[lt1silverhawk]

Originally Posted by T-bucket23

Choke is taking to long to open. Do you still have a heat riser valve in the exhaust and is it free. The choke should be fully open in about 3 minutes or so and should never close up while running. It appears in the video yours actually looked like it closed a little a few times during the warm up cycle

The truck doesn't have a heat riser valve. And yes, the choke plate does seem like it moves back towards the closed position a few times. Should I try a new choke?

[Augusto]

q-jet choke's are crap, just get a piece of wire and fix it wide open or remove the butterfly, try this first.

about timing, set your timing at 8 deg BTDC with the vaccum lines disconected and pluged at the carb, this will give you a good starting point, once done start the engine and check if the timing mark advances when you rev up the engine, should go to something like 20 degrees BTDC.

after this connect the hose to a ported vaccum source, the one with no vaccum at idle, this will give you a good average performance and no issues.

drive it and if still gives you problems replace the carb.

[fasteddy_1947]

[I have a 1977 Chevy truck with a stock crate 350 engine and a 3-speed auto transmission. It seems to be suffering from power loss when in Drive. I drove the truck yesterday to move for the street sweeper and it gave no trouble.


This morning, the truck started up just fine, but when put into Drive, it had a serious loss in power. At first I thought it hadn't warmed up right and gave it more gas but it was more of the same. So I pulled over, shifted into Park, and gave it some gas. The engine revved smoothly with no issues.


So I shifted back into Drive and started driving and still no power. For reference, it was getting to 25 mph in over 10 seconds and there was no chance at going over 35 mph. It also was making a bhup-bhup-bhup noise. I tried shifting manually but that was of no use either.


I haven't had a chance to pop the hood and look at anything, but could it possibly be that the vacuum line to the transmission has come loose?


Thanks in advance, [/QUOTE]

[BigRoy1978]

Originally Posted by fasteddy_1947

[I have a 1977 Chevy truck with a stock crate 350 engine and a 3-speed auto transmission. It seems to be suffering from power loss when in Drive. I drove the truck yesterday to move for the street sweeper and it gave no trouble.


This morning, the truck started up just fine, but when put into Drive, it had a serious loss in power. At first I thought it hadn't warmed up right and gave it more gas but it was more of the same. So I pulled over, shifted into Park, and gave it some gas. The engine revved smoothly with no issues.


So I shifted back into Drive and started driving and still no power. For reference, it was getting to 25 mph in over 10 seconds and there was no chance at going over 35 mph. It also was making a bhup-bhup-bhup noise. I tried shifting manually but that was of no use either.


I haven't had a chance to pop the hood and look at anything, but could it possibly be that the vacuum line to the transmission has come loose?


Thanks in advance,

[/QUOTE]

If it was the vacuum to the trans either the engine would...

1. Idle fast...cause of a vacuum leak

or

2. the trans wouldn't shift until you had the engine up around 3500-4000 rpm


power loss like that, where it will go to one rpm and doesnt want to get anymore is an ignition/timing problem.

[T-bucket23]

Originally Posted by lt1silverhawk

The truck doesn't have a heat riser valve. And yes, the choke plate does seem like it moves back towards the closed position a few times. Should I try a new choke?

Disconnect the choke and see how it runs. Without a heat riser that style choke will not work well. The heat riser forces some of the exhaust back through the manifold to warm it up. Using the wrong intake gaskets can also cause issues.

[lt1silverhawk]

Hey BigRoy,

Originally Posted by BigRoy1978

If it was the vacuum to the trans either the engine would...

1. Idle fast...cause of a vacuum leak

or

2. the trans wouldn't shift until you had the engine up around 3500-4000 rpm


power loss like that, where it will go to one rpm and doesnt want to get anymore is an ignition/timing problem.

