63 Power Loss on Acceleration

[Joel T.]

Hi All;

On my 1963, I finally managed to straighten out all the bugs with the drive train. Last steps were to replace the rear with a correct ratio and then to get the drive shaft balanced which it really needed. Now the car runs like a watch; tons of power and smooth as a baby's you-know-what...

Yesterday and again this morning I ran into a new issue and that is power loss during hard acceleration. This is a 340HP car with the Carter AFB. When I really lean on it, it really picks right up and pulls strong (sounds pretty good as well). After a few seconds at close to wide open, it will stumble... this is not a miss or a break up but rather a loss of power. Once I get off it and resume at less than full throttle, it is just fine. Normal cruising is fine as well as is normal gradual acceleration and highway performance.

I'm thinking fuel system problem, perhaps a pump which cannot keep up with demand at WOT. The pump in there now is from Corvette Paragon, one of their #4657 reproductions.

Any thoughts??

Thanks!

Joel

[Tom H.]

Re: 63 Power Loss on Acceleration

I would say you are on the right track. I would check the simple and obvious first. Air filter, fuel filter, spark plugs, plug wires, timing, points etc.

Then I'd check the status of the fuel delivery components. How long since a carb rebuild or adjustment of float levels ?? Sounds like a fuel delivery issue to me too. Check pump and lines. Is your fuel line setup stock ? or do you have any rubber hoses ?? Check for kinks or sharp bends in the hoses if you have any rubber ones.

It's really hard to tell without driving it, but just start checking things one by one and hopefully you'll find it is something simple.

[David D.]

Re: 63 Power Loss on Acceleration

Joel,
I am by no means an expert but I'll throw out some things that I'd look for, because it sounds like for some reason you are getting lean at top end.
1) Fuel supply

• In-line filter between your fuel pump and the carb
• In carb filter dirty or missing spring
• Float Level Too Low
• Incorrect Main Jets
• Primary throttles adjusted to open over-center or not fully open
• Power Valve. Should start dumping fuel in when manifold vacuum hits 6.5 Hg.
• Check psi level required for your carb and make sure fuel pump is supplying

2) Vacuum

• Your motor should produce power at wide open throttle with a total timing advance of 36-38 degrees. (This plus you idle setting degrees)
• Hook up a vacuum gauge to the intake manifold or base of the
  carb. With the transmission in “drive” (or in neutral on a manual car), note the vacuum reading. Your power valve should be rated at about 2” below the actual vacuum reading. A car running at 6” of vacuum, you will need a 4.5 or a 3.5 power valve. If reading is bad, your power valve may have a leak.

Good Luck,
David

[Timothy B.]

Re: 63 Power Loss on Acceleration

Joel,
I would try a new set of points first, they could be the high RPM problem.

[Jack H.]

Re: 63 Power Loss on Acceleration

Another potential is the filter 'sock' in the gas tank surrounding the fuel outlet being clogged with debris. When was the last time the tank was drained and cleaned out?

[Joel T.]

Re: 63 Power Loss on Acceleration - More Info

Guys;

Here is some more information.... The carb has had a recent rebuild, basically about 1000 miles ago. Points, plugs, wires, etc.. are all basically new, again about 1000-1200 miles ago. The fuel filter is one of those new 090 reproductions and is about a month old. Recently I reset the dwell to 30 degrees dead on and set the initial timing to 14 degrees. The distributor was checked out when the motor was built and I have subsequently installed the correct vacuum advance unit.

I do need to check the vacuum settings but as I recall this cam produces a relatively low vacuum reading. Having said this, this problem is new... did not happen (or at least was not noticed) until yesterday.

I tooled around with the car again this morning and did a few WOT runs... it pulls well until we get up to around 4000 RPM and then it stumbles... seems a bit worse today than yesterday but that could be me looking for it more. Given the quick onset of this... I think I will start with the electrical stuff first; new points and condenser.. I also have another 087 coil which I think I will pop in there as well.

Thanks for all the suggestions and I will keep you all posted.

Regards,

Joel

[Joel T.]

Re: 63 Power Loss on Acceleration

Hi Jack;

Thanks for weighing in. The tank was cleaned when I did the mechanical restoration on the car, about 18 months ago. The pickup and sender are new and is one of those made in the USA units (as opposed to the import stuff). I filled the tank this morning and as I always do, I check the bottom for crap... it was clean down below, as least as far as I could see.

Regards,

Joel

[Gary S.]

Re: 63 Power Loss on Acceleration

You obviously had good advice from guys much smarter than me but have you tried a simple R & R of a non-repro fuel filter? It sure sounds like a fuel issue but I don't fault you for looking at ignition and tune-up related issues.

That said, when I first put in new points on my 72, the book said to use a very small amount of distributor cam lube. Well, I used the adage "if a little is good, more is better". Above about 2500 rpm I had a complete bog down similar to what you described. Turns out that the excess cam lube had been thrown out and was fouling the points. I cleaned the points, wiped out all the excess lube and then my LT-1 screamed down the highway, right up to red line.

