carburetor is popping 26mm oko flatty

[Cactus Jack]

Sometimes the inlet valve isn't sealing properly in new motors and that causes popping back thru the carb ... A lean mixture merely shows a leak up ... You can have a bucket of fuel in front of a fire without a problem ... but gas the fuel up and you're dead ... IF the valves are sealing 100% and the timing is set right there's no way a flame can make it back into the inlet tract ...

I've had several new engines that popped back thru the carb when cold even with the proper valve clearances ... A quick valve lap and seat check and the problem disappeared ...

But in a lot of cases the seats will wear in and seal themselves ... and maybe carbon build up helps seal them ...

Some people adopt strange valve "lapping" techniques to speed up the self seating idea ... Rumour has it that relentless "Wood pecker-like" tapping noises have been heard emanating from Sean01 and Thump*140's garages ...

YouTube - ãƒãƒ«ãƒ–ã™ã‚Šåˆã‚ã›

 

[lifelessurf]

your a cluey bloke cactus your worth your weight in gold on this site

 

[sean01]

yep id be sorting the exhaust gasket out ASAP, you would be surprised at the problems it can create..

as for the silicon job on the manifold, id suggest you remove it totally and fix the oring.. fuel dissolves silicon..

102 mainjet should be heaps in a 160. i run a 105 in my 160 which has a massive cam, heaps of compression and an oko30mm carb..
my mate runs a 102 in his 160 he has a de-comp cam which is a medium size cam(more than standard but less than mine) also with a little more than standard comp, its not till he's right at the top of the rev range where he claims the power drops off, but shortly after it valve bounces..

one other thing, what octane fuel are you running?

 

[lifelessurf]

im running just normal 91 octane.. yeh well its either the main jet isnt big enough or the needle is to long and wont let the fuel through properly??????

 

[sean01]

JJH needle isnt it... well should be..
there the perfect needle mate, so no problems there..

what bike is this in and what ignition system are you running? maybe too far advanced?
and are you sure its not valve bouncing early?

but like if said, the combination you have should be enough to run 99% perfect, so there has to be a second issue somewhere.
which isnt uncommon as the oko carbs makes any small problems bigger..

also put a new spark plug in it as it doesnt take much to foul a plug in the tuning process, plugs usually break down in the top part of the rev range when there slightly fouled..

 

[lifelessurf]

JJH needle isnt it... well should be..
there the perfect needle mate, so no problems there..

what bike is this in and what ignition system are you running? maybe too far advanced?
and are you sure its not valve bouncing early?

but like if said, the combination you have should be enough to run 99% perfect, so there has to be a second issue somewhere.
which isnt uncommon as the oko carbs makes any small problems bigger..

also put a new spark plug in it as it doesnt take much to foul a plug in the tuning process, plugs usually break down in the top part of the rev range when there slightly fouled..

its on a yx 160 engine with a stock cdi and original lightened fly wheel. when i had the molkt carbie it was revvin all the way so it cant be the ignition and yeh its a jjh needle i went to my local shop they think i might need to take a micro mm off the diameter of the needle where it starts to get thinner. im going to buy a jetting kit off dhz which has the 35 38 41 pilot and 96 102 104 mains and try the main jets first... wouldnt the bike have to be revving off its tits to be vavle bouncing????? its definately not revvin high enough. i just done the valves also at 0.004 and 0.006 exhaust wouldnt think that would be it...

 

[sean01]

i wouldnt be touching the needle.. everyone else uses the same needle with no issues..

yeah a jet kit will be good

valve bouncing can happen when ever on these engines...some early some never
and id be double checking the valve clearance just to be sure..

if the problem is still there after you try different jets then can you post a video of the bike free revving where the problem is and while riding it..

