Rich at WOT, lean at idle and cruise

[modrummer]

How long does it take for the pulloff to release from fully pulled in to all the way out?

I'll test this tonight. I'm assuming I can just apply a vacuum to the hose to test this?

I'm wondering if I could fix the WOT issue with M series rods (maybe 50m). The bigger .036 tip might be what i need to lean out that mixture a bit more.

[Cliff Ruggles]

It's already lean on the primary side so that will only make things worse.

The order for tuning is to get the idle system up to par first.

Then determine the best main jet size with the .026" tipped metering rods.

Then dial in the part throttle A/F with the correct primary metering rods using the APT system.

Then leave all that alone and tune the secondaries for best power at WOT throttle......Cliff

[modrummer]

It's already lean on the primary side so that will only make things worse.

The order for tuning is to get the idle system up to par first.

Then determine the best main jet size with the .026" tipped metering rods.

Then dial in the part throttle A/F with the correct primary metering rods using the APT system.

Then leave all that alone and tune the secondaries for best power at WOT throttle......Cliff

I was thinking more along the lines of that I have 10:1 A/F at WOT, so a fatter power tip of the M rods would lean out that part. My cruise is sitting at 12.5:1 so I think it would be fine with the fatter rods leaning it out as well.

But I see what you are saying about getting the idle dialed in first. I was more thinking ahead that with my WOT mixture SO rich I may end up needing to try some of the fat tip rods to lean it out.

Your book should be at my house today or tomorrow so I will read up this weekend.

Plan of action is to drill out idle mix screws a small amount (.090) and see if that gives me enough adjustable range. If not, I will look into changing the idle tubes.

Thanks for the help, I'll report back when I make some progress.

[Cliff Ruggles]

It will need bigger idle tubes, DCR's and probably some bypass air for the idle system.

Keep in mind that the idle system feeds the main system at light throttle thru the transfer slots so very important to start there first.

I'd also check the MAB size in that carb, it should be quite lean on the primary side with small jets in it. 

Dial in the primary side first, idle, then heavy throttle, then cruise with the APT. 

Forget using the primary side for WOT, do all that with the secondaries after you get the primary side up to par for what you are doing........Cliff

[modrummer]

It will need bigger idle tubes, DCR's and probably some bypass air for the idle system.

Keep in mind that the idle system feeds the main system at light throttle thru the transfer slots so very important to start there first.

I'd also check the MAB size in that carb, it should be quite lean on the primary side with small jets in it. 

Dial in the primary side first, idle, then heavy throttle, then cruise with the APT. 

Forget using the primary side for WOT, do all that with the secondaries after you get the primary side up to par for what you are doing........Cliff

Ok so your book came in end of last week and I spent some time reading it over the weekend while I worked on the car. Nice work! Wish I would have bought it sooner! I kinda picked and chose what sections to read for now, but I'll go back and read the rest when I have more time.

I made some progress on the carb. Took it fully apart and measured what passages I could with a digital caliper and some drill bits.

I also drilled out the idle mixture screw holes to .093".

The Upper and Lower MAB passages were both about .120" according to my measurements (does that sound right?)

I lowered the APT screw another turn since I was running rich at cruise.

I also loosened the secondary vacuum doors spring a half turn and bent down my secondary hanger to .650" to lean the mixture out a little (running CH rods currently, as I understand it these rods should be pretty lean already?)

MADE A BIG DIFFERENCE! With idle mix screws 8 turns out, I have 13.5:1 at idle (is this about where I should be once warmed up, or should I make it a little leaner?)

My cruise at partial throttle is around 13-14:1, off throttle coasting or going downhill it is running rich at about 12:1. So I'm thinking I need to lower my APT screw a bit more to lean up the cruise.

WOT is better, but not perfect. Not much hesitation as it transitions to the secondaries,  but it does peg 10:1 A/F for a split second right as I go WOT before settling around 11.5:1.

One thing I noticed, there is a small tear in the accelerator pump rubber seal. Any idea what kind of issues this causes? I plan to order a new one from you, but I wanted to do a few more tests this week first to see if I need anything else from you before I order so I don't have to pay shipping twice.

Thanks again for the help!

[77cruiser]

13.5 for idle is good but  if you can get a better idle by adjusting the mixture screws don't pay attention to AFR at idle. Lower the primary needles a bit more to lean the cruise.
 Try loosening the air spring just a bit more & that rich transition should go away.

[Cliff Ruggles]

I would get one of our SR rebuild kits, it will have everything required for a complete/correct rebuild including a new secondary cam/spring, complete accl pump assembly with new springs, float, and a high float N/S assembly.

That carb should have the large MAB's and should be showing much leaner at part throttle or at least more control with the APT system.

Assuming you are running vacuum advance light throttle A/F should be leaner at very light load.

8 turns out with the mixture screws and .093" holes under them indicates you need to open up the idle tubes and DCR's for what you are doing.  Keeping in mind that idle fuel feeds the main system as well and is the first thing to nail down when tuning, then move on to the jets, metering rods, and APT adjustment........Cliff

[modrummer]

13.5 for idle is good but  if you can get a better idle by adjusting the mixture screws don't pay attention to AFR at idle. Lower the primary needles a bit more to lean the cruise.
 Try loosening the air spring just a bit more & that rich transition should go away.

Lowered the primary needles with the APT screw and loosened the air door spring tension another quarter turn. Some slight improvement for sure. I"m getting closer, it's pretty much fine tuning at this point.

