Hesitation, sputtering, and backfires oh my!

[Illswyn]

I have a '74 Century with the 350-2. I got it this weekend, and until today, it was running good getting up to highway speed.

Under normal acceleration, it ran fine. But try to accelerate quickly, and it sputtered and chugged. So I figured, I'll spray down the carb, run some cleaner, see how it does. I'm very tame when I drive.

But today, it gave Krystal (my fiancee) problems driving. It ran fine in the morning, fine in the afternoon, but then it started having problems.

At idle, it'll rev up just fine. But put it in gear, and the idle lowers, and giving it much more than minimal gas causes sputtering. And that is all it does is sputter, doesn't speed up even. Give it more, and it wants to stall, and backfires. Once was enough to say "It's off the road till that's fixed."

EDIT: The following was in the original message, but was inaccurate.
[Above 40, it runs fine. She said also that it runs good when it's going around a corner. All this together tells me it is probably carburetor related, although whether it is fuel or air I don't know yet.]

I'm not sure how much of that is relavent, but any help is appreciated. I'm still learning carburetors, not that I ever learned much about injection systems. I have got to find a decent manual soon.

I'm not sure if someone got my vacuum hoses mixed around, or what it is. The plug wires are ZIP TIED together. I'll be stealing wire holders from my other car to straighten that out. I was running 87 octane, I put in 15 gallons of 93 to top it off though tonight.

[GStage1]

Sounds like you need a carb rebuild. I bet your carb is original and never been touched since new.

[Special57]

I agree. I had the same problem till I rebuilt the carb. on my 350. Now it runs great.

[Illswyn]

Someone suggested the fuel filter. But my concern is that it revs up fine in neutral/park, but when it's put in gear, it seems to only want to idle.

I'll be looking for the transmission fluid dipstick tonight I guess. With it running ok above 40, I have to wonder if it's stuck in 3rd if that's possible.

[GSXMEN]

At first I was thinking fuel filter too.....then you mentioned it running fine above 40mph. A plugged filter pretty much acts like an rpm limiter. I would still change the filter anyways - cheap insurance. Personally, I prefer a good sized, quality inline filter - and take out that little filter at the end of the fuel line (in the carb).

I would agree with the above suggestions.....sounds like time for a carb rebuild. Make sure you take a strand of wire or use compressed air to blow out all the tiny passageways. The 2 barrel carbs are quite easy to go thru....very few parts, compared to a Q-jet.

Might be a good time to check some of the obvious things......vacuum line condition, spark plugs & wires, cap/rotor, etc. You might also want to have the condition of the distributor checked. Make sure the vacuum advance is working, parts aren't worn/broken, etc.

[Illswyn]

I cut off the twist ties holding the wires, put in some wire holders, and then, lost the keys into the defrost vent.

After retrieving them today, I drove the car, and in fact, above 40mph it is doing the same thing. Won't take more gas, just cuts out and stumbles. I guess before I thought it did ok, because it accelerated quicker, so I didn't notice.

[Illswyn]

Well I did the wires, plugs, cap, rotor, and the fuel filter.

It was running great, drove it to the store for a vacuum line. Got on the main road, and it drove good. There was a slight stumble, but after that, it accelerated good!

Then sitting at a light, I felt it shake a little, and the idle didn't sound right. Took off from the light, and it was like before- bogging with anything more than minimal gas pressure, felt like it was going to stall. Traffic started going around me, not being able to get over 20mph without bogging.

It seems to me like it's flooding? Like sitting at that light let the fuel accumulate too much, then when it's time to go, it lets too much gas in, making it bog? Does that sound reasonable?

I still have the carb spray and Sea Foam to go yet. I'm guessing a float is sticking or something. Maybe the float level, but I've read elsewhere not to mess with float levels except as a last resort. Being that I don't know where to begin to look for a float, I think I'm safe there.

[GStage1]

From your description now after the work you have done, sounds like your float is sinking causing gas to overflow the float bowl and seep into the carb.

[Illswyn]

Ok, so the float is sinking. What could cause that?

Basically if it comes down to a rebuild, I'll have to take it to someone. If it's something I can do with it on the car, then I might make the attempt.

