[Racer911]

Originally Posted by Arch-Angel

Afaik, I, being an owner of the same old pulsar, i don't think with carb engines, you get to time the engine as it is not an FI engine. So no ECU/injection control whatsoever. Only thing one can do is maybe go in for a rebore or change your exhaust. Imo, it is best to leave her stock since you are attached to the bike, just like i am.

guys, i think the discussion is again going all over towards ignition timing. I am talking about the valve timing, controlled mechanically by the camshaft and cams. this process is entirely mechanical. The CDI unit, or FI systems are related to fuel and spark plug timing. Or please correct me if I am wrong, is there anything I am missing over here??

I think the cam timing or valve timing can be advanced or retarded by altering the position of the degree of rotation of the camshaft in relation to the crankshaft. There are loads of articles about this but mainly on websites outside India and that too for vehicles that we dont get over here or cant afford. Hence, I started this discussion. Cant seem to find anyone who has experimented with the valve timings.

I have searched and searched and found out lots of articles in which people are either obsessing over a K & N air filter, larger carburettor, free flow exhausts, or reboring the cylinder. All this can be done, but with a lot of expenditure.

I am strictly against reboring as I do not consider that upgrading the engine. Its changing the engine altogether. What I want to do is try and squeeze out a little extra from my plain old carburetted 150cc engine. One of the potential ways I feel after a lot of reading and researching online is by trying to tweak the cam timings.

I believe this can be done because the tuning and setting of the stock engine is done keeping in mind various factors like fuel efficiency, longevity of the engine etc etc.

I am willing to compromise fuel efficiency as this bike will anyway be for occasional riding because I am a little attached to it.

The most I am willing to do is get a freeflowing air filter, retune the existing carb, or even get a bigger carb from a bigger pulsar, but thats it. After that I want to find out how much difference can be made by playing around with the valve timings. If even a slightly noticeable difference can be achieved, I am good with it. After that, maybe I'll start researching tweaking the CDI unit or an aftermarket CDI unit to alter the ignition timings.

Lastly, If i can squeeze out a little extra power from my bike, I would then like to use a smaller rear sprocket in order to reduce RPM's throughout the entire speed range.

Thanks anyone who can specially focus and throw light on the subject of valve timings or advanced cam timings.

[Racer911]

Originally Posted by alpha1

Why would you "advance" the timings when you aim is to improve the low and mid range performance/torque?

Isn't advancing done for high RPM performance? Because at high engine speeds you need to give enough time to burn the fuel and hence keep the valves open longer.

If you are talking about spark ignition, then advancing it may lead to engine knock!

I personally do not have first hand knowledge or experience about the subject, but whatever I have read until now, says that advancing cam timings dramatically alters the low end performance too. I know retarded timings lead to reduced potential of achieving higher rpms, but advancing the timing also leads to greater air and fuel intake before both the valves close. you can either visualize this or look for animations online. theres lots of stuff available online.

I have even visualized this in my mind and feel that this theory is correct, you're free to throw light on this if you have any experience or knowledge about this.

Thanks.

[Racer911]

Heres a small animation which will help to visualize why its better with advanced cam timings.

[Arch-Angel]

The reason everyone is talking about ignition timing could be because valve and cam timing come under the same topic. The camshaft has lobes which open close valves(closing is due to spring action usually) This in turn changes the factor to how much/ when the fuel goes inside or when the exhaust cycle happens. This comes under ignition timing afaik. Also, if you need to either change your ignition timings (This in turn dictates how and when the fuel will blow up inside the cylinder) dictates how much power is obtained per cycle and therefore, the torque as well. Its all down to that. Rejetting carbs will give you more fuel per cycle, increasing the power per power stroke and thereby increasing torque in general throughout the operation range. Carb bikes are usually rebored, given a filter, lightened and maybe given a good exhaust treatment in order to make them performance machines. I wanted to say, you do not have many options compared to FI bikes because a simple remap will give better performance to the FI bikes whereas we carb owners have limited options. So in my opinion, its best you keep your bike stock.
I hope we have some expert on this to comment, i'll try asking around as well.

[Racer911]

Originally Posted by Arch-Angel

The reason everyone is talking about ignition timing could be because valve and cam timing come under the same topic. The camshaft has lobes which open close valves(closing is due to spring action usually) This in turn changes the factor to how much/ when the fuel goes inside or when the exhaust cycle happens. This comes under ignition timing afaik. Also, if you need to either change your ignition timings (This in turn dictates how and when the fuel will blow up inside the cylinder) dictates how much power is obtained per cycle and therefore, the torque as well. Its all down to that. Rejetting carbs will give you more fuel per cycle, increasing the power per power stroke and thereby increasing torque in general throughout the operation range. Carb bikes are usually rebored, given a filter, lightened and maybe given a good exhaust treatment in order to make them performance machines. I wanted to say, you do not have many options compared to FI bikes because a simple remap will give better performance to the FI bikes whereas we carb owners have limited options. So in my opinion, its best you keep your bike stock.
I hope we have some expert on this to comment, i'll try asking around as well.

Hmm.. I am quite sure valve timing is not related to ignition timing. Ignition timing is basically the time at which the spark plug fires up.

The ignition timing is controlled by the rotation of the crankshaft and not the camshaft. On top of that, now most of the bikes have a CDI unit which basically means a digitally controlled spark timing according to the RPM's of the engine which are calculated as the crankshaft rotates and creates a pulse as rotating magnet attached to the crankshaft creates a pulse in a device in close proximity. Basically, it registers a difference in magnetic field as a rotation and thus shows us the RPM. Similar magnetic RPM meters are even available as addons for bicycles, and ones which calculate by detecting the electricity pulse in the spark plug wire and multiplying it by 4.

[Sutripta]

Don't know about Pulsar engines, but with both inlet and exhaust lobes being on the same shaft, I would have doubts about any improvement.

If the cam timing is off by even one crank sprocket tooth in a (single camshaft) car, it usually runs like a dog.

Interference shouldn't be a problem, but still check for it.

Regards
Sutripta

[Racer911]

Originally Posted by Sutripta

Don't know about Pulsar engines, but with both inlet and exhaust lobes being on the same shaft, I would have doubts about any improvement.

If the cam timing is off by even one crank sprocket tooth in a (single camshaft) car, it usually runs like a dog.

Interference shouldn't be a problem, but still check for it.

Regards
Sutripta

runs like a dog means good or bad??

[Sutripta]

Originally Posted by Racer911

runs like a dog means good or bad??

Bad.

Regards
Sutripta

[Racer911]

okay. hmm. but this is still something that i wanna experiment and find out for myself because i have read a lot about this stuff online.. i basically wanted to know if someone could guide me into how to do it properly.. local mechanics would be able to do it, but sometimes i just find their approach too crude and chalega style.. eg. tyre pressure recommended is 30 to 32 psi in bikes. most of the local tyrewalas will try to inflate to 40 psi on my classic 350 explaining to me its a heavy bike. and i gotta argue with them that if its a heavier bike, its even got tyres accordingly. its not like that cars are so heavy so we inflate the tyres to 80 psi. tyres are given accordingly which maintain the required level at the same 30 to 32 psi.. with local mechanics, its always a never ending arguement, and they just feel that if we know so much, why we take our vehicles to them in the first place..

I hope someone would be able to walk me through the correct procedure or inform me about specific things that need to be taken care of while making these adjustments.. if things dont work out well, settings can always be reversed