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Old 30th January 2010, 17:25   #31
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Default Question about the BS29 vacuum slider piston

Raj,

I am looking to improve the response of the stock BS29 carb. I am planning to drill out the stock vacuum port/orifice of the BS29s slide by 1/8th inch for better throttle response. I managed to find a Bajaj Pulsar 200s(BS29) slide assembly. Now, the real confusion begins. While I assumed that the BS29 has only two ports, one for the needle and one for the vacuum, I find four ports. Three are big orifices arranged in a triangular fashion. The fourth port is the vacuum port which understandably is off center. Now, since you've opened up the BS29, can you dig your memory and tell me how many ports/orifices does the bottom of slide have? This would save me the effort of opening up the carb.

Cheers,

Jay
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Old 30th January 2010, 18:25   #32
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Raj,

I am looking to improve the response of the stock BS29 carb. I am planning to drill out the stock vacuum port/orifice of the BS29s slide by 1/8th inch for better throttle response. I managed to find a Bajaj Pulsar 200s(BS29) slide assembly. Now, the real confusion begins. While I assumed that the BS29 has only two ports, one for the needle and one for the vacuum, I find four ports. Three are big orifices arranged in a triangular fashion. The fourth port is the vacuum port which understandably is off center. Now, since you've opened up the BS29, can you dig your memory and tell me how many ports/orifices does the bottom of slide have? This would save me the effort of opening up the carb.

Cheers,

Jay
The bottom of the slide has only two holes, you can see this if you look closely at the first picture on page 2 of this thread.

Currently I have the BS29 off the bike and I rechecked by shining a light at the bottom of the slide, there are only two holes. Can you please post a picture of the slide from the Pulsar. Both holes are the same size on the 500, how can you tell which is which?
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Old 30th January 2010, 22:13   #33
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The bottom of the slide has only two holes, you can see this if you look closely at the first picture on page 2 of this thread.

Currently I have the BS29 off the bike and I rechecked by shining a light at the bottom of the slide, there are only two holes. Can you please post a picture of the slide from the Pulsar. Both holes are the same size on the 500, how can you tell which is which?
Here are a couple of pics of the slider as a single unit.

In the second pic which is the bottom if the slider, you can make out three larger orifices in a triangular pattern with a single smaller orifice that is offset. The offset orifice is what concerns throttle response. Now, after some brainstorming, I have come to a conclusion that the two other larger orifices diagonal to the smaller orifice are for the TPS sensor, which we don't have anyway. Now, to use the P200s slider, we need to close these orifices. There is a little more I learnt from all these happenings. I will post about it once a few things are confirmed.

Cheers,

Jay
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Old 30th January 2010, 22:59   #34
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Jay Now i have a point here.i have a friend here who's running the BS29 from the pulsar 200 on his AVL 350.and he's just bolted it on.not a single thing touched on the carb.never even opened.So if you're saying that those holes are for the TPS and need to be closed for its operation on the bullet then how come this carb is running perfectly and infact generating amazing performance as well.


plus i checked out the carb from top to bottom.there is no place for it to have a throttle position sensor.

Last edited by navpreet318 : 30th January 2010 at 23:01.
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Old 30th January 2010, 23:28   #35
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Jay Now i have a point here.i have a friend here who's running the BS29 from the pulsar 200 on his AVL 350.and he's just bolted it on.not a single thing touched on the carb.never even opened.So if you're saying that those holes are for the TPS and need to be closed for its operation on the bullet then how come this carb is running perfectly and infact generating amazing performance as well.


plus i checked out the carb from top to bottom.there is no place for it to have a throttle position sensor.
Navpreet,

So, why two extra orifices? Like I said, these are my initial conclusions which may be wrong also. I haven't opened my LB500s carb yet. So, I am not sure still. I'll dismantle the carb and get back. Meanwhile, if the slider I have bought fits perfectly, it's a good thing as testing with a larger vacuum orifice can begin. Like I said, there is something else that is being checked and debated. I will update this thread shortly.

