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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1 Answer

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


Hi, Barry and the usual suspects are:
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What did i miss


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

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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:
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Got a1996 yamaha yzf 600 and it starts but its not getting gas so it shuts off new carb all the way thru


Hi, Ktatejr86 and the usual suspects are:
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Jul 30, 2012 | 1996 Yamaha YZF 600 R thunder cat

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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
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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 jsanfellipo@donobi.net. Just put in the subject line: Briggs Carb Fix. I'll shoot you a copy no problem.

Good luck.

John

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.
< < READ CLOSELY > >
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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