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Leaky Qjet

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leiniemann

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"Recently replaced the plastic

"Recently replaced the plastic float with a brass and along with the other internal parts in a Rochester Q-jet. Upon installation and first test It fired right away but soon stalled. There was fuel running into all four barrels. Disassembled and found that the float was set a little high, which would cause flooding. Reset using a digital caliper correctly leaking and it is a couple thousandths low if anything now. tried again and it ran much better, but I noticed that there was droplets of fuel dribbling out of the primary discharge nozzles even when the idle mixture needles are in all the way. Have disassembled a number of times to make sure that float is right and that the needle is free to set properly. Fuel level seem high so I made sure that the new seat was tight, it may have been a bit loose. Even with seat tight, needle seating correctly, mixture needles are in all the way, it still leaks and dripples. Any thoughts or suggestions. I don’t know how many more times I can take the top of the carb off without trashing the gasket.

Thanks in advance."
 
makomark is refering to my thr

makomark is refering to my thread. You will learn a ton from it. I have a question for you. If you unscrew the mixture screws 3-4 turns does the dripping stop?
 
"As for the source; Kit was fr

"As for the source; Kit was from Sierra.

Parts changed; Float, neddle, seat, seat gasket, acell. pump & spring and check ball.

Yes bowl was washed.

Have read the above thread and it sound like the same problem. I will make some checks."
 
"Having seen a recent Sierra k

"Having seen a recent Sierra kit so can't say if they use the ethanol tolerant materials - a short bit of time will tell.

Did you test the needle and seat for leakage with a vacuum pump? Check the accel pump check valve for leakage, too?

Did you blow out ALL the bowl passages with compressed air after the bath? If you didn't pull the idle tubes, you should run a small fine wire (less than 0.030" OD) thru them to make sure they are not restricted - crud loves to collect under them.

If all that's good (and what's ID'd in Jim's thread) I'd bet you need some bypass air at idle.

The wedge plate will help the carb function in many areas, especially economy in an in-line installation."
 
One question I meant to ask. W

One question I meant to ask. When I pulled the choke pulloff tube to attach my vacuum gauge the engine speeds up. Is that normal. On a pontiac website I looked at they said that is a sign that not enough air is getting in. Is that true?
 
"Jim:

Not necessarily. You

"Jim:

Not necessarily. You can pull that hose to test to see if adding idle bypass air will help though. Its not a large passage and it has no adjustment so the test is "coarse."

If you pull the hose, the engine should speed up, at idle. with the hose off, you can back out the idle screw to lower the throttle plates some. If you can get the throttle blades low enough to stop the drip from the main nozzle, you know you need to add an air passage at least as large as the open port. This may have to be repeated a few times.

I pulled another AFUA - should have typed "having NOT seen a recent Sierra kit..." earlier. Sorry"
 
"Well before I pulled the carb

"Well before I pulled the carb off I tried opening the idle mixture screws. One full turn on one and dripping stopped as long as RPM's were at about 600 or higher. No matter where I set the other one it would still drip no matter the RPM's. So I started over with disassembly and making sure all passages are clear. One thing I had not touched in the past was to take out the plug in a passage that goes through the side of the float bowl assembly above the fuel inlet and leads in to the venture that has the drip. The plug came out fairly easy. It also appeared to have had Teflon tape on it. I reinstalled plug but used a thread sealant paste instead.

The down fall with Teflon tape is because Teflon is a lubricant which lets you drive the threads deeper, it also acts as a lubricant to let the fitting vibrate out."
 
"There are a few more drawback

"There are a few more drawbacks to teflon tape use in a fuel system. That plug should have a tygon hose going down to the fuel pump. It is the "fuel dump" path in case the fuel pump's diaphram ruptures. make sure all those get reconnected.

Was the drip out of the main nozzle or that hose barb(plug)? If out of the barb, time for a new fuel pump and an oil and filter change. There shouldn't be ANY fuel in the tygon tube.

was there any crud in the passage between the idle tube and the main jet well?

What did you set the float at?"
 
"Yes the drip is from the main

"Yes the drip is from the main nozzle.

How do you pull the idle tubes? I have run twisted copper wire down them.

I covered the bowl assembly with a white shop towel while blowing and there were some grayish spot, so I would say that there was some more crude that came out of one or more passages.

