350 intake/carb suggestions

[nixtux]

Got it to start for about 10 seconds and it was puffing some nasty looking smoke. Turned it off, loosened the distributer hold-down bolt and retarded it. It went away. What's weird, I can't get the idle above 620RPM and the screw is as tight as it can go. Maybe the carb is getting more and more retarded... I don't know, it runs and drives good now. Hopefully it stays that way until I can get a new carb.

[nixtux]

Kind of weird. Went to start it and won't start. It'll crank, stop, crank, start, stop. It has a kind of whine to it so figured better not try and start it until I figure out what the whine is. Just in case there is a valve clearance issue or something. The battery should be fine. Could a starter cause it to start, stop, start, stop?

It was running fine last night. Not sure what changed overnight.

I got to thinking, it had a slight "squeak" lastnight. I figured it just needed some belt dressing but I didn't have any. If I wasn't still hungover the night before I may have paid more attention to it. I'm thinking maybe it was the alternator and it is just a weak battery. But I don't know if that would explain why it will start and not stay running. I just worry it could be a valve issue (probably because of the valve issue on the car.) Last thing i need is for the stupid thing to die. Plus I have to move this week so I have to carefully budget things.

[nixtux]

Here's my little truck. It's a stock carb'd 350 with a Turbo 400 trans. Heavy 3/4 Ton so I've had it loaded down and it doesn't squat either.
I haven't driven it in about 5 years but it's next on my list. I really wanted to get the wife's Grand Am GT together for her first but that's turning out to be a hassle.

I like that style Chevy. Mines a old ugly orange box with tons of rust on the drivers side. But I don't care it runs... I'll have to figure out what pistons are in there. Worse case, I'll buy a beater down the road when I have the car running and try to build a nice little turbo 350. I just want the experience and it's nice learning this stuff. That way you aren't dependent on other people and getting ripped off at shops. My nexts project will be redoing the top of the 3500 in my Alero. But I do need to find someone who will redo the valves. I have a shop in mind. A classmates dad is known to "do" crazier projects so hopefully. Then my step-dad and I are going to redo the top-end, less the valves. I've heard there is lots involved with that and I'm a bit timid about trying it. I also figure the last time the car ran, it ran for 2hrs and 17 miles so better safe than sorry.

That spring was for the adjustment on the passenger side of the carb. The vacuum leak was from the master cylnder. Cut the hose, put it back on and the brakes are perfect. I guess the throttle cable is loose so I'll attempt to fix that tomorrow. That way it's actually getting full trottle. Trying to find a sweet spot timing wise. Just moving the distributer slowly and seeing where it improves or not. The last advance killed it's low end power. Backing it off a little and seeing if the low-mid comes back. I like it on the low end and mid range verse high.

I had the "dwell" checked and it's at around 28-30 so apparently that's good. Had some minor adjustments made to the carb to try and improve it's effciency. But I have a bachelors party to get to.

Attached is the "Elder" as I like to call the truck. Can't see the sides, but the passenger side is decent but the drivers is horrible. But one thing at a time.

[Axe_1]

Here's my little truck. It's a stock carb'd 350 with a Turbo 400 trans. Heavy 3/4 Ton so I've had it loaded down and it doesn't squat either.
I haven't driven it in about 5 years but it's next on my list. I really wanted to get the wife's Grand Am GT together for her first but that's turning out to be a hassle.

[Axe_1]

I wouldn't worry about the rear end gear oil unless you just want the experience. Most people never change it during the life of the vehicle. If it gets changed every 50,000 miles it should be great.

If it pulls slow from 55-80 then pulls hard it could probably use a better gear, but it's not something that has to be done immediately. Going to something more like a 4.10 would probably make it scream though. Your engine is built to run in a higher RPM range than stock, so you eventually want to get it into that range. You may lose some MPG's on the hwy but you could gain them back in the city if it's geared right.

Again, without knowing what pistons are in it I would pass on the turbo. It's really up to you but it may drastically shorten the life of the engine. I'm just another hot rodder like you, but that's my advise.