[LARRY70GS]

Doug,
I think you are running lean. I don't believe you are flooding out. It is one of two things. Either the float is sticking, and not allowing enough fuel into the carb, or your fuel pump is going away. Next time the motor starts acting up, take the air cleaner off, and look down the throat of the carb. If it is flooding you will see raw gas pouring into the throat. This usually stalls the motor(that's why I think you have the opposite problem). Next take a wrench, and tap the fuel bowl. This sometimes temporarily frees up a stuck float/needle-seat. A fuel pump that is going bad will also give the same symptoms. Fuel pumps are cheap and easy to put in. If the pump is old, replace it, it's good preventative maintenance. Good luck.

[Illswyn]

Right now the only time it's acting up is in gear. It idles and revs in neutral or park just fine. And currently, it only does it after sitting in gear without moving for a good length of time, like a stoplight, or waiting to turn for a long time. If it starts choking I have been able to back off on the gas, accelerate slowly, and eventually it isn't noticable, I can accelerate again.

I know lean is bad, so maybe I'll try tapping the bowl before driving, and see if it does it still.

The bowl is the plastic part, under where the fuel filter is?

[LARRY70GS]

Frequently, a motor will rev in neutral and park just fine, and stumble under load, when the fuel level is low.

[Illswyn]

Fuel pump is only $20-30, guess I'll take a stab at changing it out.

The pump is in the engine bay, just follow the fuel line down to it, correct?

[LARRY70GS]

Yes,
Drivers side front of engine. 2 mounting bolts, and fuel line connection. When bolting it back up, you may need to rotate the engine if the new pump doesn't fit flush.

[Illswyn]

Ok, think I found the pump.

Also noticed an open hose- coming off of the charcoal canister (?) the big black cylinder at the front driver's side. It has 2 hoses coming out of it, one labeled "Tank" the other labeled "Carb". The one labeled "Carb" was hanging down in the engine bay. Where's that hose connect on the carb?

[LARRY70GS]

It probably goes in the end of the air cleaner snorkel. Take a look at the snorkel. Is there a hole at the bottom , on the very end?? Wish your problem was that simple.

[Illswyn]

Yes there is, and it just reaches that spot too. I wasn't sure, but thought it might go there. But it said Carb on it, so I figured maybe it goes to a connection on the carburetor.

I'll hook it up there, makes sense. (vapor from the gas tank goes to the can, and recycles into the intake) That's just extra, I'm sure that's not THE problem.

I hooked the other connection under the air cleaner to the vacuum source at hte front of the manifold. There were several things connected there, and one of the connections had a cap on it (cracked too) so I connected it where that cap was.

I did get the fuel pump changed today. To give you an idea of my ability, it took me from about noon till 3, then from 6 till 8, to get the old one out and the new one in. 5 hours to do a fuel pump. I'd bet a shop would have had it done in 30 minutes. But it only cost $20, and I got the experience of doing it myself. There's some satisfaction in that.

It's doing the same thing as before though. Push the gas slowly, and it goes ok. But there's a spot soon after where it cuts the engine out, it basically stalls, till you let up on the gas. Push it a little more past that spot, and it sputters.

I'm thinking now maybe since most everything else that's been mentioned has been replaced, maybe the timing is off. I don't have a light, so maybe for what it's worth, I might be better off checking if the local shop will set the timing for a fair price.

When the engine is cold, I didn't notice the choke plate being down, to block air flow. It doesn't move that I can tell.

One last thing I can think of that isn't connected, I think it's the heat riser. What connects under the air snorkel, down to the connection on the block. As I understand it pulls warm air in to speed up warming up the engine.

[Illswyn]

I took it to the shop around the corner from my house.

They drove it, adjusted the timing, points, and dwell, and it now runs much better. Only a slight hesitation where before there was a good 4-5 second pause.

They said the next step is a new carburetor. Mine has the choke tied off (figured it wasn't right) and I'm guessing could use a rebuild or replacement. But for the time being, it should be plenty good enough.

All for less than $30. Better than me buying a timing light, trying to figure it out, and then there's the whole points/dwell thing, which I know nothing about at this time.

