timing question

[firedoger]

This is for a 400sb. I was told it has a cam but it's not big maybe a rv cam. It has a Edlbrock 1405 carb with Edlbrock RPM performer intake and 1" 4 hole spacer. I also have a fuel pressure reg set @ 5psi. The dizzy is a MSD streetfire( junk).
16 degrees @ idle 650 rpm
36 degrees at 3600 rpm
18psi on vac gauge on manifold vac port

Timing with vac advance connected to man port
28 degrees
43-45 degrees @ 3600 rpm


This is my problem. In park it idles fine at 650rpm but when I put it in drive it drops about 200rpm and doesn't want to run well. I've tried adjusting the mixure screws and increase the idle rpm to 800rpm but it still drops down to about 450 -500 rpm. What could be causing this?




'

[Bigdav160]

How's the acceleration? Slipping stator in the torque converter?

[BMERDOC]

Did you use a vacuum gauge to adjust the mixture? You may be getting too high with the idle speed and uncovering the transition slots causing a rich mixture on a truck with an already overly rich idle mix. What do the plugs look like? You initial timing may be a bit excessive and the timing with the vac advance plugged in is a couple degrees too high as well (should be 22-24 degrees). I doubt you are running an EGR valve so you are correct by going full manifold vacuum. You also stated that at 3600 rpm your timing was at 36 but then said it was 43-45 at the same rpm. I'm not convinced its a timing problem but it still could use some tweaking.

[BMERDOC]

Oops! Just thought about it! You knew that it had 18 in.hg. so you musta been using a vac gauge. Was it running fine before and what did you do since?

[68gmsee]

Do you have an idle compensator?

Disregard. I was thinking of A/C compressor idle up.

[firedoger]

What is an idle compensator? It seems to also have a slight miss which is more noticeable when its in drive. I will pull a couple plugs in the morning and see what they look like. I have sprayed some carb cleaner around the carb area and I'm not detecting any leaks.

[firedoger]

Just figured out what the idle compensator is and I don't have one

[crazy longhorn]

Just my thoughts.....that 406 has a long arm? Knock 2 or 3 degrees off the total, & see where it goes? Is it better, or not? You , know where to move from there ? best of fun, Longhorn

[storm9c1]

Some random thoughts -- Streetfire vacuum advance is pulling too much advance at idle which will give you headaches when trying to tune. Some came with a stop plate. Some came with adjustable canisters. Some came with neither. What type do you have? If you have the kind with the stop plate, then use it and set it for 8-10 degrees MAX. If you have the adjustable canister, set it for 8 degrees at manifold vacuum at idle.

After you do this, unhook the vacuum advance and plug it at the carb. Then make sure idle setting on carb is NOT above the transition. Then adjust your idle mixture screws to get max on the vacuum gauge at idle with vacuum advance still unhooked. Then hook up the vacuum advance -- idle should increase. Now readjust your idle stop on the carb for 800-850 RPM in park (this should settle down during a test drive). Put it in gear and see how far it drops. If you do this right, it should drop to 600-750.

This also reminded me to check/replace your carb return spring! Make sure it is applying some good force otherwise the idle can wander due to lack of return force.

Do these things exactly in that order. Sometimes this takes some iterations before you get it just right.

Also make sure there isn't a problem with your transmission, torque converter or belt accessories adding excessive load at idle.

And make sure choke mechanism is working properly. You must do all of this on a warmed up engine! Choke must be fully disengaged as well as the idle bump cam or else you will chase your tail.

[geezer#99]

Originally Posted by storm9c1

Some random thoughts -- Streetfire vacuum advance is pulling too much advance at idle which will give you headaches when trying to tune. Some came with a stop plate. Some came with adjustable canisters. Some came with neither. What type do you have? If you have the kind with the stop plate, then use it and set it for 8-10 degrees MAX. If you have the adjustable canister, set it for 8 degrees at manifold vacuum at idle.

