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Thread: Tuning on a Micarb VM24 Carburetor of Bullet350 during High altitude-Steep Slope ride

  1. #11
    Rookie caravans's Avatar
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    Default Re: Tuning on a Micarb VM24 Carburetor of Bullet350 during High altitude-Steep Slope

    Quote Originally Posted by naraghu View Post
    thank you. My bike has done sixteen thousand kms. By adjusting the idling speed and timing it has now come to 31 kmpl. I am hopeful with proper adjustment it can be brought to 35 kmpl. I have removed the pulse air valve as I have been advised by mechanic. My earlier bullet used to give 39 kmpl on regular rides. Not accelerating too much, gentle riding around 50 kmph.
    39kmpl for a 350cc bullet on regular (city) rides is inevitably engine over-heating ! On back country tours however, such mileage is possible.

    On an avg., due to bad oil circulation (weak pumps) in a CI bullet, it's recommended to run the engine slight richer if to be used considerably. Too much rich is however bad economy & causes plug fouling. From my experience, 34~35kmpl on a good-running (read regularly used) 350cc bike is the standard achievable mileage on city rides. Anything more economic is actually slowly damaging the engine internals.

    Second, from p.o.v of mileage, PAV is a helpful add-age ! However since you have chucked it, no point in discussing !

    Third, adjusting idling speed will not affect mileage noticeably under normal running condition. If regular usage is through too many traffic signals where inevitably bike is not switched off (standard case of a ci350), then different matter however !

    Fourth, I'm not sure about the riding conditions there, but, 50kmph is too-slow for a 350cc bike. Ideal engine mixture is obtained at around 64kmph. I ride at around 70~75kmph at most instances & achieve a mileage of around 33~34kmpl. My present ci bullet has covered 87K kms.

    Fifth, my suggestion is to ride the bike more often and not only on joy rides. It will keep it more free & engine will behave in true potential. However goes without saying, it is definitely based on your lifestyles & practical situations !

    Take care. Ride safe.

    Anirban.

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    Default Re: Tuning on a Micarb VM24 Carburetor of Bullet350 during High altitude-Steep Slope

    thank you. It is difficult to ride more than 50 kmph range as I travel around in a heavy traffic zone. When I go out of city, I ride it around 70 to 85 range. I have the PAV with connections stored safely. I will fix it back and try. I have been told that more carbon fouling would happen with it. Hence I removed.

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    Rookie Jerry43's Avatar
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    Default Re: Tuning on a Micarb VM24 Carburetor of Bullet350 during High altitude-Steep Slope

    Quote Originally Posted by caravans View Post
    28kmpl is not bad mileage for a 350cc ci bike which I assume has covered 80K to 90K kms.
    In newer condition, they always give better mileage. Hence there can be many reasons for this. The general are worn out piston rings, worn gaskets, worn points assembly causing retarded timing, worn ignition-advance mechanism etc. Less probable if you service correctly are dirty air filter, clogged oil filter, clogged carb jets, leaking pulse air valve tube (if your bike has one) etc. So you need to first identify the cause.
    Also, frankly, how to set timing is beyond the scope of this type of communication. You however can obtain a workshop manual from any source to go through steps for static timing & then, dynamic timing (which is must & most important).
    You will need a non breakable straight metal rod to insert through the plug hole & a good multimeter / bulb & a mm scale & pencil/pen to do static timing. Jist is to set the points to open exactly at the moment piston reaches 0.8mm before TDC. You need to check this a number of times to be sure that basic setting has been achieved.
    Next, you need to do ping timing. For this you need to advance the timing in slow degrees until you can hear the engine pinging at 3rd-4th gear with above half throttle while riding. Next you retard the timing slowly & reach the point when it no longer pings even with throttle opening above 50% in 3rd-4th gear. Then retard it very slightly more & tighten the screws. That's timing for a cb points bike.
    Tuning, since you say you have stock jets & assuming needle is in 3rd, you only need to set pilot screw which only affects idling & very low speed riding. It is air-bleed type, so IN means rich, OUT means lean. Standard position is 1.5turns from fully closed which may vary by a quarter to half turn from bike to bike. Never go beyond 2.5 turns out. If you feel rpm still increases after 2.5turns, you need to go to the next pilot jet size or you will damage the spring tightness.
    But again, you need to go through the manual for clear understanding of steps before doing any setting change.

    Also, you don't need an RPM meter for setting timing or tuning the carb of a Std CI 350. Believe me, it only comes with experience & you will need to commit a few errors & be corrected (or be guided by a experienced person first hand) to learn how to maintain these two.

    Take care & ride safe.
    Anirban.
    I have a standard 350. Tuning a carburetor is a pain in my ass.. last month i visited kasauli and my bullet was straining and panting for air.. the climb after kalka, haryana was so tough. It was not climbing properly.. i dont know if it has something to do with the carb or clutch. As i tightened the clutch from gearbox. After coming to Delhi the plugs were black sooty. Dad told me that it was running rich. Plus the clutch had no play. And i was travelling with a pillion. So i wanted to ask do we need to tickle the carb before hills?
    Or the two screw that is one for rpm and one for mixture. So how does it work. If i open/anti clockwise the screw, will it run lean/more air or the other way around? Or it runs rich?
    Sorry I'm a newbie..
    Mine is 1990 model with pav thing😅

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    Rookie caravans's Avatar
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    Default Re: Tuning on a Micarb VM24 Carburetor of Bullet350 during High altitude-Steep Slope

    Its natural for a 350CI to pant "a bit" on real high altitude with a pillion. This has to do with the Micarb Carburettor not sucking sufficient air in as per its design. In stock setting, it should pant because that is physics. Otherwise on low/normal altitudes it will run lean with more air !


