Difference between revisions of "Jawa Tuning"

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There are many good reasons to tune a [[Jawa]]. The 207 frame is extremely light weight (95 lbs stock) and solid; it's also very compact and can be set up to have a very low profile. The 207 engine is simple in operation and one of the easier units to work on. Despite its lack of bolt-on performance, the 207 engine provides a great platform for experimentation and is thus an excellent learning tool.  The best part of all is that the engines are available readily and at a very low cost, so one can completely screw up and be back on the road for very little money. The following is a list of what has been done to improve performance on these bikes. These things may or may not work for your setup and have not yet been proven on a large scale yet. Jawa tuning is in its infancy and these procedures come with no guarantees with regards to performance, reliability, or safety. '''TUNE AT YOUR OWN RISK!''' If you have anything to add PLEASE DO SO!
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There are many good reasons to tune a [[Jawa]].  
  
Lets get started then!
 
  
 
==Ignition==
 
==Ignition==
One of the most common complaints about Jawa mopeds is the unreliability of the stock ignition system.  The 207 and 210 engines both employ a simple contactless electronic ignition system (the forerunner to the modern [[CDI]]) with an internal rotor and external stator setup which greatly cuts down on the engine's rotating mass. The thyristor unit is prone to overheating, resulting in erratic or absent spark.  A replacement unit can be [[Jawa Thyristor|soldered together from component parts]].  Some experimentation has been conducted with [http://www.mopedarmy.com/forums/discuss/1/537594/499438/ universal CDI kits] but they are difficult to install and homemade replacement thyristor units are often much more rugged than the stock unit.
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One of the most common complaints about Jawa mopeds is the unreliability of the stock ignition system.  The 207 and 210 engines both employ a simple contactless electronic ignition system (the forerunner to the modern [[CDI]]). The thyristor unit is prone to overheating, resulting in erratic or absent spark.  A replacement unit can be purchased or [[Jawa Thyristor|soldered together from component parts]].  Some experimentation has been conducted http://www.mopedarmy.com/forums/discuss/1/537594/499438/ and a thorough review of thyristor replacement units is found [http://www.jawamoped.com/JawaMoped_Electrics_-_ignition.pdf here]
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== Carburetor ==
 
== Carburetor ==
The Jawa comes typically with a [[Jikov]] 12mm [[carburetor]]. Though this unit is an efficient design, the lack replacement parts will be a limiting factor, particularly in the area of [[jet]]s. The answer to this problem is one of the simpler things to improve. A [[Puch]] [[E50]] intake can be modified to fit by using a spare cork riser and widening the mounting holes a few millimeters inwards. The end result is a very standard intake allowing one to choose between a wide variety of carburetors. A 14 mm square intake will match the cork risers and intake port perfectly.  Many have chosen to run a larger intake and a [[Dellorto]] SHA 15.15 on this setup. The Jawa runs well with SHA carburetors and can be tuned to not only perform nice on the top end but also idle beautifully.
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The Jawa comes typically with a [[Jikov]] 12mm [[carburetor]]. If you find a jet that fits, it can be soldered closed and drilled or reamed to the appropriate size.
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A [[Puch]] [[E50]] tall SHA intake can be modified to fit a Dellorto SHA, which are available from common 14/12 to 15 and 16mm sizes, and are easy to tune and find jets.
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[[Image:P1060686e.jpg]]
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Above is a modified and the as-received Puch intake. Note the mount has to be ground down to fit into recessed platform in the cylinder and the holes have to be extended inward to match mounting holes. In a similar way other intakes may also be used, or even a small diameter stock exhaust header can be cut to fit as an intake. Because of the tight fit you will need to use allen head bolts, and any washers will need to be ground down on one side to a "D" shape. You can cut your own gaskets from gasket paper.
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[[Image:Jawa carb-1-.jpg|Jawa 210 cylinder with puch tall SHA intake and SHA 15:15 installed]]
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Jawa 210 cylinder with puch tall SHA intake and SHA 15:15 installed
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A Piece of Pergo flooring can be used as a shim to fill the depression in the cylinder.  Aluminum is good too.  This avoids grinding the edges off the intake and allows it to look more finished.
  