Well it does take some time and/or revving before the transmission shifts. What's strange is that there have been times (during the past few weeks since the truck began exhibiting this problem) where I've spent time letting the truck idle for quite some time while revving it up to 4000 rpm here and there. I would then take it for a spin and everything would work fine. But other times, like in the most recent videos, it doesn't want to run well no matter what I do.


The first time the truck began running fine after first displaying these problems, it was after I checked and cleaned all the plugs, tested out the ICM, and installed a new ignition coil. See post# 9 of this thread for more details.


After that, two days later, the truck exhibited the same symptoms, but they went away after revving the engine to 4,000 rpm a few times. The same thing again happened the following day. See post #15 and #17 of this thread for details.


After that, the truck has not run well in Drive no matter what. Now the added mystery is why there is the ever so slight hesitation at the 2,500 rpm mark when revving the engine in Park and Neutral.




Hey Chet,

Originally Posted by T-bucket23

Disconnect the choke and see how it runs. Without a heat riser that style choke will not work well. The heat riser forces some of the exhaust back through the manifold to warm it up.

I do not want to sound as if I am disagreeing, but I am wondering if that would have been a problem before too. Because the truck has been running just fine in the past, save the dirty fuel / carburetor rebuild issue last year.

Originally Posted by T-bucket23

Using the wrong intake gaskets can also cause issues.

Ah those intake gaskets. Did 'em twice last year. You can see which ones on page 9. Since both you and sbchevfreak have brought up the manifold gasket issue, maybe its time to do it a third time. The timing can be tackled from the beginning too, like I should have done.

Originally Posted by sbchevfreak

Is it just me, or do the "even" plugs look to be badly oil fouled? If so, I would be looking at intake gasket sealing on that side....

I can disconnect the choke and fire it up next time, and also open up the choke plate by tying it down.



EDIT:

Hey Augusto,

Originally Posted by Augusto

q-jet choke's are crap, just get a piece of wire and fix it wide open or remove the butterfly, try this first.

I will be trying this, along with disconnecting the choke on the next try.

Originally Posted by Augusto

about timing, set your timing at 8 deg BTDC with the vaccum lines disconected and pluged at the carb, this will give you a good starting point, once done start the engine and check if the timing mark advances when you rev up the engine, should go to something like 20 degrees BTDC.

I've seen various numbers on the what the timing should be set at, ranging between 12 BTDC to 6 BTDC. I read somewhere that 10 BTDC was a safe number to start with. I'll start with 8 next time. It seems like the manifold may be getting yanked again.

Originally Posted by Augusto

after this connect the hose to a ported vaccum source, the one with no vaccum at idle, this will give you a good average performance and no issues.

Ok, so the one where the vacuum advance was previously connected to.

Originally Posted by Augusto

drive it and if still gives you problems replace the carb.

I've got another core I can rebuild, though I hope it doesn't come down to that.

[Augusto]

it has happened to me that sometimes q-jets never work well again, no matter what I make to them, I have several on the shelf that look brand new but they just don't work well, I think they wear out the internal passages or something like that because even after a through clean up and a new parts kit they just don't work well anymore.

stay away from the late models with the internal aneroid, they are the worst, and the electronic models just won't work, smog crap.

I firmly believe that the best improvement you can do to an old car/truck is buying a brand new carburator, I like holley's 1850 for SBC 350's

[cobalt327]

Originally Posted by Augusto

it has happened to me that sometimes q-jets never work well again, no matter what I make to them, I have several on the shelf that look brand new but they just don't work well, I think they wear out the internal passages or something like that because even after a through clean up and a new parts kit they just don't work well anymore.

stay away from the late models with the internal aneroid, they are the worst, and the electronic models just won't work, smog crap.

I firmly believe that the best improvement you can do to an old car/truck is buying a brand new carburator, I like holley's 1850 for SBC 350's

The idle tubes need to be removed. There are spaces below each one that can easily become plugged and cleaning w/o removing them is next to impossible. Because these orifices also contribute to the overall air/fuel ratio/fuel delivery, if they're not right drivability will suffer.

