RZ 350 Quandry

[silverstrom]

That seems VERY unlikely, Sam. You probably should look at the intake side of the bike, carbs-to-cylinder, first. Any chance that the slides were hung wide open?

SLides on the carbs you mean?

If the carbs snap back to full closed by themselves, you don't have to worry about slides staying open.

Check the gaskets on the carbs. Tops, seals behind adjusting screws, etc. Check the choke/starter circuit is properly sealed.

If a head gasket was bad enough to allow that much air into the motor I would expect to see a coolant leak, either externally, or into a cylinder. If a cylinder was pulling in coolant the engine wouldn't run away uncontrollably.

I wouldn't expect a power valve leak to cause a runaway.

Base gaskets and reed gaskets are know leakage points. You should be using case sealant on both sides of the base gaskets and reed gaskets.

Intake manifolds good with no cracks? Another know leakage point.

Based on your engine run away description it sounds like a major air leak, or several medium leaks. As I said, pressure test it to be 100% sure. Just because it worked earlier doesn't mean it's good now. Put 5 or 6 PSI into the motor and brush a soap solution on. You'll see bubbles where you have air leaks. If you find no air leaks, well, that would be very puzzling.

[sam_e787]

That seems VERY unlikely, Sam. You probably should look at the intake side of the bike, carbs-to-cylinder, first. Any chance that the slides were hung wide open?

SLides on the carbs you mean?

If the carbs snap back to full closed by themselves, you don't have to worry about slides staying open.

Check the gaskets on the carbs. Tops, seals behind adjusting screws, etc. Check the choke/starter circuit is properly sealed.

If a head gasket was bad enough to allow that much air into the motor I would expect to see a coolant leak, either externally, or into a cylinder. If a cylinder was pulling in coolant the engine wouldn't run away uncontrollably.

I wouldn't expect a power valve leak to cause a runaway.

Base gaskets and reed gaskets are know leakage points. You should be using case sealant on both sides of the base gaskets and reed gaskets.

Intake manifolds good with no cracks? Another know leakage point.

Based on your engine run away description it sounds like a major air leak, or several medium leaks. As I said, pressure test it to be 100% sure. Just because it worked earlier doesn't mean it's good now. Put 5 or 6 PSI into the motor and brush a soap solution on. You'll see bubbles where you have air leaks. If you find no air leaks, well, that would be very puzzling.

Ok that all makes sense. I saw a pressure tester from a guy on youtube that works on Banshees. I think i'm gonna pick one up since i like the way he works and details.
I'll let you know guys know what i find. It's definitely not leaking coolant anywhere so the head must be ok.

[Darrell]

I re-read your original post, and if I understand it correctly the carburetor came free when you pulled on the fuel line. That makes me think that Questo vechio was correct in being suspicious of that. Are you certain that you tightened the carburetor clamps securely? If the carb came free from pulling the fuel line, it may have been loose or not fully seated in the boot.

Silverstrom is on the money.

[sam_e787]

So i got it figured out. Some of you were right on the money.

I spoke with Mr. Toomey and he assured me it wasn't the head that would cause a "run away" like that and that it sounded like it was the Slides being stick on carb.

I took them off and redid the cable attachment and the put the slide back in and sure enough, it was not going down completely on both carbs.

I played with them for a bit and added a lil lube and started to mess with the twist throttle and letting it slam back with spring and they realigned themselves.

Now it starts easy and is very crisp.

The work Mr. Toomey did on the head was awesome and not sure why but the bike even runs cooler and better gas mileage. I am very happy with it.

I will say that i have a lil PTSD now though everytime i turn it on. lol it's gonna take a lil while before i have that feeling of thinking it's gonna go bat shit again..

Thanks everyone for the help and ideas.

It is appreciated.

[Darrell]

It's always great when you solve a problem. Good job.

[Questo vecchio rz]

Yep...a RZ350 / Banshee runs cooler
and physically noticeably faster with a correct head modification.
I learned something here as well, I've never had carbs slide issues I'll keep it in mind... If I ever have that problem.
Good job guys

[85RZwade]

A little story: I was 15, on a trail ride with my dad and some of his friends. We stopped on a bit of a hill for a break, and I decided to adjust the needle in my trusty TY175. Afterwards, I kicked and kicked but it would not start, so I pointed it downhill to compression start it...Oh, it started all right! After the dust had settled and I determined that both the TY and I were unbroken, I went back into the carb to find I’d installed the slide backwards. Dumb kid.

[brrrappp]

I have a little story that will give anyone with a screw-on throttle top a scare...
The throttle "Cap" on the top of the carb of my 1982 YZ490 popped off just after landing a big jump onto a straight. I had a short WFO straight and a steep up hill with a right turn at the top. By the time I knew the throttle was stuck wide open it was too late. The bike hit the up-hill transition at about 65mph fully compressed the suspension and launched into the trees about 20 feet up in the air above the top of the hill. I came off the back and landed on my head at the base of the hill. I have zero recollection of the event as I had a pretty good concussion. I know what happened based on the eyewitness account from the guy behind me and a few watchers at the riding area.
Bent forks, Bent frame bent wheel and bars...bent pride....no broken bones!
When I got around to repairing the bike, I discovered that the threads of the throttle-cap would get enough bite to screw on and feel tight but you could wriggle it with a bit of upward pressure and it would pop right off.
I bought a new cap and installed it with no future issues. A local road-racer with a frame jig straightened and welded the frame.

