verify my new tach and AFT gauge installation and to describe that it ran terrible is an understatement.

I have made NO changes (other than these gauges) since last time it ran, which was excellent.
* First could not start it at all; could only get it to run for a little bit using ether. tapping the accelerator to give it gas was having no effect and eventually was just causing it to flood.
* We finally got it going, roughly, but then she ran rough and at very high RPM's of 1600-2000 (compared to where I left which was 850). Playing with the idle has eratic results; it either goes really high (2000) or stalls out.
* when it was running really high I dialed down the idle to get it to come down and then I got lots of backfiring and engine would stall around 1100.
* a very heavy fuel smell around the engine
* and the oddest of all, when I look at my timing light, which was hooked up and in RPM mode, it would every once in a while go to all zeros; which means no signal. So I think that means I'm not getting a spark to plug 1 (I only see all zeroes when I turn off the engine so this is definitely odd).
* fuel pressure gauge stayed where expected; between 6 and 8.

The last point makes me think my distributor went south but maybe the cylinder is flooded to the point where the spark plug can't fire?

I verified everything just to be sure (wires correct, no vacuum leaks, etc) and I disconnected all newly installed gauges to make sure there was nothing they were doing to interfere. What gets me is that nothing was changed since the last run otherwise I would focus on that area.

I do have my old distributor so I will be putting that one in to eliminate any potential distributor problem.

Any help and/or troubleshooting tips are much appreciated

Gary
02-23-2013 09:24 PM
Landshark928
Quote:
Originally Posted by MouseFink View Post
Engine Timing 101:

Regular production distributors have timing advance that starts at 700-900 RPM. The timing advance in distributors used in high performance engines starts at 1100-1200 RPM.

1.) Engines equipped with some high performance camshafts will not idle below 700 RPM.
2.) Since the centrifugal advance in a stock distributor starts at 700 RPM, you cannot set the initial timing.
3.) In order to lock down the initial timing in a engine e/w a high performance camshaft, you must have a distributor that starts the centrifugal (mechanical) advance at 1100-1200 RPM.

A distributor with a higher RPM centrifugal advance mechanism will allow you to turn the engine idle speed low enough so you can set the initial timing before the centrifugal advance starts. After the initial timing is locked by the distributor bolt, you can then turn the idle speed above 1100 RPM and observe the initial timing plus the centrifugal advance.

If your timing is 22 degrees BTDC, the initial timing is 12 degrees BTDC with 10 degrees timing advance in by 1200 RPM. .
Funny, my timing is set at 22* at idle. Idle is 1000rpms. When I drop the idle to 700rpms the timing stays at 22* When I raise it back to 1000rpms and the rev it, it starts to build after about 1200rpms and is all in by 3000rpms, 36* total. How did I do that? Cam is .660" lift, 253*@0.050" 110LSA 106ICL

Skip White HEI distributor with tuned springs, plates and plate stop. Maybe $50 in it total. Pretty easy to prevent advance below 1200rpms with a spring change and new plates.
02-23-2013 10:14 AM
ggevaert
detonation

Ok, Thanks for the clarification; truck was running on the road great at 18 so I will continue working with 24 and keep an eye out for detonation under load.
Cheers
02-22-2013 10:13 PM
cobalt327
Quote:
Originally Posted by ggevaert View Post
Cobalt327, are you saying that even though I have a mechanical advance stop that stops it at 36 degrees I can still get detonation?
Detonation can come from overadvanced initial timing, as well as too much total timing. You would notice it at the hit of the throttler under load.
02-22-2013 04:24 PM
ggevaert
Detonation

Cobalt327, are you saying that even though I have a mechanical advance stop that stops it at 36 degrees I can still get detonation?
02-21-2013 10:12 PM
ggevaert
Timing

Thanks Gents, I have some work ahead of myself.

F-BIRD'88, Quickfuel sells air bleeds in every size so I will just get one of their assortment kits at summit for $50, they come with every size from 36 up to 75. With items that small and precise I don't really trust myself to get them correct.

Don't know what cam brand is in there; it came with the motor and I'm trying to work with it.

My torque converter is 10", I purchased it new from a local reputable racing transmission shop because I wanted a good one.

How do you know a power valve is fluctuating at idle?

Also, I'm running 94 octane sunoco fuel so that will allow me some detonation headroom.

Cheers
02-21-2013 10:56 AM
cobalt327
Quote:
Originally Posted by ggevaert View Post
Also, keep in mind that I have not been able to take the truck for a drive as I have no windshield in it yet (and its 20 below out here) so my only load testing has been with my foot on the brake and with a chock block on the wheels.

