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Honda Transalp and Africa Twin

From GummyCarbs

The Honda Africa Twin is a 650cc (RD03) or 750cc (RD04, RD07) cousin of the 600cc Honda Transalp. The earlier Africa Twins are very similar in construction to the Transalp, and many parts can be put onto a Transalp. Potential improvements include a larger fuel tank, an aluminum swingarm, taller suspension, and a rear disk brake.

Model Designations

Model designations become very important when purchasing parts, so it's important to understand the meaning of PD06, RD04, RD04, and RD07.

The Transalp imported into the US in 1989 and 1990 is the PD06 XL600V.

There are several models of Africa Twin. The important thing to remember is that RD07 parts cannot be used on Transalps, as the frame is significantly different. Many RD03 and RD04 parts, however, bolt straight up to a Transalp. The following chart shows years and models. Note that only models relevant to the US-spec Transalp are shown:

YearModel    Picture
1988
1989
RD03 XRV650
RD03 XRV650
XRV650RD03.jpg
1990
1991
1992
1993
RD04L XRV750
RD04M XRV750
RD04N XRV750
RD04P XRV750
XRV750RD04.jpg
1994+RD07 XRV750
XRV750RD07.jpg

For a full breakdown of Transalp models (PD06H, J, K, PD10, etc) see Deti's page.

For a full history of the Africa Twin (RD03, RD04L, M, N, P) see this page (Japanese).

Fuel Tank

RD03 and RD04 fuel tanks, which are identical apart from color scheme, will fit directly onto a Transalp frame. An RD07 has an entirely different frame, so its tank will not fit a Transalp.

Interference

Without the support bracket, the RD03/RD04 tank's petcocks may interfere with the Transalp engine's oil lines. This does not seem to be an issue with later Transalps, which may use a different oil routing more similar to the NT650 Hawk.

Support Bracket

The Africa Twin tank requires a support bracket, which is mentioned here (image).

This item may be listed on Ebay Germany as "Verkleidungshalter" (translates as "Fairing bracket"). It certainly appears to be the exact same part as what is commonly listed as "Kühlerhalter" ("cooler holder").

It appears in both the XRV650K and XR750N microfiche as 64209-MS8-000 PIPE COMP., COWL MOUNTING.

Fuel Pump

The Africa Twin gas tank requires a fuel pump in order to get the last few gallons into the carburetors. First, a few safety precautions:

  • An anti-siphon/cut-off valve is critical in motorcycle applications.
    • When the gas tank is higher than the carburetor, gasoline may leak into the carburetors while the bike is parked. This could result in cylinders filled with incompressible gasoline and bent connecting rods when one attempts to start the engine. It could also result in a massive fuel leak and a fire.
  • An RPM-related cut-off is also critical. A mechanical fuel pump will, by its nature, stop pumping when the engine stops. An electric fuel pump, without a cutoff, will continue to pump fuel. In the event of a crash, would likely cause fuel to be pumped continuously out of the bike, resulting in a fire. Purolator/Facet recommends an oil-pressure cut-off switch for their electric pumps, so that it only runs when there is oil pressure from a running engine.

Stock Africa Twin

The Africa Twin's OEM fuel pump is electric, and it's prone to failure due to internal electrical contacts which arc and destroy themselves. The pump itself can be hardwired and controlled by an external relay, which prevents the arcing problem.

Substitute Pumps

Fuel pumps are rated in flow rate (gallons or liters per hour) and pressure (PSI).

In selecting a fuel pump, the right pressure is critical. Carburetors have a float bowl which works a bit like a toilet's valve system. Sealed floats are pushed upward by their buoyancy as fuel fills the float bowl. When enough fuel has entered, the floats press a needle valve closed, stopping additional fuel from entering the float bowl.

