I'm actually fighting the same thing on my '82 450 right now. A few weeks ago I go to pull out of my street into traffic and without any prior warning the bike has no bottom end power. It still ran but felt like I was running on one cylinder til it got up to about 4000 and then suddenly everything is fine. I promptly turned around, went home, changed my pants, and pulled the carbs off the bike. Upon disassemble we discovered a few things. We found a series of problems ranging from a damaged spark plug and boot (brother laid the bike down a few weeks back) to one of the accelerator pump holes being clogged. My carbs also had a set of air cutoff valve which were torn and corroded in their holes. I'm currently waiting on a new set of idle needles before I slap it all back together.
A gunked up carb wouldn't necessarily cause a lean condition. For example your choke is an enrichener and it could be stuck open or perhaps you might find the DPO (dipshit previous owner) "customized" the choke cable which ended up binding and causing the choke to be partially closed most of the time. Or it could be a large number of other things. There are a wide variety of other control valves and circuits inside those carbs and anyone of them could be stuck or clogged. The best way to fix it is to sit down with a few bottles of carb cleaner, some scotch-brite, and a set of dentists picks and meticulously disassemble the carbs (one at a time), clean them and learn how they work. This is best done in an aluminum baking tray because there are a lot of tiny parts that can disappear on you. Squirt the carb cleaner in various holes to clean them and figure out where they lead to and what they do. Make sure you've got good flow through all the passages. If you find any rubber parts that look questionable replace them if you can. You can never use too much carb cleaner and DON'T force anything that doesn't want to turn. These old carbs have usually had water in them at some point and you'll find that the jets or something will have corroded in place. The last thing you want to do is break something in there because then you'll have to drill it out\find a replacement or get a whole new carb. From your description my gut agrees with surfswab; either the enrichener plungers are being held open for whatever reason or there is something wrong with the idle needles or circuit. A few basic things to check. Now this definitely sounds like carburetor trouble to me but there are a few other possibilities that should be considered. One thing that could be happening is you're not getting consistent spark at lower RPMs until the alternator starts putting out sufficient current. Easily checked by hooking a spare plug up to one of the plug wires and leaning it against the block in a dark garage or at night. Look for a lot of misfires at lower RPMs. Some missing especially off idle is normal but you should have a large blue spark fairly consistently. Another good check up is a cylinder compression. This will tell you if there is a leaky valve or cracked ring, ect. You need a compression gauge for this one but I believe you can rent them from AutoZone for free as long as you bring it back. Just make sure you bring a spark plug and check that the gauge has the right thread or thread adapter. Pull out all the spark plugs and then screw the gauge into the first cylinder. Make sure the choke is off and open the throttle all the way and turn the engine with the starter a few turns until you get a maximum on the gauge. Write it down and move on to the next cylinder. As long as they are all within about 20psi of each other and around 150psi the motor should be fine. You can do this with a hot or cold engine. Baring this you may want to adjust the idle mixture needles. On a lot of these bikes the idle needle is sealed using a few different methods. This is so the average idiot can't mess with them and change the emissions of the bike however there are ways around it. On mine this took the form of a plastic plug covering the needles and then the needles themselves having no pattern for any sort of driver. To fix this I pryed the plug out and then drilled a small hole in the needle so I could use an easy-out to remove the needles themselves. Once out I used a hacksaw to cut a flat blade screw driver slot in them. Cheap but effective. Hopefully that was more helpful than confusing. Let me know if you need help or want anything I blathered about explained better. -- 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.
