Sachs 505 1a performance

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The Sachs 505/1A is the most common of the 505/504 series engine. It's distinguished by the tapered cylinder marked 40kph. A stock horse power rating of 1.8 puts it on par with most Puch E50 engines and thus deserves a second look as a potential platform for tuning. Though there are not many kits for these, there is some potential nonetheless for a little creativity to take the place of bolt on parts and a thick wallet. During the course of this article I will be referring to the 505/1A, though everything mentioned should apply to the 504/1A as well, but for the sake of clarity I shall only be using the 505 designation. Details of the differences between 505 and 504 are covered here.

Regarding the B,C, and D Engines

These are the less common variants on this design, and will not be addressed in this article except for in the following:

505/1B If you have one of these heavily restricted engines you can replace the cylinder/jug, header pipe and carb to convert it to a 505/1A and then proceed to the following sections

505/1C some things apply to this engine, it shares it's cylinder with the 505-1D which is better ported, but has the 42mm "A" crank stroke instead of the 44mm D stroke. You can install the "A" cylinder on this as well but you would not want to, because it would be a downgrade. Essentially a 505/1a with a "D" piston and cylinder.

505/1D This engine produces 2.7HP stock! It has a better jug, carb and a longer 44mm stroke than an "A". The C and D also have a flat intake mount which allows them to be flipped forward to easily fit a 15 Bing or SHA carb. The C/D jug can be swapped in place of the jug on your 50x/1A or B for modest easy performance gains. The mounting holes on the jug are slightly different but can easily be drilled out using a base gasket as a guide.

For more info see: Sachs_Motor_Differences

Fuel System

The stock setup of the 505/1A features a 14mm intake with a "Square" Bing 12mm carburetor (stamped 85/12/101). They are different from the Bing used on Puch as it has a shallow square float bowl secured by 2 screws -- much like a Dellorto -- as opposed to a round threaded bowl. The shallow bowl allows it to clear the engine case, and this carb is therefore not easily replaced. Unlike the C and D jugs, the intake port on the A and B is angled and thus cannot be replaced with C or D intakes and cannot be flipped toward the front on this engine. It also uses jets unique to the "square" Bings. Square bings are also found on some late model Puch Korados. The D engines have a higher-performance 12mm carburetor which doesn't use a needle (85/12/104), and if available can make a good replacement for stock "A" carbs. The intakes are not interchangeable, C & D (flat port) are identical, A uses a 14.5mm angle port intake and the B bolts up the same as the A but only a 12mm intake.

These carbs are notorious for leaking. There's little room to adjust float height between always off and always flowing. They also require good cork float bowl gaskets which can be hard to find replacements for, but the gasket kits available at and elsewhere include this gasket.

Boring The Stock Carburetor

The square Bing can be bored out to 14mm, but to allow for some margin of error, I recommend 13.5mm. This carburetor body can be bored with ease as it can be quickly stripped and it will sit nice and flat on the bed of your drill press. It also does not have an idle circuit in the traditional sense, rather it has a notch cut out of the back of the slide allowing fuel to be drawn from the main jet. This means that you won't run the risk of closing off your idle jet, nor will you need to re-open it with picks. Fortunately, there are now jets available for it on, previously these required you to drill out your jet. Alternatively, you can use the jet holder atomizer tube from a round Bing and then use standard Bing jets, the end result is a robust and easily serviced 14mm carburetor. For detailed instructions on boring your Bing, see Over Boring Carburetors 101.

In conjunction with boring the stock carburetor it is also possible to convert your old square Bing carburetor jet into a jet holder. This enables you to use other manufacturers jets in your Bing carburetor, which means you are capable of serious tuning without replacing your carburetor. This has been successfully completed with a conversion to 5mm threaded Dellorto jets (used in SHA series).

Mounting a Dellorto SHA:

The Dellorto SHA is a very close fit, and with some simple modification to the intake it will not only fit on the engine, it will also still fit under the side covers. There are a couple different ways of doing this, but before you start check the fit of the carburetor as due to slight model differences and casting variations it may already fit or require little more than an extra intake gasket.

Alternately the stock intake can be cut short and a radiator hose clamped around it to hose mount carburetors to the side.