Cheers,

Jay

Last edited by JayPrashanth : 30th January 2010 at 23:29.
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Old 30th January 2010, 23:48   #36
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Here are a couple of pics of the slider as a single unit.

In the second pic which is the bottom if the slider, you can make out three larger orifices in a triangular pattern with a single smaller orifice that is offset. The offset orifice is what concerns throttle response. Now, after some brainstorming, I have come to a conclusion that the two other larger orifices diagonal to the smaller orifice are for the TPS sensor, which we don't have anyway. Now, to use the P200s slider, we need to close these orifices. There is a little more I learnt from all these happenings. I will post about it once a few things are confirmed.

Cheers,

Jay
@Jay - The center hole is for the needle. The other two large holes are most prominently visible when peering inside a carb mouth, my bad I missed the small hole, was probably hidden behind the needle. After seeing the pic you posted, I again checked specifically from either side for the small hole and it is there on the LB500's BS29, as far as I can tell the slide you have is identical to the slide in the 500's carb.

Last edited by Beast_of_Burden : 30th January 2010 at 23:59. Reason: need to correct
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Old 31st January 2010, 00:03   #37
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@Jay - The center hole is for the needle. As to the tiny little hole, there is a plastic washer that sits right under the circlip. This plastic washer has a tiny notch/protrusion that would fit into that hole and will close that hole once you have assembled the needle in the slide. My take on it was that notch is probably meant to prevent the needle from turning, but there is about 1 mm of vertical play in the needle and this hole might be open at idle, when the needle is resting and is pushed up. No idea if that somehow plays into the carburetion at idle.

After seeing the pic you posted, I again checked specifically for the small hole and it is there on the LB500's BS29, as far as I can tell the slide you have is identical to the slide in the 500's carb.
Nice man. Then, the two other off center ports are for vacuum. We need to drill em out then. Meanwhile, here is a update, our LB500s might have a rev limiter built into the TCI module. Now, how to take it off, what are the +ves/1ves are subjects to be pondered upon. On first impression, it is a good idea to have a rev limiter as bullets don't like high rpms. But, will disabling it give a real boost or better performance? There are TCI modules that come without the limiter as well. Meanwhile, did you buy the P200 oil cooler? Meanwhile, the slider I bought costs INR378 and this includes 12.5% VAT. If the mod works, it would be a great VFM alternative to say a VM/TM carb.

Cheers,

Jay

Last edited by JayPrashanth : 31st January 2010 at 00:10.
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Old 31st January 2010, 00:41   #38
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Nice man. Then, the two other off center ports are for vacuum. We need to drill em out then. Meanwhile, here is a update, our LB500s might have a rev limiter built into the TCI module. Now, how to take it off, what are the +ves/1ves are subjects to be pondered upon. On first impression, it is a good idea to have a rev limiter as bullets don't like high rpms. But, will disabling it give a real boost or better performance? There are TCI modules that come without the limiter as well. Meanwhile, did you buy the P200 oil cooler?

Cheers,

Jay
The vacuum is created behind the rubber diaphragm, if it isnt regulated I suppose the slide would be stuck to roof of the carb most of the time as the vacuum would prove too strong. The holes at the bottom of the slide sort of regulate the vacuum, if you make the holes larger there would be less vacuum behind the diaphragm no? This would result in the slide reacting a little more slowly to the changes in vacuum in the intake, how would that improve throttle response? I am guessing about the purpose of those holes at the bottom of the slide, so correct me if i am wrong.

I am hunting for the LB500's external oil line first, as i dont want to be left without an external oil line if the mod gets messed up. I have tried in a couple of stores but they dont stock this item for the LB500, they do have after market parts for the std 350 and the Electra. Once I secure this item, I will start running around to the Bajaj service centers. I am in B'lore the coming weekend, will try at the Jayanagar brand store as well. Is the cooler easily available at Bajaj service centers?

