Bogging questions - Team Camaro Tech
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post #1 of 31 (permalink) Old Jan 7th, 02, 09:40 AM Thread Starter
 
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I have a ZZ4 motor with TH350 and 4.10 gears. I am having a major bogging problem when the gas is stomped (at any rpm). I initially set the timing at 10 BTDC and used an Edelbrock Performer 750 CFM carb. Had popping, and bogging. Adjusted accel pump linkage position from small squirt to big squirt. Got a little better but still not good. Adjusted idle mixture up and it got a little better. Still bogged for several seconds when you stomped on it . Finally went to max rich idle adjustment and still had bogging. Then replaced carb with my old q-jet. Having same problem with bogging. Adjusted timing to 4 BTDC and the engine seems to have less power and even seems to be missing. Here are my questions:
Is more advance better or worse for "bogging" issues? Should I try more than 10 degrees advance?

My timing light seems to skip strobes at idle. Is this normal or am I really missing sparks?

Any suggestions?

Thanks,
JT
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post #2 of 31 (permalink) Old Jan 7th, 02, 10:07 AM
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Secondary air door is opening too fast. Adjust for more spring tension to keep door shut tighter.

Set everything back to what you had before started, use vacuum gauge and set for max vacuum reading. Should be nice and steady reading, adjust idle mixture screws and timing for highest reading, may have to turn timing back to 10 degs.

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post #3 of 31 (permalink) Old Jan 7th, 02, 12:12 PM
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Based on what you mentioned about the timing light thing...open the distributor and make sure everything is clean and not worn...and make sure the wires are nice and properly routed...make sure plugs look good..
Make sure to have an advance curve of about 1000 to 2800 steep slope...ending somewhere around 34 to 36 degrees...or what ever you can get to without the pinging...
I would use a base timing of 10 to 12 degrees..
The Quadra-BOG is my favorite carb...there are lots of neat tricks and adjustments to get them snappy and responsive...
Make sure to use secondary rods that are no bigger than .05 ....like .044 to .048 range..
With engine running lightly press on secondary choke plate at the rear of it..it should be slightly stiff only droping about 1/8 of an inch... to adjust the tension lossen the allen key on side and turn screw-spring..make sure to have screwdriver in place first to prevent spring from unwinding.... to get the 1/8" play use a needle nose and carefully bend the secondary choke pull-off rod... WHen adjusted correctly you should have mild tension when pressing lightly on the rear on the secondary choke going down 1/8" and it should snap shut...
Tighten the spring-screw in small increments when test driveing the car to see if this improves the situation..
Also make sure to check the choke pull-off vacuum canister... Make sure it is working and holds a vacuum....This hole should be enlarged just slighly with twist wire-drill so that the choke unloads the diaphram in about 1 second...
Regards
Chris


[This message has been edited by cerrem (edited 01-07-2002).]
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post #4 of 31 (permalink) Old Jan 7th, 02, 01:25 PM
 
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Are you setting your time with the vac. hooked up?(a no-no)The Edelbrock should work if you go up on squirter size.(has a 37 now-go to a 41)
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post #5 of 31 (permalink) Old Jan 8th, 02, 03:33 AM Thread Starter
 
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Thanks for the input. I will try all this during the weekend. This motor only has 5 miles on it, so I don't believe the dist is worn. My plugs may be fouled due to rich mixture I was trying which may cause the missing... but doesn't explain the timing light issue. I will recheck the wires, routing etc... and return to 10-12 degrees BTDC. I did set timing with vac adv disconnected. I am committed now to stick with the q-jet instead of the Edelbrock 1411. I checked the secondary jets and looks like they are 43B (slotted). So should be OK there. Will post results.
Thanks,
JT
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post #6 of 31 (permalink) Old Jan 8th, 02, 09:32 AM
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JST12- I just finished rebuilding my Quadra-Jet and did alot of studying and reading on them. While I am by no means the expert, I can say that all the resources I have looked at point to the secondaries as the biggest reason for bogging. I would be happy to copy the page describing adjustment of the secondaries if you don't have it and put it on the fax or you might want to pick up a copy of "Rochester Carburetors" by Doug Roe. It is absolutely a steal for $18.00 if you are going to work with your Q-Jet. The other thing I would look at is the distributor to see if it's advancing. It sounds like it is brand new, but assuming a part is new and can't be the problem has been killing me lately.
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post #7 of 31 (permalink) Old Jan 9th, 02, 03:38 AM Thread Starter
 
