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[SiddJ]

Hallo everyone, I have had some strange symptoms with my bullet that I think are linked to the carburettor. Starting up the bike is fine, running it up to 50 mph is fine, but unless on a dead level road getting it up to and past 60 mph is a struggle, with the bike lacking any oomph. Putting the choke lever down briefly (bad practice) gives the bike the necessary power, which leads me to believe that the fuel/air mixture is too weak. I've raised the throttle needle from the first notch to the third, which has helped considerably, and the float level is fine (Mikarb). I also suspect the actual fuel circuit since the original owner replaced the original air filter with a conical filter. The whole carburretor therefore sits rather loosely held on with cable ties, and is probably vibrating quite a bit.


 Any ideas?!!! I have checked the ignition timing etc, have looked for blockages in the fuel lines/tank but can't sort it out! Starting to go crazy looking for the solution! 

[Alan R]

Hi SiddJ---- 350 or 500 ?? Which carb is fitted ??, What exhaust system is fitted ??  Check-out the main jet size. Have a look in our hosts catalogue for reccomended jet sizes for different combinations of the above. The brief application of the choke is the main indicator that there is a lack of fuel supply at the top end of the rev range when under load. Another sign would be that if you roll the throttle back a bit the engine picks up ?? While you're at it --- if the whole set-up is now much more free-flowing than before you might need to change the spark plug to a more suitable rating. Finally---the standard speedo is optomistic at the best of times. Nice to hear from you---stay in the groove !!

[TimG]

Hi SiddJ


The clue is in the replacement of the original filter setup with the conical one. This will allow more air through the carb, thus weakening the  mixture significantly.


As Alan R says, check your main jet size. When I replaced the filter on my Classic I asked our hosts what size jets they recommended. These will of course vary depending on which flavour of Enfield you have.


When it's right, you will get a significant hike in mid-range torque.


Also - has the original exhaust been replaced by a free-flow item? This will allow even more air to flow.


More info needed mate...


Cheers


TimG

[Riggers]

Hi Siddj - I had exactly the same problem with mine (Classic 500 Year 2001). Is yours the same bike? I replaced the tea caddy with our hosts conical filter, removed all the PAV crap, and added an open silencer. This little lot sent the carburration haywire. Having sorted out pilot, slide, needle and cutaway I was left with a bike that wouldn't go beyond 50 without the same symptoms as yours (despite fitting our host's largest main jet - 135. The solution in my case was to drill the main jet out to 1.5mm and hey presto! the illness was cured.


Hope this helps.


Tony R.

[Midge]

If the carb is wobbly there may be air getting sucked in. On the 500 the Amal rubber intake manifold hose AM/2622/123 (Page 16 of the catalogue) is a better option for the Mikcarb and will hold it correctly.

[Alan R]

Hi guys---if you go to Allens Performance Carbs, and look on their jet size chart you'll see that a 1.5mm size gives a flow rate of 300cc's/min, whilst a 1.25mm size gives 170 cc's/min. Hitchcock's 135 jet size(cc's/min) equates to a hole size of 1mm approx. So that would seem to be about right. ie}--3 stages to try-----1mm, 1.25mm, 1.5mm. Riggers---is that the bike in the photo recently ??

[Riggers]

Hi Alan - Yep the very one!


Cheers.

[SiddJ]

Hallo everybody- thanks very much for all your replies- they have been very helpful. Just a few notes- the bike is a 2003 ES start bullet 500, the carburettor is a micarb vm28 and the exhaust and silencer are the standard export types.


  I think my plan is to put back the original air filter so that the carburettor sits correctly as currently the throttle cable is rubbing against the fuel tank and probably frothing the petrol. Then if necessary will alter the main jet settings.


Thanks again for all your advice!