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[Admin]

Looks like I've stitched up a deal on an '83 RZ250, checkout eBay item# 300228908565

Same bike as the 350 which was available in the US in '84/5 - might have been called an RD, but not to be confused with the earlier non-powervalve models.

I always wanted one of these bikes when I was younger, friends of mine had them and they were the boy-racer bike of their day... fast, light etc. so this is an opportunity to add to the collection and relive some of my not-so-misspent youth!

I want to go into this with eyes wide open. The bike looks cosmetically great and the current owner has a list of stuff he says has been done, so I'm reasonably confident that everything is above board mechanically as well.

Questions:
Does anyone currently have an RZ250/350/500 to give me an opinion?
What issues do these bikes have given the course of time apart from the usual wear-and-tear?
Are parts available?


Any info greatly appreciated
Cheers
Paul

[Admin]

Nice looking bike Paul.

Wayne, on here, has a RZ350 and I think a couple of others also.

[Admin]

Paul, I have an 84 RZ350 and an '82 RD350LC (currently for sale on Ebay) which is the earlier version without power valves. I have had the RZ for about a year. In that time my assessment is that parts are relatively cheap and just about everything is readily available. There are a few specialty items that command prices higher than I am willing to go, like, used Toomey exhausts at $6-800, used solo seat $4-500.

I think a complete rebuild on the motor will not break the bank. You can buy a brand new crank that fits the Banshee 4 wheeler for about the same cost as rebuilding the old one and it is exactly the same crank. I am betting the crank in the 250 is the same one as well. I would not be surprised if the 350 cylinders are not a bolt up as well.

I don't know about the 250, but the 350 I have is the most fun bike to ride that I own. It handles better than any old bike I have ever been on and will mortally fly if you keep it turned up, and I weigh 225+ with all my gear on. It is certainly not a cross country bike, but for day long rides on rural roads it is a hoot to ride.
I think the 250 has a pretty big following in Europe but I don't think they were ever imported to the US.
I wouldn't hesitate to buy one if it is in good condition and the price was right.

Wayne

[Admin]

Paul, I just went to Ebay and looked at the the bike you bought. NICE! Mine is also the red/white/blue version.

Congratulations!!!

Wayne

[Admin]

I think a complete rebuild on the motor will not break the bank. You can buy a brand new crank that fits the Banshee 4 wheeler for about the same cost as rebuilding the old one and it is exactly the same crank. I am betting the crank in the 250 is the same one as well. I would not be surprised if the 350 cylinders are not a bolt up as well.

Hi Wayne,


AFAIK the 250 bottom end is identical to the 350.

350 barrels and head onto a 250 bottom end was/is a popular upgrade - problem is I think, 350 stuff is becoming unobtanium.
Everything does just bolt up but I think you have to change the oil pump as well, as the 350 is metered differently.

The bike I've bought is ripe for this upgrade. I'll be keen to get my hands on the necessary bits at some stage.
Do you know of a reliable supply in the US or do you have any 350 parts you're ready to sell?

I'm looking forward to getting it home to my place to do some fettling!


Thanks
Paul

[Admin]

Paul, the 350 jugs and such show up on US Ebay quite often. They don't give them away, but they are not cost prohibitive either. If the bike you bought has power valves, the servo motor is probably the same, power valves may be different, so I would try to buy jugs that already had the PV's in them.
If your lower end is good, it is probably a fairly simple swap. The oil pumps come up on Ebay as well. I bought one for a spare a while back for $30. Gasket sets are fairly cheap. Most stuff is still available from Yamaha. I replaced the water pump impeller, bearing and seals, oil pump gear, etc and it did not cost very much to do that and it is really easy to do, took about three hours and I had never seen the inside of an RZ motor before.
I have a Parts manual for the RZ350 but I don't know if it covers the 250 or not. I expect a lot of the parts are interchangable. It is really helpful when working on the thing because it has exploded views of every assembly with associated parts numbers. If you would like a copy of the parts manual, PM me your address and I will make a copy and mail it to you. It may take a while because I will have to photo copy each page individually on my printer. I probably can't do that to the shop manual becasue it is a bound book whereas the parts manual is a photo copy set that comes apart for copying.


Wayne

[Admin]

Paul,

We (my sons and I ) had a bunch to RD400 and RD250's a few years ago when I lived in Melbourne. They were fun but not so reliable.

After I moved to Chicago back in the early ninties I bought a Yellow/black RZ350 with Spec 2 chambers and a corbin seat. That thing is the most fun bike I have owned.

There is no comparison to the old air cooled piston melters. I'm old and slow and everytime I swing a leg over it I become some sort of spotty faced hooligan all over again. It wheelies, does stoppies and the handling is nice and sharp.

