tuning questions (kinda long)....

i read through a bunch of posts on the Autolite 2100 carb, and think i've got an idea of where to start. but, before i rip the thing apart, i thought i'd share my start-up experience with y'all.

i spent the last month of free nights porting, polishing, cc'ing the new E0 head, not including the week i waited for the maching shop to fix the valve seats i dinged with the grinder (*sigh*). it got a 3-angle valve job with all new parts and a 2-bbl adapter. i just got it running yesterday, it fired right up, and it idles well, but on the road it 'surges' at light-medium throttle just driving at 2000-2500 rpm and just feels sluggish up to 2,500 rpm. it responds pretty well to larger throttle openings, and i did punch it WOT from start (once i was comfortable it wasn't going to fly apart) - it took right off toward 4,000 rpm, then stalled big time. so, the good news is i think there's bunch more horsepower there once i get it sorted out.

here's what i know for sure:

I set a new TDC mark with a dial indicator while i head the head off, and i set the initial advance at 12 degrees. the recurved DSII from reincarnation auto adds another 12 degrees at 2,000, 18 degrees at 2,500 and pegs at 29.5 degrees at 2,950 rpms. i don't have the vacuum advance hooked up at all, but it would add 20 degrees at 14 inHg if i did.

the autolite 2100 came with 49F jets, and has some idle circuitry work done to it by some guy who says he knows what he's doing (k. praxl).

vacuum at idle is about 19 inHg. at the light throttle when it surges it's running in the 12-18 inHg range. any heavy-footedness brings it right down to 5 inHg or less.

fuel pressure after the filter is about 3.5 psig, and it drops a little when i goose it sitting in the driveway, no gage in the interior to watch it when it's on the road. idle screws ended up at 1-3/4 turns out, that was high vacuum at 700 rpm or so.

compression is 144 to 148 in five cylinders, 155 in No. 4. odd, i checked 'em twice.

other mods as listed below, it's the stock cam with 1.65 yella terra roller rockers, autolite 46 plugs/indexed/0.045", headers, duals, t5, etc.

so, two things i'm wondering about are low fuel pressure and lean main jets. the low fuel pressure comes to mind when i punched it and it took off for about three seconds then just stalled at 4,000 rpm. as for the jets, it actually feels like it's running rich, but i see other posts where guys are going to 60's on the jets to get the motors to run right.

thanks in advance for any other thoughts....

Howdy Scott:

Nice project. You should try another turn out on the Idle air screws. You might try more initial advance too. With your combo I'd try 16 btc and see how it likes it. Make sure your idle speed is as low as you can get it.

What do your spark plugs say?

If you get the 1.14 sorted out and like it, you will love a 1.21/1.23 on your 200.

Are you using a Holley power valve? You can and they are much more likely to function closer to their rating the the wimpy Autolite version.

Keep your progress reports coming.

Adios, David

after just 10 minutes of running in the garage and maybe 8 miles of driving, the plugs had tan tips with some soot down in the hole, some tan on the insulators, too. however, those plugs already had 1,000 miles on 'em. i'll try opening the idle screws and advance the timing later today, will also pick up an air horn gasket and verify the existing main jets, float height, pick up some larger jets if i can get lucky, and some fresh plugs.

i saw your post on changing to the holley power valve, i'll work on that, too.

thanks, david, keep you posted....

any advice on which Holley power valve to use? do i pick the vacuum rating based on my actual vacuum at WOT, or do i want the power valve to come in earlier (at part throttle)?

thanks again.....

The part throttle surge is indicative of a lean condition caused by too small main jets. Opening them up will cure the 2000-2500 condition.

If it feels flat or is bucking at WOT you need to swap power valves, either for more flow of earlier opening. Look at the number on the current valve and replace it with one that has a larger number. Usually they open at between 6.0 and 8.5 inches as marked on the valve. You'll have to experiment to get a good result, but it sounds like you are very close.

Howdy Back:

The test for a lean jet is to drive at a steady speed, say 55 mph. If you feel surging at a steady speed, it is an indication of a lean main jets.

There are two theories in selecting a PV to get you in the ball park. 1st is to determine idle vacuum and half it. ie- 19" = 9.5 or 10.5. The other is to drive at a steady cruize speed to get a vacuum reading. Choose a PV 1 number lower than that reading. With a stock cam you will find a higher number matches your engines vacuum characteristics. The goal is to find an opening point as high as possible, but below the lowest point within the normal curise range. I'd start with an 8.5 and assess from there.

It is unlikely that your Autolite PV will have any decypherable rating numbers on it. And even less likely that the actual vacuum pressure needed to actuate it will be the same as it is rated. While you have it apart you might want to note the diameter of the two Power Valve Channel Restrictions(PVCR). They are located on either side of the recessed bowl under the threaded seat of the PV. On a 1.23 they measure about .035"- sorry I don't recall the PVCR on the smaller carb.

