Question about Yamaha YZ 250 Motorcycles

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YZ 250 1995 2 stroke have spark,cleaned carby & fuel tank,good compression, mixture 35.1 cannot start my legs going to drop off... Timing has not been touched also use to start & run fine....

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If you have a good fat spark and timing is stock, with good compression, your problem is likely fuel/air mixture. Assuming you have good quality fresh fuel/oil. Set air mixture screw one and a half turns out. What is the condition of the reeds and reed holders. Is there a build-up of fuel/oil residue on the piston port skirts or the crankshaft? Check for absolute seal between carby and reed valve manifold. Check for obstructions through airbox inlet, filter and inlet to carby. Ensure the governor is not fouling. The site link below has exploded view diagrams for all components of the bike to see how it all works. Good luck, cheers.

http://www.cmsnl.com/yamaha-yz250g1-1995_model10278/partslist/

Posted on Jul 16, 2010

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How do I fix a ryobi bp42 that will not start


It's a 2 stroke & it's relatively new. as long as you didn't score the piston by neglecting to add oil to the fuel mixture, the most likely problem is fuel issues. It only takes a month or 2 to have ethanol fuel absorb enough moisture to ruin the fuel mix. Return all carb settings to original settings. Empty your tank, get rid of your fuel, remix with NON-ETHANOL FUEL MIXED WITH A PREMIUM SYNTHETIC 2-STROKE OIL, such as echo or husquvarna. Purge all the fuel from your lines and primer. Remove the spark plug & pull the cord a few times to dry out the cylinder, run a flame under the spark plug to dry it out. Add 3 drops of fuel mix to the cylinder then replace the plug. Put it on full choke & pull 1 time. Then on 1/2 choke pull to start in 1 or 2 pulls. Still won't start; replace plug & air filter. Let it warm up for 5-10 seconds then turn choke off.

Sep 13, 2015 | Ryobi Garden

1 Answer

I have a 1994 ford escort and it's not getting eoungh power I've change the battery, sparks plugs and the alternator don't know what else to do please help


Did you check the timing? If the timing is off there will be a reduction in performance and power will be greatly reduced. If the engine is "pinging" or "knocking" under heavy acceleration, your timing is advanced, and pre ignition is occurring (that's when the spark has ignited the fuel in the combustion chamber prematurely), resulting in a knocking sound. When the piston is compressing the air/fuel mixture within the combustion chamber, the spark plug produces a spark from current it receives from contacts closing in the distributor cap. (Where all the spark plug wires are plugged into) if that spark come BEFORE the piston finishes it up stroke or compression stroke, the piston is then being slowed down from the kinetic energy produced by the exploding fuel. Thats where we loose our power. Idealy, the spark should come AFTER the piston has rotated over the top of its stroke, It has reached its limit in compression and is on its way back down then the spark should ignite the compressed fuel, thus giving the piston an additional "shove" back down to start its "Power" stroke, once its reached the bottom of the power stroke (stroke #2 of 4) it is then carried back up for the "exhaust" stroke pushing the burnt fuel out of the combustion camber and into the exhaust manifold, one it has reached the top of that stroke it begins its journey back down to start stroke number 4, the Intake stroke. Drawing in air/fuel mixture to again be pushed back upward to compress the air/fuel, and repeat the process over and over again. Now that I have thoroughly bored you to tears, Yeah, check the engine timing, if its not the timing it may be a vacuum leak.

May 11, 2015 | Ford Cars & Trucks

2 Answers

Car turns over but won't start. Boyfriend checked the spark plugs , says vetting spark. It says he did a compression check to it. Starter is a year old, battery new, we replaced fuel pump 3 weeks ago...


