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1

Ask the gurus / Re: Erratic revs

« Last post by CX PHREAK on Yesterday at 13:23 »

Leak down test has to be performed at TDC compression stroke - the same point that you would do the clearance adjustment.

Get all rockers on the rock and do the test there.

2

Ask the gurus / Re: Erratic revs

« Last post by gm on Yesterday at 10:47 »

thank you again
after a bit of mucking about we found TDC before power stroke (tell me if that is the wrong terminology) all valves were closed I rechecked valve clearances all good after a minor adjustment.
We then proceeded to BDC before compression stroke with both valves closed tried the leak down test and could feel air coming out of the exhaust header no air out of the inlet.
I'll tighten again and recheck the compression although it would seem the LHS exhaust valve May be the issue.
gm

3

Ask the gurus / Re: Erratic revs

« Last post by Seagrass on Yesterday at 07:58 »

If you think you had the valve clearances wrong try the compression test again and see what results you get.

Seagrass

4

Ask the gurus / Re: Erratic revs

« Last post by gm on 17-Apr-21, 17:25 »

Thanks CX PHREAK
You were correct.  After going through the cycles a few times I figured where the TDC on the exhaust stroke was and adjusted the clearances appropriately.
I'll get back to attempting the leak down test and see if I can find the problem. 
I still think it will be a valve issue.
thanks again
gm

5

Ask the gurus / Re: Erratic revs

« Last post by CX PHREAK on 17-Apr-21, 16:11 »

I think that is your problem. Verify that you are on the compression stroke on that cylinder and readjust the clearances.

Or you are on the wrong stroke now and the exhaust valves are open. Rotate one full turn and recheck. If the clearance is now normal you are {were} on the exhaust stroke. Or the gap is big from your readjustment. There are 2 TDCs in a 4 stroke cycle as they rotate twice to go suck, squash, bang, blow.

If it's not that you may have burned the valves and as they recede into the head they move up taking up the adjustment.

Rotate it through the cycles turning clockwise from the front a number of times and observe what is happening.

6

Ask the gurus / Re: Erratic revs

« Last post by gm on 17-Apr-21, 16:08 »

Hello Gurus
Its getting colder yes. 
I think I may have the wrong title on this thread, it might have been better being named erratic bike.
After a quick chat to Seagrass I attempted to perform (I think its called a Leak down test) to see if the valves were leaking air.  Before I positioned the piston at BDC just before compression stroke I thought I'd start at TDC and watch the pistons go through their movements.  While at TDC I checked the valve clearances and found the exhaust valves were now very tight and no matter how much adjustment to the tappet screw I cannot put a feeler gauge in.
is this another issue or have I done something wrong?
gm

7

Ask the gurus / Re: Erratic revs

« Last post by gm on 15-Apr-21, 12:13 »

Hi again
I checked the valve clearances and all are within the correct spec.  also checked if they were moving as the wheel was rotated and that was positive.
The plugs have had a tendency to clog up relatively quick say 4-6month (when it was being used regularly) so would you think it possible that one or some of the valves are blocked open by carbon or muck building up?
The readings do seem low although the left one seems consistently low which would account for it not firing.  This whole issue of the left side not working occurred after a long period of inactivity (12months) could that have caused any of these problems?
always grateful for your advice.
gm

8

Ask the gurus / Re: Erratic revs

« Last post by Seagrass on 14-Apr-21, 19:06 »

Those figures are so low on the left side that you must have a valve not sealing or a blown head gasket or maybe something else.

Even the right hand cylinder is a bit low, I would have expected around 165 psi

 Check your valve clearances and make sure there is a gap on all valves.

Seagrass

9

Ask the gurus / Re: Erratic revs

« Last post by gm on 14-Apr-21, 18:27 »

Thanks Seagrass
sorry for the delay (the compression tester broke)
 
I tested again with the new tester, throttle open;
Left cylinder       5psi dry       7psi wet ;
Right cylinder 120psi dry    135psi wet. 

Similar result in that the Left does not seem to be sealing.

10

Ask the gurus / Re: Erratic revs

« Last post by Seagrass on 09-Apr-21, 17:52 »

Did you open the throttle fully while doing the compression test? If not do it again with throttle wide open.

Seagrass

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