The SUZUKI RG 400 incorporates 80 years of two stroke development and can be considered as amongst the pinnacle of high performance two stroke road machines.These machines were killed off by tightening emissions legislation in the US, Europe and Australia.

Two strokes in general,became extinct by the end of the 1980's as manufacturers saw the writing on the wall, and concentrated their efforts on cleaner four stroke technology.   The RG500 was sold in Australia for a very brief period of 10 months only. They departed the scene with the introduction of unleaded petrol in 1986....

To find an RG 400 hidden away for 20 years, with only 8,600K's recorded, makes this a rare bike. Domestic Japanese Market only. The RG400 had a very short production life, and was only available for two model years 1985 and 1986.         




                         DKW's RT 350 twin, available 1956 only                      


 DKW 350......

A very good place to start as an example of  post war development of  performance two strokes, and one of the very better bikes to come out of the '50's. DKW had  features not matched for decades, such as needle roller bearing swing arm, hydraulic rear brakes and outstanding all round performance.

Not many bikes came close to the riding experience offered by the DKW RT350 in the day.




DKW 350 Triple Racing Machine 1957

 Germany had made all the great developments in two stroke engine technology by the late 1930's, as demonstrated by DKW's  fierce 3 cylinder supercharged racing machines. Unfortunately at the end of the war, the DKW factory ended up in East Germany under Russian control.  Postwar the two stroke was used primarily as the basis of lightweight  utilitarian commuter machines with most of the best technology and pre war  manufacturers in Germany and Czechoslovakia under Russian Control.  The command economy of the Iron Curtain countries had no requirement for high performance two strokes.. DKW later establish a factory in West Germany in the 1950's and produced a range of two strokes including  the wonderful RT 350 twin in 1956.... but by and large it wasn't till the Japanese motorcycle revolution of the 1960's that German know how was re-employed by Suzuki, Yamaha and others to develop an exciting range of high performance two strokes                                                                                      


 The benefits of a tuned exhaust - unburnt fuel mixture pushed back for combustion. It also provides the reason why two strokes have been legislated out of existence - at many points in the engine rev range, the exhaust will contain high levels of raw hydrocarbons going straight out into the atmosphere. ( Joseph A Schuster  Internal Combustion Overload)


    RG400 K301 100390  

K310 100390 was purchased in Tokyo about 5 years ago.  Like many vehicles dating from the mid 1980's for sale in Japan it had survived because it had very little use before being stored away in a dark corner and more or less forgotten about. With a population of around a100 million affluent people, there is always going to be something interesting turning up....

The bike had not been used for about 20 years when I bought it.  Considering that fact....... it was in reasonable condition when I got it apart from the obviously perished tyres. It looked quite intact and original beneath a thin layer of Tokyo pollution and dust.  The engine was free and turned over without any problem ... with very healthy compression on all pots.   The wheels were the standard white, with blue spokes... but the paint was not very well keyed to the metal, and was blistering and lifting  in places. .... one of the first things I did, before fitting new tyres, was to remove the paint from the wheels. Underneath the lifting paint was an anodised black finish.  While the wheels were removed I went over the rest of the bike and cleaned the fosilised crud of it.

  A lot of the running gear is well shrouded with a maze of tubes and cables running everywhere like a mad womens picnic and very hard to get to. It took quite a while to get it looking like the low mileage machine that it was. I then  filled the crankcases with Auto Trans Oil.  ATF has some great properties, one of which is that it is very beneficial to neoprene seals and other rubber parts...  Mindful of the fact that the crankcase seals had not seen any lubricating mixture for a while I left it to soak for a good while.  The coolant was also drained and the engine and radiator was filled with fresh Organic type coolant.

Then a few years went by ..........  

The day to start it arrived.. After cleaning the carburettors and fuel lines I put fuel in the tank and on the first kick it almost caught ....on the third it burst into life and was cheerfully filling my yard with rolling clouds of sweet smelling two stroke/ATF smoke.  I ran it for a few minutes.    After a short break I came back to it and started it again. This time it lost two cylinders and slowly wound down to a complete stop.


RG  had literally run out of spark...  Armed with the workshop manual I run a multimeter over the various ignition circuits, starting with the low tension magneto. All items associated with the engine ( ignition coils and rotating coppers/magnetic bits) came back with normal readings... when I got to the CDI unit .. the "black box" at the rear of the bike, I was getting open circuits on some pairs, and readings well out of the specified range on others.   The CDI unit, as well as amplifying the low tension magneto output also controls the ignition advance. A rather vital item.

Back to Japan..... and one used CDI unit later purchased for $20 from YAHOO Auctions..... it was running again...... 


