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Discussion Starter · #1 ·
Hey guys,
So this is probably going to be long and wordy, as this is sort of a last resort and I have tried about everything I can think of. The problem I'm having is that my bike (2007 Suzuki Bandit 1250) wont rev past a certain RPM. It felt in the beginning as if the bike had a slight misfire under heavy and abrupt throttle input. But over time it has gotten worse, currently I have about 1/8th usable throttle. Anything above that and the bike falls to idle and just sits there if it is in gear. If it is in neutral and full throttle is applied then the bike will fall to idle and then blip up to about 4,000-5,000 RPM and then fall back to idle. It gets worse as the bike warms up. I took it by my local shop and they told me it was probably a fuel flow issue as i had a aftermarket exhaust and live at 3,333 elevation. So I bought a fuel controller and things got better and almost perfect. The bike consistently rev'd all the way through the RPM's for about 2 days. After that it started acting back up.

Here is a list of what I have done/checked in order hat it was done:
1. New OEM Spark plugs (Previous ones were slightly white but not bad, indicating that the bike was running lean and not getting enough fuel)
2. Fuel system cleaner ran through tank
3. Fuel controller installed (power commander FC)
4. Throttle body, fuel rail, and injectors removed/cleaned as well as every sensor in that location being checked for resistance and correct adjustment (TPS and STPS)
5. Known good ECU installed
6. Fuel pump assembly removed and dissembled (Verified fuel pump was working by straight wiring to battery and cleaned strainer filter which was not very dirty to begin with)
7. Checked ignition coils (Looked for proper resistance and inspected for cracks/dry rotting. Resistance numbers looked reasonable as I couldn't find a good figure for what they should be, they all read 1.6 when cold and 1.8 when warm)
8. I'm sure I'm forgetting things, but that is fairly accurate.

And now here is a list of things that I find strange/thing is necessary for you guys to know to help:
1. The bike will make one good pull after the tank has been taken off for any type of service/work, it then quickly decreases back to 3,000 RPM being my max usable RPM after about 3-5 minutes of riding.
2. If I cut off my bike after it can only rev to 3,000 RPM but isn't yet at running temp, if it is off for only around 2 minutes I can accelerate up to 4,500-5,000 RPM for one pull. Then it decreases back to 3,000.
3. There are no vacuum leaks that I or the local shop up here can find.
4. It is getting worse as time goes by and is worse under load/uphill.
5. When I first noticed the problem it was a jerking at high throttle and RPM, but would not fall to idle. Also I could roll on gently all the way through the RPM range.
6. The bike runs slightly better with a full tank of gas.
7. It is getting to be time for a new chain (Don't think this is relevant, but want to paint the whole picture)
8. No check engine codes are being thrown.
9. The time frame of this started 2 weeks after I bought the bike (used) till now. I have put around 2,000 miles on the bike through this.
10. Previous owner said he never had the problem (whether that is true or not I can't vouch for).

Please help! I'm running out of ideas and can't find any previous forum out there that lists these problems/symptoms. Any ideas, suggestions, or even questions would be much appreciated.
 

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There are several good clues that point directly to:

A vacuum accumulating in the tank......try cracking the cap open to test.
OR
A bad fuel pump or restricted fuel line.

I had a wild idea too.....maybe the air filter media got sucked into the inlet and is blocking the air flow.
 

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speaking of filter medium, other suzuki's have a problem with the insulating material on the underside of the fuel tank being loose and obstructing air flow.
 

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Also check the fuel hose has a slight downward slope and isnt kinked...on prevoius B12s it could be an issue....although it was the carburetted model.
 

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1." The bike will make one good pull after the tank was taken off....."

Install a K&N engine air filter and replace the gas tank's fuel cap. The aftermarket has some cool looking fuel caps. Neither of these is expensive and one or both of these might be your problem.

MiseryCity
'08 Bandit 1250S
 

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Install a K&N engine air filter
Sorry but this is NOT a good idea.
Low restriction air filters were/are made primarily for RACING applications.......and there is an even chance that it will make a street bike run worse and not better.
 

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The fuel pump may have an internal filter that is non sevicable. The work round is to drill it out then fit an inline one externally on the fuel line. The Australian Busa forum has the steps posted last time I looked and the pumps will be similar if not the same.

I would check the fuel delivery/flow rate...it should be in the specs. Disconnect the line at the injectors and feed it into a container then time the delivery of a known amount.


