1 barrel rochester carb 1967 problem

[Ozzy2013]

Hey guys need a little help its cold here 15-25 degrees. I rebuilt this carb checked the timing ,points etc .The fuel pump is good the truck cranks for a long time before starting .If you use the choke or pump the petal it seems to make it worse.. After it starts and warms up it runs great and starts easy. The compression is good also its a 250 6 cyl didn't find any vacuum leaks either. It is a 1967 Rochester b carb do they have inherent problems? Thanks figured I would ask im sure some of you have ran into a similar problems. New brass floats and they are set properly also. Thanks Oz

[18436572GMC]

I have never worked on a one barrel, but to me it sounds like an accelerator pump issue. Someone may say otherwise

[VWNate1]

Before touching the carby you *must* go back and check and adjust all the tune up stuff ~ points ? .016" or 33° dwell , timing 0° ~ 10° BTDC @ idle and there *must* be no vacuum signal to the dizzy @ idle , if there is , you have the vacuum advance hose on the wrong carby nipple .

Spark plugs to .040" if points , .060" minimum if HEI .

Remove the air cleaner and peer down the venturi while you open the throttle ~ the *instant* you begin to move the throttle , it should begin pi$$ing fuel , not dribbling .

Often the accelerator pump is worn and so doesn't work or allows raw fuel to be sucked out and dribble , causing flooding .

Check the Auto Choke : dead cold remove the air cleaner and depress the throttle to the floor , as soon as the throttle opens the choke's bi metallic spring must yank the choke plate fully closed .

If not , GENTLY bend the rod using two pliers and *only* bending it where it already has bends , DO NOT mangle it to look like a snake ! .

Once these are done the correct cold start drill is critical :

key on , depress the throttle to the floor then release , then crank the starter ~ failure to turn the key on before depressing the throttle , means the idle stop solenoid won't be properly set causing flooding .

Remember : pumping the throttle while cranking , makes it harder to start , ALWAYS ~ you must first squirt in raw fuel then allow the throttle to close so it gets sucked in by the high vacuum .

Try these steps and see how even a totally worn out I6 engine *instantly* springs to live , always , every time .

If you're still running points , consider buying an HEI dizzy from a later model , new they're under $100 , junkyard is under $50 . the difference in power , smooth idle and easy starting hot or cold , will amaze you plus better fuel economy .

You can also increase the spark's intensity by running a closer points gap , like .012" , this works especially well on old 6 volt systems but remember : any time you touch the points , you then *MUST* re adjust the timing ! .

Give it as much timing as it will take without ping , knock or dieseling .

Rule of thumb : every .001" change in the points gap , changes the ignition timing by 3° so it's critical to check and adjust it .

[Ozzy2013]

Thanks timing ,points, vacuum line hooked to the only and correct port, plugs, are all set to spec.New accelerator pump pissing strong stream, Manuel choke on this carb .Good compression on the motor no leaks .I will go over everything again .Thank you for all of the input it is greatly appreciated .I am going to put a hei distributer on it next just don't want to spend too much going to drive it while I get the 402 big block rebuilt to go in it.Oz

[19673ontree]

Hey man , I have owned and drove 67 to 72 chevy trucks with the awesome 250 6 cylinder engine and one barrell rochester carb for the biggest part of the last 40 and I can tell you how th ey act if everything is in perfect tune you have the points set correctly and its in tip top shape if you leave the truck sitting a day or two and it cold it will crank a while till it starts pumping the gas don't help pull the choke and when it starts let it w arm up then you are free to drive anywhere in the world you want to go whether its 120 degrees or 30 below zero but sadly a 250 6 cylinder will not run under water other than that they are a marvel of engineering LOL

[VWNate1]

O.K. then ;

Go for a good used HEI dizzy complete with wires and everything , open the spark plugs up to .070" and watch it roar into life every time .

Or this : http://www.ebay.com/itm/NEW-CHEVY-6-...9dfad9&vxp=mtr

Me , I more trust the old original stuff but sometimes the flyweights and bushings etc. need replacing , lucky for us GN used the same mechanical parts and module as the V-8 dizzy did .

Early 250's were set to 10* BTDC but by 1967 the smog tests mandated TDC timing , depending on your engine's health one or two degrees timing makes a HUGE difference ~ if it cranks over fast & easily , I'd start with 10* and back it off one or two degrees at a time if it pings or diesels .

*DO* unplug that vacuum hose when it's hot idling to see if there's any vacuum signal .

