Too much advance

feliz · Posted: June 20, 2009, 11:28 pm Post subject: Too much advance

I've done a search but can't seem to really find and answer other than to check the springs and they look OK. I did my valves, points, timing, changed plug caps, wires and plugs, did the cam chain and synced the carbs today. Anyway, when checking the advance it doesn't stop advancing, it goes right out of sight even though the springs look OK!! Any ideas? TIA. 650B if that matters.

dpmphoto · Posted: June 21, 2009, 12:48 am Post subject: Re: Too much advance

Did the bike run ok before all of this work?Did you check the plugs what do they look like ?or cam chain tension,or lose a bolt for the vacum port.did someone have the bike apart and advance the cam.Are you sure the carbs are sinked correctly warm bike and everything else done before sync. How did you sync them? Its hard to answer your question without some more info on the bike ya know some history it could just be way leaned out how far out are your mixture screws? are those original carbs?

feliz · Posted: June 21, 2009, 12:58 am Post subject: Re: Too much advance

Bike has 1000 miles on it, ran OK before and after, I just bought it and wanted to check everything. Timing and sync are right on, the timing mark just keeps advancing clockwise and goes way past the mark and out of site. I just went out and checked the mechanism and can't see how it can do that though, it's dark now and I can't run it, I'll take another look tomorrow.

Retiredgentleman · Posted: June 21, 2009, 1:23 am Post subject: Re: Too much advance

Where is the timing mark when idling at 1200 RPM?

weekendrider · Posted: June 21, 2009, 8:08 am Post subject: Re: Too much advance

The dogs/stops on the ATU plate wear and spread. The backs of the sling weights wear also. You might try new bob weights and springs.
Trying to peen/hammer the stops in will result in them breaking off. Resulting in melted pistons.

feliz · Posted: June 21, 2009, 11:49 am Post subject: Re: Too much advance

Timing at idle was right between the two marks. As you would expect from a low mileage bike all the ATU parts look brand new, can't see any wear at all. Thanks for the responses, I'll take another look at it today.

This is my first XS650, I've been restoring and riding Honda CB750s for years and my first impression of this bike is it's real easy to work on and not as fussy to tune but when initiallly riding it I noticed a distinct lack of it wanting to rev beyond about 4000. I just thought they were all that way but now I'm thinking it's due to the timing advancing out of sight at higher revs. Sound logical?

Another thing I was wondering is in all the articles about setting points they say to set one set, rotate 360 degrees and set the other. On my bike both sets of points open and close together, is this the way they all are? I've had British parallel twins that do this and the plugs just waist the spark every second stroke. All the instructions I've seen say they should open and close alternately on these bikes though.

I'll take anothe rlook at the timing today. Great forum and thanks.

pamcopete · Posted: June 21, 2009, 11:57 am Post subject: Re: Too much advance

feliz

It sounds like the PO installed one of MikesXS dual lobe cams, not realizing that the dual lobe cam is designed to work with just one set of points with a dual output coil.

feliz · Posted: June 21, 2009, 4:30 pm Post subject: Re: Too much advance

Bingo, that's the answer to the point issue. Wonder if it can harm anything or should I change it, it's only $15!! That shouldn't affect the timing though should it?

xsleo · Posted: June 21, 2009, 5:59 pm Post subject: Re: Too much advance

No, the dual lobe cam won't do as you describe. The too far advance sounds like the ATU is bad. The ATU should have stops that the wieghts hit, If they are missing or bent the timing will go over advanced.
When I got the 75 I have now the speedo read 1236 miles. I didn't believe it, easy to change the speedos. The wear on the bike indicated it had much more miles. after riding it a few monthes and it was using a quart of oil every 100 to 150 miles further indicated the miles.
I usually ignore the speedo if it has a low reading and look the bike over. If the rubber parts, foot pegs, shifter, grips. These parts hold up pretty well, if they show wear, lots of miles, When adjusting the timing chain, not many threads showing out of the adjuster, many miles.
yours may be a low mile bike if so great, just don't put to much stock in the speedo.
If you look close at the pic's on Mike's of a new ATU you can see what a new one looks like.
Can you post a pic of your ATU?

pamcopete · Posted: June 21, 2009, 6:01 pm Post subject: Re: Too much advance

xsleo,

The dual lobe suggesiton was for feliz's observation that both sets of points open and close at the same time.

dpmphoto · Posted: June 21, 2009, 6:13 pm Post subject: Re: Too much advance

Pamco good call.

xsleo · Posted: June 21, 2009, 6:16 pm Post subject: Re: Too much advance

He also asked if it would hurt anything and should he change it, and if it would effect timing. I was replying to those questions.

tacoswild · Posted: June 21, 2009, 6:43 pm Post subject: Re: Too much advance

If the stops on the advance are still there you could add some material to the inside of them so the weights stop sooner. I don't think you can add material to the weights themselves without throwing off the rate of advance. Should be possible to make it stop wherever you want by filling that space then filing back.

pamcopete · Posted: June 21, 2009, 7:39 pm Post subject: Re: Too much advance

feliz

Well, this could get complicated. If the PO installed Mikes dual lobe cam and left the stock points coils installed with therir respective points, then the coils will now be experiencing a 50% duty cycle instead of a 25% duty cycle and they will overheat.

