The Stovebolt Site Forums The Shop Area Engine Shop Choked?

so i recently got my 1951 GMC with a 228 to start. but it will not idle unless somebody gives her constant throttle, and she only stays running if the choke is semi closed, which i think is why she idles so bad but everytime we go no choke... she coughs and dies... and the carb is still a little rough but i dont know if its just because its a Rochester... the only thing i can think of is maybe not all my cylinders are firing, but my battery is too dead at the moment to check. and once i get a good charge on the battery i shall do a compression check as well.

has anybody run into the same problem as me? or have any advice?

Same problem? YES! I have seen most of them. SLOW Down, Lets take this a step at a time. It is fantastic that you got it to run at all. What are the conditions it is running at all? Is it a new purchase? Have you checked the spark plugs, Their gap? Have you removed the distributor cap and looked at the points? Checked their gap? Is that Rochester carb Clean or gummed up or worse with old gas? It does not pay to jump into an engine and throw all kinds of fixes at it wildly. Take it a step at a time. You have an advantage, It does or did run. It may be as simple as a plugged fuel filter, a collapsed fuel line or a weak fuel pump. We are all here with similar experiences to help you!

Sounds like you have a vacuum leak. Check the gaskets at the manifold and carb base, as well as the vacuum advance line and wiper motor line.

okay, so i called my uncle and it turns out i had my floats set wrong. She idles now without choke.

I have replaced a lot of parts, new plugs, wires, points, cap, rotor, coil, condenser. I just rebuilt the carb and it looked pretty darn good for sitting for 30 years. I bought her about 6 months ago and me and my dad have just been tinkering on weekends.

We've come to the conclusion that it must be a vacuum leak because 1) wipers dont work 2) the carb mist's a little bit of gas out of the top (no air filter on) and 3) there is barely any force pulling my finger when i cover the spout for the wiper hose.
My main question right now is how do i tell if its a leak or if my vacuum advance is shot?

i completely forgot, she bogs out whenever somebody hits the throttle... once we get that fixed were are going to find the vacuum leak and then set timing using vacuum and a timing light.

if anybody knows why she dies out when we give her throttle or has any ideas why please let me know, thats my main goal to fix right now

Hy Josh_51GMC, stop rushing back and forth, in order to find out what's going on it is best to be methodical. If you do indeed have a vacuum leak that could be causing your bogging issue. have someone work the throttle while someone looks down the top of the carb, every time you work the throttle you should see a squirt of gas into the carb. Check all your manifold nuts to make sure they are tight, and your carb nuts as well. Remove all the vacuum hoses from the intake manifold and plug the ports. Did you pickup a vacuum gauge yet?

I didnt find a vacuum gauge, but i was able to find a compression gauge.
All of the bolts and nuts are tight, isnt the only vacuum line the one for the wipers? besides the main vacuum line

A vacuum gauge should be easy to find -
Canadian Tire
Princess Auto

Are either of those places close to you?

Good candidates for a vacuum leak -
-carb base gasket
-cracked carb insulator
-intake manifold not installed flush to head
-intake manifold gasket failed

you should have a good strong vaccuum at the wiper port at idle.

regards,
Leon

yup, theres a canadian tire just down the hill from my house, but there always out of stock. otherwise at lordco they want $50 when canadian tire only wants something like $20... just waiting for it to be re-stocked i guess....

But im thinking my vacuum leak is probably at my carb insulator... it cracked so i crazy glued it back together.....

Hy Josh_51GMC, did you check the carb for the squirt of fuel each time you work the throttle yet? You do this with the engine off, we're trying to find out if your accelerator pump circuit is functioning. If it is not functioning then the engine will definately bog. You can perform this test yourself if you can reach the carb linkage and see the top of the carb simultaneously.

wait, will the engine is off?? should the engine be cold or should i run it for a little bit first?

okay, i just ran out and checked, its squirting gas.

i'm going to do a compression check tomorrow, in order to do so i should pull all my plugs right? and any reading above 90 should be good?

Hy Josh_51GMC, yes pull all spark plugs, block carb to wide open throttle, disconnect primary power to ignition coil, and test away, good luck.

do i need to disconnect primary power to the coil? that wire is kinda badly frayed...

Its kinda your call.
Its a safety thing.

If you don't disconnect it, the ignition system will still be operating.
The ends of the spark plug wires will be looking for a place to send the spark energy.
Your hands will be near them . . .

Alternatively, you could disconnect the wire to the distributor.

You might also consider repairing the ignition power wire.
Here's a pic of the result of a bad ignition power connection on my 55.1

regards,
Leon

okay, so i did my compression check, results are way better than i thought they were going to be
Cylinder 1) 135psi
Cylinder 2) 132psi
Cylinder 3) 120psi
Cylinder 4) 135psi
Cylinder 5) 125psi
Cylinder 6) 135psi

random question about timing, once ive located tdc and set my cap for that, i read that im supposed to pull the coil wire off of the cap hold it to a ground and turn the dist. body in short sharp burst until spark.... mine sparks at 3 different locations.......

It sparks when the points open.

is there a specific spark i should use? b/c in my shop manual it says that once u get spark, tighten the distributor clamp so that it can be turned anymore... well if im standing at the passenger fender, looking at the distributor like a clock, it sparks a 3, 6, and 9

anyways, 3B where should i go now?

Hy Josh_51GMC, okay those compression readings sound pretty good for that engine. No dead holes. I don't really understand what your talking about with the removal of the wire from the distributor cap and sparking by turning the distributor. What shop manual are you working with? The coil wire should spark everytime the points open and close, that's six times for every rotation of the distributor. They may be describing the static timing of the distributor, with the flywheel lined up with the timing mark, and the number one spark plug resting on a good ground, turn on your ignition, now slowly turn the distributor body until you get a spark in that number one spark plug, you may have to check to make sure the points are closed with the engine set at the timing mark before you attempt to get a spark, once you get a spark, tighten the distributor in that position. That should give you close enough timing to get it to start after all it was running before wasn't it. You can always fine tune it later with a timing light.

Im working with a 1947-54 models 100-400 maintenance manual for GMC trucks.
i accidentally read one step and then skipped ahead to ignition timing... my bad

Anyways, i set the timing back to original, where should i go next? i do not have a vacuum gauge yet, but i friend has sent me a new base insulator pad for my carb, hopefully that fixes the leak