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Team, I need some help. I have a 1980 XS1100 Midnight Special. The engine backfires and stutters at 4500 RPM’s. I’m 99.9% sure it’s NOT the fuel or timing system and I believe it’s mechanical. (Is valve timing an option?)
History: This bike has 18,600 miles on her. I've swapped out the carbs and the Yamaha ignition system in 2009 and installed an Electronic Fuel Injection (EFI) system; that was 4000 miles ago (14,320 on the Odometer when I got her). In 2011, I rode the bike 2,644 miles. It’s been running good. But last October 25, 2011, I when for a ride and after a short stop, the bike would not run past 4500 RPM’s. It started fine, but would NOT run good enough to get home. Two weeks later, I rode her again and got 5 miles down the road before the backfire condition returned. It has NOT run good again.
Things I’ve tried: I’ve replaced the spark slugs and spark plug wires, swapped out the coils and ignition system. I’ve checked the timing advance system with a timing light; it advances with increasing RPM’s as expected. The cylinder compression readings are 160, 160, 150, 160 psig. The intake manifold vacuum is the same on all four cylinders at idle and tracks steady as you increase the engine speed, so it’s not a sync problem. The backfire and stutter condition is the same whether you’re riding on the road or sitting still in neutral on the center stand. The stock exhaust has good outlet flow. I’ve flushed the crank case with Sea foam and I’ve changed the oil and filter. I totally drained the gas tank and added 93 octane Chevron gas. No change. The fuel pressure is 38#’s and the flow is not obstructed. The screens in the gas tank are clean. No rust in the gas tank. I bypassed the ignition switch and kill switch and measure the battery voltage at the GM ignition system; it’s a solid 13.3 volts. I’ve used a lap top computer to enrich and lean the fuel settings at 4500 RPM’s, nothing seems to correct the condition. I’ve replaced the throttle body and fuel injectors, and checked the throttle position sensor. No joy.
Team, I’m stumped; any ideas? I love challenges but this needs the resources of XS11 experts.
History: This bike has 18,600 miles on her. I've swapped out the carbs and the Yamaha ignition system in 2009 and installed an Electronic Fuel Injection (EFI) system; that was 4000 miles ago (14,320 on the Odometer when I got her). In 2011, I rode the bike 2,644 miles. It’s been running good. But last October 25, 2011, I when for a ride and after a short stop, the bike would not run past 4500 RPM’s. It started fine, but would NOT run good enough to get home. Two weeks later, I rode her again and got 5 miles down the road before the backfire condition returned. It has NOT run good again.
Things I’ve tried: I’ve replaced the spark slugs and spark plug wires, swapped out the coils and ignition system. I’ve checked the timing advance system with a timing light; it advances with increasing RPM’s as expected. The cylinder compression readings are 160, 160, 150, 160 psig. The intake manifold vacuum is the same on all four cylinders at idle and tracks steady as you increase the engine speed, so it’s not a sync problem. The backfire and stutter condition is the same whether you’re riding on the road or sitting still in neutral on the center stand. The stock exhaust has good outlet flow. I’ve flushed the crank case with Sea foam and I’ve changed the oil and filter. I totally drained the gas tank and added 93 octane Chevron gas. No change. The fuel pressure is 38#’s and the flow is not obstructed. The screens in the gas tank are clean. No rust in the gas tank. I bypassed the ignition switch and kill switch and measure the battery voltage at the GM ignition system; it’s a solid 13.3 volts. I’ve used a lap top computer to enrich and lean the fuel settings at 4500 RPM’s, nothing seems to correct the condition. I’ve replaced the throttle body and fuel injectors, and checked the throttle position sensor. No joy.
Team, I’m stumped; any ideas? I love challenges but this needs the resources of XS11 experts.
As TC stated, most of us (including myself) are not quite "qualified" or knowledgeable enough to help but, sometimes one 'dumb' question from the janitor is all it takes to get you thinkin... so, here's my dumb question... is there a way to verify the FI is injecting at the correct time? Maybe it gets out of phase once RPM increases... maybe verify your pickup sensors for proper clearances..
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