Carburetor Problems On Older Cars

terry14

Well i picked up the new carb.............ran gas from gas can to carb to bypass gas tank and old gas....................same problem..........it did not help...........replaced spark plug..............cap..........rotor..........wire..........points.......checked fireing order for 6 cylinder 250 engine........fine........the old 67 ChevyII still runs rough...blowing black smoke while trying to idle.................tried to use timing light on it........chalked the pulley on harmonic balancer.........couldnt get a reading........it must have skipped timing on the belt................or could it be a valve sticking.............im clueless.............

terry14

I have just flushed out the gas tank and gas was old but not to bad..........tank in good shape...............it must be the timing ..............

Mr_Shiftright

Why don't you pop off the valve cover and just crank the engine and see if all the valves (not the rockers but the valve stems themselves) go up and down properly?

You should/could also do a simple compression test. An easy way to do basic timing in a rough kind of way would be to remove #1 spark plug, hold your finger over the hole and when you feel compression pushing your finger out, the rotor should be pointed to #1 cylinder.

You have a chain I believe, not a timing belt, which can jump time.

alcan

The 230 and 250 inline 6's used a steel crank sprocket and a fibre covered cam sprocket which meshed together. No chain.

casey_wa

Carb is a 3-bbl Keihin that was flooding gas to the point of gas getting into the oil. Removed carb and rebuilt. Installed, adjusted float levels, changed plugs and oil...idles great. Test drove and finding the the engine is starving for gas over 25 mph. Rechecked float levels and adjusted auxiliary (primary fine). Noted the at idle the primary is spraying gas into the carb. When throttle is further engaged the primary jet produces stronger spray. At no time does the auxiliary jet sprays gas even at high rpm.

Am wondering if the lack of auxiliary jet supplying gas is the cause of the vehicle not getting enough gas when driven over 25 mph? At what point should the auxiliary jet do it's job?

Am I overlooking something else?

Thanks, Casey

Mr_Shiftright

Oh man good luck rebuilding those Japanese carbs. The problem as I remember it was that the various orifices in those carbs are very very tiny passageways and it's hell to get them cleaned out. Once on a Datsun 510 I doped the carburator with a very strong solvent added directly to the engine while running at high idle. I also crossed two spark plug wires to get the engine to backfire through the carb, and I'll be damned, it worked and it ran a lot better. But as you can see, I was getting desperate.

Mr_Shiftright

Oh like the old Volvos---fibre timing gear. Well on the volvos they like to strip out against the steel crank gear. Does this happen with these Chevy 250s as well?

swschrad

had a 1976 V6-231, and timing went at about 117,000. the nylon-geared steel main gear was pretty stripped down. put an all-steel set in and the "less noise" claim for the nylon-chain-metal cam gear set was NOT verified by practice. GM just out-thought themselves.

terry14

well guys.........pulled off valve cover........everything working fine..........Im coming to the conclusion that the 250 inline 6 is tired and needs a overhaul...........going to check compression test tonight.............I purchased the 67 Nova (mint) zero rust.........out of a barn.........had zero oil in it.......(oil drain pan bolt stripped)..they may have ran it out of oil .............when i picked it up they were trying to start it with starter fluid .........the fuel pump wasnt working.............How long they were trying to start it only god knows.............worth the work though.............I mean where can you get a 67 chevy ll Nova with zero rust and mint interior for 1,000 and everything works in it..........from turn signals to dome light to glove box light.......anyone here want to bet whats wrong with it................we shall see

terry14

Compression test done... 1 140
2 135
3 140
4 135
5 135
6 140

Timing is right on as well..............so here we have a 6 cylinder that runs rough at idle while having black exhaust.........new carb.....new spark plugs....new rotor......new wires..........new points........clean fuel..........using 100LL fuel just to make sure...........timing good.........compression good.............pulled valve cover and checked for stuck valve...........everything fine...........i guess the next step is to pull the intake manifold and see whats going on there...............checked for leaks on intake manifold and found none.............maybe someone left a sock in the intake manifold.........im out of answers....................

isellhondas

Was it really a "new" carb or a cheapie "rebuilt". Even if it was a new one it may have problems. If you can still find a good carburator guy around I'll bet he can fix your problem!

