250-500cc Can't cure lean machine.

[NCSteve]

New rings -175psi compression,is that about right with race-head?

Race head = race fuel Might just be fuel related, neither of mine like shitty pump fuel.
Hard to compare compression readings unless we're both using a calibrated gauge. Fresh rings, gaskets, etc in my 300 with 100 hours on stock head = 175 psi here with decent US made gauge.

 

[yakka]

Finally made some headway today.Seems the throttle slide was too high making it lean at closed throttle.
I decided to screw idle way out & bugger me, no more hang. Needed 2 1/2 turns out to cure it. Problem is it wouldn't idle then.
So to get it idling properly at that far out had to lean the rod out to the point where it starts to get lean crackle. It was similar for both 2-3xl & 3-2m rods. Maybe i need a different one?
Still has some mid range bog but thats not the main issue right now.
Will take it out for a proper ride next week hope it doesn't melt.
Looks like this might become another lectron thread.

 

[yakka]

Race head = race fuel Might just be fuel related, neither of mine like shitty pump fuel.
Hard to compare compression readings unless we're both using a calibrated gauge. Fresh rings, gaskets, etc in my 300 with 100 hours on stock head = 175 psi here with decent US made gauge.

Have good quality guage, so 175 might be bit low with a hi-comp. head?
Never tried race fuel- very spendy. The premium 98 pump fuel is decent over here & that made no difference to my bike.

 

[shawbagga]

Was the race head always on or jus since last top end?

Has anyone mentioned squish? I'm runnin 3-2m at around 50.5-51mm(forget it's in other thread). Idle screw at bout 1 turn out

 

[yakka]

Had race-head for a long while. Did measure squish once,only remember it being about right.
With the 3-2m its at about 51.2mm to get slide at right height. (2 1/2 turns)
I'm measuring from brass seat not the plastic bit,not sure which its taken from?

 

[lankydoug]

175 psi with a race head seems pretty low to me, my 250 has 205psi stock and other bikes I have checked with race heads had around 225 psi and required 100 octane or better race fuel.

 

[yakka]

175 psi with a race head seems pretty low to me, my 250 has 205psi stock and other bikes I have checked with race heads had around 225 psi and required 100 octane or better race fuel.

Thats a worry,just did top-end too.Might have to find another guage just to be sure.

 

[lankydoug]

Thats a worry,just did top-end too.Might have to find another guage just to be sure.

If a second gauge reads low then check the squish by placing a piece of rosin core solder in through the spark plug hole then while holding on to the end of the solder make sure the other end is against the cylinder wall (not sticking through a port) and roll the engine over top dead center one time. This will compress the solder, you can pull it out and measure the thickness where the solder was compressed. There are different thickness cylinder base gaskets to adjust the squish clearance. I like http://www.maxrpms.com/ to give me advice to what the clearance should be and also do the machine work if needed.

I helped a guy on a Honda CR250 that couldn't get his Lectron working with the recommended needle. He had 160 psi with a new top end and good leakdown readings. After we had http://www.maxrpms.com/ cut his cyl head for race fuel (225psi) his bike was easily tuned and he is extremely happy with it now.

 

[yakka]

Thanks for input Doug. Did the solder thing some time ago & from memory it had about the right squish.
Looks like I now have a stock head again!
May have a thinner base gasket around somewhere.

 

[Eaglefreek]

When I checked compression on my 300 when I had the race head, it was 180.

 

[juicypips]

I got less than 150 on my 360 has 55 thou squish band be piston and rings... don't go by numbers I go by leg kick.

 

[yakka]

The 300 are low compression to start with, about 6.9:1.

 

[lankydoug]

Yes the big bore 2 strokes aren't usually in the 200 psi range stock but I've read on this forum of 180 psi stock before.

The main point I'm trying to make here is that the Lectron needle has to match the fuel demand across the entire throttle range because it is basically one circuit. The makers of Lectron needles do a great job of developing needles but if your engine is unlike most then the needle that works for everyone else won't work for you. Compression and fuel quality have a lot to do with this. On a conventional carb you have 3 overlapping circuit which allows you to adjust for this... the Lectron works great if the needle matches your fuel demand. In my opinion having one main circuit that atomizes the fuel so well is the best quality of the Lectron. It gives the smoothest most powerful easiest to ride 2t possible but it's strength is also it's weakness if your engine set up, fuel and needle don't match up.

 

[lankydoug]

Good point. Hard to do vacuum test with powervalves though,near impossible to fully seal. Did replace c/seals after problem arose & crank surface looked good.
New rubber boot that seats well on carb & clamp tight.Spray tested around it too.

Also check the case halves gasket surface especially if you have had them apart lately. Spraying around them with carb spray while it is lean surging might help but it can be tough to pinpoint an air leak

 

[Bigbill]

Spray all around the cylinder base gasket. Retorque the cylinder to lower case bolts.