Question about 1999 Yamaha YZF-R6

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Lapping the valves on 94' yzf750

I lapped the valves on my yamaha and tested to see if it seated good so I sprayed some carb cleaner down the ports and 4 out the the 20 valves did not leak but the four of them did. Is that going to be ok or should I lapp them in a few more times to see if I can get them to not leak through. I heard you are not supposed to lapp titanium or hardened valves but I don't think these are hardened. Thanks

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There should bo no leakage from the valves, do you have a grey line all the way around the seat and the valve with no black pit marks if so this should be fine also when the valves and springs are in then turn the head upside down and fill the combustion chambers with petrol wait a few moments and shine a torch up the inlet and exhaust tracts there should be no seepage.

Hope this helps

Posted on Apr 25, 2010


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Posted on Jan 02, 2017


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Very common but serious problem, I have Pulsar 150 Model 2011. Patrol leaking from Carburetor overflow line.

You say you changed the float pin. I guess you mean needle valve. If you can in your case change the needle valve seat, it may be damaged, worn, or just aged. If the needle valve seat can't be changed, you may be able to lap the needle valve into the old seat or area if part of the carb. This would be very gently done in the same manner as you would lap a head valve. Clean well afterwards and possibly you will have success. Good Luck Friend.

Jun 08, 2018 | Motorcycles


Float valve overflowing on a motorcycle

My Yamaha wr250 was leaking fuel out of the overflow badly. I cleaned the seat, changed the valved, adjusted the level. Nothing worked. In the end, it turned out the seat was damaged due to age. Yamaha did not sell a new seat for it, you have to buy a new carburetor. Here is a tip that is easy to do to resolve it provided you have already replaced the float valve, adjusted the float level, and cleaned the carb.

Items needed:
a small tube of lapping (valvegrinding) compound(Available at your local auto store)
1 can carburetor cleaning fluid.
About 5 Q-tips (If your float valve seat hole is bigger than a normal Qtip, you can purchase oversize ones at any drug store)
High speed drill

remove the carburetor, bottom bowl, float, and valve.
Put one Q-tip at a time in the drill
Apply a dab of lapping compound to the end of the tip(about twice the size of a b.b.
Stick it in the float valve seat and letter rip for about 10 seconds. The Q-tip will take on the shape of the float seat and lightly polish the seat smooth again. You might want to do this a couple of times the first time to ensure it takes.
Once you are satisfied that all scars are removed, take a can of carburetor fluid and spray out the seat. Ensure that all the lapping compound has been removed.
Put the carb back on. Try out the bike and see if you can get it to leak. If it does, repeat the process. I had to do it about 5 times to get mine to completely stop.
Final Note. This tip is provided for people that have already replaced the float valve, adjusted the float level, and cleaned the carb. If you cannot purchase another seat for your carburetor, without buying a new carb. this beats that hands down, but I strongly suggest you do the first three steps first. Anything goes wrong, your not out anything anyway.
Ride hard, or stay home.

on Aug 28, 2010 | Motorcycles

1 Answer

After cleaning carb, I now have raw gas coming out the exhaust???

Hi, Barry and the usual suspects are:
1. Dirt or other foreign matter between float valve and its seat.
2. Float valve sticking.
3. Float valve and/or valve seat worn or damaged.
4. Float misadjusted.
5. Float cracked, leaky or damaged.
6. Excessive "PUMPING" of hand throttle grip.
Good luck and have nice a day.

Btw, I’m available to help over the phone in case u need at

Oct 26, 2015 | GAS Motorcycles

1 Answer

What did i miss

Valves have to be seated by lapping. If you skipped this then the valve seat is not correct.

Aug 11, 2014 | Poulan Pro Yard Tractor 2006 and Newer...

1 Answer

Can not get my sons yz85 to start,bike starts when carburator cleaner is sprayed into open carb,then dies off.

Hi, Anonymous and the usual suspects are:
1. Fuel cap or fuel tank is not venting properly.
2. Fuel filter clogged.
3. Fuel line pinched or kinked.
4. Float needle and seat sticking.
5. Float level too low.
6. Carburetor bowl vent line clogged/blocked/pinched.
7. Idle adjusting screw set too low.
8. Air/fuel mixture screw set too lean.
9. Idle port, transfer ports, slow air jet clogged.
10. Slow fuel jet clogged.
11. Faulty fuel pump.
For more information about your issue and valuable "Free" downloads that you will need please Click on the links below. Good luck and have a nice day.
Dirt Rider Magazine
Dirt Bike Carb adjustment
YAMAHA YZ85 LC Owner Service Manual
OEM parts for Yamaha
YAMAHA YZ85 Owner Manual

Btw, I’m available to help over the phone in case u need at

Feb 17, 2014 | 2004 Yamaha YZ 85

1 Answer

Virago 250 ran good until last parking. then, about two weeks later, what looked like a gas/oil blend began pouring out of the breather when cranking. engine would not start. removed carb and replaced...