I dropped it off yesterday around 4pm, it was out waiting to be picked up when I stopped in at 9am. I told him I was stopping in just to make sure they knew it wasn't a Chevy 350, because I'd heard of a lot of shops not making the connection. But he was aware of the difference. (:

[Marco]

$30?

Can't beat that with a stick :TU:

[Illswyn]

I was pleased that they were realistic in not expecting me to want to rebuild/replace the carburetor, suggesting I drive it first. I think they knew if I drove it, I'd be out the door for only $30.

[nailheadina67]

Sounds like a carbon tracked distributor cap to me.......:Smarty:

[Illswyn]

Maybe so, but it did it still when I changed the distributor cap and rotor.

[nailheadina67]

It could also be a carbon track on your coil tower.........I've seen that before. Also loose distributor shaft bushings can cause backfiring. :bglasses:

[EEE]

I'm having a very similar problem since a few days back. The car runs fine, but under load it bogs and hesitates. When it's in park it runs fine while idling and at higher rpm's. I'll go through this post to see if I can do anything about it. It isn't bad, I can drive it, but if I floor it, it starts to act up. I'll go out and have a look at it now. Back later.

[eleetlark]

HI all! my first post! have been reading this forum for months and have finally got my new(used) 350/350t 72 skylark WEWT!

Ive driven it alot in the last 2 weeks (ALL GOOD) and yesterday, finally found an open road & ran it upto 90mph and tested the new brakes ((drum :( )) and shocks...since speeding it yeterday, my carb has been bogging at launch ( seems like its lean in that i dont smell gas and it lights right back up....)...

I can always just coax the peddle and get the rpms up and "power through the bog" but it seems inapropriate to bark my tires at EVERy red light* ... (notice the happiness in my typing from thoughts of a V8)

-should i spray it down with cleaner? (im a NewB so dont laff)
-I dont want to tear it down.. ill prolly change plugs/fuel filter/air filter/dist cap/ adjust timing with a friend before even considering playing with my carb ....

Any help is appreciated....thanks in advance..& also please use somewhat common terms inthat im real green but wanto learn... thnx again

-leetlark

[eleetlark]

Another thing....Im in the tacoma/seattle Wa area 98465 & would love it if anyone had the time / inclination to sow me how to rebuild my carb - \
thanks again- eleetlark

[doc]

Guys there is one possibility that no one has mentioned. The old original type ign. coil will go bad and run fine untill the engine heat gets it good and hot then it will begin to break down and misfire. It will get progressively worse untill it finally goes out, then you will find it for shure. Other than that I would check the vacume advance and make shure it was not leaking down and clean and lube the mechanical advance to make it work correctly. :Brow:

[PolishBuickGuy]

It seems that we have 2-3 people with this problem, including me. I have the bogging at slow acceleration, and bad bogging, like almost about to stall if I want to accerate quicly (ex. 20-50mph). I just rebuilt the carb.

The carb was from a 455, but its on a SP350, I was told to set the float level according to the 455 setting, thats what I did, was I suppose to set it according to 350 setting?

Thanks
Slawek

[doc]

Well, I typed for an hour and then hit the wrong blasted key and lost all of it. I will return later and do it again. :af: :af: :af: :af: :af:

[PolishBuickGuy]

the secondary air valve spring [the one that controls the flapper valve above the rear butterflies on a qjet] is TOO LOOSE. I usually tighten this adjustment to make the valve open a little later when the rpm s are up to prevent bog.

Is that the bolt that adjusts it?

[doc]

O K Slawek, in the pic You sent the screw with the allen head on it that comes in from toward the bottom of the carb is the screw that holds the spring tension locked in place. The spring tension screw comes IN FROM THE SIDE of the carb. Loosen the allen screw first and turn the side tension screw to the right untill you reach the desired tension,then lock the side tension screw in place by tightening the allen screw. :laugh: :3gears:

[71GS455]

O K Slawek, in the pic You sent the screw with the allen head on it that comes in from toward the bottom of the carb is the screw that holds the spring tension locked in place. The spring tension screw comes IN FROM THE SIDE of the carb. Loosen the allen screw first and turn the side tension screw to the right untill you reach the desired tension,then lock the side tension screw in place by tightening the allen screw. :laugh: :3gears:

One addition to this. Have a screwdriver in the side, spring tension screw, as you loosen the allen screw. Otherwise it will spin itself back once the pressure is relieved.

