GT380 Timimg....

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Dbailey
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Joined: Tue May 22, 2018 8:37 pm
Location: Portsmouth UK

GT380 Timimg....

Post by Dbailey »

All... looking for some guidance / confirmation of the process I’m following...

Setting / checking Timing...

Book states set piston @ TDC and set the points gap for that cylinder @ 0.35mm then back off the piston to 3mm BTDC checking when the points close. If they close too early rotate the complete assy to adjust , too late move it the other way. What I’m confused about is if @ tdc the points should be opening to the max I.e on the crown of the cam surely you rotate the backplate first to make sure the points are fully open... or do you ignore this and move the backplate @ 3mm BTDC to find the close point then recheck the gap @ TDC...

I’m starting with the right hand cylinder which seemed as good as any...

Any advice would be good.

Thanks
Dave Bailey
teazer
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Re: GT380 Timimg....

Post by teazer »

My way is to throw away the points and replace with electronic ignition, but that's not what you asked.

First rotate the motor until points are fully open. Set the gap on that set and repeat on the others. Do not move the backing plate at all when setting gaps. Your points may be fully open at TDC but that's not relevant to anything, so I ignore that part. Just get the points gap set when they are fully open.

Then do the timing. I think that one set is fixed, so you do that one by moving the backing plate. Then set the timing on the other two by moving them on the plate.
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Alan H
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Re: GT380 Timimg....

Post by Alan H »

NEVER EVER turn the engine backwards when timing.
Proof that four strokes are over complicated
Dbailey
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Location: Portsmouth UK

Re: GT380 Timimg....

Post by Dbailey »

O too late.. I put it in 6th and dropped back from TDC to 3mm before.. so what could I have screwed up?
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Alan H
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Re: GT380 Timimg....

Post by Alan H »

It's just backlash on the points which will affect tbe timing. Just turn forwards in the correct engine direction using a spanner on the points cam end nut.
Proof that four strokes are over complicated
Dbailey
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Joined: Tue May 22, 2018 8:37 pm
Location: Portsmouth UK

Re: GT380 Timimg....

Post by Dbailey »

Alan thanks.... Well the afternoon has certainly been interesting.. The bike runs but is down on power I think.. Compression is all good @ about 120 PSI for each cylinder, Starts mostly on first kick and the new plugs that have only done 60 or so miles are a browny colour. I though the next thing to check was the points and the timing...

So Left cylinder @ TDC and I looked @ the points.. Apparently they should be fully open at this stage but they are nowhere near fully up the ramp of the cam so I didn't see the point of setting them @ this stage however if I did it might help the BTDC points position. . I then went to 3mm BTDC and checked the points to see if they were just closed although I did this by reversing the motor with teh back wheel in 6th which thanks to Alan I now know is wrong. No matter how far I rotate the main timing plate for the fixed points the gap does not even start to open on the full range of the slot. At this point I put the plate back to where it was and thought I need to get some advice or at least think about it a bit more.

Below is the picture of TDC and the position of the CAM for the left cylinder which is nowhere near fully open. Left points left cylinder top point Right Cylinder I think....

Image
Dbailey
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Location: Portsmouth UK

Re: GT380 Timimg....

Post by Dbailey »

Just in case the other image didn't work....

Image

Thanks
Dave B
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mizzytheman
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Re: GT380 Timimg....

Post by mizzytheman »

When adjusting the ignition timing on a GT380 you should rotate the engine from the rotor side of the engine otherwise the backlash will be in the opposite direction.

You also risk damaging the nylon cog that drives the points cam if you rotate the engine by using the nut that is fixed to the end of the points cam.
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Alan H
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Re: GT380 Timimg....

Post by Alan H »

Less strain on that with the plugs out, but yes, gently does it anyway.
Proof that four strokes are over complicated
Dbailey
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Joined: Tue May 22, 2018 8:37 pm
Location: Portsmouth UK

Re: GT380 Timimg....

Post by Dbailey »

So plugs out and 6th gear then rotate the rear wheel in the direction of forward travel is not ok?

Also any thoughts on the cam position picture?

Thanks
Dave Bailey
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