Timing/Tuning Help

[kalewud]

I've been working on my first bike for a year, 1980 XS650 Special. I've gotten to point where most of the cosmetic work is done (bars, rims/tires, new electrical), it idles great, though I can't get it running well beyond 1/4 throttle. I'm not trying to start another 'help me tune my carb' threads, but I'm just looking for some advice, mentorship, and willing to pay for any significant time to help me get this thing running right.

Bike specs:
- 1980 XS650 Special
- Hugh's Handbuilt CDI (came with the bike, previous owner installed...partway/incorrectly which I reinstalled)
- Pandemonium 2-into-1 exhaust
- VM34 carbs

I've been on with Hugh a number of times regarding the system, checked all my electrical specs (battery/reg/ignition coil, pickup, etc), but I can't seem to get my timing correct which I suspect is the underlying issue. I've found TDC, but setting my pickup at Hugh's spec does not show it firing when it should. I've reached out to him again but haven't been able to get a reply as I know he's busy.

I've confirmed:
- Valve specs
- Compression
- Air leaks around carbs
- Carb jetting (as much as I can 'tune it', given that it is misfiring in the 1/4-3/4 throttle range).


If anyone can give insight into:
- Timing - If I advance the timing tab beyond spec, I can get it to 'fire' at the correct time, with some advance when I give it throttle. Does changing this tab beyond spec have any detrimental effect?
- VM34 carbs - I purchased from Niche cycles, I had a ton of backfire on some of the smaller jets (17.5-22.5 pilot, 165-180 main), so I just have it running richer which at least lets me idle.

Happy to share any pics, video etc. As I mentioned, I'm new to this but have spent many hours on these forums, learning as much as I can, and just hit a wall and stuck at this point.

Thanks for all who contribute to this forum.

 

[Signal]

Sounds like you are doing well already doing your own research, good work.

Trying to fix possible carb problems with a dubious ignition will be hard work.

Timing: Dont ride your bike with the timing over advanced it can lead to major damage.

I suggest you confirm your timing marks with a degree wheel and piston stop for accuracy.
Then check the ignition timing again with a timing light.
After you have confirmed that the ignition timing is correct, advancing correctly and in good working order then start on the carbs.
You may even find the carb problem gone.

Does the rotor have a key installed on the crank some CDI systems only use the taper to lock the rotor and it may have slipped if loose or removed and not put on again in the correct location.

Also check the reluctor (rotor bump) to pick up gap 0.4mm is used on other systems.

Good luck and yes we like photos.

 

[Its been a long time]

100% agree, first priority check the actual timing with a degree disc on the crank. If necessary make your own timing marks. As stated above, there may not be a key between the rotor and the crankshaft. In which case the rotor can be installed in any position you choose which isn't helpful for things like ignition timing. Sounds like you're going in the right direction with it.

 

[kalewud]

Thanks, I'm fairly sure I found TDC correctly (https://www.hughshandbuilt.com/2012/12/11/tdc-find/). Here are a few photos and a video from the last time I checked/set it:

I'm going to retrace my steps and film a quick video to share though. To confirm, when I'm at TDC (or what I think is TDC), I spin clockwise, stop at a certain degree, and when I spin counter clockwise, I end up at the same degree (but other side of TDC 0)...right? I saw my piston stop was hitting the valve at one point in the rotation, so I'd have to take it out, spin a bit, and put the stop back in once the valve was out of the way. Is my piston stop too long?

 

[Signal]

The length of the piston stop determines how many degrees before or after TDC the piston is stopped.
What is happening I think is the inlet valve is contacting the shaft of the stop.
If you turn the motor over and look in the plug hole you will see the inlet valve moving.

It probably the way I am reading your explanation but to clarify when moving the crank shaft turn it until the piston hits the stop and record the degrees.
Do this before and after TDC the centre point between the two reading is TDC.

I find rather than using a fixed pointer a piece of wire like welding rod makes it easier to make the adjustments to set TDC. Rather than loosen and move the degree wheel you just bend the wire half of the difference. Makes the process a lot faster I think.
Flatten the wire with a hammer to get a more accurate pointer and paint it a bright colour if you really want to go for it.