Be sure to recheck your float level and the position of the accelerator Pump actuation arms. The lever on the throttle shaft is called the "Over travel" lever and has either 3 or 4 holes in it. They are numbered from the bottom. The arm on the accelerator pump is called the "Pump lever". It will have 2 holes. "Inside", or closest to the pump and "outside" fartherest from pump. A good place to start is to have the OT in the #3 hole (3rd from bottom) and the PL in the inside hole. This is all assuming that the rod connecting the two arms is the standard one for your carb and that its shape has not been altered.

Your description sounds as if your running out of gas in the float bowl. Two possibilitieas are a low float setting or a weak fuel pump.

Keep in touch.

Adios, David

thinman56

Sounds like you have a fresh engine. I wouldn't worry about your uneven compression till after it breaks in.

3.5 psi is low and it drops when you goose it? I would definitely consider the full pump as the culprit but before you replace it check the fuel line for restrictions, you could have gunk in the tank plugging up the works. Check this by pulling the fuel line off the pump on the supply side, with a full tank you should get a strong stream not a dribble. If you don't get a strong stream the pull the line at the tank and check again. Remember to keep a bucket around to ketch the gas in. Not only is it expensive now but it's a fire danger.

As for your surging, the way I would test it is to get going at a constant throttle and vacuum reading and when it starts to surge back off on the throttle to increase the vacuum one inch. If the surging goes away until the car stabilizes at the new throttle setting then you’re to lean, if not then open the throttle enough to lower the vacuum by one inch. If this cures you surge temporarily then you’re to rich.

I' leave your idle alone for now it sounds correct.

By the way it looks like you did a nice job on your engine, congrats.

69.5mav

so far replaced the fuel pump, reset the float level to 3/8" below gasket surface (up from 3/4") and advanced the initial timing to 16 btc. tried backing the idle screws out, but it just loaded up at idle, so they're back at 1-3/4 turns. accelerator pump arms are right where you suggested, david.

the fuel pressure is still low, 3.5- 4 psig, and the float level allowed it to go another second when i punch it, but then it bogs down same as before. still surging going down the road.

tonight i'm going to take my fuel lines apart and check for clogs, blow them out, carb, too. i know the filter is clean, i checked pressure without it, and the gage is right at the carb inlet. got some drills, i'll try 69.5 mav's test and if it's lean i'll open up main jets, then replace the power valve. one thing at a time, of course, so i know what happened.

thanks again.....

thinman56

Now that I'v read your latest post it seems to me that your surge and WOT problems could be related to your fuel supply problem.

I'd tackle that first. Be sure to check out the tank as it has its own fuel filter in it.

Others on this board have had some wird blockages in their lines that ran them ragged for a long time. Start at the source (the fuel tank) and make sure flow is strong before moveing on toward the carb. When your back at the tank you will need gravity to force the fuel out so it will be a judgement call but you should see a strong flow.

69.5mav

thanks, man, i read some other posts from guys who looked a LONG TIME to find this problem, i'd be thrilled if it's this simple. but, will also press on with carb tuning to get the most out of it.

cheers

If you have no reason to suspect crap in the lines, I was wondering about your fuel pump. Is it new?

jackfish, yes, replaced the fuel pump. also blew out the fuel lines, no big chunks but the pressure did go up to 4.5 psig. the good news is i also drilled out the jets to 0.055", and that fixed the surging, although it still feels a little 'soft' at cruising speed. it draws 15-16 inHg vacuum at 55 in fourth gear, about 2,300 rpm. i'm going to try 0.059" (my next drill size) and see how that goes. also tried to WOT test, still gives it up at 4,000 rpm, also does it when i approach 4,000 rpm slowly, though. i was thnking about what else might be rev limiting, given that the head is rebuilt with all 1980 parts and valves shouldn't be floating. when i got home, i noticed the choke butterfly was half-closed. would this restrict air flow enough to limit to 4 grand? is it possible the carb (1.14 autolite 2100) is just not big enough?

well, now i gotta get a flight and by the time i return there will be snow on the ground and my mustang will be put away until april. thanks for all the help, i'll have to pick the tuning up in the spring. hope to be ripping the suspension apart over the winter.....

cheers

thinman56":o3u1ojqj said:

would this restrict air flow enough to limit to 4 grand? is it possible the carb (1.14 autolite 2100) is just not big enough?

Click to expand...

Take a look at your vacuum at 4000 under load. If it seems high, then the carb is restricting you. Another possibility is that the exhaust might be restricted, but you upgraded that didn't you?

i had a 80 with the E0 head, all stock (.20 over bore on the block), would just *stop* at 4k even if i had pedal left. if you are still using the log, that could be limiting your incoming air? these guys sound more knoledgable then me, but it's a thought if you are still using the stock log.

Howdy:

The Autolite 1.14 should be more than enough for your engine. The adaptor is a limiting factor on your current set up. Next would be the stock cam. The 1.14 should be able to easily peak at 5 grand, even through the adaptor.