Good luck
 

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Discussion Starter · #8 ·
Found it! It was the internal fuel filter. Cleaned it with a braided wire and brake cleaner. Screams like a banshee now! Thanks for all the replies
 

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K&N Air Filters

Sorry but this is NOT a good idea.
Low restriction air filters were/are made primarily for RACING applications.......and there is an even chance that it will make a street bike run worse and not better.
Easy Rider, you need to catch up a bit. K&N filters are common place in hundreds of THOUSANDS of ordinary street bikes, dirt bikes, ADV bikes AND ordinary cars and trucks. I've put them in over 35 motorcycles that I personally have owned including the 6 I own now plus in my cars and all my friends' and relatives bikes and cars. Every single one has run better, WAY better, because it allows the engine to BREATHE. Better performance and better gas mileage. The only caveat is that if you have a carburetted bike you will need to re-jet the carb to handle the greater air volume( which is what I did on a carbed 1500 Vulcan and a 6-carb Honda Valkyrie. The fuel modules in fuel injected bikes automatically compensate. The owner of the '07 Bandit that started this string fortunately found the problem, but my own '08 Bandit is essentially the same bike as his and I can assure you it does not run worse after installing a K&N. While I agree with you that, HISTORICALLY, low restriction air intakes were a RACING ONLY only application (take for, example, velocity stacks that had NO filter in them at all), because those engines most often were (and still are) torn town frequently after racing or racing season and rebuilt to restore the engine to what it was before it inhaled a lot of piston ring-eating grit out of the air at very high sustained rpm
 

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Easy Rider, you need to catch up a bit. K&N filters are common place in hundreds of THOUSANDS of ordinary street bikes, dirt bikes, ADV bikes AND ordinary cars and trucks.

Every single one has run better, WAY better, because it allows the engine to BREATHE.

The only caveat is that if you have a carburetted bike you will need to re-jet the carb to handle the greater air volume( which is what I did on a carbed 1500 Vulcan and a 6-carb Honda Valkyrie. The fuel modules in fuel injected bikes automatically compensate.
And I think you need to get over yourself.

I suspect that there are nowhere NEAR that many high-flow K&N filters in use, partly because even K&N recently started marketing "long life" filters that have characteristics closer to OEM to avoid some of the problems of using a racing filter.

Your "caveat" is a big one......which you did NOT mention in your original post.......and even applies to many/most fuel injected engines because the OEM fuel manager can NOT properly compensate for the different characteristics of the high flow intake. So then you need to get an after-market fuel controller......and THEN the pipes are too restrictive but changing them is illegal.

Most amateur "mechanics" have no business changing things on their engine because the odds are about 50/50 that it will turn out worse instead of better.
 

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Most amateur "mechanics" have no business changing things on their engine because the odds are about 50/50 that it will turn out worse instead of better.[/QUOTE]

I was referring only to the lifetime filters made by K&N. And I agree with you that, all things considered, it is best that those without a LOT of mechanical experience should NOT make any changes to their bikes. There's a reason the manufacturers have designed the bike as it comes from the factory. Keeping the OEM structures and components is the safest route to go and, further, changing anything while the bike is still in warranty can, and often does, void the manufacturer's warranty.

I hope the above is evidence that I got over myself.
 

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There's a reason why I haven't resorted to lifetime K&N oiled filters. They have less flow resistance, but there's a reason for that. It has to do with the containment of very small dust particles. The factory grade paper media does a better filtration job in this regard. I make it a point to replace the media more often for better efficiency. Where I live is very dry and dusty. I tend to keep my vehicles including my bikes longer than most people.

Now there is one exception. I replaced my 1971 Honda CB100 factory foam oiled air cleaner with a K&N lifetime. The reason is simple. The factory foam unit deteriorates over time from the oil and must be replaced, which I consider annoying. The K&N doesn't, and the foam unit isn't as efficient in dust removal as a paper unit. This I considered a good compromise.
So, one doesn't need to be a noob to remain faithful to OEM quality paper air filters. :cheers: :lol4:
 

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The fuel pump may have an internal filter that is non sevicable. The work round is to drill it out then fit an inline one externally on the fuel line. The Australian Busa forum has the steps posted last time I looked and the pumps will be similar if not the same.

I would check the fuel delivery/flow rate...it should be in the specs. Disconnect the line at the injectors and feed it into a container then time the delivery of a known amount.


Good luck
it was the best tip I could find about this problem!! Thank you very much you safe my day!!
I opened the fuel pump took the internal filter and clean it as much as I could, then put it back together and the bike works perfect!
Best regards
 
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