bog
 

I'm having a problem leaving the starting line that I can't seem to solve. My car is a Nova 350/270 that runs in H/SA. When I leave the line it flashes the converter to stall speed (usually around 4800 to 5000) but then instead of pulling on up to 2nd gear shift point it falls back to 4500 for a second and then pulls on up. This just kills the 60 ft times. I've tried two different carbs (Q-Jets) and they both do the same thing. Checked fuel delivery, tried different air cleaner bases and tried adjusting fuel pressure. Could it possibly be something in the torque converter. If I had stator trouble would it try to pull the motor down like that on launch. Thanks for any advice. .

Re: bog
 

try another convertor stator probably damaged during burnouts--Comp 387

Re: bog
 

Leaving off a two step, or from a high idle and flashing?

Re: bog
 

Alan: I'm leaving off the two step at 2900. I didn't mention this in the other message but on one pass when I put the Hedworth carb on, it didn't fall back. thought I had found the problem but the next pass with same carb it did it again. Thanks for any replies Bill

Re: bog
 

Could be a few different things including carb(very importanty) or a sprag problem or stator selection thing. If the converter is too tight it will pull the engine below it's peak torque and it will labor untill it gets back to peak and then take off, it will also be noticeable on the gear change, pulling the motor down below peak tq. Is this a "glide or a three speed set up? How high do you turn the engine? Do you have any dyno number's on the engine? Looking for peak tq. and how much.

Re: bog
 

Bill, has it always done this, or is this a new problem?

You might try changing your two step RPM up or down in 200 RPM increments.

The problem you describe doesn't really sound like a loose stator shaft.

It sounds like the converter MAY be about 200 RPM or so too tight.

You might also try tightening the secondary air door an 1/8 turn.

There is a small baffle that attaches to the top of a QJet, on the two screws behind the choke horn. If you do not have one, you might want to get one and try it.

You might try a little more timing on the starting line.

Re: bog
 

x2

Re: bog
 

A Q-jet problem....I'd bet on it.....

I sorted thru 3 carbs and had one that worked perfect......The other two gave me problems off the line no matter what I tried.....and I tried a lot of adjustments....

A Hedworth carb did not work for me unless the engine was cold.... once it was warm it did exactly as you described.....I bought one and hoped it would cure my issues and it did not......Driving the car off the footbrake was very difficult with the way the secondaries tipped in....

I got one from another racer that worked very well and was easy to stage and race with.......

Re: bog
 

Bill, i would bet it is a Quadrajet problem. Getting them to work perfect with a 2 step can be a pain in the but sometimes.

Re: bog
 

Ironically, I run the same combination, in a GSA Nova. I bought a new fuel pump, and relocated it. I also went with new fuel cell, upgraded from hard 3/8 aluminum line to 1/2 in braided, changed fuel pressures, carbs, all the same stuff you mention. My car did it off of footbrake, and worse when I two-stepped the car. Still to this day, the car doesn't always act right, especially in good, cool air. No matter the combination that I try, my car will only run if its really, really lean. I mean like shouldn't even run its so lean. But, if you fatten up the carb at all, it absolutely falls on its face. I eventually got the problem somewhat cured, by putting the rods back into the front of the carb. This definitely got my car to leave on the two step. But please, someone tell me what to do, or why my car can not be fattened up and run?

Re: bog
 

I had similar issues when I first put a good engine in our H/SA Camaro. It had been fine with our home-built 11.80 engine, but would practically shut off when the front wheels got airborne with the new power. We tried two professionally prepared carbs, borrowed a known working carb, three fuel pumps, two regulators, pressure up, pressure down, float level up and down, and on and on. We could make it consistent with extreme jetting, but it wasn't nearly as fast as it should have been.

One day I unbolted the fuel pump while the fuel lines were still on. As it dropped downward, I heard fluid moving when gravity took over. It was like in the cartoons, when a lightbulb appears over the character's head.

I re-mounted the pump a lot lower. The pump inlet is now three inches below the the fuel cell outlet, and the pump body is visible under the rear valance. The inlet had previously been about an inch below the cell. Picked up 3+ tenths the next weekend.
Don't know if the same thing will work for Bill or Chad, but it costs nothing to try.

Re: bog
 

q/jet carbs are very finicky its important to have enough fuel pressure to the regulator to keep the fuel going forward on launch and not to much that your regulator can`t control the pressure from the pump. if it can`t the regulator may bounce or pulse allowing fuel to slowly blow by the needle and seat causing richness for launch making you lean down. I am having similar symptons also w/different combo. hope this helps. magnafuel is the best regulator on market for high pressure pumps. wade owens got my attention from his previous post about moving down his fuel pressure.

