You have the same set up as I do? I am in Tx also. Any black smoke when you floor it. I am not expert I am in the same situation trying to learn my self. Could it be your main jetting it to great? That and also the secondary flap may be to "loose"? It also looks like you have to much timing. Is all your timing in by 3000-3200rpm? You might consider lowering your vacuum advance timing.
Once more the setup for 35 degrees of mechanical advance:

14 initial + 21 centrifugal + 12 Crane adjustable vacuum advance without EGR = 47 total.

14 initial + 21 centrifugal + 16 Crane adjustable vacuum advance with EGR = 51 total.

14 initial + 21 centrifugal + 22-24 stock vacuum advance = 57-59 total. Too much!

http://www.73-87.com/7387garage/drivetrain/hei.htm





QuadraJet carbs have three basic tuning variables, and these get people all confused: Primary Metering Jet, Primary Metering Rod, and Secondary Metering Rod. Attempting to cure problems by tuning the wrong variable results in lots of frustrations for tuners and car owners.
When tuning, we think of each of these variables as controlling a different operating range: The primary jet size determines the fuel mixture at Wide Open Throttle (WOT). The primary metering rod determines fuel mixture at cruise speed and determines responsiveness of the idle mixture screws and off-idle performance. The secondary rods are a high-rpm compliment to the primary side, and are used for final “tweaking.”


http://answers.yahoo.com/question/index?qid=20061129093318AA7bB3K


Here is a link to my question I asked here the other day.
http://www.hotrodders.com/forum/tuning-my-air-fuel-ratio-carb-219700.html


What AFR sensor are you using?
What is your fuel pressure set to?
What HEI are you running?

 

I was not looking carefully when I tested, but I don't think there was any black smoke. As I mentioned before, in general it starts and runs very well, but just doesn't have much upper end. To address some of your points/questions.

The HEI is a stock large cap GM replacement from Pace performance, and you are right, my vacuum advance provides too much advance. It probably should be limited down to about 10-12.

I haven't measured the rise in centrifugal advance in a while, but from what I remember the springs bring all the centrifugal in by about 2400 rpm. This was the way it came from Pace.

Fuel pressure is about 5.5-6.0 psi, using a stock mechanical pump. I've measured it at speed (pressure gauge duct-taped to the windshield!) and it holds up at RPM.

My AFR gauge is an Innovate Wideband DB gauge, using the LM-1 and heated sensor. I only have a sensor in the driver's side pipe.

Main jetting and primary rods are stock for the carb, which is from an '86 Chevy 1 ton truck. I know the jet is #73, but I could not read the numbers on the primary rods. However, I would expect them to be fairly lean.

Ruggles book recommended about 3/4 turn tension on the secondary spring, so that is what i used. I think I did it right, but you never know.

I already took off the choke pull-off to see if i could get it to release faster. However, the hole that affects the delay is very very small and fairly deep inside the tube. I'm afraid my drill bits may break if i try to drill it out bigger to get the delay down below 2 seconds.

I may just lean out the idle screws and see what effect it has over the entire RPM range. If that doesn't change much it would also be easy to try swapping secondary rods to see what happens.

Thanks,

Bruce

 

the info is here http://www.hotrodders.com/kb/carburetor-articles
or http://www.73-87.com/7387garage/drivetrain/damon.htm
there are allot of articles on trouble shooting your carb.
Some quadrajets like 4 psi or they tend to run rich or flood easy.
cut back on the initial timing a few degrees

 

I was not looking carefully when I tested, but I don't think there was any black smoke. As I mentioned before, in general it starts and runs very well, but just doesn't have much upper end. To address some of your points/questions.

The HEI is a stock large cap GM replacement from Pace performance, and you are right, my vacuum advance provides too much advance. It probably should be limited down to about 10-12.

I haven't measured the rise in centrifugal advance in a while, but from what I remember the springs bring all the centrifugal in by about 2400 rpm. This was the way it came from Pace.

Fuel pressure is about 5.5-6.0 psi, using a stock mechanical pump. I've measured it at speed (pressure gauge duct-taped to the windshield!) and it holds up at RPM.

My AFR gauge is an Innovate Wideband DB gauge, using the LM-1 and heated sensor. I only have a sensor in the driver's side pipe.

Main jetting and primary rods are stock for the carb, which is from an '86 Chevy 1 ton truck. I know the jet is #73, but I could not read the numbers on the primary rods. However, I would expect them to be fairly lean.

Ruggles book recommended about 3/4 turn tension on the secondary spring, so that is what i used. I think I did it right, but you never know.

