The Air Cooled Monoshock Thread

Discussion in 'Trials' started by Brewtus, Feb 19, 2018.

  1. Brewtus

    Brewtus Buffoonery, Inc.

    Joined:
    Jul 30, 2008
    Oddometer:
    4,857
    Location:
    Portales, New Mexico
    Just as the title says, post your ACM bikes, stories, and experiences here.

    I just got my first ACM yesterday, a 1986 Montesa Cota 304. Dragged it home, and naturally washed it right off the bat -

    20180219_110210.jpg

    Serviced the chain and air filter, new plug, and did some minor adjustments on it. Fired it up and let it blow all kinds of spooge out of the pipe due to the bottom end being filled with premix. After 10 minutes it cleared out and idled. Rejetted from a 140 to a 130 in the Amal, and it ran much crisper. :D

    Since I have been spoiled on Modern Trials bikes I am planning a footpeg relocation to make this tall sumbitch easier to maneuver, but otherwise this old gal is a hoot to ride. Engine is nice and tight, decent power (more tuning is definitely in order), brakes are acceptable (front brake replaced with an AJP unit), and the suspenders are good with a Works Performance shock. In Progress pic -

    Message_1519065806196.jpg

    I started this thread to avoid filling up Motobene's ACM Competition Experience thread with builds and stories. What are yours?

    More to come.... :thumb
    #1
  2. DyrWolf

    DyrWolf Long timer

    Joined:
    Jan 21, 2012
    Oddometer:
    1,036
    Location:
    RICHMOND VA
    Poor old thing 8F874FE8-E6A9-4C5A-95B0-DB7D5C7E763C.jpeg 12195E71-E7E1-4A89-8B1D-3F48182A87B1.jpeg
    #2
    Norman Foley and Brewtus like this.
  3. motobene

    motobene Motoing for 46 years

    Joined:
    Mar 9, 2013
    Oddometer:
    4,798
    Location:
    Wichita Mountains SW Oklahoma
    Hey that Cora 304's header pipe goes on forever!

    Oh those arch-pain footpegs....
    #3
  4. lineaway

    lineaway Long timer

    Joined:
    Oct 1, 2011
    Oddometer:
    7,742
    Location:
    nm
    Those foot pegs are an all thread up grade.:D
    #4
  5. Brewtus

    Brewtus Buffoonery, Inc.

    Joined:
    Jul 30, 2008
    Oddometer:
    4,857
    Location:
    Portales, New Mexico
    I'll post a pic of the pegs later to show off the upgrade. :-)

    Getting schooled on Amal carb tuning, sneaking up on getting the 304 to run nice and crisp. Swami Brewtus predicts a VM26 in this bike's future, but for now I'll deal with the Amal and the jets supplied with the bike.

    Quickie riding impression around the place reveals that it handles very well and it has a nice progressive clutch action. It's lighter than the Reflex (thankfully!) and the AJP front brake upgrade works pretty good. The Works shock outperformes the front forks, so a service will happen soon. The only minor fly in the ointment is the sportbike-like location of the footpegs, and I will rectify that pretty soon. I'm enjoying the bike so far, and am looking forward to competing on it. :D
    #5
    motobene and Old Geezer like this.
  6. Huzband

    Huzband Team Dirt

    Joined:
    Oct 4, 2006
    Oddometer:
    7,197
    Location:
    Cowford, Fl.
    First you buy a bike with an RC51 frame. Now you get one with a CR480 pipe. I can't wait to see what's next. :D
    #6
    Brewtus likes this.
  7. Brewtus

    Brewtus Buffoonery, Inc.

    Joined:
    Jul 30, 2008
    Oddometer:
    4,857
    Location:
    Portales, New Mexico

    As promised, the peg mod made by the PO or the PPO...

    20180222_133123.jpg

    Hey it works right? Kudos to whomever for making the best out of material on hand to widen the pegs!! :D

    While running the bike today, I did notice that the tank was being vented pretty hard upon throttle opening. To the point that air was blowing out of the cap vent to such a great extent that I could make it whistle by partially blocking off the vent hose. I removed the fuel cap, and watched fuel bubble and toil when the throttle was opened. WTF?? Okay, time to burn out the exhaust and check ignition timing....

    The mid box did weigh something like 8lbs. when I removed it. Time to break out the propane torch. :evil
    #7
  8. lineaway

    lineaway Long timer

    Joined:
    Oct 1, 2011
    Oddometer:
    7,742
    Location:
    nm
    Remove the main jet from the fuel cap.
    #8
    Huzband, Norman Foley and Brewtus like this.
  9. PSchrauber

    PSchrauber Long timer

    Joined:
    Jan 3, 2011
    Oddometer:
    1,212
    Location:
    Summer: Kemiö, Finland; Winter: North Germany
    Nice bike I had one and owning the preprocessor. Keep a careful eye to the kick starter mechanism and just look up if the inner stip plate is still in correct position and hasn't start to bend. If so, the teeth of your kickstarter mechanism will crunsh super fast.

    Carb anything else then the AMAL is an improvement. The bike uses tremendous amounts of gas with the AMAL a DellOrto will pig the bike up.

    The bike is good the differences between the 304 and the 242 are just the front brake and rear suspension, you might think about a conversion to its former roots:evil.

    Looking forward too more and if you need the carb adjustments for the DellOrto I can help out which would save a lot of testing and money.
    #9
    Norman Foley and Brewtus like this.
  10. PSchrauber

    PSchrauber Long timer

    Joined:
    Jan 3, 2011
    Oddometer:
    1,212
    Location:
    Summer: Kemiö, Finland; Winter: North Germany
    Last not least 01:
    Please look up the bushes of the swing arm, the needle bearings are very brittle and need much of care,
    try to mount good once not cheap stuff these will break down fast, Industrial FAG are good ones.

