Yet another post about Carb Issues

[tufmustang]

So I drilled through a good chunk of the posts (through page 66) and haven't found anything similar to the issues I'm having, though there do seem to be quite a few issues getting carbs to behave.

'67 Coupe w/ automatic transmission and power brakes (ABS Conversions of Orange County)

200ci Engine rebuilt following the CI specs for a "moderate performance street motor" recommendations:

CI-provided polished and ported late-model modified large log head
Deck not zero'd, but shaved to achieve ~9.0 CR
Cylinders cleaned and bored to .040 over
Double-roller timing chain w/ timing advanced per CI recommendations
CI 264/264 CAM w/ 110 lobe
CI DUI Ignition
CI single exhaust headers
CI Weber 32/36 carb, direct mount

Took it to a dyno guy who races (v8's but knows i6's) who rejetted and adjusted, timed, etc. That got it to run (prior to his work it would barely run and 2 experienced mechanics couldn't tune it well - good on the frwy, bad on the street; bad on the frwy, good on the street). Tech said vacuum is good and timing is set properly. Fuel/Air mixture was also supposedly good. About 500 miles after it was tuned on the dyno (1000 miles after the rebuild) the crank went bad. The machines shop says it was way rich and the oil broke down due to gas contaminating it. There has not been a single person who agrees with them. Regardless I had to have it torn down again and replaced the crank.

It's running okay and I followed procedures to adjust the screws on the carb (did that myself). However my experience is as follows:

1.) Idles okay (not great, but not stalling) so not really an issue. I think it should be smoother
2.) Power is not great - a little better than stock, but not what I expected or should be based on what I've read.
3.) Getting 10-12 mpg - I get better mileage on my Chevy 283 v8 w/a Holley 4-barrel (been getting this since the rebuild, both of them)
4.) Adjustment screws (idle and mixture) say I'm running rich - screwed in 3.5-4 vs 1.5-2
5.) Plugs say I'm running lean - white and clean

I can take it back to the dyno tech and have him work on it some more, but I wanted to get opinions first from the experts.

Thoughts on why the gas mileage is so bad?
Why don't I have the power I should?
How do I get this to run the way described?

I'm in the Los Angeles area if you know any contacts who can work on it.

Thanks

 

[MPGmustang]

many people get idle air fuel mixed up with driving air fuel,
The Idle screws only affect how rich/lean the idle is, you have to swap the jets in the carb to get the right air fuel while driving.
the 264/264 110 cam is boarderline wild in a 200ci, I'm running the same but with 274 exhaust, it is rough, the power band does not start until 1800rpm, as you are running a c4, have you changed your torque converter to a looser one?? A stock converter will affect this cam against it's potential. I think this cam can use more air than you're giving it, a weber 32/36 is small, about 240cfm, your engine combo can easily take 280-310cfm.

and one last thing... the DUI, from DUI it's not too great, it has full ignition advance at 3000 rpm, yes that's great, but 90% of that ignition is in @ 2000rpm, and that's bad. what you need IIRC is mr gasket 929 kit, get the silver springs on those DUI weights (you don't need to change weights), then bump timing up to 16-19* static, take a washer to your screw holding the vacuum canister and limit how far back it can come, this will get you right in the perfect ball park. I did this with my holley 350cfm and my DUI with 264/274 220* cam, and it made a huge difference. the vacuum canister from DUI IMO is crap, I got a replacement one from autozone that goes to a late 70's chevy truck with the largest engine I could find... I forget what it was as my cousin knows better than me on that.

that should steer you in the right direction, I would first tune that ignition, and if it doesn't help enough then go with the torque converter, when checking the plugs, make sure to do it on "the side of a highway", meaning after you full throttle for a good 10+ sec's under load, turn the car off and coast to a stop on the side, remove #3 - inspect - replace, then remove # 6 inspect and replace, that should give you a WAY better reading of what your engine does on load, and that's the best time to 'read plugs' most do it as a drag strip.

 

[CoupeBoy]

With the CI DUI, where are you pulling your vacuum? It must be from the head/intake somewhere.

That MPG does suck, I get about 30% better with my 289/C4/Edelbrock 600CFM @75+mph. (no ticket means I was never speeding)

Some of this is going to come down to the amount of changes that you did at one time. Not everybody can afford to go 'whole hog' as you did so the changes are more incremental and easier to diagnose when one thing goes wrong. Plus driveabilty issues are hard to do in person and difficult over the internet..

