Welcome to my Hondamatic page! This is one of my favourite bikes and I've collected a fair amount of goodies for this model over the years. Some of this is a reference dump for me so beware!
Index:
Downloads
CB400/CM400T FSM - Most repair procedures
CB400A/CM400A FSM Addendum - Hondamatic specific repair procedures
CB450SC/Nighthawk 450 FSM
1978 CB400A Hondamatic Owner's Manual - PDF in 24.20MB
1979 CM400T/CM400A Hondamatic Brochure
Hondamatic 400 Yahoo! Groups Archive - 147MB
CB400/CM400 O-Rings, Seals, and Bearings spreadsheet
New to Me Repair Tips for CB400/CM400/CM450/CB450SC
Tires and Tubes
CB400 Series
- Kenda Challenger K657 100/90-19 Front
- Dunlop D404 100/90-19 Front
- Kenda Challenger K657 110/90-18 Rear
- Dunlop D404 110/90-18 Rear
- 3.25-4.00 19 Tube for Front
- 3.00-3.50 18 Tube for Rear
CM400 Series
- Kenda Challenger K657 100/90-18 Front
- Dunlop D404 K657 100/90-18 Front
- Kenda Challenger 120/90-16 Rear
- Dunlop D404 120/90-16 Rear
- 3.25-4.00 18 Tube for Front
- 4.60 16 Tube for Rear
NOTE: 130/90 on Rear is pushing the absolute limit and will cause clearance issues. Don't do it.
Carb info
- 1978 CB400A - VB24A #72/105. Slow jet #42. Needle 13D. White piston cushion.
- 1979 CM400A - VB24B #65/110. Slow jet #38. Needle D449. Black piston cushion.
- 1980/1981 CM400A - VB24C #68/112. Slow jet #38. Needle 54D. White piston cushion.
- 1982/1983 CM400A - VB24E #68/112. Slow jet #38. Needle 54D. White piston cushion.
NOTE: Referenced from Jim/LongDistanceRider's thread at VHT. See here for more info.
Chain and Sprocket
- CB400: DID 530 100 Links. 16T Front Sprocket. 37T Rear Sprocket. JT Part Number: JTF278.16 and JTR246.37. Sunstar Part Number: 50816 and 2-517837.
- CM400: DID 530 102 Links. 16T Front Sprocket. 35T Rear Sprocket. JT Part Number: JTF278.16 and JTR246.35. Sunstar Part Number: 50816 and 2-517835.
- CM450A: DID 530 102 Links. 17T Front Sprocket. 34T Rear Sprocket. JT Part Number: JTF278.17 and JTR246.34. Sunstar Part Number: 5081 and 2-517834.
Recommend brands are JT Sprockets and Sunstar (RIP - find NOS or dead stock)
Batteries
- Yuasa YB12A-A - OEM Conventional Battery.
- Mighty Max YB12A-AGEL - Gel Battery
- BikeMaster TruGel MG12A-4A1 - Gel Battery
NOTE: Conventional batteries cost about the same as the Mighty Max gel battery. Get the gel. Lithium ion will offer no benefit and may not charge properly. These bikes do not rapidly discharge with headlight on at idle like the earlier Hondas.
Oil
Oil must meet JASO MA specs. Most are using Shell Rotella T4/T5/T6 15W40. This meets the specs. T4 is conventional and cheaper. T5 is blended synthetic. T6 is full synthetic. T4 is fine to use. If you must have something that is on the JASO list with the certification Honda GN4 10W40 directly from the dealer (don't bother online it's overpriced with shipping) is probably the best deal.
Oil filter is Honda Part Number 154A1-413-505. Used for all years. Price is cheap from the dealer, don't bother saving a dollar or two with aftermarket.
Air Filter
- CB400 - Hiflofiltro #HFA1210 - NOTE: Foam filter. Needs oiled.
- CM400/CM450/CB450SC/Nighthawk 450 - Emgo #12-91400.
NOTE: These bikes do not respond well to "pod", "velocity stack" and K&N "lifetime" filters. Pods and K&N NEED oiled and expect to go up to 10 jet sizes to compensate. You will not unlock any additional hidden power by doing so.
Brake Pads and Shoes
- 1978-1981 Front Pads: Emgo #91-51804 (Sintered) OR #64-51854 (Full Metallic). EBC #FA45 (Organic).
- 1982 CM450A Front Pads: Emgo #91-51808 (Sintered) OR #64-51858 (Full Metallic). EBC #FA69/2 (Organic).
- 1982 CB450SC/Nighthawk 450 Front Pads: Emgo #91-51823 (Sintered) OR #64-51873 (Full Metallic). EBC #FA90 (Organic).
