bog

[Chad Mahlosky]

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?

[Tony Curcio]

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.

[brett3533]

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.

[Robert Simpson]

Tony you have a PM.

Originally Posted by Tony Curcio

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.

[Vic Santos]

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

[Dave Jung]

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

[Danny Ashley]

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

[Paul Merolla]

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

[SS 230]

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

[Monte Howard]

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.