    Last not least 02:
    Mount the chain tubes this is one of the best inventions Montesa ever made.
    I think you have a steel swing arm instead of Aluminium so the chain can't
    hurt so much the swing arm but it will also the chain get stressed
    so much more through dirt.

    Last not least 03:
    The very first protoype of the 304 which was set up by Win Suiker form the Netherlands (Former Montesa Importer),
    and with the Andrea Codina as a rider, that was the first apperance of the 304 back then.
    Interesting too that it was more an archivement of importers and dealers to keep this model line developed,
    while in Spain the love went more towards the 330 and later 335.
    These did not progress further but the 304 was followed by many models like 307, 309 and 310.

    [​IMG]
    #10
    Norman Foley and Brewtus like this.
  11. Brewtus

    Brewtus Buffoonery, Inc.

    Joined:
    Jul 30, 2008
    Oddometer:
    4,857
    Location:
    Portales, New Mexico

    Are you saying my fuel cap needs to be rejetted? :lol3

    20180223_113330.jpg

    PSchrauber, thanks for the tips. I'm leaning towards an OKO carb after reading good things about them on Trials Central. After cleaning out the exhaust first....
    #11
    Norman Foley likes this.
  12. Brewtus

    Brewtus Buffoonery, Inc.

    Joined:
    Jul 30, 2008
    Oddometer:
    4,857
    Location:
    Portales, New Mexico
    Someone did a lot of mods to this old 304. Standard models have a full cradle frame, but someone modded this one for a skidplate -

    20180313_160046.jpg

    20180313_160117.jpg

    I also mined down through several layers of paint to find some original graphics -

    20180313_155442.jpg

    The pics I've seen of these didn't have a black background behind the military stencil graphic, so who knows what's up with this particular bike. It's not an early production run (VIN is in the 3000s) so I don't think it's a prototype, but I know very little about these '80's Montesas.

    More to come.... :thumb
    #12
    jonnyc21 and Norman Foley like this.
  13. Brewtus

    Brewtus Buffoonery, Inc.

    Joined:
    Jul 30, 2008
    Oddometer:
    4,857
    Location:
    Portales, New Mexico
    A bit of a cross-post, but I added another ACM to the Brewtus Scuderia today -

    20180314_160727.jpg

    Got it for Miss Bitters to compete in MWVTA this year. She rode it for about 45 minutes today and really dug it!

    Yes, I know the fender is taped together. Had to be in 1 piece for the pic. :lol3
    #13
    Huzband and jonnyc21 like this.
  14. lineaway

    lineaway Long timer

    Joined:
    Oct 1, 2011
    Oddometer:
    7,742
    Location:
    nm
    Put the crossbar back on the bars.
    #14
    LemmeTry, jonnyc21 and Brewtus like this.
  15. Brewtus

    Brewtus Buffoonery, Inc.

    Joined:
    Jul 30, 2008
    Oddometer:
    4,857
    Location:
    Portales, New Mexico

    I would, if a crossbar would have been included. :lol3 Methinks I could probably dig one up around here, though.
    #15
    jonnyc21 likes this.
  16. 2whlrcr

    2whlrcr gooligan

    Joined:
    Jan 30, 2005
    Oddometer:
    11,482
    Location:
    Dubuque, Iowa
    But it looks like a modern bike without it!
    #16
    Brewtus likes this.
  17. PSchrauber

    PSchrauber Long timer

    Joined:
    Jan 3, 2011
    Oddometer:
    1,212
    Location:
    Summer: Kemiö, Finland; Winter: North Germany
    Nice 305 too we have one guy here that collects 305's he has several.

    I don't know why someone did that ro the 304 frame that was a strange idea to cut out the front lower rails but leave the rear no real benefit beside weaken the frame a bit. I would weld up the former rails again. Montess did not use crazy steel like SWM or late Bultacos.
    #17
    Brewtus likes this.
  18. Huzband

    Huzband Team Dirt

    Joined:
    Oct 4, 2006
    Oddometer:
    7,197
    Location:
    Cowford, Fl.
    Stop teasing me with Mopar pics.
    #18
    Brewtus likes this.
  19. Brewtus

    Brewtus Buffoonery, Inc.

    Joined:
    Jul 30, 2008
    Oddometer:
    4,857
    Location:
    Portales, New Mexico
    Been chasing down running issues with the 304. Wire Hand and I had several conversations about it, and decided taking a peek at the ignition system would not be out of order. He was kind enough to send me the flywheel puller he bought for it (thanks!!) so I removed it to take a peek. I found the woodruff key down in the stator, and it was too small for the crank/flywheel anyway. I modified a TY80 key (go figure) and it fit perfectly. I then noticed that the condenser was loose internally, allowing the wire connection to move around in the housing. Another modified TY80 part, and we were good to go. Reassemble, set point gap, kick, and...

    No spark. Not even a little. :fpalm

    How does the old saying go? "It started out running poorly, so I tuned it to a standstill". :shog

    *Sigh* I think I'll go work on a big-block Mopar now... :bluduh
    #19
    Buschog and Huzband like this.
  20. PSchrauber

    PSchrauber Long timer

    Joined:
    Jan 3, 2011
    Oddometer:
    1,212
    Location:
    Summer: Kemiö, Finland; Winter: North Germany
    Did you adjust the points?
    They should be 0,4mm.

    Did you look up that the points are aligned to each other, you might take #400 or #600 sand paper for metal, then fold the paper once an pull a bit of 5cm two times through the points just to get both points flush.

    Does help a bit best is if oder points are replaced against NOS as the metal of the replica points is nowadays to soft.

    If you have difficulties getting points, condensers or coils ... I should have them ... in need PM. A small parcel is easy to sent.
    #20