Date: 29-03-24  Time: 02:35 am

Author Topic: Low power full throttle mid rpm  (Read 2559 times)

Ministras

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Low power full throttle mid rpm
« on: 20 May 2018, 09:07:57 pm »
Hello again everybody, a few days ago i completed my driving exams (hurray) and took my bike for spin. It was amazing as it should have been, but i ran into some problems (as it shouldnt have been). At around 6.5-8k rpm at full throttle the bike seems like it almost cuts fuel off. Then at 8k right at the power band the bike flies all the way to max rpm. It seems to happen at 2-3rd gear, too scared to try first and not enough space to go 4+ gear  :o .


So what are your suggestions? Last owner didnt winterize the carbs, are they the problem? How can the power stop, then come on at full force later?

redmandan

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Re: Low power full throttle mid rpm
« Reply #1 on: 20 May 2018, 09:54:15 pm »
Sounds like you might have some blocked channels/jets, particularly if the previous owner didn't winterize the carbs. It's a little daunting if you've never done it before but a carb strip down and rebuild is not too difficult. If the bike is new to you and you just passed your test it's a great way to get to know your bike too.

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Re: Low power full throttle mid rpm
« Reply #2 on: 20 May 2018, 10:10:32 pm »
 It may be worth running it for a while on premium fuel, and/or trying a fuel additive carb/ injector cleaner, Forte and Marvel Mystery Oil get good reviews. It might not work but it beats stripping the carbs if you can avoid it, Good luck.
« Last Edit: 20 May 2018, 10:11:56 pm by vinnyb »

tommyardin

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Re: Low power full throttle mid rpm
« Reply #3 on: 20 May 2018, 11:05:49 pm »
It may be worth running it for a while on premium fuel, and/or trying a fuel additive carb/ injector cleaner, Forte and Marvel Mystery Oil get good reviews. It might not work but it beats stripping the carbs if you can avoid it, Good luck.


 :agree
Get some carb/injector cleaner additive for petrol engines and give the fuel tank a double dose of the stuff, if it says add 50ml per 5Ltrs shove in 100ml. There is a very good chance that it will clear it out, if it does not do it again with the next petrol fill up as the stuff sometimes take a while to remove built up varnish in carbs.


If it does not do it it will have only cost you the price of the additive if it does do it you have been saved a lot of hassle and you have still been riding your Yammy.
Win win if it works, if it does not work the rest of the fuel system will have had a spring clean fuel pump and lines.
What you describe would indicate a partially blocked jet or jets, especially as you ride through the flat spot and the bike surges forward again on to full boil, so it not an blocked air filter, as it would get worse not better as you continued to full throttle the same can be said for a fuel filter,  as it runs fine at low and high revs it can only really be a partially blocked jet.
I could just be just one carb that is messing about, a  flat spot at those revs is much the same as a bike only running on three cylinders, and that effectively dead cylinder is putting a brake or load on the other three, so in real terms your are running pretty much on half power as you go through that flat spot, no wonder it feels like it takes off once past that flat spot.


https://www.ebay.co.uk/itm/1-x-WYNNS-PETROL-INJECTOR-CLEANER-ADDITIVE-325ML-ALL-PETROL-ENGINES-AND-CARS/131898749933?hash=item1eb5c733ed:g:k2MAAOSwARZXo1yN


Wynns is a reputable make and also the link above is a good price, sending off for a bottle myself just to run through my system.

tommyardin

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Re: Low power full throttle mid rpm
« Reply #4 on: 20 May 2018, 11:10:56 pm »
In fact I have purchased two I will put one through the SLK as well as the FZS600  :lol

darrsi

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Re: Low power full throttle mid rpm
« Reply #5 on: 21 May 2018, 06:46:38 am »
As above, try the most inexpensive way first, it may be all that it needs.


I've always used this gear, in fact i'm using it right now in my tank, and is the only one i've ever tried that i notice a difference after a few days.
During winter my bike probably doesn't get up to a decent running temperature when it's very cold as my commute isn't very far so it appreciates a system clean up at least once a year.


Used to be £15 a bottle in Halfords but they've stopped selling it so at least now it's a sensible price online. 


https://www.ebay.co.uk/itm/STP-Petrol-System-Cleaner-Fuel-400ML-Powerful-Additive-Petrol-Treatment-/323244674523?_trksid=p2349526.m4383.l4275.c10
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Re: Low power full throttle mid rpm
« Reply #6 on: 21 May 2018, 10:04:37 am »
What is winterising the carbs? My bike has lived outside in all weathers, summer, winter, sometimes sat for 2-3 months at a time. I've never bothered doing anything with the carbs and never had a problem with them...

The problems I have had are around corrosion of the caps and plugs. It happens every year, as water sits around the top of the engine. It does exactly what your describing. Misfires at full open throttle. Back off on the throttle and the revs pick up.
It's to do with having a week spark and as the resistance of the air fuel mix changes it misfires.

