Raw40

can someone please help have just rebuilt my thunder tiger pro .15 motor and fitted a new novarrosi slide carb. Have set all of the carb basic settings ( had them off the Paris racing site as suggested on an earlier post) the motor will not idle at a low enough idle speed even if I turn the idle speed screw below its minimum setting. I think the motor is drawing air ( induction leak) through the front or main bearings, have sealed the carb and backplate, and then sprayed WD40 on the front bearing whilst the motor is running to try and identify the problem. Motor slowed to an acceptable level and then cut out. Is this a common problem and is there any way I can seal the front bearing cranck area to cure the problem.

Sydewynder

There is no way to seal the front bearing since it needs to spin freely. You need to replace it if you suspect that it's bad. Is fuel leaking out of the front bearing?

Can you adjust the idle speed screw till the opening in the carb is closed? I ask because you mentioned below the minimum setting. You should be able to get the opening completely closed.

Raw40

Hi sydewynder, yes I am able to close the slide all the way down and I have noticed oil/ fuel leaking from the front bearing onto the rear belt after a run.

Sydewynder

Hello Raw40

So you can close the carb opening all the way and the engine seems to be able to run and draw air in from somewhere? Checked the o-ring on all the needles plus the idle stop screw to see if any are cracked or damaged.

If there is excessive fuel leakage then I think you need to replace the front bearing. You should be able to tune the engine to run well with little or no fuel/oil leaking.

Is there much in and out and side to side play in the crankshaft when you wiggle it? (Engine not runnng please )

Raw40

Hi sydewynder, yes I have checked the O rings on the jets etc all seem to be ok, the axial endfloat on the crank is 0.007", radial is 0 the bearing looks as if it's in a reasonable conditon apart from having a steel dust seal would it be better if I try and get a bearing with rubber seal?

Sydewynder

You can use rubber sealed bearings but someone who's an engine guru here (Motorman) said he's seen some where the rubber seal piece heated up and seized onto the crankshaft causing the shaft to fail. Even so, many manufacturers are using rubber seals now so I would give it a try. I looks like you've determined the bearing is bad by the WD40 spray test. Did you do a similar test on the backplate and carb?

Btw way, how's the crankshaft? The area around the front bearing and the journal where the window is? Is the journal damaged. Some engines such as the Novarossi design the crankshaft to help prevent oil leakage and maybe air leak.

Distroey

if there isn't a brown mark on the crank where the bearing would rest i doubt its the bearing. Also there should be oil coming out of the front bearing, not alot but some.