Topic: CB400f engine performance, what HP can you get ?

[jacksonc]

Hello there, very excited new owner of a '75 cb400f in blue. Haven't got it on the road yet but I was wondering what sort of numbers or performance people have gotten from this bike. I have found the cams and big bore kits etc for it. I plan on slapping a Dyna S on it before I even ride it, probably won't bore it.  37 HP from 24ci seems pretty decent stock, I'm just curious if its hard to get big gains from this cool little motor or if it really wakes up. If anybody has run theirs on a dyno I'd love to see the numbers. I put my '92 750 Nighthawk on a dyno and got 62 HP it was fun

[Industrial Rat400f Killer]

This site is just scratching the surface.
http://www.ttr400.com/

I have a 400 engine that I'm building right now that should be a lot more power with higher revs when it's done but I'm not sure how much to expect. You have to spend more money to get a lot of power out of the 400's than you do other bikes. I like the small high revving engine the most though so it's worth it to me to build one.

[jacksonc]

Yes I am looking forward to keeping it tached up with the 6 speed, and having a small bike with good performance. I had a K4 750 that I was working on but it was in pretty sorry shape and I ended up selling it, and having two 750's seemed redundant at the time. The 400F is more about handling and sportiness which I like. I just have seen lots of reports about what to expect from 836 750s and such so I was wondering if there was some for this one. Thanks, Jackson

[Industrial Rat400f Killer]

If you have yahoo email account there is a cb400f yahoo group. It bet you could find somebody there with a dino graph after building and engine.

[MaaseyRacer]

I too am curious about this. I am not expecting crazy insane numbers, but I have a webb cam, RD valve springs, a set of CR26s, and I am about to buy some 54.5mm pistons. I am curious to see how much power this thing makes. However, from what I have read I am going to need to buy a set of rods as the stock ones will not do so well with the higher revs.

[rudi]

Stock engine , totally new Build Up ,Pistons 1 o/s , Bearing Shells, mild Porting , STD Exh.,
Yoshimura St 1 Camshaft, Piranha Ignition , Rubberhose removed from Airbox Intake, Keyster Carb Overhaul kit installed
and so on...
 My Dyno Results : 43 HP on the Rear Wheel measured on a Dynojet Rolling Road Tester

[jacksonc]

rudi, 43 HP sounds pretty good for the work you got in it, bet it gets moving down the road good

MaaseyRacer, that motor sounds like its going to be hot ! I have read that you have to modify the tank to fit the CR26 carbs, but nobody said how, I'm guessing its with a rubber mallet.

Rat400F, I was on the yahoo cb750 group in the past but their setup is pretty old feels like when I first got on ye olde internets circa 1996, and it often times out without loading pages for me.

[jessezm]

On tank modification with the CR's, I think it's the petcock that they interfere with.  Don't know, though, 'cause I don't run them.

My 400F has the 54.4mm pistons ($145 shipped from Japan--though they are made in Taiwan--from Ebay member cruzinimage), and a Webcam, dyna coils and ignition, and A LOT of weight shaved off.  I can't tell you the HP yet, and I'm still breaking her in, so I haven't seen the upper rpms yet either.  I have a feeling, though, that it's a big improvement from stock...

Unfortunately, I've got the leaky head gasket problem common to these models, so I'll be breaking her back down shortly for a quick top-end and then will run her in proper and report back...

[MaaseyRacer]

Unfortunately, I've got the leaky head gasket problem common to these models, so I'll be breaking her back down shortly for a quick top-end and then will run her in proper and report back...

Check the head to see if it is warped, I have notice that several of the SOHC4s I have worked on have warped heads.
Also did you rejet? If so what jets? Did you have your carbs bored? I am very curious to see the power your motor makes, as I am months away from my bike running.

[iomtt9]

If you look on page 4 of High Performance and Racing..... My 400 Racer by Specweld he's one of my mates we all took our bikes to the Dyno and he got 56 bhp at the rear wheel, theres a little info on his bike. If you E Mail him he will answer any questions for you to get more power from your 400/4, he may even tell you about his camshaft that he's been running for years and we have just found out that one of the cam lobes was reprofiled back to front !!!!!!
He's had the bike a lot of years and i can tell you that it flys !!! Also if you are building a serious racer, race rods are a must, check out his pics.

[jessezm]

Unfortunately, I've got the leaky head gasket problem common to these models, so I'll be breaking her back down shortly for a quick top-end and then will run her in proper and report back...

