First Dennis, you sound like a professional, so thank you for your time and patience. Now, first: When I say "lost" I refer to this bike and how it ran for me prior to an extended period of neglect. I've owned this bike since '01. The previous owner/s all apear to have been tinkerers too. Next, I tried to get a look into the carbs like you suggest while mounted and hooked up with no luck, I can't see in there?! While I had the carb assy. off I only removed the bowl cover, not the top, but the vacuum slides seemed all at least consistant and all floated smoothly. Ya know you might be on to something regarding those jets sizing, I assumed the number on the jets was accurate but they may have been drilled out when a pair of cobra F1 slip-ons were installed. I coughed it up for just two of the slow-jets, none of the main jets, due to the slow-jets having shown some damage due to their having been messed with. After, it held idle more smoothly and with the use of less choke to start and less during warm-up, but no change in the severe messfire isolated between 3500-4500RPM. The symptom is present if you rev the bike in nuetral or while riding. While in the carbs I removed and inspected for blockages but not the accuracy of the part number versus actual size of the jets. The choke if applied seems to help quite a bit, although it idles real high, 2500RPM while it's applied. Without owning a wire guage set, is there any known correct size alternate guage? In reference to the plug inspection, I will road-test as needed and reply again soon. Thanks again for your time.
Graham M. On Nov 24, 8:34 pm, Dennis Hammerl <[EMAIL PROTECTED]> wrote: > You ask a great question but it needs parameters to qualify it. You say lost? > By that do you mean it was better at some time before ? The 650 has a quite > distinct burst at 4500RPM when it comes into the sweet spot for it's tuning. > If you have ridden others that worked better then we have a case to work on. > They have a single accelerator pump that feeds all carbs via a passage way. > Even so, the pump only provides a short squirt of fuel when opening the > throttle. With them off and the bowls filled, operate the throttle linkage > and observe the discharge from the intake valve side. There was a wonderful > book on carb basics by the Mikuni people, I haven't seen one in years. Mine > was stolen by a customer. The book had a great explanation of the sequence of > jet systems. Idle, several stages of slight throttle opening, slow jet, and > the transition to the main. The slides are controlled by vacuum and also > meter fuel via the jet needle / needle jet combination.The > needle jet is also the emulsification tube. Blockage at ANY point causes > problems. I try to never remove the diaphragm caps and disassemble them. > Because of the age of these bikes and the high cost replacements, they are > better left alone. I test them by lifting them with a finger and releasing > them. With four to test, any one that does not feel "right" may be torn or > otherwise defective. (Right=a breathing noise, and some resistance to lifting > with a controlled return) Yes, they are critical to mid-range performance. > However, a failed one would not allow acceptable high speed performance. I > dismiss the ignition as a problem because in all my years I have not seen a > failure mode that was RPM related. Yours idles smoothly and goes good at high > RPM. > Now, lets take a different approach Are you sure the replacement slow jets > are the right size ? I've sweated my way through many customer carb problems > only to find that somebody had already re-jetted the bike. After that, I > always check the jets with a wire gauge set to ensure they haven't been > drilled out. An over-rich condition exhibits almost the same as a too lean > one. Plug checks become vital. Try to induce the problem RPM range for as > long as you can (IE: up a grade at a fixed throttle position) shut the motor > off, pull the clutch and coast to a stop. If you could hold it that way long > enough, the plugs will show what the condition is. An over-rich condition > looks like a lean one since the intake tract air speed is too slow to carry > in the excess fuel. Lets say the plugs look as though a lean condition > exists. Repeat the ride and slowly add choke to it. Gets worse ? Gets better > ? The choke is an enrichener and is adding fuel as opposed to a choke > butterfly that would restrict air. Now they both sound as though they would > do the same thing but that isn't so. The butterfly is actually causing an > increase in air speed as it's closed. At a certain point, the increased air > speed may make things work fine. > Sorry, no easy answers. Have you examined the rubber spigots that hold the > carbs ? They are known to crack and let in air. With the motor running, spray > them with carb cleaner and note if engine speed increases. > After all this boring BS, try for a detailed description of throttle opening > / road speed / engine speed. > > --- On Mon, 11/24/08, Graham Kraker <[EMAIL PROTECTED]> wrote: > From: Graham Kraker <[EMAIL PROTECTED]> > Subject: [Nighthawk Lovers] What happened to my middle??? > To: "Nighthawk Motorcycle Lovers!" <[email protected]> > Date: Monday, November 24, 2008, 4:01 AM > > I've tried about everything I know of to repair this loss of midrange > power as my bike revs up with no luck. Such as: plugs, wires, carb > removal/disassemble/clean/inspect/install, air filter, petcock rebuild > and countless hours with no sucsess. It idles way better now and has > more top end than ever, but it still feels like cylinders 1-2, or 2-3 > die during acceleration unless I keep the rpms over 4500. I learned > that the slow jet may play a role in this and no change except the > smoother idle after replacing them. I heard somewhere else about an > accelerator pump, but can't locate/identify it. Since the carbs main > aperature is vacuum controlled possiblly I have insufficient vacuum > under 4500rps, but why the vacuum seems cool at idle and high? > > Open to speculation and educated guesses > > Thanks Graham M. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Nighthawk Motorcycle Lovers!" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/nighthawk_lovers?hl=en -~----------~----~----~----~------~----~------~--~---
