Hi. My '93 has a giant flat spot at highway speeds. It's like from 1500-3000 when on the freeway only. When I am riding and let off the throttle to slow down, I go to accelerate again and there is a minor rise in Rpms and then dead throttle and then you are going at speed again. It's frustrating and hard on the rear end. Around town it is smooth and responsive. No probs. Can't recall when it appeared. I've been through the carbs and did the pair removal as well as the carbon tank removal. I've even heard heard that airflow rushing past the vent tubes can cause this but I tucked them under the belly pan. Any ideas thanks. Oh and I tried the air cleaner holes mod and it made it way worse. So I'm guessing it's an air or vacuum issue. But I triple checked the hoses and caps and put on new insulators. And installed a new fuel pump, filter, and diaphragm.
giant flat spot at highway speeds.
- Thread starter FireAndIce
- Start date
Are you running a K&N air filter? If so, remove the foam sleeve, it restricts the air flow.
I'd downshift at least once before hitting the gas again...
+1 on lugging the engine - doing more harm than good.
Suggest removing the vacuum petcock. It can really hold back the fuel needed when accelerating. It's an easy modification.
I'd check the fuel cap vent. Then vacuum petcock, fuel filter and flow test your fuel pump output.
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Thanks for the ideas. It does let one hell of a rush of air out of the tank on fill ups. Is this normal?
Probably normal, mine does it too, to some degree. BUT, I would check the clamp on the side of the gas tank that secures the small hose from the gas cap. Mine was collapsing the hose. I changes the screw to a longer one so the hose wouldn't be completely occluded. Will still get some pressure build-up in the tank, since the relief valve in the cap is probably spring loaded. You should be able to blow through the relief valve with some effort.
How bad is the "bog" ? If you are cruising on the interstate at 75 mph, and you downshift to 4th gear and then open the throttle, how long does it take to hit 100 mph ?? Don't use a stopwatch ( please keep both hands on the handlebars ) , just count one-thousand, two-thousand, etc.
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So I removed the vent hose from the cap and a ton of the bikes original performance came back. I was very surprised and no giant rush of air when I went to fill up. There is still a small hick up when I'm on the freeway and slow down behind a car and roll the throttle back on to pass but it's much better now. Is it case closed? Don't know yet. Did not get a chance to do the 75mph test.
I doubt you have solved your problem. The hose itself does nothing but convey fumes, or excess overflow fuel. The air pressure differential, upon opening the tank, is quite normal.
Make sure your rear brake isn't dragging. Mine was and the bike was a dog on the interstate above 70 mph. One day it was fine and a few day s later , it was dragging.
Avtrician
1500 RPM is hardly Highway speed, as its only about 40KPH (25MPH) 3000 is about 100KPH (58 MPH). If down to 1`500, change down a gear or two.
Why was the brake dragging? Bad hose?
I have to repeat...I'm not lugging the engine. Please realize this. I'm simply trying to rev the engine back up as I release the clutch while at speed. I'm saying the bike does not rev as you let the clutch out. If you were to be traveling at 4k, grab the clutch and resume riding, the motor would have the flat spot as you try and return to 4k. It does seem better with that hose off and with cooler weather.
I have to repeat...I'm not lugging the engine. Please realize this. I'm simply trying to rev the engine back up as I release the clutch while at speed. I'm saying the bike does not rev as you let the clutch out. If you were to be traveling at 4k, grab the clutch and resume riding, the motor would have the flat spot as you try and return to 4k. It does seem better with that hose off and with cooler weather.
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Caliper pistons were sticky. There was "whitish" corrosion built up in the groove the dust seal slips into.
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I'd agree with this. At 1,500 - 3,000 RPM I'd expect pretty leisurely acceleration. You need to drop a gear or two if you are in a hurry. The 1100 has amazing "get up and go" torque at 5,000 - 6,000 to redline.
wow im back the bike is in europe. I hadnt ridden it for awhile. The bog is just from no throttle back to speed. Once youre going its no prob to get to 100.
If removing the vent hose seemed to have solved your problem, maybe the hose was occluded. The little clamp it slips through on the side of the tank ( near the top ) can pinch the hose. I replaced the original screw with a longer screw and self-locking nut. The distal end of the vent hose could also be clogged with gunk. See if you can blow through the disconnected hose end easily.
Thanks still does it with hose off. I'm really thinking this has something to do with the removal of the pair. Maybe the airflow under the bike is affecting the works somehow now that the hoses are more direct to the carbs etc. maybe should have left the charcoal canister on. Whoops.