Shanewalker123 Posted April 19 Share Posted April 19 Could I have some advice. I have a 2002 Honda vfr800 vtech when I start it’s rough and when throttle applied it wants to die. After 30 seconds it jumps up to 2000rpm and throttle is fine. No issues after that I can turn it off and back on and there is no problem.Any advice or help would be helpful? Quote Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted April 20 Member Contributer Share Posted April 20 Sounds like you might have a bit of stiction with the Wax unit linkages, etc. Try cleaning and lubricating all linkages, a spray of some WD-40. See if that makes any difference. You might also benefit from a Starter Valve Synch procedure. While you're in that area. Pop the vacuum hose off the FPR Fuel Pressure Regulator, check the hose is dry and no weeping of fuel from the FPR vac hose fitting. Weeping fuel = Ruptured diaphragm. And.......Download the Service Manual from the forum if you don't already have it. 1 Quote Link to comment Share on other sites More sharing options...
Shanewalker123 Posted April 20 Author Share Posted April 20 Thank you I will try this and update you. Can I say one thing in the Haynes service manual it says not to dismantle the wax idle unit. Should I spray into without touching it or should I dismantle it? Many thanks shane Quote Link to comment Share on other sites More sharing options...
Member Contributer Presson Posted April 20 Member Contributer Share Posted April 20 Best not to dismantle the wax unit. Clean it up with wd40 and a brush - an old toothbrush perhaps. Clean the linkages on both intake banks. 1 1 Quote Link to comment Share on other sites More sharing options...
Shanewalker123 Posted April 21 Author Share Posted April 21 Thank you for your help. I did what you said. When I start the motorcycle still it hovers around 1000rpm as soon as I touch the throttle it dies. I turn it back on it goes up to 1750rpm (warming up) after 2 mins it goes around 1200rpm and runs like a dream and throttle is okay. Is this normal? Quote Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted April 21 Member Contributer Share Posted April 21 2 hours ago, Shanewalker123 said: Thank you for your help. I did what you said. When I start the motorcycle still it hovers around 1000rpm as soon as I touch the throttle it dies. I turn it back on it goes up to 1750rpm (warming up) after 2 mins it goes around 1200rpm and runs like a dream and throttle is okay. Is this normal? No mate not normal. "I did what you said." Excellent, I'm glad the FPR wasn't leaking! Have a close check of all the Throttle Body vacuum hoses, look for any small cracks or damage, especially make sure All the hoses for the MAP sensor are good. - Any Fi fault codes? - How old are the Spark Plugs? - What fuel is currently in the tank? Octane, Ethanol level and how old? Quote Link to comment Share on other sites More sharing options...
Shanewalker123 Posted April 21 Author Share Posted April 21 -Put it all back together I am going to take it apart again and re check everything. -I did check all the hoses and they seemed fine no cracks etc. put some silicone grease on them to soften them up a bit. -gt85 the linkages and pushed in and out to help lubrication they didn’t seem stiff or seized. -Funnily when I put it back together there didn’t seem to be any flashing of the FI it just went on and off as normal when I turned the engine on. do I need to reset it could the fact that it needs resetting be an issue? -when I got the bike (1 month ago) it had fresh oil on spark plugs so I replaced the seals around the spark plug and it stopped leaking. Cleaned up the plugs with some heat and put them back in. Apart from the oil they didn’t seem bad. -When I first got the bike it struggled to start first time. After emptying the tank of previous fuel I put in v power fuel and some redex to clean and it now starts first time just rough to start with throttle hesitation. -I thought it was fuelling issue but will come back once I have done further investigation. thanks for your support I didn’t realise forums were so helpful. Hopefully I get this sorted had nothing but problems with it since I got it. To be honest it has put me off Honda. I’ve had all major Japanese bikes and this is the only one where the issues keep coming. I am only persisting because of the lovely v4 engine sound. kind regards. Shane 1 Quote Link to comment Share on other sites More sharing options...
