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Old 14th October 2007, 09:45   #1
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Post How to tune your carb properly

Read this article here, thought since 99% bikes sold in India are Carbs, this would be helpful.

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Last few days of mine were lost into digging information about Fuel Injection and Carburettor and thankfully with help of some of my friends and netsphere I was able to get a good dose of knowledge.
P200 being a carburetted one I concentrated on carb mostly.As you might be knowing, carb plays a vital role in welfare of your bike's health.A detuned carb can greatly reduce the performance and efficiency.While a neatly adjusted carb can do wonders.
The fact also helps that carbs are much easy to tune/alter than FI.It doesn't need all that electronic gadgetry which FI needs. Once you get to know the basic hardware of carb its easy to do a makeshift operation on it in case anything goes wrong.
In my case the fuel efficiency had gone awry and engine was jerky in 1st and 2nd gear.When I enquired with some, it turned out that carb was set for too rich mixture(which meant it was forcing more than necessary fuel into engine).

Locating the volume control screw is easy.In fact its the only screw on LHS of carb other than the one for setting idle.Besides its bronze color so no mistaking!

As from the pic, I don't need to say the obvious, But will say it nevertheless!
Turning right the carb will channel less fuel and more air making it lean while turning it left will channel more fuel and less air(as in my case).
So adjust it accordingly.
However don't go overboard on either side. Maintaining it on a perfect position is best and will give you right amount of performance coupled with efficiency.

(Remember one thing turning it completely towards right or left doesn't mean peak efficiency or performance respectively) For engine's health you must maintain the balance.
There is one cliche though. Before you embark onto this learn to read your spark-plugs.Don't panic!!Its easy and a must know for enthusiast biker.
Remove both the sparks and check their electrodes for color.
If its more on the brownish side your bike is running on leaner mix if its way too much black your bike is running on rich mix. So ideally it should be dark-brown(almost black but not black!).
When you adjust the volume control ride the bike for a few kilometres and then check for color of the spark plugs tune it accordingly until your bike is running on balanced mix.
One more precaution to take- Don't turn the volume control like you do with normal screws.Do it slowly and only by half or a quarter turn at a time.Its much sensitive.
Source

Last edited by BUSA : 14th October 2007 at 09:46.
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Old 14th October 2007, 14:48   #2
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Carb tuning is best left to the mechanics, because for most people it will be a hit and trial method and the last thing you want is messing up the setting! In fact is most cases the factory setting is the best one to have and so don't even ask the mechanics to fiddle with it, unless there is some thing seriously wrong!
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Old 14th October 2007, 18:29   #3
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Quote:
Originally Posted by yogesh sarkar View Post
Carb tuning is best left to the mechanics, because for most people it will be a hit and trial method and the last thing you want is messing up the setting!
I second that opinion. Its best if a carpenter did the carpentry work .

My RX 135 used to be my test mule for all my doubts and end of the day I always had to head to garage and have my mechanic set it right.

So leave it to the mechanic, he does it best.

Last edited by rjstyles69 : 14th October 2007 at 18:32.
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Old 14th October 2007, 18:42   #4
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Turning it right used to be rich and turning it left used to lean out , or am I confused .
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Old 14th October 2007, 19:44   #5
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Hi,
How do you remove the spark plugs? Do I need any special tool for that??
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Old 14th October 2007, 21:20   #6
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There will be small pipe looking tool in your toolkit, you can use it to remove the sparkplug.
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Old 14th October 2007, 22:07   #7
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Quote:
Originally Posted by black12rr View Post
Turning it right used to be rich and turning it left used to lean out , or am I confused .
Yep.. ideally u would tighten(turn clockwise) the airscrew for a richer mixture and loosen (turn Anti Clockwise) it for a leaner mix.
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Old 14th October 2007, 22:32   #8
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You mean in the toolkit that comes with the bike or an aftermarket one??
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Old 11th October 2008, 20:30   #9
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I know it's an old thread but i chanced upon it..thought i'll make it clear for anyone reading this in future.

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Originally Posted by black12rr View Post
Turning it right used to be rich and turning it left used to lean out , or am I confused .
The carb pictured above is a Mikuni BS carb, and the screw mentioned in the article is a volume control screw.

With volume control screw you tighten it for a lean mixture and loosen it for a rich mixture. This is because it controls fuel and not air.

