[pathik810]

Originally Posted by bikertillidie

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

[ArizonaJim]

Originally Posted by pathik810

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.

[LazyGunner]

Originally Posted by bikertillidie

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!
LazyGunner

[ilangop]

Originally Posted by pathik810

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

[adrian]

Originally Posted by LazyGunner

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.

[LazyGunner]

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.

[Azzitcr]

I recently bought a used Classic 500 desert storm and the original owner had the EFI converted to a carb fuel system. Unbeknownst to him the mechanic had put a 350 carburetor instead of a 500 one (UCD 33). This thread has proved to be vitally important for me in knowing what I need to know to get the get the correct carburetor installed. One questions though. Is there any power change from converting from fuel injection to carburetor? I know the 500 twin spark produces about 27bhp. How much change in power am I looking at?

[ilangop]

Originally Posted by Azzitcr

I recently bought a used Classic 500 desert storm and the original owner had the EFI converted to a carb fuel system. Unbeknownst to him the mechanic had put a 350 carburetor instead of a 500 one (UCD 33). This thread has proved to be vitally important for me in knowing what I need to know to get the get the correct carburetor installed. One questions though. Is there any power change from converting from fuel injection to carburetor? I know the 500 twin spark produces about 27bhp. How much change in power am I looking at?

Dear Azzitcr,
The UCE 350 sports a BS29 carburetor from Mikuni. And going by the spec sheet of DS500, engine is going to churn out 27 BHP at 5250 rpm. Whereas if you look at the tachometer of the TB500 the red zone for rpm already starts at 5500rpm. Which means, under normal driving conditions no one is going to utilize the max power and whatever power is delivered using the BS29 is sufficient. The only difference you will observe will be on the top speed.
Take clues from the spark plug color and engine heat and confirm with a knowledgeable mechanic about the jetting in the BS29. You still can keep going with the BS29 if the jetting is right.
Happy riding.
-Ilango

[Azzitcr]

Originally Posted by ilangop

Dear Azzitcr,
The UCE 350 sports a BS29 carburetor from Mikuni. And going by the spec sheet of DS500, engine is going to churn out 27 BHP at 5250 rpm. Whereas if you look at the tachometer of the TB500 the red zone for rpm already starts at 5500rpm. Which means, under normal driving conditions no one is going to utilize the max power and whatever power is delivered using the BS29 is sufficient. The only difference you will observe will be on the top speed.
Take clues from the spark plug color and engine heat and confirm with a knowledgeable mechanic about the jetting in the BS29. You still can keep going with the BS29 if the jetting is right.
Happy riding.
-Ilango

Thanks for the insights ilango sir
Would you then recommend keeping the current carburetor? (BS29) I ask this because I'll be using my 500 for long jaunts, and I really need all that extra grunt up the high mountain passes. I've seen the 350 and even the Himalayan lose power significantly near the leh region. I also rode the classic 500 there and the difference between the 350, Himalayan vs the 500 was remarkable.

Oh and btw I run to John the mechanic in mahipalpur Delhi. That guy sure knows his bullets 😀

[ilangop]

Originally Posted by Azzitcr

Thanks for the insights ilango sir
Would you then recommend keeping the current carburetor? (BS29) I ask this because I'll be using my 500 for long jaunts, and I really need all that extra grunt up the high mountain passes. I've seen the 350 and even the Himalayan lose power significantly near the leh region. I also rode the classic 500 there and the difference between the 350, Himalayan vs the 500 was remarkable.

Oh and btw I run to John the mechanic in mahipalpur Delhi. That guy sure knows his bullets 😀

In that case see if you can fix the fuel injection system back. I believe you rode a EFI 500 in that high altitude and not a carburetted 500.

[gunin]

Thanks for the wonderful write-up bikertillidie.

Dear fellow Bhpians, I have a 2012 Classic 500 and recently my fuel pump went bad and I have decided to go for a partial conversion (retaining ECU) to carb setup like in this thread. I have made a list of the following items to be procured and need guidance on some of them:

1. Fuel tap (Classic 350)
2. Rubber Carb Flange (Bullet 500?)
3. Pentagon Shape Flange (From thunderbird)
4. Fuel Tap (Classic 350)
5. Accelerator cable (Classic 350)
6. Alley key bolts for mounting fuel tap.
7. UCD 33 carb from Bullet 500
8. Rubber bellow/ hose between air filter and carb.

I have doubts regarding sourcing carb flange and the Rubber bellow/ hose between air filter and carb as to which model RE will fit. Your expert suggestions will be of great help to me.

[epicenter.rulez]

Hi Gunin,
Have sent you a PM, please check.

Originally Posted by gunin

Thanks for the wonderful write-up bikertillidie.

Dear fellow Bhpians, I have a 2012 Classic 500 and recently my fuel pump went bad and I have decided to go for a partial conversion (retaining ECU) to carb setup like in this thread. I have made a list of the following items to be procured and need guidance on some of them:

1. Fuel tap (Classic 350)
2. Rubber Carb Flange (Bullet 500?)
3. Pentagon Shape Flange (From thunderbird)
4. Fuel Tap (Classic 350)
5. Accelerator cable (Classic 350)
6. Alley key bolts for mounting fuel tap.
7. UCD 33 carb from Bullet 500
8. Rubber bellow/ hose between air filter and carb.

I have doubts regarding sourcing carb flange and the Rubber bellow/ hose between air filter and carb as to which model RE will fit. Your expert suggestions will be of great help to me.

[jobinjv]

Hi

I own a 2010 Classic 500 and to date has only clocked 5000 Kms.

The FI has given me its fair share of headache. I plan to convert it to a carb system and was thinking of a Mikuni 32mm system.

Is it worth to maintain the ECU or just do away with it ? Change the wiring to a 350 or a 500 or Just keep it as such.

Should the magneto and coil be changed or maintained. I am looking for a hassle free maintenance, where in I can drop in and go for a ride rather than clean the FI.

[srini1785]

Originally Posted by jobinjv

The FI has given me its fair share of headache....

List out the headaches and probably you might get the correct balm for it. EFI is in every way more efficient.

[ashwinprakas]

Originally Posted by jobinjv

Hi

The FI has given me its fair share of headache. I plan to convert it to a carb system and was thinking of a Mikuni 32mm system.
.

Do give this post a read.

https://www.team-bhp.com/forum/motor...ml#post4813880 (Royal Enfield Classic 350 - It's here, finally!)

Ive shared links of a comparatively cheaper than Hitchcock kit from Indimotard and have suggested alternatives to get the job done at an even cheaper rate.

The upisde of using UCD33 from NS200 is the matching TPS connector, but the BS32 from the P220 is cheaper by about 1k but lacks provision for TPS, not an issue if you'd be scrapping the C5's wiring.

Cheers,
A.P.