Hi guys, I was on here a long time ago trying to get a rebuilt CCC carb on a stock rebuilt 305 to run right. I finally got the dwell set properly w/ the help from you guys. What I was left with, is that the car starts extremely easy cold (choke is set to ~ 3 minutes pull off at 70 F) but heavy part throttle has a huge dead spot until the car is totally warmed up. I still have not been able to figure out how to get rid of the huge dead spot. It's a stock 305! I am swapping a built 327 under the CCC setup to see how it does in the meanwhile before I convert the 3rd gen to a TPI type setup like I did on the 2nd gen, but I am worried that I have not even gotten the CCC dialed in to my liking on an engine with a sub-0.400" lift cam!!!

What would make the time spent after the choke has pulled most of the way off, but before the car has run up to full temp, have such bad part throttle manners? I am getting 30 deg ranging dwell in closed loop and everything seems to be happy. Carb is fresh and pump shot is fine.

 

Have you got all the emissions equipment on it still? Exhaust crossover passages, EFE, Thermac valve, etc.?

 

Have you through of tuning the CCC Q-Jet ecm?

 

No I am not going into the Q jet ecm. I already have the car set up as a CCC car so I am going to keep that induction setup until I have the time to set up another holley stealth ram '165 setup in this car like I have in my other one. I do not like the CCC setup and it is probably going to run horrible when I put the 327 I have w/ 0.503"/0.510" roller cam under it. Maybe it will run well enough to drive. Probably not but we'll see.

Yes the thermac is still installed. There is no heat crossover -- I have the blockoff block installed because I am running a 1987 TPI 305 long block, including 350 TPI manifolds and exhaust. All of the AIR, etc is all totally functional.

This part throttle dead spot happens even in the summer time -- I wouldn't think that with a bone stock 305 and all stock engine management equipment, that just the heat crossover would make that much of a difference in hot weather?

 

Without the exhaust crossover it's normal for it to need a longer choke opening time.

 

These carbs had a little link that blocked the bottom secondaries from opening when the choke was on. I believe it is on the drivers side and is easily removed. Could be your problem.

 

Does the dead spot disappear shortly after the carb goes into full feedback mode, O2 sensor fully warm and ecm begins trimming mixture based on O2 readings? If you're not sure you can drive it with the dwell meter connected and once it starts wavering you'll know it's looking at O2 readings. A scan tool works really well too, I recently got an autoxray myself.

During the period between the CTS hitting setpoint and the O2 sensor getting hot enough to send good signals to the ecm, it will run on it's 'last known good' data for dwell (based on TPS and VAC). I wonder if that's the period of your trouble. Last known good data gathered during a 100 degree drive home with A/C on, morning warm up 55-65. Reaching I know.

I don't think lack of the EFE would cause this much of a problem. What's the setpoint of the EFE TVS? Anyone? It would probably close before your issue disappears anyway-maybe before the choke opens in Summer, although the heated manifold benie may last a while..

Try driving it one morning with the CTS unplugged. Keep the ECM in warm up mode longer. See how it does.

 

Do you have an open element air cleaner on it? If snorkel, do you have the thermovac operating?

 

I can believe that a blocked exhaust crossover would cause the cold engine soggies. It makes a fairly dramtic difference in exactly the period of time you're having problems (even without the EFE valve). The intake heats up very slowly without it- basically just heat conducted into it from the heads. Remember the oil takes a lot longer to come up to temp than the coolant does, which means the oil being splashed on the bottom of the intake isn't helping out for quite a while either.

I've always recommended against blocking it or using an "air-gap" style intake on a daily driver for this reason. You may be feeding it the right amount of fuel, but if that fuel isn't atomizing correctly in the intake (puddling, condensing on the passage walls) it will act lean.

 

The heat crossover on the intake manifold itself is not blocked. It's a stock iron Qjet manifold w/ EGR and all. The only piece of emissions equipment that is missing is the EFE valve. The air cleaner is the STOCK single snorkel w/ the thermac. TI misspoke when I said "no heat crossover", I meant "no EFE". It is not a modified setup. it is a THis totally stock type CCC setup on a stock totally lame 305.

Yes, when it goes closed loop it runs a ton better. The part throttle issue goes away. It's just a warm-up annoyance factor until it does go closed loop. THe car just about dies if you give it much gas at all until it's warmed up.

I am not talking about going onto the secondaries. Heavy part throttle on the primaries, is where the problem occurs. I would never go onto the secondaries on an engine that is not warmed up.

 

Look into the vacuum circuit that operates the EGR valve. In most engines the EGR should not open until the engine is up to operating temperature. Disconnect and plug the vacuum line to the EGR valve at the valve. See if the issue corrects itself with the EGR vacuum hose disconnected.

 

My EGR on the 1983 CCC setup is controlled by the EGR solenoid via computer. You can hear the buzz of the EGR solenoid come on when closed loop kicks in. I will check to see if the solenoid is actually preventing vacuum from reaching the EGR valve when I am open loop and the solenoid is not enegrized. Good idea.

 

Not sure exactly how the '83 is set up, but my '82 EGR system was basically an air leak, allowing air to flow through from the nipple on the back of the carburetor air horn through the normally-open solenoid (which is T'd to the vacuum supply with the EGR valve) when the EGR valve is supposed to be closed; activating the solenoid blocks off that leak and applies vacuum to the EGR valve. On the '86, the solenoid is normally closed; activating it applies vacuum directly to the EGR valve, deactivating it vents the EGR valve. Weird, but the factory apparently did it two different ways.

 

I had a a few different PN solenoids-- hmm. I see the OE # for 83-84 is 1997125 and it should be stamped on the side of the solenoid. I am going to check it as soon as I get home. Watch me have used the wrong solenoid. I am pretty sure it is correct though. Will check.

 

Just unplug the line at the EGR valve itself (temporarily) and see if the problem goes away. If so, you know something in the EGR vacuum control system is whacked. Yes, an EGR valve opening on a cold engine will also cause definite part throttle drivability problems.