Japanese domestic market VFR 750 F 1986

I understand this model, produced specifically for the Japanese domestic market was rated at 77hp or similar?
The same year model for export was rated at 104 -105hp depending on whom you listen to

So what are the differences in these two engines - they were both called RC**E with one having 07 and the other 24 where the ** is shown in my description?
My understanding is the bore and stroke are the same - so is it cams and carburation that brings about this huge difference in power?
What about the valve sizes - were they "all" small at that time?
Anyone with knowlwedge on the subject, not just speculation, is greatly appreciated
I currently own one of each and wonder what it would take to bring that extra hp to life?
Could at least a part of the story be a very "under-rated" output was specified for the domestic market for political reasons? And thus, the difference may be somewhat less in reality?

 

I believe the Japanese market was very tightly constrained in the past with tough licencing and machinery restrictions. It was a real challenge to get a licence beyond 250cc, and 400cc was the next threshhold. After that, I believe there was a 750cc domestic maximum, with 77 ps as a maximum output, and 180km/hr as a limited top-speed. I don't know for sure how the bikes were restricted but would expect something like carb slide restrictions, those were certainly employed on other restricted Japanese bikes (where the carb top has a stop to prevent the slide lifting beyond a certain point). The bikes also had to be fitted with a 90 km/hr warning light on the dash, a sure sign that you have a genuine JDM product.

 

I purchased my Japanese import as a non runner with a seized bore due to water being used instead of coolant, a story for another time except that it is now in lots of small pieces awaiting a sleeve in one bore to keep it all standard.
That said, the bike has a red lamp with SPEED written on it adjacent to the ignition switch which the previous owner told me was to do with speed limiting though he did indicated a top speed of 180km's /hr. He said there was a trick to circumventing this but it was irrelevent to me since the bike did not even run and I took little interest in what he said at the time believing 180 was plenty fast enough for me. He did not know / or say anything about reduced power output.
There is no doubt of the bikes origins in any event as it was imported from Japan in 2001 and had undergone Queensland Government recognition at that time with the prescribed plate of authenticity riveted to the frame. Due to the very low km's (29,000) I believe it worthy of restoration BUT would like to compliment the work with an upgrade in power to that of it's international siblings - if I can reliably establish just what is required

 

I had a 1997 VTR1000F that was a JDM, and that also had the 180 km/hr limited speed. Disabling the limiter was as easy as removing a single wire from the back of the speedo. I believe the limiting signal was transmitted from the speedo housing to the ECU. The wire was pink/green.

 

Thanks for that Terry, I will check mine out, a lot of years between the two bikes but I have heard similar stories
Now I just need someone to tell me how to unleash those extra 30 hp
I am really surprised with all the JDM product floating around the world that no one has the answers

 

I don't know specifically about the 'F' model, but the VFR750 (R) was restricted to 77hp for the Japanese market too. To derestrict a Japanese spec. 'R' model, you'd need to replace the CDI (black-box), swap the exhaust end-can & the intake (air-box), and increase the size of the carb jets.

 

Has anyone out there actually done the modifications to a Japanese Domestic Market VFR750F?
It seems amazing to me that with the number of these early JDM models now circulating around the world, that there is no definative answer
This is just the sort of information I join forums to find. I restored a '69 H1 Kawasaki and frankly without the pool of knowledge available on the Kawasaki Triples Forum, I could not have done it. They were/ are a great help.
This is not a critisism of the VFR World Forum but as claimed the "largest forum on Honda VFR's" I am gob smacked that nobody can give me a clear and definative answer with specific dot points to restore those 30 missing ponies.

I thank WeeVee and Terry for their contributions but one thing this forum lacks is a "Knowledge Data Base" where any interested party can research and find reliable facts on every aspect of our bikes. Tips and tricks for restoring any aspect and where to look when things go wrong.
I went so far as to ask help for spare parts from CSMI in the Netherlands only to be turned down flat "because it was DJM" and they have no information!
And I am told the ABS fairing components are rare and very hard to find any "good bits" so am now repairing what I have using a brilliant technique I found on YouTube.
The system uses MEK solvent - no hot welds, and small patches can be "chemically welded" with impressive results. One must have plenty of G-clamps to hold things together for 2-3 hours till the bond becomes permanent but otherwise it is quite straight forward. Even bolt holes can be filled using a "slurry" made by disolving swarf produced by drilling into scrap ABS and then disolved in a small amount of MEK, which later with evaporate and leave a solid fill that hardens up over 3 -4 days to match the surounding product. ABS sheet can be procured from various suppliers and those who use it in their manufacturing processes will sell you off cuts!
A health warning though - always use MEK in a well ventilated area, preferably outdoors!!!

 

Nothing definitive, but some more info that might help. I would bet it is a physical restriction for the power, like reduced inlet sizes and smaller jets to go with it.

https://www.vfrdiscussion.com/index.php?/forums/topic/79321-vfr-engine-restriction-how-made/

 

I'm hearing you Captain, and agree with your sentiments. Someone already told me privately that a Honda JDM bike they once had, was fitted with limit stops inside the carburettors.
Since I own a Dec '86 build JDM plus a Dec '88 export (sold new in Australia and fitted with AU compliance plate) and neither had been ridden since 2009 I decided the '88 was the best to build first (it does run while the '86 was seized due to water in one pot)
Thus, there has been no urgency to solve this issue right now, just collecting information for the future, and so far I have not pulled the carbies down.
Exhaust system is standard, with same diameter pipes and factory mufflers as the later bike, only the later one is not SS and is routed differently due to the larger valves and different port angles.
I also was told by another that the CDI would be different and weevee's comments would seem to reinforce this thinking.