It's a lot easier inspecting your caps and plugs then taking your carbs apart.
« Last Edit: 21 May 2018, 10:05:29 am by Bretty »
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vinnyb

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Re: Low power full throttle mid rpm
« Reply #7 on: 21 May 2018, 10:39:31 am »

What is winterising the carbs? My bike has lived outside in all weathers, summer, winter, sometimes sat for 2-3 months at a time. I've never bothered doing anything with the carbs and never had a problem with them...

The problems I have had are around corrosion of the caps and plugs. It happens every year, as water sits around the top of the engine. It does exactly what your describing. Misfires at full open throttle. Back off on the throttle and the revs pick up.
It's to do with having a week spark and as the resistance of the air fuel mix changes it misfires.

It's a lot easier inspecting your caps and plugs then taking your carbs apart.
I think Ministras means adding fuel stabiliser to prevent the fuel breaking down over time while the bike is stood. Have you tried ACF50 around your plug caps and plugs it should stop that happening.

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Re: Low power full throttle mid rpm
« Reply #8 on: 21 May 2018, 12:28:42 pm »

Hello again everybody, a few days ago i completed my driving exams (hurray) and took my bike for spin. It was amazing as it should have been, but i ran into some problems (as it shouldnt have been). At around 6.5-8k rpm at full throttle the bike seems like it almost cuts fuel off. Then at 8k right at the power band the bike flies all the way to max rpm. It seems to happen at 2-3rd gear, too scared to try first and not enough space to go 4+ gear  :o .

This could be alsorts, from stuck cold start valve/s to pin hole/s in a diaphragm, air leaks and possibly blocked or restricted pilot/main jet fuel circuit.



So what are your suggestions? Last owner didnt winterize the carbs, are they the problem? How can the power stop, then come on at full force later?

Winterise carbs........ another myth that has appeared over recent years.  Providing the bike is correctly maintained (very important that bit) you need to do nothing to anything to store it over winter other than garage it and keep the battery charged.  If you were taking it off the road for say a year or 2 then it would be wise to take precautions.  The other myth UK/Euro fuel goes off and blocks you pilot jets, it doesn't.  What does is suspended debris in the fuel,  The main one being rust, how does the rust get there water in the fuel from cheap/poor traders who allow there fuel to get too low before refilling their tanks.  Others are storing the bike with an empty tank over winter, dents in the tank these can damage the coating on the inside and rust then forms, filling up from a fuel can that's got crap in it.

I've recently (3 weeks) took my XJR1300 out of the garage.  It's been in there since Mid Oct 17 with half tank of fuel connected to a Optimate charger nothing else.  I primed the crabs (very important that bit) by turning the fuel cock to prime, put the choke half on (same system as Fazer) hit the starter and it started, got on it and rode it.  The bike rides perfectly the fuel has been in the tank for 6 months, when I got home I topped the tank up with fuel I've had stored in 20lt metal fuel can (commonly known as Jerry cans)  that fuel is about 8-9 months old, I've used the almost every day since, and I've topped up with garage fuel there is/was no difference. 

The same applies to my other bikes all start, and ride as they should all their fuel is at least 5 months old, fuel doesn't go off certainly not over winter.  Some years ago I took my Fazer off the road for 3 years, it was just left in the garage connected to an Optimate, nothing was done to it before or during other than the odd start up perhaps once a year.  It started first time every time and rode perfectly after the 3 years, the fuel was 3 years old!

Based on your other posts (cam chain noise) this bike clearly hasn't been cared for it's possible candidate for a bike that's been clocked i.e. it's got far more mileage on it than it's stating.  Looking at the pictures you posted on U tube I'd say it's looking very ratty for a 40km (25k) bike it's certainly not been looked after outwardly.   As I stated in my other post, take it somewhere that's recommended by other bikers, see what they say.

Good luck keep us posted.

Later

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Re: Low power full throttle mid rpm
« Reply #9 on: 21 May 2018, 01:55:53 pm »
Presumably you can determine the likelihood of rust going from your tank to the carbs by inspecting your fuel filter under the tank.. If it's a dirty rusty colour or white.
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Gnasher

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Re: Low power full throttle mid rpm
« Reply #10 on: 21 May 2018, 02:27:58 pm »
Presumably you can determine the likelihood of rust going from your tank to the carbs by inspecting your fuel filter under the tank.. If it's a dirty rusty colour or white.


Not always, filters change colour as they're filter fuel, these particles are that small they get through the filter.  All bikes will have some particles in the float bowls, it looks like brown dust suspended in the fuel normally in the float drain cavity.  When the fuel evaporates from the bowls the particles from into a dry sediment, get enough of the stuff suspended in the fuel and it starts to build up in certain areas where fuel sits while the engine isn't running i.e. jets.