After you do this, unhook the vacuum advance and plug it at the carb. Then make sure idle setting on carb is NOT above the transition. Then adjust your idle mixture screws to get max on the vacuum gauge at idle with vacuum advance still unhooked. Then hook up the vacuum advance -- idle should increase. Now readjust your idle stop on the carb for 800-850 RPM in park (this should settle down during a test drive). Put it in gear and see how far it drops. If you do this right, it should drop to 600-750.

This also reminded me to check/replace your carb return spring! Make sure it is applying some good force otherwise the idle can wander due to lack of return force.

Do these things exactly in that order. Sometimes this takes some iterations before you get it just right.

Also make sure there isn't a problem with your transmission, torque converter or belt accessories adding excessive load at idle.

And make sure choke mechanism is working properly. You must do all of this on a warmed up engine! Choke must be fully disengaged as well as the idle bump cam or else you will chase your tail.

A little more about your transition slot. If you can turn your mixture screws in all the way and the motor doesn't slow down or die then your transition slot is uncovered and your idle is too high.

[firedoger]

Ye ha Chester is dead. Thank you for everyone's help! I got it resolved . I hooked up my vac gauge and was able to get a few more out of it. I had at 18 yesterday and by following the advice I was able to get it to 20 which made all the difference. My idle is at 850 rpm and when in gear it's happy and smooth at 600 rpm. Is 850 rpm to high for it to idle at?
Storm9c1 I hate that Streetfire dizzy. I have the stop plate and an adjustable vac can. I have the stop plate set at the smallest point which I think is 10 degrees. I had the timing set yesterday at 16 and this morning it was 18. That dizzy drives me crazy! I'm looking for a small cap replacement any ideas?

[storm9c1]

Eh, 850 is not too high at idle. I like to keep my V8 vehicles right around there anyways -- it makes the alternator happy and keeps the engine cooler with the additional fan and WP speed. On a hot day after driving it for a while, I expect your idle to fall down a little and settle in around 750-800 anyways, so don't worry. The idle speed in gear is more important.

I'm not a big fan of the Streetfire either. It's an "offshore" cheapo distributor -- and with the stock weights and springs, it's almost unbearably annoying. I change the weights, springs, and vacuum canister on those right away. Otherwise you may have some fighting to do.

I prefer a good quality large cap HEI. You have lots of options for a small-cap setup as well if that's the direction you need to go.

[crazy longhorn]

Every body wants to state 850 rpms, on the mechanical advance(start point)....all the kits I have played with, will not go this way? Many of you guys, have played the old "proved & true" Crane advance kit, & have modified it , as told.....I don't give a crap, on what the next guy said! I have used those Crane kits, for many yrs. The advance starts @ 800 rpms (not 850). Put the TOTAL , where you want it @2800. I like to shoot, for a 33-35 total on a sb chev....cut the decks , for quench, & you can live with more total timing? Longhorn

[firedoger]

Originally Posted by crazy longhorn

Every body wants to state 850 rpms, on the mechanical advance(start point)....all the kits I have played with, will not go this way? Many of you guys, have played the old "proved & true" Crane advance kit, & have modified it , as told.....I don't give a crap, on what the next guy said! I have used those Crane kits, for many yrs. The advance starts @ 800 rpms (not 850). Put the TOTAL , where you want it @2800. I like to shoot, for a 33-35 total on a sb chev....cut the decks , for quench, & you can live with more total timing? Longhorn

I'm trying to figure what you are explaining. My block has been decked and I have no idea what my compression is. Are you saying to set my idle at 800rpm then hook up the vac can ? And have all the timing in at 2800rpm? With a total timing of 35 degrees. Please be patient with me I'm learning as I go.

[storm9c1]

Perhaps he is trying to say that at 850 RPM, you may start to tip into the mechanical advance at idle. I run heavy springs and light weights on a truck, and never noticed a problem as long as I don't exceed 850. It's easy to check with a timing light. Perhaps he is also giving advice on what RPM should be all-in? Good advice, but again, since I run light weights and heavy springs, mine isn't all-in until probably 3000-3200. Works on my machine! With higher compression, you need that. Lower compression, you can get away with more aggressive timing numbers at lower RPM. That's why it's a factor. Just be sure you don't ping throughout the power band, and the timing is all-in at 2800-3200 (somewhere in that range), and you don't have mechanical advance tipping-in at idle. Trial and error man.