For a while I had a very low mileage 86 VFR750, but when it was time to downsize, I kept the RZ - It's more fun.

If you had unlimited funds you could drop a Cheetah or Cub top end with a stroker Banshee crank and get up to about 136 hp out of it. there's a guy in Qld building RS250 Aprilias with 500cc RZ350 motors. try him for barrels etc.

All I need for mine is a Simpson bandit to go with the Draggin jeans

[Admin]

Well, my LC sold for $1125. I thought it would bring around $1500. It needs a thorough going over, but is presentable and runs and rides OK. It does need a little fine tuning and clean up. Some one got a good deal though.

Wayne

[Admin]

I picked this up yesterday for $500. It does not run but the PO said it was running when he stopped riding in 2003 because of his age. He did not buy it new, but has had it for a long time, I think he said since 1986. It needs all the regular stuff a bike that has been neglected needs, but it look pretty good. It is an 1978 Honda CB 750 F3.

I already have the front brake calipers cleaned up and ready to re-install. Master cylinder seems to be in good shape, so I am going to leave it for now except for a good flushing.

Rear brake will get done tomorrow.

I will probably just get it running and re-sell it. I have to many bikes already.



Wayne

[Admin]

Wayne first thing to do is Ditch the Original Carbs.Find some Early 75-76 Carbs to go on it.I have the Same trouble with Mine.Looks like you got a Steal.

[Admin]

Wow thats one clean lookin honda. if it runs as good as it looks you made out great

[Admin]

Jug, looking on Ebay, I see several earlier model carbs listed. Are there some that are better than others. Honda uses a casting number in the carb body to identify the carbs. Do you know which casting numbers are the best onces to use? If I have to buy some, I may as well get the best ones.
According to what I have read, the slow jet (I assume that is the pilot jet)on the stock carbs on this bike are fixed and cannot be changed, and the needle is not adjustable. I don't know how in hell you can even tune the damn thing. All that leaves is the main jet and the air screw (and/or idle mixture screw).
I am probably just gonna sell it once its running correctly, so I don't think I want to go to the trouble of changing carbs unless that is the only way I can get it to run right. But, it has gone 21000 miles configured like it is, so it can't be all bad.

Wayne

[Admin]

That would be an F2, not an F3.

The F2 engines were only 1976 thru 1978, and they were different in pistons, cams, valve angles and other head components. They used a wider valve angle, so larger valves could be fitted, and with that, cans with different lobe centers. Earlier pre-F2 cams, pistons, valves and other head parts don't interchange with the F2 engine parts.

As far as carbs, anything in between 1970 and 1974 should work and fit, they are all OEM Keihin carbs. Stay away from the hot rod CR Keihin's, really hard to tune, lots of jets to change to get close, but usually, no cigar. There are sets of 29mm Mikuni smooth bores out there, and they work well, even on stock engines.

I worked as R&D Chief at R.C. Engineering for three years, and we did a bunch of those later two valve F2 Honda's. I was also the crew chief on the nitro-methane fueled Honda 750 engine'd double, two 1001 cc Honda early 2 valve inline 4's, V8, one facing forward, the other the same from the head gasket down, with that head reversed on the cylinder, intake manifold and 3-71 GMC blower up side down between both engines.

[Admin]

Tuner, good info. I thought the 77 was called an F2 and the 78 was an F3, my mistake. I am going to clean up the stock carbs and put them back on it for now even though they are the crap EPA carbs, have almost no adjustments and probably have the motor strangled. I don't have a clue what condition the rest of the motor is in, so until I find that out, I don't want to spend a bunch of money. It may not run great with these carbs, but it has gone 21000 miles with them, so it at least will run.

Wayne

[Admin]

Set valves COLD, intake .002, exhaust .003. To do so, bring one timing mark to TDC, lets sday it is 1-4, set the loose pair of valves. Rotate the crank 180 degrees for 2-3 TDC, set the loose pair. rotate the crank another 180 degrees, 1-4 will be up again, set the loose pair, again for the last pair. The adjuster covers can get heat welded onto the head. The rubber O rings get heat set and are sometimes hard to get off. Once off, use a bit of anti-seize on the rubbers, and they will be happy again. Use the correct size six flute boxes end wrench for those caps, the break really easily.

Camchain will be set cold, engine OFF. rotate crank to 1-4 TDC, losen nut, then bolt on chain tensioner. If you so desire, put a rod or screwdriver into the rear hole on the tensioner, and push the center rod forward. Some tensioners don't need this, but checking doesn't hurt, Don't force the rod, just make sure it is fairly tight, with no slack. tighten the bolt, then nut.