A thumb is not test for compression as 10lb/sq " will blow your thumb off. Have a proper compression test done. Next although it is sparking the question to ask is it sparking at the right time and to the right cylinder. Pouring fuel into the cylinder is a waste of time as the air/fuel ratio will be too rich to ignite even if the spark was occurring on the compression stroke. So here are some simple steps to follow to get it going
Have a compression test done to determine if there is sufficient compression to ignite the mixture
2 check that the spark is occurring at the cylinder at the right time ( no 1 cylinder on timing mark on compression stroke.)
3 . If it is EFI engine then check that the injectors are actually squirting if carby engine check that the fuel is in the fuel bowl With engines you have to have a combination of 3 things for the engine to work They are compression -which you will be checking for--2 spark timing--- which you will be checking for and lastly 3 fuel into the cylinder at the right time ==which you will be checking for
you only have to be missing one of these and you had best take it to a professional mechanic to get it started.

Jul 13, 2014 | Cars & Trucks

1 Answer

Can't start my yz250fp dirt bike


Have a trained tech service and properly jet the carb and set idle and idle mixture.
If you have spark, compression, and the valves are adjusted properly the only thing left is the carb. The FCR carb is as complex as the entire engine!

Apr 04, 2014 | 2003 Yamaha YZ 250 F

1 Answer

I have a SRM2100 trimmer, it will not run unless the choke is full on and of course after it runs in this mode a little while, it fouls the plug and quits. I cleaned the carb, installed new kit, new...


hi there jaybolt

here is a website for parts

http://www.partstree.com/parts/?lc=echo&mn=SRM-2100+Type+1+S%2FN%3A+001001+-+159490

all being well and compression and spark and timming , muffler is clear , carby is clean , and diaphrams are all ok you mention carb rebuilt , fresh mix , and fuel filter and lines are good

does the unit run with 2 stroke mix in the plug hole - then stop ?
if yes assume compression and spark are ok,, if no check compression and spark and muffler

will the unit run with 2 stroke mix sprayed into the carby throat, then stop ?

if it does sounds like you have a air leak somewhere in the intake system

could be at barrel base gasket, c/case joint, manifold boot/ block gasket, carby gasket , impulse hose ,if this unit has one , c/case main seals leaking

2 strokes need air tight c/cases in order to pump fuel / air / oil mixture from c/case to cylinder
and to create a vacuum for entry of fuel/ air / oil mix from carb to c/case

symptoms of air leak are -: hard to start, wont idle, stalling, low power, inconsistant idle, over rev
overheat

pressure and vacuum testing can be done by blocking off intake and exhaust with rubber and metal plates , then fitting adapter to spark plug hole , and placing piston at bdc , pressureise cylinder to 7 to 8 psi of pressure and check areas , base gasket, manifold joint, main seals, , impulse hose ? for leaks with soapy water - if leaking bubbles will be evident

if no leaks and pressure is held at 7 psi for at least 2 minutes with dropping - presure test is good
next do the same test using vaccuum again go to 20 - 30 inch / vaccuum

if vaccuum held unit is ok

suggest take a good look at carby and recheck its rebuilt correctly and setup particularly if P and V test are good and spark coil tests good with a coil load test using a spark gap of 6.00 mm to stress the coil ( simulates spark under compression load)

have a look and let me know what you find

cheers pauly46

Jul 03, 2011 | Echo Garden

1 Answer

Tanaka TBC 160- very hard to start, any suggestions for possible reasons? Replaced the gas mix but it starts up & then stops running. tried new gas mix, checked throttle- seems to operate, Any...


hi there

paul 46 here.

all being well and compression and spark and timming , muffler is clear , carby is clean , and diaphrams are all ok , fresh mix , and fuel filter and lines are good

does the unit run with 2 stroke mix in the plug hole - ?
if yes assume compression and spark are ok,, if no check compression and spark and muffler

will the unit run with 2 stroke mix sprayed into the carby throat ?

if it does sounds like you have a air leak somewhere in the intake system

could be at barrel base gasket, c/case joint, manifold boot/ block gasket, carby gasket , impulse hose ,if this unit has one , c/case main seals leaking