I already took off the choke pull-off to see if i could get it to release faster. However, the hole that affects the delay is very very small and fairly deep inside the tube. I'm afraid my drill bits may break if i try to drill it out bigger to get the delay down below 2 seconds.

I may just lean out the idle screws and see what effect it has over the entire RPM range. If that doesn't change much it would also be easy to try swapping secondary rods to see what happens.

Thanks,

Bruce

I had to run a pressure regulator with the stock pump to get my pressure down. I would also try to put more tension on the secondary flap and see what it does.

 

the info is here http://www.hotrodders.com/kb/carburetor-articles

One link (page 3), "Rochester Quadrajet Common Problems and Decoding" is broken...

 

Thanks, I fixed it
Buick site changed it, I had to bounce it to the other site
http://www.florida4x4.com/tech/quadrajet/500cid.com/Quad.htm

 

Did you try the stock curve for the stock engine? Do the throttle plates open freely or sticky?

Less timing might get your burn with the piston closer to the explosion.

 

I've read through the linked article, and articles by Lars Grimsrud and several others who seem to have a good handle on the Quadrajet. However, there are two challenges I've found:
1 - Quadrajet models changed features several times over the years, so some "hints" only apply to certain years and types.
2 - I don't appear to have the traditional bog that everyone is trying to correct. I can hit the throttle and get fairly good initial response, but then it flattens out quickly. I don't want to fix one problem and then create another.

By the way, I am using the Qjet to replace an Edelbrock 1406 that also ran fairly well, but the Edelbrock obviously leaned out too much at cruise (my Quadrajet does not have the lean cruise problem). I am running both carbs on a dual pattern Performer 2101 manifold.
- When I ran the 1406 at a steady 70 mph I could see the AFR drop to about 16-17, and then as I hit the throttle it would kick up to the power mode and drop down to about 13-14. Using richer rods helped resolve the cruise problem but I had to use the richest rod/jet combo I had in the tune kit. I never really got it where I wanted, but I could see what happened when I swapped rods.
- If I used the wrong step-up spring I could see the AFR go lean and I could feel the bog. Swapping springs kept minimized the AFR drop and removed the bog. It was really easy to see the effect of the spring swap.

The reason I switched from an Edelbrock 1406 to a Quadrajet is to try to get a better mix of fuel mileage and performance. Gas mileage on this truck sucks, and if I can get a little better mileage and still maintain performance I will be very happy. I also like the challenge of learning how the Quadrajet works.

Thanks,

Bruce

 

I posted this same question over on Cliff Ruggles forum on his web site, but I'm not sure he monitors it over the weekend. I'd like to work on it this weekend, so I'm also interested in any ideas from the hotrod forum.

I rebuilt my 17080213 carb (80's vintage with APT) using the Ruggles HP rebuild kit and throttle shaft bushing kit. Carb starts and runs great at lower speeds, although after it warms up the AFR shows about 12.5 when idling in park. I assume I need to lean this out. At 50 mph cruise I have an AFR of 13.5 and vacuum is about 14-15". At 70 mph the AFR is about 13.0 and vacuum is about 14-15".
I also provided a lot of background info at the end of my posting.

When I floor the accelerator at about 45-50 (2200-2400 rpm) I do not get any obvious bog. It downshifts and starts to accelerate fine up to about 3000, then begins to lose steam and finally flattens out (very slow rise in speed) at about 3500-4000. It doesn't feel like I'm getting much out of the secondaries. I am using the dark blue power piston spring and stock setting on the accelerator pump. APT is 3.5 turns out. At 4000 RPM with the pedal floored the AFR is showing about 11.8-12.0.

Adjustments I am considering:
1. Open up the hole in the choke pull-off to reduce delay. Currently its about 2.5 seconds.
2. Adjust tension on secondary flaps. Its now at about 3/4 - Which way should I go?
3. Try richer CP secondary rods. Stock for this carb is the G hangar and DP rods. I have an R hanger and CP rods from another carburetor. I could get AY rods from Edelbrock.

Thanks,

Bruce

Background Info

Other stats: 75 GMC pickup, Edelbrock performer manifold, replacement GM 350 crate engine, stock 8.5 compression heads, 194/204 @.050 cam, iron manifolds and dual exhaust, TH350 and 4.11 gears. Initial timing at 12 degrees. HEI distributor with 22 degrees mechanical and 22 degrees vacuum. Idle vacuum is 20".