Mounting Dellorto SHA, PHBG and 15mm AMAL Carburetors with Ease:

If you're out to find the easiest way to mount a bigger carb on your sachs and still retain the rearward facing intake - consider buying an intake riser from treats. Note that these risers DO NOT WORK ON A/B ENGINES they only work on C/D engines and the 70cc athena kits as they are for flat intake port cylinders only. Included as a bonus is a stainless metric socket head cap screw to plug and delete the decompression valve! Whooo!

Sachs Riser @ Treatland

-Using washers and JB weld-

The first way requires no skill or really anything other than wrenches. You start by removing the two intake bolts and washers. Next you remove the intake and reinstall it with the two washers, both on the rearmost bolt between the intake and the intake port. This will angle your intake perfectly, allowing the carburetor to slip on easily, clearing the top of the engine. The last step is resolving the problem with this method; that's sealing the big gap left over. This could be filled with plumbers putty or a similar compound so long as it is both heat and gasoline resistant. Plumber's putty may be neither so read your labels well!

-Making an Intake Riser-

Sometimes just an extra or thicker intake gasket can push the intake up enough to give the needed clearance, but if not a riser can be made. This is more desirable as the likelihood of sealant breaking loose and being sucked down the intake is much less. For making a spacer, I chose 1/4" Masonite (basically the cardboard stuff that goes on the back of your entertainment center). It's derived from paper pulp so it should compress and behave the same as a paper gasket. You start by tracing around the base of your intake and then cutting it out with a fine toothed hand saw (hack saw works, coping saw works even better). Once it is cut out and trimmed up nicely, get a stamp pad and push your CLEAN intake into it and then "stamp" the whole pattern onto the masonite. Start by cutting out the center whole by drilling in the middle of it then grinding the rest of the material off with a Dremel. Next use a C-clamp to fasten the spacer to the intake and a piece of scrap wood underneath making sure your holes are lined up. You will now use the bolt holes in the intake as drill guides so as to attain the proper angle, choose a close fitting drill bit and drill through the spacer and into the scrap wood. Once you've cleaned up all the little "fuzzies" and bits of peeling paper, your intake spacer will be finished! Now you need only mount up your intake with your new 1/4" thick gasket. This moves the carburetor up and will clear the engine case and should clear the frame. In some cases the spacer may require some tapering to achieve the desired angle. This can be done by sanding or any other appropriate grinding method. It is also worth noting that if you are using a 15mm or 16mm carb, you will need to further modify the intake. Simply grind down the diameter of the intake where the carb attaches until the plastic sleeve that came with the carb slides on with no resistance. At that point use a sealer, or glue of your preference to fix the sleeve to the intake creating a perfect sealing mount for your new carb. Having done this on my G3 I found that it still took some fiddling to get it to clear the frame, but it does. In the case of other frames the fit may require a thicker spacer to be made or may have no trouble at all. The only other modification required at this point is to drill a small hole in your side cover to run your throttle cable.

For the C and D intakes, the mount is flat unlike the A and B jug. With the C/D the intake has a 14.5mm ID, and can easily be removed and reinstalled facing forward to avoid the engine clearance issues and fit an SHA or similar carb. This may require simply cutting the top-right cylinder fin.

==============Added by JensAroo===============

SHA 15 fits with little spacing required. A 3/16ths or so cork gasket works well. The SHA 16mm is too big to use without porting the intake as the inner diameter of the intake is only 15mm or so. Use a length of pop can for a shim between the carb and intake because the original plastic one is too thick. The pop can will need to coil around a creating a few layers to be thick enough. A rubber o ring from the autoparts store will seal the carb to the intake. Jetting should start mid 60s. Plan on getting a 7x5mm knarp to adjust the throttle cable on the throttle side. The carb side fits well enough on the stock cable. The idle screw can only be accessed with a 6mm wrench as it is really close to the frame. A lever choke may also be inacessible without bending the lever.

Cylinder Porting

The stock porting of the 1A cylinder is adequate in most ways. The transfers are good sized and the intake port is certainly large enough considering that the largest intake pipe for this engine is the 90 degree 14mm. The exhaust port though can be raised by 2mm. This is probably the most significant difference port wise between the "A" and "D" cylinders and is an easy adjustment to make. Just make sure to take your time. Doing this requires a fairly significant jetting change.


