[Xaman]

Hi all.



I have a fairly new to me 01.



I'm losing power at highway speeds, feels like its running out of gas. It'll recover with a few throttle blips and then ride fine for a mile or two, but will die when I try to downshift...



I just put a new Clarke tank (TW variety) on from the group buy, and put a brand new petcock assembly on at the same time (my old one had been leaking). The first time it happened, i looked Inside and i was halfway down the taller petcock screen. So i flipped into reserve and it seemed to be okay. But earlier today it happened while on reserve, but i could see the fuel was totally covering the reserve screen. I drained the float bowl just in case and was able to gimp along 3-4 miles to the next gas station. I filled up, called my wife and told her to be ready, and after a 10 minute cool down snack (had my daughter with me) started the 15 mile journey home...



It ran perfectly fine now.



So it's seeming to want to run well the first 100 miles on a new full tank of gas, but not when it gets down below the 1/2 or 1/3 range. Does that sound like something obvious to any of you guys? I'm certainly not a mechanic, but want to be able to trust this old bike.

 

[assquatch20]

There might be some kinda shavings coming through. While it's still doing okay, throw an inline filter on the line to the carb and see what it catches or if anything changes. Try to buy a decent one. If you want to cover all your bases immediately, you can do that by cleaning your tank, petcock, and checking jets out. Inlet or pilot jet clog will kill it when you pull the clutch sometimes.

 

[pgilles]

Maybe check float height and float needle valve/needle valve seat. I believe there's a screen on the float seat as well to prevent debris from entering the float bowl, could be gummed up with debris and/or varnish from old gas. If partially plugged, it would run well at lower rpm then as you increase rpm's and increase the need for more fuel it wouldn't be able to flow the needed amount to keep it sounding like it's running out of gas.



Pic is from this thread: http://tw200forum.com/index.php?/topic/937-tk-carb-photos-and-parts-identification/

 

[Scottbenson]

Always look first at what changed prior to the problem.



#1-Fuel tank change...........Most likely problem would be the new tank is not venting. For every ounce of fuel dispensed, an ounce of air has to be able to enter the tank to replace the lost fuel. There is a vent in the fual cap itself, or if a California model, the tank vents through a hose connected to the vapor canister. A simple way to see if you have a venting problem is as soon as you experience the symtom, remove the fuel cap and if you have a venting problem, the symptom will immeidately go away for a short time. My best guess is that you do have a california model and the rubber vent hose was pinched during the install of the new tank and you simply need to remove the tank and determine at what point the vent hose is pinched and re-route it to eliminate the pinching.



#2-New petcock........If this is an issue, you can remove the fuel hose from the petcock to the carburator. Turn the petcock to the on position and the fuel will either flow freely or it doesn't. If it doesn't, your petcock has a restriction or is clogged and dissassembly should show the problem area. This is all assuming that you do not have a venting problem as stated in item #1 above. If you have a venting problem the fuel will also not flow from the petcock freely. If you remove the fuel cap and the flow from the petcock immediately becomes stronger, you definitely have a fuel tank vent issue.

 

[lizrdbrth]

Good advice for a stock tank, but you could drive a bus through a Clarke cap vent.



Just sayin'.

 

[Scottbenson]

I'm not familiar with what a Clark tank cap looks like but if it has a hose on top that vents to somewhere, I would blow through the hose just to make sure a bus isn't stuck in the hose or make sure the end of the hose opposite the cap isn't pinched or sealing against something. Definitely sounds more like a petcock issue if the venting is good.

 

[Xaman]

Thank you all for the advice.



I got to ride again today, after checking and hoping it was a venting problem. The hose out of my cap is clear. How do I check the cap to make sure it's venting well enough?



I have an IMS tank on my WR250 and it had 4 holes on the underside of the cap, while this Clarke tank has only one. I blew through the hose and could definitely feel air coming through that hole on the underside ofthe cap...



The petcock is flowing fuel. I assume it's "enough" flow, but really don't I ow what to compare that too.



On my ride today, it ran fine out of the neighborhood, but lost power again about 5 miles out on the FM road (running 60+ mph), but never died, I was able to blip the throttle numerous times over the next half mile and made it to the back roads. It ran perfect on back roads at 40 mph and even the main drag (55mph) for another 20 miles. The perfectly on forest service roads (40mph) for another 20 miles.



Finally, back on the FM road for 7-8 miles before it bogged again at 60-65 mph. It never died, and I gimped back to the neighborhood where it ran fine again in 1-4 gear.



Seems to be happening at 5th gear in pretty close to WOT...



What next? Tear down the carb? I've never done it, but willing to try...

 

[Scottbenson]

I don't see where you removed the fuel cap "WHILE" you were experiencing the problem. If you have a fuel tank venting issue that is contributing towards a fuel flow problem the issue would almost instantly go away for a period of time. I would agree that it sounds like the tank is venting properly, but I would sure try the remove the cap thing because it is so quick and easy.



Failing the above, I would look at the petcock and make sure it is flowing fuel freely with no obstructions.



If all the above fails, is it possible you are simply flogging the beast to death at high throttle and RPM and overheating the engine to a point of shutdown? I know most people say you can run these bikes at 28 million RPM for 100 years without problem, but with stock gearing I would be very uncomfortable running my TW at 65 for anything other than a very short span.

 

[Xaman]

Scott,



I did unscrew the cap actually while I was riding (dangerous I know) and it "may" have helped. Unfortunately it was right at my turn off to the backroads, where it always runs fine.



And the petcock is definitely flowing gas, but agin, I have no way of knowing how much gas it's supposed to flow. Mut I feel like it would empty the tank if I let it flow overnight.



As far as the overheating, i guess that could be possible...and might account for the problem happening at high rpms in 5th gear only. Does it actually have an automatic shutoff of some kind?