Enjoy that 402 ! who's paying the fuel bills ? .

[Ozzy2013]

Originally Posted by 19673ontree

Hey man , I have owned and drove 67 to 72 chevy trucks with the awesome 250 6 cylinder engine and one barrell rochester carb for the biggest part of the last 40 and I can tell you how th ey act if everything is in perfect tune you have the points set correctly and its in tip top shape if you leave the truck sitting a day or two and it cold it will crank a while till it starts pumping the gas don't help pull the choke and when it starts let it w arm up then you are free to drive anywhere in the world you want to go whether its 120 degrees or 30 below zero but sadly a 250 6 cylinder will not run under water other than that they are a marvel of engineering LOL

YUP! Thanks that's my problem to a tee!Sounds like you know them well.Oz

[Ozzy2013]

Originally Posted by VWNate1

O.K. then ;

Go for a good used HEI dizzy complete with wires and everything , open the spark plugs up to .070" and watch it roar into life every time .

Or this : http://www.ebay.com/itm/NEW-CHEVY-6-...9dfad9&vxp=mtr

Me , I more trust the old original stuff but sometimes the flyweights and bushings etc. need replacing , lucky for us GN used the same mechanical parts and module as the V-8 dizzy did .

Early 250's were set to 10* BTDC but by 1967 the smog tests mandated TDC timing , depending on your engine's health one or two degrees timing makes a HUGE difference ~ if it cranks over fast & easily , I'd start with 10* and back it off one or two degrees at a time if it pings or diesels .

*DO* unplug that vacuum hose when it's hot idling to see if there's any vacuum signal .

Enjoy that 402 ! who's paying the fuel bills ? .

Ha ha yea cant wait for the 402 it wont be a daily driver so i wont mind spending the money on fuel ,Having the power will be well worth it.Thanks again for all the info when it warms up some i am going back through it again.

[C10_ustacould]

I've got a '71 with a 250/4 speed (granny low) that has an HEI dizzy. I have issues with a stumble off idle and when under a load at cruising speeds 55-60 mph (climbing a hill). I have been fooling around with the timing and the air/fuel mixture and it is a little better and a little worse. the stumble is less severe but now the idle is so high I can't adjust it any lower. I set the timing on 4° at idle with the vacuum advance disconnected and I ran the mixture screw all the way in then 2.5 turns out. Then I turned the mixture screw out until I reached max vacuum. At this point the idle rpm is about 1200-1500 and the idle adjustment screw won’t reduce the rpm anymore. I’m lost with this configuration; I’m thinking I need to get back to a baseline but how? Anyone have advice?

[19673ontree]

you need to turn the adjustment screw on the carb back so that the idle screw works again , many things can cause a stumble the one thing that makes mine stumble is when it needs spark plugs I had to put a new set of plugs in mine 3 or 4 years ago cause when I went up a hill it stumbled and was very rough running the plugs were bad new plugs fixed it , I put new points in mine last year ? Or year before last ? No maybe it was 3 years ago ? But anyway a combination of points and plugs would probly help yours too ,,

[19673ontree]

Ohh ok you have an hei , I bet the plugs need replaced

[C10_ustacould]

So should I run the mixture screw in until just before it stumbles at idel?

[19673ontree]

Originally Posted by Bucks68

So should I run the mixture screw in until just before it stumbles at idel?

Id put new plugs in it first then yes

Do this : take the idle screw out , adjust the mixture screw back till the engine dies , put the idle screw back in and adjust the idle to about 900 , bet it will run fine ,

[C10_ustacould]

Will do, thanks for the assistance.

[Ozzy2013]

I am replacing the fuel pump rebuilt the carb and put new plugs in helped a lot.Now it runs out of fuel with the choke on warming up !Lol

[VWNate1]

First things first ~

ascertain there's NO vacuum signal at idle then fiddle with the carby ~ as mentioned dirty spark plugs cause all manner of poor idle and off idle stumble issues , did you open their gaps to at LEAST .060" ? .

Failure to do things in the proper order guarantees you'll be chasing your tail .

-Nate

Originally Posted by Bucks68

I've got a '71 with a 250/4 speed (granny low) that has an HEI dizzy. I have issues with a stumble off idle and when under a load at cruising speeds 55-60 mph (climbing a hill). I have been fooling around with the timing and the air/fuel mixture and it is a little better and a little worse. the stumble is less severe but now the idle is so high I can't adjust it any lower. I set the timing on 4° at idle with the vacuum advance disconnected and I ran the mixture screw all the way in then 2.5 turns out. Then I turned the mixture screw out until I reached max vacuum. At this point the idle rpm is about 1200-1500 and the idle adjustment screw won’t reduce the rpm anymore. I’m lost with this configuration; I’m thinking I need to get back to a baseline but how? Anyone have advice?

