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So had a problem with a Holley 4412 accelerator diaphragm that was loosing it's rubber after only 3 months from factory, can't find the 50cc locally. Decided to swap the freshly rebuilt 2100 that came with it, but just getting a start, quick idle to 1000rpm, then quickly tapering down to zero rpm in about 2-3 seconds. Started with mixture screws at 2.5 out, and kinda played around from there to no change. So tried another 2100 clone I have that hasn't had more than an hour use- same scenario idle speed screw is all the way loose but still the same start, rev to 1000-1100 rpm then go downhill till stall. All in about 3 seconds. If I stab the gas pedal as it's dying it will do it all over again til I let it stall. Can't find a vac leak and replaced all vac plugs on carbs. Before this, I was having a stall in gear, and acceleration problem, but when I found the leaking acc diaphragm (rubber missing all the way around edge of circle) I chalked the stall issue up to this. It's an 73 f100 fe-390, new fuel pump, fuel lines, pickup tube/sender, filtersure seems like a vac leak to me but a bad one. Just not finding it
Do have an egr plate under it, but just to act as a spacer. Nothing hooked up to it. I will check pcv in the morning. Have a peice of heater hose on it to carb, and might be collapsing after 2 years. Can't find real pcv hose around here, and never think about ordering some.
Even if the EGR is not hooked and used as a spacer it could still be the cause.
Bad gaskets between plate and manifold and plate and carb but that will not show up using spray is the valve stuck open because of carbon.
Dave ----
Is the idle screw backed off on all of them? If it is you need to screw it in until it just cracks the throttle blades. If they're completely closed it'll never idle.
If that isn't it, and if you're not 100% sure any of those carbs are OK, your best bet is to get a rebuild kit with instructions for whichever carb you want to run, rebuild it and bench set all the linkage/screw settings to make sure it's 100%.
Have you pulled the fuel line off the carb and had someone crank it to see if it looks like you're getting good fuel flow?
Yeah went through entire fuel system other than the Holley carb.
waiting to find a 50cc diaphragm
Oem 2100 carb , and clone both worked great when put on shelf, AND , both producing same result
Idle speed screw not mixture screws all the way out, or buried, don't matter idle is same. Quick climb to 1100 rpm then drop to stall.
Mixture screws 2.5 out and played with em a little both directions To no difference. Choke is wide open every time. If I full choke it will run 30 seconds longer, but real rough, and unsteady till stall.
Yeah went through entire fuel system other than the Holley carb.
waiting to find a 50cc diaphragm
Oem 2100 carb , and clone both worked great when put on shelf, AND , both producing same result
Idle speed screw not mixture screws all the way out, or buried, don't matter idle is same. Quick climb to 1100 rpm then drop to stall.
Mixture screws 2.5 out and played with em a little both directions To no difference. Choke is wide open every time. If I full choke it will run 30 seconds longer, but real rough, and unsteady till stall.
Even if the EGR is not hooked and used as a spacer it could still be the cause.
Bad gaskets between plate and manifold and plate and carb but that will not show up using spray is the valve stuck open because of carbon.
Dave ----
^^ this.
suggest you start by physically removing the old EGR valve/block from the spacer, and then make sure you put a tight fitting blocking plate over that.
That will eliminate 1 source of fuel/air contaminant, and then further allow you to look for additional issues of air leak at gaskets.
If impractical to block off the EGR spacer, you could just get a "dumb" spacer with no function other than plenum volume to go between carb and manifold.
Sorry. Not egr. Spacer has a coolant inlet, and outlet, not exhaust. With no path into intake plenum. Coolant lines have never been hooked up in the 6 years I've had it
Sorry. Not egr. Spacer has a coolant inlet, and outlet, not exhaust. With no path into intake plenum. Coolant lines have never been hooked up in the 6 years I've had it
Eventually you might want to pull that and make sure you have no unintended sneak air. But moving on.....power brakes? split diapragm in booster?
Here's what I now have for carb mounting. pcv valve is free and operational heater hose going to pcv spacer is pretty soft, and oil saturated will put a new section. Gonna cinch everything down and plug that booster hose then give her a try
OK, no porting in your manifold under the carb/spacer--check.
what's the underside of the PCV/watter passage spacer plate look like?
yes, would fix your PCV hose set up, but still verify brake booster is not cause of leak.
thick gasket sandwiched between the plate and the carb looks 'wavy' for lack of a better term. May need to replace that.
use X-torquing pattern on carb, don't over tighten. If you have leaks, then it's for sure time for a new gasket.
Ok bolted all back up, after relaxing pcv hose...
started and ran like chit as long as my foot was holding the gas pedal down a bit. Truck shaking like a rodeo bull. Tried turning up the idle to no change took off booster hose at booster to a loud pop due to vacuum left in it. Plugged and started .. no change. It doesn't just rev up and die anymore, but it's much too rough to idle by itself at all
