Qjet tested with questions

[72_EB]

A little off the line bog and some irratic idling, a wee bit of intake or exhaust backfire (more like rumble, I don't think the typical Qjet rumble though).
Think I need to do the Autozone 4 hole adapter like Motoman did? Will this help?
Would it help to seal the intake to carb and gaskets with some good copper paint?
Carb runs nice when warm? A little off idle stutter though.

Also, think I can get by running it forward instead of backward?
I hate to have to make a backwards bracket.

Any ideas out there? Man, I love this carb already. Might try it out tomorrow at Lake Geneva Raceway if I'm feeling brave.

 

[bnk70bronco]

It sounds like you are having the same symptoms that I am having. I just got mine on this week and have been playing with it today.

Can't get a steady idle. I don't have a vaccum leak that I can tell. I sprayed carb cleaner everywhere and it never increased the idle.

How do you intially set one of these bad boys up?

I am going wheeling tomorrow so I will get to test it out.

 

[ballistic64]

The first thing Id reccommend,if you didnt do it already,is to inst. a carb kit if its a used Qjet.As for your idle problem you should be able to screw both your idle mixture screws in (just so they seat,not tight!) and it should stall the engine.If it doesnt your primary throttle plates are adjusted to far above the idle needle hole (curb idle) and are getting fuel from the off idle port also.Properly adjusted your engine should maintain an idle with just the idle needle hole (curb idle) below the primary plates,as you slightly step on the gas the primary plates will pass the off idle port (which is a bigger port than the idle needle port and supplies more fuel) and more fuel is supplied.Once these are adjusted correctly you may wind up testing and adjusting the power system,this is controlled by manifold vacuum (internally).
During conditions of high maniflod vacuum (idle etc.) vacuum holds this power valve down,during low vacuum conditions (flooring it,heavy load) vacuum drops off and a spring pushes the valve (main metering rods) up allowing a richer mixture of fuel to enter the main metering system.The reason I suggest a carb kit
(along with a long thorough soaking in carb cleaner) is because the main metering system (which the power valve is a part of) controls fuel metering from off idle to wide open throttle conditions and any dirt or gunk in the system is going to affect the metering system especially if theres crap built up in the air bleeds.If your carbs new, you dont need to worry about this and can start adjusting as needed.Start with your idle system and go from there.

 

[Rustytruck]

I agree with the above most problems I have seen with an off idle stumble is from the idle speed set screw is set too low and the idle mixture screws are used to balence out the mix to give a proper idle speed. Try raising the idle a couple of hundred rpm and use the idle mixture screws to bring the idle back down. Basically right now your butterflys are to closed and need a little more air and then adjust the fuel mixture. This is entirely backward from how you set all other carbs but it is how it works.

 

[72_EB]

Here's the progress.
I ditched the other space and fabbed the Autozone one this weekend. JB Welded the bolts in the adapter and just bolted it up 5 minutes ago. Idle seems improved, but I did get one intake backfire. D@$M!!! Could still be an air leak somewhere. I'm gonna try and take if for a spin later today for some more results. I'll let you know what happens.

 

[BB8s]

Check the gaskets - I had similar problems - and took it to a local carb guy who showed me how the different years of Q-jets had different gaskets - he swapped mine for one that had individual holes and did not cover the small ports right in front of the primaries....
I've had my Q-jet on for 3 weeks now - and it is smooth as silk.
From idle though acceleration - pulls like a champ.
I originally started with the open plate - like the ones in BC's kit, but changed and fabbed a 4 hole adapter - it made a huge - as suspected.
Last weekend I climbed and descended a hill / then drove way off-camber - these situations would have made my 2 bbl autolite and the 4 bbl carter cough and die. The Q-jet never faultered

 

[velpoe]

I have the typical adapter that you get at Advance and have heard of potential problems with them running correctly. Does anyone make the 4-hole adapter commercially? I know people have fabbed some, or improved the type I have...just curious. I still don't think my qjet is dialed in correctly.

 

[bnk70bronco]

Mine definately needs some work. My right idle mixture screw won't effect the engine running at all. All the way in or out it never changes. What does that mean?
It seems to have no power when going like 55 mph and I get on the gas.
It did do pretty well on the trail when it was idling ok but it died a couple of time right when I got to the top of a hill. I know it is not working the way it is supposed to.
Where should I start to get this thing going?

 

[bnk70bronco]

I don't quite understand what ballistic is talking about. Are those things inside the carb or something I can adjust on the outside to get the idle working correctly? Thanks for any input.