I'm still suspious of the fuel delivery. I know you said that you replaced the fuel pump, but sometimes the eccentric that drives the pump goes flat, offering less pump stroke. IF it is reduced enough it effects engine performance at higher rpms and at higher temps. Works better at start up and/or cooler conditions.

And YES!!! your choke at less than vertical can effect performance.

Try moving the floal up again, to the max. If it helps to some extent, but not completely, consider an electric fuel pump supplement.

Keep posting changes and results. I hate it when I don't get to hear the end of the story.

Adios, David

Off the mainstream of answers but one could suspect ignition also; just one bad ign wire and it could die above 4000 (had just such problem with my SBF). Looking at your pics this is unlikely as to my eye you seem to have goods stuff there but worth double-checking anyway.

Otherwise I don't see why it would not rev to around 5K easily if you drill your jets to 59 (same size that was about optimal for me), and have ign advance like that (total advance @ +4000 even over 40). Stock valve springs will float at around 5K.

thinman56":312d6h66 said:

i don't have the vacuum advance hooked up at all, but it would add 20 degrees at 14 inHg if i did.

Click to expand...

Would hooking up the vacuum adcvance not make a difference?

well, now i'm 9000 miles from my garage and car, and by the time i return there'll likely be snow on the ground and salt on the roads and my mustang won't see the road until april. however, over the winter, i'll check:

fuel system - i like the idea of an electric boost pump, i'll look through old posts for advice. i did not take notice of the vacuum reading at WOT when it stumbled, that would have been a good thing to do, and if it's still acting up when i get it on the road again i'll check that. i suspect the half-open choke plate is at least part of the problem. i'll replace the power valve with a holley 8.5 or so this winter, and some guy on ebay has lots of jets for these, i'll pick up a few and try some combos.

ignition - i hope the ignition is okay, it's all brand new stuff, but i'll review all connections. i see there's a lot of discussion about whether to hook up the vacuum advance when you switch to the DSII, but if i'm not mistaken the concensus is to leave it disconnected and just run the mechanical advance. any further comments on that?

anyway, sorry to make you wait for the end of this story, dave, but i'll definitely post the update next spring. thanks again to everyone for all the feedback.

scott

Howdy Back Scott:

Yup! We just got our first dose of permanent snow. I've got a 500 Holley on the bench that was waiting for a U-joint upgrade, that will likely not happen now until the 8" gets installed. I was really enjoying the cool fall weather, but in Idaho snow is inevitable.

The vacuum advance is not a problem for the performance problems you're having. It will effect economy when you start driving alot. Your Autolite has a ported vacuum source for the DS II. I use the ported vacuum source and recommend it. Even though the price of gas has come down, why waste it?

I wouldn't mess with changing main jets until you solve the fuel delivery problem. Even then, it's unlikely that you'll need to change more than a number of two either direction.

The Autolite 1.14 is rated at 300 CFM. Your stock '67 Autolite 1100 was rated at 150 CFM. If it's right, the 1.14 is more than enough!

Think Spring!!!

Adios, David

well, the spring chores have waned to the point where i broke out the mustang finally. i read through my notes and this post to see where i left off, then went out and tried a few more things. first i took it for a ride and buzzed it up to 4000 rpm uphill, downhill, flat, under acceration and just creeping up easy, and in all cases it starts to sputter and pop at 3800-4000. vacuum goes to zero when this happens. i called MSD to see if they'd ever heard of a unit rev-lmiting for any reason (i just have a 6A, no built-in rev limiting). they said check and see if the voltage drops below 10 volts at that rpm, if so, it'll cut out. they also said make sure it's grounded to the block, which it is. so i wired up my volt meter into the cab, and tubed my fuel pressure gage in as well, and took another ride. voltage stayed strong, 13-14 volts, right through the sputter, and fuel pressure dipped a little, from 4.5 average to maybe 3.5, but it did that gradually and never went to zero. i also removed the choke flap, no change, and i had changed the main jets to 0.057". it runs great through 3700 rpm or so.

my favorite guess today is weak valve springs, i had a valve job done, but the shop was a little shaky and it does 'pop' just a little when it starts to sputter. remember i have the stock cam and 1.65 lift rolloer rockers. what about plug wires? they're all new MSD wires, but some sit right next to each other. how would i provide further insulation to make sure they're not cross-firing? it even occured to me the limit light on my tach might be feeding back to the MSD unit, so i cranked that up out of the way, no impact. oh, and i pulled my adapter out and opened it up some, smoothed out the edges. it's made by the machine shop, not a clifford, it's possible that the shape is bad. i've posted a pic (including a gratuitous background shot of my hand-made bench-top maple cigar holder) in case the shape of the adapter raises any alarms.

a steady 3.5 psig fuel pressure seems like it'd keep the carb full, am i wrong about that? the fact that it sputters at the exact same rpm at all different loads hints to me that fuel delivery is not the problem. thanks again for any further ideas.....