XT350 lightweight adv

OBS460

Well-known member
I put 115 miles on the XT today and logged oil temps.

65mph+ is now 30F+ cooler (used to run 245-255F, now it stabilizes around 215F), about 20F cooler around town (used to sit at 230F in stop and go, now it's around 205-210F). It cools off much faster once moving from a stop, before once heat soaked it didn't want to cool down at all.

All in all I'd call it a win! For $45, I can't complain about these findings at all. It should help extend oil life, so I can change it less and recuperate my money spent.
 

OBS460

Well-known member
I've noticed that the XT consumes a little oil when ran above 5000rpms for a period of time (commuting to work). The compression tests out strongly, there's no oil deposits on the plug, and no smoke indicating excessive blow by. There was also a slight amount of weeping out of the valve cover gasket (new gasket).

Looking at the factory breather arrangement, I noticed it was a simple hose leading to the air box. The issue is with a single cylinder engine, the piston is moving the same amount of air in the combustion chamber as it is in the lower end. Without some sort of check valve, you end up with a large amount of air cycling back and forth.

As a cheap experiment, I added a brake booster check valve in line to the air box. I then ran the engine at 5000rpms with the breather disconnected, and again connected with the valve.

20210914_104135.jpg

With an open hole, the crankcase built slight positive pressure.

20210914_134129_exported_98309.jpg

Reconnecting the tube with the check valve brought it down to a net zero pressure. This should promote better ring seal, as well as minimize air movement (and oil escaping as a byproduct).

20210914_134206_exported_122470.jpg

When I got to work today I didn't notice any weeping from the valve cover, so it appears to be promoting better drainage to the lower end. I may expirement more with adding a breather on the clutch side as well and see if I can get it to draw a vacuum overall and add a little performance.
 

calicamper

Expedition Leader
I've noticed that the XT consumes a little oil when ran above 5000rpms for a period of time (commuting to work). The compression tests out strongly, there's no oil deposits on the plug, and no smoke indicating excessive blow by. There was also a slight amount of weeping out of the valve cover gasket (new gasket).

Looking at the factory breather arrangement, I noticed it was a simple hose leading to the air box. The issue is with a single cylinder engine, the piston is moving the same amount of air in the combustion chamber as it is in the lower end. Without some sort of check valve, you end up with a large amount of air cycling back and forth.

As a cheap experiment, I added a brake booster check valve in line to the air box. I then ran the engine at 5000rpms with the breather disconnected, and again connected with the valve.

View attachment 682097

With an open hole, the crankcase built slight positive pressure.

View attachment 682098

Reconnecting the tube with the check valve brought it down to a net zero pressure. This should promote better ring seal, as well as minimize air movement (and oil escaping as a byproduct).

View attachment 682099

When I got to work today I didn't notice any weeping from the valve cover, so it appears to be promoting better drainage to the lower end. I may expirement more with adding a breather on the clutch side as well and see if I can get it to draw a vacuum overall and add a little performance.
Interesting testing. Thanks for sharing
 

perterra

Adventurer
I've noticed that the XT consumes a little oil when ran above 5000rpms for a period of time (commuting to work). The compression tests out strongly, there's no oil deposits on the plug, and no smoke indicating excessive blow by. There was also a slight amount of weeping out of the valve cover gasket (new gasket).

Looking at the factory breather arrangement, I noticed it was a simple hose leading to the air box. The issue is with a single cylinder engine, the piston is moving the same amount of air in the combustion chamber as it is in the lower end. Without some sort of check valve, you end up with a large amount of air cycling back and forth.

As a cheap experiment, I added a brake booster check valve in line to the air box. I then ran the engine at 5000rpms with the breather disconnected, and again connected with the valve.

View attachment 682097

With an open hole, the crankcase built slight positive pressure.

View attachment 682098

Reconnecting the tube with the check valve brought it down to a net zero pressure. This should promote better ring seal, as well as minimize air movement (and oil escaping as a byproduct).

View attachment 682099

When I got to work today I didn't notice any weeping from the valve cover, so it appears to be promoting better drainage to the lower end. I may expirement more with adding a breather on the clutch side as well and see if I can get it to draw a vacuum overall and add a little performance.

