Unfinished Business 4 – Engine Trouble?

Flat Spot?

In the month or so after buying the GSXR, I have noticed that the engine was not performing as it should.

At low and middle rpms, the engine felt lethargic. I owned the K1 prior to this K4 and the engine was torquey almost everywhere (minus some what of a small flat spot around 5-6k perhaps caused by the removal of the exhaust valve). Twist it and she will leap forward with enthusiasm.

This K4, on the other hand, only sped up sedately when I wound the throttle. Her exhaust also made a gurgling or burbling noise when I twist the throttle. It sounded like someone has phlegm in his throat. My suspicion was that there was poor fueling from the FI system.

In the initial service, I discovered the missing secondary butterfly plates. A search online revealed that there are owners who remove them in order to eliminate any obstruction to the airflow into the throttle bodies. Apparently this helps the bike to get some additional top end performance. However, this modification also robbed the engine of low and mid range power. Perhaps this was why it felt like I was riding a 400cc bike.

Unfortunately, there was no part number for the 4 butterfly plates that I needed. Suzuki sells the whole throttle body as one part. I looked through Ebay but had no luck there. However, I was able to find a used throttle body for not that much money.

Proverbs 3:5-6
New King James Version
5 Trust in the Lord with all your heart,
And lean not on your own understanding;
6 In all your ways acknowledge Him,
And He shall direct your paths.

Horrid Fuel Consumption

During this period or a month or so, I was riding the bike on and off not to go anywhere but just to try and enjoy it. I was also already fiddling with the handlebar positions, suspension settings and tire pressures to find something that I like.

The rides were mostly short rides around the neighbourhood or to a shop to buy food and the like.

After 1 or 2 tank fulls, I realised that the bike was giving me horrible fuel consumption. With a full tank, her low fuel light lit up as soon as 180kph. I was not going fast and this translated to about 14km/L.

My K1 never dipped below 15km/L even when I was stuck in city traffic. Usually, the low fuel light would come on after 210km, so this could not be normal.

My guess was that I was riding on lower tire pressures 33psi/36psi and that it was also partly caused by the missing butterflies.

In the meantime, I took out the spark plugs and they were black. On top of that the plugs were one stage hotter. The stock plug to use was the NGK CR9E while the plugs that I found inside were CR8E IX (expensive iridium ones). I swapped them with the new plugs while waiting for the throttle body to arrive.

The standard heat range CR9E

After it arrived, I took out the butterfly plates and put them onto the bike. Another round of throttle body balancing was also done. I also pumped up the tire pressure to the manufacturer’s setting of 36psi/42psi.

While researching on the butterfly plates, I found out that there are cross head screwdrivers that are NOT philips screwdrivers, but JIS. JIS stands for Japan Industrial Standard and basically all cross head screws used in Japanese vehicles are JIS heads. Philips heads are slightly different and if we use philips screwdrivers on JIS screw heads, we may strip them. So I ordered 4 JIS cross head screw drivers #0, #1, #2 and #3. It is worth considering getting a set of JIS cross head screw drivers if you own Japanese machines and work on them cos they fit the screws perfectly and you will have less worries of stripping them.

Here you see a JIS #2 in action on removing the butterfly plates from a used set of throttle body
Close up on the throttle body butterfly plate
Cleaned butterfly plates on the bike
Balancing the throttle body after the plates were installed

Better Mid Range

The bike immediately responded stronger at the bottom and in the mid range. The torquey engine that I knew was mostly back. It was definitely an immediate improvement for sure.

Twisting the throttle no longer gave me a sluggish acceleration but a good kick in the butt. However, the gurgling/burbling exhaust remained and after a tankful of petrol, the poor economy was also there. At least now I can rule out the lower tyre pressures as the significant cause.

Throttle Position Sensor and Secondary Position Sensor, the Guilty Duo

The engine was running mostly fine now but the poor fuel economy remained. This was puzzling, because other than the full system, the bike was mostly back to stock.

This got me stumped and I started to think that the rich fuel mixture had something to do with the FI system. If it were a carbureted engine, then the carbs may have different needles, jets or may need a good cleaning.

So first thing I did was to buy a fuel injection cleaner and put it into the tank. It may have helped with the cleaning of the injectors but it did not improve the fuel economy.

I searched around the web to see if I could find some hints and stumbled on a thread of a CBR1000RR owner who also had very bad fuel consumption. The cause was traced back to the Throttle Position Sensor and the Secondary Throttle Position Sensor.

I got out the trusty PDF manual (thank you Internet) and took a closer look. I did check the TPS during the 1st throttle body balancing but did not during the 2nd. I also did not check the STPS at all. Were they causing the bad fuel economy?

So on a warm sunny afternoon, I lifted the tank again. With my dad’s help and a multimeter, I checked the STPS and it was way off. A little twist and fiddling got it to where it should be. I checked the TPS just to be sure and it was also out. Another little twist again and it was in spec.

The top is the STPS and the bottom is the TPS.
The STPS needs to be between 0.48-0.52V when the butterfly valve is fully closed.
The TPS indicator has to be in the middle bar on the LCD when the engine is idling at 1150rpm

A ride immediately after that confirmed that this had something to do with the poor running. The engine was more responsive everywhere. The gurgling/burbling was almost gone except for a very slight and short duration. The fuel economy also improved. Now I am averaging around 16km/l which is reasonable for this engine. I was happy!

However, it was too early to celebrate because another mysterious problem has surfaced during this time but I will have to leave that for a future post.

4 thoughts on “Unfinished Business 4 – Engine Trouble?

  1. Good job! Great to hear you solved the fueling issues. If I ever get a gixxer can you be my mechanic? LOL

    1. Thanks for your comments. To be honest, I am just an amateur. There is no sheltered work space where I can do more serious work. The things that I do are simple repairs and maintenance mostly. In the next update, you will see something that I always dislike tracing – Electrical Issues! Also thinking of a name for this bike as I have not named her since I got her 6 months ago.

  2. Looking forward to your next update. I hate electrics too… studying it was a nightmare.

    How about Big Daisy? English name of Dua Daiji (hokkien: big problem) Lol. Just joking…

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