Bultaco Metalla Mk2

[belldane]

Hello Everyone

I suspect that some of you may have owned one of the above bikes at some stage (and now decided to go a bit slower) and I am hoping you may be able to help with a problem I am having.

Bought the bike sight unseen and when I got it home discovered that all that was claimed in the ad was not factual, but that is my problem now.

The bike starts with no trouble after a couple of kicks. When I go for a ride, 1st and 2nd gear no problems. If I increase the revs above approx 3000rpm the bike starts to splutter and run erratically. Just does not like high revs. Things I have had checked are coil -seems fine, swapped for another spare that I have - same problem. Changed the points, plug, the plug cap and condenser with new new ones - same problem. Checked timing.-spot on -same problem. Carby cleaned many times and according to hand book right jets, needle position, etc ' also new needle and seat -same problem. Air filter has been cleaned also muffler removed in case it was clogged up somewhere and still the same problem.

I am starting to wonder if the the person who supposedly restored the bike did something to cause the problem.

The only options open to me at the moment are to start a complete restoration of the motor and to make sure that all is ok, but before I do that can you think of anything else I should check on? Maybe crank case seals, air leaks somewhere, even the wrong cylinder or piston for the carb jetting? Oh! one thing I forgot was that the original Amal carby has been replaced with one bought in England, which was suppossed to be the same as the original.

I am at your mercy. Thanks for any help you can provide

[feetupfun]

You have not said if the erratic running is throttle-position dependent or not.

Because you have said that first and second gears are OK but not the higher gears, I suspect the problem is that the fuel level in the float bowl is not being sustained under conditions of high demand. This is because when accellerating through the gears, the throttle is usually held open for longer in the higher gears, yet while the bike is idling before you start to ride away, the fuel level is more likely to be able to recover).

To check for this you will need to check the flow rate through the whole fuel path ie from tank though tap, hose, in-line filter if fitted, banjo fitting filter and float needle/seat and with the fuel tank cap in place all at the same time.

The original fuel taps on Bultacos are notorious for being restrictive but your problem may be anywhere in the system.

It would help with the diagnosis if you could work out if your problem is throttle-position dependent.

It is possible for an ignition problem to be RPM dependent, but if it was that, you would probably have the problem in all gears.

[nh014]

I agree with Feetupfun on the fuel supply, had some of that with my Metralla. I'd also suggest you replace the crankshaft seals. Here are some restoration tips that I've had in my Metralla file that may be of value to you. Sorry if the original author happens to read this, but I've lost track of where I found them on the internet.

RANDOM RESTORATION NOTES:

Shocks & Front Forks:

Both rear shock & front fork springs are single-rate rated at 50 lb. / in. compression

Spring dimensions:

Front Fork: height: 198.2 mm; outside diameter: 41.93 mm; inside diameter: 31.15 mm; spring wire dia.: 5.39 mm

Damper Fluid: Hugh's Bultaco recommends 5 wt. oil for the original Betor shocks. Fork oil spec from the owner's manual is 30 wt., John Sommerville recommends 40 wt. for un-worn forks. (I used Bel-Ray fork oil & shock oil)

Carbs / manifolds:

For engine s/n's M23.00.001 - M23.01.470: 27mm Amal Monobloc w/ straight manifold, s/n M23.01.471 through M23.03.890 30mm Amal Monobloc w/ straight manifold, after s/n M2303891: 32mm Amal Concentric w/ 'gooseneck' manifold.

Bare frame weight = 30 lb.(!!!!!!); Swing Arm = 6 lb.

Metralla Brakes (160mm) - 6.30" x 1.6" - Brake Swept Area: 31.65 sq. in. - Radius x S.A. (braking coefficient): 99.69 sq. in.

Flanders Company has a Motion-Pro petcock (p/n 121-12039) that works well for the oil petcock to the fuel tank. It has a fairly large I.D. that allows the oil to flow when pushing the pump piston without as much "shove" as a standard "on-off-reserve" one. The 1/4 in. NPT threads that it has can be easily cut down and a 12 X 1.5mm die run down it to fit the tank threads.