 

[fane]

hey everyone ive been workin on the bike and this is what ive done, i done the valve clearance they were definately too tight i saw a video on youtube sayin that the top valve should 0.004 and exhaust valve 0.006 so i did that instead of 0.003 top n 0.004 bottom. i then tightened up the o ring on the adapter which attaches the carby to the manifold. which had a small gap on each side so i siliconed around the edges of the pipe to fix any leaks. i didnt do the exhaust gasket because i didnt think it really needed it from previous experience with engines ive had an engine doesnt actually need a exhaust at all so i thought a small leak would not come into this type of problem.anyway i started the bike and it sounded a bit lumpier and the carby dont pop any more nor does it run as hot as it was before which had the pipe glowing red. i started working on the idle screw and air screw to get it idling right. i got it on the road went through 1st 2nd then about half way through 3rd it just stop reving up engine was still running but not accelerating i then moved the clip on the needle down to 4th notch from the bottom it made no difference i then moved it down to 5th notch the very bottom it still did nothing so im assuming it is the main jet since this jet has alot to do with power delivery from 3/4 to full throttle as i said before it is running a 100 main so im going to put a 102 maybe even a 104 on wednesday.... anyone have any suggestions of what it could be other than that im so close to getting this carby right just want to say thanks aswell to the guys that have helped me out yesterday on this thread, very grateful.

i thought the valves should be 3 and 4 thou not 4 and 6 thou.

i use 3 and 4 thou

 

[lifelessurf]

i thought the valves should be 3 and 4 thou not 4 and 6 thou.

i use 3 and 4 thou

yeh ive read that too but check this vid out

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[lifelessurf]

i wouldnt be touching the needle.. everyone else uses the same needle with no issues..

yeah a jet kit will be good

valve bouncing can happen when ever on these engines...some early some never
and id be double checking the valve clearance just to be sure..

if the problem is still there after you try different jets then can you post a video of the bike free revving where the problem is and while riding it..

yeh ok for sure if the problem keeps going ill have to take a video on saturday as i usually work late everyday...

 

[Barnesd09]

If its a stock YX160 with stock cam, try 37 pilot, needle clip second from the bottom, 98 Main jet (Or even a 96, just depends how hard you are going to rev it) and air screw 1 1/2 turns out.
Make sure valves have correct clearance, and a clean air filter and clean sprak plug.

A glowing red pipe would indicate a lean mixture. And a 36 is too small for a 160

I have a stock yx160 and have just been through this process, and everytime I mod something, the jetting changes. a port matched and cleaned manifold and port matched and cleaned exhaust will need a 38 pilot, and with the daytona ignition advance I'm now back to 100 main.

You will need a jet kit and anyone thinking that you can tune or adjust a carby without a range of jets it kidding thesmselves. I personally carry 5 of each jets and have a log book for different air temps, different mods and different engines so I know what has worked and what hasn't so I can continually improve my jetting, to get it spot on for different conditions.

 

[ClassicHonda50]

Hi lifelessurf

I am from Cessnock as well, which local shop did you go to?

I take my bikes and our customers bikes to Nigel Pitsch, he runs the dyno in town and is familiar with the YX160:

If you have no luck sorting the problem out give Nigel a call, he is a very handy man to have so close. Here is an article about Nige from a few years ago.

Nigel Pitsch, a brief history -

I began my working career as a fitter and machinist in 1976, gaining my trade certificate in 1979. I worked in heavy industry until 1983 during this time I gained several post trade quals. from 1983 on I decided to go fully into motorcycles which has been my passion for most of my life, from the time I owned my first bike in my early teens.

I started my first motorcycle job at Ron Fordham Motorcycles in Gosford, in a partnership arrangement where we subcontracted the workshop services; I was there for 2 years.

From there I decided to learn more about the engineering side of motors so I worked at a small engine reco shop, called The Bug Factory. I built some interesting stuff there; several convertible Volkswagen Beetles and some really hot motors. It was a great place to work but it was time to get back to bikes, so I bought Redline Motorcycles at West Gosford from Bill Mitchel who was moving north in 1988. The business specialized in BMW motorcycles. We had contacts with the Police Dept and we serviced and repaired their bikes from Gosford and the North Shore areas of Sydney.

I sold that business in 1991 and moved back to Cessnock to live in Ellalong, close to family. During this time I started Pitstop Motorcycles in Cessnock Street, renting space from Steve Kervin for 2 years.

An opportunity came along and I moved to Cessnock Motorcycles to subcontract the workshop services until 2000, with a change in ownership affecting my arrangement and new tax laws causing problems with subcontractors, I move again back to Cessnock Street with Cross Country Action now operating from the address where I had been some years back.

I started a dyno service there and during this time I was able to get involved with “Supermoto Racing” turning spanners for Mark Avard. I worked the European season in 2001 with the Hussaberg factory team then 2002-03 with Pacifico Corona a beer company, then in the USA.

