Tuning a TBucket Dart 400 cuin Engine

Bit of a scary moment today. Went for a drive by myself and went south to my best test
track thinking that I wanted to make a 1/4 mile run that the speedometer records my
time. First gear was all spin that I was not ready for, so I missed my shift point. Went
to 2nd gear and lifted off the throttle, except the throttle didn't come back to idle. It stuck
at something less than 1/4 throttle, so I could control it with the brake. Slowed it down
and kept shifting down in gears and got off the road shutting the key off. Whoeee don't
like those kind of rides.

Blipped the throttle by hand and it finally went to it's idle position..... with engine off.

It stuck again on the way home, but just stabbing with my foot fixed the throttle. This was
all at low speeds this time, not a problem.

The only change has been the secondary main jets, but what's that got to go with the
throttle shaft I don't see.

I looked thing over, even checked the bottom of the air cleaner for throttle marks and found
nothing so far. Will check more in the morning.
 
Probably best to head to the local 1/4 mile Race Track with the T-bucket for You Rick. Test there.
 
have you located the reason the linkage was binding up yet?
PICTURES???
 
Just weird.
Your so detailed Rick.
Check to make sure the Carburator baseplate gasket is not hitting the baseplate butterflies .
 
It seemed to drag for a few times, but nothing now. Could have been some dirt
in the transmission TV valve that has cleared now. Trimmed the baseplate gasket
before it was even installed the first time.

Since I also suspected the TPS and while examining it further, the throttle jammed
with the engine off. It took awhile but I finally found the problem. I had the
carburetor off last weekend, therefore I had to remove and replace the throttle
return springs. One of the dual springs got twisted while installing them. Now I
have to wonder about all those tests that came after that point in time.

I hate intermittent problems, they are the worst!

FP02_JammedThrottleSpring_6182.jpg
 
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glad you located the issues ,source ,
(love the picture as the picture does sure help clarify the reason the linkage might bind)
 
Indycars said:
Bit of a scary moment today. Went for a drive by myself and went south to my best test
track thinking that I wanted to make a 1/4 mile run that the speedometer records my
time. First gear was all spin that I was not ready for, so I missed my shift point.
Click to expand...
Sounds like you're on the right way with that carb tuning :).
 
Decided to do something different and record a WOT session. The car must be running
better now because I'm getting uncontrolled wheel spin in 1st gear. Before I started
tuning they would squeak all the way thru 1st gear, but not out of control.

On the plot below, I eased into the throttle instead of just stomping it and the rear tires
still wanted to get into uncontrolled spin. So I had to back pedal some to keep the RPM's
under 6000. You can see on the plot where I got 2nd gear and the G's went back up. The
AFR is all over the place with me in and out of the throttle, so can't tell much about the
carb on this run, but it sure was fun.

Just normal driving now is barking the rear tires going into 2nd sometimes.

2015-08-17-1926_WOT.jpg
 
Lol WOT pass in first and second? its not going to happen(not with traction anyway haha).
It do not look to bad. The WOT pass are a bit short to really tell anything but they look "normal", i use to do my WOT test in 3rd gear on a hot sunny day.(with 4 speed manual trans).
Just opening the primary to 50% on 4th gear at around 2500rpm and i get wheelspin on a wet road :O.
With the weight of that t-bucket, your going to be very carefull once its tuned.
 
Looking good. Seat of the pants feel is what your after. If your chirping tires without even trying, your real close. The one thing I see in question is the lean spot just before you let off the throttle. Wonder if that's your secondaries opening too fast or your PVCR a bit too small. The throttle transition was fast so it's hard to tell. You might want to try a stiffer spring on the secondaries.

2015-08-17-1926_WOT.jpg
 
bytor said:
Wonder if that's your secondaries opening too fast or your PVCR a bit too small.
Click to expand...

I ran this test 5 minutes before the WOT above and looks like I got the same lean spike
in the AFR. The test below is again like all the others, a 3rd gear only acceleration test.
So you think it's the Secondaries coming in to soon and leaning out the mixture??? I do
have the lightest spring available in the carburetor right now.

PVCR was .061", now are .070" during this run.

2015-08-17-1921.jpg
 
Indycars said:
I ran this test 5 minutes before the WOT above and looks like I got the same lean spike
in the AFR. The test below is again like all the others, a 3rd gear only acceleration test.
So you think it's the Secondaries coming in to soon and leaning out the mixture??? I do
have the lightest spring available in the carburetor right now.

PVCR was .061", now are .070" during this run.

View attachment 5996
Click to expand...


Humm.. It looks like the lean spot begins just after the power valve starts to open at 6.5hg. When it goes rich again is when I assume your secondaries are opening/open. Bump up your PVCR and see if the lean spot changes.
 
It go lean, then rich, then it goes normal.
Sound like too small accelerator pump squirter nozzle to me. if it was the pcvr the AF will not jump around like that no? ?.
Well am used to dual pumper, i dont know if that is because of the vacuum secondaries. can't really help there sorry.
Can't tell when the secondaries are opening so its not easy.
 
http://garage.grumpysperformance.com/index.php?threads/holley-carb-power-valves.1639/

http://garage.grumpysperformance.com/index.php?threads/holley-carb-secondary-springs.8126/

Id be looking at two sized leaner on secondary jets and one step richer on the PV, IE if its a 6.5 try a 7.5

2015-08a.jpg


8vt6l0.jpg
 
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But my vacuum at idle and in gear (automatic trans) is 8.5 inhg. Don't I run the risk of
the PV opening at idle, are they really that accurate compared to their ratings. I read/video
that says 2-3" below to 1/2 of idle vacuum. One inch seems too close.

Comments please!
 
you really won,t know how it will work untill you test it,
Id suggest changing the rear jets first, test that change,
then add a stiffer spring to slow the secondary throttle plates a bit,
test that,
then I generally have an assortment of power valves,
go up or down,on the power valve a step at a time,
take notes, youll start to see a pronounced trend, that should tell you whats needed
those computer graphs, taking lots of detailed notes and reading spark plugs will be very useful
SL1000w.jpg

http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/

http://garage.grumpysperformance.com/index.php?threads/reading-spark-plugs.3949/

http://garage.grumpysperformance.com/index.php?threads/holley-accelerator-pumps-cams.1790/

http://garage.grumpysperformance.com/index.php?threads/holley-annular-vs-down-leg-boosters.5229/

http://garage.grumpysperformance.com/index.php?threads/holley-carb-tune-info.264/

http://garage.grumpysperformance.com/index.php?threads/spark-plug-info.202/
 
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With a carburator I have found Wideband 02 Sensors most useful at WOT.

Other than I tune by reading spark plugs and driving it.
 
No data or plots to look at tonight guys. Got all the way out there (18 miles round trip)
and the cross winds were giving me hell and THEN I passed the State Police. Figured that
was too many NEGATIVE omens ..... it was time to go home and come back another day.
 
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