GZ250 power increase.

[Quimrider]

My experiences with the K&N filter if anyone else wants to try that:
130 or 132.5 pilot jet (can't decide which is better.) (120 factory jet)
needle shim eliminates flat spot.
pilot screw set at 1 1/4 turn out. (1 5/8 turn out from factory)

Caveat: Each bike is different, climate variables and modifications affect carburettion. My results are presented as a starting point for someone wishing to do the same.

My bike has always had a flat spot approx 5-6k rpm. Modifications include, 4 extra 3/8" holes in exhaust from a previous owner, and 16t front sprocket. Prior to doing anything else I would hit a brick wall at 70mph and if there was any wind 65mph was difficult to maintain. I purchased a K&N SU-5589 air filter and installed it. Took it for a spin knowing it would be bad. Wow! it was so lean it would misfire like crazy even with the supposed flow restricter. I first tried a 140 jet. It ran smooth, flat spot was gone, but the exhaust smelled awfully rich. It also sounded/felt slightly different. Very subtle and hard to distinguish over the now very audible intake noise. The best adjective I can think of is a slight "chug." I next tried a 130 jet. Flat spot was back, slightly worse than it was with the original jet and air filter. My needle valve has no adjustable slots so I did the "needle shim" and simply moved the washer to the other side of the e-clip. This seemed to be the ticket. constant pull thru entire rev range. The acceleration is ever so slightly weaker than with the 140 jet so I think it may be a tad on the lean side. I may try the 132.5 jet. While testing with the 140 jet I was able to hit 83mph with a slight tail/cross wind yesterday. While trying to maintain 70mph it only dropped to 68mph a couple of times. While my top speed hasn't increased much, It's noticeably stronger in the 65-70mph range which is what I was looking for. It's hard to draw any conclusions from my speeds since it's been quite windy here in northern Ohio the past couple of weeks. Also I wasn't able to get the idle screw to go lean. It was about 1 5/8 turns from factory. I backed it out to 1 3/4 turns and started the bike (already warmed up engine) and screwed it in at 1/4 turn increments. At 1 turn out it would idle rough and stall. I settled on 1 1/4 turn out as this seems to idle fine. I'm open to suggestions on this as the idle still seem rich.

[trykemike]

Hey quimrider how you doing ? I followed your instructions for the tach . Great enhancement.
my bike is running perfectly.
since I drilled 4 7/32 holes inside the ring 1 '' from the centre outlet the idle remains 1300-1500 steady before it rose when hot to 2000 rpm
the accelleration is smooth and quicker
I tested 50 -70 yesterday with a strong head wind 25-40 kph it was smooth and responsive did not run wide open because of the cross wind.
I can easily pass 8000 rpm in 3 rd and 4 th but have not tried 5 th yet ( too windy )
I just did not want to run too lean if I do manage 8000 rpm in 5 th ( I will only touch it then back - off ) I just thought it may need a little more juice.
No rush I just bought the jets along with other parts ( oil filters etc )
I'll be patient then wait before messing up a working combination that I have now
I have 13000 km on the bike.
thanks for the feed back. I like you only need good power mid-range

[Quimrider]

trykemike,
Glad to hear someone has got some use out of my posts. My bike runs much smoother now. I'm not sure if it's the tweaks to the carb or the free flowing air filter. The biggest difference I've noticed is that at lower speeds I'm using significantly less throttle which I'd expect with a less restrictive intake. I gotta keep an eye on my speed. I find myself wanting to use the same throttle position as before and end up speeding. I suppose I'll adjust after a few weeks. Also I switched to using the horn for the tach. power supply. I should probably update that how to. Since I changed that at the same time I was messing with the carb I'm not sure what made the difference, but the tach doesn't seem to bounce as much and the idle is more consistent. It feels like I have faster acceleration, but I think that's probably just in my head I have gotten mine to idle fairly consistently at 1000-1300. My idle creeps up toward 2000 when it's hot too. 9 of my 15 mile commute is expressway so I'm usually 7/8 to WOT. The 16t front sprocket took a little off the top end but made the freeway more comfortable. It also allows me to drop down to 4th on the freeway if I need the extra power. Either these engines are pretty tough or I got lucky. I did once accidentally down shift to 3rd instead of upshifting at 68mph. I guess I was quick enuff to get on the clutch. I was shocked at how little difference there is between a 130 and 140 jet. I figured it would run aweful if it was rich. I first bought 140-150 jets from the same guy Jame got his. When 140 seemed too rich I got the 130-137.5 jets I figure I could get a little more power with the 132.5 jet, but I'd rather run a little lean to get better fuel economy. I plan to add one of those brake light flashers and put in a relay to cut off the head light when you start the bike.

[jonathan180iq]

When you get around to electric work and the hedlight relay, a picture is worth a thousand words.

[trykemike]

hey quimerider looks like I sent multiple posts a glitch on my part.

I will install the 125 main jet this weekend.

[Water Warrior 2]

QuimRider, just a heads up for you. If you want a brake light modulator they can be supplied by ridesafer.com. Got a combo pack from them that included the headlight and brake light modulators. Actually a good deal in my opinion as both ends modulate. Installation is quick and easy with decent instructions for technically challenged old guys like me. If I remember correctly the brake controller in under the left sidecover stuck in place with 2 sided tape. The headlight controller will actually fit in the headlight bucket and be protected from prying eyes and the elements. A very sanitary install for both units. Lynda's bike also has a SilverStar bulb in the front which is quite an improvement with not too much expense.
If you only want the brake light mod it is a good safety device that is relatively cheap.

[Quimrider]

trykemike If you're using the stock air filter and haven't tried the needle shim. You may want to try that before you swap out the main jet. I was AMAZED at how much difference the needle shim made. If I were to go back to the stock air filter I think the needle shim with the stock 120 jet would do the trick.

Water Warrior. Thanks for the heads up, but I already got the Back Off XP modulator from custom dynamics last fall. It just got too cold too quickly for me to install it. http://www.customdynamics.com/signal_dy ... ulator.htm It looks really simple to install.

[Water Warrior 2]

Quimrider, just had the seat off and found where the brake light mod is attached. So much for my memory !! It is actually mounted with 2 sided tape to the top off the air filter box just aft of the tank hold down bolts. I wouldn't look normally but I wanted to pull the tank and see if there were signs of anyone doing a valve inspection today. Looks like Lynda got what she paid for. Good thing too. She really hates to pay good money for nothing.

[trykemike]

Hey quimrider. I did the needle shim. You are correct the power delivery is smooth. Re top speed I still stop at 120 kph 7500 in 5 th gear but there is wind. I did notice that I can get there solidly and faster. I now have good power in the 80-100 kph range regardless of wind or hills. Acceleration is good to 105 kph.

I took the bike for a 200 km ride on saturday cruising 80 - 100 kph avg 90 kph ( 5500-6000 rpm ) . I ran 20 km on ther freeway @ 90-100 k/hr . I got off then ran secondary hwy avg 80-90 k/hr. The big hwy was very busy , windy with lots of big trucks and busses etc. NO FUN !

I will stay with the 120 jet for now.

I can hit 8000 rpm + in 4 th gear ( 105 k/hr )

[Quimrider]

trykemike, I can usually keep a steady 120kph (75mph), but I use the 16t front sprocket so the engine is turning about 500 rpm less. That is with no head wind. With a head wind I can only maintain a consistent 112kph(70mph) sometimes having to shift down into 4th. there is a chart here that shows rpm vs speed: http://www.gz250bike.com/viewtopic.php? ... c&start=90