Neil,no matter how good a carb they are,most are gonna be put off if they think they have to strip them down before they fit em.
Not everyone does what you do,so they have to sort out there machining tools & quality control .
How many barry grant s are there out there already fitted & not performing to there potential.
Personaly,I would buy another knowing it had to be striped first.
I agree Adam it is bad and you're right when you say most will be put off buying one.
As for how many are already fitted and not right, well that's a good question, we (as in FBO in the states and me here) see a small amount that are really bad quality wise, these are easily put right, made easier by knowing where the problems are.
By far the biggest problems are caused by people just buying the wrong Demon then trying to make it work
as in
1. the application needs a speed but if a speeds good then a mighty must be better, right,
2. The CI needs a 750 Demon (whatever model) but an 850 holley was removed so an 850 demon is fitted, motor runs lean, owner thinks he has a killer motor as he had to increase jet sizes by xyz, this actually makes the problem worse
3. Not enough initial timing in the motor, exhaust stinks, may overheat, crap idle, then spend days trying to lean the carb down before finally finding the idle eze to bandaid the timing problem
4. Not enough convertor, gear
5. Mechanical Speed on a heavy auto car
Initial timing, recommended by BG (these figues can still be too low)
Speeds up to 750 14* to 16*
850 Speeds 16* to 20*
Mightys 18* to 20* minimum
Race, Race RS, Kings, King RS 20* plus
There is no load on the motor at idle, the only thing to be aware of is the motor kicking back at the starter, this is why we ask for a starter kickback test.
The higher the initial (to a point) the cleaner the idle will be
the initial is set to 2* less than where the motor kicked at the starter, this varies depending on a whole range of things, we then use the vac can connected to manifold vac to pull in a lot more JUST at idle, as soon as you're on the throttle the vac drops off leaving the motor on the curve which can be controlled much better than any can.
If anyone has seen a Mopar distributor on a machine while pulling vac timing you certainly wouldn't that happening while driving, timing is all over the place
Adams motor for instance ought to kickback at maybe 20 to 25, whatever it is will be the initial -2*... total 34* at 3100/3200rpm BUT the can would pull timing at idle for a much higher figure
Anyone can say what they like but it works every time, this motor is eye watering rich at idle, running on, and does overheat, the fuel hasn't enough time to burn completely and is loading cylinders, i'll bet anyone anything it's totally different when the initial is increased
I used to like 12 initial (with vacuum advance but limited to a max of 10 degrees) but love 14 on my car now.
BTW vacuum advance has no effect at WOT.
My understanding is that increasing the initial more helps bigger cams, loose converters and lighter cars. Or all three at the same time.
Small blocks in particular seem to like a higher initial and sometimes higher max timing. But this should NOT be a crutch to fix a badly tuned carb.
I personally find the bigger, heavier big block cars with modest gearing and tight converters like less initial. Which is why I start at 12-14 degrees on these cars (which make up most of the cars I have tuned) with the vacuum advance still attached for cleaner plugs and better mileage at part throttle.
If it was a very serious and big engined street/strip or race car I would do what Neil does.
As for giving the fuel time to burn.
If the throttle blade position is in the correct reletionship with the transfer slot and the idle mixture set just slightly on the lean side then everything will burn completely with no problems as long as the idle speed is less than 900rpm which should be possible by drilling holes in the throttle blades.
I would then adjust the timing curve of the dizzy to throw in half the timing by 2200rpm which should result in lots of timing just over idle speed and closer to the speed the engine only just starts to load up on most higher than stock converters. This is the point you need a lot of timing. More timing at idle only helps bigger cams a little. Most still need more air.
One thing I thought of to try one day is look at how the initial timing increases the rpm at idle. You know how engine idle speed increases with timing up to a point and then flattens out?
I want to know what rpm it does this at and if setting the initial just at this point is of any benifit. As long as it is over 12 degrees and less than 18.
Something to play about with next time I tune my own car I think.
I will not be using vacuum on my car from now on so my initial timing may end up something like what Neil suggests anyway. But I have always found it best to taylor the timing curve to work with THAT engine I am working on. Rather than come up with a timing curve that tries to apply to all. The ideal being a curve that is 2 degrees below pinking at high load and Wide/Part throttle at EVERY rpm from 2000-3000rpm.
Because of my high stall converter this may need a higher initial because the converter does not fully load until 3000 anyway at the moment.
Unless you only ever drive at full throttle I don't see why anyone would not use vaccuum advance on a street car.
You lose nothing at all (since as Dave says it has no effect at WOT) and you gain part load fuel economy and power. OK, you can get the power just by opening the throttle more, but with the price of gas and the fact that most of us are on part throttle most of the time ( ) on the street, I can't see a reason not to use it...........
Gavin Chisholm - 414ci W2 Stroker SmallBlock Panther Pink '71 Challenger convertible - in bits Car progress can be viewed here
Neil is gonna curve the dizzy.
Did a kickback test as Neil suggested & found the motor to like 20* initial,problem is,@ 3000 revs the motor is @ 50*.
Can't set the initial @ 14*,which is where it wants to be to give me 35* @ 3000 revs,cos it spits out raw fuel from the rear end & runs backwards when you turn it off.
So,as a band aid till i get the dizzy back fron Neil,I have the vac can connected to the vac port on the carb which is below the throttle plates,which is giving me that little bit more initial(8*) above what the motor is dialed in @(14*)the idle is crisp & clean & starts on the button with no running backwards.
Obviously when I hit the throttle the vac is lost & I get the 35* @ 3000 revs.
.
) on the street, I can't see a reason not to use it...........