Meanwhile, I have bought a VM28 and installed it. The idling is perfect and the midrange is good too, tomorrow morning I will test it out on a longer ride. This without making any adjustments. It appears pilot and main jets are interchangeable between VM28 and BS29 as the CMW store lists the same set of Mikuni jets as being suitable for the CI 500 as well as the AVL 500. The stock pilot I believe is a 25 and the main is a 110. I dont have a bigger pilot but have a 130 main jet which I might sub tomorrow after the test ride. Speaking of throttle response, the VM28 is the ticket, it is really really quick. But the downside is that if you open the throttle too quickly, the bike will bog and die. The bike seems to be breathing far more easy, but also makes more of that kad kad suspected piston noise during acceleration. The CV carb is infinitely more forgiving in this regard, it is far less jumpy, unless one is incredibly hamfisted it is nearly impossible to bog the BS29, in that sense it is indeed idiot-proof.

I know you are exploring the limits of the LB500, frankly having that rev limiter on is a good thing, as many have pointed out it will shake itself to bits. I was under the impression the overly restrictive exhaust and intakes were soft rev-limiters in effect and were there for a reason. Anything over 100kh for any length of time is inviting disaster in short order IMO, I will soon find out if I already have LOL.
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Old 31st January 2010, 11:07   #39
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Originally Posted by Beast_of_Burden View Post
The vacuum is created behind the rubber diaphragm, if it isnt regulated I suppose the slide would be stuck to roof of the carb most of the time as the vacuum would prove too strong. The holes at the bottom of the slide sort of regulate the vacuum, if you make the holes larger there would be less vacuum behind the diaphragm no? This would result in the slide reacting a little more slowly to the changes in vacuum in the intake, how would that improve throttle response? I am guessing about the purpose of those holes at the bottom of the slide, so correct me if i am wrong.

I am hunting for the LB500's external oil line first, as i dont want to be left without an external oil line if the mod gets messed up. I have tried in a couple of stores but they dont stock this item for the LB500, they do have after market parts for the std 350 and the Electra. Once I secure this item, I will start running around to the Bajaj service centers. I am in B'lore the coming weekend, will try at the Jayanagar brand store as well. Is the cooler easily available at Bajaj service centers?

Meanwhile, I have bought a VM28 and installed it. The idling is perfect and the midrange is good too, tomorrow morning I will test it out on a longer ride. This without making any adjustments. It appears pilot and main jets are interchangeable between VM28 and BS29 as the CMW store lists the same set of Mikuni jets as being suitable for the CI 500 as well as the AVL 500. The stock pilot I believe is a 25 and the main is a 110. I dont have a bigger pilot but have a 130 main jet which I might sub tomorrow after the test ride. Speaking of throttle response, the VM28 is the ticket, it is really really quick. But the downside is that if you open the throttle too quickly, the bike will bog and die. The bike seems to be breathing far more easy, but also makes more of that kad kad suspected piston noise during acceleration. The CV carb is infinitely more forgiving in this regard, it is far less jumpy, unless one is incredibly hamfisted it is nearly impossible to bog the BS29, in that sense it is indeed idiot-proof.

I know you are exploring the limits of the LB500, frankly having that rev limiter on is a good thing, as many have pointed out it will shake itself to bits. I was under the impression the overly restrictive exhaust and intakes were soft rev-limiters in effect and were there for a reason. Anything over 100kh for any length of time is inviting disaster in short order IMO, I will soon find out if I already have LOL.
Don't buy the Bajaj oil cooler. There is something better and cheaper too.

Cheers,

Jay
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Old 31st January 2010, 15:08   #40
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Originally Posted by JayPrashanth View Post
Don't buy the Bajaj oil cooler. There is something better and cheaper too.

Cheers,

Jay
@Jay - Whats the alternative to the Bajaj oil cooler?

I had a chance to do a 60 km ride on the back roads to test the VM28 now on my LB500. Initial impressions were encouraging, started easily on a cold morning and idled quite well even when cold. Here are some observations:

1. In the lower gears, all I need to make brisk progress is to open the throttle very very little. Open it just a little bit and the engine revs build. Open just a tad more and it will knock.