Re: bog
 

Assuming the tune up is at least close (and I can't emphasize that point enough), the main causes of a Q-jet bog typically are related to:
- Too much fuel pressure. Do not depend on one of the little small online gauges for this. Double check your gauge with a second gauge.
- Air valve tension too loose. Keep in mind that adjustments should be made in small increments, like 1/8 turn at a time.
- Weak fuel system. Simple test. See how long it takes your fuel system to fill a one gallon container. Most SBC stockers with a Q-jet should flow a gallon in no more than 30 seconds through the entire fuel system, regulator and all.
- Improperly sized needle/seat (too big or too small) and/or improper float adjustment.

This is not an all inclusive list, but it is some of the more common things. A problem that I see too often is that a racer will just assume these things are good rather than take the time to actually check. Hope this helps. Give me a call if you want to talk more about it Bill.

Dean

Re: bog
 

To add to what Dean said, I have seen people leave the filler block out of the top of the float bowl in a QJet. They think they're gaining float bowl capacity, but they are not. Do not leave the filler block out, it keeps the fuel where it belongs.

Re: bog
 

Tony you have a PM.

Re: bog
 

Bill, I've been flogging Q-Jets for 23 years in my SS car and I still learn new stuff all the time! Your bog problem is most likely too much fuel during the launch. I see it a lot in EGT traces. When the mixture is just right the EGT's continuously climb during the run and the RPM stays flat at the stall speed and then increases to the 1-2 shift point. When it is too rich the EGT's go down or stay flat after the launch and then go up--RPM sags at that point (bog).

First: you need the right jets and secondary rods for max power from dyno testing (you would be surprised how many Q-Jets don't even work on the dyno).

Second: tune them for the track. "G" loads and wheel stands totally change Q-Jet metering. Generally the secondary rods should be leaner than the dyno rods and primary jets should be OK plus or minus 1 size. Idle and driveability are another problem which you can address later.

Finnaly: once you are close FLOG THE HANGER and the SHAPE OF THE RODS; they control the A/F ratio during the opening of the air valve where the bog typically happens. The air valve should be fairly tight; too loose and you get a lean bog and it is hard to tell the difference without instrumentation. Another common problem is that many racers think the more open the air valve the more power. This is only partially true for very high powered engines. An air valve that is too far open will definately lean out the fuel curve at low RPM. Most engines benifit from closing the air valve and it will help make sense of your test data. The choke pull-off should take about 1 second.

All of the above assumes your fuel system is adequate and all testing is done on the same day! Weather, especially humidity, has a big effect on metering requirements depending on your application.

Also I've found that no two Q-Jets are the same!

Like I said I've been doing this 23 years. I am almost there!

Good Luck! Vic Santos

Re: bog
 

My car does this exactly as you guys have described. I even have the torque converter out right now and my guy just told me today, that there is nothing wrong with it. So I am on the carb thing now as well. What should the fuel pressure be? What is too much and what is not enough? Same scenario, does it when foot braking, and worse when trying to launch on the 2-step. I was sure it was converter. thanks, Dave

Re: bog
 

Although most bogs are carburetor related, many aren't. Just this past week a racer called with the same problem as described and although he had two other builders work on his Q-Jet he wanted me to look at it. Knowing there wasn't enough time because he wanted to go to Joliet, I told him if he would pay the shipping that I would let him use one of mine for the weekend. He called today to say that the problem still exsisted and this made him look elsewhere. He found that his intake gasket was leaking on the bottom side. This is not an uncommon scenario in the carburetor business. I've had racers who were convinced they had a carb issue only to find out they had a bad ground wire on the fuel pump, an ignition problem, epoxy came out of the intake, insufficient fuel delievery, etc. As stated earlier, getting a Q-Jet to work off a two-step can sometimes be challenging. Whenever a rev-limiter is used, a rich condition occurs when the button is released. I've seen this on the graphs of my customers who have the RacePacs with wide-band oxygen sensors. It will drop down on some cars to 10.5. Once this condition is corrected the car will leave the line a lot cleaner. Bill and Dave, you could very well have carb issues but don't rule out other areas.Finally, I must say that I enjoyed Mr. Santos' comments especially where he said no two Q-Jets are the same. Amen brother! I too am still learning and keep trying to build a better mouse trap. Danny

Re: bog
 

As a future Q-Jet racer, I'm saving this thread for future reference...lots of very good info...thanks, fellas.

