Engine cutting WFO

[Baja_Crazy]

Hi all im seeking some help regarding a frustrating problem

 

So i took the 5b out all was fine everything running perfect. abouth 15 min in it then suddenly it died while it was wide open initially i thought it seized but that wasn't the case.
she wouldn't start so i closed the low and she fired opend jet again fired as normal so it flooded its self.

then it proceed to do this five or so times.

 
so i checked the plug was spot on but put a new one in anyway
checked tank breather
killswitch  
air purge/ bulb on carb was full so i don't think its heat soaking.

 

out of that got nothing, went home crimped the connectors on the coil re attached checked it over 
Next day went out again it was perfect for the entire outing.

went out this evening and the same happend it once again cut out around 10 min into the run at WOT and decided to it multiple times

 

any and all help is much appreciated.

[daddy woo]

now I'm just guessing but as you seem to think that it's flooding I'm thinking maybe a little bit of crap has got in the diaphragm valve and is sticking one or other open, or maybe the coil is failing and starting to break down when hot?. As i say I'm a bit of a newbie to large scale so just a guess but Have been around motorbikes for a long time so hopefully I can be of some use!!

[Fly In My Soup]

On 24/10/2017 at 18:33, Baja_Crazy said:

Hi all im seeking some help regarding a frustrating problem

 

So i took the 5b out all was fine everything running perfect. abouth 15 min in it then suddenly it died while it was wide open initially i thought it seized but that wasn't the case.
she wouldn't start so i closed the low and she fired opend jet again fired as normal so it flooded its self.

then it proceed to do this five or so times.

 
so i checked the plug was spot on but put a new one in anyway
checked tank breather
killswitch  
air purge/ bulb on carb was full so i don't think its heat soaking.

 

out of that got nothing, went home crimped the connectors on the coil re attached checked it over 
Next day went out again it was perfect for the entire outing.

went out this evening and the same happend it once again cut out around 10 min into the run at WOT and decided to it multiple times

 

any and all help is much appreciated.

 

Seems like you've covered the basics......

 

I too thought the same as daddywoo, as in you've sucked crud/foreign objects up the fuel line where they've lodged in your carb jets or diaphragm....

 

But....if that was the case you would have the symptoms you have from a cold engine(I have personally experienced this) not solely when warm.

 

My thinking is your running lean at wot... the symptoms predominantly present themselves when the engine is warm when running but also has the symptoms of ...only idling when choke on, running really hot, foul smell from exhaust fumes (n2o)

 

My suggestions :

 

- tune her when she's warm (five or so minutes) by turning both your L + H needle out (richer) 1/16th of a turn.

 

- try fresh fuel mix

 

- tighten your head/ case bolts 

 

- try spare carb ( a must have item for your toolbox)

 

- re gasket the entire engine inc. carb etc etc to rule out an air leak

 

If none of that work, I would re ring the piston, if that doesn't work I'd then look for a new head!

 

Heres some tips from a moto X site about different symptoms

 

Lean

• Reduced Power - Sluggish at certain RPM's. Wide open throttle yields no power. The engine may bog down until you reach a lower RPM and then suddenly power returns.

• Difficulty Starting

• Spark plugs are clean - No residue. Insulator may be white.

• Runs better at higher altitudes - AFR becomes normalized due to reduced atmospheric pressure allowing fuel into the venturi easier.

• Backfires - Popping on deceleration for a lean idle circuit or backfires in general.

• Runs on choke - The vehicle may run on choke when it's warm but stalls if the choke is turned off.

• Idles poorly - Fluctuations in idle RPM, stalling

• Engine runs hot - Due to more oxygen than fuel combustion temperatures are hotter reflecting on a temp gauge.

• Hanging idle - The engine idles high and then drops and stalls. Typically a lean condition caused by an air leak between the butterfly and the head or a vacuum line that is not attached.

• Sharp Odor - The exhaust smell may be sharp and burn your nose. This is NOx or Nitrogen Oxide. It's created by high temperatures in the combustion process between nitrogen and oxygen. Although NOx is present in all exhaust it can be more pronounced in higher combustion temperatures associated with lean conditions with more oxygen. More oxygen=higher burn temp

Rich

• Reduced Power - It has less power but seems to be OK and runs.

• Reduced Fuel Mileage - Your using more fuel per cycle so your mileage becomes worse.

• Rough Idle - Combustion takes a just a bit longer with more fuel and at lower RPM's the engine can idle rough. Unlike a miss-fire on a spark plug this idle seems fine if the idle is turned up just a bit.