[sam_e787]

I have a little story that will give anyone with a screw-on throttle top a scare...
The throttle "Cap" on the top of the carb of my 1982 YZ490 popped off just after landing a big jump onto a straight. I had a short WFO straight and a steep up hill with a right turn at the top. By the time I knew the throttle was stuck wide open it was too late. The bike hit the up-hill transition at about 65mph fully compressed the suspension and launched into the trees about 20 feet up in the air above the top of the hill. I came off the back and landed on my head at the base of the hill. I have zero recollection of the event as I had a pretty good concussion. I know what happened based on the eyewitness account from the guy behind me and a few watchers at the riding area.
Bent forks, Bent frame bent wheel and bars...bent pride....no broken bones!
When I got around to repairing the bike, I discovered that the threads of the throttle-cap would get enough bite to screw on and feel tight but you could wriggle it with a bit of upward pressure and it would pop right off.
I bought a new cap and installed it with no future issues. A local road-racer with a frame jig straightened and welded the frame.

That SUCKS! Lucky no broken bones.

That kinda sounds like what happened to a guy that use to race when i followed Motocross, Doug Henry i believe his name was.

That was a nasty back compression for him.

[(F5)]

The fact that it was hard to start as I was reading from the beginning made me think of slides not being home. On screwtop carb bikes you can often reverse the slides to similar effect.
A mate had an RM with knackered screw top that would spring off. Drilled some holes and self tap screws from the side. At 16 there is somewhat of a lack of mechanical sympathy.

[Darrell]

I was trying to get my RZ350 race bike ready at a time when I was working a ton of overtime. I got everything together but the throttle was hanging up just a bit, keeping the engine from returning all the way to idle. I rationalized that, since I never closed the throttle all the way on the race track anyway, that it would be okay and I could fix it "later." I took the bike down the steep, twisting road to my house to test it wearing a pair of jeans and a t-shirt. Almost all the way to the bottom of the hill the throttle stuck wide open and I crashed pretty hard in a curve. Steep drop off on one side, trees on the other. Naturally my first thought was for the bike, laying on its side and screaming at WOF, so I ran over, shut it off, and stood it up. I was looking it over and could hear fluid dripping from somewhere, and was looking for the leak when I noticed the liquid was warm and red and the leak was actually me. I'd done a pretty fair job of dermabrasion on my shoulder, knee, and most of my left arm. The worst of that was having it all scrubbed out by a doctor on the following Monday, AFTER my Sunday racing, which I only did to prove how tough I was.
I consider myself to be a pretty bright guy, but I made knowingly made several bad decisions all in a row there... rushing to prep the bike, ignoring a problem, no riding gear... At least the bike was okay!

[Ricino]

Oh, man... those scary "WOT" stories...

Some time ago, I soda blasted my OEM MIC carbs. I also blasted the slides and removed that black coating.
That sort of teflon coating was very worn out. I still haven't used those carbs because I'm not done with my project.

Should I then avoid using those slides??? I guess yes...

[brrrappp]

I consider myself to be a pretty bright guy, but I made knowingly made several bad decisions all in a row there... rushing to prep the bike, ignoring a problem, no riding gear... At least the bike was okay!

"At least the bike was Okay"
LOL
I will always remember when I was under 20 that my thoughts were - I heal and that's less expensive than bike parts.
At this age when I sling a leg over my MX bike I never think about sacrificing my body to save the bike anymore.
HOWEVER......
Even now- at well over 50, I feel I would take a bullet to save the bike when I'm aboard the RZ350.

[(F5)]

Groan, its coming back to me. So different scenario, same result. Race bike nipped up a little in practice, bugger, grabbed the other one and joined next race. Started well back as just 2 warm up laps to clean tyre off etc. Launch, corner 2 I back off as uphill corner approaches but the carb doesn't believe me. Hit the brake in disbelief but on reflection should have pulled the clutch first.
Driven rear slides front and flicks me over the highside like one of those poor saps in a wrestling match. Except that it wasn't practiced or on a sprung surface. Lights go out.

Turns out the throttle was a whirlpool type and the cover had been disintegrating over the years/crash damage and something or a part of it dropped into the scheme and stopped it closing, maybe 1/2 way, at least how I figure. Many months of not riding, sleeping sitting upright, operation(s) and end of racing. Had nightmares about it, was unexpectedly violent. And my fault for not replacing critical parts, even though I think I was super unlucky. We made a new cover out of metal this time and it was fine with next rider/s.

[Darrell]

I was lucky, I guess. I've had a couple of high-speed get-offs, but never broke a bone or did any real damage. I had a high-side on a TZ-250, but landed back on the saddle and "saved" it. I put "saved" in quotation marks because I didn't do anything except fly into the air and land back on the bike and that was pure luck, no skill involved. I have a picture somewhere of me flying head-down and heels up over my bike at Willow Springs, but I landed on my feet and no harm done. And I crashed at the end of the back straight at Sears Point just after it was paved. It was a practice day and there were really, really fast cars on the track. I'd wait until they went past, then get in three or four laps before pulling off to let them go by again. So I'm sliding down the track at 140 or so, trying to look back behind me to see if I was about to be smashed by a race car. And my last race was at Seattle International Raceway, now Evergreen, when I got T-boned by another rider when I lost the rear end, wound up WAY outside the turn, and the guy behind me followed me instead of holding his line. There was a big gouge on the tank where my knee should have been from the other rider's front axle, tire marks on the tank, and somehow I suffered nothing more than being lights-out for a minute or so. (My wife saw that one.) The other guy broke his collar bone.
Racing was fun, though. Too bad I had no talent....