Carb Leaking On Recently Purchased Ty250

[motophotog]

Hi all,

I've been riding dirtbikes and streetbikes my whole life, but am 100% new to the trials world. I picked up a 76 Yamaha TY250 last night here in the Seattle, WA, USA area.

Brought it home and went inside to eat dinner. about an hr later i could smell fuel in the house. Drats. Went out to find a puddle of fuel under the bike. Fuel was accidentally on reserve, not off (still not good to find this much fuel on the floor) I come back out and find more fuel so i take a further look and the the bottom of the float bowl, the drain is dripping 1 drop of fuel every 2 seconds.

Here is my question... does that mean I have a dirty or faulty float needle? Or does that mean that I have a faulty petcock, and it simply cannot turn off the fuel, so the fuel has no where to go but out the bottom of the carb? Thanks in advance, this is my first post to TC, and I did run a search before posting. Thanks again,

Darren

Seattle WA

[goudrons]

Sounds like the inlet valve to the float bowl is sticking and the float isn't shutting the fuel off when it should as the valve should stop the fuel even if the tap (petcock) is knackered and won't shut off.

Has the bike been stood for a while? Gummed up old fuel can cause this, I always drain the fuel out after use.

Float height too high? And it's not shutting off before the float bowl is full.

Or is there rust in the tank? And it's jamming the valve open. (I can't remember which had the alloy tanks?)

Take the carb off, strip it and clean it well and reset the float height.

It might be worth fitting an inline fuel filter between the tank and carb as well, they are very cheap.

Check and sort the tank out, if it's needed there are cleaners and sealants that can sort out a tank if it's not totally rotted.

Edited September 26, 2012 by goudrons

[motophotog]

Goudrons,

Thanks for the reply. I'll tear the carb apart tonight for a minimum of a good cleaning!

How do i "set the float height"?

[goudrons]

Ok, first this isn't your carb, but the process is very similar.

http://www.trialscen...&attach_id=6019

Remove the float bowl gasket first.

Follow pics 1 and 2 so the floats just rest on the inlet valve but does not squash the little needle all the way in, just so it shuts the fuel off.

Then measure the gap between the two red lines, but you must measure from the float bowls sealing surface (on the carb body) with the gasket removed to the top of the floats.

The height should be 24mm (+/- 1mm)

The tab that actuates the inlet needle will bend, if the height is incorrectly set, this needs gentle pressure to alter it until the required height is achieved.

This may also help in identifying a worn inlet valve/needle.

http://www.tytrials....-Twinshock.html

Edited September 27, 2012 by goudrons

[motophotog]

Thanks Goudrons, thats exactly the issue! FIxed!

Next issue! Got the bike started, warmed up, went for the first test spin on the street. (just want the bike to run a bit)

Runs good! Only thing I need to look into, once I turned the headlight on to high beam, and came to a stop sign, when I went to come back onto the gas to get moving, the bike didnt want to rev back up... It didnt die, but it sounded bogged. Craziest thing. I turned the headlight off, and she started revving again? Would that be a stator problem?

[goudrons]

Headlight? Not seen one of them on a TY for a while, most have had the lighting removed long ago and are ran a pure twin shock trials bike. Over here in the UK we can just use them on the road with just a horn, but it's only for daylight use.

There are two coils on the stator, a source for the ignition and a lighting coil for err lights.

I'm unsure why one would interfere with the other unless there's a bad earth that both these coils share (earth from the stator to frame?) or they meet via some ignition switch on the handlebars.

But I'm not an expert on these lighting set ups (I presume it's direct AC without battery with some sort of diode to limit the output??), my TY175 had all the lighting binned long ago, now it runs an electronic ignition, no lights, points, condensers, it's bliss!

So all I can suggest is checking all the earths and connection and perhaps the resistance and output of each coil on the stator plate (need to find out what these should be)

There are electronic kits available for the 250 with and without a lighting coil.

This one has a lighting coil.

http://www.electrexworld.co.uk/acatalog/STK-402L.html

It may be it's just a coincidence the headlight, and it's the carb still, might have ran lean on your run to the stop sign and as you've messed with the switches and it's idled a while, it's richened back up??

Have you check it has the correct jets? Float height correct? Pulled the plug to check the colour?

Is it dragging rust or ***** from the tank and blocking the jets? Failure to pick up and rev off idle can usually be traced to a blocked pilot jet.