Transmission? Poor acceleration.

[garyd1961]

I don't mean to be crude but with your lack of knowledge the best thing for you to do is to find a good trustworthy mechanic and take the truck to them.

[telly]

Originally Posted by garyd1961

I don't mean to be crude but with your lack of knowledge the best thing for you to do is to find a good trustworthy mechanic and take the truck to them.

I have come to this website from time to time because the members have always been insightful and helpful. Most of you have more knowledge than I, which is why I come for suggestions even if I already have a good idea of the problem. But just because I don't know every diagnosis due to symptoms doesn't mean I am not capable of doing the work myself and saving $. If I run across something I feel I can't do, then I will go to a shop. If you don't want to help, then don't. And no, I'm not upset...you've just misjudged me. And now, onward we go.

[garyd1961]

"doesn't mean I am not capable of doing the work myself and saving $."
OK, it's your truck, do what you wish but it is obvious that you have very limited mechanical knowledge. You are not saving any money by doing it yourself if you don't know what you are doing.
The reason I suggested taking it to a shop was to save you from causing more damage to your truck and costing you more money to fix in the long run.

[telly]

Thanks

[telly]

Originally Posted by truckster

What are the RPMs doing as it loses speed? Are they decreasing in proportion to the decrease in speed? If not, it could be that your trans is slipping.

So, after warming the engine, I drove it around the loop this afternoon. The transmission was shifting smoothly (around 2800 rpm). When I went up the hill, the engine rpm went from 2600 down to 2300 while the ground speed went from 55 to 51. On flat ground the engine did not want to exceed 3000 rpm at anytime.

Hope to have time to compression test the cylinders tomorrow afternoon.

[garyd1961]

It's not the trans, you have an engine problem. I seriously doubt it came from too much oil though. It could be a lot of different things causing it, timing, carburetor, distributor, worn cam, bad wires or plugs, water in gas, and some more I can't think of right away. Check timing and compression first.

[telly]

Originally Posted by garyd1961

It's not the trans, you have an engine problem. I seriously doubt it came from too much oil though. It could be a lot of different things causing it, timing, carburetor, distributor, worn cam, bad wires or plugs, water in gas, and some more I can't think of right away. Check timing and compression first.

If I can tomorrow after work, I'll check compression and then reset the timing. The distributor, cap, rotor, wires are all new within the year and while it's still possible that one of those might be the culprit I'm a bit doubtful. I have wondered if the carb might be out of adjustment, though. I'll pour some SeaFoam into the gas to see if that helps any.

[mongocanfly]

Grab you some new fuel filters as well...if you got a q-jet don't forget there's one in the carb to..I've tried seafoam before but never could tell it ever helped anything...just because you had new ign parts a year ago doesn't mean their still good..I've seen new, bad parts before...I'd checkem over good..

[truckster]

My first instinct would be to double-check the timing. It sounds like it had more power before you re-timed it, so that's what makes me suspect timing.

[telly]

Originally Posted by truckster

My first instinct would be to double-check the timing. It sounds like it had more power before you re-timed it, so that's what makes me suspect timing.

I reset the timing due to backfire and it was after noticing a loss of acceleration/power. I'm going to reset it anyway, just to be sure.

[telly]

Originally Posted by mongocanfly

Grab you some new fuel filters as well...if you got a q-jet don't forget there's one in the carb to..I've tried seafoam before but never could tell it ever helped anything...just because you had new ign parts a year ago doesn't mean their still good..I've seen new, bad parts before...I'd checkem over good..

I just changed the in-line fuel filter this afternoon before taking it for a spin. It's not a q-jet (wish it was since I've rebuilt the one in my Camaro and also the one I had in the '70 C10 Stepside I used to own). It's an Edelbrock carb - I have never worked on an Edelbrock.

I agree on the ignition parts. I'll go there after the compression check.