In 2004, 5 and 6 I worked with GP Motorcycles of San Diego but the hectic pace and too much air travel caught up so I retired from the US Supermoto scene.

This year I’m back into road racing with Fraser Bros Racing in the OZ Superbikes acting as tech/crew chief etc, our rider just won the OZ B grade title last weekend but unfortunately it came at a price, a busted collarbone.

So that’s about it working on bikes has been the biggest part of my life. I’ve been fortunate to work on a number of factory race teams for Off Road, Motocross, Supermoto , and also satellite teams in Road Racing. I count myself privileged that I have a job that after 24 yrs I still enjoy and look forward to what each day brings. NP ■

Remember I told you guys I’d spent over $1300 on my K at one of our “top dealers” and their “top mechanic” wasn’t able to sort out the backfiring; under filled the oil & coolant then recommended I dump my radio. Nigel is the bloke who diagnosed a cracked header in less than 30secs; drew my attention to a severe lack of oil and had the radio working in a few minutes. Yay Nigel. You Da Man. ED ■

Cheers

Jaimie

 

[Cactus Jack]

If its a stock YX160 with stock cam, try 37 pilot, needle clip second from the bottom, 98 Main jet (Or even a 96, just depends how hard you are going to rev it) and air screw 1 1/2 turns out.
Make sure valves have correct clearance, and a clean air filter and clean sprak plug.

A glowing red pipe would indicate a lean mixture. And a 36 is too small for a 160

I have a stock yx160 and have just been through this process, and everytime I mod something, the jetting changes. a port matched and cleaned manifold and port matched and cleaned exhaust will need a 38 pilot, and with the daytona ignition advance I'm now back to 100 main.

You will need a jet kit and anyone thinking that you can tune or adjust a carby without a range of jets it kidding thesmselves. I personally carry 5 of each jets and have a log book for different air temps, different mods and different engines so I know what has worked and what hasn't so I can continually improve my jetting, to get it spot on for different conditions.

That's telling it how it really is Barnsie ... you can't get any more accurate than that ... :grinning-smiley-003

As for valve lapping , I only showed that Japanese guy doing a "Pops Yoshimura" valve lap job for a joke ...

Here's the proper way to do it ...

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Lapping and blue checking the valves and seats gets engines running as smoothly and as powerfully as the possibly can ...

 

[Cactus Jack]

hey everyone ive been workin on the bike and this is what ive done, i done the valve clearance they were definately too tight i saw a video on youtube sayin that the top valve should 0.004 and exhaust valve 0.006 so i did that instead of 0.003 top n 0.004 bottom. i then tightened up the o ring on the adapter which attaches the carby to the manifold. which had a small gap on each side so i siliconed around the edges of the pipe to fix any leaks. i didnt do the exhaust gasket because i didnt think it really needed it from previous experience with engines ive had an engine doesnt actually need a exhaust at all so i thought a small leak would not come into this type of problem.anyway i started the bike and it sounded a bit lumpier and the carby dont pop any more nor does it run as hot as it was before which had the pipe glowing red. i started working on the idle screw and air screw to get it idling right. i.

That info verifies that the popping problem was indeed caused by blow back thru the inlet tract due to an inlet valve leak ... The engine sounds "lumpier" and idles better because it's now getting a denser F/A charge and is getting it's max compression ...

Valve clearances can be tailored to suit the needs of the rider ... An engine that's used sedately can get away with the minimum specs ... but an engine that's going to be thrashed and heated up needs slightly extra clearance ... It won't cause any harm ... but additional tappet noise can bug some people ...

At the end of the day too little clearance will cause more problems and damage than a slightly larger clearance ...

As Sean and I have stated in previous threads increased valve clearance slightly reduces overall valve lift and duration ... minimum clearance gives max lift and duration ...

 

[lifelessurf]

Hi lifelessurf

I am from Cessnock as well, which local shop did you go to?

I take my bikes and our customers bikes to Nigel Pitsch, he runs the dyno in town and is familiar with the YX160:

If you have no luck sorting the problem out give Nigel a call, he is a very handy man to have so close. Here is an article about Nige from a few years ago.

Nigel Pitsch, a brief history -

I began my working career as a fitter and machinist in 1976, gaining my trade certificate in 1979. I worked in heavy industry until 1983 during this time I gained several post trade quals. from 1983 on I decided to go fully into motorcycles which has been my passion for most of my life, from the time I owned my first bike in my early teens.

