FAQ

The following steps should help alleviate this problem 

• Ensure head and barrel mating surfaces are perfectly flat.
• Replace the cylinder head studs/bolts with new items.
• Use genuine Yamaha Head and Base gaskets
• Use steel cylinder head washers (the ones on the long head bolts) from the late XT600E,these compress less than the SRX items.

Unleaded fuel is fine for an SRX. The compression ratio is relatively low so there is no need for the higher octane provided by Super Unleaded or LRP, in fact your SRX will probably run better on unleaded than anything else.

Yes but you will need an SRX600 engine. The crankcase mouth on the 400 engine is too small to accept a 600 barrel. This could be machined but it will probably be cheaper in the long run to source a complete 600 engine. 

Fifth gear is a weak spot on early SRX and XT engines. I have heard a number of theories as to why, the most probable one being that the gears are simply to small for the size of the engine. I have stripped three SRX/XT engines and all have had worn fifth gear pinions. The gears are relatively inexpensive, the problem is you have to strip the engine to change them.

Starting is a doddle, hot or cold, with the right technique. 

Turn over a couple of times and find compression. 

• Full choke if cold, none if warm. 
• Ignition on, and stand up on kickstart and follow through smoothly, rather than jab. Some may prefer to keep on sidestand to avoid overbalancing. 
• Throttle closed until you get towards the bottom of the kickstart stroke, then open just a fraction. 
• Choke down to half almost immediately, and closed fully soon afterwards. 
• If you cook it up, then it tends to flood, and any attempt to kickstart will have you dissolving in a pile of sweat. But it will bump start with sufficient momentum.

Source: John Bushe.

• The light is a speed  warning light is activated by a sensor in the speedometer, and all the wiring is contained within the speedo head and idiot light binnacle. Easily disconnected if it annoys. 

Source: John Bushe.

• The electric start XT, head and cylinder are not the same as the SRX. The principle difference is that the two studs on  the  bottom of the head at the front and rear, which help hold the head and  cylinder together, are spaced further apart on the XT600E, than on the older SRX/XT/TT engines. This allows the XT to keep the cylinder casting  thicker  at the front and rear of the engine. The XT cylinder also has more  material  in other parts of the cylinder, making it a better choice for race engines. The SRX engines are famous for breaking at the cylinder base flange when  hopped up and raced. The XT cylinder should be a much less prone to this  problem. Therefore the XT600E cylinder and head are not  interchangeable with the SRX parts unless you use both together. It is possible to weld the SRX head and relocate the studs to fit the XT cylinder, but it doesn't  seem  worth the effort unless you have an expensive ported head you want to keep.   

• The XT600E head is fitted with 1 mm larger valves than the older SRX/XT engines. 

• The XT600E cam cover has an additional 6 mm screw in the cover-to-head bolt  pattern, located at the end of the cam chain tunnel.   

• The oil tank overflow/breather fitting is fitted next to the engine breather on the SRX, on an XT600 it is located on the cam cover.

• On the XT600 the swinging arm pivot passes through the rear engine mount, to accommodate the engine mount has a 17mm diameter hole, however the SRX uses a standard 10mm diameter bolt, so a spacer is required when fitting an XT engine to an SRX.

Source: Ken Canaga, Joe Abeyta.

• The XT600 clutch and alternator covers are magnesium based and a different shape to the SRX items.

• The XT600 kick-shaft differs from the SRX item. The XT uses a pinch mechanism to secure it, where as the SRX item uses a fine threaded nut on the end of the shaft. The shafts are however interchangeable and do not require the engine cases to be split.

• The XT600 gearbox has different ratios to the SRX. (Apparently The XT400 shares its gearbox with the SRX). 

• The oil tank overflow/breather fitting is fitted next to the engine breather on the SRX, on an XT600 it is located on the cam cover.

• The XT600 engine is 595cc compared to the UK SRX600 608cc.

• On the XT600 the swinging arm pivot passes through the rear engine mount, to accommodate the engine mount has a 17mm diameter hole, however the SRX uses a standard 10mm diameter bolt, so a spacer is required when fitting an XT engine to an SRX.

Source: Jean Christophe WOLFIN, Steve Hayward

This may be done but the following points need to be noted (Note I have not carried out this modification I am merely relaying information given to me)

• The steel spacers located in the cases at the upper rear engine mount need to be changed for the SRX items. The XT  runs  the swing arm pivot shaft through the cases here, and it is much larger in diameter than the mounting bolt on the SRX. Other than that the engine will bolt in. 

• The XT uses a different clutch cable than the SRX. It is routed differently to clear the electric starter nose. It looks like it should work in the SRX  as  long as you use the XT cable.   

• Ignition systems are different. The CDI black boxes and coils are not interchangeable so an XT600E unit with matching coil will be required. 

• The XT600E output sprocket is offset about 1/4" to the left, compared to the SRX. This may be solved by using a standard XT600 sprocket and machining it 1/4" thinner (only machine the spline area) to allow it to be fitted closer to the engine. The bolts heads that retain the seal must also be machine down to clear the chain. 

• The SRX tach drive may be fitted onto the XT600E head in place of the blanking cover.

• The XT uses a different primary gear ratio in the engine (different clutch basket and matching gear Note: I have a UK XT600 engine and this is not the case with this engine). The SRX primary gear set is interchangeable).

• The SRX oil tank has to be relocated to allow the electric start to be fitted.

• The XT600 engine cases are magnesium based, they are a lot lighter but are a different in appearance to the SRX items.

Source: Ken Canaga

• The manifold from a Yamaha YFM600 Grizzly (ATV) bolts right on

• A40mm Mikuni from a Suzuki DR650, which just happens to be the same carb as on a Grizzly. For jetting, I went with a K&N Hop-up kit (again, for the Grizzly), and the jetting seems to be close.

• You will have to get rid of the airbox and use a clamp-on. The biggest problem is the oil tank. It is right where the carb comes down. I ended up removing the SRX oil tank and mounting an XT600 oil tank along the inside of the frame on the right hand side, behind the side cover. Everything fits, but there's not much room left.

• As far as the tank goes, the carb will be at the exact spot that the petcock comes out of the tank. I never tried the stock petcock, so I don't know if it will work. I ended up making a flat fuel outlet that I bolted to the tank. I had to raise the tank up about 1/2 inch, but it looks fine.