Pulling my hair out!

[Mercury Mike]

I pulled the carb again. The accel pump was sticking, I freed it up good, and then put it back in the car. Reverified TDC on the compression stroke. Stabbed the distributor right where it was supposed to be. I made that rubber line for my gas line to the carb like I'd planned. It looks good and I'm really happy with it. And it doesn't leak! It all worked out pretty much exactly how I wanted it to. So.... it fired up and ran for a minute, gave me that glint of hope I was looking for. Took me quite a bit of carb tuning, and it ran... real fast. Then it started to stall in and out. If I hit the gas pedal, it stalled more. Then it kicked over, and idled nice for about a minute. Just hummmmmmm. I was pretty stoked on that. I am gonna re-recheck the timing tomorrow. After it ran good for about a minute, it went stall, catch itself, stall, catch itself, then stalled out. I couldn't even get it to run like that anymore. What'm I doing wrong? I'm glad I got the long warranty on my crate 200, 'cause if it's the engine after only 7 or 8 months of operation, I'm gonna call for my money back, and just build the 200 that's coming out of my grandpa's mustang with the money that I paid for that crate. I wish I'd had the experience and knowledge that I have now when I first bought that crate engine. I could've rebuilt the one that originally came out of my car myself for a lot cheaper. We'll see how it goes! I'm definitely prepared to go all the way. I just HATE driving my mom's Pontiac POS. I'm responsible for maintenance on that damn GM too. She's got a couple cars so at least it's not inconvienient... =) Ooh! And switched to 15w40 today. I'm gonna do everything I can tomorrow to get her running again.

 

[pedal2themetal45]

I DONT THINK ITS THE MOTOR
I almost wonder if it not a electornics prob... What kind of Dizzy are you running ( I don't remember if you stated in other postz). Points/electornic?? are all the wires tight? + wire to coil from dizzy and such.. Can you get it to rev up any...... If not what does it do when you try to rev it up..
Start it in the dark and watch for sparks jumpping around Dizzy, coil, plugs... might be a cracked dizzy cap..
Good luck
tim

 

[addo]

Let's go through the basic function of a simple carb like yours (as I understand it, and am happy to be corrected ).

At idle, the throttle blade is barely open. Airspeed through the venturi is pretty tiny. The metering screw controls how much fuel dribbles out from the little slot below the throttle blade. That teensy amount of fuel is enough to run your motor. Whether or not the throttle spindle leaks is irrelevant, because the fuel supply is below the air source.

As the throttle opens, airspeed through the venturi picks up, and this causes fuel to be sucked through the main jet. The faster that air flows, the harder it sucks - up to the physical limitations of the jet. With many carbs, as venturi airspeed increases a channel in the carb causes air pressure to progressively restrict fuel dribbling from the idle slot.

When a motor loads up, manifold vacuum decreases and this causes the power valve to open, releasing extra fuel through another port. It doesn't open at idle because manifold vacuum is quite high then.

Accelerator pump operation is independent of vacuum and (prior) throttle blade position. It will move up to the maximum travel (pump stroke) and deliver a preset amount of fuel for each stroke.

So - look back at these phases of operation and you should be able to troubleshoot the carby. If it doesn't idle then you are not getting a steady trickle of the right volume (relative to air) with the throttle plate near shut. Float level/fuel pressure may be a culprit, causing fuel to leak in via other passages.

If it stumbles on acceleration, then it is either getting too much fuel too fast (uncommon), or not delivering enough in time with the throttle blade opening. That in itself could be from physical problems with the accelerator pump.

Problems at low speed (part throttle) are likely due to either the fuel flow not developing out the main jet, or the idle metering not phasing out. It can also be overfuelling because a low vacuum condition is causing the power valve to open.

Higher speed/wider throttle issues are more commonly jet blockages, fuel supply or power valve problems.

Having said all that, I've got one project with twin Webers that I can't get to run right, and haven't got the nerve yet, to dig into! but take an analytical look at the carb, work out for sure which internal passage performs which function and you'll be far closer to eliminating carb issues.

 

[Mercury Mike]

Pedal - It stumbles more when I try to rev it. I think you're on to something. As I was going to sleep, I was thinking... points, gaps, distributor, timing, coil........ I'm gonna do electrical today or tomorrow. I'll get back to you for sure! Thanks for the help!

 

[JackFish]

I dunno, I'm thinking float adustment or fuel delivery problems.

Float level/fuel pressure may be a culprit, causing fuel to leak in via other passages.

Is it flooding, or starving, or both?

 

[Mercury Mike]

I will cleck float clearances too. =)

 

[Lazy JW]

Since it starts and runs a while when cold I am thinking the ignition can't be too far from correct. Is the choke engaged upon startup? If it is working correctly and the engine starts and runs a bit, then dies when the choke opens, you probably have a lean condition.
Joe

 

[matt1967]

my '67 200 with the Holley 1940 has an irratic idle also. it raises and drops, and if it's cold, it will not idle, it will just spit, and sputter then die. I have to hold part throttle for about 5 min's b4 it will idle at all. the carb was rebuilt in may. I'm not real worried about it as I'm going to tear the engine down for a rebuild soon and I won't be using that carb, but I'd like to work that out, cause it gets annoying.

 

[Mercury Mike]

LaGrasta bought an exhaust manifold from me awhile ago for real cheap, and now he's paying me back by selling me a brand new out of the box carter 1 bbl. Stoked on that. =) I'll be getting it from him tomorrow. That holley is just on it's last leg, and no matter how many times I rebuild it... it just kind of dies. Also, a needle valve broke in it. Gonna check the fuel pump pressure as well. Double check timing, get that carb on there, and get everything set up. I'll post back tomorrow.