Check you oil level first and foremost, sounds like your bike IS flooding. When you replaced your float needles did you inspect the seats they sit in?? if they have a nick in them they wont seal and flood. remove the carbs and bench test them. you may need to lap the seats if they are nicked if you need to please contact me and i will give you step by step on that part.
Good luck

Apr 19, 2011 | Yamaha YZ 250 Motorcycles

1 Answer

The bike as not been used for two year carbs are clean new plugs engine no NC25E-1402627, Starts well rev's to about 2000rpm then starts to backfire and will not rev higher, would like to check the valve...

Intake valve clearance .04mm

Exhaust valve clearance .06mm

Good idea, some motors are worn a bit, so even at factory settings they may work but you'll here the tapping which means the valves would need to be adjusted tighter. to say .03mm & .05 mm

The valves could operate up and down good but not be seating = Needs Valves lapped in.
Do a leak down test to determine which is leaking.

Loose battery connections that vibrate at higher rpms can cause breakdown.

A faulty CDI that won't advance will make it back fire.

I agree with your decision to check your valve clearances first. Make sure all wires are good and tight.

Nov 30, 2010 | 1997 Honda Steed

1 Answer

I have a 8hp briggs and stratton model 190432 with a carb 390323 that gas just pours out the bottom can anyone help?

I had the same problem with my 190402 tiller engine (on a 1978 Sears RT-8 that my brother gave me). The carb leaked like crazy when I got the tiller, so I rebuilt the carb. Bought a new float, but the old one was fine (the hot water test you can read about if you do a Google search).

After rebuilding the carb and checking the float system (carb apart, hold carb top upside down with the float and needle installed, then blow into the gas inlet to see if you can pass some air. My carb top passed that test, and I guess it's a valid test. Never tried that one before . . .

Put the engine back together, and the carb leaked gas fairly steadily, but at a much lower rate.

I read a comment from someone that sounded flat-out wrong, but the Briggs rep. who responded to my email said to do the same thing. In fact, the rep. sent me a Briggs document showing what to do. It's like a tech sheet. Nice customer service (and I never even bought their stuff directly!!).

The problem I had was with the emulsion tube and its seat inside the carb. You probably have the same problem. You need to buy a new one emulsion tube because you are going to ruin the old one. The tube seats against the carb at a place that is below the fuel level -- can you see the problem?

Take the old tube, grind off the threads (I used my Dremel tool). Get some lapping compound (I used water-based stuff from the local auto parts place). Put some compound on the seating part of the tube, insert the tube, and use a screwdriver to lap the tube against the carb seat. Check it every once in a while. I think I probably did it for 3 to 5 minutes, not very aggressively, and added compound one time.

Look for a smoothness to the carb seat. Thoroughly clean out the carb. I used spray carb cleaner for the initial rebuild and the lapping compound clean-up. Put the carb back together and check for leaks before starting the engine. Start the engine, and hope that the leak stays gone.

I haven't had any problems yet, and I've used the tiller for about 4 to 5 hours so far. Maybe 6 or 7, but I've been using it for about a month off and on.

If you want me to send the pdf version of Briggs' document regarding this fix, send an email to me at Just put in the subject line: Briggs Carb Fix. I'll shoot you a copy no problem.

Good luck.


Apr 03, 2010 | Air Tools & Compressors

1 Answer

Back fires

Remove the water trap bowl at the bottom of the petcock, (gas valve). Any water or trash in the bowl? Drain a cup of gas from the tank. Any water or trash in the cup? Dump it, clean it and re-mount it, ( not all bikes have a water trap bowl ).
Drain the carburetor. There should be a screw on the lower side of the carb float bowl. Remove the screw then replace it after the fuel drains. Turn the gas back on and wait a minute for the carb to fill with gas. Install a new stock NGK spark plug and start the engine. If the bike doesn't start and run properly then shut off the gas and remove the carburetor from the engine.

Remove the float bowl and clean the entire carb with a spray carb cleaner from the auto parts store. Wear protective goggles to avoid getting spray in your eyes. Spray into all the little airways and fittings in the carb. Remove the two screws on the outside throat of the carb and spray into the screw holes as well.
Be sure to put these two screws back in the same hole they came out of. IMPORTANT > do not tighten these two screws down. Only screw these in until they LIGHTLY seat. Now turn each screw one and one half turns outward. Put the rest of the carb back together, clean the air filter and install the carb. Let the float bowl fill then start the engine.

Get the engine warmed up then set the idle speed. The backfire, whether through the carb or the pipe is usually caused by a valve not fully seating. This can be because of a carbon buildup on the valve seat and valve face or the valve could be 'burned'. It is not much hassle for the shop to lap the valves to give a fresh face on the valve seat and valve face.

Please rate this solution. Thanks!

Mar 31, 2009 | 2004 Honda CRF 450 R

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