The Transalp's carburetors are designed to accept gravity fed gasoline. Pumping fuel in with a fuel pump may overwhelm the float & needle system, pumping too much fuel into the float bowl, causing an over-rich condition. A worst case scenario would end in hydraulic lock and a severely broken engine! Even without this worst case, running an overly rich mixture would cause poor fuel mileage and increased cylinder wear as the excess gasoline washes oil from the cylinder walls.

How Much Pressure Is Needed?

The pressure created by a column of water is about 0.433 PSI per vertical foot. Assume that the fuel pump is mounted at the lowest point on the frame, the carburetor inlet is no more than two feet above this point. So, if we were pumping water instead of gasoline, we would require only around 0.866 PSI or less to overcome gravity. Gasoline has only about 75% the density of water, so the Transalp should require no more than about 0.65 PSI to overcome gravity.

A real life example can be found in the KTM 950. This post states that a stock KTM 950 fuel pump puts out 2.2 PSI (at the carburetors), draws 1 amp, and pumps 23.4 liters (6.2 gallons) per hour. So, the KTM's carburetor floats and needle valves can hold back at least 2.2 PSI. We don't know how much the Transalp's needle valves can hold back, but we can assume it's certainly no more than 2.2 PSI!

As detailed below in the Electronic Fuel Pump section, about 0.3 PSI is lost per foot of fuel line between the pump and carburetor.

How Much Flow Rate Is Needed?

This post provides an interesting, simple method of estimating pumping capacity requirements for a 100hp KTM 950 Adventure:

Assume 100 hp, this is 75kw.

In an hour at fuel load the engine will produce 75kwh/hr of energy. Assume the engine converts 33% of the energy in the gasoline. We need to input 250kwh of gasoline. Gasoline has an energy density of about 8.76kwh/l. So the max fuel flow rate is about 30l/h. This is 8 gph.

I left a bit of slack in the calculaitons by rounding up. Made the flow rate come out higher then it actualy is. It's close to 7gph which is the output of a 40177, so close I'd go for it and see what it does in the real world.

Since the Transalp puts out around 1/2 the horsepower of the KTM 950 (50 hp versus 100hp), it would seem that 4 gallons (15.14 liters) per hour should be sufficient.

  • This page has Modrover asking for advice on regulating a fuel pump. Are new float needles required? He gives up in the end, returns the Transalp to stock form, and buys a real Africa Twin.
  • This post on ADVRider's Orange Crush section, has tips on selecting and mounting fuel pumps.

This link says that the Honda Hawk NT650V fuel pump is rated at 600cc (0.630 US qt) per minute, which is approximately 9.5 gallons per haur.

Mechanical Fuel Pumps

Mechanical, vacuum-operated fuel pumps are powered by vacuum from the engine. Mikuni produces a compact one for motorcycles. It pumps 14 liters (3.7 gallons) per hour at 3.2 PSI, costs around $20, and is fully rebuildable. They produce other pumps as well, but the 14 liter version is the only one suitable for the Transalp.

MikuniDF44-221.jpg

According to this post, 'Modrover' found that the 3.2 PSI from the Mikuni pump was too much for the Transalp's float needles to handle:

I own a '88 XRV650 now, but did the AT tank mod to my Transalp awhile back. I used this pump and found it to be a bit more than the stock needles could take. It was pumping too good!  ;^)

Dellorto also makes a vacuum-operated fuel pump, which seems to be popular on karts. It has a built-in adjustable regulator. It costs around $50.

Pros:

  • Inexpensive ($20ish).
  • Rebuildable.
  • Automatically stop pumping when the engine stops. i.e. they won't continue pumping gas all over after a crash.
  • Output may increase with engine RPM?

Cons:

  • Almost certainly too much pressure for the Transalp's carburetors.
  • May be less reliable than electronic pumps.
  • Requires a new vacuum line.
  • Potential for vapor lock in hot conditions. Engine heat boils the gasoline in the tube between the pump and the carb, so the pump begins ineffectively pumping and compressing gaseous gasoline.
  • Only available in a single pressure rating which, according to 'Modrover', is too much for the Transalp's float needles.
  • May not have an anti-siphon/shut-off valve, which could cause the engine to flood with fuel when parked.

