yz timing and restrictive exhaust
Posted August 13, 2000 - 09:38 PM
The tricky thing is that I use just 6 plates WITH the quiet core. Yes, it is almost as quiet as the stock bike but with little bit more bang than stock (not difficult to beat!!). I'm running on road 80% and 20% trail.
I switched to dvp needle and yz timing 2 days ago. I started to jet the bike but it seems harder than expected. First attemps was at 172,48, 3rd clip but the bike stalled with fast throttle open and seems low on power compared to my old setup (172,48,3rd clip, wr timing, DXM). I raised the clip and the problem was less present. Now I'm at the first clip and the jetting is still far than perfect!!
May be next try will be a setting often seen on the discussion group, something like 175,48, 4-5th clip but this is a blind trialand I'd like to understand what happening.
Big question: How using a more restrictive exhaust affect the jetting of a yzedded wr compared to a yxedded bike with a non-restrictive exhaust (like most of you use)
Posted August 13, 2000 - 01:03 PM
That being said with your current pipe and YZ timing I would try
Fuel Screw = 1.5
MJ= 168 no more than a 175
second choice everthing the same but a 48Pj with the fuel screw at 3/4 turn out max.
Posted August 13, 2000 - 02:41 PM
In any case, I can already see the benefit of the yz timing over the wr at least on road. It kicks sooner and rev easier and I'll have to watch the speedo and the cops now.
Concerning the main, with wr timing and 168, i was hearing a metal sound so it was way too lean. I raised to 175 and the sound diseapeared. A while after I downsized to 172 adn it pull harder. May be I'll try the 170 one day but it is close to the way too lean 168.
Posted August 15, 2000 - 12:45 PM
i've slipped in a little article on my exploits last weekend called "teeth & pins"- have a look.
over here in britain the pipes i believe aren't as restrictive as yours & they are about 92db as standard.
the YZ timing has been a huge improvement & as you can see from my notes i was lucky first time with the jetting first time out.
in my experience the jetting goes up initially when you de-restrict a bike at either the pipe or inlet. after this all tuning brings the jetting down.
once when i had my ducati singing i got down to the smallest main jet that dell o'rto made!!!
Posted August 21, 2000 - 05:25 PM
I did a 10 km on road and it boost the mid a lot. I can now raise the front wheel just with gaz. Remember that I am geared 15/45 and this is not and open muffler! My second gear is almost the third gear of the stock wr of my brother!!!
I won't go back to the wr timing for sure, the bike surge is perfect and controllable for me, I love that power!!! I should post the next try to jet it better. Maybe the next stage is the octopus surgery...
Posted August 21, 2000 - 06:49 PM
Please enter you exact jetting configuration I think you said
Fuel Screw = ??
Needle = DXM but what clip position ??
Main Jet = ??
Posted August 22, 2000 - 03:42 PM
the bike is more poweful that ever but I can't say if this is the optimum. The only symptom is that the bike is harder to start when cold. It just have a little constant backfire on closed throttle deceleration.
Posted August 22, 2000 - 05:14 PM
For starting I would try the fuel screw at 2.5 and see if it helps. You may get a little better response out of the DXM needle by raising in 1 clip position; might want to give it a try some day.
Posted August 23, 2000 - 03:11 AM
1-Do the needle straight portion diameter influence starting or just off idle response?
2-The bike just have a small hesitation when opening the throttle quickly. Is it a good test to see if the clip is at the good position? I would try the clip at second position from that point of view but I was wondering if the bike could be too lean elsewhere.
If I put the fuel screw at 2.5 turn, the popping on deceleration diseapear completely. I heard that little backfire poping at deceleration is normal. Does that mean that no poping is not normal and a symptom of another jet misjetted (like the needle or the pilot?)
We have a big ride this week-end. I'll gear downer if possible, 16/45 is pretty fast in a tight trail!!!
Posted August 24, 2000 - 06:00 PM
For the same combustion circuit (inbox and exhaust), Should the main jet be the same when changing timing from wr to yz? I mean, my mains was perfect at 172 before and I just changed the timing on the bike (jetting too). Should I expect to have to raise it by switching to yz timing?
Posted August 24, 2000 - 06:42 PM
The starting is primarily controlled by the pilot jet, the pilot air jet and the fuel screw setting when starting without the choke. With the Choke then the start jet is in play. The needle straight section diameter has a very slight effect on starting but will work in conjunction with the Pilot, and fuel screw for between approximalty 0 to 1/4 throttle.
Snapping the throttle is not a good test for needle clip position. A minor bog sometimes cannot be eliminated. A major bog when snapping open the throttle can be eliminated with jetting and proper accelerator pump discharge set up.
A little poping on decelleration is ok but so is no poping its up to you. This minor poping on decelleration is caused by a slight lean condition when the thorttle is rapidly closed. When you open the fuel screw you are slighlty richening the fuel mixtre from 0 to approx 1/8 throttle opening so when the throttle is closed rapidly the richer mixture may be enough to not cause any poping. The same effect can be had by reducing the needle straight section diameter but other changes would have to be made. Through jetting you are trying to get the most consistent response top to bottom for your bike setup riding conditions.
In general the YZ cam timing wants to be a little richer coming onto the main jet. This can be controlled by needle taper and main jet size. With the restrictive exhaust setting you are running the main jet selection will probably not vary too much between WR and YZ timing.
With everything I seen in this discussion so far sounds like the following jetting would be vary close for your situation
PJ = 45
Fuel Screw = 1.5 to 2.5 (testing required)
Needle DXM #4 oR #5 (testing required)
Main Jet 170 to 175 (testing required)
With your big ride coming up I would make set the needle at #4, go with the 172 main and set the fuel screw a 2.0. Ride it this way for awhile and get a good feel for it and then make only one change at a time to dial (fine tune) in the remaining final jet settings.
I thought I answered most of these question last night but must have screwed up the posting process.