BBC thoughts

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
prairiehotrodder
Expert
Expert
Posts: 612
Joined: Sat Dec 24, 2011 10:02 am
Location: melfort saskatchewan Canada

Re: BBC thoughts

Post by prairiehotrodder » Thu Oct 19, 2017 3:22 pm

I had a chance to go for a drive today. With the engine fully warmed up it was running so rich at cruise that it was off my gage. My gage starts at 10-1. Would this be what I should expect from carbs that were not calibrated for a t-ram? I changed the primary main jets from 80 to 75 on both carbs just as i put the car away for the winter. We will see next spring. I am asking these questions because i just want to know if this is typical for starting from scratch tuning a t-ram?
Brian
The Word of God is quick and powerfull
www.therocketshop.blogspot.com

statsystems
Guru
Guru
Posts: 1101
Joined: Sun Apr 03, 2016 1:17 am

Re: BBC thoughts

Post by statsystems » Thu Oct 19, 2017 4:32 pm

prairiehotrodder wrote:
Thu Oct 19, 2017 3:22 pm
I had a chance to go for a drive today. With the engine fully warmed up it was running so rich at cruise that it was off my gage. My gage starts at 10-1. Would this be what I should expect from carbs that were not calibrated for a t-ram? I changed the primary main jets from 80 to 75 on both carbs just as i put the car away for the winter. We will see next spring. I am asking these questions because i just want to know if this is typical for starting from scratch tuning a t-ram?
Brian

Now, take the carbs off for the winter and send them to either BLP or Mark Whitner and let them put a TR tune up on them. If you don't, the car will be slower, dirty and no fun to drive.

Again, I pointed out to you that cam and carb are the two biggest killers of TR performance there is. I also said you would end up spending more in the end buying off the shelf carbs than spending the money up front for the right stuff to begin with.

If you add up the time you will waste trying to sort it out yourself, plus the actual monetary output, you will easily have tripled the original costs.

prairiehotrodder
Expert
Expert
Posts: 612
Joined: Sat Dec 24, 2011 10:02 am
Location: melfort saskatchewan Canada

Re: BBC thoughts

Post by prairiehotrodder » Thu Oct 19, 2017 5:07 pm

sorry statsystems but i'm gonna have to disagree. Tuning and replacing jets doesn't cost much. I'm sure any carb would need a little tweaking even if it was calibrated for a t-ram. Having a t-ram is all new to me but i will figure it out and learn what it wants. The money difference between custom TR carbs and what i have was about $1000 difference. These are real nice carbs and i'm happy with them. Just have to learn what the new setup wants. I have received lots of helpful advice on speedtalk already and i'm gonna keep moving forward.
Brian
The Word of God is quick and powerfull
www.therocketshop.blogspot.com

statsystems
Guru
Guru
Posts: 1101
Joined: Sun Apr 03, 2016 1:17 am

Re: BBC thoughts

Post by statsystems » Thu Oct 19, 2017 5:55 pm

prairiehotrodder wrote:
Thu Oct 19, 2017 5:07 pm
sorry statsystems but i'm gonna have to disagree. Tuning and replacing jets doesn't cost much. I'm sure any carb would need a little tweaking even if it was calibrated for a t-ram. Having a t-ram is all new to me but i will figure it out and learn what it wants. The money difference between custom TR carbs and what i have was about $1000 difference. These are real nice carbs and i'm happy with them. Just have to learn what the new setup wants. I have received lots of helpful advice on speedtalk already and i'm gonna keep moving forward.
Brian

Ok.

F-BIRD'88
Guru
Guru
Posts: 5654
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: BBC thoughts

Post by F-BIRD'88 » Fri Oct 20, 2017 1:55 am

A 80 primary jet on a 750 seems big to me. I would drop the jetting to 70 pri and 76 secondary
on both carbs. What is the primary power valve channel restriction size?

At what road speed , rpm and throttle angle was it so rich?

How was it just off idle as you just get going off idle? 1200-2000 rpm ish?
Any snow there yet?

prairiehotrodder
Expert
Expert
Posts: 612
Joined: Sat Dec 24, 2011 10:02 am
Location: melfort saskatchewan Canada

Re: BBC thoughts

Post by prairiehotrodder » Fri Oct 20, 2017 9:30 am

this carbs came with 80 / 90 jets. Yes that does seem big to me. I'm gonna check the PVRC size and the IJ size. I tried it at a slower cruise with as little throttle as possible and about 3000 rpm, and a faster cruise of 4000 + rpm and more throttle. Both were extremely rich. With the 3.5 PV and the idle screws out about 1.25 turns i got the idle pretty decent. I have not tested WOT.
Brian
The Word of God is quick and powerfull
www.therocketshop.blogspot.com

prairiehotrodder
Expert
Expert
Posts: 612
Joined: Sat Dec 24, 2011 10:02 am
Location: melfort saskatchewan Canada

Re: BBC thoughts

Post by prairiehotrodder » Fri Oct 20, 2017 12:30 pm

With the t-ram i understand that each barrel of a carb feeds a intake runner and intake valve. This should mean that the butterflies on the carbs open equally (not progressively) and have the jetting squared. Is this line of reasoning true?

Also - statsystems, the only part of what you said that i didn't agree with is it costing 3 times as much. I'm sure you are right and i don't doubt that you know what you are talking about. My cam may well not be optimum and dedicated t-ram carbs i'm sure would have been better. They couldn't have been worse! This time on this cam i'm gonna try what I think is best and see what the results are. Maybe i'll be disappointed but i'll show the results good or bad.
The Word of God is quick and powerfull
www.therocketshop.blogspot.com

User avatar
FC-Pilot
Pro
Pro
Posts: 216
Joined: Tue Mar 17, 2009 2:23 pm
Location: Peoria, AZ
Contact:

Re: BBC thoughts

Post by FC-Pilot » Fri Oct 20, 2017 1:27 pm

You may want to down size your IFR as that will make a big difference in you light cruise AFR. There is plenty more that can help, but I am not a carb guru, so you may want to search other posts and stuff.

Paul
"The latest tests prove exactly what my money tells them to prove".

F-BIRD'88
Guru
Guru
Posts: 5654
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: BBC thoughts

Post by F-BIRD'88 » Fri Oct 20, 2017 10:24 pm

When just sitting in the driveway and running what does the AFR gauge do if when you open the throttle from idle to raise the rpm (1200 up to 2500 rpm) part "throttle transition". ??

Is the afr in this throttle reasonable 14:1 ISH +/- or does i go pig rich 12.5:1 or richer?
or does it go lean 15:1+++ ???

Anywhere in the 15:1 to 13:1 mid afr is good..

Then when opening the throttle more to where mains fuel flow starts what does the afr gauge do?

Is this the point where it goes very rich?
Make sure the air bleeds are clear or there is nothing stuck in the emulsion wells.
Remove each air bleed and blow out with shop air.

if the primary main jet is just way too big then both throttle angle points afr will be too rich.

Swapping the primary jets to 70 should help trim both driving points.

You can do all this while running in the driveway to get it close.

I suggest 70 72 pri and 76-78 sec jets.

( if the IFR's are just too big they may need resizeing smaller but first you want to get the primary main jet roughly in the right zone)

F-BIRD'88
Guru
Guru
Posts: 5654
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: BBC thoughts

Post by F-BIRD'88 » Fri Oct 20, 2017 10:36 pm

Before installing these carbs did you flip them over and look at the throttle opening at idle to see the T-slot edge exposure or all 8 throttles? Or just bolt them on?
You want the T-slot edge exposure about .020" on all 8 barrels.

Post Reply