Engine Performance problem
1973 Other Buick Models V8 Two Wheel Drive Automatic 175000 miles
I've recently had the carburetor (4 barrel), the distributor, points, and plugs overhauled in my 73 Buick Centurion 455. My problem is that it accelerates fine for easy increases in speed. But it won't go into passing gear. As a matter of fact, if you stomp the gas completely (and suddenly), the car will not respond- it will just cough without power. Why will it respond to easy acceleration with its usual ease, but not hard? I always keep 93 octane gas in the tank since the owner's manual calls for 91 or better. Thank you in advance.
Hi: First, great car! Now I have some questions. Are the secondaries opening on the carb? Also, how did the mechanic set the points? Did he use a feeler gauge or did he set dwell? This is important. If the dwell isn't properly set, it will cause poor performance. Let me know. It's most likely one or the other. If the carb is working correctly and the dwell isn't, timing / spark ill not burn the fuel properly. Check the secondary by opening the throttle all the way, the secondary part or the two large barrels in the rear should open, and squirt some gas in. Do this with the car off of course. If they don't open, the linkage to it needs to be adjusted, do that by bending the little rods that go to the secondary. As for the choke, with the car cold before the first start, open the throttle and release, the choke should now be closed all the way, as the engine warms up, it should open all the way, it will be in the straight up position. To adjust it, the black round brake lite thermostat cover have several screws, usually 3, loosen the screws and adjust to be closed for the first start, just enough so it closes, but not so much too force it closed hard! If it doesn't adjust well or open fully, you might need the bi-metallic spring inside the cover, this is the thermostat. Let me know what you can find.
November, 18, 2008 AT 9:20 AM
Thanks. Yes the secondaries do open manually for me. The mechanic set the points with a dwell meter to 30 degrees (spec is 28 to 32). I don't know what the timing is actually set to, but the spec is 4 degrees BTDC. Side question: if the car is regularly running on 95 to 99 octane (spec gravity 0.710 - 0.700), should the timing be advanced a little to account for the increase, or is the increase small enough not to affect the timing? So, when I squirt a little gasoline into the secondaries, what should that accomplish? Clear the clog if there is one? Do I start the car after squirting gas in? Also, I was under the impression that the only way to get the secondaries to open was to put the car under load (heavy acceleration or something) while moving not sitting still. Does loosening and tightening of the bake lite screws adjust the choke? Also, are there two sets of screws (one for cold choke and one for hot) or do you just adjust for cold and hot takes care of itself?
Thanks again. What about the carburetor? Leaner? Richer? Could my response problem be due to improper balancing of the carb? Since I don't have a dwell meter, how can I check the balance and be sure it is at proper richness/leaness?
Thanks in advance.
November, 18, 2008 AT 9:41 AM
Hi Again: The fuel should be fine. You could try to advance the timing, but if you go too far, it will cause starting and pinging problems for you. I wouldn't go much more than 6 degrees BTDC As far as the dwell, if it's at 30 degrees, that's perfect. The problem must lie with the carb. Are you seeing any black smoke from the ehaust. Do you know what the mechanic set the calibration point for transfer to the carburetors secondary fuel metering system?
November, 20, 2008 AT 7:21 AM
I'm not seeing any black smoke from the exhaust or anything. I just know that when completely warmed to operating temperature, the car won't use the secondaries (it seems). I say this because when you plunge the pedal, nothing happens. Literally. The car loses it's power (the engine does not rev, the car doesn't move any faster, nothing). However, if I take my foot off the gas and slowly depress it (NOT all the way) about 3/4 of the way, the car seems to have a boost. But it's still not like before the carb was rebuilt. (I think I got screwed).
Choke may be good enough as long as its not closed by the vacuum created at the throttle, and yes open the throttle by hand so you can see if the secondaries are opening at full throttle, also the DETENT cable to the transmission is hooked up right?
The other adjustment for a gas starved engine is the mixture screws, basic setting is turn each one(two screws) all the way in gently, then back out 2/12 turns, then use a dwel meter and fine tune them until the highest RPM is reached. Then set you idle speed.