If you're missing the rear sprocket cover, contact Peter at Butaco Parts Australia. He provided fiberglass replicas that are near perfect.

Tire selection turned out to be Avon "Universal" race tires - 80/90-18 on the front & 90/90-18 on the rear (although this is considered a bit large for the stock WM-1 rear rim, but seems to work fine). 28 PSI front & 30 rear seems ball-park for an 85 kg. rider.

The Metralla owner's handbook calls out the ignition timing spec. as 3.5 - 3.7mm BTDC, this may be because of the availability of 100+ octane fuel at the time. In actual use this is far too advanced and produces pinging, overheating, hard starting and reluctance to accelerate in higher gears. (update) - with the carb jetting that I ended up with below, I decided to try a little more advance & am running it at 3.2mm BTDC. With that timing and the jetting below it seems to actually start more easily than before and revs a little more freely with no tendency to ping when it gets hot. I'm running Chevron 94 octane unleaded & Belray SI-7 oil @ 32:1.

The lock ring that holds the air filter into its plastic housing will likely pop out when you're clipping along at 100k since it gets pretty "buzzy" up there. Drill 4-5 small holes (1/16" or so) around the circumference of the air filter housing next to the clip groove then after installing the clip, use some loops of lock wire to secure it.

If you're using the oil pump, be sure to install "Viton" 'O' rings on the plunger if you plan to use synthetic 2-stroke oil. Synthetics seem to swell conventional 'O' rings and seize the piston in the plastic housing.

If you install a primary chain tensioner, stock or Sammy Miller, the roller will fail in a few hundred miles. The roller has no other bearing surface on its pivot pin other than the rubber that it's made of causing the roller to come apart. I've installed a Delrin roller with ball bearings to fix the problem - at 400 or so miles the Delrin roller shows no wear at all.

I found the stock Amal 32mm concentric jetting to be close, but not quite right for my sea level - 20-25 deg. C location. I ended up with the following for carb settings: (update) MJ: 230; PJ: 35 (a little richer than the stock # 30 - easier starting, & does not tend to die without revving with warm starts); needle jet: 107; needle: 'X' @ middle clip position; slide: #3.0; air screw: 1.5 turns out. Arriving at the correct jetting was a hair-puller that turned out to be partly because I was sold a replacement needle jet that was marked as a #106, but very worn to the extent that it was a lot larger than a # 107. Figuring this out took a while, but once an actually new, correct size # 106 NJ was installed (thanks to Speed & Sport) it ran much better, but still needed a #2.5 slide to keep from pinging @ 1/4 throttle when hot. The #107 NJ & 3.0 slide seems to be the best combination so far. Feeling such a noticable difference with only a .001" increase in NJ size confirms why it's recommended to periodically replace the brass NJ due to wear from the steel needle. These jetting figures are with a stock 8.5:1 CR head.

If you're trouble-shooting starting or running problems, you'll probably want to do a bottom end leak-down test. I built a rig shown here. Pump up to 6 PSI with the piston at T.D.C. - no more than 1 PSI loss per minute is OK.

Two things that I wish I'd done while the engine was going back together:

(1) Chamfer the LH case at the kick starter shaft boss & shaft bushing to allow installation of an 'O' ring. I incorrectly assumed that the seemingly small amount of clearance between the k/s shaft and case wouldn't allow gearbox lube to leak, but it did. I had to resort to a specially made bushing and 'O' ring installed from the outside - not the best way to seal it.

(2) Hugh's and others have a "slick-shift" selector drum available. The standard shift set-up is pretty clunky & false neutrals are routine This mod is supposed to improve things.

[belldane]

Thanks for the ideas. Problem was the carby. The bike had at some stage been fitted with an Amal (same size, shape and jetting) but built in England. I bought another Amal carb, this one made in Spain and the difference is outstanding. Revs cleanly and just wants to rev and rev some more. Maybe the insides are different but who knows. Anyway, thanks again for your ideas.