Re: bog
 

Bill, in my last response I suggested tightening/closing the air valve and testing different hangers and secondary rod shapes. Here are the reasons.

The launch is difficult to sort out using a Q-Jet and every application is different. The first thing that happens when you let go of the button is "G" loads are applied to the carb; up to 2 1/2 G's depending on power and weight. The fuel is pushed back in the bowl and wants to stack at 45 degrees for 1 G and 63 degrees for 2 G's. It doesn't really happen this bad because of all the stuff in the bowl but you get the idea. As fuel is pushed back in the bowl it raises the float and momentarily SHUTS the inlet valve until enough fuel is consumed to lower the float and allow more in ( approx 0.3 sec ). In my car it then takes 1.1 sec before the bowl refills and the float shuts off fuel again ( about when I land from a wheel stand ). Fuel flow does not become steady until 3.5 sec into the run. At the point where the inlet valve reopens it is critical to have a fuel system with HIGH FLOW AT PRESSURE otherwise you will go lean.

( Talking about pressure I've tested 5 fuel gages and a transducer with a 183" column of water ( 6.61 psi ) and none read the same. The worst was off by 1.5 psi! )

In my testing I've found the amount of fuel IN the bowl is critical to the launch. To control this I've made the bowl as big as possible and I've changed float level until I got the best EGT & G level traces and the best 330 ft ET. ( many people feel the higher the fuel level the better- not based on my testing )

The fact that the fuel is stacked at the back of the bowl causes another problem-- the engine needs a leaner rod during the launch than at the other end of the track where the fuel level has stabilized at a lower level. The end result is the secondary rod is usually a compomise based on 1/4 mi ET. This usually results in the rod being too rich at the launch and too lean at the top end. This can be offset, somewhat, by using leaner hangers and short tip sec rods to lean the mixture during the first second when the air valve is opening. This can only happen when the air valve is closed when on the two-step. The only way I've been able to science this out is to make sure the air valve is closed when on the two-step. When the air valve is open on the two-step you have a 750 cfm carb wide open at a low RPM and you have to do lots of other things to richen the mixture since there is very little carb signal

If the air valve setting is too far open you will have to run richer rods and jets to offset the reduced carb signal and the launch will be WAY too rich.

Once you get close to the right set up you very seldom have to change primary jets or secondary rods more than one size and change only the hanger.

I know there are very succesful foot brake cars and my hat is off to them. I tried it for 5 years and couldn't get it right.

Re: bog
 

bill, did you fix your problem,if so what was it?

Re: bog
 

Check your choke pull-off also.

Take the Vacum Line off the carb,push in the arm ,and put your finger over the vacum hose.

Then let your finger off the vacum line and make sure the arm comes out fairly smooth, or just put a new one on and make a run.

Re: bog
 

Re/ the pull-off, on my car I found it important to bend the link so that, when the pull-off is fully pushed in, the air valve can only open a hair, maybe .010-.020". There is an enrichment circuit that is exposed to airflow as the front edge of the air valve begins to open which could cause excess richness if it is exposed at idle or when you're up on the converter. I cured a problem on my car by bending that link so that the air valve could not begin opening until the pull-off began to relax as vacuum dropped. My understanding is that this hole acts as a secondary accelerator circuit, drawing fuel into the secondary side to transition until the main circuit is providing sufficient fuel. One of the carb guys could explain this much better, but it is another Qjet thing to check.....

Re: bog
 

Note : Bill said he's leaving off a two step so the carb butterflies would be WFO on the line.
The choke pull off (vacuum break ) doesn't have as much importance in that situation.
The secondary accelerator pumps are made to function as soon as the flapper starts to open. In this situation , it would already be open or pulsing it's way to open.

Re: bog
 

No, I haven't fixed it yet but it's not from lack of trying. I've changed or worked on everything that has anything to do with the car leaving the line and It still comes back to haunt me .I thought I had it fixed at the pro-am race in Baton rouge: Ran fri- sat- and sunday with no problems.Car had good 60' ft times (high 140's) and then at my last pass in elim's it bogs 300 rpm's, goes a 153, and I lost. I haven't ran it since but I'm reasonably sure it's fuel related. Thanks for reply on air valve ; I checked to see if it's working but I didn't check what you said you looked at. It's hard to get something lined out when you don't race a whole lot.

Re: bog
 

Do not think this is crazy, however are you absolutely, 100% sure your foot is staying in the gas? We chased this problem for 2.5 years only to find that the two step made the carleave so hard (picked up .05 in the sixtey) that the seat gave enough for the accelerator to move. Just a thought.