Spitfire & GT6 Forum

so i have spent the better part of a day trying to tune my HS4's
according to my "Tuning SU Carburetters" guide (1968 by Speed and Sport Publications)
i should adjust the jet to the top of the bridge and then back it out two full turns.
then cycle through adjusting idle and mixture.
so...i have the engine idle steady around 500-600rpm and when i lift the lifting pin the idle bumps up bit then settles
and the air "hiss" is the same in both carbs. however i have a smokey exhaust...kind of a whitish/brownish in color, possibly sooty.

according to the manual that indicates a rich mix. however, if i try to lean it out untill the smokey exhaust is better i can't get a steady idle and the lifting pins cause it to stubble and die.

so... do i settle for a smooth idle and sooty exhaust or crappy idle and not so sooty exhaust.

i should say that i have no real idea of the head condition. the engine does have good compression (150, 152, 150, 151) and a fresh tune-up.

or...does my car smoke just because i don't have any emission stuff on it?

either way i am getting a wicked headache from sitting in the garage with this thing.

thanks as always for the advice.
~B

Hi Bill,

I see from the pic thread you are running some kind of pancake air filters. That
should work fine, what needles are you using in the HS4's?

Setting up HS4's are all about finding the right balance of air, fuel and timing.

I have no emission equipment on my car and it does not smoke.

Al

Bill,
I think you should get the idle "nice" don't pay too much attention to the smoke, and try driving the car for a while to see how the plugs look. Our modern oxygenated fuel doesn't burn like gasoline used to. So setting the mixture is different too. If your plugs look alright and you don't have soot on the back of the car you are doing pretty good. Going to the lean end of things to eliminate the smoke might give you white plugs and the danger of piston damage that goes with them.
Good luck,
Paul

Thanks Al and Paul.
I am doing all of this without the air cleaners on it... i am assuming that they will richen the mix a bit when installed.
I am not sure which needles i am running. They are the ones that came with the carbs. This setup came off of a (suposedly) running spitfire in Great Britian. It is the "ball bearing" style dashpots and pistons. So i have to assume for now that the needles are the stock units.
when i got the car last year it had a weber dgv on it and a sooty bumper ( see pics in my other thread) i figured that because of the weber intake runners being differnt lengtjs that the PO had been running it rich... now i am begining to question everything ...lol
When i started this tune i felt like i turned the jet nuts out(rich) an awful lot. But this being my first attempt at SU i had to trust the idle and stick to the manual...
i will get back after it once my head clears...it is raining here today and even though i have the car backed up to the edge of the garage and the fans running i am still getting a head full of exhaust... and it smells rich...
I will keep yoy all posted and feel free ti share any ideas you all may have on this.
Thanks
~B

I agree with Paul, set the mixture a little towards rich, pop the air cleaners on
and go for a spin. Check how your power and driveability are. I set my idle at
about 800 rpm's with the HS4's. If you go more lean see if adjusting the timing
will result in a smoother idle. You will have to adjust timing, mixture & idle
settings to get a balance. If you can't achieve what you want, pull the needles
and see what they are.

If the car can't be driven, that's no fun. So, working with what you've got, set it to be most driveable, and enjoy the smoke.

Yes, the air filters and especially the cover will reduce air flow and create a higher vacuum. It can be enough to substantially alter how the engine runs.

Chasing a better needle profile is possibly worthwhile. At least identify what you've got for future reference and research.

Thanks everyone for the helpful info.
i think i have got it pretty close adjusting just the carbs.
i have yet to mess with the timing. i wanted to get the mix as close as possible before i added another varialbe to the mix.
for now i have removed the filter elements and replaced them with a fine mesh SS screen material wraped around the coarse mesh that held the foam element in place. as i don't drive it in the rain or on dirt or gravel roads i figured it should be fine until i get it all dialed in.
i will play with the timing tonight and/or tomorrow and see what i can come up with.
at this point i think i have got it to where i am adjusting out levels of "perfection"
i tend to get a bit OCD when it comes to this sort of thing.
hopefully the third moon of jupiter will be in line with pluto tonight and i will be able to adjust my tune to perfection!!!
thanks again for all the input.
~B

Hey Bill, you will probably find that adjustments to your timing will effect the mixture settings. Generally, you want to get the timing set before you deal with the carb settings.

In reality, I find the process to be a bit iterative. I think it makes sense to twiddle with the carb sdjustmest a bit to get the car running smoothly so that it is easier to set the timing. Then I go back and readjust the mixture and idle settings a second time.

Brian,
i am with you on this one.
the car was running "well" with the other carb (weber DGV) and the timing and tune up was correct and recent (plugs, wires, cap, rotor, coil all new with less than 1000 miles on them) I put the SU's on and it fired right up but was running a bit rough and rich.
so i figured i would get a "base line" on the carbs and get it running as smooth and clean as possible then move to the timing then back to the carbs...then back to the timing....then back to the carbs...

FYI. i am running the pertronix on the delco 204d with vac retard (not connected)
~B

Brian,

I too had issues with my dual HS4 set up - was running rich. Changed the needles and voila - problem solved. No longer rich, idles great - much better power and far more drivable. The needles that came with the set up were ABT - switched out to ABD - huge difference. Good luck!

Richard,

Congrats on finding a better needle. The ABT & ABD are quite a bit different in profile. What are you using for the air filters and what setup do you have on as far as the exhaust?

Al

I'll have to look into that ABD needle. My HS4 setup also came with the ABT needles. While I am not running rich, I have noticed a bit of a flat spot at about mid throttle at some temperature conditions.

Here is a needle chart from Mintylamb:


MintyLamb ::Minty Compare-o-rama

Just choose the 0.090 size and then put in your needles to compare.

Hey, that is a cool tool. It would appear that the ABD starts to richen up significantly over the ABT right about where I would think my flat spot is. I'll have to find a place to buy a pair to see what happens.

Hi Al,

I have K&N filters and headers. The carb set up came with ABT which I was told are the standard needles. I had would get the idle correct and adjusted the mixture as best I could using the lifting pins to test, adjusting in or out depending on the sound resulting from lifting the pins very slightly (1/16 or 1/32 of an inch - don;t remember). Although the various books and on-line articles say the initial basic adjustment for mixtures was two full turns down, my car wouldn't run at that setting - I was much further down. I pulled the plugs and they were black. Wasn't getting black smoke out the exhaust, but plugs were all black. Moving to the ABD was like night and day. Plugs are the perfect color (no more black) and acceleration is much improved. I actually spent time learning about the various needle profiles and have experimented a little more - I am now running with AMM. Not a huge difference to ABD, but I believe the mid acceleration is better.