runs very good but shutsdown after couple miles

[Rip]

I have a ST90 that runs very good in general, however lately after running around the yard and up and down the subdivision I head out on a county road for around one mile to two miles and it shuts down . Like it runs out of fuel or floods out just after slowing down . I have 75 micron fuel filters on it ,which seem fine since it runs good before I go long distance , any ideas what is causing this.

 

[dirtbkr188]

Make sure the gas cap is venting properly, otherwise, the pressure builds up in the tank and causes a "vapor lock" of sorts, and the fuel won't flow. The next time it happens, get as close to the gas cap as possible and listen for a hiss when you crack it open. If it does, the cap isn't venting.

 

[Old Guy Too Many Bikes]

Also check for something that may be restricting your fuel flow. Open up your drain cock at the bottom of your float bowl and make sure you're getting a good flow. If you're getting just drips and dribbles, check for obstruction in tank or clogged screen in petcock or carb.

 

[kirrbby]

Definitely check your valve adjustment. When the bike heats up, the valve stems expand/lengthen slightly. Could be JUST enough to leak compression.

 

[-Nate]

When it shuts down does it slowly loose power until it stops or sputter a bit first ? .

Does it ever back fire ? .

Once in a blue moon the exhaust can get plugged (mice most often) and cause this too .

 

[Rip]

When it shuts down does it slowly loose power until it stops or sputter a bit first ? .

Does it ever back fire ? .

Once in a blue moon the exhaust can get plugged (mice most often) and cause this too .

never back fires, does sputter. died again today. took spark plug out after it died, couldn't see spark. waited awhile an nieghbor sprayed starting fluid in cylinder and it fired up . shut it back down and wouldn't start again. runs very well very morning until it gets warmed up , then shuts down usually just arfter running hard then slowing down. thinking could be vapor locking as I have fuel filters resting on cyinder head. Also I been told could had low compresion which i does does smoke an burn some oil. No sure what to test next?

 

[OLD CT]

Replying to excellent suggestions would help. Did you check any? Valves set cold. Gas cap? Fuel flow?

 

[Rip]

Yes , inlet valve .002 and exhust valve .004 , took gas line off at carburator and emptied tank with full stream of fuel. Also ran wire in gas cap vent holesand blew them out.

 

[OLD CT]

Have you removed and cleaned the emulsion tube under the main jet in the carb?

 

[Rip]

Have you removed and cleaned the emulsion tube under the main jet in the carb?

No, it is a new carbuator with about 40 miles run time ,however I took carb apart yesterday an cleaned. I didn't remove the emusion tube though. does it just press out?

 

[OLD CT]

Should unscrew out or threaded. If it is a new carb with filters, it shouldn't be clogged up.

 

[-Nate]

Just for grins, try changing the condenser, use an old one that you know worked before .

The Emulsion tube in round bowl carbys presses out, use a soft dowel to knock it out from the top ~ I use a pencil but since this is a new issue and you've not mentioned any dirt or grit in the float bowl maybe skip that for now .

 

[-Nate]

Without being there it still sounds like a fuel failure to me .

Carry a spare spark plug in your pocket and the next time it dies use that to test the spark, remember : it's a low power system so even when it's perfect the white sparks are tiny and hard to see in bright light, maybe try rolling it behind a tree, building, truck or whatever to get some shade .

If your hearing is good, the next time it peters out stop quickly and lean your ear next to the tank before you loosen the cap, it may make a small whoosh sound as the air rushes in .

 

[OLD CT]

I'm thinking he should carry a small jar/ little screwdriver with him and ''shut the gas off as soon as it stalls'' and check how much fuel is actually in the bowl by draining it on the spot. Could be a low float height situation. You can also test, right now by turning the gas on wait a second or two then turn it off and drain to check how much is in the bowl before you do the road falter test to look for any changes.. I can remember riding for a mile on only ''a bowl full'' on my 140cc. Nice float height!

 

[-Nate]

O'Reilly's Auto Parts stores (and many others) sell clear plastic fuel hose that fits the drain nipple on the float bowl .

I have added a line and looped it up and over the carby so I can check the fuel level whist riding....

BE CAREFUL WHEN DOING THIS ! .

 

[Rip]

Ok , so i have re checked previous suggestion today . This moring it fired up first kick and i made it to my mail box and it sputtered out dead. took back to shop and rechecked valve clearances , timing points gap, fuel flow . Still dead after three hours. checked spark with a device that lights up when you kick start it . ( gives false hope ) it lite up dull. put spark plug against head to ground , no spark. checked battery charge , very low. recharged battery for three hours , fired up first kick and stayed running fine . So it appears this bike needs full charge to stay running, is the problem the rectifier? what keeps it charged? Need help on next step.

 

[Rip]

Also iI tested the compression with throttle open , 135 lbs . This was after about 7-8 kicks.

 

[-Nate]

O-Kay then ! now we're getting there .

Yes, it needs a FULLY CHARGED BATTERY to keep running .

NO, the alternator won't run it unless the battery can hold at least 6 volts DC over night .

What you do now is : find an AGM battery that will fit in the same hole ~ what I do is : drain and clean the old battery and take it to the local electronics store, most will have multiple choices, get the one that's closest in size .

In none are quite right, take two slightly smaller batteries that when duct taped together make up the correct size .

Unless you've already done so, go to pardue brothers . something or another, they're in Florida and will sell you a *MUCH* better rectifier that the old stock one ever was, for less $ and they sell them 'Plug And Play' with the correct connectors or MPC's depending on your year .

Glad you stuck to it, you're going to have a GREAT Spring & Summer riding ! = .

 

[-Nate]

O.B.T.W. : May I be a little bit of a grammar nazi ? .