swschrad

sticking float, or poorly adjusted needle valves. there is too much gas coming out of that carb. it needs to be tuned at least, and rebuilt at worst, and brought into alignment with the standards for THAT engine on THAT year nova. the rochester carb was easy to misalign, but worked real nice when it was dialled in.

burdawg

I pretty much agree with what others here have said. I could write a whole page about the crappy rebuilt parts I've dealt with, but I'll save you all the reading. It sound like you have checked all the necessary areas. I would look at that float level, and make sure the needle valve in the float chamber is working.....

terry14

The previous owner took off the single barrel holley..........and then installed a rebuilt Carter from NAPA..............then I purchased a rebuilt Rochester from Advance Auto.................I dont have a clue..............im going to pull the intake manifold out today and see what I find.............................I would like to thank you all for your input...............I will let you know what i find..............terry

terry14

Hello guys..........well i FOUND THE PROBLEM.............you guys were right................just for fun........my dads got a 1966 Chevy stepside truck he bought in 1966 from dealer with 20k miles on it now..........like new condition........his favorite out of 12 antiques............the 1966 Chevy has the exact engine that the 67 chevy II has...........250 6 cylinder...........so i took the carb. off of that engine and placed it on the Nova 6 cylinder....................whammo........ran good.......so after the original Holly didnt work...........then the rebuilt Carter from Napa didnt work........and the Rebuilt Rochester from Advance didnt work.............I have learned something new about carbs..............now im going to rebuild the original holly and i should be ok...........thank you all for your help.............terry

wireman11

I am trying to find the best approach. My 66 seems to be taking in too much fuel, If I hit the accelerator, It conks out when cold, smells too much like gas also. Rebuild? New? Where do I get adjustment tips?

terry14

After rebuilding that Holley I had for that 67 Chevy ll it worked perfect.......I suggest rebuilding the carb. and seeing if the problem is fixed.........if she still gets to much gas then play with the float level...................after reading all my posts here you can see what i went through on that 250 straight six of mine

old_tercel

Hello, I have a 1986 Toyota tercel 1500 cc w/carburetor that is suddenly giving me a stalling problem. It was 29 deg. this morning and for a good 30 min I could barely drive. More I pressed accelerator, the more it would stall; could barely make 10 mph. Strange thing is after 30 min. stalling problem seemed to disappear. This is original Totyota carb, with 142,000 miles but has been very reliable. I have never made any adjustments other than idle speed and keeping interior well sprayed w/carb cleaner. Here's what I am wondering: since car runs too cold (I could switch thermostats) is that the #1 issue? Or is this a pure carburetor issue--something sticking that carb spray would likely cure? Or do any of you all have other thoughts? Car does idle somewhat rough but has been that way for last 2 yrs.
thanks for any advice -LIG, Atlanta Georgia

alcan

Before starting it next time it's been sitting for a while, remove the air cleaner. Open the throttle by hand, and see if the choke plate closes. If it doesn't, that's your cold start problem. If it does, start the engine and make sure the choke is pulled open slightly by the vacuum pulloff.

old_tercel

I'll give it a try tomorrow morning. Predicted to be 29 deg. again.

old_tercel

Thanks for the tip, Alcan. Well here are the results. I put a bottle of dry gas in the tank and sprayed choke plate and throat with carb spray to dissolve anything. Checked the choke plate this morning (closed with throttle engaged and with ignition on). Car warmed up for 10 minutes and choke plate gradually opened as expected. Drove car --was 29 deg. again this morning-- and the car performed flawlessly.
Here are my guesses: 1) moisture from gas tank interfered with choke plate (ice?); 2) dirt or debris from bottom of gas tank (I was nearly empty yesterday morning) got into carb. I am being more careful now!!! Thanks

edublu

Not sure what is happening but the truck jerk in many of the gears. I changed the fuel pump and filter.

Thanks

steed3

You might have an overloaded "charcoal canister".If it has been loaded up with too much exess vapor,s or is so old that it can,t function properly anymore,replace it.Test it first though. from TTomace@aol.com

gphi

I have a 90 toyota tercel with carb problems. When the engine is cold the vacumm
at the auto choke is nil and the idle is very low.When it heats up it is fine.
If I put a direct vacumn line from the air cleaner to the choke the idle is good when cold but when the engine heats up the choke does not disengage and the motor
idle races. Does anyone know what I can do?
thanks
ed

otisplatejr

1973 chevy pick-up, 350 engine, auto tranny. Has been sitting for 4 years, attempted to start and fuel is spiting back through carb. Also some flame spurted out of carb.