Vacuum can is the stock MSD one, it has a vacuum advance stop plate installed and set to 13 degrees; with the vacuum hooked up, at idle my timing was 30 (so +6 from initial) and at all in (3000 rpm) it ran at 42. Keep in mind that was at idle and not under load.

Mine is a GM HEI so the article you note is very relevant and, yes, I did read it thorougly.

I do plan on adjusting the idle mixture screws; that is the plan this weekend; I just wanted to get timing done before going there. (but I do understand it sometimes is not a linear exercise; you think everything is set, take it for a drive and end up re-adjusting everything ) but that's the fun part.

Cheers
Good deal. My only comment at this stage is that you cannot judge detonation (or the lack of it) w/o driving the vehicle. You can't duplicate the same load it'll see on the road using the brakes, unfortunately. What you'll want to do is go back to ~18 degrees initial and test it on the road after it's roadworthy. Then readjust from there. If you choose to leave it as-is, just be uber cautious and listen carefully for detonation.
02-20-2013 08:42 PM
F-BIRD'88 if the power valve is fluctuating at idle change to a 4.5". It must stay closed at idle and closed when idling in gear when manifold is lowest.
What is this 224deg .450" lift cam? A dirt track motor "lift rule cam"? Brand?

These cams usually need a 10" torque converter. And the typical "2500 stall" is not loose enough at idle.

usually a "2500 stall" is a cheap tweeked stock diameter 12"+ GM converter.
02-20-2013 08:30 PM
F-BIRD'88 I suggest you go back to the 70 idle air bleeds. The wide band will show you what it really wants for a pri idle air bleed. You can make your own by soldering up and redrilling with a .062" drill bit (1/16").
Then as that will likely be a bit too rich as shown on the AFR gauge (off idle, transition) you then fine tune the size by hand a little at a time using the drill bit as a hand hone in the air bleed, till its just right.

You tune the off idle with the AFR gauge.. not the curb idle. The curb idle is set according to the manifold vacuum gauge and best idle quality (it will be between 12.5 and 14:1 at idle)

The off idle must not shift too far lean or rich as your open the throttle. +/-14.7 is good.

Then watch the gauge as you open the throttle further and the primary main jet flows fuel.
takes a bit to find the best balance and a good transition.

Very small changes make a big difference. a .004" change is a lot.
By custom hand sizing the soldered up air bleed by hand you get it much more exact than buying different bleeds.

any all air leaks will throw off the AFR gauge, including header gasket leaks.

You must always test the final size of the air bleeds with the air cleaner installed. Ya it matters.
That's how sensitive they are.

You can shift the AFR of the idle circuit by hand with fingers partically over/restricting the idle air bleeds and watch the effect on the AFR gauge
while the engine is running at idle and off idle. (when you open the throttle a bit from idle)

I bet you will end up with a custom pri air bleed size between .065" and .070" The afr gauge shows you the way.
02-20-2013 08:10 PM
ggevaert
Timing/Carb

Hi,

F-BIRD'88, Idle timing is rock solid. Interesting about the vacuum, i thought that was odd but attributed it to the cam and low idle RPM; I will have to review the cylinders if any are missing; not sure. (i'm rather hard of hearing so I need to use alternate methods to investigate those types of things, any suggestions?). I did check for vacuum leaks with propane and none were found. I will hookup the wideband AFR this weekend.

Using a Quickfuel SS 680VS with pri and sec idle air bleeds changed from stock 70's to 74's. (as recommended by quickfuel when I provided them with the engine specs). The high speed air bleeds were left alone and are 28/28.
Everything else on Quickfuel was also left alone (primary main jet 68, Secondary jet 78, pri nozzle 31, needle and seat 110, power valve 6.5). As I got through my carb dialin I will be reviewing each of these to ensure they are the correct setup for my application.

I actually bought a wideband AFR electronic setup that I have not yet hooked up. Was planning to get basics on engine done then go back over the setup with it on. Never used one before so need to learn how.

cobalt327, I understand; At the beginning of this timing exercise I started at 18 degrees initial with an advance stop of 18 degrees (which was working well) but I decided to go higher to see how that would look. Hence my original question as I was trying to understand the reasoning for why we set initial timing where we do and why we stop where we do. I did increase the timing 2 degrees at a time from there, every time checking for starter issues or detonation and found none all the way to 24. I stopped there for no reason other than I was worried about going higher. Also, keep in mind that I have not been able to take the truck for a drive as I have no windshield in it yet (and its 20 below out here) so my only load testing has been with my foot on the brake and with a chock block on the wheels.