Axe

[nixtux]

Very cool! That sounds like a nice healthy street cam, and that 3.73 12 bolt should do fine also. Trucks normally run a tighter gear than cars because they came with taller tires, but that's a great gear ratio for the street/Hwy mixed driving.

Axe

It's a nice little truck. It has the 3/4 ton suspension so even if the box is loaded and pulling a trailer it doesn't slump at all.

The 3rd gear is really long. It shifts from 2-3rd at around 55MPH. I've taken the truck to about 105MPH, maybe a little --- only once. Just because I wanted to know if it could get up there. It has very little power from 55 to 80 but after that I think it pulls faster than my 3.5l intrepid did.

The differential fluid has never been changed that I know of. At most it has 15-16k on it, but the last time it would've been changed was in 2005. Should I have that changed every year? It's not a 4x4. But I think it's proper to change it every year... But I'm not sure.

The last question, you don't think that would be a good motor for a small turbo? I don't really care for the extra power, it's just the knowledge learned from doing it that I want. It has more than enough power for me anyway.

I think I found the vacuum leak, the hose from the carb plate to the valve cover was half out. I put it back in and it seems to be a little better now. We'll see.

[Axe_1]

Very cool! That sounds like a nice healthy street cam, and that 3.73 12 bolt should do fine also. Trucks normally run a tighter gear than cars because they came with taller tires, but that's a great gear ratio for the street/Hwy mixed driving.

Axe

[nixtux]

I'm not sure what kind of pistons. Maybe there is a receipt that'll shed some light but I have to get that from the guy who was going to buy the truck. A basic runover. The work was done in 2002, the truck had 82,300mi. It has 98,680mi now.

Rebuilt 350 with .03 Block Bore (355)
Rods & mains .010
Comp Cam 242 Extreme Energy
Comp Cams Double Roller Timing Chain
B & M Torkmaster 2000 High Stall Torque Converter
Rebuilt TH350 /w shift kit
Elgin valve springs
Flattop pistons
Quadro-Jet 750cfm 4-barrel carb
Electric choke

I think the gear ratio is 3.79 (something like that.) It's a GM 9 bolt rear-end I think. I don't have the papers and I haven't looked at them in a couple years.

Found this on a old post of mine. Has the cam specs too.

1973 GMC Super Custom

350 .03" bore (355)
rods and main .010"

From Comp Cams Limited Warranty Card

Value lift .47 .480
Duration .006

value timing open close
at 0..6 INT 28 BTDC 60 ABDC
EXH 74 BBDC 26 ATDC

Cam specs
AT 106 Intake center line
Intake Exhaust
Duration .050 224 230
Lobe lift .3180 .3200
Lobe separation 110.0

Flattop pistons - 9/1 Compression
Comp Cam 242 Extreme Engery
Rochester quadrajet Carb
Headers 2 1/4 pipes /w mufflers (not too loud)

T350 /w shift kit
Torkmaster 2000

3.73 Gears - 12 bolt rear-end

[robertisaar]

If they are below that they draw a vacuum all the time, and if they are above they draw when the throttle plate is open. (I think I got that right) The brakes need vacuum all the time, if that helps.

this is correct. been a while since i've dealt with carbs, but the venturi effect(IIRC) will draw vacuum above the plate when open, but under the plate is in vacuum at all times(except when WOT, but the engine is still drawing air, therefore fuel, as well).

[nixtux]

12-16 sounds right on the timing. Not sure what the total advance should be off hand, but if you stay in that range at idle there is a sweet spot that will accelerate well, not overheat, and still crank with the starter.

Not a big fan of B&M, not because they are bad but because they charge a lot and are directed at the masses. The 2,000 stall may not be quite enough for this engine, but adding a vacuum canister should help that. There are 2 different ways to rate the stall and most companies like B&M use the one that sounds the best.

I wouldn't consider a boost unless I was sure what pistons were in there. I know you want to go small on it, but I personally wouldn't add any with stock Cast Aluminum pistons. You really need Hypereutectic or Forged Aluminum if you want it to last any time at all. I'd say getting the carb, timing, and vacuum right will give you as much power as you're looking for.

If you still have the stock points distributor they make different advance kits to adjust the rate of advance, but again, I'd just throw in a stock HEI, change out those wires, and be done with that.