The original carburetors  were removed for cleaning.  One clear indication that they needed attention was no fuel would easily enter the float bowls. With the float bowls removed it was clear that the units would require a lot of tidying up from the effects of varnish and gum from old fuel and oxidation of the brass components.The needle valves were gummed up, jets and needles coated with varnish and most of the idling jets were partially blocked.

The lower two units are really a perfect trap for water and dirt in the fuel to migrate towards, as any muck in the fuel lines will take the lower path at the split in the fuel hose that feed the lower units.  Cars in the 50's often used to have a clear glass bowl mounted at the lowest point on the fuel line before the carb to trap any water or sediment. Any muck would fall out rather than enter the carb, and form a visible sludge at the bottom of the bowl. The bowl could be easily removed and cleaned - the lower carbs on the RG do much the same unfortunately.

The upper two were in a much better state.

Petrol has a life of about 12 weeks before its starts to breakdown - turning bright stinking yellow like dog piss and forming a very hard gum as it evaporates.

I have been told that modern petrol is quite different from what we were using 10 or more years ago.  It often contains alcohol and other additives. It is destructive to fuel systems if left for even brief periods of unuse.

The first place the gum appears is around the needles and seat, then block idling jets. The usual outcome is the float needles seize closed and no fuel will run into the float chambers. The only solution is to dismantle and clean the parts -  Carb cleaner or straight acetone is a good solvent. Sometimes petrol gum can defy solvents... one solution is to use a paint stripper gun to gently heat the varnish to make it hard and then chip it out. Poking a wire through the gum is not effective as it is very elastic.

Over time each unit was cleaned and replaced on the bike... 3 of the 4 were operating correctly, but one was still not accepting fuel. There were signs that the units had been the subject of some earlier attempt at a clean out... one of the idling jets had the screw driver slot sheared off, and a brass float bowl drain screw had been snapped into two parts. A close look inside the problem unit revealed that one of the float support legs - cast into the body of the carb had been snapped at the base, preventing the float from rising straight. this would have been done while attempting to knock out the pin retaining the float to remove the needle and seat for cleaning. The float was jamming and needle valve was not releasing - . I made a temporary fix and had the RG running properly.  One thing that I hadn't resolved fully was getting the choke brass pistons unsiezed.  One had come free after liberal use of WD40 but the other wasn't budging. It seems that any moisture about creeps into the fine gap between the body of the carb and the brass piston and oxidises the aluminium - and then the clearance is filled with white oxide, wedging the piston firmly. Just another reason why you just can't leave a bike like this unused.

I wanted to replace the damaged carb body and had my feelers out in Japan. I found a single correct body, and at the same time very tidy complete set of  carbs and associated gaskets, O rings, and collars.   I dug deep and paid the asking price $500, and made the right decision for sure.... These units were in perfect condition and just took away any weakness that the bike may have had...... 

Fitting included the 4 throttle cables to route through the existing maze of wires, the four port timing control cables, tubes and hoses, plus the two choke cables and the associated handlebar attachments, but worst of all was re cabling the oil pump, a very fiddly job in all. Carbs were then synced as was oil pump metering


Settings... are best adjusted with the carbs off the bike...

.Idle stop screws .. the throttle slides should be adjusted to be open 0.5mm as measured from the engine side of the carburetor throat, using a feeler gauge.  For the upper carbs  - turn the thumb screw.  Lower carbs turn in the brass screw with a suitable flat blade screwdriver. Located on the upper side of carb body. Air pilot jet screws -  very gently turn in the brass screw ( upper right corner of the carb body) until they have fully seated ... then back off 1.6 turns

                          Pictured above carbs were fitted to the bike




 Flat Slide Carburettors & Rotary Valves.Tuned length chambers, rotary valves, CDI ignition and ECU controlled exhaust port timing


 Carbs are identical to RG500 but jetted richer 

 The bike has a complete fairing ( as shown complete in lower pic) in generally good and original condition. Some defects are evident such as a scrape on the lower right from a minor fall, about the size of orange, and a very small corner piece missing on the opposite upper fairing.   The top right has what could be Barry Sheenes signature lightly scraped into the blue paint it. More likely the end of another motorcycle handlebar when it was containered here. Some of the original fairing screws are missing and have been replaced by non original items and a small upper fairing support bracket is cracked - no big deal to fabricate an alternative.. . Belly pan was fitted to the RG 500 but after a long search of images on the web I have not seen an RG 400 with one. I can confirm that RG 400's were not sold new with a belly pan, but they were available at extra cost, so it is completely original in this state.

Finding all the small items put away 4 years ago was a bit of a challenge.  I have had boxes of RG stuff spread all over the shed for years now, but thanks to good luck and a bit of management it is all together.