Check the head to see if it is warped, I have notice that several of the SOHC4s I have worked on have warped heads.
Also did you rejet? If so what jets? Did you have your carbs bored? I am very curious to see the power your motor makes, as I am months away from my bike running.

I am going to check the heads.  I had them milled flat by the machine shop, though, and the mating surface on the cylinder side was very carefully dressed as well, but not milled. 

As for jetting, my starting point is:
mains: 90
pilots: 38
needle: stock needles, one position richer from center
Air screws: 1 3/4 turns
K&N Pod filters

I find it makes good power everywhere, but is running a bit rich and once warm I have to rev to about 3000rpm to get a good take-off from stoplights without bogging a bit.  I think I am going to drop the needle back down to stock, or maybe even one position lean, and then start doing my plug chops, but I am really impressed so far.  As for the carbs, I have not had them bored yet, but eventually I may do some more work to the heads (high performance springs and retainers, port and flow) and at that point I may send the carbs off to Rick Denoon as well.  I spoke to him about it, and we agreed that without free-er flowing heads and more open headers (I'm using the stockers because the look so sweet), I wouldn't really realize the full benefit of having them bored.

[MaaseyRacer]

As for jetting, my starting point is:
mains: 90
pilots: 38
needle: stock needles, one position richer from center
Air screws: 1 3/4 turns
K&N Pod filters

I find it makes good power everywhere, but is running a bit rich and once warm I have to rev to about 3000rpm to get a good take-off from stoplights without bogging a bit.  I think I am going to drop the needle back down to stock, or maybe even one position lean, and then start doing my plug chops, but I am really impressed so far.  As for the carbs, I have not had them bored yet, but eventually I may do some more work to the heads (high performance springs and retainers, port and flow) and at that point I may send the carbs off to Rick Denoon as well.  I spoke to him about it, and we agreed that without free-er flowing heads and more open headers (I'm using the stockers because the look so sweet), I wouldn't really realize the full benefit of having them bored.

I may end up going the bored carb route in the end. I have read about all the issues getting the CR26s to run on these bikes. I have an MC again and a Kerker.  I will probably end up running the MC Again.  I also am not sure what if any head work I am going to do. Also I think my webb grind #3 cam might be a bit much for the street, but will probably allow the CRs to work in my favor.

[jessezm]

As for jetting, my starting point is:
mains: 90
pilots: 38
needle: stock needles, one position richer from center
Air screws: 1 3/4 turns
K&N Pod filters

I find it makes good power everywhere, but is running a bit rich and once warm I have to rev to about 3000rpm to get a good take-off from stoplights without bogging a bit.  I think I am going to drop the needle back down to stock, or maybe even one position lean, and then start doing my plug chops, but I am really impressed so far.  As for the carbs, I have not had them bored yet, but eventually I may do some more work to the heads (high performance springs and retainers, port and flow) and at that point I may send the carbs off to Rick Denoon as well.  I spoke to him about it, and we agreed that without free-er flowing heads and more open headers (I'm using the stockers because the look so sweet), I wouldn't really realize the full benefit of having them bored.

I may end up going the bored carb route in the end. I have read about all the issues getting the CR26s to run on these bikes. I have an MC again and a Kerker.  I will probably end up running the MC Again.  I also am not sure what if any head work I am going to do. Also I think my webb grind #3 cam might be a bit much for the street, but will probably allow the CRs to work in my favor.

Yeah from what I've heard, the stock carbs are a better match for street use than the CR's.  The reason I went with the webcam #2 grind was so I could keep the stock springs and retainers (and also cause I'm not racing, just riding around town/backroads).  I would love to get a more free-flowing exhaust, but I can't fathom changing the pipes!  Rick was even telling me that people used to cut the stock pipes and remove the inserts and weld them back together, but that sounds pretty perilous to me... 

[jacksonc]

You guys have got me wondering now if anybody ever tried carbs from another small four bike like the CB1, FZR400 or Bandit 400 ? they are probably CV for better throttle response.

[rudi]

Hy jacksonc,
try KAWASAKI ZXR 400 Carbs !!
You can use them 1:1 , the Carb Assy match the Intake Ports / Rubbers from your Honda CB 400 F exactly
400 Bandit , CB 1 Carbs are to widh and you could not seperate this Carbs and make them smaller
You need bigger Intake Rubbers (availabel from Mikuni) and 4 individuall K.a.N Filters.
Than the Rolling Road or Try and error Work starts for the Set Up...
I am just on this way....

