Hesitation at higher speeds around 6k RPM

So I've got myself a nice (read beat-up) new (read used) 1983 Spectre 550 and I've put about 200 miles on it since picking it up. I've only taken one long trip on it, about 130 miles, but while riding I noticed that at higher speeds with the tach at 5.5k-6k RPMs the engine would feel like it was bogging down or loosing power intermittantly. If I put down the hammer while this was happening it would go away for the most part and pick right up but while holding a steady throttle, I had noticably less power.

A few things you should know about the bike:

1 - my second tank of gas, filled before the 130 mile trip, was premium in the hopes that the higher temp might clear out any deposits in the engine

2 - my electrical system seems a bit weak since at an idle my turn signals blink VERY slowly and all my instrument lights are dim even while moving

3 - the carbs and intake were completely rebuilt right before I purchased the bike

So being a car guy I know there are pretty much three things that can cause this: fuel, air and spark. Would anyone take a guess at where I should start? I'm inclined to start with the spark and take down the ignition system to clean it but could that tank of premium gas be the problem?

Post edited by: coffeedragon, at: 2007/07/25 20:32

First, welcome to the site. Second, you bought an OLD bike and should like take the time to tune it and go through everything thoroughly. I have heard too many new owners of old bikes claim that the previous owner did this or that but it is best to baseline the bike's state of tune... you are already experiencing problems that would likely be eliminated by a good check of everything. I suggest you do the following in more or less the order listed:

1. compression check / valve clearance check and adjust
2. change all fluids on bike including brake fluid
3. change carb holders if they are not absolutely new
4. trace every bit of wire on the bike. Take all connectors apart and clean with CONTACT CLEANER and dab with dielectic grease before reconnecting. REPLACE any connector or connection that is questionable; that is where you see signs of overheating or the connection seems loose
5. check fuse box. If there is ANY sign of heat, just replace the fuse box with a more modern fuse box from the autoparts store
6. after starting bike, remove the wire connection that connects the stator to the regulator/rectifier and measure AC voltages per your shop manual and make sure stator is generating AC voltage at the appropriate levels, then reconnect and measure DC voltage at the battery at idle and at 4K rpm to check function of regulator/rectifier; probably a good idea to top off the battery with distilled water first and have it load tested at an autoparts store
7. carefully inspect the coils for cracks; replace if any are observed; check wires and caps at the same time. You might want to check primary and secondary resistance (your manual will tell you how) on the coils to make sure that the resistance hasn't crept up over the years which will cause the spark to be week
8. check voltage to the coils; see the tech article on our website for COIL REPOWERING under wg'w Tech Stuff Index
9. tune/sync carbs; change any installed fuel filter and if one is not installed, install one.

Sounds like a lot of stuff but it is an afternoon's work and if you go through these steps, you will eliminate or fix about 95 percent of any problems on the bike and your riding will be far more trouble-free.