Once the idle tubes are removed, the passages for the idle restrictions and the idle tubes (they're next to each other in the main body casting) can be properly cleaned out.

If the idle tubes were removed carefully, they'll go back in using the original collars just fine. Otherwise, Ruggles sells replacements, both pressed (like stock) or threaded.

The aneroid type APT was a '75-only deal for the most part. There may be carbs on either side of '75 that have it, but they'll be rare.

The feedback Q-jet as used w/the CCC emissions system can be used for drag racing by removing the metering rods, then rejetting it using smaller jets w/o the metering rods. An electronic Q-jet carb set up like this will not be a good candidate for street use- just for drag racing/WOT use mainly, although it'll work well enough to get back to the pits after a run.

[lt1silverhawk]

So, here is the game plan:

- Inspect vacuum line from intake manifold to transmission. Reapir/replace as needed.

- Switch vacuum advance line back to where it was previously installed on the carburetor (no vacuum at idle).

- Disconnect the choke, tie open the choke plate and try starting and running the truck.

- Test out transmission modulator.

- If all goes well, then yank the distributor and redo the timing.

- If all does not go well, then its time to revisit an old friend, the carb rebuild thread. Will pay special attention to the idle tubes.

- Fuel pump volume test still recommended?

- Concerns about the intake gaskets were raised. Do they look ok here (#130)?



Looks good?



I probably won't get to work on the truck until Saturday or Sunday, so it will be a day or two before results are posted.



As always, thank you very much for the continued help

[BigRoy1978]

- Inspect vacuum line from intake manifold to transmission. Reapir/replace as needed.

Good for maitenance, but imo not your problem

- Switch vacuum advance line back to where it was previously installed on the carburetor (no vacuum at idle).

could be an issue, I like to run the one that gives timing at idle...helps out mgp a little

- Disconnect the choke, tie open the choke plate and try starting and running the truck.

could also be it, explains the nasty plugs...

- Test out transmission modulator.

one again...I would save this one for last.

- If all goes well, then yank the distributor and redo the timing.

Dont pull the dist! Just reset the timing by ear, your balancer may have slipped and then you CANT set it right by a light. I urge you to reset the timing, by ear, first.

- If all does not go well, then its time to revisit an old friend, the carb rebuild thread. Will pay special attention to the idle tubes.

- Fuel pump volume test still recommended?

I dont think its even an issue...all my luck with stock pumps tell me they either are good, or shot...no in between.

- Concerns about the intake gaskets were raised. Do they look ok here (#130)?

everything looks fine to me.

[lt1silverhawk]

Thank BigRoy, I'll keep those things in mind.


I've been doing some reading today and have come across two topics that I can use some help on.


Been reading another thread on this forum ("what qjet to buy?"), and there was some discussion on the block off plates for the intake manifold gaskets. As I have mentioned before, this truck does not have a heat riser valve. I did use the block off plates when I redid the intake manifold gaskets. Could they be causing any issue(s)?


I was also looking up information on HEI vacuum advance, how they work and how to recurve them, when I ran across a page this page: "Adjustable Vacuum Advance And HEI Distributor Recurve". The author states that, as part of the timing procedure, Lars Grimsrud recommends setting total timing at 36 degrees, instead of a base timing and going from there: "How to Set Your Timing for Peak Performance ". What are your thoughts on this?

[BigRoy1978]

Originally Posted by lt1silverhawk

Thank BigRoy, I'll keep those things in mind.


I've been doing some reading today and have come across two topics that I can use some help on.


Been reading another thread on this forum ("what qjet to buy?"), and there was some discussion on the block off plates for the intake manifold gaskets. As I have mentioned before, this truck does not have a heat riser valve. I did use the block off plates when I redid the intake manifold gaskets. Could they be causing any issue(s)?