Mr_Shiftright

Well first he'll have to drain the tank and add fresh fuel, and may have to remove the carb and clean it out as well. No doubt all kinds of various buildup in there.

steed3

Some older chevy,s had a good idea-it was If the oil pressure got dangerously low the fuel pump would shut off,so that you don,t destroy the engine by having too low of oil pressure.

Toms

steed3

My first car was a '66 chev chevelle w\250 6cyl.
I had a problem w\oil residue on the ignition coil,
shorting it out,causing poor performance.
I cleaned the top of the coil w\gumout spray then a
shot of break cleaner,to remove residue left from
the gumout.checked wire connections on coil also.
this solved the problem.

Toms

65fastback

I just bought a 65 mustang fastback. It has a 302 with 2bbl carb (Ford 2100 series). The car was driven and tested before delivery to me with everything running and driving fine, but the carb had an idle problem. The carb was then changed, idle was fixed...however now a problem. If I push on the gas, or try to drive the car, the engine dies/stalls almost immediately. The car idle's fine. I can start the engine fine, but as soon as you try to push on the gas more than super slowly, the engine dies/stalls. Any ideas? I would assume since the only thing that changed between running fine and not, was a different carb, the carb must be problem. However, looking for ideas. Thanks.

bolivar

My first guess would be the carb need a new 'power piston'.

When you open the throttle, the power piston squirts a little gas into the venturi. When the throttle opens, the air flow increases faster that the 'ususal' flow of gasoline can increase. This leans out the mixture, and the car will stumble, stall. The gas squirted in via the power piston richens the mixture and corrects this problem.

Did they just 'swap' another old carb to correct the idle problem? If so, they swapped an idle problem for a power problem.

Overall, the carb should be opened up and rebuilt. Many times you cannot buy just a power piston, you will have to buy a whole rebuild kit, which includes a new power piston. So, just rebuild the entire carb.

65fastback

I picked up a carb rebuild kit this morning and will try that this weekend. Yes, they just swapped problems...not the best way to handle it. Thanks.

burdawg

With the engine off and the air cleaner removed, look down the venturies while opening the throttle to see if a small stream of fuel is being squirted in. If not, then either the power piston is bad as bolivar said or there's some other problem, blocked passages, mis-adjusted (badly) power piston linkage, extremely low fuel level in the bowl, etc. If this was a rebuilt carb then anything is possible, many of them today aren't worth the box they come in.

65fastback

Actually, the carb on there now is an orginal Ford carb for the 65 289. The strange thing is that the car was running great before this carb was put on. I am hoping a new kit will solve it. Could this be caused by water in the gas tank? I have a bottle of dry-gas I was going to try as well to clear out an possible moisture. All advice is appreciated. Thanks.

Mr_Shiftright

On a nice car like that I'd consider an aftermarket NEW carburetor like Edelbrock, etc., for better running and economy...and just put the old carb in a box if somebody wants it when/if you sell the car.

Or by a NOS new carb from a Mustang vendor...don't screw around with rebuilds is my advice.

65fastback

Where would you suggest obtaining a NEW Edelbrock from for an old 302 like this one? And how much do you think it would set me back? Thanks.

Mr_Shiftright

Well I was just throwing out ideas---Edelbrock might not be the right choice for you as you seem to be running a stock 302...usually Edelbrocks are 4-bbl. carbs if I recall...so you'd have to switch manifolds...

Here'a website if you are curious---at least you can get an idea:

http://www.edelbrock.com/automotive_new/mc/carbs_acc/carbs_access_main.shtml

Best thing would be to get a copy of Hemmings Motor News and browse the Mustang Parts section. (www.hemmings.com).

isellhondas

Isn't the original engine and I remember the 289's used a different carb than the later 302's did.