[C10_ustacould]

Originally Posted by VWNate1

First things first ~

ascertain there's NO vacuum signal at idle then fiddle with the carby ~ as mentioned dirty spark plugs cause all manner of poor idle and off idle stumble issues , did you open their gaps to at LEAST .060" ? .

Failure to do things in the proper order guarantees you'll be chasing your tail .

-Nate

That is were I went wrong, I have the vacuum advance to manifold vacuum, switched it to the side of the carb nearest the valve cover and the idle went down as the timing was removed. I'll check/replace the plugs and go from there. Any adjustment in heat range with the HEI?

[VWNate1]

No spark plug range change .

My old 250 is plumb worn out and passes a LOT of oil so I had to upgrade to the stock 1976 HEI or scrape the plugs every 200 miles...

Just open them up so the HEI can do it's thing then set the timing to 0° ~ 8° BTDC @ idle , no vacuum signal , once you have that done , use the idle stop to set the idle to 700 ~ 1,000 RPM hot in neutral then S L O W L Y turn the mixture screw in as you watch the vacuum gauge , ideally it'll climb and the engine idle better/faster until the needle begins to flick , then stop and back it out 1/8 ~ 1/4 turn and go for a drive , see how she goes , if it diesels you can set the idle speed back down to 600 RPM but it's better to use the original idle solenoids , the brackets are hard to find but the 305 V-8 uses the same idle solenoid with an additional bracket that easily snaps off by bending with pliers .

If you have the electric idle solenoid , use it to set the tune then disconnect it and use the carby's idle stop screw to set the idle to 400 RPM's , this stops the designed in dieseling .

Let us know how it all works out .

[C10_ustacould]

What were the idle solenoids for? Mine doesn't have one on it.

[Steeveedee]

The idle solenoid on your year truck was for pulling the idle up when the A/C was on. No A/C, no solenoid.

If you have points, they should be set 28 to 32 degrees dwell. Longer dwell (greater than 33 degrees) means retarded timing and lower saturation time on the coil, thus less power. I usually set points to 28 degrees dwell, since as the rubbing block wears, the dwell angle increases. This gives a measure of protection against rubbing block wear-in.

Long cranking times can be caused by high resistance in the ignition start circuit (yellow wire from starter to coil) or not having a proper ignition source when retrofitted with an HEI distributor. Most people put in an HEI distributor without consideration for cranking voltage, just hooking it to the "run" side of the ignition switch. The Kettering ignition (points) system vehicles get the voltage from different places than the HEI systems do. Unless you wire in a "start" source for power when retrofitting an HEI, it will be hard to start.

For the temperatures you are talking about, pumping the pedal may be required. However, pumping the pedal on an automatic choke vehicle can cause the choke to open if you push the pedal too far, and then it will be even harder to start.

[VWNate1]

Actually the idle solenoids were an anti - dieseling device added to all models from 1968 onwards but often removed by folks who don't understand what they do nor how they work .

Often they'd quit working and even back then they were $ to replace so they were discarded often . the correct one as I mentioned before is long out of production , why I use the still available V-8 version .

To prevent the low voltage (yellow wire) problems with an HEI dizzy , I simply added one of those cute little cube relays to the engine to cab ground strap screw and powered it off the starter lead 2" away , using the yellow wire to kick the relay by the key .

HEI's take more power than do points ignitions so relieving the key switch of the ignition circuit draw is wise any way .

The easiest and most accurate way to set the points is to remove the spark plugs and adjust them on the fly as you crank the engine over , this allows you to compensate for all dizzy slop and wear etc.

[C10_ustacould]

Have a pic of the relay trick?

[VWNate1]

Maybe ~ you'll have to look in the pix I posted before ~ my truck is still in the paint jail and I don't think he's touched it yet

[Shaky]

When I get a '67 I usually replace the one-barrel with the '68-up design. I think it's a better carb.

[VWNate1]

It is a better design , it's also made of Aluminum instead of the old pot metal so they last far longer .

They're out there on E-Bay very cheaply once you know what to look for .

Every year or two , GM made yet another improvement to them , just like they did to those old 'B' series carbys .