Honda GB400 now GB650

[ICE180]

I finally found a NX650 engine for my 400GB I was told that they bolt in
well it bolts straight into the frame which was great even the top mounts are the same
The only difference was the stator had some extra wires coming out of it......

I did cheat and get the shop to do it as I would have possible stuffed it up and had to get them to sort out my stuff ups
so I though best to get it done right the first time

I am putting a braided brake line on the front and some decent brake pads as I might need more stopping power now

[BAD DAD]

Can't wait to see some pics ? Sounds interesting

[cave weta]

Ooooh - PM me your address- I want to see the beast- Ive owned so many bikes that Ive lost count -but My GB is the most fun road bike Ive ever had!

[Road kill]

So how does it go ?

[ICE180]

It goes really well now still some fine tuning as it is back firing when you come off the throttle will put a bigger pilot jet in the carb
it has the 650 carb on it .
The gear shaft is about 40mm shorter so we are putting the GB400 gear shaft in the engine so I can change gears while have my foot on the foot peg

the really bad part is it looks no different as the engine is the same as the 400 just a bigger bore etc

I did take it for a spin today but I think the gearing might be a it high so I will probably put a smaller front sprocket on it as I was in 2nd doing almost
95km/h and it still was trying to pull past 7000rpm.

I have the 400 CDI on it as the 650Cdi did not work .

will take some pics soon I will also do a dyno run as I have what the old 400 was putting out on a dyno to compare

[ICE180]

some pixs as you can see I need to sort out the gear shifter

but it fits in really nice

[ICE180]

Well we ground of the welded gear leaver last night and decided to try and keep the change pattern the same 1 down and 4 up

so I pick up a Gear leaver with a complete linkage system on it from the wreckers to see if we can do this
might have to make some extra bits to attach but will keep you posted
otherwise I will have a race pattern 1 up and 4 down........

[ICE180]

almost done put a larger Pilot jet in 50 still too small so I drilled out the 48 to 56 as the next size up was 55

Just a matter of putting it in and testing tuning etc

The clutch was slipping so used the old fibers from the GB 400 and put new steels and springs in the NX650
fibers same part for both engines so that was handy as i have a couple spares now

[ICE180]

Damn the CV carbs being so temperamental The pilot jet is good but still back fires on close of throttle
pulled of the air cut of valve and had a look at it seemed OK
will look for air leaks now as I want to get it sorted so I don't feel as though I am running the engine too lean and hurting it

spent more time in the shed found that the standard GB 400 carb jets were 45 pilot and a 165 main
so I think that I will up the main jet on the carb and the pilot as well as I have added an extra 250cc to feed fuel into I might be too lean over all

the 165 main jet on the GB400 seems rather large but it must be for a reason
I had a 2 spare carbs from GB400 that i pulled apart to check jets sizes

will try a 60 /160

[ICE180]

The Carb is all sorted for now minimal back firing occasionally runs a lot better sits on 100k a@3700rpm
put in a 160 main jet left the pilot at 56 and did these mods as it was the same Carb


Daves carb Mods -XR650L
http://www.4strokes.com/tech/honda/xr650lcarbmods/

Will get it onto a dyno soon to check Air Fuel mixture and power of course

[ICE180]

Just an Update on the CV carb


the back firing has almost gone but I think I might need to look at the needle now to get it perfect so some more tweeking to be done

I lifted the needle up some more the other day and the Back firing got worse and you could see the black fumes comming out out the exhaust so I think It was too rich
put the needle back to what it was and the black smoke out the exhaust has stopped

the black fumes happened when you blipped the throttle.

[gloplg]

Just an Update on the CV carb


the back firing has almost gone but I think I might need to look at the needle now to get it perfect so some more tweeking to be done

I lifted the needle up some more the other day and the Back firing got worse and you could see the black fumes comming out out the exhaust so I think It was too rich
put the needle back to what it was and the black smoke out the exhaust has stopped

the black fumes happened when you blipped the throttle.

Hi Ice. Just found this thread. Does the nx650 have a hemispherical combustion chamber as the gb does??? I am an interested GB400 owner and have sometimes wondered about re-engining my bike.

[ICE180]

the Carbs are the same apart from the NX carb has the semi-foced CV type with a link arm to force open the carb piston the first mms

I have 2 GB400 and this is the only difference between them ops also the Main jet holder has 3 holes round the top on the NX carb

I was still getting popping on De-acceleration after hard acceleration but under normal use and mild acceleration no popping/backfiring
put in a larger pilot jet 58 but still was happening not as much but I had black smoke coming out the exhaust unburnt fuel so I have put a 52 pilot
in no black smoke but more popping after WOT
Look at header pipes found some black soot on them so I will replace the Copper exhaust gaskets hopefully this is where the extra air has been getting in and causing the backfiring

[ICE180]

put in the new copper gaskets on the 52 pilot jet was too small put a 55 in it still a little to small
back to the 58 and I put a larger Main jet in 165 pulls much better at WOT fells more like it should might go 170 yet

The reason for all the jets etc is because I am running a cycle works exhaust headers and pipe its a straight through system

got taking the carb of and changing the jets down to 45 -60min now depending if any of the rubber connectors refuse to go round the carb

[ICE180]

well I got it on a dyno at last



went to a 50 pilot jet and a 165 main

the biggest improvements were made when we drilled so holes in the side of the air box to let the sonic wave out the air coming back into the air box was more than the 400 so it was not a happy slider in the carb sounds odd but it just worked
was running lean in the mid range so we sanded the needle down a bit to richen it up
also routed out the intake manifold to as large as we could get it .need to do the engine intake side next time i have it apart

do some other small tweaks and got 36.15hp at the rear wheel so I am happy as factory 25 years ago it was 40hp at the crank
It also has 40ft Pounds of Torque so very easy to leave in 2nd gear round town
so I am happy might have to get a hot cam next