    Climbing any mountain takes more effort (power) for the engine. With a pillion it requires much more effort (power). Power comes with more petrol in the mix (this can be done by lifting the needle in the carb). In lower mountains, this power objective can be fairly achieved in conjunction with advancing the timing a bit. While riding up, the higher rpm will burn off the carbon from the plug & while descending, the plug will accumulate carbon. Back on the plains, the needle should again be lowered & timing reset to initial (keep a pencil mark on the points before advancing initially to find this fast).


    But in real-high altitudes, the engine efficiency is vastly compromised owing to less oxygen. So in stock carb setting, it is already loosing power due to rich mixture as you saw your plugs getting sooty. In such conditions one will need to lower the needle to reduce petrol in the mix in conjunction with advancing the timing a bit (with an ear very open to detect pinging sound during ascending in which case the timing is to be retarded a bit again) . This will act as a compromise but will not increase the power & the bull will still pant a bit, but less so. Also if idling is going "too-bad" & the rpm screw is already turned-in to extreme but not working, the pilot-jet screw can be turned outwards by quarter turns to increase idling air. Back on the plains, much more importantly than the previous case, the needle needs to be lifted again & the timing reset.


    All the above are stated considering no change in Jet sizes & are the only few things to play with to get a CI going up & down !


    A minimum cluth play is desirable. Too tight & the gear will slip. Too loose & it will be hard to find the next gear. Clutch has an optimum setting that has nothing to do with mountains or plains. That is considering the plates are in good condition.


    Tickle the carb you asked. Do you have amal carb in your bike ? In micarb there is only a choke. However in either case, that helps ONLY IN COLD-STARTING & not in running.


    I dont think being a newbie is to be sorry about considering I was once too many years back ! You always start somewhere ! Most importantly you are interested & that great ! If you would really like to enjoy the beauty of Bulleting, I would suggest you start with a good User-manual for setting the basics right. Would go a long way in improving your relationship with your bullet (& also save your ass ).


    Take care. Ride safe.
    Anirban.

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    Default Re: Tuning on a Micarb VM24 Carburetor of Bullet350 during High altitude-Steep Slope

    Quote Originally Posted by caravans View Post
    Its natural for a 350CI to pant "a bit" on real high altitude with a pillion. This has to do with the Micarb Carburettor not sucking sufficient air in as per its design. In stock setting, it should pant because that is physics. Otherwise on low/normal altitudes it will run lean with more air !


    Climbing any mountain takes more effort (power) for the engine. With a pillion it requires much more effort (power). Power comes with more petrol in the mix (this can be done by lifting the needle in the carb). In lower mountains, this power objective can be fairly achieved in conjunction with advancing the timing a bit. While riding up, the higher rpm will burn off the carbon from the plug & while descending, the plug will accumulate carbon. Back on the plains, the needle should again be lowered & timing reset to initial (keep a pencil mark on the points before advancing initially to find this fast).


    But in real-high altitudes, the engine efficiency is vastly compromised owing to less oxygen. So in stock carb setting, it is already loosing power due to rich mixture as you saw your plugs getting sooty. In such conditions one will need to lower the needle to reduce petrol in the mix in conjunction with advancing the timing a bit (with an ear very open to detect pinging sound during ascending in which case the timing is to be retarded a bit again) . This will act as a compromise but will not increase the power & the bull will still pant a bit, but less so. Also if idling is going "too-bad" & the rpm screw is already turned-in to extreme but not working, the pilot-jet screw can be turned outwards by quarter turns to increase idling air. Back on the plains, much more importantly than the previous case, the needle needs to be lifted again & the timing reset.


    All the above are stated considering no change in Jet sizes & are the only few things to play with to get a CI going up & down !


    A minimum cluth play is desirable. Too tight & the gear will slip. Too loose & it will be hard to find the next gear. Clutch has an optimum setting that has nothing to do with mountains or plains. That is considering the plates are in good condition.


    Tickle the carb you asked. Do you have amal carb in your bike ? In micarb there is only a choke. However in either case, that helps ONLY IN COLD-STARTING & not in running.


    I dont think being a newbie is to be sorry about considering I was once too many years back ! You always start somewhere ! Most importantly you are interested & that great ! If you would really like to enjoy the beauty of Bulleting, I would suggest you start with a good User-manual for setting the basics right. Would go a long way in improving your relationship with your bullet (& also save your ass ).


    Take care. Ride safe.
    Anirban.

    Thank for the valuable information.. it was because of clutch slipping.. it had no play actually..
    Last week i went to manali.. it was 600km one sided from my home.. it performed better than before..
    But still it was lacking some power..
    The biggest mistake i did was carrying a hefty pillion. We both weigh 85kg.. being a heavy bike.. it did very well.. the only thing i suffered was the clutch was overheating when going to solang Valley. The road was full of vehicles. And the play was increasing and the bull would stop after some time because of constant pulling and releasing the clutch.. i have a 4 clutch plate transmission.. is it natural for old bullet?
    And one more query.. i have a 17 inch sprocket.. is this the reason for the bull to not perform the best?
    I have read somewhere that front sprocket affects initial torque and top end torque..
    Thanks
    Jerin!

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