seanycozzie16v Posted February 29, 2016 Share Posted February 29, 2016 Quite a weird one this. Bike runs but only on the rear cylinder. I had the fuel tank off the thing and not sure i've located the vacuum and fuel lines correctly. Bike will run with the choke on but won't rev I have to twist the throttle lot of times to get it to rev. Any one got any suggestions. Both plugs are sparking. Quote Link to comment Share on other sites More sharing options...
eastanglianbiker Posted February 29, 2016 Share Posted February 29, 2016 if both plugs are sparking do a compression check also have you tried swapping the plug leads over if they will reach as it more than likely a single coil meaning both plugs spark at the same time so you can swap plug leads over if they reach and then see if the front cylinder runs,but go with compression check.on the fuel tank the bigger hose will be the feed to the carb and the smaller hose will normally come off the inlet at some point and go onto the vacuum side of the fuel tap,have you also tried to run it with the petrol tank cap off as it could be creating a vacuum within the tank if the breather is blocked Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted February 29, 2016 Author Share Posted February 29, 2016 The vacuum is on the back of the fuel tap yeah going to the middle of the inlet. This line has like a spring covering the line itself. The second line going to the fuel pump is to the right of the fuel tap. If so this is correct. I do have one vacuum line though that I can't find where it goes? Goes onto the side of the carb on the left hand side of the engine. Looks like a vacuum line. Quote Link to comment Share on other sites More sharing options...
eastanglianbiker Posted February 29, 2016 Share Posted February 29, 2016 that might be an overflow hose going down under the engine to remove any over flow of petrol away from hot engine the 2 pipes you can see are the correct ones to the fuel tap and you cant get t hem round the wrong way normally due to being different sizes have you checked the fuel pump is working correctly and i think you need to check compression in case one of the valves have closed up on front cylinder head Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted February 29, 2016 Author Share Posted February 29, 2016 Not yet checked compression. But there seems to be some there. Can feel it against the exhaust. I don't think the front cylinder is being fed fuel. As I pulled a brand new plug out of it and it was not wet and doesn't look like it's been firing.Any chance the carb could be feeding the rear cylinder and not the front one? So as far as vacuum lines go. One from the fuel tap going to the inlet one from the fuel tap going to the fuel pump. One vacuum line going to the left airboX and another going to nowhere as I can't find where it goes. Sticky valve or jet or float bowl in the carb? Also the bike is very hard to start. Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted February 29, 2016 Author Share Posted February 29, 2016 Also how do I go about testing the fuel pump? Quote Link to comment Share on other sites More sharing options...
Stu Posted February 29, 2016 Share Posted February 29, 2016 are these a twin carb bike or one carb feeding both cylinders? Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted February 29, 2016 Author Share Posted February 29, 2016 One carb feeding both cylinders stu Quote Link to comment Share on other sites More sharing options...
eastanglianbiker Posted February 29, 2016 Share Posted February 29, 2016 if it has got a fuel pump you should hear it working for a few seconds as you turn the ign on and then as you turn the engine over on the start button......forget that ive just seen its vacuum operated i assume you have all the vacuum pipes onto it correctly? Quote Link to comment Share on other sites More sharing options...
Tango Posted February 29, 2016 Share Posted February 29, 2016 Single carb and single coil?......I'd deffo be checking the valve clearances and compression..... Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted February 29, 2016 Author Share Posted February 29, 2016 single carb and 2 coils. just found a split in the inlet manifold. its rubber and its on the cylinder that not firing. cant see if its completely split but could be an issue. havent got a compression tester but im sure the cylinder itself is fine Quote Link to comment Share on other sites More sharing options...
Mr Fro Posted February 29, 2016 Share Posted February 29, 2016 Is it something you can nip a bit of tape round to see if that's the problem? Quote Link to comment Share on other sites More sharing options...
eastanglianbiker Posted February 29, 2016 Share Posted February 29, 2016 Is it something you can nip a bit of tape round to see if that's the problem?wrap some gaffer tape or insulating tape round it to see if that helps but to be fair the plug should still be getting wet one way to see if the rubber has split right through is start the bike up and spray a bit of wd40 at the inlet rubber if the revs increase then its leaking Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted February 29, 2016 Author Share Posted February 29, 2016 tried that eariler. plug still not getting fuel. surely the plug would be soaked with fuel if it was being fed correctly? Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted February 29, 2016 Author Share Posted February 29, 2016 bike is very hard to start also. takes piles of cranking and several twists of the throttle to even get it to run and even if that it gives a few pathetic splutters. Quote Link to comment Share on other sites More sharing options...
eastanglianbiker Posted March 1, 2016 Share Posted March 1, 2016 its time to strip the carb check it is all clean and the jets are clear then set it back to basic factory settings and see if the bike runs then but it could also be the vacuum fuel pump playing up due to a air leak or something Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted March 1, 2016 Author Share Posted March 1, 2016 How does the carb be set back to factory settings? Quote Link to comment Share on other sites More sharing options...
eastanglianbiker Posted March 1, 2016 Share Posted March 1, 2016 normally the mixture screw you would screw in untill you feel it tighten up then turn it out about 1 1/2 turns is rough setting to what it should run and then can be fine tuned from there to get it right,have you had the carb apart at all?if so have you checked the jets are all clear and the float height is correct?but its still sounding like it could be either vacum problem or compression problem on the front cylinder Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted March 1, 2016 Author Share Posted March 1, 2016 Where would I check for vacuum problems. How many vacuum lines are there. I don't know where the mixture screws are. Is the mixture screw covered by a small plastic blanking plug? I'm not really used to carbs only really fuel injection Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted March 2, 2016 Author Share Posted March 2, 2016 Ok cleaned the carb and located all vacuum lines correctly. The bike is still very hard to start. I find that by keep hitting the starter button numerous times if fires up straight away. I can hear popping and back firing as if the 2nd cylinder wants to fire into life. Funny how though that the starter button needs loads of little pushes for it to start Quote Link to comment Share on other sites More sharing options...
eastanglianbiker Posted March 2, 2016 Share Posted March 2, 2016 one possible reason could be a dodgy starter motor drawing all the current away from the cdi and the longer you have button pressed the longer it keeps the spark killed for,but once it is running is it now running on both cylinders or still only the rear one,also when did it last have fresh petrol in it ? Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted March 2, 2016 Author Share Posted March 2, 2016 Not running on the 2nd cylinder but occasionally makes a few backfires pops and bangs. I also find that by disconnecting the power wire going to the front coil it starts easier Quote Link to comment Share on other sites More sharing options...
eastanglianbiker Posted March 2, 2016 Share Posted March 2, 2016 has each cylinder got it own coil then i thought they were single coil so it could be the coil is knackered swap them over and see what happenssee if it t hen runs on the front and not the back you know its had it Quote Link to comment Share on other sites More sharing options...
seanycozzie16v Posted March 2, 2016 Author Share Posted March 2, 2016 Spark is coming from both coils though. Yeah a coil for each cylinder. Faulty ht lead which is shorting out against the body causing it to not spark for both?? Quote Link to comment Share on other sites More sharing options...
eastanglianbiker Posted March 2, 2016 Share Posted March 2, 2016 ht lead shorting out to the frame will cause the problem when testing it outside the engine for a spark you might be twisting it just enough to make it work and then not once back into the correct place also check the condition of where the lead screws into the cap as that can get corroded Quote Link to comment Share on other sites More sharing options...
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