The main difference with those vacuum lines to the carb is if the ports are above or below the throttle plate. Work the throttle by hand again and you can just look to see where the throttle plate shaft goes through the carb.

If they are below that they draw a vacuum all the time, and if they are above they draw when the throttle plate is open. (I think I got that right) The brakes need vacuum all the time, if that helps.

Axe

Forgot to add that after that I would consider my gear ratio before a boost.

Also, I've had a lot more fun in a beat up project car/truck than I ever had in something too nice to run hard.

I'm not sure what kind of pistons. Maybe there is a receipt that'll shed some light but I have to get that from the guy who was going to buy the truck. A basic runover. The work was done in 2002, the truck had 82,300mi. It has 98,680mi now.

Rebuilt 350 with .03 Block Bore (355)
Rods & mains .010
Comp Cam 242 Extreme Energy
Comp Cams Double Roller Timing Chain
B & M Torkmaster 2000 High Stall Torque Converter
Rebuilt TH350 /w shift kit
Elgin valve springs
Flattop pistons
Quadro-Jet 750cfm 4-barrel carb
Electric choke

I think the gear ratio is 3.79 (something like that.) It's a GM 9 bolt rear-end I think. I don't have the papers and I haven't looked at them in a couple years.

[Axe_1]

12-16 sounds right on the timing. Not sure what the total advance should be off hand, but if you stay in that range at idle there is a sweet spot that will accelerate well, not overheat, and still crank with the starter.

Not a big fan of B&M, not because they are bad but because they charge a lot and are directed at the masses. The 2,000 stall may not be quite enough for this engine, but adding a vacuum canister should help that. There are 2 different ways to rate the stall and most companies like B&M use the one that sounds the best.

I wouldn't consider a boost unless I was sure what pistons were in there. I know you want to go small on it, but I personally wouldn't add any with stock Cast Aluminum pistons. You really need Hypereutectic or Forged Aluminum if you want it to last any time at all. I'd say getting the carb, timing, and vacuum right will give you as much power as you're looking for.

If you still have the stock points distributor they make different advance kits to adjust the rate of advance, but again, I'd just throw in a stock HEI, change out those wires, and be done with that.

The main difference with those vacuum lines to the carb is if the ports are above or below the throttle plate. Work the throttle by hand again and you can just look to see where the throttle plate shaft goes through the carb.

If they are below that they draw a vacuum all the time, and if they are above they draw when the throttle plate is open. (I think I got that right) The brakes need vacuum all the time, if that helps.

Axe

Forgot to add that after that I would consider my gear ratio before a boost.

Also, I've had a lot more fun in a beat up project car/truck than I ever had in something too nice to run hard.

[nixtux]

That spring sounds like the inside Throttle Return Spring. They fall off all the time when installing the carb. The outer one is green or blue and more like a Quarter size in diameter. (again from memory)

If the idle is right but it's hard to stop there are 2 main ways to fix it.

1. External Vacuum Cannister - Mount it somewhere under the hood and run between the main intake port and the brake booster for extra vacuum.

2. Torque Converter - (Best solution) Larger stall speed will allow the tranny to slip at the higher RPM. Just remember that any slippage is friction and adds heat to the tranny so it's important to select the right one for the Vehicle Weight, Engine HP/RPM Range, and Gear Ratio/Tire Diameter.

Actually the BEST solution would be to add both as you have the time and money.

I have a Darrell Young 2600 Converter in the M/C and it's perfect for the heavy car with a potato cam. It's Flash RPM is more like 2800 in this setup. I would also recommend a Trans Cooler. It's like a tiny radiator. Cheap and very easy to install but could save you thousands in transmission repairs.

Axe

I got to thinking on the vacuum lines, I think I may have mixed two of the smaller lines on the carb. I've been meaning to switch them and see if the brake presure returns. I checked the metal line that connects to the rear of the carb and it's tight. The fluid is full as well. I know the brakes are good because they were grounded out about 500 (maybe 1000) miles ago. The rear drums anyway. It was winter and they kept locking up. Turned out to be debry got stuck between the drum. Also they brakes were all replaced around 15,000 miles ago.

