Hi everyone. I'm new to this forum but I have had my Riviera for 20 years. I am hoping that someone can help me out with this. I drive my car infrequently, but I noticed that it was not accelerating the way it used to. So here's the story. The bottom of the motor has never been touched, it only has 80k miles on it. I had the heads done two years ago because the head gaskets rotted out. I checked over the ignition system only to find initial timing was at 5 degrees btdc. My manual said it should be 12 degrees. I upped the timing only to find that now, over 1200 rpms, it had a miss out of both exhaust pipes. The vacuum advance pulls in only 14 degrees more, the mechanical another 10. According to my book, all was within spec. I took the dist cap off and found the rotor already pointing to the next cylinder. ou: I then took the distributor out, cleaned & oiled it, new points, condenser. I also put in a timing chain in it figuring that to be the problem. After firing it up and checking everything, it seemed to be fine. It definitely had much better acceleration. But after a hundred miles or so, it started to miss again over 1200 rpm. :af: Even tried a different carb, no difference. So my next step is to do a compression check as well as checking the valvetrain. Anyone have any thoughts as to what it could be? Thanks. Darrell
Timing Is your 401 a dual quad motor? I've had both single and dual four barrel and believe that the correct timing for single four barrel is 2 and 1/2 degrees BTDC and 12 degrees for the dual quad. Tom
According to my 63 Service Manual, initial timing for an auto trans engine on premium, initial timing should be 12 degrees BTDC. Maybe it is a misprint? As far as the cam goes, that is a good question and I will pull the valve covers off to see if anything looks abnormal while the engine is running. Is it a common problem with nailheads that they will wear out cams as fast as 80k? Thanks for the feedback.
engine problems O K When I read what you did initially to the engine I did not see ''replaced the dist cap , rotor , wires, and spark plugs''. From the way you describe the way it runs I suspect an electrical problem. [secondary ignition break down] :Brow: When you step down on the accellerator the resistance in the secondary part of the ign. system goes up due to increased compression pressures and resistance in the spark plug wires and spark plugs, usually causing what is described as a high speed miss. This miss will be erratic. :Smarty: Running a compression test will tell you if an engine can be made to run. If the cyls. are at least 90 lb and eaven then the engine can be made to run with a tune up . If not , then no amount of tuning will correct the problem untill the mechanics are corrected. :Smarty: the secondary system is the coil, dist. cap, rotor, ign wires and spark plugs. If the coil is weak it can do the same things. Does the coil have 80k on it??? It is not likely that the cam is bad. If one is rebuilding a engine then replace a cam with 80k on it due to pitting and wear, but not untill you rebuild. You have gotten most of the goody out of the cam but I wouldnt replace it untill the rebuild. :Brow: In the old days to replace the points, condenser, spark plugs, ign. wires, dist. cap and rotor, was called a ''minor tune up''. To do all that and over haul the carb was a ''Major tune up".
The 12deg initial was for 2x4 set-up which came with a different distributor. 2-4 Deg is fine for the stock set-up and avoids overheating. Have you checked dwell on the points? I'm inclined to think of ignition related problems as well.
I appreciate the info. I did replace the points and condensor, but not the rotor, dist cap, wires and plugs. The coil I believe is Ok, it is not the original but not sure how to test it. The dwell is set correctly. I can replace those items to see if it solves that problem. The other issue is an idle that is a little more choppy, especially when I back the timing down to 5 degrees btdc. It does not miss. It has been that way for as long as I have owned it. (I wish it ran as smooth as my vette motor). The vacuum advance does not pull in anything at idle, but does eventually pull in the amount of timing listed on the spec chart. Is that correct?
I found a chiliton's manual and it said to set the timing at 2-3 degrees btdc. So I will adjust that back. It probably has that miss because the initial timing is set at 12 degrees now. So much for the Buick Service Manual! Next I need to find out if the vacuum advance is supposed to pull in any timing at idle. If anyone knows where I can find that out, please tell me. Thanks guys.
vac advance Personally I would hook up the vac advance where it would work all the time. The no vac advance at idle came as a result of emmissions, at the expense of gas milage. the vac advance hooked up to a port just under the primary barrels of the carb will give advance at idle which will cut engine temp and increase gas milage and power. Be sure to ck the vac diaphragm for leaks and the line going to it. I wondered if some one had ,before you got the car, installed a super wild cat cam. Or a vac leak at a line some where. Any where there is a diaphragm is a leak prone area. [heater water, A/Cdiaphram]
Vacuum advance increases advance at idle and when vacuum is high. You should notice a far smoother idle when the vacuum hose is connected. If you don't its possible you have a diaphram problem. Also check to see that internal weights swing free and disrtibutor plate rotates freely. Change the cap and rotor its a cheap fix and avoids the car dying completely.
You said after you changed points it ran better without changing the timing. I would check the voltage of the resister on the firewall (or it could be in the wire itself) going to the distributer. It should have 12 volts coming in and about 7 volts going out to the distributer so that the points don't burn up to soon. I wouldn't think 12 degrees intial timing would cause the miss. My car has a little more than stock cam and was running very rough at idle with low vacuum, part of the problem was the carb gasket that was put on did not cover all of the heat crossover under the carb and was causing a slight vacuum leak. Runs great now and I run 12 degrees intial advance. Just another couple guesses to try. Good luck.