2. The heavy exhaust note that was a feature of the overjetted BS29 has gone really soft. I am running my LB500 with a short bottle, now it feels like a free flow exhaust ,the engine has a new found willingness to rev but the exhaust note is actually quieter. It cruises much more smoothly at a 100, however I find myself consciously making an effort to keep it around 90 kph these days.

4. If I open it even a 1/8th too early, the engine goes off into a fit of noises what seems like knocking. Cannot say for sure what this noise is, but it is quite pronounced with this carb, less so with the BS29 but it is very much present with either carb. Once the revs build, the noises go away and bike effortless reaches a 100.

5. I have to be really careful not to open the throttle more than the minimum initially. things improve as speeds climb, for example in 5th gear engine is quite tractable from 55 to 100 and wider throttle openings are easily tolerated over 60 kph in 5th.

6. I did a plug chop immediately after the ride, it looks a light shade of gray, not a trace of oily residue. The ceramic isnt bone white, just a dull shade of gray. I also noticed the engine wasnt running hot like it used to with the stock BS29, so I am not everly concerned with over heating with the VM28.

The difference between the two carbs is like chalk and cheese. While the VM28 is really quick to respond(perhaps too quick), the BS29 feels ponderous by comparison. The VM28 throttle needs to be worked with great care, large throttle openings at lower revs simply is not possible with the stock jetting. The BS29 OTOH is vastly more forgiving, one does not need to pay too much attention to what the engine is doing at any given time. As long as you are not in too tall a gear for a given speed the BS29 is just fine, although somewhat ponderous as noted above.

I need to experiment with the jetting on the VM28 and decide between it and the BS29. Right now, the VM28 is excessively sensitive to throttle inputs right above idle. Suggestions/experiences for jetting the VM28 are welcome.
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Old 31st January 2010, 17:39   #41
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Originally Posted by Beast_of_Burden View Post
The vacuum is created behind the rubber diaphragm, if it isnt regulated I suppose the slide would be stuck to roof of the carb most of the time as the vacuum would prove too strong. The holes at the bottom of the slide sort of regulate the vacuum, if you make the holes larger there would be less vacuum behind the diaphragm no? This would result in the slide reacting a little more slowly to the changes in vacuum in the intake, how would that improve throttle response? I am guessing about the purpose of those holes at the bottom of the slide, so correct me if i am wrong.

On a CV carb, the venturi isn't fixed. As you open the throttle, the air coming in increases and the pressure drops in the venturi.[FONT=Verdana] The low pressure in the venturi travels through the vacuum port in the vacuum piston to the chamber above the diaphragm.[/FONT] So, when you make the vacuum slide large, the pressure change(drop) happens quicker thus making the throttle response quicker. The vacuum pressure won't increase with larger. Rather it will decrease quicker than with the stock ports. And we aren't the first ones to think about this. The Harley boys have been doing this for ages.
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@Jay - Whats the alternative to the Bajaj oil cooler?

I don't know the exact brand/unit as of now. One of my good friend's in Pune has bought one already. He hasn't talked to me about the details yet.
All i know is it is cheaper and it is wider as opposed to longer. This means it will fit flush with the downtube making it look aesthetic. Will update you shortly.

If you want the Bajaj cooler, it is available pretty easily here in BLR.
Don't worry about sourcing, I had a look at it yesterday.

I had a chance to do a 60 km ride on the back roads to test the VM28 now on my LB500. Initial impressions were encouraging, started easily on a cold morning and idled quite well even when cold. Here are some observations:

1. In the lower gears, all I need to make brisk progress is to open the throttle very very little. Open it just a little bit and the engine revs build. Open just a tad more and it will knock.

2. The heavy exhaust note that was a feature of the overjetted BS29 has gone really soft. I am running my LB500 with a short bottle, now it feels like a free flow exhaust ,the engine has a new found willingness to rev but the exhaust note is actually quieter. It cruises much more smoothly at a 100, however I find myself consciously making an effort to keep it around 90 kph these days.