Neither of the carbs have tubing going back to the fuel pumps, but I have seen an un-used fitting on the fuel pumps, this must be were the tube goes on. I will certainly get them hooked up again. The last thing I need is a bilge full of fuel. Great pointer, thanks you.

Float set at 9/32" per spec sheet in kit."
 
"I'll email you a picture

"I'll email you a picture later today...as they say one is worth a 1000 words. The caveat is that if you pull the idle tubes you need to realize they are very soft and easy to bend. Replacements are available but best obtained from a junkyard carb. (Same part in the auto or marine versions.)

The best secret to the whole operation is a propane torch with an adjustable fine tip.

If you're gonna pull them, I'd also get a set of 61-80 wire drills. I think 0.035"ID is the preferred (modified) size for a 'stock marine" big block"
 
"Try this first: With the eng

"Try this first: With the engine warm and idling, take a hammer and tap strongly on the carb body in a horizontal fashion (not up and down). If the idle speed changes in any way, the needle and seat on one or both of the floats are not seating correctly. You should be able to pound on it a dozen times over with no change in idle speed or quality.

Jeff"
 
"Most resent attempt was to ta

"Most resent attempt was to take top off and use a smaller dia. Wire in the idle tubes. It took a bit but I was able to get the smaller wire all the way down the tubes and after working the wire a while I could feel there was less of an obstruction. The side that would not stop dripping, now it dose not drip if idle mixture screw is out 1 ½ turns, the other is good at 1 turn.

I am going to add some Seafoam and see if that helps clean any remaining build up, unless there is a better product to clean out build up.

I am going to stay away from Jeff’s hammer method, because I don’t always trust myself with a hammer when something is not going well, if you know what I mean."
 
"Most resent attempt was to ta

"Most resent attempt was to take top off and use a smaller dia. wire in the idle tubes. It took a bit but I was able to get the smaller wire all the way down the tubes and after working the wire a while I could feel there was less of an obstruction. The side that would not stop dripping, now it dose not drip if idle mixture screw is out 1 ½ turns, the other is good at 1 turn.

I am going to add some Seafoam and see if that helps clean any remaining build up, unless there is a better product for the build up.

I am going to stay away from Jeff’s hammer method, because I don’t always trust myself with a hammer when something is not going well, if you know what I mean."
 
"with the "both floats&#34

"with the "both floats" I'd say that was a reference to a non-qjet carb.

glad to see yoou found something in the tubes...buildup up them is a big reason for poor idle. quicksilver's 'power tune' is great for removing carbon based build up but I think the best was to clean out the crud is to pull the tubes and blow it out.

It could be corrosion vs varnish or other build up...I've seen a few lately. I'd guess the big reason is the fuels evaporating so fast leaving any 'stuff' at the bottom of the fuel chamber. when it gets wet again, the first restriction is the bottom of those tubes.

glad you made some progress"
 
"I don't trust myself with

"I don't trust myself with a hammer sometimes either, especially when I really ticked off.

The wire cleaning of the jets tells me that your carb needs a thorough soaking in carb cleaner, for the internal passages are also gummed up. Still, you might get lucky....

Jeff"
 
"Jeff,

Just wondering, will

"Jeff,

Just wondering, will a thorough soaking in carb cleaner remove the black paint on the body of the carb. I have an extra Q-jet that I hope to clean and rebuild but was thinking of just using a spray can of choke and carb cleaner.

And where are these "idle tubes" located? Not trying to hijack this thread, but perhaps add to it.

Thanks,
Erich"
 
"It might take the paint off--

"It might take the paint off--you can put it back on, of course. The idea is to take the gunk out of the passages. The idle passages (not "tubes") are drilled in the carb at right angles and covered with lead plugs.

Jeff"
 
"Depends upon the cleaner and

"Depends upon the cleaner and the paint and how it was applied. For a 1/2 hour, probably not; overnight, most likely the paint will softenup.

A q-jet has idle tubes that are pressed in, with a vertical orientation. With the air horn removed, look at the primaries. on the 'inside' of each will be two small brass colored circles. One has a 'recessed cup' in it, the down channel restriction. the other will be close to flush and have two concentric brass rings - these are the idle tubes. The idle air bleed sits 'in between' these two metering devices."
 
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