Try tightening in 1/4 turn increments. If you get rid of the bog, then back off an 1/8th of a turn and see if it bogs again. If not, that's a good place to lock it in.

[71GS455]

Regarding the hesitations, that sounds very similar to what happened to me when my coil went out in my 71 GS455. I managed to limp it home. After trying a few things, I put in my 30 yr old coil (was running a Petronix setup in those days) and it ran just fine. I eventually threw out the Pertronix and went back to points in it.

[71GS455]

Doug,

Where are you located? I've got a 2bbl carb you could try out if you'd like, but I'm in WA.

[PolishBuickGuy]

Thanks for replies, since mine bogs only when i get to the secondaries, ( not even under full throttle) it seems to me that it is to tight and wont open, am I correct?

Slawek

[PolishBuickGuy]

Ok, I did the secondary spring adjusting. Didn't help. The car still sputters, grr. Sometimes it dies, sometimes it recovers.

When I accelrate hard I can hear the valves knock, could this mean that my timing advance was not working, I wish someone that knows Buicks could just see this.

What should the timing be set at? (degree's?)
Thanks
Slawek

[doc]

O K Lets go to the next possibility, You may be getting secondary ign. breakdown. This occurs when the eng. is loaded. make shure the rotor , dist. cap and wires are in good condition, no cracks in the cap or rotor and no carbon tracks.
check each tower in the dist cap for corrosion. and check each wire for broken or burned places. dont forget the coil and coil wire . set the ign timing WITH THE VAC ADVANCE DISCONNECTED, I think at or about 0 deg. on that eng. and after tightening the dist hold down then reconnect the vac advance. While you have the vac advance line in hand suck it down and hold it with your tongue to see if it leaks and wont hold vacume. if it leaks down replace it.
Check the spark plugs, eaven if you recently replaced them, all plugs are not created equal. Personally I would go with Motorcraft gapped to about .035.
Finally try switching ign coils with some one who has a known good coil and see how the car runs. :blast:

[PolishBuickGuy]

Ok, Today I replaced the cap, rotor, wires, and plugs, still sputters. Changed the coil (with a different one,not new), did'nt help. Then, I went to the gas station and filled up my almost empty tank with a full tank of 89 octane gas. Still sputters. What could be the next possibility? Could the Timing still be off? When I have the timing light flashing at the degree marks, What should the nick be at?

I haven't checked if the vacuum advance hose is good, I'll do that tommorow.
Thanks

Slawek

[71GS455]

Thanks for replies, since mine bogs only when i get to the secondaries, ( not even under full throttle) it seems to me that it is to tight and wont open, am I correct?

Slawek


Actually that's more the opposite - it would be too loose and they're flapping open. I would try tightening them.

On my 71 GS455, I went to an aluminum intake and started getting this bog. I had to tighten the secondary air valve up just a little bit to get rid of it.

[PolishBuickGuy]

Actually that's more the opposite - it would be too loose and they're flapping open. I would try tightening them.

REALLY? :eek2: Crap, I did it the wrong way then, crap again. lol, I'll see if that works. THANKS!

Slawek

[PolishBuickGuy]

One addition to this. Have a screwdriver in the side, spring tension screw, as you loosen the allen screw. Otherwise it will spin itself back once the pressure is relieved.

I accidently did that. :Dou: How can I fix that? I turn it both ways, It doesn't do anything. Which way is tightening? Thanks

Slawek

[RagTop69GS]

The correct adjustment on the flap is 1/2 to 1 full turn after the flap touches the stop. Set it only tight enough so that you don't bog on WOT :3gears:

[PolishBuickGuy]

Today I set the secondary spring tension to as much as it can without the spring poping out, and it still does the same thing even when I had the tension loose.

What could be the next possibility? I'm starting to think fuel isnt gettin there. I have a new fuel pump. I think it's float level. I set the float level according to the 455 level (this carb is off a 455) , but this is a 350GS we're dealing with? Since the 455 need more gas than the 350, shouldn't it be enough for the level I have it set now?

Thanks for the help so far, we will figure this out! Need more tire rubber!, J/k :3gears:

Slawek

[PolishBuickGuy]

Please help, I'm totally stumped.

