banoffee Posted February 28, 2011 Report Share Posted February 28, 2011 Not in a position to get it on a dyno yet however the 750 slingshot has a midrange flatspot that's annoying me. Have rejetted bikes many times before however on this bike the carbs take a lot longer to get on and off so thought it would be good to bounce my ideas around before ripping it apart. Bike is standard apart from a micron 4-2-1 system with a fuel end can (baffle left in) and a K&N airbox element (running the smaller bung meant for stock jetting). Hesitates when between 4 and 6k on mid throttle but clears pretty quickly. A lot worse on a cold day. Goes like a bastard once past it. Given this behaviour which is worse when cold and the minor mods, this makes me think that maybe it's a little lean on the needles (maybe raise them one notch) and it might like just one size up on the mains. Thoughts? Link to comment Share on other sites More sharing options...
Kayla Posted February 28, 2011 Report Share Posted February 28, 2011 Not in a position to get it on a dyno yet however the 750 slingshot has a midrange flatspot that's annoying me. Have rejetted bikes many times before however on this bike the carbs take a lot longer to get on and off so thought it would be good to bounce my ideas around before ripping it apart. Bike is standard apart from a micron 4-2-1 system with a fuel end can (baffle left in) and a K&N airbox element (running the smaller bung meant for stock jetting). Hesitates when between 4 and 6k on mid throttle but clears pretty quickly. A lot worse on a cold day. Goes like a bastard once past it. Given this behaviour which is worse when cold and the minor mods, this makes me think that maybe it's a little lean on the needles (maybe raise them one notch) and it might like just one size up on the mains. Thoughts? It sounds like it's slightly lean on the needle and fine on the mains, so I'd be tempted to raise the needles one clip but leave the mains alone (one change at a time!) You can raise them a half a position by using a small washer under the clip, although this might mess with your OCD Was carb icing ever an issue with these bikes? I just ask because you say it's worse on a cold day. Link to comment Share on other sites More sharing options...
El Gringo Posted February 28, 2011 Report Share Posted February 28, 2011 I agree, 1 notch on the needles. I always go back to your recommended reading Banoffee, the dynojet trouble shooting chart. I also agree with slingshot carbs being a pain in the proverbial to get on and off, especially with the airbox present. Cheers Chris Link to comment Share on other sites More sharing options...
gurninman Posted February 28, 2011 Report Share Posted February 28, 2011 I'd also go with just raising the needles slightly - see how it is after that, but I don't think you'll have to touch the mains As for carb icing... I certainly never had a problem with my 750 Slingy and it was used every day for the time I had it. Link to comment Share on other sites More sharing options...
lorenzo Posted February 28, 2011 Report Share Posted February 28, 2011 To be honest, my experience recently has led me to comclude that it's the floats. I say that because I know a bit about needles, pilot and main jets and what you've written doesn't fit in with any of that stuff! If it was lean then it wouldn't hesitate, it'd be sharp in terms of response, but then would really clear up once it's on the mains only, so it sounds like it's slightly rich. Then, to conflict with that, you say it's worse when it's cold, which says lean. Take a look at a thread called 'carb tweaking' which I did a few weeks back, there's some really good advice there. Link to comment Share on other sites More sharing options...
banoffee Posted February 28, 2011 Author Report Share Posted February 28, 2011 cheers all for the input Link to comment Share on other sites More sharing options...
El Gringo Posted February 28, 2011 Report Share Posted February 28, 2011 Just a thought, Nicked from the Dynojet guide 7. Engine accelerates until the midrange then pauses, stumbles, or shuts down until you back off the throttle. This problem gets worse the higher the gear used. Insert Dynojet related waffle If these items check out, lower the needle down to fix a slight pause or stumble. Lower the needle and install a smaller main jet to fix a more severe problem. Perhaps ever so slightly ovalled emlusion tubes? Richness stumble on the way up? Link to comment Share on other sites More sharing options...
lorenzo Posted February 28, 2011 Report Share Posted February 28, 2011 Here's the factory pro page relating to tuning stuff, put your sunglasses on, it's worth the eyestrain. Link to comment Share on other sites More sharing options...
banoffee Posted February 28, 2011 Author Report Share Posted February 28, 2011 cheers. yep, am a fan of the DJ tuning guide for basics and had a look at the factory one before. given that it is a LOT worse on a cold day I've gone for raising them one notch, which I did this afternoon. roll on the next dry day Link to comment Share on other sites More sharing options...
cagimaha Posted February 28, 2011 Report Share Posted February 28, 2011 I'm running the same micron system and K&N pod filters. I've got bigger mains in (135 mikuni ones) and the needles raised a notch and the powerjets blanked as standard and the arse dyno reckons it's pretty close. There's a slight hesitation at around 9500RPM but it's very slight and pulls seamlessly otherwise. I reckon it might be worth shimming the needles before going up a whole notch but going the whole notch will probably get rid of the flatspot anyways. Link to comment Share on other sites More sharing options...
banoffee Posted March 1, 2011 Author Report Share Posted March 1, 2011 good to know, cheers Link to comment Share on other sites More sharing options...
banoffee Posted March 2, 2011 Author Report Share Posted March 2, 2011 tried raising the needles a notch and going for a blat, it's now better when the engine is cold but just as bad when it's hot. time to try lowering them a couple (from current position) next. am glad they're easy to get to Link to comment Share on other sites More sharing options...
banoffee Posted March 3, 2011 Author Report Share Posted March 3, 2011 lowered them and it's no better took the needles out and had a closer look - some visible wear on them. new carb bits it is then! Link to comment Share on other sites More sharing options...
banoffee Posted March 6, 2011 Author Report Share Posted March 6, 2011 Carbs are off the 750L and found that the mains are 100, somewhat smaller than I expected (117.5 for UK market, 127.5 for non-California US). The powerjets appear to be 0 (i.e. blanks) so was a bit surprised. The bike is a Japanese market import that has an 'M-MAX' type derestrictor box next to the CDI so thinking if that's working correctly I need 117.5 mains as a starting point now and might help to explain why it runs like a bag of poo. Needles definitely knackered (on order as well as emulsion tubes). Link to comment Share on other sites More sharing options...
lorenzo Posted March 6, 2011 Report Share Posted March 6, 2011 Personally I'd take it for a one off dyno run for £20 or so at your local dynoery, then get yourself an AFR trace that you can work out what's gonig on at what revs. I knew my bike was running badly but the actual tweaking was all done by working out what needed doing to correct genuine known facts rather than just by feel. £20 spent on that and you're only spending the same price as a set of mains anyway. Link to comment Share on other sites More sharing options...
banoffee Posted March 6, 2011 Author Report Share Posted March 6, 2011 great minds think alike, definitely the plan once its at least got the right bits there that aren't knackeed Link to comment Share on other sites More sharing options...
banoffee Posted March 7, 2011 Author Report Share Posted March 7, 2011 Picked up a UK CDI as different part number. It's the only way to be sure, other than taking off and nuking the whole site from orbit of course Link to comment Share on other sites More sharing options...
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