Early RFVC 250 performance modifications.

[sonic_attack]

What are the options, and associated advantages/disadvantages of modifying the RFVC engine of my 1984 XL250R?

I understand they are viewed as a bit of a "grenade motor" though one of my mates owns one of these, and he has thrashed the hell out of it for years with no trouble other than getting the carbs balanced by someone who knows what they are doing now and again.

I figure there must be some RFVC purists out there who've modded their sled into a reliable, fast, retro rocket! ?

so where would I start?

cheers, S_A

PS: the power from standard is enough for thrills really, but you know how it is......No matter what you have its never enough eh?

[Dwight_Rudder]

Run synthetic oil and leave it stock. It is an awful engine and runs extremely hot. Modifiy it and you chance ruining it big time.

Cher'o,

Dwight

[XR6's_rule]

I owned an '84 XR250 and at the time considered doing mods to it but I ended up thinking that I was better off putting the $$ into something newer and ended up buying an '88 XR600, the best bike all-round dirtbike I've owned.

[Bultaco206]

Dwight's right on. Leave it alone. The best things you can do is run synthetic oil; make sure it's jetted properly (a little fat is good); keep your valves adjusted; and don't putt with it or leave it to sit and idle.

In stock form it's a hand-grenade just waiting to blow. Start fussing with it and you'll have a mess in no time.

[ptguy]

Dwight, or anyone else who knows the early RFVC motors, why do these early ones (83-85 XR250 and 350 as I understand it from reading this post and many other similar ones on the subject) run so hot? What is wrong with the design? Did Honda not design enough oil flow around the combustion chamber to carry away the heat? Maybe not a big enough oil pump? Did they slow down the piston speed for less friction (via changes of stroke?)

I'm curious here (I have an engine design background). In 1986, Dwight, you say this engine was SO MUCH better than the one it replaced. What design changes were made to the 1986 XR models that made it so much better, with respect to heat control and durability?

I'm interested in a "History Channel" lesson here on the XR. I'm restoring my '88 and would like to know why my bike is so much better than a 1983-1985.

[Kev_XR]

I'm not sure what was wrong with the 1983-85 design, but Honda replaced the engine after 3 years and that is unusual. Typically, the engines seem to get a major revision ever 5 to 10 years. The XR200 that was recently retired was based on a 125cc engine designed soon after the earth cooled.

When I was looking for a used XR200, which is based off the XR250 in 84-85. A lot of the used 84-85 XR200's were listed with rebuilt top ends and/or new heads. Yet, you'll find the 84-85 XR200, 250, or 350 owner has never had a problem and run the bike hard for years.

[XR250rdr]

86 saw the return to the single carburator as well as a 3mm increase in stroke plus an oil cooler. The oil pump was unchanged from the 85 model. Dwight has also mentioned that Honda improved some of the oil galleys.

I've been running my 84 pretty hard for the past few years and I have had almost no problems with it. I run solely Maxima Extra full synthetic and change it often.

The one time I did have problems was slogging through some monster whoops (thanks to the SCORE trucks) and deep sand in 95°F weather. The bike overheated and muschroomed the valves, but made it home alive.

Ohh and btw...there was no 83 XR250.

[Dwight_Rudder]

Dwight, or anyone else who knows the early RFVC motors, why do these early ones (83-85 XR250 and 350 as I understand it from reading this post and many other similar ones on the subject) run so hot? What is wrong with the design? Did Honda not design enough oil flow around the combustion chamber to carry away the heat? Maybe not a big enough oil pump? Did they slow down the piston speed for less friction (via changes of stroke?)

I'm curious here (I have an engine design background). In 1986, Dwight, you say this engine was SO MUCH better than the one it replaced. What design changes were made to the 1986 XR models that made it so much better, with respect to heat control and durability?

I'm interested in a "History Channel" lesson here on the XR. I'm restoring my '88 and would like to know why my bike is so much better than a 1983-1985.

You are right about the oil flow as in 1985 they lowered the compression and added an additional oil pump. To try and deal with the problem. These engines got so hot as to boil petroleum oil in the heads, burn your ankles and melt the dip stick off, or even worse I have seen it fall into the engine. Part of the problem was the complicated dual carb setup that loved high RPM.

In 1986 they added an oil cooler, still had the lower compression and dual oil pump and redesigned cases and oil passages. They also went to the single carb and a lower RPM cam. I always set mine up for Torque not RPM / Horsepower.

The 1985 XR350 had these mods already and was a great bike.

Cher'o,

Dwight

[ptguy]

Thanks for the history lesson. Its interesting to see that Honda let a "less than robust" engineering design out the door back then. At least in the auto world, Honda and Toyota are known as the "quality and durability" leaders, and you hear so much about XR250's being "bulletproof", so its interesting to see that they are "human", and mistakes do happen. Sounds like the 84-85 XR250 was Hondas "trial and tribulation" bike. Seems they finally got it right in '86, and had it right since.

[Kev_XR]

Ever hear about the early 90's Toyota V-6 truck engines? Many blew the head gasket and had to be rebuilt. Everyone blows it now and then.

[sonic_attack]

Thanks for replies,

Kinda thought so, so i'll not bother.

cheers for everything.