Resources:

Electronic Fuel Pumps
Honda Fuel Pumps

It's likely that other Honda motorcycle fuel pumps could be used on the Transalp. Some models use pumps which are internal to the gas tank, which is probably not suitable for adaptation to the Transalp. Some likely donors are:

  • VT600
  • VT750
  • VT1100
  • NT650V Hawk
  • CB-1
  • PC800
Relay Protection

Honda fuel pumps are known to fail as a result of contact arcing. This page explains how to avoid the arcing using a diode.

Aftermarket Fuel Pumps

Update: As of 2020, I run a Facet Posi-Flo 60304. This is an updated, plastic-bodied version of the older cube pumps. Despite the plastic case, it appears to still be susceptible to moisture, so take care when locating it on the bike.

Facet (a Purolator company) makes solid state fuel pumps, which claim to have no moving parts or diaphragms to wear out.

Facet CubeFuelPump.jpg
Facet-PosiFlow.png

Pros:

  • May be more reliable than mechanical pumps.
  • Available in a variety of pressure ranges.

Cons:

  • More expensive ($33 - $63+ from online sources).
  • Not rebuildable.
  • Requires a switched electrical supply, preferably one which cuts out when the engine dies so that the pump doesn't continue pumping gasoline onto the ground after a crash, leading to a fiery death and all of your loved ones talking about what an idiot you were at your funeral.

Resources:

  • Facet-Purolator's fuel pump web page.
  • This post describes using the Facet 40105 electronic fuel pump from Aircraft Spruce and Supply.
  • This post mentions that Purolator's filter (F10028) screws into the Facet pumps, and is much shorter than Facet's own filter.
  • This post mentions that the Wix 33049 filter may be compatible.
  • This post says it's important to seal the Facet pumps with silicone or rubber sealant to prevent shorts in the event the pump gets wet.

Short list of Facet pumps (pumps which are obviously unusable on the Transalp have been omitted):

ModelPressure
(PSI)
Flow Rate
(gallons/hr)
Check
Valve
Anti-
Siphon
Comments
401053 - 4.5psi30 GPHnonoToo much pressure, no shut-off valve
401712 - 3.515 GPHyesyesLikely too much pressure, same specs as 40178, but with Packard connector and less dry lift
401782 - 3.515 GPHyesyesLikely too much pressure
401631.5 - 2.5psi17 GPHyesnoPossibly too much pressure, and no shut-off valve
401771 - 27 GPHyesyesProbably a good choice
402521 - 1.5psi6.5 GPHyesyesProbably a good choice, Packard connector

I have installed the 40105, which clearly puts out too much pressure, since it starts too easily when cold, and runs worse at idle with the pump engaged. Also, it is capable of pumping around 7.5 times the volume of fuel needed by the Transalp engine! Finally, it has no anti-siphon/cutoff valve, which means fuel could continually leak into the carburetors, cylinders, and crankcase when the bike is parked!

The 40252 and 40177 are most suitable for the Transalp. The 40252 uses a 'Packard' connector, which is simply a brand of sealed quick-connector. Either can be very hard to find, but this post recommends trying J&N Electric. Pegasus Auto Racing carries the 40177 for $62.99. It can be had for somewhat less from Facet's west coast distributor.

There is talk on ADV Rider of the 40171 (2 - 3.5 PSI) causing flooding on the big KTM bikes, and many people add a fuel pressure regulator to compensate. This seems to add more support for a very low 1 - 2 PSI pump.

This post claims to have recommendations from a Facet engineer:

1-The Fuel Pressure from the Pump looses about .3lbs /foot in PSI. So if the Pump from its location to the Carbs is about 2.5 -3 feet, so there would be about a 1 lb loss in PSI from its Max potential.