 
== Exhaust ==
 
== Exhaust ==
There are no bolt-on pipes for Jawa. At this point, two things have been done with some success. First off, one can remove the stock baffle and open up some new passages to improve flow. This is of course cheap and keeps the bike looking stock. Typically 3-4 1/4" holes are drilled into the stock baffle, equally spaced and oriented around the original opening.
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There are no bolt-on pipes for Jawa.
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If you match the Header diameter, you can install a clamp on such as the Jamarcol Fuego 28mm clamp-on chamber.
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Any pipe can be hacked and welded to make work. If you have access to a welder and the skill to make it nearly air tight, you can weld any chamber to the stock JAWA header.
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The stock exhaust port is quite small and you will have to relocate and install larger studs but Puch or tomos or other flat port exhausts can be also made to fit. You need to cut it to fit the recess around the JAWA cylinder's exhaust port, and drill out the stud holes to the correct location to match the JAWA. Don't forget to make a mount for the exhaust in the rear, and never mount to the swingarm.
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[[Image:Jawa cylinder exhaust porting-1-.jpg|350px]][[Image:Jawa cylinder large header-1-.jpg|350px]]
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Jawa exhaust, ported - note the edges are widened and 2 larger and wider bolt holes have been drilled and tapped to fit a larger Tomos header, and the exhaust bore has been opened to match.
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== Cylinders ==
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Jawa cylinders consist of an aluminium jug with with an iron sleeve pressed into it. This sleeve can be pressed out to give better access to the ports for modification. See thread here for elaborate cylinder sleeve porting: http://www.mopedarmy.com/forums/read.php?1,4034618. The 210 cylinder is superior to the 207 cylinder due to its two additional angled transfer ports. It also has a larger flange around the exhaust port making it easier to modify for a larger header. This cylinder can be bolted to the 207 engine with no modifications.  
  
One can use the Tomos two-piece BiTurbo and a copper reducer fitting, 1-1/2" diameter, from a hardware store to mount the new muffler to the existing stock header on a stock 207 type Jawa. The original header will need to be trimmed some, but care must be used to not cut too much so that the muffler doesn't hits the pedals.  If one heats up the header with a torch and grind the copper fitting so that it is flared slightly, the copper fitting can be tapped in with a mallet and will produce an interference fit. Additionally, copper expands more than steel when heated, so the fit will tighten when heated together.  Then simply tighten down the muffler to the 1" copper fitting with the supplied bracket.
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There is a commercial rototiller that has an engine which is a derivative of the 210 engine, allowing access to 80cc cylinders. Not much info but there is a video [https://www.youtube.com/watch?feature=player_embedded&v=LJeWCSxU1_w on Youtube here]
  
Of course, almost any performance exhaust can be forced to work.  The most common issue is mounting the exhaust to the frame.  Stock Jawa exhausts mount beneath the muffler while most mopeds mount above. "Straight" exhausts such as the Techno Boss can simply be flipped upside down but angled and non-symmetrical exhausts (such as the BiTurbo and Techno Estoril, respectively) require the stock mounting bracket to be modified. This can be as simple as using steel mending braces (available at any hardware store) or as complicated as relocating the stock mount.
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Additionally you could always weld up the cases and move the studs to use a different cylinder, considering the small end bearing size and stroke. Puch cylinders may be close, and have been adapted to the JAWA 210 by Euro tuners. The JAWA has an atypical 14mm wrist pin making cylinder swaps very difficult. JAWA also have a shorter 41mm stroke vs the much more common 43 among major moped brands.
  
The stock mount was not designed to carry the weight of larger performance exhausts and will flex under stress. This problem can be solved by either strengthening the stock mount or adding an additional brace to divide the load.
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=== Porting ===
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Stock Jawa port timing is pretty okay but the ports are really small.  The stock cylinder has a cast iron liner so it should be pretty easy to modify the ports. For more information read about [[Calculating port timing]] or seach porting. The safest conservative porting is to open up the intake and exhaust and widen both by ~2mm, but do not raise or lower the top or bottom edges. This keeps the timing the same but allows much better flow. If you're installing new intake or exhaust you'll want to match those to the cylinder.
  
