'88 Corlla Valve noise?

[excelent3]

I recently purchased an immaculate '88 Corolla with 72k miles on it. 5-speed, carburated.

When starting out at the very beginning of acceleration, I can hear the valves clattering. It only clatters briefly at load in the beginning of acceleration, but not throughout the load range of acceleration like it would if it were pinging. It is not a pinging noise. It is definitely valve noise.

Also, it only makes this noise after it is warmed up, never when it is cold.

I was told that is may be carbon build up on the valves, once the motor is up to temp, the carbon heats up around the valves, which cannot seat properly.

It was recommended that I ad Lucas fuel additive to a full tank of gas, to get rid of the carbon. Still makes the noise.

I then added Sea Foam to the oil, and the gas. Still makes the noise.

I also must say it is very sporadic.....even after is warms up it seems to come and go.

It seems to idle higher than it should, maybe it is just adjusted a bit high.

Timing belt, I do not know if it has been changed as I did not receive any service records, but the car appears to have been very well taken care of, as it is spotless.

I am wondering if the timing may be advanced and would cause this, or maybe the timing belt is stretched?

What would be the proper process of elimination be here? I don't know how to tell if the timing belt has been replaced, etc..

[chronoti]

timing belt wount cause this, i found some stuff called valve medic wich is basicaly a detergant soloution for the oil it worked for me but mine did from when it started till it was off..... have you tried puring the seafoam directly in to the carb when it was running? that does better work for cleaning out the carbon build up. also lucas oil additive and a thicker oil might help.... the previous owners might have changed it with 5w and maybe 10w would be better as it wount thin out as much when it heats up.

for your timing belt i say dont risk it if you have a doubt about the belt it's better to change it

[excelent3]

Good advice. I will go with the heavier oil when I do my next change, and try the direct in the carb treatment also.....

[cobrajet25]

It is a really bad idea to switch to heavier oil in cold weather. I assume it is VERY cold in Wisconsin this time of year, and if you put a heavier oil in your car you will not be doing it any favors. You really want the oil as thin as possible during cold weather so it flows freely on start-up, and if you put heavier oil in you will only be masking the problem, if it even helps at all. Check your ignition timing and run some fuel system cleaner through it, and you may take care of your problem.

Does this only happen under light load (like releasing the clutch to accelerate)? My car does this a little, and I suspect that it not a valve problem but rather the engine is somehow running a little lean when I first step on it. You might check your accelerator pump. This is a pump that shoots a tiny jet of gasoline into the carb throat when you first step on the gas to keep the engine from stumbling and bogging down. If this is malfunctioning, the mixture might be slightly lean when you first accelerate, causing a light ping which could easily be mistaken for valve clatter. This ping would disappear very quickly as the engine revs up. It could also be a small exhaust leak at the manifold, which might produce a similar sound. Regards, Aaron

[excelent3]

Aaron-

You described to a "T" . If I put it in 4 th gear at very low speed, it will produce the same noise......It is noticeable only right after I put it in gear, and step on the gas, never throughout the entire range of acceleration. Is it difficult to check out the acclerator pump? I know how to remove the air cleaner/cover and get the carburator exposed. Their must be some linkage or accelorator cable I can give it gas from under the hood.

EX3

[excelent3]

Aaron-

Remember, I have already run Lucas gas treatment through one tank, and I am on my second tank of fuel with Sea Foam additive, so I'm up to about $15 worth of additives. Are you suggesting I get some type carb cleaner and spray it right in the carb? Will it make that much of a difference? I have been trying to put off having the timing checked, but it may be advanced, as my idle seems a bit high at times....

Comments?

[cobrajet25]

It definitely sounds like a ping you are hearing. Two things usually cause this....a lean air/fuel mixture or incorrect ignition timing. If the accelerator pump is bad it will need to be replaced. I am not entirely sure your car even has one, as my car is fuel injected, but I can't see why it wouldn't have one. All other carbed cars I have seen do. Cleaners won't help if the pump is bad, but they can't hurt either. You can check the pump by removing the air cleaner and looking down the carb throat as you open the throttle. This can be done with the engine running or stopped. You should open the throttle quickly and look for a small jet of fuel coming from a tiny pipe in the throat. If you don't see it, then your pump (if you have one) is probably bad. These pumps usually use a rubber diaphragm, and when this goes bad (and they do after 15 or so years!) then the pump doesn't work at all. This is normally accompanied by a slight stumble on acceleration.

You might also check to see if this car has a vacuum advance on the distributor. A vacuum advance is a diaphragm on the distributor that advances your ignition timing based on the amount of vacuum in your intake manifold. Since the amount of vacuum created by your engine is based largely on how fast the engine is turning, vacuum can be used to advance or retard your timing at higher RPMS. Not sure how much of this makes sense! Anyway, if this is bad or even just sticking, then your timing could be a little off when you step on the gas. I am really shooting in the dark here...perhaps some of you guys with carbed 4A-Fs could give us a brief rundown of what the problem could be here? Regards, Aaron

[fredk]

try just retarding the timing just a little

[excelent3]

Thanks guys, appreciate the input.....I will take this info with me to a mechanic....EX3