Slawek

[doc]

O K what are you stumped about? give as many details as you can. :pp

[PolishBuickGuy]

Ok, What I'm stumped about is the secondary studdering. I tried the spring adjustment, didn't work. Cap, roter, wires, plugs, didn't help. Switched coil with different one, didn't help.


What could be the next possibility? I'm starting to think fuel isnt gettin there. I have a new fuel pump. I think it's float level. I set the float level according to the 455 level (this carb is off a 455) , but this is a 350GS we're dealing with. Since the 455 needs more gas than the 350, shouldn't it be enough for the level I have it set now?

^^^^Thats what I need help on.

Take note of:
since mine bogs only when i get to the secondaries, ( not even under full throttle)

Thanks

Slawek

[doc]

If you can find another carb and switch it out to see what happens. There is a possibility that you are getting fuel thru the primary barrels and not the secondarys. another possibility is this, didyou put in new points and condenser and if you did are they gapped correctly? Email me and give me your phone no and I will call you to discuss this thing.

[PolishBuickGuy]

Doc, i PM'ed you.

[TXGS]

It could also be a carbon track on your coil tower.........

It will make it backfire... Trust me!

[PolishBuickGuy]

Alrighty, I haven't been to the board lately, I have been trying to fix my car sputtering problem, I have changed: Cap, roter, wires, plugs, points(at 17thousanths), condenser, coil. I tested the compression in all 8 cylinders, they were all 145-155 psi exept one, which was about 125.

I don't know what to do now. I think I'm gona change the float level higher. Or could it be something in the fuel line that is'nt gettin enough fuel to the carb on time?

Thanks, I have done what you guys have told me so far.

Slawek

[73 Centurion]

It's been mentioned several times, but have you had the carb rebuilt? You've hit all of the easy fixes, it might be time to look at the carb.

[PolishBuickGuy]

It's been mentioned several times, but have you had the carb rebuilt? You've hit all of the easy fixes, it might be time to look at the carb.

Yes the carb has been rebuilt, what in the carb could be causin the problem?

Thanks!
Slawek

[PolishBuickGuy]

Anyone?
Thanks

[beatlebuick]

All these ideas are all great. I think it may be the fuel tank pick up screen in the tank. You may be picking up rust in the tank.The engine will idle all day long, but once you put the engine under load where more fuel is needed, the pump starts sucking faster causing the screen to collaps. When you shut the engine off the pressure in the line eases and the screen unplugs. Just a thought.

[PolishBuickGuy]

I changed the carb to a true 350 carb, and it fixed the problem, now I have to get the timing right. What degree should it be good at? I think I have it at 5* now and it basically sucks.. bad under acceleration. When I set it above 6-8 it would ping a lot. Could it be because I'm using 87 octane gas?

Now I have a new problem, I flushed my radiator, and put in a 50/50 mix of antifreeze/water, and now I have a leak!, from the water pump. Should this be fixed imidietly or can I drive with it for bit, it doesn't leak that bad.

Oh yeah, I forgot, I got a letter that I have to go take emmisions test, I though cars over 30 didnt have to do it, BTW, I'm in Illinois. Should this car (1970 350GS) pass the test easly, is there anyway to "tweak" the car so it has a greater chance of passing? like leaning it out or something?

Thanks for all the replies about the carb problem.
Slawek

[Shrav]

I changed the carb to a true 350 carb, and it fixed the problem, now I have to get the timing right. What degree should it be good at? I think I have it at 5* now and it basically sucks.. bad under acceleration. When I set it above 6-8 it would ping a lot. Could it be because I'm using 87 octane gas?

I don't know your engine (so hopefully someone who does can chime in here!) but the emissions tag on my '71 Centurion says MINIMUM octane rating 91. Back in the days when I had my '80 Trans Am I would set the timing according to spec and then keep advancing it until I got the most rubber from it on take off. It would be a hard hot start but I was more concerned about how much tire I could leave down back then!

[doc]

Hi lad, I am finally back home, good to see you fixed the carb. You need to fix the leaking water pump. The shaft can break off and the fan go through the radiator. Major bucks when that happens. not hard to do.