First, a story. I have had no end of troubles from my old girl, ever since my top end rebuild. The list...

Stock Vortec Heads
Vortec style intake
New Radiator
Lunati Bracket Master 2 cam (what you all call the RV cam...it's small, .458/.458 max lift...which is about all the springs on the vortecs can handle)
double cam gears w/chain
2.5 inch duals, through sanderson shorty headers, no cat, cherry bomb mufflers (which I HATE)
new summit fuel pump
new water pump
recurved distributor

All in all, I guess it makes pretty good power, considering I spent just under a grand on all of this...BUT, I have had real issues with under hood temps. My spark plug wires were getting cooked by the headers...so I wrapped the headers. Still...due to the wrap, now the heat got CLOSER to the boots...so I bought boot protectors, and the Accell U groove shorty plugs. That was a F A I L. Those are the wrong plugs for the vortec heads...they are too short, meaning, they don't even make it all the way into the chamber...so, I had an EXTERNAL combustion engine, lol. It was running so lean, that my headers would glow RED HOT, after a decent amount of driving.

So, now I have the correct plugs...and decided to make SURE it's not too lean again, buy also dialing the carb over to the richer side. And now it feels like I have lost power. Is there a way to tell if I am running too rich, without ruining spark plugs? It idles fine...even runs fine, no bogging, beyond what it does normally, due to my having T10 4 speed, and 3.08 rear gear. It doesn't smell of excess gas, though to be honest, I might not be smelling it, due to all the other smells this car creates, lol.

Anyway, thanks in advance for any help, guys!

 

unless i missed it, how about what carburetor you have and what changes you have made to it?

 

Hey, that's important, huh? And I actually read over my post, just to make sure I didn't leave anything out, too, lol.


It's a stock Q-Jet. Nothing done to it, other than it was rebuilt about...7 years ago, by a carb guy in SC. Prior to top end rebuild, it worked just fine. Heck, it works fine NOW...it only ever does what I set it to do...it's just a matter of ME setting it properly.

 

What are the new plugs gapped at??

 

if the plug ceramic tip is a light brown there is nothing for you to do. Did you do anything internally to the Quad after the rebuild?

 

I am assuming that you are talking about adjusting the two idle adjustment screws on the front of the Q-jet baseplate. Adjust them to where you get the highest manifold vacuum, and that will get you pretty close.


Keep the shiny side up!
Scott

 

Couldn't tell you the gap off the top of my head, but I did check them. They were gaped correctly out of the box. I'm not asking about ignition, or spark. I'm wondering if there is way to tell if you are running too rich, WITHOUT ruining a set of spark plugs, ie, a way to tell BEFORE, know what I mean? Dumb question, but how would I check vacuum? My brakes felt fine while driving...and last, can running too rich hurt hp?

 

Oh...and what I adjusted was a black dial on the passenger side of carb...to the left, towards rich.

 

You adjusted the choke. You'll also want to adjust the air/fuel mixture screws located on the front of the carb; there are two, one for each side of the carb. Buy a vacuum gage from Harbor Feight or any auto parts store and connect to vacuum system, then adjust the two screws until you get highest vacuum reading. I would screw them all the way in (clockwise) and be sure to count the turns so you know how to get back to where you were (just in case) then back out 3 turns as a starting point. Adjust both sides equally until you get best measurement. I'd recommend emailing Lars and get his paper on how to tune the Q-Jet. It will cover adjusting choke and air/fuel mix screws.

After I did my top-end rebuild, I rebuilt the carb following Cliff Ruggle's book. Cliff is very knowlegdeable too and can answer many of your questions. He has a forum on his web site that is very useful for recommendations and troubleshoting questions.

 

No the only reason I asked, was if the gap was way off, you would have loss of some power. And that's what you said it felt like. Wasn't trying to be a smartypants or anything.

 

If you post up your carb number I can give you a setup and jetting recommendation for it. Adjusting the choke (as you did) will have no effect on how lean or rich the carb runs once it's warmed up, although if you adjusted it excessively towards the "rich" side, you may have set your choke tight enough that it will never fully open, causing your power loss (since you just locked out your secondaries by doing so).

However, it sounds like you're running retarded timing - not a lean carb. Retarded timing will make the headers glow red at idle and light throttle. A lean carb will not make it that hot, since there is not enough energy being produced at no-load idle to make the idle mixture cause red-glowing headers. Make sure you have at least 18 degrees initial timing, a correctly hooked up vacuum advance, and 36 degrees total timing. I'll bet that will solve your problem.