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Thanks DenverRS/SS. I'll look for the Roe book.
As an update, I went out this morning before work and reset the timing to about 11 degrees. I also checked the routing of the plug wires, and all looks good. I found that the inductive clamp on my timing light was not closing tight, so when I put a rubber band around the end, the stobes looked perfect. It's a new timing light too...go figure. Just like you said Denver- can't always trust "new" as being good. Anyway I used the light to check the advance as the engine reved. I am getting about 33 degrees total mechanical advance with vac advance disconnected. When I connect the vacuum advance, the timing goes up to about 45 degrees advance at 3000+rpm. Is this normal? Also, I have the vacuum advance connected to the driver side carb port (only one I could find with no vac at 700rpm) but if the revs get to 1000rpm, the advance snaps to 30 degrees. Is this sudden vacuum the way it is supposed to work? I then checked the secondary choke and I was able to push it down the rear about 1/4 inch so I will try to adjust it to 1/8 inch and see if there is an improvement in the boggage. Thanks all. JT
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post #8 of 31 (permalink) Old Jan 9th, 02, 06:37 AM
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To answer your question about vacuum advance...
You should use manifold vacuum...
The vacuum advance is ONLY suppose to advance at IDLE and CRUISE MODE ... When using manifold vacuum...the vacuum is highest durring IDLE and CRUISE , thus making advance at those times only... It improves idle and helps fuel economy at CRUISE mode..
If you were to drive the car and very slowly increase speed till you get to a cruise mode..the vacuum advance would not significantly reduce..
Now if you gunned the pedal or went up a hill or sudden load ( fast rate of change)...then the manifold vacuum would drop and this would relax the diaphram in the vacuum advance canister and result in the vacuum advance retarding itself or just going back to normal as if you did not have vacuum advance...To what degree this happens depends on the curve and the loading..
Without vacuum advance you go back to using only the centrifigal advance in the distributor...
The best way to set the motor is with the vacuum advance hose disconnected and plugged.
Set base timing around 12 degrees ...then adjust centrifigal advance curve to start in at about 1000 RPM and end around 2800 RPM...the overall advanve will most likely be 32 to 38 range...just take it as far as you can but not pinging....
Then once that is set..then hook-up vacuum advance...at idle you should have full vacuum and notice a 8 to 10 degree advanve at base timing when connected the vacuum advance hose line...
As for the QUADRA-BOG ...use a pliers to carefully bend the secondary choke pull-off rod ..so that you remove most of the play so that the secondary choke plate has just a tiny play like 1/8" the most you may have to reduse that a bit more..this is adjusted with engine running and confirm the choke-pull-off vacuum canister is working and fully depressed inward...
Now use that spring screw adjustment on the side to then adjust the secondary choke plate for "mild" tension..it should not be loose or too tight when pressing the choke plate with engine running... You will need to test drive the car and keep monkeying with those settings till you get the feel for adjusting it just right...

Regards
Chris
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post #9 of 31 (permalink) Old Jan 9th, 02, 08:15 AM Thread Starter
 
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Chris, thanks for taking the time to provide all the info. The ZZ4 manual said to connect to a timed port with no vacuum at idle, but I see what you are saying and will change to manifold vacuum if it will give the best performance. I will try this, and also tweaking the spring tension on the secondaries. Should be able to test drive a few laps around the block this weekend. Thanks again. JT
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post #10 of 31 (permalink) Old Jan 9th, 02, 09:45 AM
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" The ZZ4 manual said to connect to a timed port with no vacuum at idle" ...

Well...you may need to be carefull..since there are some vacuum advances sytems that work the OPPOSITE as normal.. Also timmed vacuum could also imply a time delay valve that opens vacuum when motor is warm...for emissions reasons...
Go to auto store and get a hand-held vacuum pump ( also doubles as a break bleader) and hook this to vacuum advance and write down the advance degrees vs. vacuum reading... need a timing light to do that one..
Make sure car idles in the 600 to 800 RPM range..
A side note: Testing WOT on a carb in your own neighborhood is a good way to become a unpopular nieghbor....try somewhere a bit more deserted..
Regards
Chris


[This message has been edited by cerrem (edited 01-09-2002).]
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post #11 of 31 (permalink) Old Jan 9th, 02, 10:12 AM Thread Starter
 
