Modified Carbs and Airbox Mods.

[koko64]

  yep

[Speeddog]

Never got to play with one much at all.

I think Tony's old enough.  

(They've been used on Harleys, only reason he's old enough to know... )

Anyone old enough to remember the SUs?  Tune rise by changing the weight of the oil.

[Speeddog]

I think the slide/spring/damping is the classic stability vs. fast response conundrum.

[ducpainter]

Anyone old enough to remember the SUs?  Tune rise by changing the weight of the oil.

I have a set of tools for synching twins...as well as a Uni-Syn.

[koko64]

And on an old mates MG.
Harley blokes had issues getting them to clear the 5 gallon tanks. I thought about one for my shovel but ported a Keihin 38mm instead to make a poor man's S&S.

[koko64]

Regarding my ported BDST, it's running rich in the midrange and gives excellent response  with the DJ 730 needle and spring. With the 37.5 pilot jet I can easily get 300+km per 18 litre tank, so it's the needle profile and spring. The needle is on the 3rd notch as per the DJ instructions.

[Howie]

I have a set of tools for synching twins...as well as a Uni-Syn.

Mine went to the new owner of our 1967 Volvo.

[koko64]

Boxy, but good Na, 1800S? They looked alright, a bit English. I bet you hated the later model styling change.

[Howie]

Boxy, but good Na, 1800S? They looked alright, a bit English. I bet you hated the later model styling change.

Yep.  I did like the next generation too.  Used to repair them. 

[ducpainter]

Mine went to the new owner of our 1967 Volvo.

I'd like to have another B-GT someday. I'll keep them just in case.

[koko64]

Currently testing bigger pilot jets on the rich side for more acceleration from lower rpm's and roll on performance. Testing a bit too rich 42.5 pilot jets with the aggressively tapered DJ 730 needle and soft DJ "stage 2" springs on conservative clip positions (#3). Getting very good throttle response but fuel range per 18 litre tank has dropped 20-25 miles, (185 to 160 miles). I'm thinking that the profiled slide face flows more air acting like a larger cut away. It's definitely power tuning Vs economy and the throttle response is more lively. The fuel must be atomised quite well as the plugs are drag racer rich but not fouled.

Interesting how DJ goes for the stock pilot jet, soft springs and richer needle taper and root diameter while FP goes for richer pilot jets, leaner needle taper and root diameter and heavier springs. People I've talked to like the DJ approach in tuned 900's and the FP approach in tuned 750's, probably due to the 900 needing sufficient air volume while the 750 needs sufficient air velocity running the same 38mm carbs with less capacity.

There are so many possible combinations of jetting, needles, needle positions, spring rate that makes tuning flatslides seem easy in comparison. Flatslide logic is a series of overlapping linear circuits in sequence. The issue with CV carbs is due to the two parallel and concurrent systems that influence each other. The parallel systems are theoretically supposed to work in harmony, but as we know thats not always the case.

Be great if Santa would give me a flow bench for Christmas

[koko64]

https://www.flickr.com/photos/150482584@N03/shares/cZ662B
IMG_1099 by Tony Kokonis, on Flickr

Same jetting for more response, but different plugs/gaps solves the issue of too much fuel at cruise rpm/load. The Iridium plugs with hi power coils and strong ignition wires burn that fuel with positive results for real world riding. This ignition set up supports the "rough" solution of jetting a non accelerator pump carb for throttle response.

Using iridium plugs with large 1-1.1mm gaps and high voltage coils allows running a rich 42.5 pilot jet
providing more throttle response mitigating not having an accelerator pump. Roll on throttle response and sudden acceleration is improved which is usually a weak point with these carbs. With normal plugs its just too rich, but with large gapped Iridiums the extra fuel is utilized giving the response without fouling. When you jet leaner for smooth cruising and economy the response is weak.
Fuel economy was definitely better with the large gapped iridium plugs compared to regular plugs. The extra combustion effeciency must have had me cruising easier with less throttle and less wasted fuel as economy improved 1/2 a litre per 60 miles. This solution allowed me to "over jet" the pilot jet for throttle response which I couldnt previously get away with. The carb work, airbox/velocity stack mods and "response" jetting supported with strong ignition all assisted performance.
Will be doing some back to back testing against a similarly modded 900SS which has FCR39's to get a measure of how well this all works and whether it's worth the effort.
I did a lot of road testing and fuel economy tests to measure this. The thread on Iridium plugs in the tech section covers this "supporting mod".

[Howie]

Good job 

[koko64]

Thanks mate. if they made a 41.5 pilot jet Id use it.

[Howie]

You could go old school, solder and re-drill.  Not very accurate since you can't drill a perfect hole.