I've heard some complaints about B&M. It has a B&M 2000 stall. The main complaint is they don't take a lot of power. In this setup, I don't think it'll be a big issue. Albeit, the current stall on it is enough to make it jump 5-7MPH between shifts at WOT. I've been reading about doing a blow through carb. Considering one day, maybe trying to do a small turbo on it. It's a ugly orange 73' rust bucket but it's a fun truck to drive. First things first, brakes, exhaust leaks, and a reman carb. Maybe down the road, some plumbing for a small 8 or so PSI turbo. Assuming it can even handle it. It seems like fairly cheap and easy mod anyway. It has flat top pistons, 9:1 compression, ect ect. I'm not a mechanic. This stuff is a hobby that I enjoy and would like to actually understand it better.

I redid the timing light at temp and ran it up to around 2800RPM's and it looked like the timing was at around 25Deg. I think that may be a little too advanced. I'll probably back the distributer a little bit. I was reading comp cams camshaft PDF and they said to spec it stock and maybe advance it by 4 after that... I think that's what they meant. I got inturrupted when I was reading. But if it's suppose to be advanced 4degs, does that mean it should be between 12-16 since the truck should be (stock) around 8-12. FYI, I think it says 8-12 on the sticker under the hood.

[Axe_1]

That spring sounds like the inside Throttle Return Spring. They fall off all the time when installing the carb. The outer one is green or blue and more like a Quarter size in diameter. (again from memory)

If the idle is right but it's hard to stop there are 2 main ways to fix it.

1. External Vacuum Cannister - (quick fix) Mount it somewhere under the hood and run between the main intake port and the brake booster for extra vacuum.

2. Torque Converter - (Best solution) Larger stall speed will allow the tranny to slip at the higher RPM. Just remember that any slippage is friction and adds heat to the tranny so it's important to select the right one for the Vehicle Weight, Engine HP/RPM Range, and Gear Ratio/Tire Diameter.

Actually the BEST solution would be to add both as you have the time and money.

I have a Darrell Young 2600 Converter in the M/C and it's perfect for the heavy car with a potato cam. It's Flash RPM is more like 2800 in this setup. I would also recommend a Trans Cooler. It's like a tiny radiator. Cheap and very easy to install but could save you thousands in transmission repairs.

Axe

[nixtux]

There should be a little screw on the side with a spring around it to adjust the idle. The point end should be resting on a metal tab. To make sure you have the right one, open the throttle plate by hand and the screw assembly should move with it. Turning that a small amount in will raise the idle, out will lower it.

Lopey is good but if the RPM's still jump up and down at he right idle speed (750-900 depending on the cam, compression, ect) you more than likely still have a vacuum leak. Look for an open port on the intake and base of the carb. The large one one the carb between 1/4-1/2 inch in dia should be the float bowl vent. That should be vented to the charcoal cannister, or just left open for now.

How big was the spring that fell off? There should be 2 large springs used for the throttle return, one inside the other.

Axe

I did some adjusting with the idle. I got it between 780-860RPM at temp. I had to turn the screw a couple turns. Not sure how it drives with the new idle. I figure I'll wait until there is little traffic just in case it decides to idle really high making it difficult to stop. I'll check on the vacuum lines tomorrow. I have to redo the thermostat as well. Hopefully the expensive rubber gasket will seal it up properly.

The spring was white and yellow-ish and a little over a inch high. About the diameter of a nickle.

[Axe_1]

There should be a little screw on the side with a spring around it to adjust the idle. The point end should be resting on a metal tab. To make sure you have the right one, open the throttle plate by hand and the screw assembly should move with it. Turning that a small amount in will raise the idle, out will lower it.

Lopey is good but if the RPM's still jump up and down at he right idle speed (750-900 depending on the cam, compression, ect) you more than likely still have a vacuum leak. Look for an open port on the intake and base of the carb. The large one one the carb between 1/4-1/2 inch in dia should be the float bowl vent. That should be vented to the charcoal cannister, or just left open for now.

How big was the spring that fell off? There should be 2 large springs used for the throttle return, one inside the other.

Axe