mattb_uk Posted April 15, 2013 Share Posted April 15, 2013 Hi All, First post so, Hi! I've been racing CB500 and various other bikes for a few years but fancied somethign a bit different so got myself a FZR400RR with a 600 thundercat engine conversion. This was all done buy a guy who has done a few of these conversions and to my knowledge has all the required mods etc, and uses all the Thundercat loom and the tank sits higher to accomodate the thundercat airbox. Right, now my problem.... Stationary the big starts and runs sweet as a nut, BUT when i put it in gear and try to ride the bike it won't rev past 6k rpm. Getting up to 6k rpm it is as smooth as anything but hit 6k and its just bogs and barbles. Logic suggests its quite a simple fix but i have no experience of these bike really so not sure where to start. I have read about throttle position sensor problems but its so smooth up until 6k (and past in neutral) so that makes me think its not that. I could be wrong. Someone suggested it could be the carbs being block as when it draws from different jets one of these might be blocked? Could it be the ECU is knackered? Like I say, logic (mine anyway!) suggest that its something simple, a component failure of some kind but I have no idea what one? Any help greatly appreciated as am hopefully doign a trackday on it in a coupel of weeks! Cheers, Matt Link to comment Share on other sites More sharing options...
Moderator Cynic Posted April 15, 2013 Moderator Share Posted April 15, 2013 Suppose the first question is. Has it ever run right? Then have you spoken to the builder/previous keeper. Link to comment Share on other sites More sharing options...
mattb_uk Posted April 15, 2013 Author Share Posted April 15, 2013 Hi, yeah that was the first thing I did, I can only take his word for it but it was apparently running fine, and he did a few track days on the bike, the engine has only done 5k miles too. Matt Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 15, 2013 Moderator Share Posted April 15, 2013 Far too complicated for me Matt, good luck. I'd hate to suggest £££'s for an ecu only for it to turn out to be something else.... but...is there a fuel pump and does that work? Link to comment Share on other sites More sharing options...
pilninggas Posted April 15, 2013 Share Posted April 15, 2013 Hi All, First post so, Hi! I've been racing CB500 and various other bikes for a few years but fancied somethign a bit different so got myself a FZR400RR with a 600 thundercat engine conversion. This was all done buy a guy who has done a few of these conversions and to my knowledge has all the required mods etc, and uses all the Thundercat loom and the tank sits higher to accomodate the thundercat airbox. Right, now my problem.... Stationary the big starts and runs sweet as a nut, BUT when i put it in gear and try to ride the bike it won't rev past 6k rpm. Getting up to 6k rpm it is as smooth as anything but hit 6k and its just bogs and barbles. Logic suggests its quite a simple fix but i have no experience of these bike really so not sure where to start. I have read about throttle position sensor problems but its so smooth up until 6k (and past in neutral) so that makes me think its not that. I could be wrong. Someone suggested it could be the carbs being block as when it draws from different jets one of these might be blocked? Could it be the ECU is knackered? Like I say, logic (mine anyway!) suggest that its something simple, a component failure of some kind but I have no idea what one? Any help greatly appreciated as am hopefully doign a trackday on it in a coupel of weeks! Cheers, Matt Simple checks: Trapped petrol pipes [pinching when the tank is refitted?]. Blocked fuel tank breathers. Coils knackered -check impedances and check for arcing to the frame. Does the bike have fresh fuel - stale fuel can do give these symptoms with bigger four cylinder engines. For me it's likely one or both of the first two, particularly as the bike has a non-standard tank position. HTH Link to comment Share on other sites More sharing options...
Moderator drewpy Posted April 15, 2013 Moderator Share Posted April 15, 2013 if the bike's been standing any while, the modern fuel leaves a varnish and gums up the carbs, try some carb cleaner. also is the battery ok and charging? ecu won't like it at high revs if the volts are low. i suspect a main jet if its at the higher rev range Link to comment Share on other sites More sharing options...
mattb_uk Posted April 16, 2013 Author Share Posted April 16, 2013 Hi Again, Thanks for all the advice, all sound logical so hopefully it is one of them. A garage evening tomorrow, so will let you know how I get on. Matt Link to comment Share on other sites More sharing options...
mattb_uk Posted April 18, 2013 Author Share Posted April 18, 2013 Well, I had a play around with it all last night and although Its not cured yet i think im heading in the right direction. First things first, checked the battery connections and they were a little loose, i had a GSXR in the past that had a fault and that was just the battery connections not being as tight as they should of been. I hoped it would be as simple as that, it wasnt, but the symptoms were perhaps slightly better. Next I drained the old fuel, found a bolt in the fuel tank and drained the carbs. The float bowls all had screws that were basically only finger tight, if that, and some had fallen out alltogether. I have now taken them apart and cleaned them all and re-tighted all the screws. I then took it for another spin and it was a bit better, even pulled clean to about 10k in a couple of gears but not consistently. The symptoms now seem to be anywhere between 6k and 10k rpm. I will attach some pics in a bit, the modified airbox sits ok on the carbs but perhaps isn't the tightest fit it could be. My current thinking, is that it ran better the second time because the battery had a bit more charge from the first run, rather than anything to do with the carbs. Does this sound plausible?! It makes sense to me as the previous owner said it ran fine before and i probably let it sit for a while before i started it and have never taken it on a long ride. I currently have the battery off and charging, and will try it again later. Im trying to check the simple stuff first before i waste money on new electrical bits and bobs. Sorry if this is all a bit jumbled! Link to comment Share on other sites More sharing options...
