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Old 02-20-2008, 03:33 AM   #1
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Default XB8EC with Novarossi Plus21-5KT HELP! Engine problem.

I have an XB8EC and Plus21-5KT. I bought it second hand with only a couple of litres through the motor. It was great for about 1.25 gallons, then it went bad. It mostly runs badly - I am always chasing a tune. Sometimes it runs great for a few minutes, then I can't get a tune again. It always flames out after a few minutes running. It is VERY frustrating. If I knew what the problem was, I could just fix it!!

I have changed both bearings, the conrod, fuel tank, exhaust gasket, air filter, cleaned the carbie and crack tested the block/crankcase. Still has the same problem.

Can anyone help me??

The only thing I can think of is that the old front bearing had a plastic outer seal and I replaced it with a metal outer seal.
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Old 02-20-2008, 04:02 AM   #2
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I think you need to replace that front bearing.
The metal is just a dust shield and not a seal.
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Old 02-20-2008, 06:24 AM   #3
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This is what you need to do to an engine to save your self time and keep your smile!!
Put silicone around the carb neck, back plate, carb boot.
Remove all tuning screws except the idle screw...and put white teflon tape on the threads (around 4-5 turns).
Put silicone around the carb grab screw from both sides.
When installing the flywheel cone on the crankshaft put a very small amount on the side it will touch the bearing...this will seal the area between the bearing and crankshaft.

Now the simple part:
-Check the engines compression
-Change glow plug
-Check how old is your fuel you use
-Check the head screws and tighten up
-Open all needles and retune from the beginning.
-Check what "rageworks" said...metal shielded bearings are no good.
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Old 02-20-2008, 06:48 AM   #4
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I would definitely check the front bearing. Remove the engine, block the exhaust port and carb inlet with your fingers. Take long fuel hose connected to the carb, and screw the HSN out till its about 1-1.5 mm above the brass collar. Blow into the fuel hose while holding the carb barrel open and see if you feel any air blowing out the front bearing or any where esle for that matter. A lot of the metal shielded bearings will leak once the grease washes away from the race, specially the one side shielded ones.
Did the bearings go out on this engine while running or just replaced?
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Old 02-20-2008, 07:42 PM   #5
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put a rubber sealed front bearing back in it , not so much for air leak but for shielding the inside of your engine from the dirt !!! metal shields are for higher rpm onroad engines did you pull all the orings out of the block when you heated up the block to change the bearings out ? if not , replace them with new orings , when installing the orings put some oil on them (rbmods synthetic after run oil) . check rod slop , make sure crank journal is within tolerance and not out of round , make sure rod is installed the right direction (tapered fit on bottom bushing goes towards crankchaft), make sure you put the right head shims back on the head button when you installed it , make sure a wrist pin clip didnt come out and scratch the piston and sleeve , above all , if there is no pinch left in sleeve , get a new one
bottom line ; all anybody can do online for ya is to offer suggestions based on experiences they have had or seen in the past .
good luck ,
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Old 02-21-2008, 04:05 AM   #6
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Originally Posted by ezveedub View Post
........Did the bearings go out on this engine while running or just replaced?
I just replaced them to try to fix the problem with the engine not running well.

Thanks everyone for your help. I will put the plastic sealed front bearing back in, replace the o-rings and check for leaks.

I have already tried a new glow plug, and my fuel is a couple of months old (I am carefule to only open the fuel container when I am refilling my fuel bottle).

The engine has compression, but I will pull the sleeve and piston out and check whether the piston fits through the top of the sleeve.

I will keep you all posted with progress.
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