philwright Posted March 25, 2018 Share Posted March 25, 2018 Been out for a ride on my 750j slingy this afternoon all was well until I was on my way home and it started running lumpy and rough ,got me home though ,now it wont start ,the starter turns freely and there is petrol getting to the carbs but it wont strike up, havent got round to pulling the plugs to look for a spark yet,will do that tomorrow time permitting,any thoughts please?... Quote Link to comment
Sheep Posted March 25, 2018 Share Posted March 25, 2018 Fuel getting to the carbs.....but is it getting past those into the engine? Quote Link to comment
wraith Posted March 25, 2018 Share Posted March 25, 2018 Has the bike been stud, maybe plugs Quote Link to comment
philwright Posted March 29, 2018 Author Share Posted March 29, 2018 (edited) Right...I;ve spent all day ,up to now ,trying to figure out what the problem is, i have changed the plugs ,fitted fresh coils/leads and the bike will start on full choke but its not firing on all cylinders ,sometimes its 3&4 other times its 2&3/1&2 etc ,if it was 1&4 or 2&3 pots all the time I could narrow it down to the coils but its random , AND I've got a spark on all 4 plugs, the spark does look a bit weak though, not strong blue like it should be...and petrol is getting through the carbs cos the plugs were wet when I put the fresh ones in....looking in the workshop manual its starting to point to the CDI/ECU...any advice from you knowledgeable chaps would be most welcome. Edited March 29, 2018 by philwright typo Quote Link to comment
no class Posted March 29, 2018 Share Posted March 29, 2018 Had a gs1150 do this.... intermittent spark.... shortly after ..... none. Cdi packed it in ..... swopped one from another bike..... back in buisness . In your case I would check the bowls for crap or debris..... then you can positively rule out the fuel . Quote Link to comment
philwright Posted March 29, 2018 Author Share Posted March 29, 2018 Ok Thanks for that, i will clean the float bowls out tomorrow just to be sure...then I'll be on the lookout for a used CDI. Quote Link to comment
CockneyRick Posted March 29, 2018 Share Posted March 29, 2018 Could also be the diaphragm in tap, put it on free flow & see if it'll run off choke. Other than that, CDI for me too Quote Link to comment
Gixer1460 Posted March 29, 2018 Share Posted March 29, 2018 Just cos the plugs are wet doesn't mean fuel supply is correct - just those cylinders aren't running correctly. Could be too much fuel or not enough to fire so just wets the plugs! if it'll run on choke but not when off it sort of suggests fuel to me? Quote Link to comment
philwright Posted March 29, 2018 Author Share Posted March 29, 2018 Thanks for all replies...I have tried it with fuel tap on all positions, just seems strange that the bike was running okay last sunday when out for a ride ,started to notice lumpy running and slight loss of oomph when overtaking a van, thought nothing of it, it got progressively rougher until I got home when it wouldn't start at all, just left it overnight and tried it next day and it would only start reluctantly on full choke but not on all pots as described above, will not run at all off choke, and I must admit first thoughts was fuel/carb problem, i am checking which cylinders are firing by feeling which downpipes are hot, and they are randomly firing on and off, no pattern....next job is to take carbs off and give them a good once over,i'm not really sure what to be looking for though, carbs are a bit of a dark art to me...any pointers appreciated, I will still get a used CDI though just to rule things out, theres one or two on the bay, if it makes no difference when fitted I can return it. Quote Link to comment
bluedog59 Posted March 29, 2018 Share Posted March 29, 2018 Just check you are getting a good fuel flow out the tap first. It could be clogged up. Quote Link to comment
philwright Posted March 29, 2018 Author Share Posted March 29, 2018 2 minutes ago, bluedog59 said: Just check you are getting a good fuel flow out the tap first. It could be clogged up. I have taken the tap out of the tank just to check and the filter looks like new...how do I check the flow with tank disconnected from carbs, I thought fuel flow was controlled by vacuum action,with tap on free flow (prime) am I right in thinking petrol should flow whether connected to carb pipes or not? Quote Link to comment
Gixer1460 Posted March 29, 2018 Share Posted March 29, 2018 On prime the tap will flow fuel - usually less than optimal to run continually in use - basically a lever moves the diaphragm in the tap so doesn't need vacuum. Quote Link to comment
wraith Posted March 29, 2018 Share Posted March 29, 2018 If you connect and pipe onto the tape where the vacuum pipe would go, then suck on the pipe (when tank is off/disconnected from the bike/carbs ) if the tape is working as you suck you will get a patch of fuel on the floor. Quote Link to comment
no class Posted March 29, 2018 Share Posted March 29, 2018 Open the oil filler cap on the motor and see if you smell fuel..... if so..... dump the oil and do a flush.... Quote Link to comment
philwright Posted March 29, 2018 Author Share Posted March 29, 2018 Just realised ,the vacuum pipe between the tank and the carbs is missing, i assume this is crucial to fuel flow!!...it must have come loose and been lost last time I rode it, I will get a new vacuum pipe connected tomorrow and see what happens ,it cant be as simple as that surely?...will also have a smell for petrol in the oil and change it if needs be....fingers crossed. 2 Quote Link to comment
philwright Posted March 30, 2018 Author Share Posted March 30, 2018 SORTED......just fitted a new vacuum pipe between tank and number 2 carb top stub and it fired up straight away on all 4 pots, unbelievable that I missed such an obvious thing as a poxy 5 inch length of plastic pipe, and that it would have such an effect on the bikes running, Thanks to all the replies above ...I;m off for a blast! 1 Quote Link to comment
CockneyRick Posted March 30, 2018 Share Posted March 30, 2018 (edited) That's why i said do it on prime PS no-one likes a smartarse Edited March 30, 2018 by CockneyRick Quote Link to comment
philwright Posted March 30, 2018 Author Share Posted March 30, 2018 Tried it on prime before I sussed out the missing vacuum pipe, fuel got through but it still ran like shite , I thought prime just filled the float bowls after they have been emptied, with vacuum pipe fitted it meters the fuel flow properly to all carbs ...I think...anyway all ok now. Quote Link to comment
CockneyRick Posted March 30, 2018 Share Posted March 30, 2018 (edited) No, the metering of fuel is done by the float, the prime just keeps a constant flow to it. The Vac will stop all fuel movement when engine isn't turning over. Downside to prime is if a float sticks (which they do) then the freeflow will just keep going & dump all that fuel thru carbs into & past the cylinder/pistons into your oil With Vac, the fuel will freeflow if the float sticks, but as it's running, it will mostly burn it off before getting past the pistons, & will stop flow when engine is shut off. Edited March 30, 2018 by CockneyRick Quote Link to comment
philwright Posted March 30, 2018 Author Share Posted March 30, 2018 Thanks for the useful info mate. Quote Link to comment
philwright Posted March 31, 2018 Author Share Posted March 31, 2018 (edited) Just a recent pic...seems to be running a lot better than it did too...maybe the fresh coils /leads/plugs have made a difference Edited March 31, 2018 by philwright typo 7 Quote Link to comment
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