2- BEST to Install the OUTLET End Higher than the Inlet End.

3- Pump is suggested use is Under 180 F degrees.

4- Recommended Filters for the Facet is 74 Micron Media and Not Less since those may impede proper fuel flow. Some sold in Parts Stores are 10-15 Microns...unfortunately, many are NOT labeled.

This Polish Africa Twin page quotes an email from Facet indicating that the 40177 is best for the Africa Twin, followed by the 40104 and 60104 Posi-Flo.

Hi Kuba

Thank you for your email. The best Facet fuel pump model/part number for your application is a 40177 Cube Solid State pump. This pump is rated for 1-2psi, 7gph which will not over run your carb’s. However the next best part number would be a 40104 Cube or 60104 POSI-FLO, both are rated for 1.5-4 psi, 25gph. Please tell me where you are located and I will try and help you find these part numbers.

Paul Puleo
National Sales Manager
Motor Components, LLC
(w) 607-737-8371
(f) 607-737-8335

www.facet-purolator.com

Pressure Regulation

The Africa Twin's fuel pump is voltage regulated. At around 1,000 RPM, voltage to the pump is about 3V. At higher RPMs, it reaches 12V.

  • This XRV.org.uk post mentions voltages.
  • This thread discusses the stock Africa Twin fuel pump versus the Facet. It is indicated that the Africa Twin has some sort of regulation circuit which varies the input voltage from 3V up to 12V, and has a cut-off for safety (when the engine stops turning, it shuts off the electric fuel pump).

It may be possible to use a fuel pressure regulator:

  • This regulator might work (Mr. Gasket adjustable 1 - 6psi). Reviews are mixed.
  • Holley 12-804 1 - 4 PSI regulator, $28.
  • This post mentions using a "PRO54" regulator set to 1.5 psi on a KTM 950.

Rear Suspension

Rear Shock

This post claims that the PD06 Transalp, RD03 and RD04 Africa Twins all have a shock length of 375mm.

With the RD04/RD07 swingarm, 1.5cm additional shock length gives 4cm additional height.

Transalp Rear Shock

As mentioned on the Transalp page, WP specifies 14.69 inches (373.13mm) as the stock shock length.

This post says this regarding a shock for a '92 Transalp:

Ohlins don't list a shock for any Transalp now, so that's a bit of a dead end - I guess it's been discontinued. However Hagon list the same part number for "TRANSALP XL600V-H,J,K,M,N,P,R,S,T (PD06)" from 1987 onwards. By my reckoning that covers well past 1992, and if Hagon list the same shock for all those models then the Ohlins from an '89 bike should fit the '92 model without any problems as well

Hyperpro list:

  • Spring: XL600V '87 - '00 SP-HO06-SSB01, XL650V '00-'06 SP-HO06-SSB013, XL700V '08- SP-HO07-SSB024
  • Shock: Hyperpro no longer lists a shock for anything earlier than the XL700V.

Africa Twin Rear Shock

  • Ohlins HO 645 for the Africa Twin 1995 - 2002 (RD07).
    • Based on the S46HR1C1S.
      • 46 - 46mm piston diameter.
      • S - monotube/singletube.
      • H - gas pressurized with external reservoir.
      • C1 - compression damping adjuster located on reservoir.
      • R1 - damping set with clicking knob with right-hand thread.
      • S - hose-mounted hydraulic spring preload adjuster.

This post indicates that 1.5cm extra shock length translates to 4cm additional height. It also indicates that an 80kg rider will do will with the 90nm spring from Ohlins.

'kordix' adapted a KTM LC4SM rear shock to his RD07 Africa Twin.

  • 2004 and 2005 model KTM LC 4 SM rear shocks listed at 415mm eye-to-eye.

