Slipping gear? Maybe bad valve adjustment?

[member43148]

Cool video.
I don’t actually use the tdc mark to check clearances.
I watch the cam lobe back side and find the most loose clearance position and note that orientation.
Only rotate in engine run direction from there and make several revolutions confirming clearance gap.
I like .003 / .004 - on intakes.

 

[Jim]

With the plugs out, rotate the crank slowly CCW. As you approach the TDC mark, you'll start to fall into what's called valve overlap. When you get slightly past the peak on one valve (the exhaust), the spring from that valve will pull the cam down into the valley of the overlap.... one valve closing, the other opening. The crank will come to a stop there and it'll take a bit more force on the wrench to start rotating again. Don't continue, stop right there... where it naturally want's to stop. Now if you look at the timing, you'll be within a handful of degrees one side or the other of TDC. Close enough! Now, set the valves on the opposite cylinder... the one that didn't fell into the overlap valley. Pretty simple really, it sets itself in the right place and stays there.

Rotate the crank one full revolution and set the others and Bob's your uncle.

 

[Jim]

Just watched the video. On the first valve, it took a bit of a push for the feeler to pop in 'tween the valve and the adjuster. That's a little too tight. You want the feeler to slide in fairly easy and just feel a slight drag as you slide it in and out (quiet down in the back).
Looked to me like the drag was a bit more than "slight."

The rest of the video was pretty much unwatchable, so I couldn't tell much else about your technique..... I said quiet down in back...

 

[Jim]

Case you were wondering why clearance is important...

The amount of clearance determines the degree (at the crank) where the valve will close. The intake valve is closing as we start into the compression stroke. A smaller clearance at the rocker means the valve will stay open slightly longer. Remember, we're on the compression stroke. With the intake still open, we ain't compressin' squat. Compression starts when both valve close and not before. So this leaves less time (degrees of rotation actually) for compression.... and our compression ratio suffers as a result... enough to make a difference between good power and not so good power.

The exhaust clearance can have the same affect because it opening early robs degrees of rotation from the power stroke... so our bang for buck isn't contained as long and power suffers.

 

[Owen8]

Just for clarification, I’m not setting the valves at TDC? I set them individually, when the opposite valve falls into the valve overlap valley? Should that valve feel loose? I’m going to give it a try today.

 

[Jim]

Yes, TDC. The overlap "valley" happens within 5 or 10° of TDC. close enough for valve adjustment. When one side is at overlap, the other is at compression. Both are a TDC (360° crank).

Put one side at the valley and adjust BOTH valves on the other side, rotate 360° and do the other side.

 

[Owen8]

 

[Jim]

Yes, that's the side you adjust... but there's an easier way to get there.

As you rotate the crank ccw, watch the exhaust valves. One ex valve will open... and as it starts to close, the intake will start to open. That's the point where it's stuck in the overlap valley.
So watch the exhaust. When one opens and then starts to close, you're in overlap. Do the valves on the opposite side.... the other cylinder.

 

[Owen8]

 

[Jim]

Yes. In that vid you are wiggling the left cylinder valves.... those are the ones you adjust... yes.
Then rotate one full revolution and do the other (right) side. Then rotate again and "recheck" the left. Then rotate again and "recheck" the right.

 

[AUTOMAN]

Hmm. Watching with popcorn here.

 

[Owen8]

Ok! What gap would you say is ideal for Intake and exhaust? I’ve been doing a ton of research and everyone seems to have fix feelings about the intake and if it should be set at .004 or .003… I’ve even seen people say .0025

 

[Jim]

.003" intake
.006" exhaust

That's pretty much the universally accepted clearances.

 

[Owen8]

Didn’t help any of anything made it worse… it’s sputtering now and when I shifted it into neutral and tried to go down my drive way it was struggling to roll down it… I don’t know what that means exactly

 

[Owen8]

I read a thread of some fella with a xs400 and he resolved a similar issue by replacing his pickup coils… any thought on this? I’m certain my valves have been set perfectly but now the bike just keeps getting in worse and worse shape the more I fool with the valves…

 

[member43148]

Will your bike start up and idle off choke warm?

 

[jetmechmarty]

I read a thread of some fella with a xs400 and he resolved a similar issue by replacing his pickup coils…

A 1978 XS650 does not have pickup coils. Has this bike been converted to electronic ignition?

 

[Wingedwheel]

Has the timing been checked?

 

[Owen8]

Yes it has been converted to an electronic system… not sure what the brand is as it was on the bike when I bought it. I don’t have a timing light so I have not checked the timing either…

 

[Its been a long time]

Yes it has been converted to an electronic system… not sure what the brand is as it was on the bike when I bought it. I don’t have a timing light so I have not checked the timing either…

Post a couple if pictures of the pick ups and the igniter. Likely someone can tell you what you have. If the bike runs, definitely a good idea to check the idle speed timing and the advanced timing. Use a timing light.