4. If I open it even a 1/8th too early, the engine goes off into a fit of noises what seems like knocking. Cannot say for sure what this noise is, but it is quite pronounced with this carb, less so with the BS29 but it is very much present with either carb. Once the revs build, the noises go away and bike effortless reaches a 100.

5. I have to be really careful not to open the throttle more than the minimum initially. things improve as speeds climb, for example in 5th gear engine is quite tractable from 55 to 100 and wider throttle openings are easily tolerated over 60 kph in 5th.

6. I did a plug chop immediately after the ride, it looks a light shade of gray, not a trace of oily residue. The ceramic isnt bone white, just a dull shade of gray. I also noticed the engine wasnt running hot like it used to with the stock BS29, so I am not everly concerned with over heating with the VM28.

The difference between the two carbs is like chalk and cheese. While the VM28 is really quick to respond(perhaps too quick), the BS29 feels ponderous by comparison. The VM28 throttle needs to be worked with great care, large throttle openings at lower revs simply is not possible with the stock jetting. The BS29 OTOH is vastly more forgiving, one does not need to pay too much attention to what the engine is doing at any given time. As long as you are not in too tall a gear for a given speed the BS29 is just fine, although somewhat ponderous as noted above.

I need to experiment with the jetting on the VM28 and decide between it and the BS29. Right now, the VM28 is excessively sensitive to throttle inputs right above idle. Suggestions/experiences for jetting the VM28 are welcome.

About the VM28, of course it will react faster since it is designed to, but you can't really whack the throttle open and expect it to catch on like the CV. That's what the cv carb is all about, it basically slows down the speed at which the slide opens. The CV carb is designed to open as quickly as the engine's airflow can keep up. In the VM, the slide opens too fast and the vacuum in the venturi becomes almost nil. So, fuel isn't sucked in, which in turn causes starvation. The only way out maybe is to go richer on the overall jetting, right from the idle, pilot, to the needle and main jet. Even this can't guarantee fuel starvation. Bottomline is you have to learn to chop the throttle crisply, not quickly. This is why I'm thinking about porting the BS29 so that I can have the best of both worlds. Good response as well as no starvation at any throttle opening.

A gray on the plug is slightly lean. On the VM28 a chap was running mains of 160-180 for the LB500 and still the LB500 managed to burn it. But he was running a free flow intake. Also, two spacers were used to richen the needle too. Mileage was crazy with sub 20s. I am not sure about the pilots. Even his top end improved though the venturi was smaller by 1mm. Mileage was crazy with sub 20s.
Replies in bold.

Cheers,

Jay
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Old 31st January 2010, 18:16   #42
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Originally Posted by JayPrashanth View Post
Don't buy the Bajaj oil cooler. There is something better and cheaper too. ..
struck gold? which one it is?
Quote:
Originally Posted by Beast_of_Burden
.. . Open it just a little bit and the engine revs build. Open just a tad more and it will knock. ..
Thats usual with quick/wide throttle inputs VM carb goes lean momentarily, its a side effect of fast response capability. BS' can be made quick responding., seems Jay is attempting that both you guys.
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Old 31st January 2010, 19:07   #43
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Rennjit,

Will post the details shortly, as and when I get them.

About the slider porting, there is an issue. The vacuum ports are right on the sliders wall. Now, porting that is a difficult task. So, I'm thinking of how to go about doing it. I have a spare slide already. Any ideas?

Cheers,

Jay
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Old 1st February 2010, 00:28   #44
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.. The vacuum ports are right on the sliders wall. Now, porting that is a difficult task. So, I'm thinking of how to go about doing it. ..
Though i'm no good with carb internals i presume wall thickness is the restriant here, drilling not possible. precision m/c'ing process like sink/wire Edm can enlarge the orifice into any shape also retaining enough wall thickness. Would be a bit costly though.

Last edited by Rennjit : 1st February 2010 at 00:30.
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Old 2nd February 2010, 18:55   #45
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Default What is the recommended plug gap?

What is the recommended plug gap for the LB 500? I read somewhere that it should not be more than 0.6mm.
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