2 strokes need air tight c/cases in order to pump fuel / air / oil mixture from c/case to cylinder
and to create a vacuum for entry of fuel/ air / oil mix from carb to c/case

symptoms of air leak are -: hard to start, wont idle, stalling, low power, inconsistant idle, over rev
overheat

pressure and vacuum testing can be done by blocking off intake and exhaust with rubber and metal plates , then fitting adapter to spark plug hole , and placing piston at bdc , pressureise cylinder to 7 to 8 psi of pressure and check areas , base gasket, manifold joint, main seals, , impulse hose ? for leaks with soapy water - if leaking bubbles will be evident

if no leaks and pressure is held at 7 psi for at least 2 minutes with dropping - presure test is good
next do the same test using vaccuum again go to 20 - 30 inch / vaccuum

if vaccuum held unit is ok

suggest take a good look at carby particularly if P and V test are good and spark coil tests good with a coil load test using a spark gap of 6.00 mm to stress the coil ( simulates spark under compression load)

have a look and let me know what you find

cheers pauly46

Apr 30, 2011 | Tanaka Commercial Grade "Inspire" Design...

1 Answer

Rebuilding a bike which has bits from here and there. Believe motor to be 1986 GSX750. it runs, carby has fuel in it and seems to be working alrighty, plugs are sparking, but engine backfires a fair bit...


it probably isnt a firing order problem, or it probably wouldnt run

one coil fires 1 & 4 cylnder, the other coil fires 2 & 3 cylnders, as the pick up gets its signal from the crank, it sends a spark to each cylnder on the exhaust stroke as well as the compression stroke, ignition timing also doesent change as it is electronic and cant drift out like when points wear.
a short in the ingnition or kill switch can occasionally cause a backfire
Backfire can also be caused by
lean mixture, dirty carbs, loose carb clamps
leaking inlet or exhaust flanges and gaskets
tight valve clearances, burnt valves

make sure everthing is clean and tight, good air filter and exhaust, check valve clearances ,and give it a compression test, check the valve timing, incase it has been assembled wrong,(they rarely jump a tooth unless the chain and tensioner are completely stuffed)

Mar 03, 2011 | 1986 Suzuki GSX 750 ES

1 Answer

Fuel goes from tank to carby but doesn't start. (air and spark ok) Do I need to remove the carby? How do I best do that?


standard diagnoses procedure - make sure you have good compression, make sure you have spark, make sure you are getting fuel to carby, if you have compression & spark and fuel to carby bowl then you probably have blocked jets in carby

Aug 31, 2010 | Honda CMX 250 Rebel Motorcycles

2 Answers

Poulan pro 42cc,18",PPB4218 is very hard to start and runs for a short time and then will not start when hot. It worked well first year, badly this season.Changed spark plug and cleaned fuel filter and...


check basics 1st fuel , air, compression, spark , timming
then secondary compression ie crankcase air tightness
2 strokes need air tight c/case in order to draw in & pump mixture

check your tank breather is working,

has this saw been sitting a while ? if so might pay to rekit carb

check your carby diaphrams are pliable and inlet screen is not blocked and metering needle is set flush with chamber floor,
are hi / lo needles set base settings are 1-1/4 turns out from lightly seated , final hi setting is done while @ full rev and needs to 4 stroke slightly

check ignition spark under load ie while under compression load- could be a weak spark

check timming key

check for a air leak at cylinder / manifold block gasket or carb joint

check barrell bolts are tight everything been = engine should run

cheers

Aug 29, 2010 | Poulan Pro 42CC 2 Cycle Chainsaw, 18"

1 Answer

1992 yz 250 won't start


A couple of things.1.Check the fuel oil mixture is correct.It seems rich.2.Check that the carby is not running to rich.With new reed valves etc.it may need to be set back to the original manu. specs.With older parts it may have been retuned to make it run with the old parts.(carby jetting etc.)3 make sure the fuel oil mix is using a good quality oil.It does make a world of difference.I hope this is a start to get you going.

Aug 24, 2009 | 2003 Yamaha YZ 250 F

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