Pmtg mentioned the float bowl, so I guess that's another place to look. I'm just a bit nervous aout breaking into the carb area, but I probably need to quit being such a wimp..

 

[mhomadness]

The vent still could be the problem, take it out to a stretch where you can test it for a proper length of time. When the symptoms occur, just loosen the fuel cap a bit, make sure your tank is not so full that fuel splashes out. Loosening the cap should vent it well enough to tell if this is the problem. Run it with the cap loose like this for a while, & see if that fixes it. If so, you found the problem. If not...



Don't open the carb just yet. Try this. Remove your new tank & dump the fuel out into a clean pan. Look for plastic debris, etc. that could be clogging the fine screen on the petcock. Now with the tank off, the gas cap off, & the petcock set in the normal position, see if you can easily blow through the petcock, by attaching a piece of fuel line to it, & blow. There should not be much resistance in regular setting or reserve. If you get a small to fair amount of fine debris out of the tank, there is a good possibility that this stuff is preventing proper fuel flow at high demand. Upon finding this, remove the petcock & clean the tank & petcock. REMEMBER: ALWAYS DO THIS KIND OF WORK IN A WELL VENTILATED AREA, AWAY FROM SOURCES OF COMBUSTION!! You should do this outside, away from the house, with the pan on the ground, to avoid possible static electricity, which can ignite vapour. Sorry to be a mother hen, but I would be negligent if I did not give proper fuel handling warnings.



You indicated the bike ran fine before the new tank, and other people have said they cleaned manufacturing debris from their new tanks prior to installation, worth a try. m.

 

[assquatch20]

I support the idea to make sure the vent and petcock are working, but barring that, I'd get into the carb and look for a sticking or maladjusted float. Plenty of resources here to get through it. For float adjustments, it's kind of a universal process so youtube could take you a long way.

 

[Gerry]

Seems there are a couple of folks having carb/fuel issues. At this point I am inclined to suggest a sticking float/valve. One of the other fellas indicated he gave the carb a tap with his pocket knife and it started right up. I had this problem with my Honda XR 200. As I had installed a fuel filter on the line, I could see that it appeared empty even though the tank had plenty of fuel. When I would tap the side of the carb with a small rock, I would see fuel flow into the filter and the bike would run. You certainly seem to be dealing with a "fuel flow" issue. I think given the testing already done, venting is not the issue.



Have you re-traced the routing of your fuel-line since the new tank install. It could be that you have a sharp bend/kink that is impacting high demand fuel flow.



These kinds of situations can be a neat challenge for 'us' but a pain in the butt for the guy riding the bike. Good luck. Gerry

 

[Scottbenson]

Ok.....I changed my opinion. If venting is not an issue, I am now leaning towards "REPLACING" the float needle and seat.



The reasoning behind this is that the problem only occurs during periods of full throttle and high RPM. A byproduct of both of these are higher than normal heat. With the carb directly behind the cylinder head and directly in line with the heat transferred to the cylinder head, I am suspecting the carburator is getting hot, the float needle is sticking in the seat and temporarily interupting fuel flor. When the heat subsides, the fuel flow returns to normal.



I had this exact issue in the carb of a Dodge truck I had. It was hard to diagnose, but when away when I replaced both the needle and seat.



This is all assuming of course that venting is definately the issue.

 

[STEVE IN SOCAL]

I'm not familiar with what a Clark tank cap looks like but if it has a hose on top that vents to somewhere, I would blow through the hose just to make sure a bus isn't stuck in the hose or make sure the end of the hose opposite the cap isn't pinched or sealing against something. Definitely sounds more like a petcock issue if the venting is good.

Made me lose a sip of coffee out my nose....funny

 

[Point37]

i have a clark tank on my bike...i put a tank vent on mine...hoses can get hot kink in the sun...my husky had this problem...it would sort of "cycle"...starve for fuel, get some fuel, the engine would surge and the bike would speed up and then starve again...to test, i pulled the hose off and rode around for a while and it rode fine so i replaced it with a vent and its fine now...but like these guys said if it ran fine before it's something that was swapped out...gas cap, gas cap hose, petcock, fuel filter (if you're running one), fuel screens, fuel hoses...what was wrong with your old gas tank?...could always swap the tank back and see if it works good...if so then the only thing it could be on the clarke tank is the cap/cap hose...if it's not that put the old petcock back on and see if the new one is the problem...process of elimination



http://www.ebay.com/itm/ATV-DIRT-BI...ries&hash=item2c617b6754&vxp=mtr#ht_530wt_905

 

[qwerty]

If you can blow in the vent hose and air comes out of the bottom of the cap your venting is adequate. Human senses probably would not detect the miniscule flow rate of air needed to vent the tank.



Did you read and follow the tank installation instructions? I'm guessing you didn't, and you have debris that came in the tank in your fuel system.



Rinse the tank clean. Take off the petcock, turn the tank upside down, and stuff a water hose turned all the way up in the cap hole and slosh it all around until all the gobblygook is washed out. Dump the water from the tank and allow to air dry.



Disassemble and clean the petcock. It has a filter screen that may be clogged just enough to not allow enough fuel to flow for sustained WOT operation. The petcock is used on much larger bikes than a TW, so it will flow PLENTY of fuel if it is right.



Blow the fuel line out with compressed air. Reinstall making sure there are no kinks or collapses.



If this doesn't solve the problem, you'll need to go into the carb as some goobly **** slipped through the screen in the petcock. Carefully disassemble and clean everything. Check the float height during reassembly and it will all be good.



The only ways a TW engine will heat up enough on the highway to seize are 1) no oil, 2) running 3+ jet sizes smaller than stock, 3) fuel with a VERY high ethanol content, or 4) ambient air temperature over 120*F.