I recently purchased a 1987 Suzuki Savage. So far, everything runs just fine except when I start reaching higher speeds. Although I can get up to just above 75, (top speed is suppose to be 80ish) if I try to maintain a speed of anything above 65, after about 30 seconds it starts to chug, almost like I'm out of gas. I have to roll on the throttle to maintain speed, and then, it starts chugging even more and doesn't respond to the throttle at all. I lose my speed down to about 50 mph. If I let off the throttle completely, it will recover and I can then maintain my normal highway speed of 60 mph. Any ideas?

and check your float level...
Should do 80+ easy.... top is near 90....

Let's see, we have suggestions for spark and fuel, so that leaves the oxygen part of the internal combustion trio out of the loop.

I call oxygen!

Is your engine getting enough at higher speed?

Have you looked at the air filter?  

Good luck on solving this rather annoying problem!

 First thing to do is put in Sea Foam in the gas it will probably clear it up.

justin_o_guy2 wrote on 08/27/09 at 06:43:21:
Yep, sounds like it isn't getting gas fast enough.  When it next starts to falter, switch to PRIME and see if that works.  If not, pull the petcock out and see if the strainer is clogged with debris.  If PRI works, you have a vacuum loss that isn't pulling the diaphragm open--of course, at full throttle the engine vacuum is at a minimum, anyway, everything needs to work right.  If a new vacuum hose doesn't do the job, either find a good used Savage petcock or switch to a manual Yamaha Raptor ATV petcock...said to fit right in.

Not a thing wrong with covering the quick, cheap, easy bases first.

Well now I'm stumped. The float level is at about 29mm (manual says 28 +/- 1 mm). The spark plug I replaced a few weeks ago looks fine. I tryed that float bowl test justin suggested, but the fuel just came flowing out...

   

It really really sounds like it's running out of gas.

Here comes some questions, and Yea I know dumb questions, but sometimes the dumb questions jog the memory for something else.

-It runs the same in Prime,  that rules out the Petcock vacuum line but doesn't rule out a dirty / varnished up petcock screen.  Something to check since it's an older bike.

- Just replaced plug,  Is it still clean?  Is the Gap correct?

- Just cleaned carb,  How dirty was it?  

- Older bike,  have you done a compression check?  

- Are the valves adjusted correctly?