250-500cc 2007 WR 250 Getting Hot And Feeling Weak.

Hi all i just need a little help, today i took the wr out for its first run since the engine has been rebuilt. I did a couple of heat cycles and took her for a steady run. After about twenty minutes i came to stop and i noticed that she was really hot, much hotter than my 99 wr ever got.

The bike also has oversize GMX Rads fitted and filled with evans npg. The other problem i have is the bike seems weak in the middle of the power and the carb settings are listed below for the guru's.

PJ 35
60 Needle 3rd Clips
Stock slide
400 MJ
1.5 A/S
The bike runs on fully synth mix @50.1 and premium unleaded fuel.

starts and idles fine just looking for ideas and solutions the heat issuse and the weakness

new piston and assuming that the cooling circuit is 100% OK (no blocked lines or leaks)

did you check for the clearances of the piston in the cylinder if it gets really hot the piston is simply dragging to much in the cylinder

you would not notice this in heat cycles but when you put load on the bike.

with replacing only the piston the jetting is normal not effected to much (might be a little that normal can be solved with the needle clip)

but a dragging piston (due to a bigger expansion of the piston than the cylinder) can cause also a cause for a weaker feeling
your plug should be in that case still looking good.

I would run a little more oil in the fuel mix especially with breaking the piston in.

Robert-Jan

Hi RJ yeah the plug looks fine a nice tan colour i did raise the needle today from the 3rd to 4th clip but i wont get to try her till sunday. I did run the the motor for a few minutes today with the rad cap off to check if the coolant is going round the system and all was fine there. I forgot to add that the first break in was done 40.1 for the first gallon of fuel. it looks like i may need to check the cylinder but im sure that every thing was in spec. Thanks for your help so far..

I would for sure mix the oil/petrol ratio to 35:1 in the first few tanks.

Personally when everything is worn in to each-other I run also on 40:1 without a problem.

Robert-Jan

well i never had the chance to go out on sunday, so i pulled the barrel back off and measured the ring gaps and every thing is within factory spec. When i put the motor back together it started on the second kick. So i'm still looking for ideas on what to do next.

If coolant circuitry is fine and piston and ring within factory specs it could only be 3 variables more in the equation

jetting, ignition, load on the engine that could have an effect on the running temp of the motor.

jetting can be seen on the plug and the ignition should normal not be changed by the work's you performed

still you could try a new plug but I find it very unlikely that the problem is in the ignition.

did you clean your exhaust system ?

it could be that you pipe is blocked for a big part by carbon deposits


Robert-Jan

Hi Oneal,

Did you happen to put a forged piston in it?

Forged pistons dont expand as quickly as cast pistons, which may be the reason you can run it for 20 mins before it starts to get really hot.

What is the piston to bore clearance?

Forged pistons generally require more piston to bore clearance than cast pistons.

Make sure the power valves are not hanging up open or closed.

Also make sure your side valves are set properly.

Hi Ausky the motor was rebuilt using all pro-x includng a pro-x cast piston, the pv moved ok when i took the rod off to remove the barrel but i didnt check the side ports so i guess im going to go and have a play with it later. Thanks to everyone for all the input so far.

Was there any change with the needle in the 4th?

During break-in, the piston rings are in much higher contact with metal than what would normally occur. As the piston rings heat, they transfer heat to the piston and to the rest of the engine. Normally all engine components hydroplane on a cushion of oil, during break in, this is not the case. It is important that you run your engine under load, but for very short bursts or intervals. There is no way for your cooling system to keep up with this additional heat until your parts have fully seated.

Thanks guys i havent had chance to do anything to the bike today, im packing back up to return to work so the bike will have to sit for the next 14 weeks. When ill start a fresh thanks again for every ones input