I was also looking up information on HEI vacuum advance, how they work and how to recurve them, when I ran across a page this page: "Adjustable Vacuum Advance And HEI Distributor Recurve". The author states that, as part of the timing procedure, Lars Grimsrud recommends setting total timing at 36 degrees, instead of a base timing and going from there: "How to Set Your Timing for Peak Performance ". What are your thoughts on this?

The block offs shouldnt be causing this big of an issue.

on my street vehicles I set the timing to where when the engine is warm, it will start smoothly...just a couple degrees before it starts to lug the starter when it tries to fire.

But the method mentioned is a great one.

I would tie the choke open and try it...just to eliminate that. then concentrate on the timing.

[Augusto]

Originally Posted by cobalt327

The idle tubes need to be removed. There are spaces below each one that can easily become plugged and cleaning w/o removing them is next to impossible. Because these orifices also contribute to the overall air/fuel ratio/fuel delivery, if they're not right drivability will suffer.

Once the idle tubes are removed, the passages for the idle restrictions and the idle tubes (they're next to each other in the main body casting) can be properly cleaned out.

If the idle tubes were removed carefully, they'll go back in using the original collars just fine. Otherwise, Ruggles sells replacements, both pressed (like stock) or threaded.

I tried once to remove them but they were pretty much stuck in there and I feared damagin 'em, what would be a good way of doing it? heating up the casting maybe? what would be a good tool to grab them without crushing?

thanks for the tip, I'm sure this will cure some of my "junked" q-jets

[cobalt327]

Originally Posted by Augusto

I tried once to remove them but they were pretty much stuck in there and I feared damagin 'em, what would be a good way of doing it? heating up the casting maybe? what would be a good tool to grab them without crushing?

thanks for the tip, I'm sure this will cure some of my "junked" q-jets

If you look closely you can see there is an outside collar and the inner idle tube. Use a flat punch about 0.085" diameter to drive the tube out of the collar. Don't drive the tube down too deep, just carefully tap it down about 1/8" or so. If you go much further the bottom of the tube will hit the bottom of the passageway.

Then take a fairly long (at least 1") wood screw or drywall screw that fits the top of the collar. You can grind the sharp point off the screw so the screw threads bite into the collar before the tip of the screw touches the tube you just drove out of the collar.

I always use a small pencil type butane "torch" to warm the exposed area adjacent to the tubes instead of pulling them cold. 10-12 seconds is all it takes. A good cigar lighter could work well for this- you don't want nor need a big amount of flame/heat. This makes it VERY easy to pull them.

Side cutters work excellent- I use a 2" long x 1" wide x 3/16" thick strip of wood (made from a piece of wood paneling but could be most anything) across the carb body to protect it as well as making it easier to lever the screw/tube out. The strip- when positioned fairly close to the screw extending up from the tube- helps removal by letting the tips of the cutters reach downward from horizontal to grip the screw, then when levering the tubes out the cutters have enough room to remove them before the handles and your hand touch down, if you follow. Then tip the carb upside down and the idle tubes will fall out.

Then you can get into the passageway and flush/scrub it out so there's nothing in there to clog things up. Take a thin stiff wire to probe/clean the idle restriction tube then use compressed air and/or carb cleaner spray to flush the restriction tube. This blows all the crud into the (now empty) idle tube passageway so it can all be removed.

Hopefully that'll make a big difference in how the "unfixable" Q-jets will work for you.

[T-bucket23]

Originally Posted by BigRoy1978

The block offs shouldnt be causing this big of an issue.

on my street vehicles I set the timing to where when the engine is warm, it will start smoothly...just a couple degrees before it starts to lug the starter when it tries to fire.

But the method mentioned is a great one.

I would tie the choke open and try it...just to eliminate that. then concentrate on the timing.

Block off plates with that style choke dont go together at all. if the exhaust is not allowed to cross over it will take forever for the choke to open.

Lock the choke open, clean the plugs and try it. I think you will find the problem will be gone.