Carburetor UCD33 - enhance fuel flow

Sasa

Mediocre pilot - Average mechanic - Crazy tinkerer
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main jet will only be useful at wide open throttle. If you knock I suggest you modify the needle position in the carb. there should be notches on the needle, I suggest you move the needle upward one or two notches.
The needle shift will enrich the whole curve, specially with partialized throttle.
Then if it's still not sufficient, you move forward with a bigger jet...
 
I suggest you move the needle upward one or two notches.
I have not looked inside the carb, this pic shows the needle (no. 11) but lifting it means what? putting a washer under it? is it threaded so I just turn it to lift it? any idea? and how much lift you suggest?
 

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7 is a circlip
11 is the needle
7 needs to be installed lower on 11 that will raise it.
 
7 is a circlip
11 is the needle
7 needs to be installed lower on 11 that will raise it.

Exactly. The circlip 7 is installed in one of several Groves the needle has (usually 3 or 4). You can try install the circlip 7 in the lowermost groove, that would raise the needle to its uppermost position.
 
It was suggested to "raise the needle" and upon trying we found no mechanism inside the carb that would allow for such thing.
When trying to "jugaard" it by lifting the swimmer the carby would leak.
I even tried out a brand new carb - but that did not even run well (not related to our problem). So its back to the old idea of upping the jets - they are on order, a week or so...
 

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Like Sasa said the main jet hardly gets used so just the primary and the jet needle.
I was surprised when that parts diagram showed a needle that was adjustable as I have heard it is not and others have used washers to raise it.
Anyhow that must be done some how or the needle needs to be made thinner at the appropriate position. ( That's how Mr Honda used to do it)
That is how it is done, adjusting the Float level is of little use as having extra fuel in the bowel doesent help it get thru the jet unless there was not enough in the first place.
 
If a garden hose has 2 Taps in line and one is fully open and the other is Half closed then the flow is halved can't get away from it.
That needle is the important thing as it is tuned for a 411cc engine.
 
If a garden hose has 2 Taps in line and one is fully open and the other is Half closed then the flow is halved can't get away from it.
That needle is the important thing as it is tuned for a 411cc engine.
Dool, I am not an idiot, I understand the principle, however as you can see from the pictures there seems to be no mechanism to lift the needle as you proposed earlier. if you require additional detailed pictures I can provide them but I have looked and the thin needle in the middle is fixed and there is no way to change its position without destruction.

I have read in the Hima thread in the advforum a long time ago that someone said he "lifted the needle by adding some washers" if memory serves. but I do not understand how he could have done that given the internal construction of the carb.
 
The pictures are all of parts not related to the mod we are discussing here.

Can you take a picture of the rubber assembly that holds the needle? from the inside it would be better.
They install the needle in the rubber part (4 or 2 in the diagram above) so there must be a way to disinstall it and modify.

Pictures would be helpful as I don't have one at hand...
It was suggested to "raise the needle" and upon trying we found no mechanism inside the carb that would allow for such thing.
When trying to "jugaard" it by lifting the swimmer the carby would leak.
I even tried out a brand new carb - but that did not even run well (not related to our problem). So its back to the old idea of upping the jets - they are on order, a week or so...
 
will take pics next time I am in the shop, likely tomorrow or day after.
 
The parts Pic showed the circlip but I also think it incorrect.
The 2 Taps analogy was because being after being unable to adjust the needle you were ordering larger jets.
You may have to make the needle smaller.
The latest pics show the Bowl and Float but the needle is being discussed. IMG_20230313_211756.jpgIMG_20230313_211704.jpgIMG_20230313_211719.jpg
 
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The parts Pic showed the circlip but I also think it incorrect.
The 2 Taps analogy was because being after being unable to adjust the needle you were ordering larger jets.
You may have to make the needle smaller.
Reduce the diameter of the needle on a lathe in not exactly the work of the average Joe. It should be done following a specific profile to provide the right throttle response.

One might argue that you could leave the shape as is, just remove few cents of a millimiters to enrich the mixture: it might work or it might not, only way would be experimenting and that is the kind of experiment where you cannot go back! :)
 
Needles are Cheap 😉 so is Labour.

Fine Sandpaper and spin it in your fingers. Put it in the Drill, no need for a Lathe! It is the simplest of Valves

But apart from that.
The last pic I put up shows where the needle sits, I cannot believe it could be so hard to make whatever it is sit a mm or 2 higher.
 
Got the bigger jets, will disassemble the carb today, search for the needle, if possible lift it and also install the bigger jets. then see how that works on the knocking.
 
Sandpaper and a drill, mark the needle with a texta when it is fully open and make it smaller bellow the mark.

To do this you need first to remove the Needle and it may well be that you can see it is easier to lift it then.

Perhaps this same Carby was once fitted to a 500, therefore it would be expected that the Needles are different, have you checked this possibility?
 
there is a repair kit for the 350 carb but not for the ucd33
 
Bit hard to believe that the needle can not be found, is India a big Hay Stack?
We even get needles in Punnets of Strawberries 😁
But irrelevant if you are unable to modify it or lift it then someone isn't trying to hard enough IMO.
 
ok all good, found the needle, shortened it by ca. 1mm, also installed 135main and 20pilot. so far all good but tomorrorw long test ride.
 

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