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Mechanics 101 Can't get it to run right? Find a trick to add HP?
From the first oil change to completely rebuilding the engine,
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Old 08-06-2018, 09:23 AM   #1
Tippon
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Default Too much air?

My bike ( 2000 600F UK model ) felt like it was running a bit too rich, and was rumbling and popping when I came off the throttle, but was struggling to start too. I thought it was over fuelling, so I took the carbs off and adjusted the fuel mixture screws. I screwed them back in, then screwed them out one and a half turns to start with.

The bike will now only start on full choke, and runs rough until the engine warms up. It also idles at about 600 RPM rather than about 1500. When the engine does warm up, it doesn't quite surge, but it's similar. I'll be holding the throttle steady and the bike will 'pause' for a split second, then accelerate briefly, as if it's suddenly got to the right revs.

Imagine doing 40 in 6th, then dropping to 4th while still doing 40. The bike would pull as if it should be going faster for the same throttle position.

As I'm writing this, I'm thinking that I've fouled the throttle cable, but I'm 99% sure that I didn't. I'm on the way to the garage to pull everything off again and check for anything obvious.

Other than

a leak letting too much air in
fouled throttle cable
idle screw adjustment

is there anything you think could be causing this?

Thanks
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Old 08-08-2018, 05:48 PM   #2
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Quote:
Originally Posted by Tippon View Post
My bike ( 2000 600F UK model ) felt like it was running a bit too rich, and was rumbling and popping when I came off the throttle, but was struggling to start too. I thought it was over fuelling, so I took the carbs off and adjusted the fuel mixture screws. I screwed them back in, then screwed them out one and a half turns to start with.

The bike will now only start on full choke, and runs rough until the engine warms up. It also idles at about 600 RPM rather than about 1500. When the engine does warm up, it doesn't quite surge, but it's similar. I'll be holding the throttle steady and the bike will 'pause' for a split second, then accelerate briefly, as if it's suddenly got to the right revs.

Imagine doing 40 in 6th, then dropping to 4th while still doing 40. The bike would pull as if it should be going faster for the same throttle position.

As I'm writing this, I'm thinking that I've fouled the throttle cable, but I'm 99% sure that I didn't. I'm on the way to the garage to pull everything off again and check for anything obvious.

Other than

a leak letting too much air in
fouled throttle cable
idle screw adjustment

is there anything you think could be causing this?

Thanks
Your description of the original symptoms was... of a lean condition. If the bike was running rich, it wouldn't be popping on decel. That's lean....

The bike running description now... is also lean, but worse.

It could be an air /vacuum leak, but... I'd suggest it possibly may be the carbs need cleaned and properly reset.

Krey
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Old 08-09-2018, 03:09 PM   #3
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I don't think it's a air leak because then it would be idling higher Rpm's not lower like you described but i thought that the air fuel screw was supposed to be 2 and half screws out at stock ??? Maybe some one else could help me on one And also sounds like carbs need to be cleaned better and properly esp. piolit screws.
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Old 08-09-2018, 05:36 PM   #4
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Yes, 2.5 turn as a starting point, up or down. Yes you may need to clean the carbs.
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Old 08-10-2018, 10:18 AM   #5
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UK models are different for the a/f setting. Stock would be 1.5 on those.

Yes, the jetting and setup is that much different.

Krey
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Old 08-10-2018, 01:25 PM   #6
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That is correct...
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Old 08-11-2018, 08:02 PM   #7
Tippon
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Thanks for the replies guys. Sorry I haven't responded sooner, but I put my back out trying to get under a friend's bike looking for an oil leak. I haven't been able to look at mine yet, but should be able to in the next few days.


Quote:
Originally Posted by Kreylyn View Post
Your description of the original symptoms was... of a lean condition. If the bike was running rich, it wouldn't be popping on decel. That's lean....

The bike running description now... is also lean, but worse.

It could be an air /vacuum leak, but... I'd suggest it possibly may be the carbs need cleaned and properly reset.

Krey
Thanks Krey. I was told years ago that the popping is from excess fuel burning in the exhaust, which kinda made sense, so I didn't have a reason to question it.

I had the carbs cleaned fairly recently, then balanced them myself. I did them on the bench first, then with vacuum gauges. Judging by the amount I had to turn the fuel mixture screws in this time, I got those wrong. I thought I'd set them all to 2.5, but they were all further out. Either I was too cautious screwing them in at the start, or they worked loose in a few hundred miles of town riding. I'm holding my hand up to that one...

I've just checked the manual for the air / fuel mix, and it does say that the 600 should be 2 1/4 turns out. It's the 750 that's odd. I'll go for the 2 1/4 turns and see if it helps.

Thanks again for the help
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Old 08-13-2018, 09:34 PM   #8
Tippon
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Well, that went horribly wrong

I stripped the bike and took the carbs off. Adjusted the fuel mix, then refitted the carbs. Attached the airbox and tank, and started the bike.

Sounded rough, but started almost immediately. I realised that I hadn't primed the carbs, so stopped the bike, turned the tap to prime and gave it a few seconds then started the bike again. I could hear fuel running, but it seemed to be running for longer than usual. I looked down and there was fuel pouring through the bike...

I turned everything off and removed the air box so I could get a better view. As soon as I turn the tap to Prime, fuel just pours out of carbs 1 & 2. It may pour out of 3 & 4 too, but I wasn't waiting to find out.

I ran out of time tonight, so I made everything safe. I'll check the carbs thoroughly tomorrow, but do you have any suggestions please? I'm guessing at a stuck float, but the fuel seems to come from the bottom of carb 2 first, then carb 1, then the air pipe between them. I've uploaded a video here (The bike is level, but my phone isn't):

https://youtu.be/gMMNESDQD80
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