This is a stumbling block for this engine as Sachs uses a one-piece cylinder and head. To increase the meager 8:1 compression, one can leave out the base gasket. However, this will retard your port timing, so this if it is done it should be done in conjunction with porting. For any more increase to the compression ratio the cylinder base will require milling.

Also, the 505/1D engines use a slightly longer stroke crank, 44mm vs 42mm, which increases both engine volume (47cc to 49cc) and compression (8:1 to almost 10:1). A D crank can be swapped into any Sach 504 and 505 cases, but can create ignition issues for the 504 due to different taper for the magneto. The longer stroke makes more of a difference in kitted bikes, where the increased bore of the cylinder combined with the increased stroke gives even more of an engine volume boost.

-See:,3283033 on how to tell if you have a "D" crank

Leaky Decomp

Also, commonly the problematic decomp (decompression) valve can leak creating an in-cylinder airleak and drastically lowering compression. The bike may still start and can even run well except with often cut out at higher speeds and may be confused for four-stroking. The decomp exhausts out a small hole on the left bottom side of the jug. Oily residue around this can be indicative of a leaking decomp. Fortunately they are entirely unecessary for starting and can be easily omitted and plugged off with an m10x1.5 bolt.


The decomp plug bolt must be long enough to bottom out against the BOTTOM of the hole; if too short, it will bottom out on the outside and air can still leak past (see top-left). A long bolt will plug effectively and be easier to turn in without hitting the cylinder fins. Alternately a setscrew such as the one pictured solves the problem and gives a clean finished look. Some riders use a BB under the bolt to make sure it plugs the hole, but this isn't strictly necessary and damage to the cylinder can occur from overtightening against a BB.


The stock pipe can be modified by drilling additional holes in the baffle or removing the baffle entirely. This removes the restriction but does not provide much of a poweband. Some Sachs have a restricted 22mm header which at very least should be replaced with the alternate 26mm diameter stock header.

If you can weld, you can put any exhaust on any bike. For those who can't, the options seem to be rather limited. Gianelli and MLM make the only two sachs-specific exhausts, however other options include Peugeot exhausts with a similar flange-mount, and 2 part exhausts using the existing or available replacement headers. The stock mounting bracket can be replaced with a hook or hoseclamp to support the back of your alternate exhaust. A piece of 1/8 inch steel would be more than sufficient.

The Gianelli Circuit pipe has come back into availability recently, but suffers from a number of issues notably it's high price tag, low performance gains, and serious difficulty mounting it reliably. Ask anyone with one, they fall off ALL THE TIME.

It's also possible now to find 2 part exhausts through and elsewhere with a 26 or 28mm sachs header that will clamp on the same as the standard stock exhaust. You can then buy clamp-on expansion chambers like those from Jamarcol for a 28mm header and clamp that on directly. You can also cut down your header pipe to an appropriate length (shorter = higher RPM or simply just match your 2 piece exhaust's header length) and slide the expansion chamber on.

Peugeot and Vespa exhausts also use a similar design where the exhaust clamps onto a lip on the exhaust of the cylinder. Unfortunately because of the angle of the cylinder, most Peugeot exhausts extend too far out and on a Sachs will nearly hit the ground. Spring mounted SPX exhausts allow most maneuverability and clearance. The springs can be hooked to the cylinder itself by drilling holes in the bottom of the cylinder fins. Many people have had good results using the Peugeot SPX Alsil Quich pipes, which are inexpensive and fit snugly over the stock Sachs header lip, and require only the spring mount holes and a custom rear exhaust mount as described above.

MLM has also recently started producing a Sachs specific performance pipe that's been reported to have good performance and a wide powerband, both on stock and kitted setups.


See Sachs clutch modifications


The gearing on the Sachs mopeds is fairly limited. The stock gearing is quite low, as is typical of stock mopeds, and gearing up can be a good way to get the best gains from your better performing engine. The front gear is always 11 tooth, and no smaller gears exist, however 12 and 13 tooth front sprockets are readily available. The 12 tooth requires some grinding to fit with the chain. Moving further up to the 13 tooth option requires even more grinding of the case in order for the chain and larger gear to fit. This is best done with the cases split in order to carefully watch the depth of the grinding and prevent going all the way through to the clutch cases, but can be done externally with the motor together using a Dremel with a sanding drum and checking depth with the new sprocket and a piece of chain mounted on it. Approximately 3mm will need to be removed at the deepest point (right where the 2 case halves meet) and also some meat will need to be removed from the tab behind the sprocket.

