Hi guys, I'm new to the Olds family, and just picked up a 65 Ninety Eight. It starts fine from a cold start, and idles great and revs fine. Then, after about 10-20 seconds, the idle dips down and chugs and wont rev. It runs fine briefly from a cold start, but always does this afterwards. I also recently put in some new gas, and the old gas had been sitting there for a while. Anyone know where the fuel filter is on this thing? Cant seem to find it. Thanks!

 

Check vacuum operated choke pulloff on the carb. If it doesnt open the choke flap some after a second or two after engine warms you will have the trouble you speak of....also check operation of choke. If you have a 4 jet rochester carb the filter is likely to be in the carb at fuel inlet. Make sure air filter is relatively clean. Make sure carb is not gas starved or flooding.

 

Be careful pulling that filter out. I got mine out and then it just fell apart. Glad it didn't do that inside.

How old's the gas? In a 65, you should be able to sipon it out, You might have to

 

1965 4GC have a sintered brass filter in the carb inlet which may be hard to find. You can probably use the short paper filter the later Chevy QuadraJets use. If you take that fitting apart, be very careful. They're worse about stripping than a QuadraJet. I would personally remove the carb inlet filter and install a metal can filter on the fuel pump suction line.

4GC do not have a separate choke pulloff like a QuadraJet. The vacuum piston that operates the unloader is inside the choke housing and may be stuck. You'll have to disassemble the choke housing to get at it, and if you're not familiar with these old carbs I'd make sure I had a shop manual handy.

You might get away with removing the choke stat cover and spraying some PB Blaster or other strong penetrant in there, then working the piston back and forth in its bore to free it up. Also possible the internal vacuum port is plugged- no vacuum, it can't retract and pull the choke flap open.

 

Wow, thanks for the help guys, i shall try this tomorrow!

 

Ok. The choke works fine, it opens right up. Any other ideas? Bad gas? I've tinkered with the carburetor a bit and all the linkages seems to be moving freely.

 

I always use the soft line, between the tank and the frame. During future PMs, the hose gets changed along with the filter.

Norm

 

Just a thought, If the car has been sitting for a while, you might want to check the exhaust as well. You never know what might have crawled up there and died. Or made a nest. What goes in must come out, and if she cant breath, she wont run.

 

Just saw your earlier post. Sounds like it would most likely be a fuel delivery problem. I don't have anything to offer beyond what has already been posted.

 

Fuel delivery is easy to check. Pull the fuel line off the carb, insert in a safety can, and crank the engine to see if you're getting adequate fuel. I forget the amounts, but you should be able to see the fuel pump pushing gas through the line.
I had a similar problem years ago and did all the obvious stuff before finding that the rubber fuel line from the gas tank to the metal fuel line under the car was deteriorated. The heat of the exhaust made it pliable and the fuel suction pressure caused it to collapse. Replaced this piece and my problem went away. It's worth a shot. Good luck!

 

Thanks for the input! I'll get out to pull the filter and check the lines and pump once this Florida rain stops for the day. You guys are great!!

 

Alright, after taking off the fuel line to the carb(and putting a huge kink in it and having to replace a few feet of tubing) I found the fuel filter to be in good condition but replaced it anyways. The guys at the auto parts store said to check the floats, but can't find them. Do i have to take off the top layer of the carburetor? Should I have a pro do this? I'm pretty mechanically inclined. Thanks

 

Before you dig into the carb, "check the obvious first". Did you check fuel delivery at the carb cranking the engine and watching delivery into a safety can? If that's adequate, then you want to look in the carb. Just be prepared with new carb gaskets (rebuild kit) since you will probably destroy old gaskets when taking off the top of the carb. And yes, that is where you will find the float.

 

To elaborate:

But, in this case, the pump is not a likely suspect.

Non vented cap on a non vented tank? Symptoms should have taken longer than 20 seconds to appear, but the test is easy enough. Loosen, or remove, the cap and start the engine.

Norm

 

How far does the choke plate open immediately after a cold (sits overnight) start? If it doesn't open at least 1/8", the pulloff mechanism may still not be working. I've had a couple cars that required 1/4" or more opening to eliminate the cold stutter.

If it smooths out again after a couple minutes run time when the choke spring has had time to heat up and open the choke, I still think it's the unloader isn't working and the choke plate is staying closed too far or too long.

EZ way to find out is, when it starts stuttering, manually open the choke plate a little at a time and see if it clears up. The point at which engine smooths out is the choke opening the engine wants.

If it were floats, it would be a chronic condition, not just when cold. You shouda asked the parts monkey if he could get you new floats and then watch the look on his face when he tried to look them up.

 

OK, the floats were not stuck, and i did plugs/wires/cap/rotor change and nothing has changed. It still starts fine and idles semi-ok, but still bogs down when i give it gas. One thing I noticed... The choke doesn't seem to ever be closed. It stays wide open, but i will go and double check. Also I will tke off the gas cap like mentioned above and see what happens.

edit-did the gas cap thing and no difference. Any more ideas?

 

Now you tell us, after we've chased rabbits down the wrong trail for nearly a week.

If the choke doesn't close on a cold start, what you have is a LEAN COLD START condition. In other words too much air for a cold engine to run.

Try this. First make sure the choke plate can move. After the car starts, manually close the choke plate down to where it smooths out- probably 1/8" or so open.

Then you need to figure out why the choke doesn't close. Possible the vacuum piston mentioned earlier could be stuck, even more possible the choke thermostat is burned out/wore out or simply adjusted wrong. Or the choke linkage could be gummed up and stuck. Or I have known people to wire the choke open for reasons known only to themselves.

Get a can of choke/carb cleaner and spray everything that moves on the choke linkage. Spray it till it's clean.

Check choke stat setting. A 1965 4GC should be set at "INDEX" position- the slot or arrow on the choke stat cover should be aligned with the center mark on the choke housing.

With cold engine and choke stat set properly, when you set the choke/fast idle to start, the choke should snap closed and you should feel some spring resistance when you try to move the choke plate. If you don't, that tells you the choke stat is bad. Any parts store replacement you find now is going to be a generic, one-size-fits-all part. If you want to try tracking down a NOS Rochester part, here's the part number:

Group 3.750, p/n 7031440, 1965 all 4 barrel carb except 330 engine.

 

I really appreciate your help on this, my wife and I cant wait to take our kids out for our first cruise. OK, set the choke stat, was adjusted off, and sprayed it all off with cleaner and manually closed the choke like you said, and it never changed the engine rpm, just started to die when it was almost closed. However, after a minute I cannot close it again manually, so it opens and stays open fine. It will sit and idle kind of low all day, then when i give it gas after idling for a few minutes it starts to rev up for a second then bogs back down, with an occasional backfire. Hmm

 

Sounds like the choke is functioning now.

I'm thinking this carb may need cleaning and rebuilding. You might be able to set the slow idle speed up just a bit but these cars are designed to idle around 500 RPM.

What you describe now sounds like accelerator pump, or it's possible the distributor advance mechanism is bound up which will cause similar symptoms. Anything is suspect on a 43 year old car.

Did you install new points and set the timing while you were into the tuneup?

 

I didn't do the points or timing while i was in there, but will look into that. The accelerator pump is working fine, i can see that working. I'll check the distributor advance mechanism now. Thanks

 

OK, it was definitely the spark advance. a friend of mine backed it off a bit and brought a timing gun to use and she runs like a champ. Thank you all for you help!