Vacuum can is the stock MSD one, it has a vacuum advance stop plate installed and set to 13 degrees; with the vacuum hooked up, at idle my timing was 30 (so +6 from initial) and at all in (3000 rpm) it ran at 42. Keep in mind that was at idle and not under load.

Mine is a GM HEI so the article you note is very relevant and, yes, I did read it thorougly.

I do plan on adjusting the idle mixture screws; that is the plan this weekend; I just wanted to get timing done before going there. (but I do understand it sometimes is not a linear exercise; you think everything is set, take it for a drive and end up re-adjusting everything ) but that's the fun part.

Cheers
02-20-2013 01:34 PM
cobalt327
Quote:
Originally Posted by ggevaert View Post
Wow, lots of discussion.


Thanks for the continued assistance;

Cheers
Larger air bleed = leaner idle. If this is QF recommendations, I'd stay w/it unless the engine performance/plugs/a-f meter dictates otherwise.

As has been said already, use as much timing as the engine wants. The upper limit is determined by how it starts up, if it pings at throttle tip in (this will become more evident when the vacuum advance is brought on-line). But using the absolute maximum amount of initial timing isn't necessarily the best way to go about it. It is my opinion that using a medium amount of initial timing (which gives a broader amount of mechanical timing) should give better control of the spark timing over a broader range of engine rpm.

An example of this thinking is seen here, where Demon carbs recommend 14-16 degrees BTDC for your engine/cam/carb size as a safe starting point. I'd recommend you work upwards 2 degrees at a time from there.

When it comes time to set up the vacuum advance, if for some reason you end up using 24-plus degrees initial, you may find using ported vacuum better than manifold vacuum. Generally speaking, you won't need more than 10-12 degrees of vacuum advance.

More on timing is here. The page is on GM HEI, but the timing info is relevant regardless of the distributor.

DO NOT be hesitant to readjust the idle mixture screws! They should be readjusted after just about any change made to the engine perimeters (timing, idle speed, plug heat range, idle air bleeds, etc.), and as long as the engine is fully up to temperature (fully- as in after a drive or a long warm up if still undriveable), you cannot go wrong readjusting them as needed.
02-20-2013 11:41 AM
F-BIRD'88 The large idle air bleeds may be too large. I dial mine in using a AFR gauge.
Makes a big difference. The vacuum gauge should not hunt at idle. is the timing stable at idle?
Is one cylinder missing?

yup probabily a 106LSA cam.. They like lots of idle timing 24ish should be plenty.

What carb model? what are the pri and sec air bleeds sizes. what was stock orignionally?
Why did you change it?

The tuning on then idle air blleeds is critical very small changes make a big difference.
The AFR gauge makes it real easy.
02-19-2013 08:05 PM
ggevaert
Initial timing

Wow, lots of discussion.

Let me answer some comments/questions:

1. Mousefink, My initial timing is 24 degrees; Mechanical advance curve is set to come in at 1200 and be all in at 2800; I have verified this with a good timing light. Timing did not budge at all until we hit approx 1200 then started to go up. My idle is set at 800 and is stable. I use an MSD 8365 with custom stop advance bushing (14 degrees). And, yes, it starts just fine with 24 degrees initial timing, actually on the first turn of the key.

2. F'bird-88, don't know LSA for sure; tag on the engine said 450 lift, 224 duration, 206 lobe centre but I think the 206 is wrong? (maybe 106?, it was hard to read that part of the tag clearly)
Manifold vacuum at idle is 8-12 (bounces fast between that range) at 800 rpm; I could not find my notes with the readings in gear, will redo that next run, likely thursday night.
Have not got as far as idle screws yet, they are, however, set at 1.5 turns out on all 4 corners from the factory (I verified). I would hope they would be active as otherwise that means my transfer slot is too exposed. (which I initially set to 0.025)

3. TommyK, thanks, I'll put that on my list. I do have a mini starter with rather high torque capability and I have the headers closest to the starter wrapped. Went through 2 GM starters in 1 year before I learned that one; no issues now in 2 years.

4. I was told that the reason the recommendation for high performance engines to be set to 1100-1200 idle is to ensure proper oil splash and cooling on the cam. I prefer to keep mind a little lower at 800-900 but that is not yet set in stone; we'll see where she settles when I'm all done.

Also, keep in mind that I have larger idle air bleeds installed in the carb so that will also affect 'stock' thinking. This was a recommendation by Quickfuel to smooth out my idle and makes sense to me.

Thanks for the continued assistance;

Cheers
02-19-2013 01:48 PM
33Willys77 I say, stop trying to confuse people. The one that started this topic noted he has an MSD distributor. He can very well have 22 degrees initial. Mine is set at 34 degrees weather its at 600 RPM or 6000 RPM. I'm done here.
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