This is on my 2003 Daytona, MC1000 Sagem with O2 sensor. I've got a problem that wasn't there before I did the valve clearances on my bike and would really appreciate any ideas you all have as to what I have messed up! Here’s what I did. Adjusted valve clearances (they where mostly tight). Replaced CCT spring with one from Sprint Manufacturing. Replace plugs. Balanced throttles and re-set TPS. Here’s the symptoms: Bike starts, idles and seems to run well, except if you give it loads of throttle on a test ride. If you open the throttle quickly, it stutters and won’t accelerate. If you back off the throttle a little, it will accelerate all the way up the revs. This issue wasn’t there before I did the valve clearances. A lot of the valves where tight. Now they are on the loose side of the spec. Here’s what I’ve tried so far to fix it (with an unsuccessful test run at each stage): Replaced Fuel filter and internal fuel lines. Checked fuel pressure - (a healthy 3 bar) RE-balanced throttles checking the the IACV is between 30 – 35 steps at idle using TuneECU (I had ballsed this up the first time). Re-set TPS. Checked TPS (0.59 v at closed throttle and moves smoothly though the range on the map in TuneECU) Re-applied TOR tune from TuneECU. Replace original plugs! (really scraping the barrel) I’m going back under the valve cover this weekend to check if the cam chain has jumped a tooth and re-check the clearances, although I must have checked them three times before I put the valve cover back on. Can anyone think of anything else I could have messed up that I should check? One thing that happened when I was balancing the tank on blocks of wood to balance the throttle bodies the first time was that if slipped and the bracket that the two screws that hold the airbox on go through got bent down. I was worried that this may have impinged on the injector rail and introduced an air leak, but spraying carb cleaner around the area produced no change. Thanks in advance for any thoughts!
If you stop and think about it...... Any issue with valve timing would making starting more difficult and exist throughout the rev range and unrelated to throttle opening. At this range (over 300 miles) what you describe sounds more like a fuel/air mix problem; either insufficient fuel or an inlet manifold leak. I would focus on inlet leaks first (manifold o rings?) and fuel pressure second.
Hi Callumity, Thanks. Your point about valve timing is very re-assuring and make sense. I have ordered injector seals and throttle body o-rings this afternoon. Although the bike was running fine before and so you would think that these obviously weren't a problem beforehand. The tank did fall of its support when I was balancing the throttles the first time and I fear they may have been knocked out of position, so I will be dissembling and renewing the seals. I'll let you know whether this resolves the issue...cheers.
Hi Thanks for your reply - I've had the tank on and off loads of times trying to troubleshoot this and unfortunately, trapped fuel lines is not the issue...
Perhaps a filter is clogged enough to only effect fueling at higher throttles how many filters are there in total some have one in the tank and one in line.
I had this on a 600 Yamaha. The daily commute didn't show any issues at all. As soon as I was on the way to the IOM for a week, full throttle was a big no no. Replaced filter once on the island and it ran great after totally cured. Out of curiosity split the old filter and there was nothing obvious to see inside.
Hi Sprinter, Thanks for the reply - I initially thought it could be the fuel filter as well, as i had had the tank off and any rubbish could have been dis-lodged. However I replaced the filter and the internal fuel lines and still the problem persisted. :-(
Re-reading your initial post I'm still thinking weak mixture. Snap throttle open and big rush of air but is the fuel there to match it? Four stroke single carb off road bikes used to be like that and the answer was a power jet carb to squirt neat fuel in.
Thanks - the extensive searching of forums for similar symptoms I have been doing has yielded a lot of results for bikes with carbs. My main area of attack is now going to be the throttle body and injector seals which I have ordered but probably won't arrive by this weekend as one of the parts is on back order with Fowlers, so that will be a job for next weekend. I will keep you updated!
Is the 3 bar fuel pressure test with or without the tank on? A friends ST had the valve clearances changed and fired up with ease after. It ran for a good five minutes no issue. He gets it out the following day and it wouldn't start. The tank had nipped the pipe at the rear to reduce flow to near zero. Maybe yours is partially nipped so the dribble will keep up with lesser demands than full throttle?
not sure if it is relevant but what about the hose that allows air into the tank?? if that was blocked it would create a vacuum.