Bike stopped revving after sitting for two weeks

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wip3
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Joined: Sat Oct 24, 2020 2:49 pm
My Bike: zxr400

Bike stopped revving after sitting for two weeks

Post by wip3 » Sat Oct 24, 2020 3:02 pm

Hello,

I've stumbled on a weird problem with my bike. I was sick for about two weeks and my bike was sitting for that time. Before letting it sit it ran flawlessly. Now the bike starts and idles normally, but it doesn't rev past 4k rpm without the choke. If I pull the choke to the max I can rev it to 8k.

First thing I did was check that there was fuel going to the carbs. There doesn't seem to be any issues with the tap, fuel pump or fuel filter. There's fuel going to the carbs. The slides aren't sticking and when trying to rev the bike the slides try to rise so there seems to be vacuum. I then took the carbs apart and checked the vacuum slides and cleaned the jets. This did nothing.

I then tried to get the bike to rev higher by manually lifting the slides while I was keeping the revs as high as they would go with the throttle. Strangely playing with the slides does absolutely nothing and isn't even noticeable on how the engine runs. Doesn't this seem like the bike is now running only on pilot jets?

Anyone have any ideas what I should do next? I'm quit baffled by the fact that this started after sitting for only two weeks.

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banner001
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Re: Bike stopped revving after sitting for two weeks

Post by banner001 » Sat Oct 24, 2020 9:19 pm

Definitely isn't getting enough fuel.

Its pretty much impossible to block the main jets, how did you clean the jets?

Have you checked for all 4 exhaust pipes getting warm/are all the spark plugs firing.

Have you tried with the petrol cap open incase you are making a vacuum?

You have not had loads of petrol run into the crank cases have you?
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

wip3
Posts: 2
Joined: Sat Oct 24, 2020 2:49 pm
My Bike: zxr400

Re: Bike stopped revving after sitting for two weeks

Post by wip3 » Sun Oct 25, 2020 11:12 am

banner001 wrote:
Sat Oct 24, 2020 9:19 pm
Definitely isn't getting enough fuel.

Its pretty much impossible to block the main jets, how did you clean the jets?

Have you checked for all 4 exhaust pipes getting warm/are all the spark plugs firing.

Have you tried with the petrol cap open incase you are making a vacuum?

You have not had loads of petrol run into the crank cases have you?
Cleaned the jets with carb cleaner and compressed air. They were perfectly clean to start with tough.

Haven't checked the exhaust yet I'll need to do that. Feels and sounds like it's running perfectly on all fours.

Tried running it with the petrol cap off but it made no difference.

I don't think there has been any excess fuel in the crank case.

I assume there are breathers for the float chambers. Could a problem with a breather cause the carb not being able to pull fuel from the chamber?

Ewetea
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Re: Bike stopped revving after sitting for two weeks

Post by Ewetea » Mon Oct 26, 2020 8:20 am

Since the bike runs, but will not rev, it suggests that fuel is not reaching the carbs fast enough. Check the supply of fuel from the pump by disconnecting the pipe to the carbs and putting it in a bottle. Press the starter button and observe the fuel entering the bottle. If it fills quickly, then the pump is OK, but if it only dribbles, then the pump is faulty (or the filter is blocked). Keep trying!

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banner001
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Re: Bike stopped revving after sitting for two weeks

Post by banner001 » Mon Oct 26, 2020 8:40 am

I would be tempted to remove all of the jets, clean the outside of the carbs as best you can and then get them ultrasonic ally cleaned along with the separated jets, this should ensure that there are no internal blockages.

Carb cleaner is only good for removing fuel varnish, won't do anything for rust or dirt particles.

Also flush out your tank and refill with fresh fuel just to make sure it wasn't contaminated, clean the tank internal fuel filter whilst you are at it
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

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