1. Husqvarna Motorcycles Made In Sweden - About 1988 and older

Two Cr500's Help!

Discussion in 'Vintage/Left Kickers' started by vintagemxr, Sep 4, 2018.

  1. vintagemxr Husqvarna
    AA Class

    Husqvarna Motorcycle:
    400 Cross, 450 Desertmaster, 450 CR
    Other Motorcycles:
    lots
    A few years ago I bought a 1984 CR500, made sure it ran, rode it a couple times and put it away because I had things to do before I could get to it. A couple of years ago I found a 1983 CR500-same story. Earlier this summer I dug the '83 out and started to put it in order.

    After getting it pretty well sorted, I started to ride it like I meant it, and found out that it would "die" when I had the throttle pinned, just like it was running out of gas. Figuring it was a fuel problem, I started addressing items that could cause fuel starvation. I have done lots of jetting changes, opened up the petcock, made sure the fuel line was big enough (5/16) even modified the drain plug/main jet well to open it up around the main jet. No results. Got ahold of another 40mm carb that is in obviously good condition and went through all the usual suspects with it, nothing. Thinking of the old adage that most carb problems are really ignition, I put another Motoplat on it with no change. I've set the timing as fast as the factory spec 2.8mm to as slow as 2.0mm. This has been my summer and I'm pretty much stumped.

    The problem only shows up at about 5/8-3/4 throttle and above, under load, at which point it dies out. I can come to an immediate stop and it comes down to a nice even idle, so I'm assuming that the float bowl is full. I can hold the throttle wide open and it will die, then run like a striped ape for a second then die again, not like a lean condition but like its running out of fuel. Main jets have been as small as 330 up to 390, needle valve assy is a 3.3 and I've even opened it up a bit. I've set the float level from 19mm to as high as about 15mm at which point it leaks fuel out of the overflow when on the sidestand. All other jetting is pretty much factory spec. It isn't RPM related, I can pin it in first on flat ground and it continues to run until I'm scared to hold it open any more. In second or higher on a bit of an uphill it will die out before it gets close to max RPM's.

    It starts pretty easy considering what it is, it runs really well after all the fine tuning I've done with the exception of high throttle openings.

    A week or so ago I decided to quit messing with the '83 and get the '84 going. Guess what? Same damn thing exactly! What am I missing? Someone here has to know!
  2. silverstreakNZ Husqvarna
    Pro Class

    Location:
    Christchurch nz
    Husqvarna Motorcycle:
    82cr500,76gp360,90wr250,81 420AXC
    Other Motorcycles:
    74 tm400 , 02 gasgas ec 300
    My 82 500 would suck the bowl low and not run through all gears . Get the biggest fuel filter and hose that will fit .
    I know u said you checked it but it sounds very like fuel tap or hose issue to me .
    Is the float level correct ?
    Sit another tank on it and take it for a ride ?
  3. motomwo Husqvarna
    AA Class

    Location:
    Imbler Oregon
    Husqvarna Motorcycle:
    Many vintage big bore and automatics
    Along with the suggestions above, also remove the fuel valve from the tank and check to make sure the screen/strainer is absolutely clean. And check that fuel flows freely out of the fuel valve. If it is old and crushed remove it and run a hi flow external filter. Also make sure the tank cap vent is clear.

    If all the above does not fix the problem then your magneto or coil maybe getting weak.

    Marty
  4. vintagemxr Husqvarna
    AA Class

    Husqvarna Motorcycle:
    400 Cross, 450 Desertmaster, 450 CR
    Other Motorcycles:
    lots
    At this point there are no fuel filters in it anywhere. It has the karcoma petcock which I have drilled all the passages as big as I can without making things to thin. I've done this with my older 400's also. I'm starting to believe that ignition might be the real problem but thinking that two systems have failed in exactly the same way bothers me a bit.
  5. grouty Auto Lover ...

    Location:
    South West UK
    Husqvarna Motorcycle:
    78 390WR, 78 390 AMX, 500 Humph
    Other Motorcycles:
    works 73 CCM 520, another 73 CCM520
    May sound daft .... but maybe you have a family of mice ! I would check the exhaust systems on both bikes are clear of nests and latrines :cool:
    They may be partially blocked.
  6. stormer254 Husqvarna
    AA Class

    Location:
    England
    Husqvarna Motorcycle:
    More than I dare let her know
    Other Motorcycles:
    Yes!
    My guess for what it's worth is a tarred up spark arrestor, poke some holes through the screen.
  7. suprize Husqvarna
    Pro Class

    Location:
    Bendigo, Australia
    Husqvarna Motorcycle:
    WR 400, bike in a box Moto Villa 350
    Other Motorcycles:
    ktm 300
    another classic is the fuel tank breather line, if it isnt clear, teh fuel tanks partialy vacuums, restricting supply..as soon as you get off the main jet, its all good(ish). my nephew had a yammie wr 400 and he was working as a cattle wrangler and he would blast out to the back country to round up some cows and she would die and not start for 15 - 20 mins. 2 full engine teardowns and significant shop time he spits it and gives it to me and i go riding with no probs...on the way home i take the road and open her up and Bwwwwaaahhhhh it stops. i wait 10 mins kicker into life and head off slowly opening it up in top then i felt it lean out, i shut down a tad (needle) and it picks up and so on... i open flat out..it dies to a stop and i pull the tank cap and Fwwoooosshhh. she sucks in a gut full of air. A chinaman ( somec*&t ) had slipped a ball bearing into his breather line:D and a full tech wkshop couldnt figure it out. check your cap for wasps nest
    justintendo likes this.
  8. vintagemxr Husqvarna
    AA Class

    Husqvarna Motorcycle:
    400 Cross, 450 Desertmaster, 450 CR
    Other Motorcycles:
    lots
    Thanks for all the replies, they are greatly appreciated. The rodent nest was in the 84's air box when I pulled it out of the barn. No sign that they set up housekeeping in the exhaust. I pulled the silencer apart and ran it like that with no change. I've made sure that the vents on the tank and the carb are all clear as I've run into that problem in the past also.