If, on the other hand, the PO installed Mikles dual lobe points cam with the correct dual output coil, then he may have just negleted to remove one set of points. Some people do this so you always have a spare set already installed.

So, if in fact the bike was converted to Mikes dual lobe points cam with the correct coil, then what you could be observing is eratic strobe operation due to using the wrong polarity plug. A dual coil produces both a positive and a negative plug voltage...the strobe works best with the negative voltage...so, just try swapping the timing light to the other side.

You could also check under the tank to see if you have two coils or only one.

feliz · Posted: June 21, 2009, 7:42 pm Post subject: Re: Too much advance

I took a picture and I'll try and post it. I even inspected the advance mechanism with a magnifying glass and see no evidence of wear whatsoever and everything seems to function OK. I redid the points, cam chain, timing and carbs again today with the same result. The bike runs great but my only concern is that running at speed with the timing so far advanced can't be good for it. Thanks again to all the responders.

pamcopete · Posted: June 21, 2009, 7:46 pm Post subject: Re: Too much advance

feliz,

Go back one post...I think I was posting that at the same time you were posting your latest.

feliz · Posted: June 21, 2009, 7:50 pm Post subject: Re: Too much advance

Pamco, I have two coils, I know because I changed the plug wires yesterday. I too was concerned about the coil's duty cycle and overheating which is the only problem I can see with it. I've had british bikes that operate that way intentionaly with no ill effect.

Another thing I've noticed is that no one with these bikes seems to set the points using dwell, something I've always done with other bikes. I checked the dwell on both points today and it was exactly the same which means I did a good job at least setting the points the same, not saying the gap is correct though, just that they're the same.

kingwj · Posted: June 21, 2009, 8:25 pm Post subject: Re: Too much advance

Just a guess but there is a pin locating the points cam and also a pin locating the advance unit. I'd check to make sure the pin is in place on the advance.

xsleo · Posted: June 21, 2009, 8:53 pm Post subject: Re: Too much advance

From looking at the pics. I would say from the appearance of the bike the speedo is right, it looks great, wished mine looked half as nice.
Your ATU looks to be complete, no missing parts. I'm not sure what it might be. I'll keep track of this thread to learn something.

pamcopete · Posted: June 21, 2009, 9:29 pm Post subject: Re: Too much advance

feliz,

If one or both of the coils has the wires to the terminals crossed, then that would also produce a positive voltage to the plug wire associated with that coil and could result in erratic operaiton of the timing light.

Do both cylinders exhibit the extreme advance?

feliz · Posted: June 21, 2009, 11:22 pm Post subject: Re: Too much advance

Yes, both cylinders the same.

dpmphoto · Posted: June 22, 2009, 9:04 pm Post subject: Re: Too much advance

There are some posts with the same problem over at the garage

tacoswild · Posted: June 22, 2009, 9:18 pm Post subject: Re: Too much advance

It's a pretty simple system really and 100% mechanical. If it's not assembled wrong (and it's pretty easy for that to happen with the different locating pins that have to be in place and the little disc can be put on wrong) then there just has to be wear in some part.

y old one had wear at just about every possible point, the pin in the rod had worn out it's hole and it jiggled around. The disc had big grooves worn in it's slots and the weights were worn both on the tabs that fit into the slots and on the back of the weights where they hit the stops.

If you're worried about damaging the engine you can check it without the bike running, just follow the same procedure as doing the static timing but wire or wedge the weights full open. My guess is you have wear in the grooves of the disc, the tabs of the weights where they fit into the disc, or the disc is on wrong.

feliz · Posted: June 24, 2009, 6:04 pm Post subject: Re: Too much advance

I agree it's a pretty simple system but that doesnn't mean it's always simple to diagnose and retify problems, look at the number of posts here and on other forums in respect to this issue. Thanks to everyone for their responses so far.

After close inspection I can find nothing wrong with my ATU, the parts all look like they just came out of a shipping crate but I'm going to start replacing them just the same. Also going to replace the dual lobe cam with a single lobe cam after PamcoPete figured that one out. I'd chuck the whole thing out and replace it with a Pamco unit but I have to get the ATU working correctly in any case.

y question now is which side is it easier to remove the rod from, points or ATU side? TIA

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