I used all stock parts, except for the the idle tubes, float and other parts that came in Cliff's kit. APT is set to the original setting of 3.5 turns out. Power piston spring is the dark blue one from the rebuild kit. Carb has a new a secondary pull-off connected to both the choke and the secondary air flaps (Airtex 1C1148). Primary pull-off (Airtex 1C1044) is there, but doesn't seem to do much. Spring on secondary flaps at about 3/4 turn.

The first thing I would do is lessen the tension on the air valve spring. Not to make it open any quicker, but to be sure that the spring tension isn't perventing the air valve from fully opening.

The next thing I would do is check to see that you're getting full opening of the secondary air valve. Some carbs had amount of the air valve opening set to a lot less than it's capable of. The fix is easy, just look where the red arrow (below) is pointing, that's the stop. It can be carefully bent to set the opening amount.

I will use a Dremel to slot the linkage to make bending it easier- I prefer that over grinding the stop in case it needs further adjustment to lessen the opening amount, because the idea is to increase the opening until you either reach the max it will open or to where it doesn't help performance any more- in which case you'd decrease the opening back to where it was best. The linkage can be bent several times w/o breaking as long as the cut isn't made so there's not enough metal, and it's not bent too many times.

Once that's squared away you can go about quickening the opening rate by enlarging the pull off orifice. I like to go very large on the factory-installed orifice, then solder the opening shut. From there, enlarging the orifice is as easy as using a small numbered bit in a pin vise. If you go too large, a touch w/a soldering iron will close it back up. And plan on going too large during the tuning of the orifice size, because you will keep enlarging it until you go too far and get a bog, then you back up to where it was best (just like the opening amount of the air valve).

You can certainly try a richer (smaller tip diameter) secondary metering rods. The hangars are not going to make any real difference until the secondary actuation is a lot closer than it sounds like it is now, so keep using the same hangar. Accelerator pump changes aren't going to matter w/how well it pulls past 4000 rpm, leave that for if there's an off-idle problem.

BTW, you running dual exhaust and long tube headers? Low restriction air filter?

 

Cobalt - I'm headed in the same direction you suggested for troubleshooting.

I think I verified the air flap opening when I did the rebuild, but I'll look at it again. I have been trying a few other things this morning.

- Adjusted idle mixture a little leaner and closer to 14.7; didn't seem to change anything other than idle speed
- Switched to the richer CP secondary rods; no noticeable change in acceleration
- Disconnected the secondary choke pull-off (looks exactly like the one in your picture) and plugged the vacuum line, just to verify it was releasing the secondary lockout completely when vacuum dropped; no significant change

Adjusting the tension on the air valve spring is the next step. Its not a fix look forward to since its hard to reach the allen wrench fitting and turn the tension screw at the same time when the carb is mounted.

I have stock exhaust manifolds and full 2" duals. I was using an Edebrock 14" air cleaner with a 2" spacer under it up until the last few runs, when I noticed the choke rod may hitting the side of the spacer. I need the spacer so that the air cleaner clears the HEI cap. The last two runs I reinstalled the stock air cleaner. It has a nice tall filter, and I can reverse the lid to get air in all around the perimeter.

Bruce

 

My belief is that a rod change would not cause a noticeable change in wot. Air door will, being rate via choke pulloff /doorspring, and open amount.

A stock engine probably will not beneft from a performance curve.

Sounds like it is getting more fuel than it needs. Leaner is meaner, but air mixture volume from the door opening is different.

Dumping more fuel in than the engine can burn , then compensating with more timing is not going to make it faster.

 

I loosened up tension on the secondary spring to about 1/8 turn and it didn't seem to change anything.

Based on AFR it is running on the rich side at cruise (13.5) , so I need to figure out how to get it closer to 14.7. I find this a little surprising for a stock '86 vintage carb with original jets and rods. This was my baseline setup, so the only change from stock is the higher float setting recommended by Ruggles.

It runs about 11.8 at WOT, which is a little rich, but not bad for WOT. However, I was also surprised that using richer rods did not seem to change the AFR at WOT.

This engine is set up for my truck (heavy) and I want low end power/response. It may just not have enough cam to keep things going above about 3500-4000 rpm, but the power flattens out more than I expected.

Thanks,

Bruce

 

I loosened up tension on the secondary spring to about 1/8 turn and it didn't seem to change anything.

Based on AFR it is running on the rich side at cruise (13.5) , so I need to figure out how to get it closer to 14.7. I find this a little surprising for a stock '86 vintage carb with original jets and rods. This was my baseline setup, so the only change from stock is the higher float setting recommended by Ruggles.

