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RZ350 hard to start

Discussion in '2-Stroke Machines' started by Motofun352, Sep 1, 2017.

  1. Motofun352

    Motofun352 Well-Known Member

    My '84 RZ350 is a SOB to start...I know it shouldn't be this way. I have to pump the throttle several times and kick to get a couple of bangs. I do this about 30 times until I can catch it with the throttle and rev it up. Have to keep it at 4000 rpm for about 2 minutes until it will settle down and run at idle without stalling. Once it is warm it will start with 1 or 2 kicks. I did have it re-bored with new pistons several years ago (.1mm over?). I cleaned the carbs also...perhaps the choke enrichener? I still run the oil injection system which I think may be over injecting oil as it does consume quite a bit of oil when running.....Ideas?
    Thanks
     
  2. pscook

    pscook Well-Known Member

    Do you have to pump the throttle before kicking? That shouldn't do anything as those carbs shouldn't have a throttle pump; i.e.: when you open the throttle, only the slides come up. Fuel doesn't rise out of the bowl until a vacuum signal crosses the needle jet/idle circuit.

    New plugs? If not, how old are the plugs? Have you inspected the coil wiring and high tension leads for connections? Good/new plug caps?

    Assuming it runs fine when warm, have you tried holding the throttle open while kicking, or just pumping the throttle, then kicking? Have you cleaned the choke circuit? Oil has nothing to do with the combustion mixture (except to displace gas), so too much oil just fills the crankcase/cylinder/pipe until it's running, it shouldn't foul the plug unless it's an extremely excessive amount of oil (or the plug gap is off/poor electrical connection/weak spark).
     
  3. Motofun352

    Motofun352 Well-Known Member

    I've tried holding the throttle open while kicking, doesn't help. I pump the throttle about four or five times, then kick and on the second or third kick I get 2 or 3 firings...repeat process many times. I'm thinking that I have to get some heat, a little at a time, into it in order for it to catch. Perhaps my last re-bore was bad and I'm not getting enough compression until it's hot? Cold compression is on the order of 5.5 :1 though 2 stroke compression testing is iffy (at least for me). Anyone know what the compression ratio is supposed to be for a stock 350?
     
  4. pscook

    pscook Well-Known Member

    Just pumping the throttle really isn't doing anything as the RZs don't have an accelerator pump. They really need air flowing across the needle jet as well as through the idle circuit to pull gas out of the float bowl and into the air/oil mixture. What has changed since it was easy(er) to start? Has it ever been easy to start? I assume you have new plugs in it, at least, right? My SOB 300 2ts were terrible to start at 10 kicks, or so I thought, but 30 kicks really shows something out of the ordinary. What's different?
     
  5. britx303

    britx303 Boomstick Butcher…..

    Pilot jets clogged/too small? Im not a 2T tuner by any stretch,so just a thought.
     
  6. lrrs517

    lrrs517 Internet Investigative Officer

    A couple of things to look at that are free and easy to just check is a cracked carb boot and reed valves that are chipped up. BTW a rich oil condition means a lean condition. Oil displaces fuel. You want that right. Check your baffles for being clogged.
     
  7. Motofun352

    Motofun352 Well-Known Member

    OK thanks, that gives me some things to explore. Since it smokes like a locomotive upon startup I'll disconnect the oil injection and try pre-mix ('cause that's easy:)). It does have relatively new gaskets on the boots and new reed valves, but those can be checked. A carb rebuild (again) isn't out of order..need to recheck the floats too, I guess. This is beginning to look more like a winter activity....
     
  8. fastfreddie

    fastfreddie Midnight Oil Garage

    Who did the rebore? If they were not versed in 2-strokes, they may not have known to relieve the bridge in the exhaust port. Now you have a scarred piston and rings that lose compression. Low compression kills starting a 2-stroke.
     
  9. 50Joe

    50Joe Registered User

    Check the tank vent and fuel petcock. The petcock uses vacuum to pull fuel into the carbs. There is a prime setting on the petcock which will allow fuel to flow withoutthe vacuum but don't leave it on that setting with the bike stored.
     
  10. Motofun352

    Motofun352 Well-Known Member

    Thanks Fred, good info...Unfortunately my RZ has always acted this way, even before the re-bore. Somehow I keep on coming back to a carb problem. My next "trick" will be to remove the air filter, mix up some pre-mix in a spray bottle and try to kick this sucker while lightly spraying directly into the inlet....have to try this outdoors...just in case.
     
  11. expat

    expat Active Member

    Check the crankshaft oil seals. Sounds like a leak somewhere if you are sure the carbs are clean and set correctly..
     
  12. d_alexand

    d_alexand Well-Known Member

    Check the tank vent & petcock as mentioned above, fuel lines, reeds, and your air screws. It kinda sounds like a combination of little issues like air screw settings and rich pilot jets.
     
  13. OldSwartout

    OldSwartout Well-Known Member

    I'm not familiar with the crankshaft seal construction on the RZ, but on any twin 2T, a leaking center seal will make it difficult to kickstart. That's more likely to happen with a rubber center seal than a metal labyrinth seal, unless the center bearing is on its way to failure. If the RZ has a rubber lip seal in the center, then a leakdown test will show it.
     
  14. erock768

    erock768 Well-Known Member

    After checking all the obvious stuff like leaking crank seals, cracked reeds, reed boots, exhaust pipe joint to head etc....I would investigate the pilot circuit or the enrichener circuit. The fact that you said that you need to crack the throttle in order for it to start after kicking a bunch coupled with the fact that it idles fine after warming up is all indicative of an over rich idle /low speed circuit. It appears that you need more air to get it to light. Once it warms up it idles ok...this is because as the engine becomes warm and the mixture is drawn through the crank case it leans out. Also to support this is the fact that you said you over bored it...a larger bore will generate more intake "signal" than a smaller bore. This effectively increases the 'suction' through the carburetor venturi which sucks up more fuel. Lean out the pilot jet one step and see what happens.

    E
     
  15. erock768

    erock768 Well-Known Member

    Also, if you had a leaking crank seal that was sucking air, or had a bad air leak the bike would start and most likely rev to the moon. If it dies when you close the throttle or it idles without "running on" you most likely dont have a [bad] air leak
     
  16. erock768

    erock768 Well-Known Member

    If I recall, (had a RZ years ago) they have keihin FCRs on them right? IF that is the case, turn in the fuel screw (not the idle screw - the screw in the bottom of the carb) a bit to lean out the lowspeed circuit, before reducing the pilot jet.
     
  17. yamageezer

    yamageezer Well-Known Member

    Also make sure the left side float bowl as a clear (clean) choke jet. The right side does not have said jet (hole is blocked up) as it just shares the choke from the right carb, via the 2" long rubber hose between the carb bodies. Of course if it has sat, maybe just dirty carbs, If you clean the carbs, be sure to install the correct bowl on the correct carb!
     

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