 

[kalewud]

Thanks, your instructions make sense. I verified that when turning my degree wheel, there was no inlet valve in the way.

Here is a video of me showing the piston stop hitting the same point on either side of TDC on the degree wheel:

I'll upload a video tomorrow of where the 'TDC' marking is on the front of the flywheel, and then when it's running with the timing light (not at 'fire' as it should).

 

[Jan_P]

It depends on " Musician's Ear "
If your rotor have slipped and the timing marks are off .
When you have found TDC try blipping the throttle and listen.
When correct it responds better than if to advanced or to late.
It also is simpler starting when it is correct timed
To advanced and to lean can damage the motor.

 

[Signal]

I dont know how Hughs instructions say to measure the distance from TDC to what you were trying to measure (start of the reluctor?) . However doing it as per your video is not that accurate.
What I suggest is after you have set the Crank at TDC, remove the timing wheel not the pointer, Then mark a thin line on the rotor in line with centre of the pointer.

Then using a strip of paper bent around the curve of the rotor mark the TDC and mark the reluctor leading edge . Then flatten the paper and measure between the 2 marks.

Then adjust the rotor so the reluctor is in the correct position relative to your pointer. The pointer looks to be 6mm so dont forget to adjust by 3mm to get the centre of your pointer from its outside edge,

When you pull the rotor be careful not to move the crank , hopefully you have the correct rotor puller a Yamaha RZ, banshee one should fit.

When you have the rotor in the correct position mark a line on the rotor in line with your reference TDC mark on the case. That way when you remove the rotor in future you can easily align it correctly. This assumes you are not using a rotor key.

Your timing is not that far off as the bike is running.

 

[kalewud]

I had those calipers close so I just wanted to show where the tab was relative to the pickup (Hugh’s instructions say 16mm from the metal on the pickup to the start of the tab).

Based on your instructions, I can continue to adjust the rotor to advance the pickup, and check timing accordingly? I can continue to do this in small increments until my timing light shows it’s at the “Fire” mark.

 

[Signal]

I would follow the instructions from the manufacturer.
I just watched your video from last year an your ignition looks retarded.
I would be concentrate on getting the full advance mark on the cover and the rotor mark to align when you rev the motor usually above 3500 RPM is full advance.
If the ignition does not advance past that mark you will be ok.
I am pretty sure the idle timing (F mark) will more or less work out .
What did the pickup to reluctor gap measure ? It can have a significant effect on the timing if it is too far off spec.

I have not installed one of Hughs systems so I am a little in the dark . but something has to move in relation to the other , either the pick up or the rotor reluctor.

 

[Signal]

Have you watched this video, the info relevant starts at 12 min. I just watched it and it explains setting the reluctor pickup distance and gap.

 

[kalewud]

I am quite familiar with that video, that’s why I’ve been confused with this setup - with everything installed to spec, the timing was retarded. I did not want to start changing that timing tab position without asking on this forum.

But I’m planning to adjust the tab, check timing, and as long as I’m not going beyond the full advance, no risk of engine damage correct?

 

[gggGary]

not going beyond the full advance,

The old XS is pretty good about warning you on "over advanced"
'Specially if you are kick starting. But it'll stop the E-start dead also if timing is getting too advanced.
But there's no reason to guess. Confirm and Mark TDC on the crank, rotor use a timing light check both idle and 3K timing.
If any discrepancy the 3K timing takes precedence.
If you aren't trying to squeeze every ounce of performance. a bit retarded from spec will offer up smoother, more enjoyable riding at a relaxed pace.

 

[Signal]

But I’m planning to adjust the tab, check timing, and as long as I’m not going beyond the full advance, no risk of engine damage correct?

Yes that is how you should do it.
Garys post is shows the timing marks on a stock stator but the information is correct.

 

[kalewud]

Thank you both, I’ll get this marked and test this weekend.