Did you degree the cam when it was installed?
What sort of vacuum (inches/hg) are you pulling at various RPM?
Do you have any other parts that you can try swapping in? (A common practice when working on computers. Pull a good working part from another system and swap it in.)
Were you able to verify that both vacuum and mechanical are working properly in the distributor?
What is your base timing?
Any chance you have a fuel leak somewhere? (like the fuel pump into the oil pan?)
May as well check the fuel pressure at the same time
Do you have a fuel pressure regulator? I have read on here that the 32/36's are very sensitive and need lower pressure.

I may not be the one to help, but I know for certain that these questions will come up.
-ron

 

[thesameguy]

I need to disclaim that I completely suck at carbs. Everything I know I learned here only recently. Oh, and reading the first chapter of a q-jet book. Carbs are black magic as far as I'm concerned. My only advice would be:

Since you have a fair amount of money in the engine, I would consider picking up an LC1 and take it back to the dyno guy for a couple pulls. He should be able to hook that up to his datalogger and give you a printout. That will tell you if/where you are running rich/lean, and perhaps give you a direction on where to turn your attention. I cheaped out and got a narrowband, but it *really* helped me quantify where/what my problems were on my bone-stock 200.

That said, my problem turned out to be my carb. It was fully, professionally rebuilt but NEVER worked right. It was either super lean or super rich on throttle and always super rich at idle. I suspect someone "fixed" it at some point and it was never right again. I swapped out carbs and wrecked plugs, and miraculously things fell into place pretty quickly. Without the A:F, I probably would have been chasing non-problems forever.

Also, can your dyno guy watch your ignition? What changes caused it to switch from good highway/bad street to bad highway/good street?

 

[CobraSix]

Okay, of the modifications you did, honestly one 2 will yield any real power results. The cam and the headers. Port and polish on these engines only yield a very small improvement, if any. Same for the carb. You are still sucking through the log head straw. I don't have direct experience with the DUI as I went with the DS2/MSD system that was cheaper and just as effective. You may want to consider sending FalconSedanDelivery a message about recurving it. He can work magic with a dizzy that you will never think is possible.

That being said, the cam alone should have offered a much improved feel. I was running a 260 cam and it had nice pull, and 25 MPG with an autolite 1100 with a T5 transmission.

One thing you never mention is what your timing is set at. 4*, 10*, 20*? Getting your idle right is part science, part art, and knowing when it's carb and when it's timing. I've had a carb so poorly tuned that it made it act like a timing issue. Went round and round until I swapped carbs with a rebuilt one and it cleared up. And I've had it the other way where my timing was so far out that it was messing with timing significantly.

So, we need some readings, and not just "the guy said it was good".

1) Initial Timing? I'd recommend 10* BTDC. it will eek out more mileage
2) Vacuum at Idle? Not sure about the 264 cam, but you should still be around 14-16 inHg at 750 RPM.
3) Plug gap? With the DUI, I'd suggest you could probably open them up to .045 and .055. That will improve power and efficiency.
4) What is your idle RPM set at? I believe with an auto, should be 800?

If your idle mix is that far out to get a smooth idle, my guess is your timing is too far advanced. start at 1.5 out from closed. If you can't get there without the car stalling, check the timing. See what it's at and what your idle RPM is at. if your timing is above 15*, then retard it until you get to around 12*. Then close the idle screw some more until it just barely runs and then open it a little more. Recheck timing, adjust to 10-12* BTDC.

Another thing to check. Is the dizzy #1 aligned correctly. Check your TDC on the #1 cylinder and check where the rotor is pointing. Make sure it's dead on the #1 wire. If it is, then you are set at 0* timing. Then advance it 10* and start from there. If you are off a tooth, it can make getting everything else set near impossible and it will make it seem like an endless loop. One tooth isn't enough to keep the car from running, but it's enough to make the timing issues look good but will actually be causing problems that look like other things (carb not responding, etc).

Small changes each step. half turns, quart turns, 2* at a time etc.

No reason, even with a C4 you should be able to get 20 MPG average.

 

[chad]

All good suggestions by some knowledgeable folk.
I like:
"...the oil broke down due to gas contaminating it..."
"...Any chance you have a fuel leak somewhere? (like the fuel pump into the oil pan?)..."

Good Luck, keep us informed after utilizing what U can...

 

[Flade99]

Sure sounds like a vacuum leak. That would cause the lean plugs, and the need for excessive idle screw setting to keep it running.