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Old 11th July 2015, 15:57   #61
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Default Re: The Royal Enfield 500 Classic thread!

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Originally Posted by bikertillidie View Post
Hi Rakesh,
The carbed version of the UCE bullet 500 uses a UCD33 carb.
Older LB500s used a BS29 carb, if I am not mistaken.
I have a query over here! If I install a BS32 in 350cc AVL engine, then it is clear that I will lose the choke facility because BS32 has an electronic choke which is not suitable to work with AVL engine.

Will that be a major issue for the bike to run without choke? Or will it be okay? Need guidance

Last edited by ampere : 11th July 2015 at 16:17. Reason: Removed bulk of quoted post
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Old 12th July 2015, 01:06   #62
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Default Re: The Royal Enfield 500 Classic thread!

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Originally Posted by pathik810 View Post
I have a query over here! If I install a BS32 in 350cc AVL engine, then it is clear that I will lose the choke facility because BS32 has an electronic choke which is not suitable to work with AVL engine.

Will that be a major issue for the bike to run without choke? Or will it be okay? Need guidance
First off, I must mention, the subject of this thread is about converting the fuel injection on a 500 to a carburetor.

That said, in my opinion trying to use a carburetor without a choke is asking for trouble.

Carburetors are set up to supply a air/fuel ratio that the engine needs to run properly when it is hot.

This mixture is much too lean (not enough fuel in the air) to provide the correct air/fuel ratio for a cold engine. In fact, it is so lean, a cold engine often won't even fire when an attempt to start it is made unless a choke is applied.

The choke blocks off the air entering the carburetor which results in a LOT of fuel entering the engine. This extra fuel is ignited more easily than a lean mixture so, even though the engine is cold, it can fire and start running.

While I'm on my soap box I'll give my opinion about changing a 29mm, 350 carburetor to a 32 or 33mm carb.

Although this is often done with the idea that some major gain in horsepower will happen, in reality, the gain is not that great.
If anything, the loss in other areas will be much more noticeable.

The gain only happens when the engine is running at its top speed. The increased area thru the carburetor will allow more air/fuel into the engine at this high speed so the drop off in torque is slightly less. This results in a power gain.
Because it only happens when the engine is running at its maximum speed, unless the motorcycle is being used for racing, no gains will be noticed at normal riding speeds and conditions.

The loss from increasing the carburetor size can be very noticeable at normal riding speeds if a regular carburetor is being used.
Although the CV (constant velocity) carburetors are much better at not doing this, this is what can happen.

The most common loss happens when the throttle is suddenly opened wide.
The engine often will totally lose its power, appearing to suddenly die.

The total power loss (dying) may be brief or it may extend over quite a long period of time. It is usually corrected by the rider at the time it happens by closing the throttle for an instant and then opening the throttle more gently.

What causes this?
Regular carburetors rely on having a high velocity of air traveling thru them to suck the fuel out of the float bowl and spray it into the air that is traveling thru them.

If the velocity of the air mass decreases a smaller amount of fuel will be drawn into the airstream so the engine will temporarily stop running.

The CV carbs are much better at dealing with this than the older style carburetors but even they will often hesitate if the throttle is suddenly opened.
The reason they are better than the old style carb is they are constantly measuring the amount of air passing thru them and adjusting the opening thru them to match the airflow.
Notice. You may have opened up the throttle to its maximum but because a CV carburetor is measuring the actual amount of air needed by the engine if it is less than your wide open throttle plate will allow, the engine will only get the amount it needs.
With a 350cc engine and a 32 or 33mm carburetor that basically means you have the throttle wide open but your carburetor is actually only 2/3 of the way open at the venturi.

What all this boils down to is, the company that designed the motorcycle did it with the idea that it should be easy to ride, responsive to throttle changes and give a good fuel economy.
They could have easily mounted a 32mm carb on their 350cc bikes but they didn't.

I think they know that the good things provided by the smaller carburetor more than offset any small gains that the larger carburetor will provide.

Just something to think about.
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Old 4th October 2016, 18:49   #63
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Default Re: Royal Enfield UCE500: EFI to Carburettor Conversion

Quote:
Originally Posted by bikertillidie View Post
It's best to stick to a carb which matches the size of the inlet manifold. Mounting a BS32 carb onto a manifold having a diameter which is 6 mm smaller will have a restrictive effect.
Can you please elaborate on the 'restrictive effect' part?

I ask this because one of my friends' carb-converted TB500 has a peculiar problem. It runs perfectly fine in the city but when you hit the highway and touch 3-digit speeds, the engine bogs and dies. Interestingly, if you open the fuel tank lid and close it, it works fine again.
With the little knowledge I have on carbs and the way they work, I'm thinking when the throttle is completely open, carb is sucking all the fuel from the little fuel reservoir but it is not getting filled at the same speed from the tank, maybe?

Or, is the carb installed is a misfit? All I can figure out is that it is a Mikuni carb. Only things I can read from the carb is -
42L05D
E539
The owner doesn't know which carb it is either. He just got it converted because somebody suggested.

Or, is it that the main jet is sucking fuel from the reservoir at a greater rate than the rate of refilling? The jet size used is wrong, maybe?

I think it is safe to rule out anything wrong with fuel tap, fuel tube, even breather pipe, debris in the tank (carb was clean) -> all of which would have caused the issue even at low speeds.

Also, apologies for the silly question, how does one measure the jets? I mean what apparatus is used?

Thanks!
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Old 5th October 2016, 09:07   #64
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Default Re: The Royal Enfield 500 Classic thread!

Quote:
Originally Posted by pathik810 View Post
I have a query over here! If I install a BS32 in 350cc AVL engine, then it is clear that I will lose the choke facility because BS32 has an electronic choke which is not suitable to work with AVL engine.

Will that be a major issue for the bike to run without choke? Or will it be okay? Need guidance
You can always mount a choke switch like this. Supply +12V through the switch, and the other wire of the choke can be grounded to the body. Hope this helps.
-Ilango
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Royal Enfield UCE500: EFI to Carburettor Conversion-choke_switch.jpg  

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Old 5th October 2016, 14:16   #65
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Default Re: Royal Enfield UCE500: EFI to Carburettor Conversion

Quote:
Originally Posted by LazyGunner View Post
I ask this because one of my friends' carb-converted TB500 has a peculiar problem. It runs perfectly fine in the city but when you hit the highway and touch 3-digit speeds, the engine bogs and dies. Interestingly, if you open the fuel tank lid and close it, it works fine again.
With the little knowledge I have on carbs and the way they work, I'm thinking when the throttle is completely open, carb is sucking all the fuel from the little fuel reservoir but it is not getting filled at the same speed from the tank, maybe?
LazyGunner
Hi, two things might be the culprit here

1. Clogged vent holes in fuel tank cap. Remedy is to clean the vent hole.

2. Float height in high (which mean fuel level in bowl is low) in the

carburetor. So in high engine rpms, all the fuel in the float bowl gets used up

before getting a refill through the float valve. Remedy is to adjust the float

height to specifications.

Last edited by adrian : 5th October 2016 at 14:18.
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Old 5th October 2016, 14:50   #66
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Default

Thanks for the reply Adrian. I guess I should check the fuel cap vent holes before meddling with the carb settings ( although I would love to do that) but if issue gets solved without getting into carb, nothing like it

Thanks again, will update soon.
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