One issue I'd like to figure out is the smell I get at idle. Part of it is that I'm running a carbureted vehicle with no catylytic converter, but I've run vehicles like that before and they didn't smell this bad. So I'm wondering if I have the PCV hoses hooked to the wrong ports, or some other vent port plugged that shouldn't be or something.

See attached pictures. The big hose circled in red goes to a T fitting with one end going to the PCV valve in the valve cover and the other end going to the charcoal cannister. The hose circled in green goes straight to the charcoal cannister. Is this correct?

And then in the rest of the pictures you can see the various ports that are plugged off. I am running full manifold vacuum for the vacuum advance.

Also, what is the port circled in blue on the back of the carb near the secondary air doors? Just another vacuum port?

[modrummer]

I would get one of our SR rebuild kits, it will have everything required for a complete/correct rebuild including a new secondary cam/spring, complete accl pump assembly with new springs, float, and a high float N/S assembly.

That carb should have the large MAB's and should be showing much leaner at part throttle or at least more control with the APT system.

Assuming you are running vacuum advance light throttle A/F should be leaner at very light load.

8 turns out with the mixture screws and .093" holes under them indicates you need to open up the idle tubes and DCR's for what you are doing.  Keeping in mind that idle fuel feeds the main system as well and is the first thing to nail down when tuning, then move on to the jets, metering rods, and APT adjustment........Cliff

Cliff,

I just ordered one of your SR Rebuild kits. I am running full manifold vacuum for my vac advance since my engine runs better with it. Tried hooking it up to ported advance and it ran very rich at idle and the mix screws did nothing (could screw them all the way in without killing the engine).

I have 18 degrees initial timing, 18 mechanical (36 total) and 20 degrees of vac advance. So I get about 38 degrees of timing at idle with the vac advance hooked to manifold vacuum. Is this too much even though my engine seems to like the extra timing?

[Cliff Ruggles]

Open up the idle tubes and DCR's and go back to ported vacuum for the advance.  It's simply WAY too lean at idle if you need to run 18 initial plus 15-20 more degrees from the vacuum advance.

I see this a lot with aftermarket camshafts as they have more overlap and degrade vacuum at idle (signal) to the carburetor and the carb was originally calibrated for a "stock" engine making at least 20" vacuum at idle speed.

Everything will get better once you modify the idle system......Cliff

[modrummer]

Open up the idle tubes and DCR's and go back to ported vacuum for the advance.  It's simply WAY too lean at idle if you need to run 18 initial plus 15-20 more degrees from the vacuum advance.

I see this a lot with aftermarket camshafts as they have more overlap and degrade vacuum at idle (signal) to the carburetor and the carb was originally calibrated for a "stock" engine making at least 20" vacuum at idle speed.

Everything will get better once you modify the idle system......Cliff

When you say "open up" I"m assuming you mean "replace" the idle tubes with bigger ones? What size would you reccommend? My MAB are ~.120", and my camshaft (Lunati 268) is currently pulling 12" vacuum at idle.

[Cliff Ruggles]

No need to modify the MAB's, but remove and enlarge the idle tubes and DCR's to get enough idle fuel to the mixture screws for what you are doing.

That cam is mild enough that you shouldn't have any problem making plenty of vacuum at idle with 18 degrees initial timing, which is pretty high for what you are doing, IMHO.

We typically like to have the initial timing around 11-12 degrees for most of the engines we build and/or tune here.  This will prevent difficult hot restarts when the engine is well heat soaked and is plenty of timing provided the CID, compression ratio and camshaft are well chosen......Cliff

[modrummer]

No need to modify the MAB's, but remove and enlarge the idle tubes and DCR's to get enough idle fuel to the mixture screws for what you are doing.

That cam is mild enough that you shouldn't have any problem making plenty of vacuum at idle with 18 degrees initial timing, which is pretty high for what you are doing, IMHO.

We typically like to have the initial timing around 11-12 degrees for most of the engines we build and/or tune here.  This will prevent difficult hot restarts when the engine is well heat soaked and is plenty of timing provided the CID, compression ratio and camshaft are well chosen......Cliff

Ok sounds good. I don't have your book in front of me (it's at home), but do I need to replace the idle tubes and restrictions with bigger ones? Or can I just drill them out to the size I need?

And what sizes would you recommend for them?

EDIT: Also just FYI if it helps, motor is a 350, 9.5:1 compression, Brodix IK200 aluminum heads, ported vic jr. intake, Lunati 268 cam, 4-speed with 3.55 rear gear.

[77cruiser]

You can drill them out if you have a numbered drill set. It will only take .002-.003 more to get what you need I think. One other thing your engine might be happier with a RPM instead of the Vic.

[modrummer]

You can drill them out if you have a numbered drill set. It will only take .002-.003 more to get what you need I think. One other thing your engine might be happier with a RPM instead of the Vic.

Ok cool. I did a little googling and saw that I could drill out the Idle Restriction. Didn't know if I could drill out the idle tubes. Guessing I have to remove them carefully and then drill them.

So I have a performer RPM intake that I was running on the motor. The problem is that the intake port to head fitment on the Brodix IK200 heads isn't great. The performer RPM intake is meant to use a 1204 gasket, and I could MAYBE port it up to a 1205 gasket (Fel pro part #s). The Brodix heads call for a 1206 gasket. So with the Performer RPM, part of the intake runner ports gets blocked. Not much, but enough that it was bothering me knowing that.

The Vic had enough material to gasket match to a 1206 gasket and mates up well with those heads. I would definitely rather run the RPM intake for the street, but I'm not sure how to make it work without having like a shop add material to the runners or something.