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Chris, No problem to do the vacuum vs advance curve check. I have the vacuum/ bleeder gun and hoses to check out the system. Believe me, I'm with you on WOT around the neighborhood. I am always screaming at the teens to slow down with my little ones running around. If I get to the stage where I can hit the gas without the vehicle almost dying, I know I'll be ready to take it to a deserted road for better testing. See ya. JT
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post #12 of 31 (permalink) Old Jan 10th, 02, 04:24 AM
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Chris - I hope you will check back and reply to this question. I have just done a lot of reading on the Q-Jets and then rebuilt the one on my 1967. There appear to be two ports on the carb that I can use to connect the distributor vacuum hose. One is a port that is found on the front of the float bowl more toward the drivers side. The second is a tube that comes out on the passenger side below the choke diaphram. First question, I think the port on the front of the float bowl is a "ported vacuum" source. The one on the side I think is a "manifold vacuum" source. Is this right? Second question, I am pretty sure that the port at the front of the float bowl is the one the factory connected the vacuum hose to, is that correct? I have tested the car with the distributor vacuum hose connected to both and it seems to run well either way. Not much difference. By the way, the timing does not advance when I connect the hose to the front of the fuel bowl location but does advance when connected to the port on the side.
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post #13 of 31 (permalink) Old Jan 10th, 02, 06:05 AM Thread Starter
 
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I went out this morning with my timing light and vacuum gun and checked a few things. The port on the drivers side front provided no vacuum at idle but went up to about 20"Hg at 3000 rpm. The port on the passenger side front provided about 15" at idle and up to 20" with more rpms. If you blipped the throttle , the vac dropped way down for a split second. Seems to match previous discussion on wanting a slight retard of advance upon mashing throttle quickly.
I also did the vacuum advance curve on the dist with base set at 10 degrees adv:
3" Hg = 0 degrees advance
5" Hg = 8 degrees advance
7.5" = 20 degrees advance
10" = 20 degrees advance
Seems to match spec for zz4 exactly.
On the mech advance:
1100 rpm - 0 degrees advance
2000 rpm - 18 degrees advance
3000 rpm - 22 degrees advance
3500 rpm - 22 degrees advance.
Seems ok to me.

If I put the dist vacuum advance numbers together with the actual manifold vacuum at the carb ports, I will get max advance at idle or cruising speeds and a retarded advance when blipping throttle ( if connected to manifold vac port on carb).
I will get no advance at idle and variable advance as rpms increase if connected to the ported(timed) port on carb.
Again, which is better?
Thanks all,
JT
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post #14 of 31 (permalink) Old Jan 10th, 02, 07:22 AM
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Very excellent !!! For getting those readings..
It appears you have a mechanical advance curve that starts at 1200 and ends at about 2800 RPM...WHich is a good street curve.. To be sure you need to re-do the measurements but at 500 RPM increments ..or try to figure the exact RPM it just starts and when it ends.. looks like you need to advance the mechanical a bit further than 22..keep incrementing that up till you feel power roll-off or start pinging ..then back down an increment in advance..on pump gas you should be 34 to 38...
As for the question about ported vacuum vs. manifold vacuum... The only difference is that manifold vacuum will provide advance at idle and cruise mode...while ported vacuum will only provide advance durring cruise mode but will let the idle remain at base timing..this is likely for emissions purposes at idle...either way..there are small differences between the two ports ...for example with ported vacuum..if you mash the pedal from the car initialy at stand-still..then it's like there was vacuum advance at all only mechanical..while if it were manifold vacuum you would initialy be advanced then when mashing the pedal the vacuum advance would retard back to base timing BUT only after a small LAG or delay in the system response time..this may be a problem for some motors while it could be good for others depending on lots of variables..
Also the Hg you measure at various RPM's while in the garage in PARK is not the same as when driving since the motor is not LOADED in PARK...and loading greatly effects vacuum.. Try running the vacuum gage with a long hose up through the hood and into the window...this way you can have a friend keep note of vacuum durring various driving and loading conditions...last time I did it myself..I was too busy looking at the gage and almost took out a few street lamps
What springs are you using for the primary rods?? The pink ones??
Regards
Chris


[This message has been edited by cerrem (edited 01-10-2002).]

[This message has been edited by cerrem (edited 01-10-2002).]
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post #15 of 31 (permalink) Old Jan 10th, 02, 08:11 AM Thread Starter
 
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Chris, I had the carb apart a while back, and honestly don't remember what color the primary springs were. They are whatever came in a 1971 Q-jet on a 350. Do you have a recommendation on primary rods/jets, springs?
Also, I had the same question as DenverRS/SS. If you are connecting dist adv vacuum line to manifold vacuum, is it customary to hook to front carb port or side port by the choke mechanism? I think one of them originally went to the charcoal canister for emissions. JT
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