As for the rear gears, most Sachs mopeds use the Italian "Z" style wheels and can interchange those sprockets (42.5mm 4-bolt square). A few different rear sprockets are available down to 28 tooth, but to get much smaller on the rear one must find either some Derbi sprockets or make some. Indian moped rear sprockets should also fit. Tomos rear sprockets can be made to work by elongating the bolt holes on the sprocket and may also require widening of the center hole - this gives a very wide range of gearing to choose from, but any off-center and you'll have a pulsing tension on the chain = uncomfortable rides and rapid wear.

Performance Cylinder Kits

This is getting into the realm where you shouldn't need to be reading about this in the wiki, however here's some info regarding kitting your Sachs.

Athena 50cc

This is a simple 38mm 50cc kit for your Sachs. It is piston port and comes with a 15mm intake and 28mm exhaust. It can also accept bolt-on exhausts and can fairly easily be made to fit Minarelli, Garelli and Puch exhausts, as well as the standard Sachs options using the included adapter. This is basically a better ported version of the Sachs D motor, and is arguably not worth the cost but does provide a simple upgrade or replacement for stock. Uses long reach plug.

Athena 70cc

This is a piston port 45mm 70cc kit by Athena. It also includes a 15mm intake which fits the 15mm round Bings and can also easily be adapted to the Dellorto SHA. Larger intakes are available from MLM to fit larger carbs. It is a rather mild kit but can easily approach 50mph. At this point some clutch issues may arise but the 70cc kit is typically regarded as the biggest you can go without seriously modifying (or rapidly deteriorating) your clutches. See: Sachs clutch modifications. Uses long reach plug.

Athena 80cc Piston Port

48mm 80cc kit by athena. You'll need to buy a larger intake from MLM or elsewhere. Not a great option and a pointless bridge between the 70 piston port and the 80cc reed kits.

Athena 80cc Reed

This is the mother of Sachs kits. At 48mm it's the biggest Sachs kit available and features the Athena reed intake. You will NEED to replace the metal reeds with carbon fiber, the metal ones notoriously fatigue and break causing catastrophic cylinder destruction. It can also accept bolt-on exhausts and can fairly easily be made to fit Minarelli, Garelli and Puch exhausts, as well as the standard Sachs options using the included adapter. Flanged intakes are included for the 15mm SHA and 19mm PHBG and can be made to fit other carbs by using rubber adapters. This kit will require clutch modification or at least periodic removal and re-buffing of the clutch pads.

Autisa 64cc

This is another piston port kit by Autisa. It uses the stock 14mm intake which fits the 15mm round Bings and can also easily be adapted to the Dellorto SHA. It is a fairly exciting kit for its size and well ported with speeds easily in the 40s. Looks externally like D, it's a very reliable kit; however the availability is extremely limited.

Airsal 70cc

Newest kit and first ever two-piece kit for the Sachs 504/505 engines. The kit measures in at 43.5 mm. The kit utilizes a removable, O-ring head. It has massive, bridged transfers yet it should be conservative enough to not destroy your clutch. The only true downside to this kit is that it uses the angled intake manifolds. Further, the included intake is actually smaller than the stock A's, measuring only 14mm instead of 14.5 on the stock. And worse, it still doesn't provide clearance for a bing or SHA, only directly fitting the stock square bing carbs. The stock intakes also do not bolt directly onto the kit; the stock intake flange overhangs the kit's base and must be ground slightly on the side toward the engine or it will hit the cases. However once cut to fit, the stock intake on this kit allows enough extra height to fit a standard 15 bing or SHA and the improved 14.5mm intake diameter. This has become a very popular option with speeds in the low to mid 40's and healthy reliability. Little is gained by the 2 piece head, but the straight spark plug angle allows traditional piston stops and timing gauges to be used. The exhaust is the original flange, unlike the Athena's which can support bolt-on exhausts, so this limits pipes to the traditional Sachs offerings.