new to me 68 Barracuda Conv, sluggish 318

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nxtdrnaybr

nxtdrnaybr

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Hi All,

So I just picked up a 68 Barracuda Convertible. I am new to the Mopar world, but to me the engine seems quite sluggish. I am first in the process of changing out all the fluids and starting fresh along with new plugs, carb cleaning.... Next will be to check/set the timing.

Here is what I know about it:
  • the 318 engine(3spd auto) was rebuilt around 1997, about 17k miles since then
  • at the time 340 J heads were put on along with valve job etc, but I can't find any evidence of any porting etc
  • It's got a Edelbrock 318/360 Performer Intake and a Edelbrock 1405 4 barrel carb
  • Dual exhaust. no headers
I am not expecting it to be a speed demon, but it just seems super sluggish. I haven't really laid into it yet since I haven't checked everything out, but what would you check or think might be the culprit for the lack of power?

I know compression may be an issue related to the 340 heads, which I'll get checked, but I would think even with that it should still have more power. It almost feels more like a V6....

1598a.jpg


1598ppp.jpg
 
Welcome to The Forum and nice car..
Sometimes it can just be a bad combination or a bad tune up... Maybe they put a high performance cam in but didn't change other things like the gearing. Sometimes an extreme highway gear can make these cars seem sluggish..
Along with all your tune up stuff definitely start with your timing first.. sometimes an old spark plug wire can be touching an exhaust manifold and leaking spark.. sometimes things might not have been tightened down in a long time and you can have a vacuum leak which will really mess with you..
sounds to me like you're doing the right thing though just getting all the basics that you would do after buying a used car. Knowing where the fluids are at knowing the last time the tune up stuff has been done.
Lots of times when people are getting ready to sell a car they don't go run out and tune it up to just try and sell it as is.
 
Possibly a timing or an advance issue? The distributors mechanical advance weights are under the timer plate. An easy way to see if they are working freely is to grasp the rotor and manually advance it, see if it snaps back. If it does not, then the advance weight grease is pretty dry and sticky. If it is, then dissassemble the distributor to where you can take the weights out and clean and re grease them. The advance weights have oillite bronze bushings pressed in them, so actually a drop or 2 of clean 30W motor oil on each one should do the trick. Check your vacuum advance canister as well to see if it's working. You didnt say if it was a points ignition or electronic. May be other things such as incorrect plugs, gapped incorrectly etc. Ask away, others here may be able to help too.
 
Timing and throw a vacuum gauge on it
 
Thanks. I haven't pulled the distributor yet to check if its points or electronic.....

I was able to find the receipt for the rebuild. It looks like a simple mopar rebuild kit and the cam listed is a PAW SSI 11309.

I'll definitely post an update once I get the timing dialed in, especially if that doesn't help.

I'll likely get to some performance tuning, but for now I just want to get the new toy running as is and enjoy for a while while i save up.
 
nxtdrnaybr said:
Hi All,

So I just picked up a 68 Barracuda Convertible. I am new to the Mopar world, but to me the engine seems quite sluggish. I am first in the process of changing out all the fluids and starting fresh along with new plugs, carb cleaning.... Next will be to check/set the timing.

Here is what I know about it:
  • the 318 engine(3spd auto) was rebuilt around 1997, about 17k miles since then
  • at the time 340 J heads were put on along with valve job etc, but I can't find any evidence of any porting etc
  • It's got a Edelbrock 318/360 Performer Intake and a Edelbrock 1405 4 barrel carb
  • Dual exhaust. no headers
I am not expecting it to be a speed demon, but it just seems super sluggish. I haven't really laid into it yet since I haven't checked everything out, but what would you check or think might be the culprit for the lack of power?

I know compression may be an issue related to the 340 heads, which I'll get checked, but I would think even with that it should still have more power. It almost feels more like a V6....

