Carburetor Thread

[TOTALLER]

Hiiii ....dude can u pls tell me where i can get a good performance carbeurator..... Something like mikuni ..... In banglore

[psr]

Experts - appreciate a little help here. This is my carb on my Rx. The model is Mikuni TM 28 running on 180 main jets (not sure what's the pilot size). The issue is, the vehicle flutters like mad; assuming the mixture was running too much rich, it was decided to change to 165 mains, which is the size in stock Rx. After changing to 165 mains, last evening the issue is horrible; after certain point of twisting the throttle, the engine shuts off (here's a video & write up as well).

I don't know what I need to be doing; some guidance is really appreciated. Tks.

There are two different things happening here. ...
1. with 180 main jet when you open throttle there is excess petrol going in causing flutter..please lower the throttle needle by a notch.
2.with 165 main jet you are getting lesser petrol when you open throttle and so the mix becomes very lean..try lifting the throttle needle by one notch,with 165 jet...
I am assuming all other settings are stock...

[aargee]

Thanks sir for the response, but after this post there were several experiments that I've done (will post it on my Rx rebuild thread soon) & I've firmly learnt that, TM28 is an overkill on stock Rx135 & that's why you see a Arial bold request on my signature

1. with 180 main jet when you open throttle there is excess petrol going in causing flutter..please lower the throttle needle by a notch.

Yes, I've done this & the needle was at top most position & even then there's a jerk, BUT, the intensity was much lower.

2.with 165 main jet you are getting lesser petrol when you open throttle and so the mix becomes very lean..try lifting the throttle needle by one notch,with 165 jet...

Ok, help me understand on this front...
180 main jet with venturi size 28 is throwing too much fuel, so I lower the jet to 165 (which is also stock size for Rx135), so why isn't the fuel flow getting lesser? Ofcourse, its clearly evident that the fuel flow is less because the vehicle CAN NEVER get beyond 60 kmph at top gear. Why is this happening? Is it the same narrow hose dia, larger hose dia issue? Pls help me understand this point sir. Tks.

[psr]

Ok, help me understand on this front...
180 main jet with venturi size 28 is throwing too much fuel, so I lower the jet to 165 (which is also stock size for Rx135), so why isn't the fuel flow getting lesser? Ofcourse, its clearly evident that the fuel flow is less because the vehicle CAN NEVER get beyond 60 kmph at top gear. Why is this happening? Is it the same narrow hose dia, larger hose dia issue? Pls help me understand this point sir. Tks.

Yes...a larger venturi,than stock, reduces the Venturi air flow velocity, so can fill only lesser amount of air and fuel. If the flow velocity is high,then even with the smaller jet bike will run near normal.
Unless the CC of engine is increased, merely fitting a larger venturi Carb will result in lower performance.

[aargee]

Yes...a larger venturi,than stock, reduces the Venturi air flow velocity, so can fill only lesser amount of air and fuel.

Got my mistake. Tks sir.

If the flow velocity is high,then even with the smaller jet bike will run near normal.

Ok, so how about changing the jet size to something even smaller, say like 115 or less? Then will I be able to near my stock carb setting?

Sorry for a noob question, where exactly does this venturi come into picture in a carb, both functionality as well as physically? Pls help understand sir. Tks.

Unless the CC of engine is increased, merely fitting a larger venturi Carb will result in lower performance.

True. Completely agreed through your education + my experience

[psr]

Sorry for a noob question, where exactly does this venturi come into picture in a carb, both functionality as well as physically? Pls help understand sir. Tks.

Here is a link which explains everything in detail and in correct perspective.

http://www.lbfun.com/warehouse/tech_..._explained.pdf

and also this link:

http://www.justkdx.dirtrider.net/printcarbtuning.html

[aargee]

Thanks sir. But with any pictures are really appreciated. Without pics, its kinda difficult to visualize things.

[psr]

Thanks sir. But with any pictures are really appreciated. Without pics, its kinda difficult to visualize things.

Use the second link..the explanation is much more detailed with picture..

[aargee]

Yes, that looks much much better. Will go through them tomorrow morning. Tks again for your continued help sir.

[psr]

Thanks sir. But with any pictures are really appreciated. Without pics, its kinda difficult to visualize things.

[dafc]

The float level matters a lot and makes a big time contribution to leaning and richening up the mixture

[aargee]

The float level matters a lot and makes a big time contribution to leaning and richening up the mixture

Pls, some explanation is solicited. Tks.

[aargee]

@Psr sir, I was going through the second link & was able to make things much better in terms of pressure & venturi. So that made me think, how come a 4 mm of difference (VM22 & TM28) make such a huge variation? Just can't imagine it.

Also, do you think if I lower the jets further, wouldn't that be sufficient to generate more pressure on the AFR mixture from the venturi to cylinder?

[psr]

@Psr sir, I was going through the second link & was able to make things much better in terms of pressure & venturi. So that made me think, how come a 4 mm of difference (VM22 & TM28) make such a huge variation? Just can't imagine it.

Also, do you think if I lower the jets further, wouldn't that be sufficient to generate more pressure on the AFR mixture from the venturi to cylinder?

No reducing jet size will reduce the petrol metered out...jets determine the max amount of fuel that can be sucked through them..it is the venturi velocity which decides on the amount of suction in combination with the bore vacuum.

[aargee]

No reducing jet size will reduce the...with the bore vacuum.

Beautiful explained sir; Tks. I'm able to visualize & all the more, able to realize my mistakes too

Now, if venturi velocity is all that matters, then, I'll put it this way. Suppose the manufacturer says a certain engine requires VM24 that is an ideal one. So, if I use VM22, wouldn't I be actually sending more pressurized AF mixture? Does that mean a performance improvement?

Yes, I understand jets plays a major role in determining the fuel quantity. Lets say I upjet on the VM22 to match the throw of AF mixture from venturi, so would that be considered as a benefit? Pls let me know, if I need to elaborate more. Tks.