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TOPIC: Dt3 timing advance

Dt3 timing advance 15 May 2018 13:08 #1

  • 360jeepboy
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How does the 73 dt3 adjust for timing advance? I'm not seeing the spring and advance lever on it.

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Dt3 timing advance 15 May 2018 14:30 #2

  • MarkT
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The mechanical advance used on some points models was only to retard the timing for easier starting... at idle speed the timing is already fully advanced.

DT3 did not have the advance feature.

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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

Dt3 timing advance 15 May 2018 14:47 #3

  • RT325
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Yep, fixed timing at whatever points gap you give it to get 3.2mm approx. That's why later cdi systems are so good & a real late dt250 or dt400 would bolt on , which is a 'must' for the 360 version of your dt3 to save ya leg from the dreaded kick back--he says limping off into the sunset lol.

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Dt3 timing advance 15 May 2018 15:12 #4

  • 360jeepboy
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Ok good info guys! Thank you!

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Dt3 timing advance 15 May 2018 15:19 #5

  • RT325
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forgot to add, do it up tight too, or bad things happen. Have a look over at 'armpit' post THE armpit, i put a pic up there i think. Bit over the top tightening but you get the idea, or they stuff the key then shaft & taper if it lets go.

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Dt3 timing advance 15 May 2018 15:51 #6

  • 360jeepboy
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RT325 wrote: forgot to add, do it up tight too, or bad things happen. Have a look over at 'armpit' post THE armpit, i put a pic up there i think. Bit over the top tightening but you get the idea, or they stuff the key then shaft & taper if it lets go.


Yea I saw that. I held mine with a strap wrench and torqued it to 29 ft lbs.

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Dt3 timing advance 15 May 2018 23:46 #7

  • Cobra
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What is your thought about advancing the timing? I noticed before you where timing it by checking the gap but if you got a new set of points from Deets then your gap should be correct as there should be no ware on the part that rides on the flywheel. So the most important thing is to make sure they are opening a 3.2mm btdc. There should be a metal indicator attached to your bottom lighting coil that aligns with the mark on your flywheel that is exactly 3.2mm btdc. Once those are aligned stick your flat head screwdriver in the adjusting slot on the points and turn slightly clockwise so the points bumper (what ever the part that rides the flywheel) is just making contact with the flywheel cam. If you keep turning clockwise you will see the points opening, thats too far go back (points are springloaded so they should bounce back but make sure its just touching the flywheel cam. NOw tighten the points screw. Usually when I tighten the points screw (clockwise) it moves the points slightly clockwise (causing the points to open early or advanced, when you kick start it the kick start lever will kick back super hard when its to advanced damn near break your leg. It does this less and less the more you retard your timing). To remedy this I usually move the flywheel mark maybe a 1/4 -3/8in counter clockwise from metal indicator on your lighting coil. This way when you tighten down the points screw it will hopefully be right on the mark. You might already done all this, but maybe someone will chime in and I will be corrected.

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Dt3 timing advance 16 May 2018 01:08 #8

  • RT325
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Yeah you're quite correct. New points & set the flywheel @ 3.2 then loosen points & let them sit on the cam & then tighten & should [in theory] then be breaking @ that point & also in theory end up with a gap within spec which is i dunno say 12--15, more like 14. But while tightening, things move. The arm off the lighting coil is easily bent so just bend it too the flywheel mark @ 3.2mm. Now--me being a lazy bugger i just set new points to a tight 15 & go have a beer, & forget about the rest lol. Never had a problem on a soft old DT motor as not very stressed with high compression & go fast stuff.

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Dt3 timing advance 16 May 2018 01:19 #9

  • Rexs Speedshop
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The later CDi systems are little better than the points ignitions. Early ones are fixed timing like points, which causes that narrow 2-stroke power band. Later ones do advance slightly in the low range but crucially there is no retard. This limits the amount of advance that can be used as over advanced ignition timing on a 2-stroke will burn a hole in the piston at high RPMs.

The trick to 2-stroke ignition is to get it to retard after it has advanced, then you get the real power from the engine. The rate it retards needs to match the engine's port timing and the use the machine is being put too. For example I supplied an ignition for an MX360 for dirt track racing. It advances just a couple of degrees, then from 3,000 RPM retards off massively, giving a smooth soft power curve that gives lots of power but lets the rider keep the rear wheel spinning with no sudden surges.

The same ignition with an MX timing curve gives a much larger advance and then starts retarding around 4,500 at a much steeper rate making the expansion chamber work hard and produce high peak power. The low rev range advance keeps the power band wide as the advance makes power low down, while the porting is sub optimal, and gives hard acceleration by moving heat the expansion chamber when the revs are high enough for the porting to be optimal. This makes the engine really sit up and go.

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Last Edit: by Rexs Speedshop.

Dt3 timing advance 16 May 2018 03:20 #10

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I'm sitting up now & taking notice. Interesting info. Just to stretch that a bit, back in my yz125 days not sure which one but think "79F model it was a bastard for switching off at max revs, almost like a modern rev limiter on a 4poke but was after i'd sold it that we learnt it had a looped black or black/red wire coming just out of the loom from the box the looping back in. We were told to cut the wire & all would be good, which it was but i'd sold mine by then. Think it reduced the amount of retard @ high revs like they over retarded it to stop us brutes down here from destroying the motors. I don't care i just wanted top end power--well top end going on & on. Was a bugger if you were off the ground on full song & it'd stumble just at the wrong time when you landed., Changing tact [& i've mentioned it before] on my "76 YZ250C it lacked strong top end right to max revs which was very annoying because my mechanically identical "75 model was strong right to max revs. So i went through the parts books & the ignition was the only difference. "75 had the old system with open looking coils & two stage pulser internal rotor that retarded to start the flicked to advance & stayed there not altering . "76 had the grey encapsed coils with internal rotor, no separate trigger & strobing it--it advance plenty at low to medium revs then retarded off more and more as the revs rose until it killed the power. Ok hook it up a gear but!!. The Yamy factory mechanics were doing a tour through the country & i had my bike on the bike bench so asked them, or asked the boss fella who spoke english & he said it was to stop them being over-revved & damaging the motor, so I just advanced the backplate from the central position to well towards the end & pretty much regained what i'd lost. No recommended by the factory but-- I mean, why do they have slots if we're not allowed to use them lol. Somedays i'm not safe to be let out.
Edit, sorry that was more directed at Rex's Speedshop.

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Last Edit: by RT325.
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