cfm carb for Buick 350...places sell 600 and 650...is that enough?

The rear one sometimes is a choke pull off . Follow linkage.should be manifold vacuum from what I remember.

 

Well, it seems to be a choke pulloff. It is now hooked up to manifold vacuum, but no change in bog when I floor it. The alan head vacuum screw inside the secondary pulloff...


...is turned all the way in (clockwise), which I believe is restricting maximum, and I have tightened the spring for the secondary flaps another full turn. Still getting some bog.

 

Best way I found to get rid of the 'bog' is to tighten up the upper butterfly flap spring so it takes more to open them up. You may have to twiddle and fiddle to get it just right. This should prevent them from popping open too abruptly when opening up the bottom mechanical secondaries. The butterfly flaps should transition smoothly into full throttle to eliminate the bog. The rebuilder of your carb should have already done this if it was 'tuned' for your application rather than just a general, generic rebuild.

Another trick is to notch the butterflies so some air gets in before they open up, allowing some gas to get drawn out as they start to open. This is said to alleviate or eliminate the 'flat spot' in the transition.

Information on this can be obtained by doing some research on the internet, or by asking one of the Qjet gurus here on this board (I don't consider myself to be one of them). Some may advocate doing this while others may not, or they use a different method of achieving a similar end result.

Start by stiffening up those butterflies though. If that solves your problem, you're good to go.

 

how old is fuel filter and fuel pump. could be lack of fuel in bowl. I usually loosen the secondarys but that's a good running motor . change filter and see if it improves. filters are cheap and worth changing regularly

 

Is there a way to test the smooth transition, (or see it) or can I only drive and see if it bogs?
The builder did not do it.

---------- Post added at 08:37 AM ---------- Previous post was at 08:33 AM ----------

The filter in the carb inlet is new, only a few thousand miles on it, the mechanical pump was replaced about 6k miles ago, maybe 2 years.
Lack of fuel in the bowl is something else I will have to consider if the flaps dont take care of it.
But I hate to dig into the carb, and have almost nil knowledge of how to. PLUS I paid quite a bit to have the thing built.

 

I scanned through here again. Lets try to get this quadrajet tuned. Need some information though.
What is your carb number?
Lets work on your bog fix. I notch the secondary air flaps on the Buick carbs. But because the hole is above the flap.
What size are your secondary rods!

Also, was the carb built for your current engine specs?

 

Thanks for the help guys.
I was reading on another site that 7/8 turn from slack is all that should be needed for the secondary spring, since mine was already tighter than slack and another full turn didnt make much difference its got me wondering.
I do have a set of secondary flaps with a hole in them, before it was rebuilt it had those on it, I put some without a hole on when I sent the carb to get built, I had heard the hole was a no-no. The builder never mentioned it.
I think I will put those back on and try a run.

Cliff R built the carb to my engine specs.
I should have the sheet from it but need to find it when I get home from work, that would say what size rods. Carb number too.

"Too much air/too soon or lack of fuel", no I dont know how to tell the difference.
What I would describe it as is, a sort of sputter, then build to power. Slow accelleration is fine, even a 3/4 throttle punch can be ok, but floor it down and the problems begin. (Pretty much when the 4bbls open)

The alan head screw in the vacuum pulloff seems to be something not everyone has?

I really wish I could see a video of the flaps while driving, but thats not do-able.

 

The carb number is 7041544, and near it, it also says IH 1621
I took a few pics of how it sits right now.







I haven't made a longer choke rod yet since putting the 1"spacer in.

 

The 'bog' (a common problem with the Qjet, hence the nickname 'Quadrabog') coming from a loose spring is a result of the upper butterflies popping open too soon without any transition, causing a sudden surge of air with no fuel. The engine will sputter, even die outright, with RPMs keeping it spinning until the vacuum can draw fuel out of the jets and then it kicks in.

There is no secondary accelerator pump. They can't just pop wide open with no transition.

It's sounding to me like your tension spring is just barely putting any pressure on it. If it has to sputter and build to power, that sounds to me like they popped wide open and the engine has to rev to compensate for all that CFM to the point where it can actually use it.

They should slowly open up as the engine needs the CFM. Your power will improve greatly when you get those adjusted properly.