== Porting ==
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=== Overboring ===
Recently the porting on the Jawa 207 has been addressed. The cylinder ports in this engine are very small, even for a stock moped engine. To start with, the [[exhaust port]] is tiny and can be widened without changing the [[port timing|timing]]. 24mm is about the limit in width before there becomes a danger of catching a [[piston ring|ring]]. Widening the port to 22mm will be a significant change over the stock 18mm and leave a nice margin of error. When widening the exhaust port, you will want to continue the passage all the way down to the port exit where the exhaust header bolts up, this is a lot of metal to remove, but a large port going into a narrow passage will not do.
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There are several piston sizes for the 207 and 210 engines. As the stock cylinder was worn out it would be bored. Each rebore increases by 0.25 mm. In the United States pistons were available up to the 3rd overbore, but pistons as large as the 8th overbore (an increase of 2 mm bore and 7 cc displacement) can be found from eastern Europe.
  
The second area to address is the minuscule [[Transfer port|transfers]]. They're not only small but they also do not open all the way. Generally it's not worth messing with transfer ports themselves, but in this case the procedure is easy and does not risk damaging the cylinder. The piston crown on the 207 is 4mm thick which leaves some room for grinding. With the cylinder head off the engine, and the piston at BDC mark the edges of the transfers on the top of the piston. Now remove the piston and draw 2 parallel lines across the piston connecting the transfer marks. Next, on each side of the piston directly between the transfer marks measure inward 6mm from the edge of the piston and make a line perpendicular to the parallel lines forming a little box where the transfer would line up with the piston. Do this on the other side of the piston as well. Next you want to grind out that little area to a depth of 2mm at the edge of the piston tapering all the way up to the perpendicular line you made where. Measuring 2mm at the edge of the piston is easy because it amounts to half way up the crown. Great care should be taken to make sure that the inlets ground in the piston crown are symmetrical to each other so as not to upset the cylinder's scavenging. the end result is that the ports are now opened all the way and the duration is increased. Porting a stock engine has shown small but noticeable performance gains with a 12mm carb and mildly de-restricted pipe. A larger carb or expansion exhaust might take even more advantage of this.
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==Other==
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Additional options to get a little more from your JAWA include:
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* Milling the head - shaving down and reshaping the head; even just removing some material (smoothly and flat) increases compression and power.  
 +
* Regearing - you can improve top speed at the cost of low end
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* Clutch - The clutch is not easy to modify but lightening the clutch (such as evenly drilling it out) could provide additional stall allowing you to obtain higher RPM power right off the line. This is not trivial and balance and strength must be considered.
  
== Overboring ==
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much of this info contributed by user Vlado
There are several piston sizes for the 207 and 210 engines.  As the stock bore was worn out it would be rehoned to accept the 1st overbore piston, then the 2nd, etc.  Each rebore increases by 0.25 mm.  In the United States pistons were available up to the 3rd overbore, but pistons as large as the 8th overbore (an increase of 2 mm bore and 7 cc displacement) have been found in eastern Europe.  This is relatively uncharted territory - early reports indicate higher low end torque due to increased compression but no substantial effect on top speed.  Aggressive porting may be required to reap the full benefit of increased displacement.
 
  
 
[[Category: Jawa|Tuning]]
 
[[Category: Jawa|Tuning]]
 
[[Category: Performance Tuning]]
 
[[Category: Performance Tuning]]

Latest revision as of 11:33, 19 December 2018

There are many good reasons to tune a Jawa.


Ignition

One of the most common complaints about Jawa mopeds is the unreliability of the stock ignition system. The 207 and 210 engines both employ a simple contactless electronic ignition system (the forerunner to the modern CDI). The thyristor unit is prone to overheating, resulting in erratic or absent spark. A replacement unit can be purchased or soldered together from component parts. Some experimentation has been conducted http://www.mopedarmy.com/forums/discuss/1/537594/499438/ and a thorough review of thyristor replacement units is found here


Carburetor

The Jawa comes typically with a Jikov 12mm carburetor. If you find a jet that fits, it can be soldered closed and drilled or reamed to the appropriate size.

