Improve mileage 350 with Quadrajet

[kikkegek]

@geezer#99:
I tried to see if opening up the throttle would activate the vacuum, but it took quite some more RPMs (couldnt read them on my own) before the vacuum started advancing. What would be best? a ported vacuum? or another port?

He it seems you know LPG? do you have any tips for me for tuning for LPG?

I tried turning the idle down, but when I unscrew the idle screw, the throttle linkage will not go down any further without pushing it by hand. So I probably need to greese the spring on it?

@TheWhiteElephant:
really love your build threat. great job. Did you put anything under the car when you degreases it? I want to do the same to my engine, but I also need to do this in front of my house.

I would really love to rebuild it, but I am a real tech geek! So I will probably not be able to do this within a day. And since this is our daily driver,we can not mis it for longer then a day! Is a rebuild easy?

[lindstromjd]

Either grease the spring or it may be stretched out to the point of not being able to pull on the throttle return strong enough anymore. New throttle springs are cheap if you do need them.

Q-jets are easy to rebuild, takes about 2 hours or so if you're inexperienced with them, but I'd try to find someone who's good with them. I had mine rebuilt by a friend who's a master with the old q-jets, and he did about 100 times better job than I did when I tried. He also fixed all the things I did wrong, which were more than I'd like to admit to.

[kikkegek]

he lindstromjd

thanks man! yeah I need to check out those springs, cause the carb is really dirty. need to clean it and grease is freshly.

I know someone who could help me with the rebuild. He rebuild several engines already and I call him all the time whenever I have questions.
thanks, I'll look into this

[geezer#99]

All I know about LPG is it likes lots of timing. Leave it on ported since you know it's working. Try some carb and choke cleaner on your linkages and down inside to clean it up.

[twincam1449]

Kikkegek,

I'm from the Netherlands also.
Riding a '79 C10 with 350ci on LPG.
Mileage is around 13MPG (5.5km on 1 liter LPG).
Make sure your engine is not running too rich.

[cor86]

This doesn't look quite right. Maybe it has been addressed, but if not, put your finger over this vacuum tree while it is running. If you feel vacuum, you need to plug all of the ports, or take the tree out and screw in a pipe plug (brass or SS).

Wait...is that coming out of the thermostat housing? I can't tell for sure, but it looks like it might be. Never seen anything like that before. I guess if it was, you would have coolant everywhere.

[kikkegek]

Originally Posted by cor86

This doesn't look quite right. Maybe it has been addressed, but if not, put your finger over this vacuum tree while it is running. If you feel vacuum, you need to plug all of the ports, or take the tree out and screw in a pipe plug (brass or SS).

Wait...is that coming out of the thermostat housing? I can't tell for sure, but it looks like it might be. Never seen anything like that before. I guess if it was, you would have coolant everywhere.

in another story that was covered, but not yet dealt with:
http://67-72chevytrucks.com/vboard/s...d.php?t=416067

It just now crossed my mind that I never really asked If it hurts to let it sit like this? Its supposed to be a vacuum switch that does not open until engine is warm and then distributes the vacuum from one hose to three others.

and yes, I am 99% sure it is in the same thing as the big hose from the cooling system goes in!

[kikkegek]

already found the answer myself. searched at Summitracing for a vacuum switch and found these:

Standard motor ported vacuum switch. Looks almost the same.

it opens the connection inside the switch to let a continuous vacuum through to the three other ports like already said by LONGHAIR.



since this switch does not result in a vacuum leak, there is no danger for now in leaving it sit there for now, although it looks strange!

thanks for the help guys!

[lindstromjd]

Yeah, that vacuum port is for EGR stuff. If you don't have any hooked up, then you don't need it. I'd check for vacuum leaks at cold idle and hot idle just to be certain, but as I remember I don't think it actually pulls any. Just re-directs the vacuum going through it.

[kikkegek]

okay, I found some bad connections on the carb 2nite. Didnt fix them yet, but wanted to share here and hear what you guys think.

Look at these pics I found:





looking at the last picture:
I found that my distributors vacuum advance is now connected to the Smog connection.
And where my vacuum advance should have been connected, it is connected to a metal line that goes to a valve in one of my exhausts???

Since I took off as much of the smog and EGR stuff as possible, I dont think I need the exhaust valve anymore. I have now idea what the function would be anyway?

[Oilbrnr]

Couple of thoughts...

First off, I personally think flex fans are crap. They are always using HP if cooling is needed or NOT. I'd put a WTB thread up in the classifieds section for an OEM fan and viscous clutch, or go electric.

Greasing the throttle return springs will do nothing more than act as a dirt magnet. If backing off the curb idle speed has no effect, try quickly opening the primary throttle shaft by hand and letting it go. If idle drops, your throttle shaft/bushings are probably worn out. That being said, you are running LPG, which I have zero experience tuning. I believe the LPG is introduced AFTER the throttle plates, so rebuilding the carb would be fairly pointless unless you find yourself running gasoline fairly often...

You mentioned new plug wires, but did you also go through the rest of the ignition? Cap, rotor and plugs? I'd think that LPG might be happier with a specific heat range plug. Again, I'm assuming here. Hopefully someone else with more LPG knowledge will chime in.