Ah hell, never even thought about this. Thanks my KLR suffers from this at speeds above 70 for extended periods
 

genasea

New member
Thank you OBS460 for sharing your knowledge of off-road motorcycle 'hacks' with the rest of us. Very informative. I have saved several of these into a permanent folder so I can remember them later. Your 'common sense' engineering changes really make great improvements on the bike, and the explanations are very straight forward. So, thank you again for sharing, we appreciate it.

Safe and happy riding to you and your daughter.
 

OBS460

Well-known member
In my younger years, I used to run Cross Country at a high school and college level. In the process, I ended up tearing up my knees pretty badly. As of late the kick start was really starting to aggravate and inflame my right knee, especially if I flooded the bike after a spill.

So, I decided to part ways with the XT350 and she went to a great new home. In her stead, I picked up a 2007 Kawasaki KLX-250S as the electric start will be quite welcomed! I'm going to start building the KLX out this week, and hopefully it's an even better lightweight ADV bike!

Link to the KLX's thread. https://www.expeditionportal.com/forum/threads/2007-klx-250s-lightweight-adv-ds.230663/

272634893_1892405314290119_2374480232392766921_n.jpg
 
Last edited:

Cabrito

I come in Peace
Congrats on the sale and the new scoot..

I still have my XR400 (Kick only), but my CRF300L Rally is a real game changer for me.

I think you are really going to enjoy having the modern dual sport. I look forward to how you set it up.
 

OBS460

Well-known member
Congrats on the sale and the new scoot..

I still have my XR400 (Kick only), but my CRF300L Rally is a real game changer for me.

I think you are really going to enjoy having the modern dual sport. I look forward to how you set it up.

Thanks!

I think I will as well. On paper, the only thing the XT did better than the KLX was overall range due to a larger tank (a Clarke is in route currently to help close that gap).
 

wrpeterson

New member
Yamaha discontinued the CDI source coil some time ago for the XT350, which created some issues when it failed on me.

After searching through a bunch of parts diagrams, I found the 80cc Raptor source coil was a similar size and resistance. I rolled the dice and decided to give it a whirl.

View attachment 679972

I had to solder on wiring, enlarge the mounting holes, and space it out .160" from the stator plate. After that, it fired right up and made good A/C voltage to the CDI.

View attachment 679973
Hello, I was also getting low resistance readings on my stock source coil, so I replaced it the same way you did, with the one from an 80cc raptor. However, I am still having issues getting a spark. When I take resistance readings after the bike has sat for a while, my resistance reads about 324ohms, just below the low spec. However after kicking the bike a few times and taking another reading, resistance drops to around 279ohms. Does anyone know why kicking the bike over would cause resistance to drop? Is this normal or the sign of some other electrical issue? Thanks!
 

tloof55

New member
OBS460, how has your rewire of the stator coil & upgrade to the Trail Tech Regulator/Rectifier worked out over a long period of time now on your XT350? I am also interested on upgrading to the same setup with all LED lights onto my old 1986 XT350 too, but from what Rex's Speed Shop (a old vintage motorcycle parts provider over in England) tells me, every AC magneto generator that they've seen that is on these older Yamaha's that has been converted from a ground to a floating input to an aftermarket Regulator/Rectifier suffers a burn out after a period of time (especially when the headlight is rewired to the DC side of that Regulator/Rectifier)...has this happened to you yet? Rex's Speed Shop says that they have done extensive testing and say that the headlight needs to stay powered off the AC side only and kept as an incandescent Halogen bulb (along with the high beam light) and only all of the other lighting that is run off the DC side of the Regulator/Rectifier can be changed to LED lights. They also have a 12V full wave Regulator/Rectifier they sell that ups the power that is delivered on the DC side vs the old OEM Yamaha Regulator/Rectifier that is only a half wave version, but they say NOT to power the headlight off the DC side due to the eventual burn out issue!

Attached is the wiring diagram of the XT350 from my factory Yamaha service manual. Can you please red mark-up the wiring changes you made on your stator coil and the new Trail Tech Regulator/Rectifier addition so that all of us that have an old XT350 can replicate the same changes you made (that's assuming it hasn't burned out on you yet!).
 

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