Gary

[Jack H.]

Re: 63 Power Loss on Acceleration - More Info

Interesting, now there are some facts to sink our teeth into (bogs at 4000 RPM)!

You know, that's the approximate 'magic' point where a Chevy SB with a 4Bbl carb will REFUSE to climb past if the carb's secondaries aren't opening properly...

[John D.]

Re: 63 Power Loss on Acceleration

Joel, If you are running NOS or foreign made Delco points I would replace them with a set of Echlin CS 786P and matching condenser. Some of the DR's will wind up to 3500 or so and take a powder. I am wondering why you used a repro 4657 pump??? Not saying they are not good though. Originals are not that hard to find. An original 4657 pump would not have the frog pads. It would just be stamped 4657 with no suffix. Later style has the pads and a suffix. Either way I would go with an original no matter which style. I see others mentioned the repro filter. I do hope it isn't that as that is one pretty repro part and should judge quite well. Dirt could be causing your problem.
Some of the viton needle and seats being sold really have a small orifice or hole in them for the fuel to go thru.
The one we use on the FI is OK for street driving but if I was racing the car I would go back to original steel one. That theory holds true in the carbs also. Are you using a repro vacuum advance? If so go to NAPA and get a B22 before they are history. I said that because the NAPA Standard B28 are gone with the wind.

[John D.]

Re: 63 Power Loss on Acceleration - More Info

Joel, I just saw your latest post on your cam putting out low vacuum. For sure change your vacuum advance. There is a zillion posts here on that. You need at least a B28. You didn't say what low is though. Although they are history I may know where u can get one. Don't use a repro as they are just for the trailer queens. Maybe you have a 236 15 or 16 around. Try that. See Dukes posts on vac advances.
I know of someone who is correctly reproducing the 236 15 or 16 ( I forget) but it will be a little while before they are ready.
Could your timing be retarded??? Hope it isn't the fuel filter for sure. I doubt it as Brian put a lot of effort and bucks into that project. John D.

[Stuart F.]

Re: 63 Power Loss on Acceleration

In my nearly 45 years of experience with my 340 hp 63, the only time it would bog out at around 4000 RPM (up on the cam) was when my plugs were fouled. This would happen any time I cruised through town in stop and go traffic and the engine heated up a little past thermostat temp (mine has the 3.36 rear so I'm lugging a little). My cure occurred back in the 70's when I went to electronic ignition, and it's even better now with a Petronix II. I have standard heat range plugs (AC-44's) and they last a long time. In the early years, I was replacing them almost every week. Once they are fouled, they won't come back, they won't clean up. They will run fine to about 4000 all day long, but when you get on it they break down. Of course, you could have any number of the issues previously mentioned in the other responses, and many are worth checking into. But you can stay away from those talking about "power Valves", etc. as you don't have a Holley (thank God!). The 340 hp w/Duntov and 11.25 to 1 Compression can be brutal on plugs. To begin with, Chevy used the wrong Vacuum advance with them and I'd recommend you follow the advice about changing it out as I did. The AFB is too simple to screw up much as well. In my opinion and experience (Speed Racer), the 63 340 hp RULES over all mid-year small blocks, including those "Lean Fuelies". It's just a great combination; simple carb, 461-x heads, Duntov Cam all put the power down when and where it can be used. Pull a 3.36 rear and you will leave all those 3.70's, 4.11's and 4.56's far behind, no matter what SBC they are running (stock of course). Mine has for 45 years.

Stu Fox

[Joel T.]

Re: 63 Power Loss on Acceleration

Hi Jack, again....

Those secondaries are wide open.... until she starts to stumble it makes the sweetest music... you know that sound... Actually, I can get her to stumble even without pushing her that hard... have had it happen with the secondaries open... or not.

Not sure if this helps..

Joel

[Joel T.]

Re: 63 Power Loss on Acceleration

John/Stuart;

Based upon one of Duke's posts a while back I did swap the vacuum can to the B28, picked it up from Napa.... While I will check it tomorrow my recollection is that vacuum is down in the 12-14 inch range, but don't hold me to that number until I check. The cam is not a Duntov but rather a Competition Cams CS 282S-10, including a set of new solid lifters.

The points which are in there are your basic Napa over the counter parts. I will look into either the ones which you guys mention or perhaps the electronic ignition option. Have you guys had any experience with the single wire set up which Dave Feidler sells???

Stuart, I hate to say this but I just swapped out my 3.36 gears for a set of 3.70's a coupleof weeks ago, and with the close ratio it is like night and day... can't believe that it is the same car!! I'll stick with the new ratio and I know where you can get set of used 3.36's cheap!

Be well and thanks again!

Joel

[Gary C.]

Re: 63 Power Loss on Acceleration

Joel, reference the electronic ignition - I've got ten years on my Petronics without any problems and would use nothing else but Petronics. If you have solid lifters don't forget to use the diesel oil per the great information that Duke and others have posted in the archives. Gary....