GK73a SP will not rev out!

wullie3xv9 · Post by **wullie3xv9** » Mon Oct 26, 2015 11:20 am

What modifications have been done to your air box? K & N filter kit with large inlet or small ??
What size main jets are fitted to your carb's? If it was mine I'd be trying main jets 2 sizes smaller than what's fitted.

If the fueling is too rich, that will slow the burning of the fuel/air mix down to the point you loose power & it won't rev out, which is what appears to be happening on your dyno graph at the start of this thread.
When it comes to main jets every bike is different so it's trial & error until it rev's out to the red line cleanly.

You've maybe read this before, but here it is anyway:-

http://www.factorypro.com/tech_tuning_p ... gines.html

P.S. Apologies if I'm teaching you to "suck eggs".

moforockband · Post by **moforockband** » Mon Oct 26, 2015 7:25 pm

wullie3xv9 wrote:What modifications have been done to your air box? K & N filter kit with large inlet or small ??
What size main jets are fitted to your carb's? If it was mine I'd be trying main jets 2 sizes smaller than what's fitted.

If the fueling is too rich, that will slow the burning of the fuel/air mix down to the point you loose power & it won't rev out, which is what appears to be happening on your dyno graph at the start of this thread.
When it comes to main jets every bike is different so it's trial & error until it rev's out to the red line cleanly.

You've maybe read this before, but here it is anyway:-

http://www.factorypro.com/tech_tuning_p ... gines.html

P.S. Apologies if I'm teaching you to "suck eggs".

Hi, thx for the advice. My bike won't rev cleanly past 12000. I've since sussed out that the pistons were touching the head, which is probably the cause of the bad running, along with 1/2 assed compression.
I have pod filters which usually require around 130 size mains IME.

stripes1976 · Post by **stripes1976** » Wed Nov 11, 2015 11:55 pm

Depending on the make of pods. I'd expect somewhere closer to 120's

moforockband · Post by **moforockband** » Sun Nov 22, 2015 1:48 pm

I had it on PDQ's dyno, and 128's seemed to be about ok. But I did find out after that the engine was heavily coked up after nearly 30 years, and tired oil stem seals so wouldn't breathe properly.
I'm hoping after rebuild and de-coke it will get new lungs!

moforockband · Post by **moforockband** » Wed Dec 23, 2015 11:09 am

Well i rebuilt it with new shells, stem oil seals and rings, and it still doesn't rev out, lol.
In the midst of drilling the MAJ out in stages to bring the super rich fuelling leaner at the top end.

moforockband · Post by **moforockband** » Sun Jan 08, 2017 9:39 pm

I sorted this a while ago, so may as well put here for anyone else in same predicament.

I've not re-dyno'd the bike, but I swapped out the small chinese pod filters for much larger RC098 S+B pod filters. This seems to have been the main issue. The S+B filters can be run dry for max air intake. These filters are made for a gpz900, so this little 400 can really suck some air in. These filters are in my opinion only just flow enough for the 33mm carbs, in std tune. Any more tuning, and a modified airbox will be required I reckon.
I have kept the jetting at 128, and she goes well now. Probably around 60 rwhp. Will post dyno graph when I re-visit the tuner.
I have a few track day vids on youtube of the bike to show what it can do.

GK73a SP will not rev out!

Re: GK73a SP will not rev out!

Re: GK73a SP will not rev out!

Re: GK73a SP will not rev out!

Re: GK73a SP will not rev out!

Re: GK73a SP will not rev out!

Re: GK73a SP will not rev out!