Hitchcocks Forum

The bullet 65 has now been fitted with a 50s style exhaust and is running on a Micarb with the middle range of jets that our hosts supply. The filter is the conical type ,the pav system is removed. It starts very easily ,usually first kick and runs fairly cleanly but has a feeling of being held back and occasionally spits back through the carb. On occasions it is difficult to hold top gear because of these problems, press on the choke lever and their is an immediate surge in power and indeed it seems to run fine with the choke on all the time until you slow down when it becomes necessary to knock the choke off.
Dave

Hello DAVID--------- your BULLET 65 is basically the old "Iron" barrelled engine with an electric start and the "Mk.1" 5-speed gearbox, and 28mm Mikcarb. carby....You've really answered your own question as applying the choke (ie making the fuel/air mixture richer) appears to be improving things--------------- thus you have a WEAK mixture in the area you mentioned........... Try these figures that RIGGERS gave a while ago... They work ok on my 500cc "Iron" engine }-------- FLOAT HEIGHT = 24MM,.... MAIN JET = 135, ...... NEEDLE JET = P2,.....PILOT = 30,.....SLIDE No = 3,.....NEEDLE POSITION = MID,..... AIR SCREW SETTING = 1.5 initially,..... AIR FILTER = TEA CADDY (ie free flowing, similar to conical),....PLUG = As standard,.....IGN. TIMING = As Standard,.....These will get you running OK, BUT}--------- you WILL have to fine tune a bit......... Incidentally I also have our hosts 8.5CR forged piston and a 19t sprocket which gives a COMFORTABLE cruising speed of 60mph plus good hill climbing as well............

Tanks Alan,
I will take everything carb wise to bits again and check against your figures,I hadn't thought about the slide being the wrong one but will also check that. Just as an aside for future thought really my needle has been set at the lowest notch ie the richest setting and I noticed that you mentioned that yours is at the mid point ,is that purely because your jets appear to be significantly larger than mine?
Regards david w

Hello DAVID, ------- generally speaking those notches in the needle are to give a bit of "fine tuning" to the needle jet itself..........Mine's in the centre because the needle jetting appears to be OK......... The idea is that you start with the clip in the mid-position and road test with note being taken as to the bikes' mid-range performance.......If it needs richening then you raise the needle (ie place the clip into the next LOWER notch) and test again......(the other way around for weakening ).. If, after several tests, you have run out of clip positions then you need to fit a bigger( Richer) OR smaller(Weaker) jet,depending on which way you were going--- PUT THE CLIP BACK TO THE MIDDLE POSITION and continue testing in the same manner.....Incidentally the standard method of describing a needle clip position is by numbering from top to bottom.. So the centre position for a 5-notch needle reads as }-- 3/5 or the lowest(richest) is 5/5................ A point to remember with carb tuning is that each progressive jetting eg}--- PILOT---NEEDLE---MAIN overlaps its' neighbour to a certain degree.......So a change in one will have a certain effect on the one next to it..............ALAS !!!............ Not to be forgotten is the slide cut-away ( affects the initial response of the carb), the choke size- that's throat diameter, the inlet tract length --- affects torque position within rev. band----- Phew !! Time to get ready for the MADMIKE EXTRAVAGANZA tomorrow.....

-------------- sorry, forgot to add}--- Irrespective of all that lot, your MAIN priority is for correct combustion, mixture etc at full load, on full throttle.. Hence the "Plug-Chop" routine and the Light Coffee color required on the plugs' reading................ get that wrong on the WEAK side and you'll suddenly get a compression reading of ZERO !! (been there, done that---- had the P**s taken for many months afterwards as well)--------know what I mean ?????????

Dave, Just a thought, my sixty-5 had a blocked float chamber breather tube from new. Started ok, ran at low speed although lean,'popped' through the carb and appeared cured by using the choke. Even the dealer couldn't find it at the first service. I think the blocked breather forms a vacuum above the float restricting fuel flow into the main jet. Actually had to use a small drill to clean it out for an instant cure.
Good luck.

Hi Alan and bob,
The carburation does seem a fairly complex subject although with all your help am beginning to make sense of it all!!
Bobs comment on blockages is interesting, using carb cleaner in every orifice has resulted in a bit of metal appearing in my cleaning tray which I cannot say from which orrifice it came. It didn't effect a cure but one wonders if their is more!,
I am becoming good at stripping down the carb. I will put the needle back to the middle position Alan and order now a larger pilot and main jet.my pilot is 27.5 and main is 117.5 so quite a bit different from yours Alan. Everything else is the same. I will report back in due course on progress
David

Hi DAVID----- Just to add a bit more since the other day......................Whilst riding to and from MADMIKE'S mini-rally yesterday, I took the opportunity to give the main jetting a good "work-out!" on some hills and think that it could go richer by 5% ie }--- will now be a 140 instead...( On ALLENS PERFORMANCE CARBS site they have a chart showing MIKUNI jet sizes and the corresponding bore of each one....RIGGERS said he used a 1mm drill to get a good mixture..This actually equates to a 140 !!)...Will have to buy one and let you know how it goes ------------

Hi Alan,
Thanks for the latest info regarding jetting,I taken it on board and can now report on the latest findings. For all who haven't been following its best to read the whole thread regarding this carburation issue. I have set the float height to 24 mm as per Instruction, the slide is no3 ,the needle is now in its mid position, needle jet is p2 , the pilot jet up to 30 and the main jet is now no130. I do have the main jet no 135 here in case this is not sufficient. The first result of the short road test is very positive!!!.
On Friday I will do a dales run up as far as hawes and return ( perhaps 80 miles or so and see how it performs) and I will report back on Friday evening if I manage to return !,,,,
David w