Just goofin around one day I wired my butterflies open and would go down the road flooring it and listen to the whhaaaaahhhh as the engine's RPMs slowed down, like I just turned the ignition switch off. It would do this for a few seconds, depending on the RPM, and at a low enough RPM, it would never kick in, it would just 'whhaaaaahhhh' all the way to it stalling out lol. When it DID catch and start revving, it wouldn't have much power until it was practically wound out.

Amazing the things you can learn just by goofing around when you're a kid.

What does this little lesson tell us? Too much CFM, too little fuel. This is an extreme case of bog, purposefully imposed.

Tighten that butterfly dude! (pssst...your butterfly flap is open)

You'll have to tweak it a bit maybe to get it where you want it.

 

The butterfly act as venturis to pull gas from bowl.if you open butterflies you will see an adjustment screw at the linkage housing.takes a small flat tip screwdriver but under it as a Allen lock screw that must be loosed first.the screw there is spring loads the butterfly valves for tension against the vacuum that pulls on them. Maybe alittle more tension .how. did it run before spacer?is spacer centered? I have had a problem with spacer gasket being cut smaller than throttle plate hole and holding carb from opening fully. Something to check.

 

It was doing all this before the spacer. This was actually one of the reasons he started this whole thread, then it got sidetracked a little and now it's back on topic.

So it's not the spacer.

By the sound of it, and based off previous experience with Qjets on stock Buick 350's, I'm 99.99% certain it's butterfly tension.

Yes, the butterflies operation are twofold: they allow for gradual introduction of air and at the same time control a lever with a 'cam lobe' on it that lifts 'needle valves' up from the fuel bowl. As this action performs as one unit when tied together, as the butterflies begin to open, the vacuum will draw the fuel up out of the bowl past the valves and into the huge plenum area for mixture/atomization.

As long as this happens progressively all is well. If they pop open too soon, there is no time for fuel to be drawn out, so you get a big surge of air with no fuel. This is what causes the hesitation or sputter, not-so-affectionately referred to as 'bog'.

 

What about this though?
I was reading on another site that 7/8 turn from slack is all that should be needed for the secondary spring, since mine was already tighter than slack and another full turn didnt make much difference its got me wondering. How tight before it breaks? Also how does the scres inside the pulloff vacuum work with it? I believe that is as closed as it can get (clockwise)...

 

Vacuum will hold them closed until the lower secondaries start to open, then it's up to the spring tension.

Check to see if the spring hasn't broken or isn't misaligned somehow. It could be a bad/incorrect spring with improper tension?

Those butterflies are popping open too much too soon for a reason.

 

New information:

I wired the secondary flaps shut. Then went for a drive.
The "bog" was worse. I expected it to be better since the flaps could not flip open too fast?
Does this conform or rule out anything?

 

Are your primary squirters working properly? If not,you need a new accellorator pump that squirts raw gas when you hit the peddle hard or fast to give the engine the extra fuel for when the throttle blades open suddenly causing a huge vacuum drop.


Derek

 

They do squirt I'm not sure how to measure properly. Someone mentioned floats could be prob? With my luck it probably is since they are inside the dang carb.

 

Yeah,I seen that mentioned,and Ken is probably right(seeing how he builds carbs for a living) if the bog isn't caused by the secondaries,or the acc. pump not working.

Looks like you'll need to learn how to check and set a Q-Jet float.o No: Its not rocket science,if you have any mechanical abilities it shouldn't be to dificult,if not,take it to some one that can do it for you. GL

Derek

 

Look down carb with a flashlight and see if both sides squirt with you work throttle.how is the distributer.timing correct?vacuum line connected to ported vacuum? Is mechanical advance working an not to tight? any possible vacuum leaks?pull filter and look inside with flashlight for rust or other junk.if junk got into filter it could be in carb too.

---------- Post added at 08:19 PM ---------- Previous post was at 08:15 PM ----------

Also start engine and look down carb .see if gas is dripping down carb.

 

Diagnosis would have been a bit more accurate if this new information was disclosed earlier. Most 'bog' comes from butterfly flaps, but if you'd have said it bogs without even having to open the secondaries, there would have been better advice.

Sorry, I'm not batting too good of an average lately. Maybe I'll stop giving advice for a while.

Just trying to help.

The way you described it earlier it sure sounded like the traditional 'Quadrabog' syndrome.

I would certainly be taking that 'rebuilt' carb back to the rebuilder so he can finish what he started.