B
blistovmhz
Guest
Hey guys.
So this is a bit of an odd ball, and while I'm no stranger to engines/mechanics in general, bike stuff is brand new to me.
I picked up an 86 Katana 750, and very long story short, it's got an 83 GS750ES motor (identified by block number) and presumably the matching Mikuni BS32SS 31300 carb (it matches the 83 service diagram at least generally).
Bike had *@%^$*@%^$*@%^$*@%^$ty K&N pods and 4>1 exhaust and there's nothing I can do about it. Can't find an air box, wouldn't matter anyway as I'll get into here shortly.
So it starts fine, idles pretty well, mids and WOT are .... substantially better than stock according to specs, but I've got some serious bog below 4k rpm when under light load. It clears up either when RPM's go over 4K (roughly), or around 3k if I pin it. When it wakes up, it does so instantly, making the bike very hard to control. It feels exactly like half the cylinders not firing, until they do and it screams.
Plugs all the same. Clearly rich. Idling the plugs look fine, WOT they look fine, but once I hit that bog, they're jet black.
Here's the thing though. Everything I've dug into on this bike, I find nothing stock, to the point I've spent the last 2 weeks just trying to identify parts.
Mains - 124
Pilots - 45
Needle Jets - Y-7
Pilot air - 170
Slides are drilled to about 1/8, and the jet needle has 6 positions, so I assume this was jetted (for the pods?) at some point, but clearly something isn't right.
Stock specs for this carb, assuming it's from an 83 GS750ES, would be:
Mains - 117.5
Pilots - 37.5
Needle jets - Y-6
Pilot air - 170
So yea, the mains and pilots look way too big, but the WOT and idle are both perfect as far as I can tell. The needle jet being a Y-7 makes me suspicious, and the jet needles all look very scratched and worn.
So I've had the carbs apart about 40x now, they're perfectly clean.
Stuff I've tried:
* Played with float heights (up and down). Increasing fuel level clearly caused it to run richer across the board, but lowering it didn't seem to have any affect. Still looks and runs perfect at idle, mid and wot, but low-mid is still boggy/rich.
* Drilled pilot air 0.1mm. No affect.
* Removed pilot air jets completely. Had to tweak the pilot screws obviously, but they DID manage to clean the idle back up to where it was, otherwise no affect. Identical response across the board.
* Needle jet was lowest position, so I tried every other position. All this got me was richer everywhere from low-mids to WOT.
So I tore the top end and cylinders down last night just for an inspection. Everything looked good other than being super dirty, and valves clearly weren't sealing, so I cleaned everything up, re-lapped/seated the valves, re-honed cylinders, opened up valve clearance to 0.011. No change. Valves are now perfectly sealed.
While I was in there though, I noticed the cam height is too large for this bike. Stock should be 34.94 and 34.36, and I'm getting 35.5 and 35. So clearly someone built up these cams a little? Or perhaps there is a common cam swap? I couldn't find any cams in any service manuals, to match mine.
So anyone have any idea's on what to do next? I find it odd that the mains and pilots are so enormous just to account for pods and exhaust, but fact is that idle, mids, and wot are all better than stock. 0-60 in almost dead nuts 3s, which blew my mind for sure. Given the vintage and condition of the bike, I wasn't expecting anything under 4.5 - 5s
.
Also, I can't find any decent bike shops anywhere local. Only shop in town that MIGHT carry a head gasket, wouldn't actually tell me if they had one. They wanted me to drive 3 hours to ask again in person. So I said *@%^$*@%^$*@%^$*@%^$ it and just re-used the OE *sigh*. I've no idea where i might be able to get jets, and even if I could, I don't really know what direction I'd wanna go. I feel like my next theory is that the needle jets and jet needles are just super worn out.
So this is a bit of an odd ball, and while I'm no stranger to engines/mechanics in general, bike stuff is brand new to me.
I picked up an 86 Katana 750, and very long story short, it's got an 83 GS750ES motor (identified by block number) and presumably the matching Mikuni BS32SS 31300 carb (it matches the 83 service diagram at least generally).
Bike had *@%^$*@%^$*@%^$*@%^$ty K&N pods and 4>1 exhaust and there's nothing I can do about it. Can't find an air box, wouldn't matter anyway as I'll get into here shortly.
So it starts fine, idles pretty well, mids and WOT are .... substantially better than stock according to specs, but I've got some serious bog below 4k rpm when under light load. It clears up either when RPM's go over 4K (roughly), or around 3k if I pin it. When it wakes up, it does so instantly, making the bike very hard to control. It feels exactly like half the cylinders not firing, until they do and it screams.
Plugs all the same. Clearly rich. Idling the plugs look fine, WOT they look fine, but once I hit that bog, they're jet black.
Here's the thing though. Everything I've dug into on this bike, I find nothing stock, to the point I've spent the last 2 weeks just trying to identify parts.
Mains - 124
Pilots - 45
Needle Jets - Y-7
Pilot air - 170
Slides are drilled to about 1/8, and the jet needle has 6 positions, so I assume this was jetted (for the pods?) at some point, but clearly something isn't right.
Stock specs for this carb, assuming it's from an 83 GS750ES, would be:
Mains - 117.5
Pilots - 37.5
Needle jets - Y-6
Pilot air - 170
So yea, the mains and pilots look way too big, but the WOT and idle are both perfect as far as I can tell. The needle jet being a Y-7 makes me suspicious, and the jet needles all look very scratched and worn.
So I've had the carbs apart about 40x now, they're perfectly clean.
Stuff I've tried:
* Played with float heights (up and down). Increasing fuel level clearly caused it to run richer across the board, but lowering it didn't seem to have any affect. Still looks and runs perfect at idle, mid and wot, but low-mid is still boggy/rich.
* Drilled pilot air 0.1mm. No affect.
* Removed pilot air jets completely. Had to tweak the pilot screws obviously, but they DID manage to clean the idle back up to where it was, otherwise no affect. Identical response across the board.
* Needle jet was lowest position, so I tried every other position. All this got me was richer everywhere from low-mids to WOT.
So I tore the top end and cylinders down last night just for an inspection. Everything looked good other than being super dirty, and valves clearly weren't sealing, so I cleaned everything up, re-lapped/seated the valves, re-honed cylinders, opened up valve clearance to 0.011. No change. Valves are now perfectly sealed.
While I was in there though, I noticed the cam height is too large for this bike. Stock should be 34.94 and 34.36, and I'm getting 35.5 and 35. So clearly someone built up these cams a little? Or perhaps there is a common cam swap? I couldn't find any cams in any service manuals, to match mine.
So anyone have any idea's on what to do next? I find it odd that the mains and pilots are so enormous just to account for pods and exhaust, but fact is that idle, mids, and wot are all better than stock. 0-60 in almost dead nuts 3s, which blew my mind for sure. Given the vintage and condition of the bike, I wasn't expecting anything under 4.5 - 5s
.Also, I can't find any decent bike shops anywhere local. Only shop in town that MIGHT carry a head gasket, wouldn't actually tell me if they had one. They wanted me to drive 3 hours to ask again in person. So I said *@%^$*@%^$*@%^$*@%^$ it and just re-used the OE *sigh*. I've no idea where i might be able to get jets, and even if I could, I don't really know what direction I'd wanna go. I feel like my next theory is that the needle jets and jet needles are just super worn out.