View attachment 1715569186

View attachment 1715569187
Click to expand...
Nice car, and welcome! It's so hard to know how close (or how far off it is) because what one calls sluggish another calls running great. Feels like a V6??? What V6? New Challenger, Mustang or Camaro? Them are all easy 14 second cars in which case if you run like that, I'd say it's running great. But all in all, I would start with:
  • timing. Initial and Total.
  • Check that the throttle is coming all the way open
  • Make sure the heat riser flap on the exhaust manifold (if it has one) is free and opening
 
Here is your cam specs. PAW considered it a "Range2" cam. 16-18 in/hg is what you should get from it.

upload_2020-7-28_14-30-11.png


Man looking at those catalog images brought back some high school memories....

The issue with 340 heads is not cranking compression is the static compression ratio. On later 318's (not sure what year) it yields a really low compression ratio.

As stated buy a good timing gun and a vacuum gauge. Do some reading here and ask questions. You'll be surprised how easy these are to work on.
 
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As others have stated, it could be a low compression 318. Putting performance heads (if they are truly are J heads) won’t help unless it’s in combination with other items. It could be a smogged distributor with a super slow/long advance. Timing could be way off. Transmission might be slipping too. Rear end gear might be low (2.45 or 2.76). To boil it down, it could be a bunch of things. Does the AC work?

Enjoy the new ride!
 
Wyrmrider said:
compression check
cam?
Click to expand...
This.
And elevation.
140 is where Performance starts
150 is Running pretty good
160 is As good as it gets with iron heads,
130/140 is typical at sealevel
120 and less is super soft
A big-port intake will only exaggerate the problem.

The usual way to bandaid a soft bottom due to low-cylinder pressure is; with plenty of stall, mid to high 3-series gears, and a fantastic tune. A small 4bbl on a smallport/small plenum, helps. Ideally you would need to increase the compression ratio to work with those heads. Been there/done that.
 
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you just bought a carwith a bad combination of parts 340 heads with low compression 318 pistons yeah it will be a skug . How does it feel once you are past 3500 rpm ? good news is you got a nice car that with a few simple repairs / work can be a screamer .
I'm sure AJ ha a thesis paper on how to get you going . lots of good people with loads of info here to get you on the right track
 
OK. Question on my kickdown linkage. From what I've been reading it does not look right. The second pic below is how it is now, which seems wrong because the linkage should be rest at the back towards the firewall at idle right? Also, I think the spring is in the wrong spot causing the problem. It is connected to the hole.

The first pic I think may be where it needs to be? I moved the spring up to the top of the bracket and it holds tension on the rod so the stud is always held at the back.

Is that right? If so, could this explain why I seem to have no kickdown and it seems to shift up to 3rd very quickly?

linkage 1.jpg


linkage 2.jpg
 
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to adjust that KD;
The carb has to be at WOT.
Then the little Throttle Pressure lever at the trans has to be all the way to the rear. then you take up the slack until the slot in that upper rod is all the way forward against the carb stud.

If this still produces very early upshifts, then there may be one of several things at play here;
1) the apply-ratio is wrong. That is to say, the carb stud is in the wrong place. or
2) the lever down at the trans is the wrong ratio, or
3) the throttle-lever is not engaging the throttle valve, or
4) there is an imbalance in the transmission's internal pressures,specifically between the governor, and the total of; line pressure plus throttle pressure. The usual reason for that, is because the rearend gear ratio has been changed without a corresponding change in governor pressure.
This can be fixed.

The plastic push-pin inserted into the slot, is telling me that the pressures are not right.

Where the spring is hooked to, for the most part, does not matter, so long as it does not tend to cause the throttle to hang open at WOT. After the the linkage is adjusted as above, the rest-position of the slot , on a performance combo is relatively unimportant. The weight of the linkage sometimes tends to push the TP lever backwards which on a grocery-getter can make the light-throttle shifts harsh..... which tends to be annoying. So then you can use that spring to pull that linkage up off the lower bellcrank and that solves that.