If it's a real early '65 it could have come with a 260 engine.

johnsonly

my 84 jeep cherokee runs excellent when cold however when the engine heats up it does not idle unless i rev the engine constantly it is a 2.5 hurricane engine that the vacuum lines may have been altered i do not know where the vacuum lines should go i do have a manual on cd but it is unclear

Mr_Shiftright

It does sound like excessive lean mixture caused by a vacuum leak, yes.

johnsonly

is there an easy way to check for vacuum leaks :mad:

Mr_Shiftright

WEll the best is a smoke machine but I don't guess you have one of those...some safe non-combustible spray that will make the engine stumble as it gets sucked into the vacuum leak (and hence to the combustion chamber) would be okay but there are tricky parts to diagnosis.

Read All About It Here: http://asashop.org/autoinc/may/TECH2TEC.HTM

diagnosticmonk

Yea man, the old Q-jets are some of the easiest carbs to modify for applications of the hi-performance nature.Those who cant get em right are runnin EFI now

andre1969

the biggest problem I have on carburetor cars is the choke. Once they get warmed up and past those cranky stages they usually run fine. I guess I've just been lucky though that I've never really had an obnoxious carb. Well, except one, a 1989 Gran Fury that, oddly, had a GM quadrajet on it! I think the car was trying to reject it, like a body organ of the wrong blood type! :P

blh7068

I just converted my original 2bbl setup on my 71 firebird to a correct year pontiac rochester 4bbl.

The car runs better...but I noticed when I was tweaking the mixture that when I goosed the accelerator(quickly), some fuel would spray out of the primaries.

Is the float out of adjustment?

bolivar

"I noticed when I was tweaking the mixture that when I goosed the accelerator(quickly), some fuel would spray out of the primaries."

No, that's exactly how they correctly work. There is a rod and valve system called the 'power valve' that squirts fuel like that. If it is not working correctly, the car will stumble and stall when you attempt to quickly accelerate.

blh7068

"No, that's exactly how they correctly work. There is a rod and valve system called the 'power valve' that squirts fuel like that. If it is not working correctly, the car will stumble and stall when you attempt to quickly accelerate."

Well, it does hesitate a little. Are you sayig that raw fuel is supposed to come out of the carb? The fuel spray hits the choke plate, then squirts up and out of the carb.

terry14

68 corvette 427 engine.........If the mechanical fuel pump is installed wrong will it make the engine run rough.....fuel pump runs off the pushrod.............engine ran good until I replaced the mechanical fuel pump (which was leaking) now it runs rough........had the fuel line off of carb. for about 3 weeks until I received the new fuel pump..........

chook

Hi im just trying to modify my 350 Holley carby, as when i go four wheel driving up hills carby floads, so ive bought this plastic spillway modification,im just wondering does it sit upright inthe carby and ,does it have to be secured with a mounting screw,if anyone has info on this please post. :shades:

bobbymcgee1980

I used to have an '82 Mercury with something called a "Variable-Venturi" carburetor. Still don't know what the heck a variable venturi is. Isn't that what butterfly valves were for? Never could get that thing running right, and rebuilding it would have cost a small fortune, so I sold that car for $1800.

About a year ago, I pulled the carburetor off my old '78 LTD's 400 engine, bought one of those O-Rielly's rebuild kits and went to work. At first, the exploded-view drawing looked like plans to the starship Enterprise, until I started taking things apart and looking at how it fit together. Took it apart to the last nut and bolt, soaked everything in gasoline for a couple of weeks, and put it all back together with all the new parts in the kit (Made lots of photos along the way. Anyone working on cars needs to invest in a digital camera!) Set all the adjustable stuff to the generic, baseline 1-1/2 turn locations, and bolted that puppy back to the top of the engine. Hit the starter and---nothing. Poured a half a cup of gasoline down the carb, (don't try this at home, kids!), and hit the starter again. Engine cranks, flames shoot out the carb, engine sputters, then dies. Pour a little more gas in, hit the starter, engine sputters, then sputters some more, then finally revs up to full idle. After that, it ran better than it did before I worked on the carb, so I've never been brave enough to mess with the fine tuning.

burdawg

When you first put the carb back on it didn't have any fuel in the bowl, so of course it wouldn't start. Half a cup is way to much to prime the engine, hence the backfire (it's flooded).
The right way to do it is to crank the engine for awhile to get fuel into the bowl. Then pump the accelerator by hand while watching for the accelerator pump to squirt fuel into the carburetor. If it does it's ready to start. If it doesn't crank it some more and check it again.