Are there alternative slide needles and/or needle jets available for HT engines?

[AussieSteve]

My stock NT carb is almost tuned well. Idle is OK. Top-end is great at WOT with an 0.73mm main jet, but mid-throttle acceleration and cruising is still rich and bogging down. I can even feel it bogging with a constant throttle setting, 1/3 to 2/3. It clears instantly if I open the throttler wide, stops 4-stroking and goes like the proverbial bat out of ****.

My problem - the slide needle is already on it's leanest setting, so nowhere to go.
This problem started when I sealed the leaks in the inlet and carb top cap, it seems.
Do I poke a few holes in my (too good) sealing, or is there an alternative slide needle and/or slide needle jet that I can try?
I'd hate to have to mess around trying to thicken the needle with solder and get a decent taper, or fill the needle jet and drill it.

Please, someone....
or
Any other options I haven't considered?
(The performance carbs sound worse.)

... Steve

 

[Al.Fisherman]

I've seen posts on here about aftermarket needle and seats that are avaiable. Do a search or check with the vendors in the vendor forum. I have the same thing happening on my bike...I'm leaving it alone.
OH and I've made my own boost bottle.

 

[AussieSteve]

vendor forum - good thinking 99.
I suspect that all these engines go rich when they're well-sealed, from what I've read.
It's not real bad, I could live with it, but we'll see what transpires.
Maybe an extra notch on the top of the needle, or a needle extension?

... Steve

 

[EnFlaMEd]

You could also try getting a different air cleaner eg. a UFO style filter or one like SBPs.

 

[AussieSteve]

You could also try getting a different air cleaner eg. a UFO style filter or one like SBPs.

Great minds...
An air filter from SBP is already on my shopping list for next week.

... Steve

 

[AussieSteve]

I've been sitting here wondering if a very thin coat of epoxy resin or lacquer on the needle would work. Not sure what to use in the presence of petrol, (gasoline).
If the epoxy was thin enough, I could dip the needle, let it dry and test, add a coat if needed, etc., until the mid-throttle mixture was lean enough.
Might need a rub with fine W&D paper, too. The needle really only needs thickening in the middle section.

Good idea? Bad idea?

... Steve

 

[professor]

A very long time ago I was messing with a Bendix-zenith carb on a turbo set-up. Lacquer worked very well on the needle, and if you don't like it - it can be scraped off I think nail polish is lacquer too.

 

[AussieSteve]

A very long time ago I was messing with a Bendix-zenith carb on a turbo set-up. Lacquer worked very well on the needle, and if you don't like it - it can be scraped off I think nail polish is lacquer too.

Hi professor, thanks for the input.
Nail polish sounds good. I don't think that fuel dissolves it. It usually needs acetone. One way to find out.
I think it would be better than epoxy, too, because it's easier to apply very thin coats until it's thick enough.
And as you say, easy to remove.
... Steve

 

[ToeCutter66]

You might be getting a vacuum at your carb when you are traveling at a certain speed. Try holding your hands near the carb and see if it changes the way it runs. My old CB750 chopper used to fall on its face at 50mph, if I covered the sides of the airbox with my knees it would start accelerating again. I ended up covering up the top of the inside of my bread box airfilter.

My build is still in progress, but I plan on making a velocity stack for my carb. I was going to get a short piece of copper pipe, same diameter or close to the opening of my carb, and flaring out one side, by driving the round end of a ball peen hammer into it.

 

[AussieSteve]

No, it's not a vacuum at a certain speed. It's rich right through the low to 3/4 throttle openings, from about 15kph to 30kph. It only starts to run leaner at full throttle.

I used to ride Honda 4's too, but not choppers. Never had or heard of your vacuum problem.

Are you still going to fit an air cleaner with the velocity stack?

... Steve