Member Contributer Presson Posted April 21 Member Contributer Share Posted April 21 Anyone know if SV imbalance/ out of synch causes rough cold starting and a tendency to die on throttle before fully warm? This may be the issue... 1 Quote Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted April 23 Member Contributer Share Posted April 23 On 4/22/2024 at 1:31 AM, Presson said: Anyone know if SV imbalance/ out of synch causes rough cold starting and a tendency to die on throttle before fully warm? This may be the issue... Just my two cents worth, I hope others with more experience in this area might chime in. Interesting question. SV synch is fundamental to good even idle, and smoothness in the small throttle opening zone, a mechanical setting, adjusted at normal operating temp, without the influence of the fast idle Wax Unit, and butterflies closed. Stands to reason this should be carried out first along with correct warm idle adjustment of 1200rpm. Assuming badly balanced SV's, and especially during the cold start enrichment phase, a slight touch of the throttle opening and the added air might cause a stall. I know of a similar effect (possibly in both hot and cold modes) on a 5gen. a faulty signal from the TPS at low throttle was measured, but not bad enough to force an Fi DTC. The whole throttle body was replaced and problem solved. All warm engine ops are normal according to Shane the OP. Perhaps signals from MAP and/or ECT are marginal at cold temps and might need checking. Watching the Wax unit action on the Starter Valves, and if the movement is smooth and gradual from cold fast idle to the warm Idle, you can then discount the Wax Unit causing any problems. 2 Quote Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted April 23 Member Contributer Share Posted April 23 On 4/21/2024 at 10:31 PM, Shanewalker123 said: Funnily when I put it back together there didn’t seem to be any flashing of the FI it just went on and off as normal when I turned the engine on. do I need to reset it could the fact that it needs resetting be an issue? No doesn't need "resetting". Info... 1. With the Sidestand down Ignition to On, Kill switch to RUN any active fault code will be displayed. 2. When riding, if an active fault is detected, your Fi will illuminate full On but will not flash a code (Honda logic is not to have distracting flashing lights while riding). Only displayed as per 1. 3. Resetting you refer to is the method of erasing historical stored codes. These could be codes like the MAP or IAT sensors disconnected during the SV synch or genuine past stored faults that have since been rectified. Quote Link to comment Share on other sites More sharing options...
Shanewalker123 Posted April 25 Author Share Posted April 25 Thank you for your help. I am yet still to sort this problem. I think my next thing to do would be the throttle position sensor. Quote Link to comment Share on other sites More sharing options...
Member Contributer Presson Posted April 25 Member Contributer Share Posted April 25 No harm in checking the TPS. However, you describe normal operations once warm so as Grum suggests, it is probably worth investigating the MAP and ECT sensors. Quote Link to comment Share on other sites More sharing options...
Shanewalker123 Posted April 25 Author Share Posted April 25 I do have some information about when I did my throttle body sync I noticed that it started really easy with no difficulty. When I watched other people doing the videos they had great difficulty. I then attempted it the second time round another day and it was really difficult I had to apply the throttle to keep it going. This is not normal could it be a faulty map sensor? Quote Link to comment Share on other sites More sharing options...
Member Contributer Presson Posted April 25 Member Contributer Share Posted April 25 Have you done the SV synch? Which needs to be done with the engine fully warm You could check the MAP; the procedure is in the manual Quote Link to comment Share on other sites More sharing options...
Shanewalker123 Posted April 25 Author Share Posted April 25 Yes I did mention in my last comment I have done a throttle body sync/ start valve sync please excuse my terminology. Quote Link to comment Share on other sites More sharing options...
Member Contributer Presson Posted April 25 Member Contributer Share Posted April 25 Not clear what you mean by I noticed that it started really easy with no difficulty. then attempted it the second time round another day and it was really difficult I had to apply the throttle to keep it going Was the first attempt before or after your SV synch work? Was the second time another day after your SV synch work? Have you checked the MAP? If so what was the result? Have you checked the ECT? If so what was the result? Quote Link to comment Share on other sites More sharing options...
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