[mongocanfly]

If its backfiring and then you lost power and then you had to reset the timing there's a chance it may have jumped time on you during one of those 7000 rpm pulls...when you check the timing make sure you get it on true tdc and then see where everything lines up..pull a valve cover and spark plug

[garyd1961]

Originally Posted by mongocanfly

If its backfiring and then you lost power and then you had to reset the timing there's a chance it may have jumped time on you during one of those 7000 rpm pulls...when you check the timing make sure you get it on true tdc and then see where everything lines up..pull a valve cover and spark plug

This is what I was thinking at work today. Why was it backfiring in the first place, it may have jumped timing or you have a worn cam. If resetting the timing stopped the backfire it's more likely a timing problem.

[telly]

Originally Posted by garyd1961

This is what I was thinking at work today. Why was it backfiring in the first place, it may have jumped timing or you have a worn cam. If resetting the timing stopped the backfire it's more likely a timing problem.

Not sure if it matters, but the engine was only backfiring during deceleration (letting off the gas after passing).

I checked the timing again this afternoon. It was still advanced 12 degrees like I had set it last. I took the truck out and ran it a few miles on the freeway. No backfire issues. It still doesn't have the power/acceleration it used to, but it did cruise along at 65mph and 3000 rpm...still wouldn't want to pass someone on a two-lane road though.

I don't have time to check compression today. Will try to do so tomorrow afternoon.

[telly]

Results of compression test:
1) 148 2) 150 3) 148 4) 150 5) 148 6) 150 7) 148 8) 150


Sucked 8oz of SeaFoam into the intake through the vacuum ports and ran the engine in the driveway until it quit producing smoke. Took the truck for a short drive and still same issues.

These are now the possibilities as I understand it; Plug Wires, Cap, Rotor, Distributor, and/or Fuel pump. Am I missing anything?

[garyd1961]

Originally Posted by telly

Results of compression test:
1) 148 2) 150 3) 148 4) 150 5) 148 6) 150 7) 148 8) 150


Sucked 8oz of SeaFoam into the intake through the vacuum ports and ran the engine in the driveway until it quit producing smoke. Took the truck for a short drive and still same issues.

These are now the possibilities as I understand it; Plug Wires, Cap, Rotor, Distributor, and/or Fuel pump. Am I missing anything?

Vacuum leak, carburetor, timing chain and gears, bad cam and lifters.

[telly]

Replaced vacuum lines to power brake booster, pcv valve (last week), vacuum advance, and another one I don't know (but it goes from the back of the intake just below where the power brake hose attaches to the back of the carb). Didn't see any others.

The carb is an Edelbrock 1406. I just read the owner's manual (which talks about adjustments as well as troubleshooting https://static.summitracing.com/glob...s/edl-1403.pdf). This manual suggests for lack of engine power to: Check air leaks (done), Choke adjustment, Fuel filter (done), Set too lean, Increase accelerator pump stroke, Fuel pressure too low, and Check secondary latching device and rod for proper movement.

I'd appreciate any insight or thoughts from those of you familiar with this carb. I've had experience rebuilding a couple of Q-Jets but none with Edelbrock carbs. Thanks in advance for any and all help.

[cadillac_al]

Is the vacuum advance working?

[jjzepplin]

OK. So here's my take on this.
What does your exhaust consist of? You could back fire on deceleration due to a small exhaust leak.
Now- if your engine is not stock- your timing will not be as well. You cannot use a stock spec. Your timing might have been just fine but you had an exhaust leak.
Timing too far retarded will make your engine a slug.
Too far advanced will give it a pinging noise cause by detonation. This is bad.
Backfiring is usually something very wrong with your cam being worn or lifters broken and possibly the very rare broken valve spring. All of which can give you good compression ratings but not diagnose the problem.
Now your compression ratings (which can be done many different ways) do not suggest a high compression racing type engine. But that is beside the point now.
9 times out of 10, the new problem with your vehicle is the old problem you just fixed.
So- I would slowly advance your timing a little at a time and test drive just till you hear the pinging and back it off a bit and you should be real close.
You should get yourself a timing "CURVE" kit and study the instructions big time and then give it a go. You will be surprised at the results.
Keep your ears on that exhaust for a leak!
Good luck and keep us posted!

