Timing with a dial gauge

[rearwheelslider]

I have a question regarding timing my bike. My fresh rebuilt engine in my 79 400F has some spark knock during accel. I set the static at 2.2mm BTDC. Spec is 2.3mm. I understand our fuel nowadays sucks and does not protect from pre-ignition as well as it used to, but still alarming to have knock when it is set to a spec. I kinda expected this and am going to dial it in with a timing light and set to 1.8-1.9mm. Is that a good number?

My question is this...
79 400F has a moveable pointer similar to DS7 and R5. I am to set the timing with a dial gauge to 2mm BTDC, move the pointer to match the line on crank, and then test with the light? Do I want it exactly lined up with the line on crank? While engine running, the light should be coming on at exactly when they are lined up? Whats odd to me, is that the movable timing mark is only as good as the static set with dial gauge, therefore if you are off at all when moving the pointer, your timing light will be off. Do things really change when its running?

Extra question:
Why didnt RD's have a mechanical advance?
It is odd to me that the spec for 400 is farther advanced than 350. Maybe someone can explain this to me. Thx!

[SoCal250]

The OE spec for the RD400F 2V0 is 2.4 mm BTDC (the RD400 1A1 is 2.3). I use 2.0~2.1mm on my Daytona, with premium fuel.
Chuck "Supertune", our former resident racer and engine builder always recommended a little less timing on a hot-rodded engine. From my notes he suggested 2.0mm for a RD400 or 1.8~1.9 for a hot motor.

The pointer is adjustable so you can set it at your desired timing as a quick reference. Once you determine the firing point, you can set the pointer.
1) So for example, if you want to use 1.9mm, find 1.9mm before TDC with your dial gauge.
2) And using your test light (or DVM or buzzer) adjust your points to fire exactly at that point.
3) Next set your pointer to line up at that point as well.
4) Repeat for the other cylinder. (but don't move the pointer, just verify that it's correct.)
5) Then, next time you need to check your timing you can use the pointer as your reference.
6) That's for the static timing. Once the engine is running you can use a standard automotive inductive timing light to verify that your timing pointer marks line up for each cylinder.

[SoCal250]

I use these for setting timing...

Gardner Bender GET-202A low-voltage test light and a pair of test leads with alligator clips. I like this light because it can be wedged into the engine or fins to hold it in place for easy viewing.

And I've had a Central Tools 6491 two-stroke timing kit for many years. Small dial fits under the tank, metric, and easy to read.

Then an old Craftsman timing light to verify with the engine running.

[Dvsrd]

Extra question:
Why didnt RD's have a mechanical advance?
It is odd to me that the spec for 400 is farther advanced than 350. Maybe someone can explain this to me. Thx!

2 strokes actually need the timing to be retarded as revs increase, so opposite of 4 strokes. Modern electronic 2 stroke ignitions do this. However, a mechanical regarding mechanism may not have justified the added cost. So constant timing it was.

As for the difference between 350 and 400, this is due to the longer 62 mm stroke vs the 350's 54 mm stroke. Converted to degrees BTDC, it becomes pretty much the same.

[m in sc]

yup ^ exactly.

they both are timed at roughly 19.9-20 degrees BTDC stock.

[rearwheelslider]

Extra question:
Why didnt RD's have a mechanical advance?
It is odd to me that the spec for 400 is farther advanced than 350. Maybe someone can explain this to me. Thx!

Interesting! I have never thoug

Extra question:
Why didnt RD's have a mechanical advance?
It is odd to me that the spec for 400 is farther advanced than 350. Maybe someone can explain this to me. Thx!

2 strokes actually need the timing to be retarded as revs increase, so opposite of 4 strokes. Modern electronic 2 stroke ignitions do this. However, a mechanical regarding mechanism may not have justified the added cost. So constant timing it was.

As for the difference between 350 and 400, this is due to the longer 62 mm stroke vs the 350's 54 mm stroke. Converted to degrees BTDC, it becomes pretty much the same.

2 strokes actually need the timing to be retarded as revs increase, so opposite of 4 strokes. Modern electronic 2 stroke ignitions do this. However, a mechanical regarding mechanism may not have justified the added cost. So constant timing it was.

As for the difference between 350 and 400, this is due to the longer 62 mm stroke vs the 350's 54 mm stroke. Converted to degrees BTDC, it becomes pretty much the same.

I never knew this about two strokes needing the timing retarded as revs increase! Good to know high engine speeds do not sacrifice power for not having an advance. Makes sense, considering the pipes put charge back in to the combustion chamber, like a forced induction engine needs less timing with more boost.

Appreciate the input guys.

[rearwheelslider]

This video is very good at explaining timing curves of two strokes.

[rearwheelslider]

I checked the timing on my bike today. The timing originally was set to 2.2mm static. But after riding it around for 50 miles and breaking it in, the static read 1.7-1.8mm.
I set both LH and RH to 1.84MM static, set the pointer on the stator and checked with a timing light. I only have a snap on digital version which is quite old. The light would jump around quite a bit until I advanced the timing on the light 1-2 degrees, then it cleared right up. Kinda odd.

I am still trying to understand exactly what changes when the bike is running vs static, timing wise.

I heard slight detonation with the original timing of 1.7-1.8. Is some spark knock normal for these bikes?

[rearwheelslider]

How are these? I have read they are known to fail. $300-400 is a lot for me, this seems like a viable option at $150


https://www.ebay.com/itm/Tytronic-Electronic-Ignition-for-RD350-RD250-R5-and-DS7-UPGRADE/113182861022?hash=item1a5a3966de:g:E6UAAOSw5KRbZRUU:rk:1:pf:1


How are the optical ignition setups? Such as Crane XR700.

[m in sc]

save some and buy a cdi or nicks dyna. those are very hit and miss.

remember, rd250/350 igntions fit as well. r5 ignitions (aftermarket) is not specific to r5

[rearwheelslider]

save some and buy a cdi or nicks dyna. those are very hit and miss.

remember, rd250/350 igntions fit as well. r5 ignitions (aftermarket) is not specific to r5

Gotcha. Who is Nick and how do i find him?

For the same price, one could go with this treat land full kit. Recommended? https://www.treatland.tv/HPI-CDI-mini-rotor-ignition-system-yamaha-RD350-p/hpi-yamaha-rd350-mini-rotor.htm

[m in sc]

a few people have run HPIs, myself included its good but charging can be.. tricky? theres posts in the how to about it down below

[SoCal250]

Who is Nick and how do i find him?

Mark was referring to Nick Pastore of Vintage Smoke who offers a version of the Dyna S ignition customized for the RD
https://vintagesmoke.com/product/dyna-s-ignition-for-uscanadian-rd400-and-daytona/
https://www.ebay.com/itm/195844170963

[rearwheelslider]

Who is Nick and how do i find him?

Mark was referring to Nick Pastore of Vintage Smoke who offers a version of the Dyna S ignition customized for the RD
https://vintagesmoke.com/product/dyna-s-ignition-for-uscanadian-rd400-and-daytona/
https://www.ebay.com/itm/195844170963

Gotcha. Thanks for the clarification.

[rearwheelslider]

Is a little spark knock normal on these bikes? I can hear it ever so slightly at mid rpm wide open. Once the revs increase, it is not audible. I have verified timing with test light. Engine not modified at all. Pump 91 gas.