bog - Page 2

Tony Curcio · 05-25-2010, 08:36 PM

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 · 05-26-2010, 03:59 PM

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.

Dean Oliver · 05-26-2010, 08:20 PM

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

Alan Roehrich · 05-26-2010, 08:40 PM

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.

Robert Simpson · 05-27-2010, 06:02 AM

Tony you have a PM.

Quote:

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 · 06-14-2010, 06:07 PM

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 · 06-14-2010, 09:17 PM

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 · 06-14-2010, 11:01 PM

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 · 06-15-2010, 01:09 AM

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

Vic Santos · 06-16-2010, 04:18 PM

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.

05-25-2010, 08:36 PM	#11
Tony Curcio Member Join Date: Mar 2002 Location: West Chester, PA Posts: 271 Likes: 1 Liked 4 Times in 1 Post	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. __________________ Tony Curcio 1860 STK

05-26-2010, 03:59 PM	#12
brett3533 Member Join Date: Jan 2007 Location: maysville Posts: 116 Likes: 15 Liked 41 Times in 13 Posts	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. __________________ Brett McFarland A/S

05-26-2010, 08:20 PM	#13
Dean Oliver Junior Member Join Date: May 2002 Location: Stuttgart, AR Posts: 53 Likes: 1 Liked 0 Times in 0 Posts	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

05-26-2010, 08:40 PM	#14
Alan Roehrich Veteran Member Join Date: May 2006 Location: Murfreesboro TN Posts: 5,066 Likes: 1,487 Liked 1,630 Times in 378 Posts	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. __________________ Alan Roehrich 212A G/S

06-14-2010, 06:07 PM	#16
Vic Santos Junior Member Join Date: Dec 2008 Posts: 27 Likes: 0 Liked 14 Times in 2 Posts	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

06-14-2010, 09:17 PM	#17
Dave Jung Member Join Date: Oct 2008 Location: Surrey B.C. Posts: 135 Likes: 3 Liked 5 Times in 5 Posts	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 __________________ 6535 stk 81 Malibu K/SA

06-14-2010, 11:01 PM	#18
Danny Ashley Member Join Date: Nov 2001 Location: Marion,In. Posts: 266 Likes: 58 Liked 108 Times in 28 Posts	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

06-15-2010, 01:09 AM	#19
Paul Merolla Senior Member Join Date: Dec 2001 Location: Papillion, NE Posts: 606 Likes: 233 Liked 292 Times in 64 Posts	Re: bog As a future Q-Jet racer, I'm saving this thread for future reference...lots of very good info...thanks, fellas.

06-16-2010, 04:18 PM	#20
Vic Santos Junior Member Join Date: Dec 2008 Posts: 27 Likes: 0 Liked 14 Times in 2 Posts	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.