Hello and good afternoon all. I am new member to the V8 Buick website and have a question about my Skylark. I purchased my car approx 5-6 years ago. It is a 1972 Skylark 2 door with a 350 with 36,000 (from odometer, I am sure it is 136,000). It was modified (rebuilt some an limited information) by the prior owner that included a 4 barrel Edelbrock 1405 carb, a cam (not sure what size), T/A Stage 1 intake, MSD ignition & Blaster coil. The question and/or concern I have is that approx 5 months ago, I noticed when I step on it with hard acceleration, it misfires & bogs. Under normal acceleration, it seems ok. While in the garage, I give it full throttle and it sputters with fuel coming up out of the rear 4 barrel. I just changed the plugs, checked vacuum lines, added non ethanol gas and rebuilt the carb thinking that would solve it. Nadda.... The car always ran great prior to this. Any ideas on what to check next? Thank you in advance for any help from anyone.
First thing I would check is the fuel filter that is on the carb, it's cheap just replace it, the second thing I would check is the two fuel lines that are right under the fuel pump at the bottom of the engine, they rot real easily, bend them to see if they are cracked and sucking air. Good luck and welcome to the board, hopefully some of the more knowledgable guys will chip in soon.
Thank you Bogus919 -----New fuel filter installed 3 months ago. New fuel line on top after steel line to fuel filter and to carb. I checked the 2 bottom lines and they feel pretty soft and crappy. I will replace them..........Thank you LARRY70GS-----When I give it throttle while in the garage, I am using the throttle on the carb and am revving it up until it makes the fuel come out of the carb (with air cleaner off) and the bogging sound (blap, blap, blap, blap). That may be at 1,800-2,200 rpm.......... I have tried timing it, but there is no timing tab, only a mark on the balancer. The other owner never installed it after rebuilding. I listen to the sound to hear a smooth idle, kinda all I can do about that at the moment. Timing light hits the line and I have tried advancing it forward or back testing different settings with no change in the bogging at higher rpms......... I am replacing the fuel lines tonight to see if any change. That would make some sense due to the fuel filter empties to half full under acceleration. Only thing is I have a fuel pressure gauge just before the carb that constantly reads 5-7psi even under giving it some.
I have heard different things such as.....Jumped timing on the chain, cam lobes worn (probably only 4,000 miles on cam), lifters or rockers loose and not tight, exhaust valves not closing. Just trying to get some input before ripping it apart and guessing.
If fuel comes out of the carburetor, the fuel level is too high. Bad float, wrong float level, bad needle/seat. Those things cause flooding. The other things you mentioned are much less likely. It sounds like a carburetor problem. I would try another carburetor (can you borrow one?) Also, get a timing tab. They bolt on to the later timing covers. http://www.taperformance.com/proddetail.asp?prod=TA_1341
Bogus919---The lines were crap and had a couple of cracks. Changed both fuel lines out....no difference. LARRY70GS---Carb rebuild a couple weeks ago, no difference in the problem. I don't have another carb for it or to borrow one. That is another suggestion someone else had that it is a fuel issue. Thank you for the website for the tab. This issue happened one day after car sat for 2 weeks several months ago that I actually noticed it. It ran great before and had plenty of power. I have it in a garage so no one messes with it. Just seems strange.
If fuel is coming out of the top of the carburetor, it is flooding. The carburetor isn't controlling the fuel level. The rebuild didn't get that right. Float level, needle/seat, or bad float. Check your sparkplugs for fouling.
LARRY70GS...........Thank you for your help. It is very much appreciated. I will look at the plugs tomorrow. 4am comes too soon to keep messing with it tonight............. I changed the plugs out with new ones before the rebuild on the carb. After the carb rebuild, what would still cause the float or needle valves to do this? Is it at all possible for the vacuum unit on the distributer or anything else that would cause this to happen? Thanks again.
Is it possible that the fuel filter is gummed up and that under heavier throttle the fuel pressure is overcoming the spring pressure in the filter housing.....causing a rush of fuel that is flooding the carb and spilling out of it? I have several ideas of what it could be but the fuel spilling issue is odd. maybe run it without a filter, just for a min, to rule that out.
Put a vacuum gauge on it. Is the needle steady or does it flicker at idle? Does it jump when you see the fuel blowing out of the carb?
Kind of doubt that fuel filter will increase float bowl pressure. Should put a vacuum gauge on it. Those carbs do run lean at higher speeds. Sounds like you need a carb rebuild with jet and rod change to tune for your engine. But it does sound like you might have a possible engine problem.I would check timing chain and valve train(possible bad valve or cam going flat) is what I'm leaning toward.engine oil has changed since roller cams so seeing a flat lobe is very possible. You have to do the diagnosis to confirm. Start with vacuum gauge and pull valve covers and see if any rockers have weak lift.
and check your fuel pressure - 5-6 lbs plenty for the edelbrock . too high ( like 8+ maybe ) could over power the needle/seat and push gas in when not needed .
I would say chances of too much fuel pressure are slim unless the return line is plugged or you have an electric fuel pump.
LARRY70GS-----A friend and I rebuilt the carb. Seemed pretty simple. The floats were adjusted according to specs from Edelbrock. Bogus919-----I replaced the fuel filter before issue, I also tried without a filter. UNDERDOG350---I don't have a vacuum gauge, I will pick one up this week and try that. alec296----Someone had mentioned that it could be the cam. But I was told that it was replaced from the past owner. That was maybe 4,000-5,000 miles ago (he could be full of S!!! about replacing it), don't know for sure. No electric fuel pump and just replaced the 2 fuel lines under the fuel pump and from pump to carb. DEADMANSCURVE----fuel pressure gauge before the carb holds at 5 psi at idle and under throttle. All of these are great input, but this issue was before and after the rebuild on the carb, fuel lines, fuel filter and spark plugs replaced. The fuel that comes out of the rear 2 barrels is like a puff/mist like a spray from a bottle and makes a blap, blap, blap, blap sound under hard acceleration (not under normal and easy takeoff). It doesn't actually spill out. I will take off the valve covers and have a look at the rockers. The cam may be the last resort. I do not want to pull this all apart until I can rule that out. Thanks to all.
A lot of aftermarket cams are going flat due to oils changing for emmisions so since it was replaced don't assume its good. If they did not break in cam right it would be junk about now.if you did not test it don't rule out any part.
The reason I said to check with a vacuum gauge is you will detect a burned valve, broken spring or flat cam that way. Just as Andy suspects. Fuel mist blowing up thru the carb and a rapid popping sound thru the carb that increases with engine speed/load means a valve is not sealed properly.