It runs about 11.8 at WOT, which is a little rich, but not bad for WOT. However, I was also surprised that using richer rods did not seem to change the AFR at WOT.

This engine is set up for my truck (heavy) and I want low end power/response. It may just not have enough cam to keep things going above about 3500-4000 rpm, but the power flattens out more than I expected.

Thanks,

Bruce

Are you using a EGR?I wonder what all that timing and coming in very quick would do for WOT. I wonder if the low compression is not making the high timing so noticable but still affecting WOT.
By screwing down CW the APT adjustment you should see it lean out some at cruise.
The cam also if its stock will not make it to 6 grand, its a low RPM torque "fuel efficient" cam. It my understanding that 3-4 grand is tops.

 

There is no EGR on the engine. This is a '75 HD emissions truck, so it only has a PCV valve.

I'm confused about your timing question. Initial plus centrifugal is 12 + 22 = 34, which should not cause any problem.

The additional 22 degrees from vacuum advance may cause part throttle detonation, but at WOT the vacuum is near zero and there will be no vacuum advance. I could try running with the vacuum advance disconnected, but I don't expect it to affect WOT.

I don't plan for this engine to reach more than 5000 rpm, but I would like to get the best performance I can out of the carb in the 3000-5000 rpm range. The mild cam may be the limiting factor, but I did not expect the cam to run out of steam until about 4500 rpm.

Bruce

 

There is no EGR on the engine. This is a '75 HD emissions truck, so it only has a PCV valve.

I'm confused about your timing question. Initial plus centrifugal is 12 + 22 = 34, which should not cause any problem.

The additional 22 degrees from vacuum advance may cause part throttle detonation, but at WOT the vacuum is near zero and there will be no vacuum advance. I could try running with the vacuum advance disconnected, but I don't expect it to affect WOT.

I don't plan for this engine to reach more than 5000 rpm, but I would like to get the best performance I can out of the carb in the 3000-5000 rpm range. The mild cam may be the limiting factor, but I did not expect the cam to run out of steam until about 4500 rpm.

Bruce

CW a bit on the APT isn't a bad idea if cruise is richer than needed, and can help economy- just don't get carried away. Not much chance you will, considering you have an A/F meter. BTW, where is the O2 sensor located? How is the PCV system plumbed- to the front of the baseplate, to the large port? The other v-cover vented so the engine can pull in fresh air?

I don't know exactly how much higher Ruggles said to set the float, but that will bring the circuits in earlier as well as supplying more enrichment. I don't raise the float level past 1/4" on my Q-jets; you might consider going back to the original float setting.

The power piston spring- is it about the same tension as the original spring? If it is any stronger, that will cause enrichment sooner, and that seems to be not what the engine wants; I'd consider going back to the stock one.

Keep us posted- you will either get it better or come to the conclusion that the cam's all done by the time the engine flattens out!

 

There is no EGR on the engine. This is a '75 HD emissions truck, so it only has a PCV valve.


I don't plan for this engine to reach more than 5000 rpm, but I would like to get the best performance I can out of the carb in the 3000-5000 rpm range. The mild cam may be the limiting factor, but I did not expect the cam to run out of steam until about 4500 rpm.

Bruce

The engine in my 79 C-10 is from a 75 3/4 ton
no smog stuff of any kind was on it.
No EGR---BONE stock, and I have no idea what the head numbers
Edelbrock Q-Jet

Winds up to 5k with no problem whatsoever
it does however, run out of "steam" before then
The truck is also gear tall, with the big truck 4-spd (3.08 rear)
I seems to like running at 2.7-3k, but will pull strong to about 4500.

 

Seems to me that you have some good skill and understanding on the Qjet rebuild and have covered many of those bases, perhaps it is not the carb?

Plug wires, plugs & gap, voltage at HEI, ground at HEI, valve springs, vacuum leak,,,just throwing it out there.

 

Seems to me that you have some good skill and understanding on the Qjet rebuild and have covered many of those bases, perhaps it is not the carb?

Plug wires, plugs & gap, voltage at HEI, ground at HEI, valve springs, vacuum leak,,,just throwing it out there.

I agree, I am thinking its may be more related to the set up of the truck.
stock 8.5 compression heads, 194/204 @.050 cam, iron manifolds and dual exhaust, TH350 and 4.11 gears.

 

I don't plan for this engine to reach more than 5000 rpm, but I would like to get the best performance I can out of the carb in the 3000-5000 rpm range. The mild cam may be the limiting factor, but I did not expect the cam to run out of steam until about 4500 rpm.