If you ever get your hands on an RG one of the things that is a bit of a pain is the crazy variations in fuel line dimensions. They were all quite hard to match. I seemed to get a slightly smaller diameter replacement for each variation making fitting sometimes difficult for the awkward unions.
Replacing the Carburettors had got the bike within striking distance of completion. It was now clearly running but it had a problem with cold starting. It would only fire on the right side. I could not continue until this issue was sorted. There is no access once the induction pipes and fairing goes back on and I had been through those carbies from top to bottom - the last thing I wanted to do was to open them up again. I left it for a month or two - always the best thing when your at your wits end.

 Later I came back to it with some motivation. Removed the left carbs, examined the jets - all clear,  and float bowls clear.

I had the carbs spread out on a work table that I was using... a collapsible plastic table I use for camping...alongside was a comfortable green mesh poolside chair I had recently scavenged at hard rubbish. I was collapsed on the chair looking at the bits when the sun lit up the bottom of a float bowl.  I then noticed that it had a hole cast into its wall. this matched a brass tube that projected from the body of the carb... that obviously went into the hole in the side of the chamber wall.   At the base appeared to be a very small brass ringed cast opening - like a tiny jet.

I tried blowing through the hole and the jet like opening - blocked.   Went to my old carbs and tried the matching float bowl.... yes the jet and the brass tube were definitely supposed to be connected.   Problem solved.    Again this was death by petrol gum.... hardening and blocking the vulnerable tiny opening at the bottom of the float chamber. This was the Choke jet - only found on the carbies with the choke actuating piston ie one for each side.

Put it together, throw some fuel in it, pull back on the choke... give it a kick... and 4 eruptions of smoke from the back straight off....








Very Soon my dreams (nightmares?) at night began to look a lot like this........

The brakes were sort of ok after a bit of use, and pretty useless before that. - a bit of clutch drag, but that turned out to be the handlebar cable adjuster had been wound in to full slack. I changed the gear box oil before the run, it was perfectly clean golden oil, and in fact could have stayed in there probably.  The filler cap is a pain to screw back on.


Part of upper fairing corner has broken off , support bracket at this location is missing on opposite side 



   Having a fuel gauge and air forks is one advantage of the Japanese domestic RG 400 over the RG 500.



The new battery went in today....   I purchased the original $84 pretty expensive too. The BMW's and Guzzi's are easy for batteries, as the generic ride on mower ones are almost a perfect fit... a few mm's too tall but will squeeze in no problems. Fitting the battery in the RG is not easy as the fuel tank has to come off. The 400 has a fuel sender in the tank, so on top of the fiddly fuel lines and various drain pipes from the tank and complete tap assembly that has to come out with it, you have wiring to worry about as well. #%@&* reconnecting it !. The wiring goes stiff with age and the affects of petrol and in this state its a bastard to deal with.

The tank had to come off anyway, as I had earlier removed it and taken the fuel cock off to give the tank a flush out and now it is weeping. I had to look at the fuel tap, as it was getting hard to turn. Nothing to report inside but I used a bit of vaseline on the O rings and cleaned it up.... and just doing that made it a thing of beauty to operate. Petrol was weeping around the fuel cock /tank joint...... I undid the two 10mm bolts and removed it to clean up the joint surfaces and apply a little touch of hylomar non setting fuel resistant gasket to the O ring seal. If I had been a little more careful in the first place I'm sure it would have been OK  ..I used some fine steel wool to take both surfaces to a shiny clean finish and tidied up the O ring seat before applying a fine smear of Hylomar to both surfaces and letting it dry a little. Battery and tank now replaced.

Later I found a series of pin holes in the base of the tank after an acid flush out had obviously removed the point of daylight.. the tank is eggshell thin.   I dealt with this very easily...sanded down the affected area to shiny metal, heated up my antique plumbers massive solid copper soldering iron, and generously tinned the surface with solder... end of leak forever.

I started the bike and was happy to note I now had a working tacho, bright lights and indicators. 

The time has come to ride. I went to my local motor registry and obtained a temporary registration permit for the following day... $50.     I have to admit I was really excited and just little apprehensive at the thought of getting it out there up in the empty roads of the Adelaide hills........ being 6'2' tall and at 56, not quite in the demographic Suzuki had in mind when this bike was marketed.

