EdwardN

iTrader: (1)

Hey guys let's talk about carb modifications, beside pilishing and reshaping sucktion side. Any ideas?

Corse-R

Yep... one and people doesn't seem to pay attention to details. Reshaping the low-end needle to change the fuel curve of the carburetor and changes too the engine response, sometimes is quite interesting to do some tests with the shape of low-end needles.

But rather than talking of carb mods, first we need to talk about carb adjustments and people need to learn what are they doing when they change the 'third needle' (sheeeesh! isn't a needle, is the main jet of the carb!).

They can vary by changing the position of the jet que fuel quantity they supply to their engines and control when the carb is mandated by the high speed needle rather than the low-end needle.

EdwardN

iTrader: (1)

This actualy I did last weekend at Cristal Park. I made needle sharp and change position of spray bar. I love the new curve ( it has remind me what we use on boats). Beside that seems like fuel economy went up tramendosly. Want to make new low end needle to shape it right the way it got to be ( calculated already angles).
About spray bar- I would love to have it on the center of hole ( regardless it closes some area of hole), I think I will need to make one too ( stock is shorter 0.5 mm then I need).
But from all this exeriments I found the whole tunning process has been totaly change. It doesn't through unburn fuel anymore.

dino.tw

I have cut the low-end needle about 2mm to solve my OPS 21 on-road which always mid range poor on fuel.

Most of time I will adjust the length of pressure line to tune the curve. It's more easy and not damage anything.

EdwardN

iTrader: (1)

Dino, how do you rate .21 OPS engine to compare to JP, MAX etc.? In the past OPS was one of the best brand in hobby. It beat easy any other like Rossi, Super Tiger etc. It was way before Novas came to market, even on the beggining Novas was way behind. Now I didn't see anybody using OPS. I saw one new, but didn't have chance to open it and study. I had OPS .12 side exhaust-it is crap.
BTW about cut of low end needle-it is depend of carb design-some of them need to cut, some of them asking to extend it. Also from my point of view, the slider needs to be work out too.

dino.tw

I can't comment on other mfg's product. It's my base line. I only can share my OPS.21 experience with you.

I bought it half year ago. I like it and I thought it's very beauty. I felt this on-road engine is more like a BUGGY engine to me. Have terrible low-end torque but high-end rpm is a bit not enough. So I re-balance its crankshaft. Why I modified its low-end needle just because it has two needles adjustable carburettor....but....the adjustable needles are main needle and Spray bar. The stock low-end needle seems a bit too long. Maybe it needs OPS pipe but I can't get it. So I choice PICCO 9897.

Now it's very fast after mod. The lap time to me are almost the same when I run my OPS or RB;Mega;Nova......etc. Maybe I'm too slow...hahaha...But due to I can't get spare conrod for it now and I don't want to damage it. So it's sleeping now.

I have too many engines and all of them are the same to me. When I find one engine is hard to adjust,it is real interested me. It is a challenge and I like to spend many time to study it. I will try to find the solution,to extract 100% power and enjoy the fun. I think a real expert can handle any engine.....There is no perfect engine,only perfect tuner/driver.

EdwardN

iTrader: (1)

Thanks a lot Dino.

afm

What are the performance gains in moding the carb's air intake shape.
I've seen some, keeping the original shape, but starting at the entrance progresively widen in a V shape up to the venturi (without altering It's dia. 5.5mm)
Others like JP and STS have a "cup" shaped entrance.
Cons and Pros????

AFM

afm

TG, or somebody. Any comments on above post?????
Thanks
AFM

EdwardN

iTrader: (1)

In my opinion, wider opening, plished is the best, one more thing-make it shorter as much as possible, but we can't do it-needs install filter. I would love to have short intake, with wide open V

Slotmachine

iTrader: (4)

A shorter intake should create a quicker throttle responce.(Less volosity)
We used to add a volosity stack to our drag racing real cars to gain mid range & top end. When you do change the intake size I do believe you have to alter your exhaust configuration.
I think thats the way it goes?
P.S. Edward.........the new team T/Shirt is in the mail. Paul

EdwardN

iTrader: (1)

Wow, it was fast! It is great!!!!!!!!!!!!!

afm

TG
Picco carbs have distance from top of air intake to carb body of 6mm, opening starts at 10mm V shaped and polished up to venturi of 5.5mm.Air fiklters hold well.

I have a Nova based carb that's been widen to max allowable size of 14mm at air intake start and machined and polished "V" shaped up to the venturi of 5.5mm, and it has a distance from top of opening to carb body of 11mm, so that means that (after measuring) I can take 5mm of distance from top to body without creating problem with air filter holding.
Is that a significant amount to take off, for performance improvement??? Or shall I leave it with original distance.

Thanks
AFM

EdwardN

iTrader: (1)

If fiter will be held securely on that distance of 6 mm, I will do on mine, But I have novas filters and they need full lenght.
Honestly, I am not afraid of experimenting and If I want to try something, I even don't think I can damage, I just do it. If it is not working, I just got replacement.

I will check if filter will holding well , I will modify intake fitting and make it smaller.