The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by Elliott Taylor, Nov 19, 2017.
from idle to the floor
okay so it could be the secondaries causing it to because they're going to open instantly on a DP. What I would do is disconnect the secondaries. Then work with the primary until it will burn rubber off idle. Then connect the secondaries and work on it. I really don't tune by the numbers but rather by seat-of-the-pants. The squirters cams, Jets Etc that work the best are the ones you use. Don't really care about the numbers. every combination is different.
Ok, we're getting somewhere. There's 2 culprits to a stumble on launch that's fuel related, one is too much fuel ( a bog), the other too little fuel ("flat spot"). The flat spot is like it want's to stall for 1/2 a second but then picks right up, the bog is, well, a lazy blob of a launch, likely accompanied by a moment of black smoke. For zipping around town a 650 is fun but you're not setting any MPH records with it. A 6000+ RPM 327 can process more CFM and with 12:1 you should be able to burn the fuel (where the energy is!). I smell some performance in the ignition too. Something tells me that if you sort your flat spot out I'd tell you to take 2 degrees out, launch at 2000, shift it at 5800 and run it "out the back door". Would likely go through the traps at about 62-6400 which is all the way through the powerband without leaving it completely. Yes, I am indeed saying sometimes a simple change in technique knocks off some ET or finds MPH. You can raise the launch RPM until it slows down, raise the shift point until ET suffers.
But, let's dig deeper. The cam timing, is it straight up, advanced or retarded? Usually 2 to 4 degrees advance will net more low end power, the opposite nets top end power. With the dome on the piston sometimes you can't mess with it and it has to go in as designed. Too bad you can't borrow a 750 Holley. I predict 2 MPH or better in the 1/4 mi with a 750. And yes, you'll always get the Holley haters but they are one of the easiest carbs in existence to tune and modify. The worst thing about a Holley is the "1st date" where you spend more time on cleaning up the sealing surfaces than tuning. Friggen OEM gaskets are like a fatal attraction but once you do it they always come right off. The old trick before improved gaskets was Chap Stick.
Your changes are telling you which way to go. Listen to it, it's almost talking to you...
I have a cleaned ready to build 3310 Holley that I will let you have cheap. I even have a kit for it.
PM me if interested.
Highlander, i installed the cam straight up. when you say drop the timing you mean about 33 total? im running a bushing that gives me 19 initial and im using the fastest springs, which the motor seems to like best
What does "run it out the back door" mean?
I call this a bog, but i see no smoke. no backfiring either so i assume isnt lean
take and put number 330 cam in with 31 squirts front and rear
try running 32 jets on all corners
with the msd box i always lock out the advance curve and set my timing at 38 degrees and see what happens
does the 650 still have the choke horn on it? if so might want to think about getting rid of that or buy a new center section for the carb (proform builds a very nice one #67203 i believe)
also not sure what power valve you are running 65 is normally stock so depending on your vacuum level you might want to go down to maybe a 45 valve or lower
a lot of trail & error
Hey. ok so i have that pump cam, just ordered a set of size 32 nozzles. I have aj assortment of power valves. a 5.5 is what im currently running.
can i just that choke horn ?
Ive thought about locking out my timing, and right now Im running aa much initial i can without locking the dist with my bushing setup.
im worried about locking the timing. Will it crank up? I have a mini torque starter.
btw what do you mean by "32 jets on all corners"?
you can mill the choke horn off yes but just not the same as buying the proform center section
i'm thinking that your vacuum could be a little low check that so you know where to go with the power valve
as far as jetting goes one thing you can do is keep up the jet tell it starts missing on the higher rpm's, then back them down until it will run flat out smooth
small block likes lots of advance but i wouldn't go over maybe 42, 38 always seems to be the right amount
i,m sorry i meant to say 72
My advice would to stop getting advice from everybody you talk to.Find someone" one person" who has a car that runs well and work with them until you get it . Tuning a car by commitee will never work.I won't give you any tuning advice, buy a Holley book off Amazon and figure it out .Best of luck.
Im not tuning by a car commitee..Im getting suggestions. I plan to take all of this info, apply what I already know, and try things out/draw conclusions.
I know lots of awesome people around here who help me out tremendously. I just dont have a good reliable motor guy. This is the first motor Ive ever built, for reference.
I could be wrong but Im pretty sure thats how you learn and im pretty sure thats the point of these forums. I' love to buy a book and "figure it out" if I felt that would work.
In addition, the reason Im asking these questions on this forum is Im pretty sure everyone doesnt have the perfect answer to every single question I ask. Hence, the reason I had many sources from many experts when I built this car.
I appreciate your input
You'll get it....try a few things, one at a time, and see what happens. It's how most of us learned.
have you cut the threads off a plug and see how fuel rings look?
have you cut the threads off a plug to see how fuel rings on plugs look?
You refer to this carb as a 650 DP but you only mention 1 accelerator pump & 1 pump cam , I'll take a guess that this is a 650 dual - feed w/ mech secondaries ...if that's the case then the tuning procedures would be different than a double -pumper...just trying to keep the record straight..
2 accel pumps and 1 pump cam. thanks
If you have two excel pumps you need two pump cams
The carb is a 4150 right?
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4150. 2 pumps cams. Youre right, sorry
Happy Thanksgiving everyone. Here's a little update: I tried size 31 pump nozzle which didn't help at all. I had a set of 25's which I also tried for kicks with no luck.
I even unhooked the secondary pump cam to see what would happen when I floored the throttle, and I got the same response from the car which is what I believe to be a bog. Any ideas ?
Correction from earlier: from what I've gathered, I believe what I'm experiencing is an off idle stumble/hesitation.
No surprise there. Of course that's not gonna work .Mechanical secondary with no dampener and very little pump shot? Now give it a whole bunch of secondary shot and see what happens.
The reason I unhooked the secondaries was to see if they were even the culprit/rule them out, not to see if that would fix the problem.
What do you mean give it a lot of secondary shot? What are you referring to adjusting?
Take DP off , 650-750 vac , change out Air gap intake ,In my opinion Miss match combination , there is so much more to a tuned engine then Jets , power Vavle , There are so many ajustments to a Carb, timing is critical in tuning, engine temps ,Fuel ratio threw entire Rpm rang , idle , Cruise ,to WOT , seat of yr pants is not a good reference , I have posted several times on tuning a engine , Lots of notes time trial and error ,
Invest in a Good Wide band O2 gauge , find yr self a commercial 4,5,6 inch Vacuum gauge , document
RPM’s Vac & AFR’s in all different rpms ranges,
Then Read up on how to Really tune a carburetor
Yr hard work will pay off
Here is a good start to learning how to tune a carb
You said you unhooked the secondary cam, not the linkage. Which is it ?
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