[telly]

Originally Posted by cadillac_al

Is the vacuum advance working?

Yes, the vacuum increases as the engine speed increases.

[toolboxchev]

Originally Posted by telly

Yes, the vacuum increases as the engine speed increases.

I believe the OP is asking about the Vacuum Advance unit on the distributor. Most have a diaphragm in them with most being made of rubber. Rubber and Ethanol based fuels do not mix, the Alcohol in the fuel eats the rubber causing it to leak and disable the unit from functioning properly.

[telly]

Originally Posted by toolboxchev

I believe the OP is asking about the Vacuum Advance unit on the distributor. Most have a diaphragm in them with most being made of rubber. Rubber and Ethanol based fuels do not mix, the Alcohol in the fuel eats the rubber causing it to leak and disable the unit from functioning properly.

I checked this and it's in working order.

[rsd66C20]

Been following your thread. I have a 327 w/ 1966 C20 + TH350, that the PO installed a Edelbrock 1406. Had similar problems that you do, tunes great at idle and basic cruise, but then lack of power accelerating or hills. Evidently, the 1406 is a very lean carb out of the box. Even tuning the jets and metering rods leaves you too lean when you need it. I found the article below which explains this in great detail. The solution is, that the Edelbrock 1405 and 1406 are essentially the same carb, except for the tuning. I bought the tuning kit for the 1405, and followed Edelbrock's instructions to tune, and my truck runs much better. I had a o2 sensor, which made it much much easier, but is not necessary.

A vacuum gauge will help determine which carb circuit you are tuning. I had to tune the "Cruise" circuit side of the carb, but never really got into the "power" circuit side....which you may be doing.

1406 troubleshooting article:
http://vb.foureyedpride.com/showthre...6-Carb-Read-On

Edelbrock 1406 manual:
http://edelbrock.com/automotive/misc...404_manual.pdf

1405 tuning Kit:
https://www.summitracing.com/parts/edl-1479

Good luck, and don't give up. I hope this helps.

[rsd66C20]

A couple of other things I missed. I like where the thread is going on checking your timing.

The other issue I had, was the PO had installed a summit HEI distributor that only added 12 degrees to the total timing, and the initial timing was only 8 deg BTDC. That gave me a total timing of only 20 deg BTDC. I ended up having to replace my distributor with a new HEI that added 20 deg (my initial=14/my total=34). My experience is SBC like 34-38 deg BTDC. After checking your initial timing (which is I assume 12 deg BTDC), slowly rev your engine up until the total timing stops advancing. Note the RPM that this is at. Is it between 34-38 deg BTDC? The rpm where the full timing is in at, is probably between 2500-3500 RPM.

On my suggestion of tuning the 1406 like a 1405. My recommendation is to start at the #1 stock setting on the 1405 chart. I ended up leaning mine out to the #22 setting.

[telly]

Originally Posted by rsd66C20

A couple of other things I missed. I like where the thread is going on checking your timing.

The other issue I had, was the PO had installed a summit HEI distributor that only added 12 degrees to the total timing, and the initial timing was only 8 deg BTDC. That gave me a total timing of only 20 deg BTDC. I ended up having to replace my distributor with a new HEI that added 20 deg (my initial=14/my total=34). My experience is SBC like 34-38 deg BTDC. After checking your initial timing (which is I assume 12 deg BTDC), slowly rev your engine up until the total timing stops advancing. Note the RPM that this is at. Is it between 34-38 deg BTDC? The rpm where the full timing is in at, is probably between 2500-3500 RPM.

On my suggestion of tuning the 1406 like a 1405. My recommendation is to start at the #1 stock setting on the 1405 chart. I ended up leaning mine out to the #22 setting.

Thanks for all the info. I'm working through it and hope to make some carb adjustments by the end of the week. The thoughts on the distributor has got me thinking. I did have some issues with the distributor and external regulator a while back (earlier thread: http://67-72chevytrucks.com/vboard/s...d.php?t=682619) but it has been over a year.