Unfortunately, I don't know what the mechanic set the calibration point for transfer to the secondaries. How do you alter that? Also, how do I properly balance the carb and be sure of proper mixture without a gauge?
November, 20, 2008 AT 9:17 AM
Hi: Based on your description of " when I slowly remove my foot from the gas, it.&Quot; it almost sounds like the fuel pump isn't providing enough fuel. Also, you may want to have the fuel pump volume and pressure checked.
As far as adjustment, I recommend you turn the air fuel screws in all the way, and back them each out 1 1/2 turns. Start there. Listen to the engine until it idles around 1K and is at it's smoothest.
Let me know if this helps.
November, 20, 2008 AT 6:04 PM
Today, I went out and bought a dwell meter just for the sake of ease. I'd like to re-tune. What order should I do the following things in?
Also, I read that using the dwell meter you set the carburetor one side at a time to achieve the highest RPMs. What does that mean? How does the meter know when I switch sides? Do I keep the meter attached to the coil and the ground? Lastly, I was told that if I have to choose, verge on the side of rich rather than lean.
November, 20, 2008 AT 11:09 PM
Hi: I think the person was talking about a tach and dwell meter. What you would be using is the tach, not the dwell. The dwell is for setting the points.
Yes, what they are refering to is correct. As you adjust the screws out (or in), the idle will increase to a point and then begin going the other way. When you hit the peak, stop and move to the other and do the same. This may require to reset your base idle, but that is easy.
Slightly on the rich would be my choice too. Let me know how it works for you.
November, 22, 2008 AT 9:42 AM
According to the instructions of the car, I disconnected and plugged the distributor vac hose. Moved the screws inward (not enough to stall the engine just enough to make it sound really hollow and shaky). Next, I turned them outward (one-at-a-time). However, I didn't get a peak max. The tach leveled out, but after that the RPM didn't decrease even if I turned them out 2 or 3 more full turns, so I put them back to the spot where the max was originally achieved and repeated for the other side. The car seemed to do well on a test drive. But now, do I have any way of knowing if I'm on the lean or rich side? PS The base idle is on target with the car in drive ( 700 RPM).
The secondaries do open when I open the throttle manually. I attempted balancing the carb in the event the mix was too lean. Unfortunately I do not have a dwell meter. I had to do this the 'old-fashioned way'-- by ear. From the sound of the car in motion, I think I have it a little too rich but that can be fixed. I'm still having the same problem with abrupt acceleration (the cough without power). What is DETENT cable to the transmission? How do I make sure it's hooked up right? Would timing cause a problem like this, but allow regular driving without problem? I know from the last time the car was in the shop, the dwell is 30, the range is 28-32 for this car.
November, 23, 2008 AT 3:54 PM
Hi: Check fuel pump pressure and volume, 9psi or so, and 1 pint in 30 seconds, Try adjusting that choke so it's fully open when fully warm. Check for ANY vacuum leaks, the advance in the distributor may not be working. Check for leaks with spray gumout, and spray vac lines and manifold, if the idle changes, you found a leak.
The easiest way to check for mixture concerns is to drive the car for several hundred miles and check the plugs. Lean mixture will show a real clean plug. Too rich will be black. Also, you could have a shop check the exhaust with an emission machine to identify output.
Sorry it took so long to get back to you. I lost a parent on Friday, and ended up in the hospt myself last night (sat.).
November, 23, 2008 AT 4:55 PM
I'm sorry to hear about your bad news. I hope you're up and about again.
About the carb adjustment, any ideas on why mine did not peak and then decrease? It just leveled and stayed there no matter how much farther I turned out the screw. (Again, mine is Rochester 4bbl). I returned the screw to the point where it originally peaked and then started on the other side. It did the same thing. I had the distributor vac hose disconnected and plugged per Chilton Manual instructions. Do you think I still achieved a balanced carb with proper mixture? How would I know if the carb is NOT in proper balance?