    I'm really starting to think that this must be ignition, it shuts down so suddenly and comes back to life quickly also. I've got a little more I can do with Motoplat spares I have around but I think I may just bite the bullet and buy something modern. Looks like PVL is available but Powerdynamo not so much right now. Anybody have suggestions on new ignition systems?
  9. suprize Husqvarna
    Pro Class

    Location:
    Bendigo, Australia
    Husqvarna Motorcycle:
    WR 400, bike in a box Moto Villa 350
    Other Motorcycles:
    ktm 300
    search motoplat on this forum and there is a place that checks and repairs
  10. GaryM Husqvarna
    AA Class

    Location:
    Austin, Tx
    Husqvarna Motorcycle:
    1981 430cr second 430 CR 500cr
    Other Motorcycles:
    1981 490 Maico
    This is common symtom also for for all things a blocked pilot jet. Yes how I am not sure, because this symtom for stalling out engine at higher revs would never seem be a pilot. But as one closes the throttle down
    after reving down straight and reapplies the throttle these 430s would bog and stop running. Yep - found pilots blocked , cleaned them, and all was fine.
  11. Huskerdoo Husqvarna
    AA Class

    My '84 500 was doing the same thing, acting like it was running out of gas on full throttle. I have the plastic tank, I went through everything, cleaning carb, petcock, etc. Turned out it was actually the petcock, but it wasn't resolved until I bought a new one. Another possible fix could be a larger capacity float bowl nut.
  12. vintagemxr Husqvarna
    AA Class

    Husqvarna Motorcycle:
    400 Cross, 450 Desertmaster, 450 CR
    Other Motorcycles:
    lots
    I think I've tried most of the fuel supply possible fixes, including petcock and float bowl nut. I'm going to put this on hold for a week or two as work is getting in the way for awhile. My plan is to really look into the ignition to see if I'm missing something there. Thanks again everybody for the responses and suggestions. I'll stay on it and post with updates on my (hopefully) progress.
  13. 1982 XC 430 Husqvarna
    AA Class

    Location:
    Seattle Wa
    I'm thinking You might have a Vacuum leak of some sort. Like its sealed up until its under full load and then starts to leak and leans it out just like it would if it wasn't getting enough gas.
  14. vintagemxr Husqvarna
    AA Class

    Husqvarna Motorcycle:
    400 Cross, 450 Desertmaster, 450 CR
    Other Motorcycles:
    lots
    I have been thinking about a vacuum leak also. I went over the inlet manifold (new one) and the reed cage and I'm confident that there is no leak there. The head bolts are tight and I haven't been able to get a reaction by spraying WD-40 around the base gasket. I'm not so sure about the crank seals. It doesn't smoke like the left side wet seal would do and it does start and run pretty well with the exception of the high speed operation. I'm certain that the seals are pretty old though and both bikes have sat around unused for awhile so..........
  15. justintendo klotz super techniplate junkie

    Location:
    mercer, pa/northwest pa
    Husqvarna Motorcycle:
    84 250,86 400,87 430,88 250,95 360
    Other Motorcycles:
    99 kawasaki zrx 1100
    time for a leak down test
  16. suprize Husqvarna
    Pro Class

    Location:
    Bendigo, Australia
    Husqvarna Motorcycle:
    WR 400, bike in a box Moto Villa 350
    Other Motorcycles:
    ktm 300
    im pretty sure if you had a dud seal you would have a seized engine now....
  17. Bigbill Husqvarna
    Pro Class

    Husqvarna Motorcycle:
    '83 250wr
    Other Motorcycles:
    0 right now
  18. ruwfo Administrator

    Location:
    NJ
    Husqvarna Motorcycle:
    1980 390CR,1982 430CR, 1987 250WR
    The other thing to double check is to see if the beasts have a 500 throttle cable in the carb, it's not the same as the 430, i learned this, after rebuilding my 84.
    The 500 cable is longer, so even if it's an aftermarket, make sure it closes all the way. A 430 cable doesn't allow the slide to fall all the way to the bottom, making it lean, and causing
    other issues.
  19. rappster Husqvarna
    AA Class

    Location:
    montana
    Husqvarna Motorcycle:
    tc449 TXC250
    Other Motorcycles:
    rmz250
    I had the same issue on my 84 cr500
    After replacing the ignition problem was cured
    Can’t explain why but it works
    Crashaholic likes this.
  20. darren7878 Husqvarna
    AA Class

    Husqvarna Motorcycle:
    79 CR390 and 84 CR250
    Other Motorcycles:
    81 Maico, 79 Kawasaki, 88 Honda
    Try an Electrex stk018 ignition on it timed @ 2.8 or 3.0 btdc.

    Not a fan of old motoplat systems myself.