I headed off just after 9am, when the traffic had eased right off.  It was a lovely still, fine day about 21C.  I live about 3.5 kms from the base of the Mt Lofty ranges where the Greenhill Road, a narrow two lane road, winds dramatically up the face of the range.  After about 6kms it spills right over the summit of the range. Here begins a myriad of quiet and beautiful hills roads - take your pick.  I made it via the back streets all the way from my house to the point where Greenhill road starts to ascend the hill and the end of urban housing. I followed a car going up the hill - and didn't get a chance to open up a little until the summit, where the car turned off.  When I did push up towards 6,000rpm, the road behind totally dissapeared in a massive cloud of blue smoke. This cloud more of less continued for another 8 kms when I reached a small town and slowed down and noticed I had lost a cylinder...    I kept going, along a busier road on the valley floor. I sat on the 100kph limit when I could, continuing to throw out huge clouds of hanging smoke. Luckily the traffic was quiet, and I hope I didn't offend too many motorists.   I reached the next town and lost another pot to the tar it was trying to digest.  Time to return home.... I turned around on my 200 twin, the two rears were still going strong,  and pushed it back up hill for about 20kms - still cheerfully throwing out smoke like a coal fired locomotive.   I got home fine - it still had enough power to manage 100kph on two cylinders.  I  removed both fairing halves to access the plugs and removed the front two, and burned them clean with a propane torch. Meanwhile a small quantity black stinking oil dripped into a pool from the base of the silencers at the join with the chambers.....   Bloody hell.  The whole rear of the bike was covered in an oily film.  This bike had come from Tokyo and had probably never had a good burn off in its road career, plus had oil thrown in the crankcase by me, not to mention a cumulative oozing of  two stroke oil from the tank down the throat of the obviously had a crankcase still full of oily ooze. It was the lower pair that suffered the most in this respect, probably from 2 stroke oil that had under gravity migrated at the speed of a glacier via the lube pipes into the throats of the carbies, then into the crankcase and straight into the lower chambers. There it gets vapourised with the exhaust heat, and rammed back into the combustion chamber with great efficiency by the reflected shock wave. Result is a lot of smoke and not much ignition.   This is a very good argument for regular use of all two strokes with forced lubrication..

Firing on all 4, I repeated the journey. On the few straights when opened up it continued to throw out a lingering haze of smoke. About 16km in, I lost a front cylinder again, and another was missing at revs.   I really wasn't surprised, as once a plug has been oiled up good and proper they often don't go far again after cleaning. It really needed a set of hot plugs and a long straight road - preferably with no one on it.

No problem, I returned home... it was still a good ride.  I pulled the bad plugs and cleaned them, returning them to the engine. On starting it was still missing and backfiring and generally running rough.  The NGK 8 R plugs had died.   R's are resistance plugs - something often required with high energy CDI type ignition systems - some bikes use a built in resistance in the plug caps and others specify R type plugs...but if you have both its not really the first choice for anyone wanting a decent performing spark plug... You need to do your research to find if R type plugs are required.  It was after 4pm now... I needed some new plugs..... B8ES was the hottest that Suzuki endorsed for this model.  I rang the nearest motor parts place and they found 2 only after a short search.  Hopped on my treadly and did the 4ks in record time to claim them.   I ditched the worst of the 8R's and screwed in the new plugs. It was getting late in the day and time for the rats to race... I didn't want to share the road with peak traffic so I started cooking an early meal. Fresh ocean fish, steamed..served with vegetables and a garlic sauce.   At 7pm after an enjoyable meal, the last of the traffic had petered out, twilight was approaching. Back to the road and my familiar route....  this time it ran hard on all cylinders... even getting a little scary at revs on the few straights. It was still not quite revving out cleanly, no doubt the other two 8R's were the reason and  it was scavenging the last of the crud.  I have to say the sound from those chambers when it hits the power band is wonderful !   On the return home I lost the daylight, and running on the headlight I eased off to a gentle run home - really pleased with the bike..... 200kms under the belt ...another good days running would have it very well sorted.

The next Chapters involve a move to Sydney and a new owner..... so this is where it ends for me. Check out Ian's story on the continuing development of the bike, simply click on the photo down the page...

While the story of the RG presented here is reasonably brief ,many many hours of work went into getting it into a running state. The RG is a very demanding bike to work on when constant adjustments are required... or more simply a plain pain in the arse..  They are not built for ease of maintenance that's for sure, and do not take well to constantly removing fuel tanks, fairings and carbies..You really have to like petrol fumes a LOT.  My advice if you are in the market... get one that is up and running well, over a cheaper restorer..but I acknowledge that many enjoy the challenge involved, but where do you get clean running, tidy RG's from anyway for less than $xx,000 ?

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                                    Team Alpha Racing ?

Mine was missing the stainless fairing retaining trim above the lower chamber as above


                                                The story continues here !!....   Click the RG image to read current owner Ian's amazing rebuild and improvement project

                                                    RG HEAVEN... Multitudes of performance parts from Japan here..................

How about a set of bespoke chambers in stainless for $3,000 ?  how about blowing $10,000 for a bit extra...?


Fantastic RG restoration by overseas reader Wayne...

The pictures tell the story..



  Email Link to Dave

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Want to read about Lee's heroic restoration of a RE5 rotary Suzuki ?

Sorting the men from the boys...