Forum

[Chris Tindal]

Last week fitted a brand new monobloc 389 to my 500 classic engined bullet. Started ok and ticked over, ran for two miles then stalled and refused to start, pushed it two miles (up a steep hill!) home and left it untill today. This morning started ok but very lumpy tickover and smokey, stalled again and simply would not start. Took the float chamber cover off and looked at the needle. It stays up, even with the float down and needs a sharp tap on the carb to make it drop, is this normal?


The once choclate brown plug is now sooty black. After what felt like 50 kicks it started again but wouldn't tick over. Finally started it again and managed to keep blipping the throttle while I got my lid on and took it around the block. Runs reall well above 1/4 throttle but when I got back it just died again and would'nt start. Then, for some reason it started easily and kept on starting with just one kick and even semi ticked over. I have done the textbook method of adjusting the air screw and tickover screw and thought I was getting somewhere. When I blip the throttle the revs don't settle back down but stay high for a while. The tickover is up and down, slow and fast as if there's an air leak (there isn't) and then it just won't start again. Has anyone any suggestions, its starting to drain me. Its a brand new 389 monobloc, 1999 500 Indian head, tea caddy airbox and rubber tube between, no air leaks, no blowing at the exhaust, carb jetted roughly for a std 500,  off the shelf from our host, slight drip from the main jet cover nut, even when tight. I've looked inside the petrol tank with a torch, clean fuel, clean petrol tap gauze.


Any suggestions welcome before it all goes in the canal.

[1950s Bulleteer]

It does sound like the needle jet is the problem. The drip will appear to be coming from that jet cover nut because it is the lowest part of the carb, even if it is flowing out from around the 'tickler' plunger which is much more likely given the symptoms youhave described.If the level of petrol is too high that will cause the drip, and if the petrol level is not constant that will give erratic symptoms that will be hard to pin down. Get the float and needle valve working properly first, you might find that all will be well, but if problems persist you have a solid basis to work from.

[1950s Bulleteer]

I would alsosay it's well worth persevering with the Monobloc. I.M.H.O. it is a far superior instrument to the Concentric.

[grunda 12]

brand new carb should not be faulty ,take it up with the supplier this kit has cost you a lot of money and should be fit for purpose ,if supplier can,t help give burlen a phone call sounds like a sub standard product to me

[RancidPolecat]

If the float needle is staying up then the petrol level will be too low, the symptoms you describe could be fuel starvation. I.E. if it stalls after a short distance and won't restatrt then the float chamber could be empty.


The poor throttle response could also be down to this due to weak mixture. The float needle should move very freely and follow the float, if you can move the float down and the float needle stays up that will be part of the problem.


The monobloc is a very good carb and should be very easy to set up. 

[Alan R]

Hi Chris---- have a look on the BSA A7 - A10 Forum where Brucie 64 had a Monoblock 389 / 37 leak on a BRAND NEW carb.---back in 2009 though. Might be of some help ??  How's the weather up there ?? It's nearly time for us here in the boarderlands to invade that there Wales again------OK, so I just love a bit of genuine Bara brith !! Yummy. PS-- I just put ---------MONOBLOCK 389 --------- into Google and followed the links.   Ta-ra .

[John Moulton]

Hi Chris. If you would like another pair of eyes to have a look at your carb, drop me an e-mail. I'm off work this week and would be available some of the time. Failing that, next weekend? can't promise anything, but don't chuck it in the canal just yet!


John 

[Alan R]

Hello again Chris------- having re-read the symptoms given and woken my brain up from it's Sunday snooze---I think you may well have two problems simultaneously ( god, that was dificult typing with just the one finger !! ).  A few years ago I was running a Bullet Sixty-Five---I bought a brand new Amal Concentric from our hosts, fitted, tuned and ran it OK for a  period of time. One morning there was a strong smell of petrol in the house (combined garage and house) and the floor was coverd in petrol !!!!! I had left the fuel tap on by mistake. Normally the float valve would shut-off any more petrol coming in BUT --upon inspection the float was 3/4 's full of fuel and had sunk !! I contacted Surrey Cycles who informed me that there was a batch of  poorly-assembled plastic floats in circulation. A new one was suplied FOC and all was well. Your float valve must be free to move at all times. Questions for you }---Is your float plastic ??  Is your float valve viton-tipped or plain brass ??  Have you a fibre washer fitted in the main jet cover assy. ??   Dan Ford's and RancidPolecat's ideas would seem to fit this scenario as well. BUT---there's always a BUT, isn't there ??----in to-day's world grunda 12 is spot-on.  So, what to do ?? Trading Standards do allow a bit of leeway so you can at least physically check the items suspected----you'll have to remove the side cover to do this anyway---If you find the float is plastic and leaking then there at least is one major contributor. In any event at least give the supplier a chance to make good ie give them a call and talk it through-- but after youv'e done those few checks. Did I read in another post that you had fuel coming out of the tickler ?? If so that is definately a mal-functioning float ie it's sunk OR trapped.  Have you been following Matt's progress with his gearbox re-build recently ?? Nil Desperadum, old china !! 

[david w]

Hi Chris ,Sorry to hear of the probs mate , Let us know how it goes ,I was thinking of that as the next mod to do. That is after the alternator upgrade and the electronic ignition, and heated grips, maybe the avon fairing painted olive green to match the military bullet 65, a single seat ,a custom rear rack, the list goes on!!!

[Chris Tindal]

Solved (hopefully) On a hunch I disconected the rubber hose to the teacaddy and left the carb open to the air. It now starts first or second kick, I can blip the throttle without it stalling or the revs staying high for ages. The tickover is constant without rising or falling and out on the road it runs really well, better than with the old Micarb. The plug has gone from sooty black to chocolate brown, not white as expected so the jets too big for the standard old type air filter. I don't think this explains some of the odd symptoms (the drip at the bottom is still there) but I've stopped and started it, ridden it, let it cooled, started it again and all that strange behaviour has evaporated. I don't want to run it like this and prefer a filter rather than sucking in pets and small children, gravel etc. but I'm happy its running sweet.


Thanks everyone for all the very valid suggestions, John thanks for offering to have a look, fingers crossed it should be ok.