Over time (years) of not being used over winter this eventually blocks the jet, the issue isn't the fuel it's the rust/debris in the tank that's slowly getting drawn onto the fuel system.  If you've got more than just a small amount of this brown looking sediment in the float bowls check your tank.     
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Re: Low power full throttle mid rpm
« Reply #11 on: 21 May 2018, 03:18:52 pm »
Buy some seafoam.
Run the bike til there is hardly any fuel in the, tip in the seafoam into the fuel tank and run it till it stops smoking. Then top up with nice expensive fuel and take it for a blast down the country lanes, razzing it as much as you can.
When you are back at home with a grin on your face the bike should be performing much better on the way home.
If that does not work out for you it will be time to clean the carbs.

Gnasher

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Re: Low power full throttle mid rpm
« Reply #12 on: 21 May 2018, 03:40:06 pm »
Buy some seafoam.
Run the bike til there is hardly any fuel in the, tip in the seafoam into the fuel tank and run it till it stops smoking. Then top up with nice expensive fuel and take it for a blast down the country lanes, razzing it as much as you can.
When you are back at home with a grin on your face the bike should be performing much better on the way home.
If that does not work out for you it will be time to clean the carbs.


It's doubtful it will clear a blocked jet and it certainly will not sort out the contamination problem i.e. the rust or debris.  These additives are little more than detergents and will do nothing to permanently sort this kind of problem. 
Later

darrsi

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Re: Low power full throttle mid rpm
« Reply #13 on: 21 May 2018, 05:03:31 pm »
Buy some seafoam.
Run the bike til there is hardly any fuel in the, tip in the seafoam into the fuel tank and run it till it stops smoking. Then top up with nice expensive fuel and take it for a blast down the country lanes, razzing it as much as you can.
When you are back at home with a grin on your face the bike should be performing much better on the way home.
If that does not work out for you it will be time to clean the carbs.


It's doubtful it will clear a blocked jet and it certainly will not sort out the contamination problem i.e. the rust or debris.  These additives are little more than detergents and will do nothing to permanently sort this kind of problem.


I was shown the brown sediment in my carbs when i had mine cleaned a few years ago, i take it there's no tricks for it to be removed via the carb drainage holes?
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tommyardin

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Re: Low power full throttle mid rpm
« Reply #14 on: 21 May 2018, 06:56:55 pm »
As above, try the most inexpensive way first, it may be all that it needs.


I've always used this gear, in fact i'm using it right now in my tank, and is the only one i've ever tried that i notice a difference after a few days.
During winter my bike probably doesn't get up to a decent running temperature when it's very cold as my commute isn't very far so it appreciates a system clean up at least once a year.


Used to be £15 a bottle in Halfords but they've stopped selling it so at least now it's a sensible price online.




 
https://www.ebay.co.uk/itm/STP-Petrol-System-Cleaner-Fuel-400ML-Powerful-Additive-Petrol-Treatment-/323244674523?_trksid=p2349526.m4383.l4275.c10


Damn! That was the one I have used before with great success, I was trying to find on eBay, but failed., But now I have the link, I had forgotten the name /make of it.
Cheers

darrsi

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Re: Low power full throttle mid rpm
« Reply #15 on: 21 May 2018, 09:14:01 pm »
As above, try the most inexpensive way first, it may be all that it needs.


I've always used this gear, in fact i'm using it right now in my tank, and is the only one i've ever tried that i notice a difference after a few days.
During winter my bike probably doesn't get up to a decent running temperature when it's very cold as my commute isn't very far so it appreciates a system clean up at least once a year.


Used to be £15 a bottle in Halfords but they've stopped selling it so at least now it's a sensible price online.




 
https://www.ebay.co.uk/itm/STP-Petrol-System-Cleaner-Fuel-400ML-Powerful-Additive-Petrol-Treatment-/323244674523?_trksid=p2349526.m4383.l4275.c10


Damn! That was the one I have used before with great success, I was trying to find on eBay, but failed., But now I have the link, I had forgotten the name /make of it.
Cheers


Make sure it's the "Complete Fuel System Cleaner" as per link, as there are others by STP that are not as effective.
Just lob the whole bottle in with a full tank of fuel.
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Gnasher

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Re: Low power full throttle mid rpm
« Reply #16 on: 22 May 2018, 09:16:52 am »
I was shown the brown sediment in my carbs when i had mine cleaned a few years ago, i take it there's no tricks for it to be removed via the carb drainage holes?


No, once the fuel has been drained it will just settle as a dust this stuff is extremely fine as i said it get through the filters.


You will always get some sediment, but I mean some no more than a thin layer in the well of the float bowl where the drain screw is, and this level isn't a probelm.  If you've got it all in the float bowls it's a sign that there either rust or contamination in the fuel system, this could be the tank, pump, filters or fuel lines.  If it's not sorted over time it will block jets.   
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Ministras

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Re: Low power full throttle mid rpm
« Reply #17 on: 24 May 2018, 08:16:07 pm »
Sorry guys gonna end the thread here, sold the bike due to another problem that i didnt want to invest money into.