Timing. This gets a little complicated. you will need a dwell met3r that uses battery power, NOT one that runs off the point set. The meter will have three wires, battery, ground, point read. Also, timing light, if dial back, leave the dial back feature OFF. You will see two points, and two point plates, one will be full circle, cyls 1-4, the other will run 2-3. Work with 1'4 FIRST. We now do a "create a specification".

Set the first set of points to .017/.018. Fire engine up and take dwell reading, this is the new dwell specification. Lets say dwell reads 48 degrees on the 8 cylinder scale. That is the spec for BOTH point sets.

Leave the first set of points at the dwell spec, and set the timing for 1-4. You may have to jockey both then point setting and timing back and forth a few times to get both right. Set the tining to the F line, NOT the full advance line. Do check the advance, and make sure the mechanical advance is working correctly. If you have to take the advance apart to clean and lube (use waterproof boat wheel bearing grease), make sure you put the points cam back on the right way, and not backwards. Then, redo the 1-4 timing/dwell. next, set the second set of points and timing to the same dwell spec, and timing for 2-3.

Carbs. If I remember those carbs, the float level should be 22mm, but do check the Honda book for specs, I may be addle pated and forgetful on that one spec. On the rubber carb holders, they take a "set" after a long life, and may not seal well with the stock clamps. I switch the clamps for narrow automotive type screw claps, like for water hoses. this way, you can clamp down on the clamps, and pull the rubber sealed off, head and carb sides. If the air box isn't in place, I strongly suggest using it if you have it, if not, Dyna-Jet stage 3 kit will get you back about 40 percent of the efficiency lost by ripping the stock air box off the bike. K&N filter for the stock air box works best.

On the fuel screws on the underside of the carbs. They need to all be the same, no separate adjustment, if one is 3 turns out, ALL are 3 turns out. the object here is to get all 4 separate engines to run as one bigger one, not 4 all over the place.

Use a mercury manometer (Carb-Stix) to set the balance. At idle, all 4 carbs should be dead same across the tubes. One thing you might find is that the carbs are dead lean with the tops off, for the adjustment, so, you might just set the tops on the carbs, take one off, adjust, set the cap back on. If I remember correctly, one carb will have no balance adjuster, the othr 3 will. Set all carbs to the non-adjuster one.

NGK D8EA plugs, gapped .032. Natural oil, Castrol GTX, 20W-50, no lighter. Those engines run a touch hot, and light oil leads to hardening if seals and too much heat. Light oils make for a real world example of the engine being a "heat pump". DO NOT USE FRAM OIL FILTERS. Use anybody else's. The Fram junk comes apart on the end caps of the filtering media (their end caps are cardboard, and the glue is trash), and if that trash goes through the engine oil passages, and especially to the .060 oil restrictors for the rocker arms. Plug them up, cam/rockers smoke right out of the engine. One nice thing the F series has over the rest of the CB 750's is, YOU DON'T HAVE TO PULL THE ENGINE OUT OF THE FRAME TO GET THE TOP END OFF.

One other area is the spark plug caps. They have resitors in them. To check them, remove them off the coil wires, they "unscrew". Resistance should be near or right on 5,000 ohms. Replace if they don't measure up. If you see something like 4,670m ohms, it is OK. I have taken some of the resistor caps apart if they have a screw slot in the plug end, You will find a cap with screw slot, resistor, brass plate and spring. Sometimes, the resistor and internal parts grow ozone, and just go nuts on resistance. Clean and reassemble. Dirty plug cap can cause a full on miss/dead cylinder.

The ignition systems use a single dual lead coil per cylinder pair, 1-4, 2-3. The coils operate thus, one lead fires from the wire, positive, to negative through the plug, the other wire fires negative to positive, a complete loop. Neither wire grounds through the coil itself, one wire is negative, the other positive, so don't freak out when you see one plug of a pair fire from the ground strap to the center electrode, that is NORMAL.

Clutch adjustment: remove the steel outer cover off the clutch cover. Yo will see the engine end of the clutch cable and the puller. Slack the cable on both the engine end and the clutch lever on the handlebar. Loosen the lock nut on the lever adjuster on the clutch cover slightly, so you can rotate the inner set screw freely, but don't remove the nut. turn the screw in (clockwise) until the screw stops full up against the clutch. Loosen (counter clockwise) the screw 1/4th to 3/8ths of a turn, lock the lock nut down. Adjust the cable to get about 3 to 5 m's of slack in the cable at the lever end on the bar. This isn't too tight, the clutch will add a little slack when the engine heats up.

Tire pressures, rear, 38 psi, front, 36 psi. Chain slack, pull the swing arm to 1/2 its travel, set the chain slack to 10mm's at the chain lower center of its run, WITH THE SWING ARM AT HALF ITS TRAVEL.

I'll probably remember more for you tomorrow, but this is just a couple of things to do to get you started.