• Spark Plugs Black - Carbon buildup on insulator and electrodes of plug. Wipes off your finger as sooty and back. Carbon is a conductor of electricity and getting considerable carbon buildup from a rich condition with ground the inner electrode down the positive insulator. When this condition occurs there will be no spark. You can clean the sparkplug with carburetor cleaner and re-use.

• Exhaust Exit is Black and Sooty - Excessive carbon buildup in the exhaust is thick and overly grimy. A properly jetted carburetor will leave a nice grey scale color in the end of the exhaust pipe.

• Odor of unburned fuel - In cases of a very, very rich mixture you may smell some unburned fuel coming out of your exhaust. This could be due to a grounded out sparkplug from too much carbon buildup preventing the combustion process in a cylinder or so much fuel that combustion is not occurring.

• Runs better with more air - If you remove your air filter and the engine begins to run a bit better with more oxygen in the mix it is likely you have a rich condition.

• Runs worse at altitude - If the bike starts to run worse at higher altitude with reduced oxygen, it's likely a rich condition.

• Black Smoke - If you have black exhaust when you rev it, it's rich. You can get a light colored rag and place it over the exhaust lightly and rev it to see if you get carbon/black residue on the rag.

[Baja_Crazy]

21 hours ago, daddy woo said:

now I'm just guessing but as you seem to think that it's flooding I'm thinking maybe a little bit of crap has got in the diaphragm valve and is sticking one or other open, or maybe the coil is failing and starting to break down when hot?. As i say I'm a bit of a newbie to large scale so just a guess but Have been around motorbikes for a long time so hopefully I can be of some use!!

 

never thought of that, i have a carb kits on the way and will be rebuilding it as i do every certain amount of hours as it is 

re the coil has had heavy use well over 140 hours on it. Im going to test the spark and (voltage if possible) at different temps.

 with the flooding i believe as it cuts its still does x amount of strokes before it stops so with the ignition cutting its not burning the fuel that is delivered under the revolutions while its not igniting   

 

thank you for the reply and help. i greatly appreciate it 

Edited October 27, 2017 by Baja_Crazy

[Baja_Crazy]

18 hours ago, Fly In My Soup said:

 

Seems like you've covered the basics......

I too thought the same as daddywoo, as in you've sucked crud/foreign objects up the fuel line where they've lodged in your carb jets or diaphragm....

 

But....if that was the case you would have the symptoms you have from a cold engine(I have personally experienced this) not solely when warm.

My thinking is your running lean at wot... the symptoms predominantly present themselves when the engine is warm when running but also has the symptoms of ...only idling when choke on, running really hot, foul smell from exhaust fumes (n2o)

 

My suggestions :

 

- tune her when she's warm (five or so minutes) by turning both your L + H needle out (richer) 1/16th of a turn.

- try fresh fuel mix

- tighten your head/ case bolts 

- try spare carb ( a must have item for your toolbox)

- re gasket the entire engine inc. carb etc etc to rule out an air leak

If none of that work, I would re ring the piston, if that doesn't work I'd then look for a new head!

 

 

 

Thank you for the reply and help i greatly appreciate it

 

Im almost certain Im not lean as it it would of locked up by now but still not ruled out.

the thing is its not doing timed/ fairly equal intervals when cutting either sometimes she will do 3-5 15 second passes wide open without battering an eye lid. but then it could cut as it hits 3/4 open around 16K revs and then proceeds to die. 

 

With jetting i fully readjust every outing once finished a run i back the high needle out a 1/4 turn.

hopefully i will get out tomorrow and i wont jet to the brink.

 

I'll make up a new mix tomorrow.

I will re torque all bolt to spec.

Shameful i know but unfortunately don't have a spare carb laying around besides a new WJ71.

Doing an entire gasket set will be the last to do from the above. But will vissualy inspect them including the oil seal 

I checked my compression around six running hours ago and it was almost spot on ( normally i check every five hours on my CY/Zenoah's) so i will check as soon as. I believe i have 36mm Zen ring hide away with  some gaskets kits.

 

its had one ring replaced in its lifetime of coming up 40 hours  which had no where near as much hours on compared to my standard top ends. so it may well could do with a ring 

 

        Thank you for the reply and help i greatly appreciate it

 

 

Edited October 27, 2017 by Baja_Crazy

[Baja_Crazy]

So i managed to get out today and once again 10-15 min in it stated cutting out 

i went over ll the coil and kills switch again 

 

for some reason i think its the battery going to pick up a cheap battery and try.

im gong to test the battery voltage at work tomorrow and see