FruitLooPs
18th July 2007, 14:24
Hey guys, got me and the gixxer guys a bit puzzled (asked at gixxer oilcooler forum too). Fairly sure I know what I need to do, but i'll write up a summary just in case.
Basics:
1987 GSXR750 Oiler
91/92 slingshot carbs (oval intake/filter end, CV type) done by previous owner with appropriate DJ Kit, unifilters
aftermarket pipe
Problem:
Missing up top (8k on), backfiring on accel and sometimes on decel. Sluggish if i pull WOT from 3/4k, then picks up fine pipe makes a droning sound like its a car going uphill in too lower gear. Goes ok if i gentle/med throttle up to about 8k. Was flying up until 3 days ago when miss started.
Cyl.1 plug has always been far richer than 2,3,4 so carbs need work - but has been fine until now. Plug was fouled when i pulled it, put in a new and bike was fine for 500m then started to backfire again.
Pulled it, and gapping had closed (nearly completely) :shit: (previous plug had done this, and it was on 3 cyl because electrode touching). Still after regapping previous plug it never closed again and ran on 4 sweetly for a number of months, so i did that to the new and went for a ride - was nice and pulled it afterwards, hadn't closed. Fixed .. or so I thought.
Had fuel tank rattle so figured replace the front rubber that was worn out and switch my other 3 plugs to new NGK's too (I also switched cyl.1 for a new fresh NGK .. again). So I did that and stuck it all back together, took it out for a ride. Backfiring again, argh figured the piston or something had mashed the gapping again, checked and it was ok - hmm. Tried diff lead for cyl.1 and that was just as bad. Checked fuelcock back on after putting tank on but it was :yes:
Plug has carbon deposits already but isn't fouled or wet, electrode area is browned slightly (still rich overall though).
Checked:
Resistance for coils:
3ohms on ignition side for coil that does cyl 1 & 4 (cant easily get other)
Both coils 15,000 ohm on HT side.
HT leads 4,000ohms for 15cm of cable or so. They're multi strand copper.
So whats up guys, Reckon that the carb for cyl one is playing up worse than normal or the DJ kit is has worn the tubes - or still gunning for weak spark (seems nice when i earth to frame, blue and visible).
I just dont see why yesterday I had it all sorted after changing cyl.1 plug and today I cant get rid of the backfire under load or aggressive decel. :dodge:
Driving me nuts. Couldn't be valves surely right? It also sometimes coughs thru the carb which I thought was explained by intermittant combustion from the plug gapping - but im not sure now..
Think the carbs need a strip and clean, but it looks like that would be a bastard to do. Might be keen if it will fix it though. Idle is rough when its playing up too, its fine when I just start the bike but if i rev it out and let it drop back it'll splutter and sound like crap and barely idle. When it was running w/out backfiring it would hold an idle nicely - and before that when it was first badly fouled it would rise 500rpm from where i set it (have to adjust the idle screw at each lights lol).
compression test to come tnight :)
Basics:
1987 GSXR750 Oiler
91/92 slingshot carbs (oval intake/filter end, CV type) done by previous owner with appropriate DJ Kit, unifilters
aftermarket pipe
Problem:
Missing up top (8k on), backfiring on accel and sometimes on decel. Sluggish if i pull WOT from 3/4k, then picks up fine pipe makes a droning sound like its a car going uphill in too lower gear. Goes ok if i gentle/med throttle up to about 8k. Was flying up until 3 days ago when miss started.
Cyl.1 plug has always been far richer than 2,3,4 so carbs need work - but has been fine until now. Plug was fouled when i pulled it, put in a new and bike was fine for 500m then started to backfire again.
Pulled it, and gapping had closed (nearly completely) :shit: (previous plug had done this, and it was on 3 cyl because electrode touching). Still after regapping previous plug it never closed again and ran on 4 sweetly for a number of months, so i did that to the new and went for a ride - was nice and pulled it afterwards, hadn't closed. Fixed .. or so I thought.
Had fuel tank rattle so figured replace the front rubber that was worn out and switch my other 3 plugs to new NGK's too (I also switched cyl.1 for a new fresh NGK .. again). So I did that and stuck it all back together, took it out for a ride. Backfiring again, argh figured the piston or something had mashed the gapping again, checked and it was ok - hmm. Tried diff lead for cyl.1 and that was just as bad. Checked fuelcock back on after putting tank on but it was :yes:
Plug has carbon deposits already but isn't fouled or wet, electrode area is browned slightly (still rich overall though).
Checked:
Resistance for coils:
3ohms on ignition side for coil that does cyl 1 & 4 (cant easily get other)
Both coils 15,000 ohm on HT side.
HT leads 4,000ohms for 15cm of cable or so. They're multi strand copper.
So whats up guys, Reckon that the carb for cyl one is playing up worse than normal or the DJ kit is has worn the tubes - or still gunning for weak spark (seems nice when i earth to frame, blue and visible).
I just dont see why yesterday I had it all sorted after changing cyl.1 plug and today I cant get rid of the backfire under load or aggressive decel. :dodge:
Driving me nuts. Couldn't be valves surely right? It also sometimes coughs thru the carb which I thought was explained by intermittant combustion from the plug gapping - but im not sure now..
Think the carbs need a strip and clean, but it looks like that would be a bastard to do. Might be keen if it will fix it though. Idle is rough when its playing up too, its fine when I just start the bike but if i rev it out and let it drop back it'll splutter and sound like crap and barely idle. When it was running w/out backfiring it would hold an idle nicely - and before that when it was first badly fouled it would rise 500rpm from where i set it (have to adjust the idle screw at each lights lol).
compression test to come tnight :)