Bruce

There is a chance the engine might not need all the flow the carb can supply at WOT; that's to say the air valve may be opening TOO far. If that is the case, carefully adjust the stop to provide less AV opening until it accelerates cleanly and strongly to redline.

 

Engine Hydraulics

If i want some forklift filters for my Mitsubishi Truck so from where can i buy the filters online? some one has suggest me this linked forklift filters. Is it OK or should i need to browse more?

 

Thanks again for all the suggestions. I haven't been back to working on this in the last few days, so I have not tried anything new.

Everything on the engine is fairly close to stock low compression SBC, except this carb is from an '86 and the cam is a little more aggressive than original. The PCV hose connects to the carb base and I have a hose in the other valve cover running up to the air cleaner. My O2 sensor is heated and its mounted in a welded bung n the driver's side exhaust pipe, just about under the driver's seat.

Float level is at 1/4", which is what Ruggles recommends. I can try disconnecting the vacuum advance and reducing initial timing to stock (4 degrees is stock, I think) just to see if it changes anything. Tightening up the air valve is also easy to try, just to see if it improves the transition.

I have stayed away from adjusting the APT, but I think I'll use Ruggles' "tip-in" procedure to see what it shows. He says to run the engine at 2000 rpm and then first cover the air horn with the your hand to make it richer, and then pull a vacuum hose to make it leaner. If RPM rises when you go lean or rich, that means the APT needs to be adjusted in the same rich/lean direction.

I asked Ruggles on his forum whether I should try leaner primary jets to get the cruise AFR closer to 14.7 (it is now 13.5), but haven't gotten a reply yet. It runs very smooth right now at cruise, so maybe I'm just chasing numbers.

Thanks,

Bruce

 

Update: I took a closer look at the carb linkage today and found out its not opening the secondaries at all. That is why adjusting the air plate spring tension and swapping secondary rods has no effect.

I had my wife push the accelerator pedal to the floor and it looked like everything operated normally. However, when I pushed open the air flap and looked down the carb throat the secondaries plates are barely open when the linkage is at full travel.

I compared the linkage to the pictures I took before the rebuild, and also to an older quadrajet I have, and I can't see any parts missing. However, on the old carb I only move the primary throttle plates about 1/4 turn before it starts engaging the secondaries, and on the one I rebuilt there is no movement of the secondary plates until you hit full rotation of the primary. It looks like the lever on the primary shaft that moves the rod to the secondaries is rotated about 30-40 degrees too far to the right.

Looks like time to study the linkage and trying to figure out what I put together wrong.

Bruce

 

Update: I took a closer look at the carb linkage today and found out its not opening the secondaries at all. That is why adjusting the air plate spring tension and swapping secondary rods has no effect.

I had my wife push the accelerator pedal to the floor and it looked like everything operated normally. However, when I pushed open the air flap and looked down the carb throat the secondaries plates are barely open when the linkage is at full travel.

I compared the linkage to the pictures I took before the rebuild, and also to an older quadrajet I have, and I can't see any parts missing. However, on the old carb I only move the primary throttle plates about 1/4 turn before it starts engaging the secondaries, and on the one I rebuilt there is no movement of the secondary plates until you hit full rotation of the primary. It looks like the lever on the primary shaft that moves the rod to the secondaries is rotated about 30-40 degrees too far to the right.

Looks like time to study the linkage and trying to figure out what I put together wrong.

Bruce

There is an override feature that will still allow the primaries to fully open even if the secondaries are locked out by the factory lock-out, so something as small as a gasket mismatch that was in the way of the secondaries could cause it.

Other causes are the baseplate being warped by being tightened unevenly when using a thick base gasket, or the linkage being assembled wrong. Most times the linkage is not removed during a rebuild, so unless you did, or you do not know if the carb was right before you got it, who knows.

I don't have a very good photo, but below you can see the actuation linkage, be sure the arrowed link is in front of the arm and not behind it (arm is shown w/the red line). Also be sure the link is pushing the arm and not going over the top of it.

 

Final wrap-up (I hope).

It was the TH350 kickdown cable that was preventing the linkage from moving enough to bring in the secondaries. Once I readjusted the kickdown cable I was able to get the secondaries to actuate and keep upper rpm response.

Now that I have the secondaries working, the secondary air valve tension that I had backed off to 1/8 turn is too light and I get a little bog as the secondaries kick in. I think I'll go back to about 1/2 turn and see if that gets rid of the bog.

Thanks for the help.

Bruce