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Find answers to Frequently Asked Questions for First Generation Firebirds that have been asked on First Generation Firebird-L mailing list. Special thanks needs to be given to all the Firebird-L owners that took the time to respond to other subscribers questions. These pages are continuously updated as new information is posted on the mailing list.
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| Q: | Throttle Problem |
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I recently purchased a 68 Firebird 400. The car seemed to be a dog
compared to the other 68 Firebirds and GTOs I have owned in the past.
After doing all the usual tune up tricks I noticed that my accelerator
pedal only throws the throttle open half way before hitting the carpet! I looked for an adjustment to compensate for the restricted pedal movement or a way to remove the carpet but neither seemed to have an obvious answer. Has anyone else experienced this? | |
| A: | If the carb has ever had really strong spring installed, it very well could have bent the inside linkage. My GTO had this happen. I bent it back and welded on a brace so it wouldn't happen again. Also, didn't the Firebirds 400's have some sort of throttle stop to keep from getting full throttle in order to "lower" the horsepower. That might be when the linkage got bent originally. Someone tried to stomp the pedal to the floor, it hit up against the throttle stop and bent the inside linkage. Just a theory. |
| A: | After a closer look I discovered that the reason my accelerator pedal was only throwing the carb half open was that the mounting bracket for the pedal was cracked in two. |
| Q: | Timing Adjustments |
| I am having a problem setting my timing on my car to the indicated specifications. What do I need to do to fix the knocking on my HO engine? | |
| A: | I've never had that much of a problem with the timing on my 400. But I don't pay that close attention to the timing at idle. For mechanical advance (with the vacuum advance hose to the distributer removed and plugged), I set the timing at 32 degrees BTDC at about 2600 RPM (you'll need some timing tape for this). Once you set the mechanical advance, disconnect the vacuum advance hose at the carburator end and hook up a vacuum gauge to the carb that you can put inside the car. Then go out for a little run and write down the maximum vacuum when running at a constant speed with the engine at 2500, 3000, 3500, and 4000 RPM (make sure the road is somewhat flat). Go back and hook up your timing light again, set the engine speed at about 2600 RPM, connect a vacuum pump to the vacuum advance and pump it up to the your max vacuum reading you read in the car. Your total advance should be 50 degrees at this point (that's what I set mine too, I know people that go higher, but not much). If you have a distributor with adjustable vacuum advance you can adjust it until you get 50 degrees. If your motor is spark knocking you'll have to back off on the timing until it doesn't. But that ussually means there is something else wrong, like your vacuum advance is advancing your timing too much, you're running too lean a fuel mixture at max advance, or you're running to high of a compression ratio for the fuel you're using. I think most people run to high compression for street gas. I don't think you should run more than 9.5:1 on plain old 93 octane. And most people with older cars have compression ratios over 10:1........................................spark knock city.................. If the production timing marks weren't cast right into the timing chain cover, I would have taken them off a long time ago. Timing tape is pretty cheap and alot more accurate. That's my 2 cents worth anyway. |
| Q: | Timing Adjustments 2 |
| A while ago there were a few of you who said that after they set their timing, that a timing light showed it to be WAY advanced, like 20-30 degrees. I think I asked once before but I'll try again. If you're not setting it with a timing light in the first place, what are you setting it with? | |
| A: |
I originally asked this timing question. I set the timing by ear and feel. I
loosen the distributor and advance it until the engine starts to miss, then
back the timing off a little. Then I rev the engine and see to see if it
pings. If it does ping, I retarding the timing a little rev the engine
again. I keep doing this until the pinging is gone or very, very minimal.
All the mechanics I know never use a timing light and use this method. |
| A: | The only problem I have ever had with using that method is that with the timing set to run it's best at 700 or 800 RPM, often it will have too much initial timing to start easily. What I try to do is set the initial by what will start easily (as much as it will take w/out trouble) then adjust the weights and springs to get the total advance I need, and have it start coming in fairly early, like 700 or 800 RPM. It's a lot of trial and error work, but it has always worked well for me. Then once I have it right I check it with a light and write it down so that I can put it back next time I have the distributor out. |
| Q: | Timing Adjustment to fix overheating problems |
| What are the steps in adjusting my timing to fix the overheating problem. | |
| A: |
Here's the deal on timing, back to basics.
First, disconnect and block off your vacuum source to the vacuum advance. Its ONLY purpose is to increase gas milage. Next, if you keep your engine at or below 800 RPM you will have no mechanical advance. So now the only timing is due to INITIAL timing. Let's say you set the spark right at TDC, the flame takes so time to form at "explode" so the force of the explosion happens AFTER TDC, piston is already on its way down, you don't get much power. So you ADVANCE the timing to whatever gives you the best performance, which is usually between 7-12 degrees BTDC. If you have too much timing and the spark happens too far before the piston reaches TDC, then the force is pushing against the direction the piston is moving and you get detonation or knock. This is BAAAAAD. As your engine RPM's increase, the amount of TIME it takes for the engine to turn say 30 degrees is much faster than at idle, but the TIME is take the flame to burst hasn't changed. So the timing is increased further by the MECHANICAL advance. Usually adding up to 20-25 degrees of advance to the INTIAL timing, for a TOTAL timing of 32-38 degrees. Finally, vacuum advance was added for the purpose of further increasing timing at cruise. Most times it is connected to a ported vacuum sorce. This source has NO vacuum at idle, the most slightly off idle and then decreases to zero again at Wide Open Trottle (WOT). When cruising you can add an additional 15 degrees or more of vacuum advance, bringing your timing up to 55-60 degrees BTDC. This is the one to be careful of, too much and you can get detonation. Always stick to the low side to avoid detonation. Remember, it's just for gas milage. One more thing to touch on. Manifold vacuum is maximum AT IDLE. All other times it acts just like Ported. If you hook your vacuum advance to manifold vacuum you will have 8-12 intial plus 15 or so vacuum for 23-27 degrees BTDC of timing AT IDLE. This will affect temp, though I'm not sure which way. I DO know, that most 1st gen birds came with a TEMP activated switch which actually switched the vacuum advance soure depending on the engine temp in order to keep it cool! The was specifically for long periods at idle. Now, lets say your car is set up this way but you SET the timing to 12 degrees WITH the vacuum advance hooked up to manifold vacuum. That vacuum advance can is giving you 15 degrees or more of advance. That would mean your REAL INTIAL timing (without the vacuum advance) would be 3 degrees AFTER TDC, which is way to far retarded. Bottom line, turn off the vacuum advance until you figure out the heating problem. Its ONLY purpose is to improve gas milage. Set the INITIAL timing to 8-14 degrees. See if that helps. |
| Q: | Additional Information in Fuel Section |
| What is the difference between this subsection in the engine section compared to the Fuel section? | |
| A: | They both blend into each other but this subsection is more focused on the engine compartment portion of the fuel system while the Fuel section is focused on the gas tank and delivery system portion. |
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