Avanti misfire

[Bob Langer]

What could be causing my 1963 Avanti R2 to misfire as it reaches 5000rpm?
Rebuilt fuel pump & carb,new fuel filter,lines and tank cleaned.
New wires,plugs,rotor,cap and pertronix & coil.
Correct timing and vacuum advance.
Idles fine with good vacuum.
Runs smooth and does not miss until it reaches 5000 rpm.
I set the valves cold and wonder if I set them to loose and this is the cause.

Bob Langer
63 Avanti
Glenshaw,PA

[bige]

The blower belts could be starting to slip at that RPM and it will feel like a misfire. The other thing to check would be centrifugal advance. The springs may be a little weak and allow too much advance at the upper RPM ranges. As an experiment back the timing down a little. Low end power may be off but if it pulls cleanly to the 5000 you know where the trouble lies.

Also, and I keep meaning to do this, run another tach in the car that you can use to compare readings. The stock tach may be reading low and what looks like 5000 could be 5500 and the valves may be starting to float a little.

ErnieR

[Bob Langer]

Blower belts are new,but I guess they can slip.Centrifugal advance is ok,springs are good.

Bob

Bob Langer
63 Avanti
Glenshaw,PA

[Mike Van Veghten]

Weak valve springs can also cause a misfire like probem.

When you say "correct timing"...what do you mean?
Correct for what the engine wants or what the book says to use? If you've set it by the book, try giving the engine what it wants (more advance), you might be surprised.

Do you "actually know" the fuel pressure? Or are you just going by the fact you've got a new fuel pump? They can be weak!

If you used the correct "cold" figures for adjusting your valves...you should be fine. About .002" loose from hot.
I've set the valves in my engines cold for over 30 years...with no problems.

One more thing to "verify"...try putting a slightly larger main jet in the carburetor. The engine may just want more fuel!

Good luck.

Mike

[Bob Langer]

Car has only 28000 miles on it,so I think I can rule out valve springs.
Timing set by the book.
I didnt test the fuel pump after I rebuilt it.Will test and see if pressure is ok.
I set the valves at .027 cold.When I set the valves it was about fifty degrees in the garage.Will that make a difference?
I had the carb rebuilt by a pro and was told everything is ok. At WOT the air fuel ratio is 11-1.I really dont want to mess with the carb unless it is really necessary.
Thanks for you input.
Bob

Bob Langer
63 Avanti
Glenshaw,PA

[JDP]

Be damn careful your not getting detonation at full boost. Unless you are running racing fuel, you likely will if set to the factory specs. Todays premium is not much better then the 60's regular.

JDP/Maryland
64 Daytona HT/R2 clone
64 GT R2
63 Lark 2 door
52 & 53 Starliner
51 Commander

[PackardV8]

Hi, Bob,

Describe your "misfire" in more detail. Does it steadily pop in the exhaust? Flatten out/lay down/stop pulling? Start to run rough?

1. It isn't the valve setting cold.
2. You can't rule out valvesprings. How long ago did the engine reliably turn a strong 5,000 RPMs?
3. The tachs are notoriously inaccurate. Temporarily install a known accurate tach and take the engine up as high as it will go, watching the two simulataneously.
4. Who rebuilt the carb? The R2s were set up way over-rich to protect against detonation.

thnx, jack vines
5.

PackardV8

[53k]

Carburetor float too low?


[img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/R-4.JPG[/img=right][img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/64L.JPG[/img=right][img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/64P.jpg[/img=right][img=right]http://www.frontiernet.net/~thejohnsons/Forum%20signature%20pix/53K.jpg[/img=right]Paul Johnson
'53 Commander Starliner (since 1966)
'64 Daytona Wagonaire (original owner)
'64 Daytona Convertible (2006)
Museum R-4 engine

[Bob Langer]

I dont notice any pop in the exhaust.It just stops pulling and runs rough at about 5000 rpm.
The carb was rebuilt by Daytona Parts.The idle is good and no hesitation at all on acceleration.
I have just started to drive the car again after being in storage for a few years.I dont remember if I had this problem before.

Bob

Bob Langer
63 Avanti
Glenshaw,PA

[StudeRich]

If none of the other good suggestions cure it, I would look for a cause of spark scatter, poor quality Dist. Cap, Rotor, Wires (resistence check them), weak ground on Pertronixs unit.

StudeRich
Studebakers Northwest
Ferndale, WA

[Mike Van Veghten]

For what it's worth...rather than say this or that isn't the problem because it's ONLY got 28000 miles on it...MANY of the things noted by myself and others "still" have merrit. Until you actually "check" them...they are "still" a possibility!

The single valve spring is "not" a long term performance part..no matter if it DID have 120lbs on the seat when new.. How much did they have when new?

Valve springs have a way of getting weak. Both internal heat and external heat. Might...be a good thing to check.

Timing - by the OEM book ISN"T the best way to good performance.

Again...rather than saying "no"...to everyones advice to your problems...most all of the things everyone's mentiones IS worth a...SECOND...look.

Mike

[KOOL R2]

I just got home from our local dragstrip with the same problem. All the suggestions that you have been given are the appropriate ones to check. I would go with Belt slippage. That was my problem. Get some
"Belt Dressing" and sand blast the blower pully grooves then try it again.
Peter Sant
KOOL R2

[Bob Langer]

I am new to the forum,and by no means want to offend anyone.All of the input is worth merit and I didnt intend to give the impression I would not check everything.Just because I didnt think it may be the valve springs doesnt mean I will not check them out.I appreciate all the advice and it will make it easier for me to find the problem.

Bob Langer
63 Avanti
Glenshaw,PA

[PackardV8]

Hi, Peter,

Again, a more precise description would be beneficial to those of us who don't own R2s.. When your blower drive belt slips, does the engine "lay down/flatten out/stop pulling" at the higher RPMs, or does it actually "mis-fire which can be heard through the exhaust"? Does the boost stall and hold at a given PSI and the RPMs keep rising or does the boost actually drop noticeably because the engine needs more air as it winds higher?

thnx, jack vines

PackardV8

[KOOL R2]

Jack,
The engine flattens out at 5000rpm. The boost ( I have a memory boost gage) stays at 5.5lbs instead of the expected 7.5lbs. There is no actual misfire sounds but you know that the car is not pulling any more. It will continue to go up in rpms to my planned 5600rpm shift point but very slowly.

Peter Sant
KOOL R2