A Puch E50 tall SHA intake can be modified to fit a Dellorto SHA, which are available from common 14/12 to 15 and 16mm sizes, and are easy to tune and find jets.

P1060686e.jpg

Above is a modified and the as-received Puch intake. Note the mount has to be ground down to fit into recessed platform in the cylinder and the holes have to be extended inward to match mounting holes. In a similar way other intakes may also be used, or even a small diameter stock exhaust header can be cut to fit as an intake. Because of the tight fit you will need to use allen head bolts, and any washers will need to be ground down on one side to a "D" shape. You can cut your own gaskets from gasket paper.

Jawa 210 cylinder with puch tall SHA intake and SHA 15:15 installed

Jawa 210 cylinder with puch tall SHA intake and SHA 15:15 installed

A Piece of Pergo flooring can be used as a shim to fill the depression in the cylinder. Aluminum is good too. This avoids grinding the edges off the intake and allows it to look more finished.

Exhaust

There are no bolt-on pipes for Jawa.

If you match the Header diameter, you can install a clamp on such as the Jamarcol Fuego 28mm clamp-on chamber.

Any pipe can be hacked and welded to make work. If you have access to a welder and the skill to make it nearly air tight, you can weld any chamber to the stock JAWA header.

The stock exhaust port is quite small and you will have to relocate and install larger studs but Puch or tomos or other flat port exhausts can be also made to fit. You need to cut it to fit the recess around the JAWA cylinder's exhaust port, and drill out the stud holes to the correct location to match the JAWA. Don't forget to make a mount for the exhaust in the rear, and never mount to the swingarm.

Jawa cylinder exhaust porting-1-.jpgJawa cylinder large header-1-.jpg

Jawa exhaust, ported - note the edges are widened and 2 larger and wider bolt holes have been drilled and tapped to fit a larger Tomos header, and the exhaust bore has been opened to match.

Cylinders

Jawa cylinders consist of an aluminium jug with with an iron sleeve pressed into it. This sleeve can be pressed out to give better access to the ports for modification. See thread here for elaborate cylinder sleeve porting: http://www.mopedarmy.com/forums/read.php?1,4034618. The 210 cylinder is superior to the 207 cylinder due to its two additional angled transfer ports. It also has a larger flange around the exhaust port making it easier to modify for a larger header. This cylinder can be bolted to the 207 engine with no modifications.

There is a commercial rototiller that has an engine which is a derivative of the 210 engine, allowing access to 80cc cylinders. Not much info but there is a video on Youtube here

Additionally you could always weld up the cases and move the studs to use a different cylinder, considering the small end bearing size and stroke. Puch cylinders may be close, and have been adapted to the JAWA 210 by Euro tuners. The JAWA has an atypical 14mm wrist pin making cylinder swaps very difficult. JAWA also have a shorter 41mm stroke vs the much more common 43 among major moped brands.

Porting

Stock Jawa port timing is pretty okay but the ports are really small. The stock cylinder has a cast iron liner so it should be pretty easy to modify the ports. For more information read about Calculating port timing or seach porting. The safest conservative porting is to open up the intake and exhaust and widen both by ~2mm, but do not raise or lower the top or bottom edges. This keeps the timing the same but allows much better flow. If you're installing new intake or exhaust you'll want to match those to the cylinder.

Overboring

There are several piston sizes for the 207 and 210 engines. As the stock cylinder was worn out it would be bored. Each rebore increases by 0.25 mm. In the United States pistons were available up to the 3rd overbore, but pistons as large as the 8th overbore (an increase of 2 mm bore and 7 cc displacement) can be found from eastern Europe.

Other

Additional options to get a little more from your JAWA include:

  • Milling the head - shaving down and reshaping the head; even just removing some material (smoothly and flat) increases compression and power.
  • Regearing - you can improve top speed at the cost of low end
  • Clutch - The clutch is not easy to modify but lightening the clutch (such as evenly drilling it out) could provide additional stall allowing you to obtain higher RPM power right off the line. This is not trivial and balance and strength must be considered.

much of this info contributed by user Vlado