Oil Question

Greetings all.

I have been told that I need to run a synthetic oil in my son's XR350R, and was hoping someone could reccomend one that I can run in both that bike and my XR650L. I've heard that one cannot use synthetic to break in a motorcycle. Since I'm going to be breaking in my '650L, I need to confirm or dispell this rumor. The XR350R seems to be nearly stock, having only an aftermarket air filter. My '650L has alot of modifications.

Another question: Will jetting a tad rich make a bike run cooler? What about running a high octane fuel? I'm determined to take good care of the '350R, and have been warned about that model and year having horrible overheating problems.

Thank you all for your input, I appreciate it greatly.

Hi. To answer your questions the best I can, here goes.

1. Use Honda GN4 oil in both bikes. There is no need to use synthetic oil in an old XR350R unless you just want to.

2. During break-in of your XRL, once again I would suggest Honda GN4. Even if synthetic oil is safe for break-in, there is no reason to spend the extra money on it. GN4 is a very good oil for any bike out there, both new and old. It has a lot of motorcycle specific additives. Keep in mind that car oil only lubricates the engine, while motorcycle oil must act as an engine lubricant, as well as transmission fluid, and wet clutch fluid.

3. Jetting a bike richer will make it run cooler, provided the intake and exhaust are opened up enough to let it breathe more freely. Jetting a bike too rich will wash oil off the cylinder and cause excess engine wear. Jetting too lean will overheat an engine and produce less power also.

4. High octane fuel has no effect on engine temperature, but low octane fuel will cause pinging and engine stress.

Octane is just the flash point of the fuel nothing more.

5. You don't mention what year your XR350 is, so I can't give you any info on it having overheating problems. If it does overheat, most likely it's an overly lean jetting issue, since that bike is air cooled, that's the only possibility.

Hope this helps you out some!


Yikes! I should have definately been more specific, I'm sorry.

The XR350R is a 1983 model with an '84 front end, but appears stock beyond that. It will have a Barnum's cam in it when it starts being used in a few weeks.

The XR650L is a 1993 model, and has the following engine mods: K&N filter, Edelbrock Pumper Carb, top end bored to 101mm (one over stock, I'm told) with an LA sleeve. Stock header with a Supertrapp EAR exhaust.

We live in El Paso, and ride primarily open roads, with occasional deep sand (me only on the '650L, my son's not that good yet), and the altitude generally stays right around 6000-6500. The '350R has stock jetting, I checked when I tore down the carbs and cleaned them.

Thanks for all your input, I appreciate it.


If ever there was a candidate for Mobil One 15/50 you are it, (IMHO). Air cooled bikes, El Paso, deep sand, kids going slow. Look into it, synthetic is the only way to go.


Synthetic to break in a motor? I wouldn't run synthetic in any motor until it broken in. The "friction" actually makes things "fit" better, ensuring a good seal between the rings and the cylinder wall. just my 2cents.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now