...and, no... unless you have a wideband Ox sensor, you cannot tell how rich or lean you are running. I can give you a fair idea based on your carb number and what jetting/rod combo you have along with APT height setting.

Lars

 

My next day off is sometime next week...I'll see what I can do about timing then, and get a carb number for you, Lars. The headers have not gotten that hot again since I changed out the spark plugs.

 

Can you give me some advice? You seem to be very knowledgable on Quadrajets. My 1979 L-48 has a Carter 17059216 (Rochester) Carb.
It has a low speed stumble below aprox 45 mph when full power is instantly applied. I have replaced the dist. cap, rotor, coil, plugs with Autolight 26 gapped at .045. Plug wires are Accel premium in exc. cond.
I just replaced the accelerator pump (it was bad) and float / needle and seat. Float set to 15/32 as per instructions. The old float looked good but since it was apart I changed it. The idle seems to have improved 100% but it still stumbles with full or near full acceleration from low speed 10/40 mph. If you lift the peddle it will take off like the acc. pump is bad but I just changed it. Just took it on a trip yesterday and got 15.8 mpg. as good as ever. Any ideas what to look for (timing, vacc advance, vacc leak, etc.) I can't find any bad hoses.

 

Mine does the same, actually...and from what I understand, it has to do with the vaccuum. When you go WOT, you loose vac, so the carb jets a shot of fuel to comp, until it can respond with a steady flow of fuel. Or something like that, lol...

 

First, make sure you are running initial timing in the 12-18 degree range with 36 total.

Check the jetting and setup on your carb. The stock jet/rod combo should be 72/40/CH. This should run fine in a stock '79 engine, but it will be lean if you have headers or an aftermarket true dual exhaust system. If you have these mods, you should bump the jetting up 2 sizes.

Raise your float level. You should be no lower than .420", and you can go as high as .375". You're currently at .470", which can induce a lean stumble.

Check your APT height. Make sure your power piston is high enough so that the inner brass sleeve is about .020" above the inner raised lip of the plastic retaining collar when the piston is in the full down (lean) position.

Lastly, and most important to your symptoms, is to make sure your secondary airvalve spring windup is set at 3/4 turn. If it's any looser, it will cause the "fall-on-'yo-face" symptom you're having. Also, make sure you have the correct secondary rods as spec'ed above and that they haven't been swapped out with something "creative."

Lars

 

Now I've got something to look for. Thanks. The timing is on and as you said the float is set at .470. Yes I am running full duals from 72 Vette. (SS) The plugs I pulled after 15,000 mi. looked perfect except maybe a little too white. The air valve spring will be the first thing I will check. TKS. Bob

 

OK, so I finally had time to work on it some, this past weekend. Lars, the carb is a rochest 4mc quad, stock from an early model 76. I tightened the air/fuel screw and secondary screw all the way to the right, and then opened them up, one turn at a time, till it sounded about right. I don't have a vacuum gauge, or a timing light...that will be another day, to really nail it down proper. Anyway, it ended up being 5 1/2 turns on the driver side, and 5 turns on the passenger side screws.

I then advanced the timing a little bit...but here is where I seem to maybe be missing something. Total timing, as in, 36 degrees total timing, that would have to do with turning the distributor, correct? As it sat, the idle sounded lopey, which is what I thought it SHOULD sound like, with a cam. I advanced the timing, turning the distributor counter clockwise to about...10 o'clock, from where it previously was, and the idle picked up, to the point it no longer sounded lopy, but more like a normal, non cammed car. It no longer sounds like horses galloping. I revved it at the carb a bit, and listened for pings, and heard none.

Now, when I get the proper tools to do this non idiotically, with the vac gauge, I would plug that where? Anywhere with vacuum? And adjust the air fuel screws to idle fast, but with as much vacuum as possible? And with the timing light, I have never even held one...how do I set what you call initial timing, etc?

Forgive me if this is a really dumb post...mechanics, I'm pretty good at...this stuff? All very new to me.

 

So neither auto zone, nor advance auto rent out timing lights, OR vacuum gauges. Cheapest timing light I found was 100 bucks, and vacuum gauge was 40. At that cost, I may as well PAY someone to do this...

 

Shameless bump...

 

This is like your 5th post where you're "messing" with timing instead of just getting it done right. You spent how much on the top, and don't want to spend $100 on a decent timing light?

An advance light is always the best buy, but if you have to go cheap: $35.

http://www.summitracing.com/parts/EQU-3551/

Vacuum gauge: $13

http://www.summitracing.com/parts/WMR-W80594/

If you're going to keep and tune a C3 - you must have the tools and develop the skills to maintain it.