[firedoger]

Originally Posted by storm9c1

Perhaps he is trying to say that at 850 RPM, you may start to tip into the mechanical advance at idle. I run heavy springs and light weights on a truck, and never noticed a problem as long as I don't exceed 850. It's easy to check with a timing light. Perhaps he is also giving advice on what RPM should be all-in? Good advice, but again, since I run light weights and heavy springs, mine isn't all-in until probably 3000-3200. Works on my machine! With higher compression, you need that. Lower compression, you can get away with more aggressive timing numbers at lower RPM. That's why it's a factor. Just be sure you don't ping throughout the power band, and the timing is all-in at 2800-3200 (somewhere in that range), and you don't have mechanical advance tipping-in at idle. Trial and error man.

That makes sense. If I remember right I'm using the lightest springs from the MSD kit and the weights that came with the dizzy. It still doesn't come all in until about 3500rpm. I tried the weights that came the MSD kit and I didn't like them for some reason. It's been over a year since I messed with weights.

[crazy longhorn]

Originally Posted by firedoger

That makes sense. If I remember right I'm using the lightest springs from the MSD kit and the weights that came with the dizzy. It still doesn't come all in until about 3500rpm. I tried the weights that came the MSD kit and I didn't like them for some reason. It's been over a year since I messed with weights.

Storm said it 'square' Sorry I missed your question to the reply? At any rate, I have used a Crane advance kit in the stock Hei dist , for many yrs. They do use the stock weights (that are fairly heavy), & the advance does start @ 800 rpms , even if the springs are pretty tight. Most of my street toys, I try to set around 2800 all in, & shoot for 33-35 on the total, then add another 8 to 10 degrees (at the crank), for the vac advance (plugged to manifold vac source). My app is a tad different than what Storm is using....his is a heavy hauler/ high compression....my app had a little rowdyer cam/alum heads, & ran stick shift or loose converter, on some lower rear gears, on that 9.8 to 1 motor. Im not here to say right/wrong....every app tunes a tad differently Both trucks work for what they were intended for My old 383, is in my bros s-10....13.1 @102 on the track, with corked up 2" exhaust, beat up old stock HEI, & an old Edelbrock carb. I think she will go mid 12's, with a few goodies, but she is still running the same tune that was on my street truck! Sorry for getting off topic....just look at the truck, for intended usage....tune from there? You will have a bunch of good guys here to help Longhorn

[firedoger]

This is in my 72 blazer and it's a street driver no hauling or towing. I just like to get on it every once in a while. I'm prolly just splitting hairs on it. One of my concerns is that I can't tell for sure if I'm getting detonation or have an exhaust leak. I have my top off and there is a lot of wind noise when driving. I hear something I just can't quit determine what it is.

[storm9c1]

Longhorn, yep, every engine and application is different. I try to give advice here based on a simple differentiation: cars versus trucks. My experience is that cars use lighter distributor springs, trucks use heavier springs, but this isn't always the case. Of course the truck in my avatar is a heavy hauler, but I have other vehicles that don't work so hard and they need heavy springs too... I'm also a little paranoid about detonation and will leave a little power on the table to save the running gear. That being said, it's always trial and error with any particular setup.

Firedodger, diagnosing detonation is hard with wind noise. I always need to do it with the windows up. With a quiet cab, the detonation sound is very unique and (for me) cannot be confused with an exhaust leak. Can you put the top on and put the windows up? Or just try heavier springs and see if the noise subsides? And/or fix the exhaust leak. LOL.

[crazy longhorn]

Agree, street/ heavy vs strip. Or street/ strip, does make a difference on the tune. Comp ratio, & camshaft do also factor into that , as well as loose converters/low gears? Longhorn