[lindstromjd]

If it's a valve right between the right side manifold and the pipe, it's called a recirculation valve. It helps your engine warm up by forcing the hot exhaust air back up into the intake. Once the engine warms up, the valve opens and lets exhaust flow through the pipe. I got rid of mine, but if you don't want to take yours to an exhaust shop, I'd just find a way to keep the valve open at all times.

[motornut]

heat riser valve on the side of the manifold/pipe if the valve isn't working it would make it run worse.if it still has a nib/ball on it, make it run parralell to the angle of the pipe to keep it open


found a pic

[kikkegek]

It is in the position that Oilbrnr is taling about, but I see no recirculation connection to the intake. It seems more like an open-close valve to me like in the picture of Motornut.

I'll check 2nite to make sure I am right and I'll check all the connections.

But am I right that the Vacuum advance en SMOG (for this EGR valve) seem to be switched in my setup? Is there a difference in how these two ports on the Quadrajet function?

You'd expect the EGR to be connected to the vacuumswitch that opens when the engine is hot?

[kikkegek]

found some answer:

What does the exhaust heat riser valve do?

Answer:
It is a device that is designed to block the exhaust flow from one bank of cylinders and force it back up through the
head, then through a small cross port in the intake manifold, into the carb base and then out the opposite head – all in order to warm the carb/fuel for better cold starts. After warming up or under more throttle, it is supposed to open up.
It ain’t the greatest design feature of GM engines. Usually, the thing never gets lubricated and freezes up in the open position. Also the port in the intake was so small, it usually carbons up solid from the overrich exhaust. Some performance intake gasket kits in the past provided block offs for the port. You could also install small plugs in the carb base plane holes.
If it works, I’d say leave it alone. If it is broken, replace or remove it. Unless you live north of the 60th latitude, it’s not any use IMHO. It draws air from over the exhaust manifold when the engine is cold in order to heat up the air entering the carburetor. This is to improve the engine driveability and emissions in colder temperatures.

[geezer#99]

Interesting quote. 3 sentences all starting with It. LOLl!! Seriously each sentence describes a different part on your motor.
1. exhaust recirc under intake warms carb
2. EGR workings
3. Heat tube to air cleaner
You've got 3 different systems mixed into one.
Where did this info come from?

[kikkegek]

Originally Posted by geezer#99

Interesting quote. 3 sentences all starting with It. LOLl!! Seriously each sentence describes a different part on your motor.
1. exhaust recirc under intake warms carb
2. EGR workings
3. Heat tube to air cleaner
You've got 3 different systems mixed into one.
Where did this info come from?

http://faq.automotiveaddicts.com/che...-heat-riser-do

But can you help me with my question on the different port on the Quadrajet?

I think they mixed up the Vacuum advance and SMOG connection on my carb. But if the two ports have exactly the same vacuum "performance" or samen vacuum source, then this does not matter.

So, do you know?
I am referring to the picture with the blue and white letters. The smog and distributor are oppositely connected in my setup! Is this a problem?

[geezer#99]

You've got ported and manifold vacuum sources. Ported is above the throttle plate. Manifold is below. What each was used for originally on your carb is irrelevant unless you're intending to make it all stock again. You can use any ported or any manifold vacuum source for whatever you want.

[motornut]

but would size matter lol hose/fittings size?

[kikkegek]

Originally Posted by geezer#99

You've got ported and manifold vacuum sources. Ported is above the throttle plate. Manifold is below. What each was used for originally on your carb is irrelevant unless you're intending to make it all stock again. You can use any ported or any manifold vacuum source for whatever you want.

he thanks man!

but since I am a total QJ newby, could you point out in the picture what above and below is on the QJ?

And would you go for ported vacuum advance or manifold vacuum advance?

[geezer#99]

Start your motor. Pull the hose or cap off any one of them. If you feel suction it's manifold. No suction it's ported. You could also buy a vacuum gauge to use to test each port.
Run your vacuum advance to a ported source.

[kikkegek]

Originally Posted by geezer#99

Start your motor. Pull the hose or cap off any one of them. If you feel suction it's manifold. No suction it's ported. You could also buy a vacuum gauge to use to test each port.
Run your vacuum advance to a ported source.

okay. And I guess if done right, I should connect the heat riser valve in my exhaust to the vacuum switch so it does not open untill the engine is properly heated? I would therefor need to get manifold vacuum for the switch, connect the heat riser valve en close off the other two connections. Since I do no longer have the warm air intake valve on my air filter, this would help in warming the engine in cold times (which it is right now with us).

I'll see what I can do this weekend and do some testing.

thanks guys!

[babyJay]

Remove the fan and put short bolts back in to hold the pulley in place since your fan has no clutch. This can be very dangerous. Climb up on top and look straight down between the timing chain cover and the backside of the water pump. You literally have to be on top of the engine. The timing tab should be back there.


EDIT! OOPS! failed to see the thread had two more pages. Ignore what I said above.

[kikkegek]

Originally Posted by babyJay

Remove the fan and put short bolts back in to hold the pulley in place since your fan has no clutch. This can be very dangerous. Climb up on top and look straight down between the timing chain cover and the backside of the water pump. You literally have to be on top of the engine. The timing tab should be back there.

I already posted in #43 that I found the timing scale. thanks anyway man!

[babyJay]

Do be careful around that fan. Those kind scare the bejeebers outta me!