- 1983 CM450A Front Pads: Emgo #91-51823 (Sintered) OR #64-51873 (Full Metallic). EBC #FA90 (Organic).
- 1983-1986 CB450SC/Nighthawk 450 Front Pads: Emgo #91-51807 (Sintered) OR #64-51857 (Full Metallic). EBC #FA69 (Organic) OR #FA69HH (Sintered).
- Rear Shoes (all years): Emgo #93-39111 (Sintered) OR #93-39161 (Full Metallic). EBC #313 (Organic).
NOTE: Full Metallic pads brake better, but can be louder and possibly wear the rotor down faster. Rotor wear is a non-issue unless you're putting serious miles on these bikes. Plus, the rotors can be found used cheap on eBay and EBC makes aftermarket. Emgo Brake Catalog here and EBC Brake Catalog here for reference.
Electronic Ignition
- Spark Plug Caps are NGK XD05F. No longer manufactured, but plenty of NOS/dead stock. Aftermarket substitutes are now available.
- Spark Plugs vary by year and geographic location, but you can use NGK D8EA or ND X24ES-U IF you are using resistor caps like the XD05F. If unsure measure the cap (disconnected). It should be 5 KOhms. If not, replace and get the correct part. Otherwise, consult your manual.
- Replacement ignition coil options are limited. Most aftermarket ones sold online are SOHC4 coils that happen to fit and are the wrong primary resistance. The CDIs NEED 0.5 to 1.0 ohm resistance or the coil will overheat and not idle properly once warm. Main option is replacing with DynaTek DC11-2 or the "GM Coil Mod". Both require making spark plug wires, a bracket, and soldering skills. Refer to the threads linked below on how to do it or order a kit from me at Hondamatic Parts.
- CDIs are going bad because the capacitors are only rated for 10 years. They are use it or lose it. Don't bother with NOS and used is a gamble. I make the CDIs, but a few other vendors do as well. My competitors CDIs are made of cheap plastic and cheap components. You can buy a CDI from me at Hondamatic Parts.
Helpful Links:
Turn Signals and Lighting
Turn signal relays go bad after a while. Replace with a CEC Industries EF32 blinker, even for the square ones.
Sylvania 1157 LED White Mini Bulb is a good replacement for the tail light bulb. This will reduce the load on the electrical system during braking and increase visibility. Grab it here.
There are no proper LED headlights that are direct fit for this bike. However, David Silver Spares has a Xanadu brand headlight that will fit the bucket. The down side is that it's meant for the UK market, but it appears to work and aim just fine. Leagues better than the original, even if it does not meet DOT. Look up part number 33120268632P on David Silver Spares.
Carburetion and Fuel
- Do NOT use any rebuild kits in these carbs. Really? Yes, really. The brass does not wear out and neither do the jet needles. If you replaced the brass you will need to source the originals or it will never run right. Even the o-rings are questionable.
- Only use OEM Float Valves/Needles in these carbs. Aftermarkets have wrong lengths and cause leaking and funny running. It's even more critical on the 1980 and later years with the unadjustable plastic floats. Part number 16011-KCK-910 for 78-79 and part number 16155-413-751 for 80 and up.
- 80 and up use an accelerator pump diaphragm. Aftermarket replacements from 4into1 and SCI are acceptable. You MUST grind it down to length. The gap between the rod and carb body are incredibly small at just 0.01-0.04mm (0.0004-0.002in). This must be correct or you will get weird dead spots around 1/4 throttle when opening the throttle quickly. The adjusting arm and stopper also need checked when replacing the rod. Its clearance is 7.0mm (0.25in). You can measure with a pair of calipers.
- Aftermarket replacement Air Cut Off Valves from 4into1 and SCI are acceptable.
- The best aftermarket float bowl gaskets are from K&L. Look up GL1100 float bowl gaskets on eBay. K&L #18-2631.
- The slow jet plugs were only available in the "packing set". Aftermarket replacements from 4into1 and SCI are acceptable.
- Float height is 15.5mm +/- 0.5mm on all models.
- Idle speed is ~1200RPM on all models.
- Initial pilot screw setting is 1 1/2 turns out on 78 MANUAL, 1 3/4 turns out on 78 AUTOMATIC, 2 1/2 turns out on 79, and 2 turns out on 80 and up.