If it was my car,tho, I would flip that slotted linkrod so that the slot was more parallel to the road.
I also do not like where your throttle return spring is anchored. Sitting up high like that, puts a lot of force on the primary throttle shaft, which will eventually wear out the bushings.... if any. If no bushings, the the baseplate will end up worn out. The spring should be down where the accelerator cable hooks to, and there should be a secondary larger spring around it, a backup in case the primary rubs thru at the hook. Each of them should individually be able to close the throttle from WOT.
Furthermore, your return spring looks generic and completely not right for this application.
And finally; taping the wires together is a bad idea. This tends to cause induction firing in adjacent wires. Mostly you can get away with this, because only on #5 and #7, do two adjacent cylinders on the same side fire back to back. So those two in particular, need to be separated by about .5 inch or more. Crossing over at 90ish degrees is ok. In your pic, you can see them running side by side all the way from cap to past the valve cover.
 
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Like this, note the double spring for the return(high tech safety feature)

upload_2020-7-30_21-51-47.png
 
nxtdrnaybr said:
The second pic below is how it is now, which seems wrong because the linkage should be rest at the back towards the firewall at idle right?
Click to expand...
Get yourself a '68 shop manual. It has the illustrations and procedures. There's nothing like reading info from the original source.
Also, a lot of material is covered in the Master Technician's Service Conference. So that's another place to look.
Master Technician Service Conference - Chrysler's Training for Mechanics

Upshifts at light throttle will occur at relatively low speeds
Upshifts at full throttle should occur at relatively high speeds.
Details of the expected ranges are in the service manual.

Kickdown into a lower gear on a '68 torqueflite. IIRC part throttle kickdown is much later. '68 will only kickdown near full throttle.

Spark plug wires: Take that tape off!!! Wires need to be seperated to minimize firing issues. Also try not to run them parallel for long distance.

Upper radiator hose: Not as critical but the corrogated ones create turbulance and resistance.

Sluggish response: Lots of possible contributors. It may have more power but not as much torque as a stock engine. Regardless, try to tune what you have. being hot rodded, tuning can not rely on the factory specs. However they do form a decent baseline to work from on a mildly reworked engine. Begin with initial timing. You will need a tachometer that reads decently at low rpms and a timing light. A factory 68 318 would have initial around 5* BTC at 600 or 650 rpm. With the loss of compression due to the heads and cam, the combustion will take longer to burn at idle. So your engine will almost certainly like more initial timing, say 10 to 12 (or more) at 650 rpm. Measure what it is, go from there with small changes. That's what tuning a hot rod requires. Lots of systematic experiments.
 
The throtte cable bracket is from a 2 barrel car. you would be better using a 340 bracket that is available. The kickdown linkage is not correct and not adjusted properly. A cable system is the cheapest and easiest at this point. Get new wires, cap, rotor, and spark plugs. Set initial timing a 10 degrees BTDC to start. Do you have J heads? You should be able to see the J between the spark plugs. If not pull a valve cover and get the numbers off the head. Make sure your carb is open all the way when a friend floors the accelerator. That should get you in the ball park till you go the next step.
 
moparmat2000 said:
Also looks like somebody stuck a plastic plug in the kickdown arm slot to limit it for some reason.
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I think it's a carrage bolt. Fits in the slot nice. It's a band aid for the correct 4 barrel kickdoen slide or a Edelbrock extension.
 
if you increase timing too much at idelyou will have to limit advance in the dist
lots of good suggestions
post up compression test so we can guess at the cam
tune first before throwing money at it
 
Wyrmrider said:
if you increase timing too much at idelyou will have to limit advance in the dist
lots of good suggestions
post up compression test so we can guess at the cam
tune first before throwing money at it
Click to expand...
Agree. Figured since no timing light, he is at least a few steps away from the possibility of having to limit the advance.
 
Thanks for all the help and tips. Thought I would post an update.

After getting through all the tune up items, I finally got the timing set and had the carb adjusted. Ended up at about 11* initial timing. Like driving a different car......
 
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