The Mikuni VM series carbs have air control screw, tighten it for a rich mixture and loosen it for a lean mixture. This is because it controls the air entering the pilot circuit, more air = lean, less air = rich.

How to make sure if a screw is a volume control or an air control?
If the screw is near the engine, as in the picture, it's a volume control screw.
If the screw is near the air filter, like in a VM28, it's a air control screw.
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Old 12th October 2008, 16:23   #10
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^ Thanks a lot Sankar. This question was troubling me since a long time and I couldn't find any documentation on Mikuni BS carbs on the web.
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Old 12th October 2008, 16:39   #11
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While we are on this thread, can someone explain what the article refers to when it talks about electronic gadgetry for tuning FI bikes? What are the gadgets and what are the problems in tuning an FI bike for more performance?
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Old 4th November 2008, 18:04   #12
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Hello bike experts - let me ask you my query. Recently I have picked up my brother-in-law's blue coloured Mumbai (MH01) registered 2004 Pulsar 150 DTSi which has clocked only 21000 kms since he bought it new. It came with an almost dud battery (4 years, so OK I guess) so I just put in a brand new Standard Furukawa battery but it ran out of starter motor juice after a couple of uses (my use is quite less, I just take it for a spin in Nasik, I have bought it for leisurely drives only) so I changed the rectifier at Wasan Bajaj and the service advisor set the carburettor. This sorted out the starter cranking rpm and acceleration also was quite OK, improved as compared to earlier. I must have driven not more than 100 kms. Things were looking good till last month. Now my specific problem - the engine does not start when the starter is actuated although cranking rpm is very brisk. The engine starts with the kick starter but stalls even if the throttle is opened slightly. The engine idles properly although idling rpm seems to be low. I increased it slightly from the carburettor yesterday. The lack of decent acceleration goes on for around a minute or so, so I drive around in 1st / 2nd for about a kilometer and then acceleration becomes normal. However, it stalls at traffic signals and starts after 5 or 6 kicks. During this time, the rpm meter also flickers between some 3000 and 14000 rpm. Maybe some wire misbehaving somewhere? Also I think the mixture strength is incorrect. DOES THE VOLUME CONTROL SCREW CHANGE ITS POSITION DURING DRIVE? HOW SENSITIVE IS THE VOLUME CONTROL SCREW SETTING? WHAT WILL HAPPEN IF I ROTATE IT BY SAY 45 DEGREES EITHERWAYS? OR 90 DEGREES EITHERWAYS? OR LESS? WHY THE DIFFERENCE IN STARTING PERFORMANCE WHEN STARTED BY KICK / STARTER MOTOR?

As is normal in my case, I introduced myself to the dealer's chief of service, gave him my background but still he gave me the usual - "leave it, we will attend" etc, I told them "no chance, I am not a normal customer and this is not a normal service transaction". The dealer now knows my background. I will get to the root cause. My problem is that I will never leave the bike with anybody because I know for a fact that everything is original as my brother-in-law has done nothing to it for 4 years. Also, I just do not have time to give it this symptom the attention it deserves. Can you guys help with your comments? It will help me in full analysis and correction. I await the same.

Also, what are your comments on the life of a Pulsar 150 timing chain?

Best regards,

Behram Dhabhar
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Old 5th November 2008, 11:58   #13
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Quote:
During this time, the rpm meter also flickers between some 3000 and 14000 rpm
I had same issue with my plusar 150 dtsi. The Battery was dead and i chaged it last year. Then every thing was OK. Again i am facing the same problem. This time also i guess the battery is the culprit.

Check the battery and wiring once again. Because you have already chaged the rectifier.

I am taking my bike for service this weekend. keep you posted.
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Old 3rd June 2012, 11:52   #14
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Default Re: How to tune your carb properly.

bump

Interesting thread - But would appreciate more inputs from Experts w.r.t the different types of carb and how to tune them correctly.
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Old 4th June 2012, 13:51   #15
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Default Re: How to tune your carb properly.

Quote:
Originally Posted by Sankar View Post


The carb pictured above is a Mikuni BS carb, and the screw mentioned in the article is a volume control screw.

With volume control screw you tighten it for a lean mixture and loosen it for a rich mixture. This is because it controls fuel and not air.
The carb in the picture is BS29 ? , then tighten the screw (clock wise ) will make it run rich and loosening it will make it lean .
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