 

[ballistic64]

Is your carb new - used? Have you cleaned and installed a kit?
Adjusting one screw in or out wont necessarily starve the eng. for fuel,but both seated lightly in should.If it doesnt,something isnt right.Start by seating both needles in and back them out about 1 1/2 turns.Start your engine and screw your idle stop screw down to 550-600.Hook up a tach and adjust one idle needle at a time to obtain the highest RPM you can get,first screw it in until the RPM starts to drop,then start backing it out until you get the highest RPM you can with that needle.Dont go farther than necessary to get your highest RPM reading.Repeat this with the other needle.You may need to do each needle a couple times.Once youve got the highest RPM you can,back your idle stop screw down to the necessary RPM.Usually an auto trans. requires a higher idle than a manual.Other than the jets,theres not a lot a person is going to do with the main metering system without special equipment.If its bogging on you when you get on it its possible you have a gummed up power valve.There are certain things you can do with the power valve (different spring rates,involves either finding different spring or cutting or lengthening the existing spring).Shortening the spring will lower the required vacuum to hold it down (shut),this usually is a mod made for better fuel economy.Installing a longer or stronger spring will raise the required vacuum to hold the power valve down (shut) resulting in the valve opening with less load on the engine,but a fine line,so to speak has to be walked here because it can take your fuel mileage to hell.Go over your vacuum lines and make sure nothing is leaking,this includes your vacuum advance on your distrib.,mod. valve on your trans if your running an auto,vacuum breaks on the carb and brk booster if you have one or anything else a vacuum line runs to,then try your idle adjustment.You may have to,as posted above,check into your mounting gasket for proper application as there are several different configuations of the gasket for Qjets.

 

[72_EB]

Boy, this tool sure makes it easier to adjust those idle screws!
$8 bucks at Napa this morning.

Got a nice smooth idle, but can only get 14-15 psi out of the vacuum gauge. Anyone else with a low vacuum reading?
Still need a spin around the block and test it out.

Also, trying to find the ported vacuum advance port.

My guess is the one on the lower right there. All the other seem like straight vacuum. This one I feel nada at idle. Maybe something with the throttle kicked. Hard to tell. Anyone?

Here are some more pictures.

I know I need to get some vacuum caps. Looks bad, but works.

Oh, which way do I turn the electric choke to make it open faster? Clockwise?
Thanks gang! I'm loving finally having a four barrel! ZOOM ZOOM!

 

[72_EB]

Oh, one more thing.

I've got my C4 and booster straight off a fitting on the intake and not the carb. Good?

Thanks gang!

 

[ballistic64]

Your right the one,your guessing for the distrib. is the timed port and shouldnt have vacuum at idle.

 

[Howdy]

yep...thats the tool you need.

Those are some crazy vacum plugs you have coming off that carb...LOL While you were down at NAPA you should have just bought some of those rubber plugs. makes it much easier.

 

[bnk70bronco]

I played around some more tonight and I think that I have a vacuum leak around the intake manifold and engine. I sprayed some carb cleaner on both sides and it raised the idle both times. Plus, my idle mixture screws really aren't making much of a difference on engine speed or anthing.
My carb runs like total garbage right now. I hope the intake getting resealed will fix the problems because I am starting to get irritated.

 

[Rustytruck]

As for the problem of the carb topping out at 55mph it is probably due to mal adjustment of the secondary air valve. (the spring loaded butterfly at the back of the carb) the air valve shaft on the passenger side has a screwdriver slot on it and under neath the carb top on the passenger side you will see a little allen screw the locks the adjustment. back the allen screw a little and adjust the tension on the shaft with the screwdriver just a little, like 1/16th of a turn and then tighten down the allen screw. this brings in the secondary side sooner and is a necessary adjustment on these carbs mainly due to them comming from a much larger engine. the 302 doesnt suck as much air as a 350 Chebby so the spring tension must be set slightly softer. Go too soft and the secondarys come in too soon and bogs or gets poor fuel mileage. too much tensin and the secondarys will not open and supply fuel as needed and acts like a 50 mph governor.

 

[72_EB]

I can't find this adjustment screw on mine! AGH! Anyone snap a quick picture? My secondaries are not opening at all!

On a good note, I got my drop air cleaner bottom from the UPS man today.

Carb runs great. Until I get out on the road! Agh. Hopefully, I solve it this weekend! I want to go wheeling!

 

[ballistic64]

I can post a pic tonight.When your facing your carb on the engine,the adjustment rustytruck is talking about is up under the left side of the secondary throttle valve (upper butterflies) shaft on the outside of the carb.

 

[72_EB]

AH HA! Just found one!

OK, cool! But one more question if I "goose" the throttle with the secondaries adjusted properly, will I see them opening? Or, I have to be driving with the motor under a load? Will the secondaries butterflies open all the way?

Thanks!

 

[ballistic64]

If you goose it to full throttle youll probably see them begin to open,youll probably have to play with that adjustment a little bit to get it where you want it.It doesnt take a whole lot of spring tension to change the setting.