pilninggas Posted April 18, 2013 Share Posted April 18, 2013 Well, I had a play around with it all last night and although Its not cured yet i think im heading in the right direction. First things first, checked the battery connections and they were a little loose, i had a GSXR in the past that had a fault and that was just the battery connections not being as tight as they should of been. I hoped it would be as simple as that, it wasnt, but the symptoms were perhaps slightly better. Next I drained the old fuel, found a bolt in the fuel tank and drained the carbs. The float bowls all had screws that were basically only finger tight, if that, and some had fallen out alltogether. I have now taken them apart and cleaned them all and re-tighted all the screws. I then took it for another spin and it was a bit better, even pulled clean to about 10k in a couple of gears but not consistently. The symptoms now seem to be anywhere between 6k and 10k rpm. I will attach some pics in a bit, the modified airbox sits ok on the carbs but perhaps isn't the tightest fit it could be. My current thinking, is that it ran better the second time because the battery had a bit more charge from the first run, rather than anything to do with the carbs. Does this sound plausible?! It makes sense to me as the previous owner said it ran fine before and i probably let it sit for a while before i started it and have never taken it on a long ride. I currently have the battery off and charging, and will try it again later. Im trying to check the simple stuff first before i waste money on new electrical bits and bobs. Sorry if this is all a bit jumbled! The poor running is probably not related to the battery - if the bike runs, the electrical system is probably reasonably good (although as i said in a previous post coils [or plugs] could be going down under load. Things like the CDI and pickup either work or they don't. looks like your fuelling is off, but don't discount blocked breathers, blocked fuel filters, blocked air filters etc. If someone has taken the carbs apart they may be all over the place. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted April 18, 2013 Moderator Share Posted April 18, 2013 OK you never mentioned a modded air box, that will fuck up your fuelling at the top end and it will run lean. Its a bit scary finding loose stuff and I would be inclined to check every single nut and bolt on the bike before use. maybe you can look at a stage 3 jet system to offset the air box mod (nit sure exactly what has been done) Link to comment Share on other sites More sharing options...
mattb_uk Posted April 19, 2013 Author Share Posted April 19, 2013 Well, you were right, its not the battery! Im going to take it to the local dyno place and get them to look at it. I am away this weekend and am hopign to do a trackday with a mate on the 29th, but have a wedding the weekend before so I dont have the time to sort it myself, plus its startign to go over my head, fueling set ups etc! Thanks for all your help, I'll let you know what the result is! Link to comment Share on other sites More sharing options...
mattb_uk Posted April 25, 2013 Author Share Posted April 25, 2013 Apparently, the carbs are all over the place! The dyno place got 26bhp out of it! yes, twenty six! I find that figure slightly odd as its never run THAT badly, and has had plenty of power up until the problem hits. Apparently there is an air leak and the main jets have been leaned off, needles raised, air screws adjusted etc, not sure why the previous owner did all that. What would people recommend? Just putting it back to stock setting and starting again from there? Does anyone know where I can find the stock settings? I have had a google and cant find much of any use. Cheers, Matt Link to comment Share on other sites More sharing options...
Moderator Cynic Posted April 25, 2013 Moderator Share Posted April 25, 2013 With a thundercat airbox i take it they are thundercat carbs. On that basis stock settings should just be a google away. It is certainly where to start from. If you have the carbs airbox etc it should be pretty close. The tricky spot will be if they are 400 carbs. As i recall this convertion is a bit tight on the carbs. Dont think i would be reccomending the builder. Or the dyno tbh as any good dyno shop would have a good idea of the right carb settings just hearing it run on the dyno. The guys that did my old 600 certainly did. Link to comment Share on other sites More sharing options...
mattb_uk Posted April 25, 2013 Author Share Posted April 25, 2013 You'd think so wouldnt you, but I cant find the standard settings online have tried "yamaha thundercat standard carb settings", most things just come up about dyno jet etc. Its got Thundercat carbs but the airbox has been cut and shut to fit it under the tank. Link to comment Share on other sites More sharing options...
pilninggas Posted April 25, 2013 Share Posted April 25, 2013 You'd think so wouldnt you, but I cant find the standard settings online have tried "yamaha thundercat standard carb settings", most things just come up about dyno jet etc. Its got Thundercat carbs but the airbox has been cut and shut to fit it under the tank. plenty of haynes thundercat manuals on ebay - they usually have all the stock settings for the carbs specified. An air leak will kill power dead (and the engine potentially), so that needs looking at. I have ran bikes with hacked airboxes, in my opinion it is what happens from the mouths of the carbs onwards that affects power and mixture, As long as the airbox filters air it should be okay. you're going to need to look at whether the main jets are original, whether the emulsion tubes are worn or have been drilled, whether the float heights are right. I have been here before, and I would say pull the carbs off, get them clean and tear them down one at a time. Replace float bowl screws (they chew up) with allen socket bolts. make a float height gauge (i use sheet ally) and get stuck into it. Do one carb at a time. Good luck. Link to comment Share on other sites More sharing options...
mattb_uk Posted April 28, 2013 Author Share Posted April 28, 2013 Well I took the carbs apart, all stock items and settings, glaring omission though....not one carb had a main jet in! I would imagine that could be my problem! Link to comment Share on other sites More sharing options...
pilninggas Posted April 28, 2013 Share Posted April 28, 2013 Well I took the carbs apart, all stock items and settings, glaring omission though....not one carb had a main jet in! I would imagine that could be my problem! Link to comment Share on other sites More sharing options...
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