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Messages - honda-san
1
« on: April 06, 2026, 06:55:37 PM »
I seem to recall that internally the K6 fuel tap is very similar to that used on the 400/4 - ie a plastic cone shaped bit which can indeed wear and therefore not fully shut off the fuel supply to the carbs when tap is in the off position.
IF the tap is leaking to the outside world, as happened with one of my 400/4's, that can be cured by replacing the o-ring between the plastic cone and outer plate. Wish I could remember the o ring size, but way back when I did not tend to make a note of such things. That particular 400/4 tap is still in use more than 20 years after changing the o-ring, and still with no external fuel leak; it does however not shut off fully, allowing a VERY slow feed of fuel into the float bowls - barely a thimble full over a 4 month lay up this past winter.
2
« on: March 15, 2026, 06:42:55 PM »
There is an advert in the VJMC Tansha magazine for supply of original Honda keys. Also a listing on eBay (item number 157299118185) for original 400/4 style plastic head keys.
3
« on: February 20, 2026, 06:55:26 PM »
I've done a few over the years, both 350/4 and 400/4 (re-built one of these last week). 350-4 and 400-4 are identical in terms of the primary chain / sprocket / starter clutch arrangement.
Whilst you can remove the primary shaft from the engine with it in situ, the primary gear, etc, is still "inside" the primary chain itself. Only way to get this out is with the lower crankcase removed - which of course means removing the engine itself.
No real problems (Haynes manual is pretty good for these), other than maybe previous owner bodges / poor maintenance, and the fact that these things are approx. 50 years old.
IF maintained properly, the 400/4 in particular is an exceptional bike. My current hack (only used in the winter these days) now has over 125,000 miles showing - and still on original pistons / rings yet does not burn oil. The cam chain and primary chains in it have now done over 95,000 miles since being replaced - and do not rattle. 350/4 is a slug in comparison and needs to be worked hard to maintain A-road speeds.
Only persistent problem has been oil weeps from the camshaft oil feed through the head gasket (every 25,000 miles or so), due to the use of crap (and expensive!) sleeve type seals around the oil jets. I am trialling a modification here to see if things can be improved.
4
« on: January 14, 2026, 07:07:07 PM »
I suspect they could be CD175 - I seem to recall there were some CD175 parts amongst the stuff you had when I collected the C72 chassis a while back?
5
« on: December 20, 2025, 05:49:02 PM »
I think I heard somewhere that these are made by Busso in Italy. Certainly cheap, but no idea of the quality.
6
« on: November 30, 2025, 06:56:56 PM »
Just spotted a genuine Honda shop manual for the CB750 K8 and F3 on eBay - might be of interest?
Ebay item number is 406419338743
7
« on: November 18, 2025, 07:11:59 PM »
400/4 breather covers were not painted (nor even clear coat / lacquered that I can tell from the ten or so examples owned over the years).
I believe the original finish was therefore "as-cast", similar to sump / carbs on the same
Chris R.
8
« on: October 02, 2025, 08:59:38 PM »
Whether or not asking prices are reasonable or otherwise is always subjective. Very often the asking price is set as a starting point for negotiations between seller and buyer.
However, as to the un-informed comment that HM300 stamped exhausts are not genuine and must be reproduction because genuine would be stamped HMCB750 HM300, REALLY!!- You would do well to do some research and get your facts straight (or try a different brand of dope!).......
The very first exhausts fitted to CB750 Hondas back in 1969 did not carry ANY stampings whatsoever.
Then factory fitted exhausts as fitted to UK and US market bikes built in 1970 and up to the end of K1 production were stamped simply with HM300. These will have a baffle fitted with a vertical bar in the outlet.
I believe that exhausts stamped HMCB750 HM300 were fitted to some European markets during 1970 – 1971, and did NOT have the vertical bar at the outlet. These European exhausts are possible the least common type encountered on bikes these days.
Hopefully others will offer further comment.
9
« on: September 11, 2025, 06:04:40 PM »
Still using my Morgan Carbtune mercury gauges, 30 or so years on. I believe Morgan still sell "vacuum" gauges just not with Mercury in them.
10
« on: May 27, 2025, 05:49:27 PM »
Curiosity got the better of me today, so I went searching out my spare rear CB750 mudguards.
Found three of them in a box. One is a plastic repro. One is a US style K6 mudguard in good solid condition, albeit with some marks / dents.
The other one is actually a UK spec (80100-300-600XW) in nice solid presentable condition. Shame someone has drilled it at the rear lower edge in a couple of places (for a mudflap possibly); also a couple of extra holes as if a different rear light bracket was fitted at some time. I guess the holes could be welded by those skilled at such things, and then re-chromed - though perhaps just cheaper to buy a US spec repro.
11
« on: May 25, 2025, 05:45:57 PM »
For exactly the same reason I have a US spec k2-K6 rear mudguard fitted to a 1970 UK CB750 - and the original black painted UK rear light bracket bolted straight on (the spacing of the four bracket mounting holes is the same). The bracket does appear to sit very slightly further up the mudguard such that the number plate is now slightly angled. The US rear mudguard also has an extra single hole at the rear for a rubber bump stop which (I think) is supposed to support the bottom edge of the US license plate (number plate). Pictures attached - the one with wet patio is the bike as bought with rotten original UK rear mudguard, the other with the US spec K6 mudguard fitted. Maybe it helps?
12
« on: May 21, 2025, 08:14:23 PM »
K1 carbs are different to the earlier CB750 (K0) type - that said, the early type K1 float bowls are the same as the earlier K0 type.
Difference between early / late K1 bowls is the drain screw - small screw head with aluminium washer on early, larger screw head with o-ring seal on later ones. The bowls are interchangeable as the carb bodies theirselves are the same an all K1 and will be marked 7A on the top of the mounting flange.
So, buy the cheaper NOS bowl or find a used one of any k series bike up to the K6.
13
« on: May 12, 2025, 07:29:47 PM »
FWIW, our 400/4's (which all have standard fuel tap arrangements) have pretty well exactly 3 litres reserve, 11 litres main (so 14 litres total).
14
« on: March 04, 2025, 07:01:57 PM »
I bought all my bikes from Coupland's back in the 70's / 80's. Curiously I spoke to Jim Morley who owned Coupland's only yesterday. Jim will be 80 this year, and sold the business just over 20 years ago now. Unfortunately the people that took the business over did not make a success of it hence its closure fairly soon afterwards.
Jim still does rebores and a few other things, working from home. He has done all my rebores (about ten now over the last 30 years), and will be doing another CB750 set in the very near future.
15
« on: December 19, 2024, 08:06:05 PM »
As I suggested, the manual does need to be read carefully as it covers both the 350/4 and 400/4.
Data specific to the 400/4 starts on page 87 in the "CB400F supplement" part of the manual.
Page 111 contains the relevant specifications. The Haynes manual is also correct in this respect as it covers only the 400/4.
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