- It is a common and beneficial mod to swap the primary jet (the smaller of the two jets on the two jet models) out to the next number. For example, changing a 72 to a 75. You can find OEM jets by playing the parts numbers game. For example, 99101-393-0720 is a #72. By changing the last 4 digits you can come up with the part number for a #75, 99101-393-0750. Sometimes jets are still available direct this way. Other times NOS vendors may have it. Otherwise, you are limited to Jetsrus and SCI.
- The slow jet is pressed in on the earlier years and was never available as a separate part. It must be extracted to be cleaned during a rebuild. If you need a replacement jet search for CBX jets on SCI.
- The emulsion tube is buried on the primay jet (the smaller of the two jets on the two jet models) and must be removed as part of a rebuild. Getting a long, thin screwdriver grounded down to length is the best way. I use "Wera 05110006001 Kraftform Plus 335 Slotted Screwdriver, 4mm Head, 8" Blade Leng". Grab it from Amazon here.
- The slow jet and emulsion tubes can still be stuck in there, even after multiple methods. When this happens I heat them up with a torch OUTSIDE WITH ALL RUBBER PIECES REMOVED. See how to do this here.
- The carbs must be separated to remove the inner air cut off valve. If you do this then you must replace the crossover tube o-rings. Something you should always do as a part of a rebuild as the o-rings dry out after years of entropy.
- Most leaks are from the overflow standpipes having hairline cracks in them and/or the drain screw being corroded or having a dirty seat. See here for my favourite method of verifying and fixing leaky float bowls.
- Assuming the float seat is clean and the float bowls are not leaking, the other major cause is aftermarket float valves/needles.
- Despite all of this you may still have a leak. Make sure the fuel line is on proper. Do not use 1/4" lawn mower fuel line. Get 5.5mm fuel line from the dealer. 1/4" fuel line requires worm gear clamps to be on incredibly tight or it will leak down the side of the carb and fool you into thinking it's the float bowls.
- Still leaking? Really look carefully at the fuel crossover tubes and fuel accelerator pump crossover tubes (if equipped). If they leak from there then replace the o-rings.
- Idle mixture screw should bog down the bike and likely stall out when fully seated and then blipping the throttle. If the RPM does not change and does not bog or stall out the circuit is plugged, the tip is bent or missing on the mixture screw, the o-ring, spring, and/or washer are missing, you have tight valve clearances or some kind of intake leak.
- Idle mixture screw has a flag on 80 and up to prevent tampering. You can grind the tab away with float bowl removed or remove the flag with a soldering gun (recommended). See links below for a video on how to do this.
- The piston cushion/spacer goes in one way. It is possible to make a ham-handed attempt to force it in the wrong orientation, distorting the cushion and possibly breaking the casting. If it feels wrong, that's because it is. STOP and flip it over.
- Do NOT bench sync the carbs by dragging a piece of wire, plastic, drill bit, etc. under the throttle plates. You WILL damage them. Instead, turn the sync adjuster slowly and watch the transition on the two transfer port holes in the carb. This is the correct and safe way to do it.
- These carbs do not require shimming the jet needles. If you are doing so to solve a performance problem you are masking a deeper issue. Even so, the stopper needs a counterbore drilled when doing so. The needles are supposed to wiggle freely. You will damage them if they are unable to move.
- Intake insulator boots for MANUAL transmission are still available from Honda, part number 16211-447-670. Automatic transmission is NOT available so you will need to find NOS or used. 1978/CB400A is part number: 16211-414-010. 1979-1981/CM400A is part number: 16211-448-000. 1982-1983/CM450A is part number: 16211-MC1-000.
- Replace the o-rings under the insulator boots if you remove the insulator for any reason. Part number is 91325-413-830, but you can replace it with a 40.0mm ID x 45.0mm OD x 2.5mm W o-ring. McMaster-Carr part number 9262K451.
- Replace the insulator and air box bands (clamps) once disturbed. They get stretched out after 50 years. Still available brand new from Honda, part number: 16219-ME9-000 and 17256-425-010.
Helpful Links:
Engine
Cam chain is getting more and more expensive. David Silver Spares sells an aftermarket that is the same brand (Morse) as the original and is a direct fit. Search for part number 14401MR4901P on David Silver Spares.
Balancer chain needs done every ~10,000 miles. Instructions are located here for the CB400A/CM400A/CM450A/Hondamatic.
Helpful Links:
Repair Videos
Links:
Reproduction CDIs
Hondamatic Parts YouTube
Vintage Honda Twins (VHT) Forum
My VHT Profile
David Silver Spares - Great source for NOS parts
CMS NL - Another great source for NOS parts
Partzilla - Good resource for OEM parts that are still available and for parts fiche listings
Mike Nixon's Motorcycle Project - Excellent articles, carb repair and machining services.
Email me
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