Swingarm

The Africa Twin has an aluminum swingarm which is is longer than the steel Transalp swingarm. It can be fitting with relatively few problems. Notably, the drum brake stopper has to be ground to fit the Africa Twin swingarm (assuming an Africa Twin disc rear wheel hasn't been used as well), and a 124 link chain is needed.

The RD03, RD04, and RD07 swingarms appear to be identical, but in fact differ. The RD04 swingarm is slightly longer than the RD03 swingarm. The RD07 swingarm has slightly different mounting spacers and bushings and requires adaptation to the Transalp. If an Africa Twin rear wheel is to be used for disc braking, note that the disc and bracket are different on the RD03 than on the RD04 and RD07. See below, under "Rear Brake".

Swingarm Parts Interchangeability

This diagram from the XRV750N microfiche is colored to indicate compatibility of many of the swingarm parts between the Transalp and the RD04 Africa Twin. Green indicates that the part numbers are the same, while red indicates that the parts differ.

RD04 Dogbones Interchangeability.png RD04 Swingarm Interchangeability.png

Chain Slider

This ADVRider post mentions two European sources which ship internationally and stock Africa Twin chain sliders.

Rear Brake With Africa Twin Swingarm

The stock drum brake housing can be machined to fit into the slot on the RD04/RD07 swingarm.

Alternatively, an Africa Twin rear wheel can be used to get a disc brake. This post provides the following information on rear brake disks:

Model Rotor Dia. Internal Dia. Bolt Center Dist. Bolt Dia.
PD06 240mm 105mm 125mm 10.5mm
RD03 240mm 105mm 125mm 10.5mm
RD04 256mm 144mm 166mm 10mm
RD07 256mm 144mm 166mm 10mm

The same post goes on to point out that the RD03 and RD04 rear caliper brackets are for different diameter disks, but they are interchangeable in terms of width along the axle. So, if you have a 240mm disk, use an RD03 caliper bracket. Otherwise, use an RD04 or RD07 caliper bracket, regardless of which AT swingarm you have.

Tabs will have to be welded to the Transalp frame to accomodate the Africa Twin's rear master cylinder. This page shows a European Transalp with its rear master cylinder reservoir attached to a plate which bolts to the regulator-rectifier.

Rear Brake Rotors for Africa Twins

EBC
  • RD03 and later Transalps with disc rear brakes: MD6097D.
  • RD04 and RD07: MD6103D, pads FA140 or FA140HH.

Buying Parts

Ebay

Ebay is a good source for used Africa Twin parts. I recommend Ebay Germany since shipping prices from Germany are reasonable, and German sellers have proved very helpful. UK sellers have either refused to ship, or charge exorbitant rates, and Italian sellers want nothing to do with me.

Payment

Traditionally, German Ebay sellers accepted only SWIFT money transfers. Ask your bank if they can perform an international money transfer. Get a copy of the transfer form, and look for "SWIFT" in the routing number area.

More recently, some German Ebay sellers have begun accepting PayPal. This makes the process much simpler and faster.

Make sure to get a shipping quote before committing to purchase!

German Terms

Finding parts in German can be tough without any language skills.

English German
Fairings Verkleidung
Tank Support Bracket Verkleidungshalter ("fairing bracket")
Kühlerhalter ("cooler holder")
Swingarm Schwinge
Brake Rotor Bremsscheibe
Sprocket Kettenrad
Sprocket Carrier Kettenradträger
Rear Hinten
Wheel Rad
Rear Wheel Hinterrad

Other

  • This post gives contact information for a seller in Singapore.

Substitution

Honda reuses parts whenever possible across models. It's worth finding part numbers on the microfiche and looking them up online. Ron Ayers has an excellent parts lookup facility.

Petcock

According to this page, "the left AT petcock is the same as the petcock for a 1990 NT650 Honda Hawk" ($55 at BikeBandit.com).

Microfiche

The Honda parts microfiche for Africa Twins is an absolute necessity. I have made PDF copies particularly relevant pages of the XRV750N microfiche:

Resources

Conversion Examples