I started my first motorcycle job at Ron Fordham Motorcycles in Gosford, in a partnership arrangement where we subcontracted the workshop services; I was there for 2 years.

From there I decided to learn more about the engineering side of motors so I worked at a small engine reco shop, called The Bug Factory. I built some interesting stuff there; several convertible Volkswagen Beetles and some really hot motors. It was a great place to work but it was time to get back to bikes, so I bought Redline Motorcycles at West Gosford from Bill Mitchel who was moving north in 1988. The business specialized in BMW motorcycles. We had contacts with the Police Dept and we serviced and repaired their bikes from Gosford and the North Shore areas of Sydney.

I sold that business in 1991 and moved back to Cessnock to live in Ellalong, close to family. During this time I started Pitstop Motorcycles in Cessnock Street, renting space from Steve Kervin for 2 years.

An opportunity came along and I moved to Cessnock Motorcycles to subcontract the workshop services until 2000, with a change in ownership affecting my arrangement and new tax laws causing problems with subcontractors, I move again back to Cessnock Street with Cross Country Action now operating from the address where I had been some years back.

I started a dyno service there and during this time I was able to get involved with “Supermoto Racing” turning spanners for Mark Avard. I worked the European season in 2001 with the Hussaberg factory team then 2002-03 with Pacifico Corona a beer company, then in the USA.

In 2004, 5 and 6 I worked with GP Motorcycles of San Diego but the hectic pace and too much air travel caught up so I retired from the US Supermoto scene.

This year I’m back into road racing with Fraser Bros Racing in the OZ Superbikes acting as tech/crew chief etc, our rider just won the OZ B grade title last weekend but unfortunately it came at a price, a busted collarbone.

So that’s about it working on bikes has been the biggest part of my life. I’ve been fortunate to work on a number of factory race teams for Off Road, Motocross, Supermoto , and also satellite teams in Road Racing. I count myself privileged that I have a job that after 24 yrs I still enjoy and look forward to what each day brings. NP ■

Remember I told you guys I’d spent over $1300 on my K at one of our “top dealers” and their “top mechanic” wasn’t able to sort out the backfiring; under filled the oil & coolant then recommended I dump my radio. Nigel is the bloke who diagnosed a cracked header in less than 30secs; drew my attention to a severe lack of oil and had the radio working in a few minutes. Yay Nigel. You Da Man. ED ■

Cheers

Jaimie

hey there i went to ming n 50's the tuner there rekon i should rub back the needle 1 thou of a mm but not being so mechanically minded like that i decided not to and alot of other people told me not too also since they are a decent needle(jjh). as for nigel ive done a few deals with him before with cross country which was his business in cessnock st. hes actually good mates with one of my friends dad at ellalong you might know him steve smaller... hes also a really good bloke that knows a hell of alot bout bikes. ive ordered a jetting kit for this w.e but if that goes to **** i might give him a call. be interesting to see what my bike puts out and what the ratio of air to fuel is.

cheers mate

 

[lifelessurf]

If its a stock YX160 with stock cam, try 37 pilot, needle clip second from the bottom, 98 Main jet (Or even a 96, just depends how hard you are going to rev it) and air screw 1 1/2 turns out.
Make sure valves have correct clearance, and a clean air filter and clean sprak plug.

A glowing red pipe would indicate a lean mixture. And a 36 is too small for a 160

I have a stock yx160 and have just been through this process, and everytime I mod something, the jetting changes. a port matched and cleaned manifold and port matched and cleaned exhaust will need a 38 pilot, and with the daytona ignition advance I'm now back to 100 main.

You will need a jet kit and anyone thinking that you can tune or adjust a carby without a range of jets it kidding thesmselves. I personally carry 5 of each jets and have a log book for different air temps, different mods and different engines so I know what has worked and what hasn't so I can continually improve my jetting, to get it spot on for different conditions.

yeh its a stock 160 with the lightened fly wheel the jet kit i bought has a 35 38 41 pilot i should get it by friday

 

[lifelessurf]

hey boys just letting you all know i got it going good now it was the jetting holdin it back i had a 100 in there but it needed a 102 and now it is doing the same thing with the dead spot round 1/4 throttle so im guna change the pilot to a 37 so all is good must say unless you know how to change jets in a carby i wouldnt suggest buying one of these very touchy lil thing goes good but once youve got it