My 1966 Buick Riviera GS has developed a backfiring problem. Under light accelleration, it pops and backfires. Under heavy accelleration (foot to the floor) it runs fine. It sounds like it's backfiring either in the headers or in the motor. I've done the timing and points, I changed the spark plugs and wires, I checked the distributor, I checked the carb to intake manifold gasket for leaks, and I made sure there were no vacuum leaks as well. The engine is pretty much all all original equipment except for the headers. The headers are fairly new, but I don't see how properly installed headers could make the car develop a backfiring problem. I'm thinking it may be carburetor related, but the carb seems to be adjusted fine. Any idea's? Thanks
I had that with my '68 Riviera, couldn't find out what it was, really driving me crazy. In the end I discovered that it was a faulty vacuum return valve in the brake booster ou: So it's worth checking that, it will take you only a few minutes :TU:.
When you install headers , it tends to lean out the fuel mixture,,,, it takes a lot of ''splaining'' , but it does.... you say it does it under light accelleration,,,, so it sounds like the mixture is leaning out and you are getting a lean back fire.... ck. the accellerator pump,,,, like suggested, rebuild the carb.... In any case richen the mixture and see if the back fire disappears.... It is not ignition break down , or it would stumble and back fire on heavy accelleration.... that means the coil, wires,plugs , dist cap and rotor are all ok.... Most likely need to richen the accel pump....
I agree with what others stated, that it could be a lean out condition. The carb could have been set up to run on the lean side and adding headers has now made it a problem. Usually you should go up a jet size or two when you improve the way an engine can breathe i.e. better intake, headers, etc. Try the other suggestions first and if they don't work out, then give it a shot. You can open up the carb and get the jet #'s, probably in the 60 to 70 range. Go two sizes larger. I believe you can get them through edelbrock. Hope that helps.
my car also backfires only upon startup sometimes it my engine will start with a small backfire other time as the engine is cranking before it starts running it will backfire only happen 3 times it has dual exhaust on stock headers engine is stock changed out the plugs and wires...distributor was new when i bought it..it also has electonic ignition dont know if that makes a difference
The kind of ign should not make a difference..... back fire is caused by a leaking valve or lean condition, or cross fire with the dist cap, wires, rotor, ect... usually.....or being out of time... could very well be a bad vac advance or a problem with the vac advance ....... But,,, given the history,,, i would tend to think that it is a lean condition caused by not enough accellerator pump shot or a defective accelerator pump.... ck and see how much ''squirt'' you are getting when you ease the throttle down as in light accelleration.... You are calling it ''back fire'' but you say it sounds like it is in the headders/muffler system.... ''Back fire '' is in the intake manifold,,,,''miss fire'' is after the mixture gets into the cyl and on out the exhaust system.... then there is ''stumble'' and ''bog'' and ''fart and fall''....:laugh: :laugh: :laugh: Any way the easiest thing to do is richen up on the accelerator pump shot and see what that does....
I think I have found the problem. I believe it is a bad accellerator pump. I went to get a carb kit from the local parts stores and they tried to tell me that my motor was a 400. The carb kits they offered me weren't the correct ones either. Anybody have any suggestions of a place to look for a carb rebuild kit or just the accellerator pump? I don't have the carb numbers in my hand at the moment, but it's the carb that came on the car from the factory for 1966 Riv GS's. Thanks alot for everyones help. Especially for helping me track down my problem.
If the carb is gold color and has small front barrells and great big secondaries it is a quadrajet.... if it is alluminum colored and the front barrels and back barrells are about the same it is a carter afb..... Look on the carb sometimes there is a little metal tag that is attached to one of the screws that will help..... Better yet ,,,, find a parts man with white hair at a indipendent auto parts store,,,, he will know something besides just what a counter computer tells him.... and ck out the link given above....
I'm curious... what did they say when you explained to them that the Buick 400 is an entirely different engine design and it wasn't available on any Buick vehicle before 1967?
First, the O'rielly Auto Parts "parts specialist" tried to tell me that I was wrong and that the kit she offers will fit my car because my car should have came with a 400 and that maybe somebody changed out the motor over the years". I tried to tell her that the car has 27k original miles on it and that I know for a fact that it has the 425 installed by Buick from the factory. I had the car outside and offered to show her. She then went on to say that people with cars like this come in all of the time and that she is pretty sure that I have a 400. I said "yeah, keep believing what the computer says", and that's when I walked out of the door. All of the time? There's only three '66-'67 Riviera's that I know of that are local here and I own 1.5 of them. I have a friend who owns a '67. So, unless there's about a hundred other people that keep them secret in their garage........
Don't you love this? Some nitwit behind a counter that has never even changed their own oil before tries to tell us (people who live and breathe this stuff and who build these and MANY others like them and have researched the snot out of them) that we don't know anything about our hobby. Hey! That got the 442 in it? sheesh!!
Welllllll, Let me shed a little light on this situation..... When Buick put the 401 inch engine into the mid size skylark there was a corperate ban on engines of over 400 inches in the smaller cars..... so..... Buick lied about 1 cu. inch..... and in their literature for 1965 and 1966 they called the 401 nailhead a ''400''.... then when the 67 s came out with ''400 inches'' confusion ran rampant.... :Brow: there was even the rumor among the mechanics that Buick had simply designed a new timing gear cover and heads and intake for the old block... Then the aftermarket suppliers give the auto supply stores information that covers 400-425 in. engines and also 400 cu. in. engines and the people at places like advance and the zone only know what the computers tell themo No: ,,, it can get really complicated , and you , a lot of times, have to litterally show them that there is actually 2 very different ''400'' engines..... I simply tell them its the one with the dist in the back..... and they look at the idiot box and it shows them an engine that has the dist in the front....:laugh: This is why I say to find a mom and pop supplier that has some one with white hair behind the counter, that knows something.....:idea2: :laugh:
Yeah,,, Yards, I had a freind that argued me down that my lark had a 405 in it.... I dont think iever convinced the poor guy that it didnt have a olds engine.....
I always have people try to argue with me and tell me that my car is front wheel drive. It's usually in the auto parts stores too and goes very similar to this. Them: Can I help you? Me: Hi, yes can you look up and tell me what size wiper blades are on a '66 Riviera. Them: They chuckle a little and say "thats one of those front wheel drive buick's ain't it!?" Me: "no, it's rear wheel driven." Them: "You sure?, cause the engine sits the right way but the transmission has 2 sideways axles poking out of it."
Ok, I got the numbers off of the carburetor. 7026240 K5-MA According to thecarburetorshop.com, they list it as a car without A/C. My car does have A/C, but the compressor is from a '67 Riviera. Either I have the wrong carb, or someone added A/C to the car? What's the difference between the 2 carbs?
