hi any have a Monobloc 375 /34 carb on my 1966 bsa c15 i have been building. am having trouble getting fuel into cylinder engine not firing, if i pour petrol direct into barrel engine fires up until this is used up/, spark plug seems dry when trying to start in normal way. have cleaned out carb all jets etc. float ok, filling ok understand that on start up carb runs on pilot system small holes these are clear. have set throttle control screw at 1 1/2 turns.if i unscrew more turns will this increase flow on start up. valves and ignition timing are set up correctly.also there is a lot of blow back of fuel from carb inlet. no filter fitted,. can any one help with question. also need to buy air filter pancake type. there is limited room from carb inlet to tinware, the carb is a AMAL 375.any suggestions on suppliers in uk thks the slug
Are you using a new viton tipped float needle? I find that these are sticking and not dropping thus not letting fuel fill the float bowl enough. I have better luck with the nylon (plastic?) float needles. When you tickle the carb can you make it over flow out of the tickler? If not then you are not getting fuel into the carb. There are all sorts of other things that might make it not start but I'd start checking this function.
thks pete for answer.have changed shut off valve it is the rubber tipped type . had just the nylon type before. found this was sticking closed, so changed, new type seems to function ok. fuel does come out the top of ticker. still cant work out why its not running, thks the slug.
have set throttle control screw at 1 1/2 turns.if i unscrew more turns will this increase flow on start up. valves and ignition timing are set up correctly.
The mixture screw (the horizontal one near the flange),controls air.If you screw it in,less air makes the mixture richer.
A good starting point for the throttle stop (angled beside the slide) is 3/4 turn in from where it first contacts a closed slide.
The fuel level in the bowl should be 1/2 way up the bowl.There might be a raised dot on the float bowl cover centre.If you take the cap nut off the pilot jet,you can connect a hose to the jet to check the fuel level.
hi all still not starting. have set and checked float in bowl. level correct to dot. tried different locations with air and throttle screws. have tried duct tape on inlet with small hole to try to choke carb. still not firing spark plug not getting fuel very dry. am running out of ideas,. cheers.
Double check your pilot circuit including the jet, if its marked as a 25 run a 16 thou #78 drill through it as it can look clean but deposits/corrosion have undersized it. The pilot circuit is what the bike starts on so a dry plug says its clogged or you are not tickling enough.
hi as kommando said, i checked pilot jet and cleaned out small carb ways.found the pilot jet was only a 20. have ordered a 25 the manual says this is the correct jet to use,found the 20 jet was partly clogged cleaned out jet seems to narrow to cone shape at end and narrows. tried with 20 jet in still dry plug. am waiting for new 25 pilot jet to arrive to try that, would just having the wrong size pilot jet effect the starting, cheers the slug
it should fire up what ever the jets are doing by the fact you are flooding the carb, try squirting some gas in the plug hole or into the carb intake. iv started engines with no carb on them just by chucking gas in them.
I would have thought it would still start,now that the pilot jet is clean. A good tickle should richen it up enough to start,even though it might not run well after it starts. Could the idle discharge holes near the front of the slide be blocked too?
great thks kommando, wak and pete.yhks for trying you help me. yes have checked fuel ways in carb are clear. some places are hard to get too, have sprayed carb cleaner down ways and seems to come out ok at other ends. have put fuel direct into barrel via spark plug holes and engine fires until it burns off.have tried to start with 20 pilot jet but thnk it may be slightly clogged at jet end. small dia wire does not go all the way to end,should it be the same all way down. like you say should still get fuel through. will try again when new 25 jet arrives and let you know how i get on. what the diff between 20 jet and 25 is it .5 thuos timing valves have all been done engine has been rebuilt. must be carb problem with dry plug all the time cheers lads tne slug.
:blushhi everyone thks for help with my carb question. fitted the 25 pilot jet in place of 20. checked all the small carb chambers all clear.now know my way round the AMAL Monobloc carb..fuel was blowing instead of sucking. after rechecking valve timing found it was timed miles out.bike starting great now, maybe i think first time in 20 or 30 years. another one lives again. with the air filter problem obtained a small 30mm cone shaped air filter. fitted to end of stock rubber hose from end of carb.air filter sits within tin ware behind battery box,. thks to all the help from the bsa guys trying to help me.. cheers the slug..
As far as the air filter goes, I use a K&N RU-2450 (marked F018G4 on base) on my B40. I had to open the hole in the shroud a little to run a piece of radiator hose for connecting it, though with the smaller inlet diameter of your 275, you may be able to use a reducer and smaller hose that clears.
A smattering: '53 Gold Flash '67 Royal Star '71 Rickman Metisse '40 Silver Star '37 Rudge Special sixtyseventy Lightboltrocket road racer...and many more.
great thks alex photo very informative. thats what my set up will look like have a reducer for pipe. is that a made up feed pipe on top of carb with 90degree bend. lot better than normal supply straight out . . cheers the slug