ant720

correct. I'm on my second re-man booster. any suggestions?

I've capped off the port from the intake and the problem goes away. which made me think it was the booster. but the booster is holding vacuum.

with the engine running and a gauge b/n the check valve and booster: not pressed- gauge steadily reads ~-20in/hg. and will hold that with engine off. pressed- the gauge raises to like -15. If i pump the pedal without completely releasing, the gauge will raise about 5in/hg per pump and the idle gets progressively worse. rpms only go down. if I apply the brakes lightly (like coming up to a stop sign) there is no stumble. If I slowly apply the brakes as far the pedal will go, there's no stumble or it's minimal. But when I release the brakes it will stumble. I'm guessing these are related to the amount of vac the booster is using. but the releasing part doesn't make sense to me. it's gotta be the booster right??

thanks for the tips. I pulled the brake light switch wires, no change. I can only find 2 vac lines, I believe everything else has been deleted. One going from the carb to the distributor and another going from the intake manifold to the booster. no T's. My next guess is something more severe: head gasket (which I have no evidence for) or intake gasket. I sprayed carb cleaner around the engine/carb/intake but didn't find any leaks.

Update: still having the same issue. The new booster is tested and good. I replaced the lines and clamps from the manifold to the booster. The engine is pulling strong vacuum. I've checked for vac leaks everywhere on the engine I can think of. But the engine still stumbles at idle and at raised rpms when the brake pedal is pressed. It also stumbles when I release the brake pedal which really has me confused. But it's fine when the brakes are held. Vacuum keeps dropping significantly every time the brakes are pumped and doesn't return to normal until after the pedal is released. Ideas??

Thanks for the replies. To clarify I blocked off the check valve port that the line from the booster connects to. So the only thing not physically tested in that case was the line from the check valve to the booster. I will recheck that line and all connections before moving forward. I've got a vacuum gauge on the way to test the booster.

So I'm getting an engine stumble on my 720 when I apply the brakes at idle, pumping the brakes fully released or partially depressed makes it worse. The brake booster and check valve passed every test I could find. I blocked off the booster vac line at the check valve, stumble gone! So obviously I have a bad booster, right? Put in a re-manufactured unit and have the same issue. Side note: the MC is not leaking and I've triple checked all vac lines for leaks. Question is: is the new booster bad too? Or am I missing something?

I'm having trouble adding pictures. But the current set up is the fuel line runs into the left barb of the 3 possible ports on the front of the carb. The bottom and right are capped off. So I should get another fuel inlet barb, install it on the right port and run a fuel line from that to the stock fuel return line? I will also get a vented gas cap.

Hey all, I'm trying to wrap my head around the fuel system after replacing a newer fuel pump a PO installed. Should I run a fuel return line with a weber 32/36 on a z24? I've seen mixed opinions. Second question(s), the fuel tank is not venting properly. When I remove the gas cap the tank is very pressurized. Why is this happening? I removed the check valve and was able to blow through both ways with a bit of effort, but nothing crazy. Should I replace the check valve? Did this pressure cause the fuel pump to fail prematurely/lock up? I also have the canister removed so the only thing b/n the tank and atmosphere is the check valve.

I've got a laser tach reading off a reflective sticker on one of the pulleys. who knows how accurate it is though

I've got an adjustable timing light ordered. I will see if I can get a lower idle after I set the total timing. If not, I'll pull the carb off and see what's in it. So I'm looking for ~800 rpm idle and 34-36* total timing? And the vac advance line is hooked up when I'm setting total timing?

Thanks Doctor. I have it set at 1000 rpm and 10* and it seems happy. Anything below 1000 it gets rough. I understand what you're saying for total timing. Is that procedure a necessity or is it ok to just set timing at idle?

Well I just found this after 1 second of googling. I'm not crazy. Will give this a try. "Set the Timing...Generally speaking you need a little more advance with a Weber than with the stock carb. A good place to start for most cars with Webers on pump gas is 12-14 Degrees advance at 1000 RPM idle and 36 Degrees total advance by 3000 RPM...This is not cast in stone and you need to make sure your car does not Detonate at these setting. If you get any detonation then you need to back off the timing..." Follow up: how does one measure total advance?

I'll start by saying I'm a total novice. Details: I'm trying to set the idle speed and timing to spec on a z24 with a weber. Hood sticker says 800rpm and 3* BTDC. Before adjusting, the idle was around 1200 rpm and it ran pretty smooth, not sure what the timing was. When I set everything to spec it runs a bit rough and sounds like it's misfiring (I'm guessing, I don't know what that sounds like...) It seems like it wants about 1000rpm idle and 5 or even 10* of timing. Any ideas? normal? Am I doing something wrong?

thanks for in the info everyone. I'm going to to try running it without the bolt and see what happens.