[jessezm]

Hy jacksonc,
try KAWASAKI ZXR 400 Carbs !!
You can use them 1:1 , the Carb Assy match the Intake Ports / Rubbers from your Honda CB 400 F exactly
400 Bandit , CB 1 Carbs are to widh and you could not seperate this Carbs and make them smaller
You need bigger Intake Rubbers (availabel from Mikuni) and 4 individuall K.a.N Filters.
Than the Rolling Road or Try and error Work starts for the Set Up...
I am just on this way....

Wow, no kidding?  What changes do you have to make to the throttle assembly?  Very interested in your results!

[jacksonc]

Yeah that sounds great, the kawi wasn't sold here in the USA so I'd just have to get some shipped from overseas thats not too hard though. I'm assuming Mukuni carb boots a universal part ? If this is the setup you are running was it hard to get it tuned or fairly straightforward ?

[rudi]

ZXR Carbs on CB 400 f :
Intake Manifolds Original Mikuni # I-VM30-200-1 Clamps has to be modified , Mounting Holes has to be slotted
Set Up : Generally . These Carbs are too rich !!
Try to find the way...In contact with the Mikuni Importer to find the proper Needel/Needel Jet/ Main jet  Combination

This Carb is mounted on a Heavy converted CB 400/450 Engine !!
Yoshi 455 Kit , Piston Skirts low friktion coated
HRC Camshaft (very rare !!)
Alloy Valve spring Caps
Intake Vaves + 1,5 mm Oversize
Exhaust Valves mod. Stock
All Valve inserts in Cyl. Head  opened (miled out)
Kawasaki GPZ 1100 Oil Cooler
Kawasaki Z 550 Elektronic Ign. (modified9

First Expiriance : When passing the 7500 rpm Mark,nothing stops you !!! In a quick Moment you are overrevving ....

[MaaseyRacer]

ZXR Carbs on CB 400 f :
Intake Manifolds Original Mikuni # I-VM30-200-1 Clamps has to be modified , Mounting Holes has to be slotted
Set Up : Generally . These Carbs are too rich !!
Try to find the way...In contact with the Mikuni Importer to find the proper Needel/Needel Jet/ Main jet  Combination

This Carb is mounted on a Heavy converted CB 400/450 Engine !!
Yoshi 455 Kit , Piston Skirts low friktion coated
HRC Camshaft (very rare !!)
Alloy Valve spring Caps
Intake Vaves + 1,5 mm Oversize
Exhaust Valves mod. Stock
All Valve inserts in Cyl. Head  opened (miled out)
Kawasaki GPZ 1100 Oil Cooler
Kawasaki Z 550 Elektronic Ign. (modified9

First Expiriance : When passing the 7500 rpm Mark,nothing stops you !!! In a quick Moment you are overrevving ....

I take it that is not for street use. There are a few of these carbs on Ebay that are reasonably priced, but they do have to come from the UK.

Do you have any dyno numbers on that thing?

[jacksonc]

Set Up : Generally . These Carbs are too rich !!
Try to find the way...In contact with the Mikuni Importer to find the proper Needel/Needel Jet/ Main jet  Combination

Have you tried getting some smaller jets from the Kawasaki dealer ? In the USA they probably wouldn't have any since that bike was never sold here but I'd guess they would over there.

[rudi]

Sorry no Dyno Results, only Testriding up and down the street....
Main Jets are not a Problem : Small round Head Keihin Main Jets are installed. Availabel in various sizes from the Keihin Importer. The Problem is also the Needle and Needel jet which are not proucing the proper amount of Fuel/Air Mixture on the way to full Throttel.

[lordmoonpie]

Hello there, very excited new owner of a '75 cb400f in blue. Haven't got it on the road yet but I was wondering what sort of numbers or performance people have gotten from this bike. I have found the cams and big bore kits etc for it. I plan on slapping a Dyna S on it before I even ride it, probably won't bore it.  37 HP from 24ci seems pretty decent stock, I'm just curious if its hard to get big gains from this cool little motor or if it really wakes up. If anybody has run theirs on a dyno I'd love to see the numbers. I put my '92 750 Nighthawk on a dyno and got 62 HP it was fun

You want a challenge? I'm just tuning my 250-4 engine, who do you think will get more power? 

[jacksonc]

You want a challenge? I'm just tuning my 250-4 engine, who do you think will get more power? 

I'm not familar with a 250 four street honda so I assume its a race/GP style bike, I know they even made a 250 six. I'm sure if its full on race engine you'd win in the power department  I'm not going to go all crazy on my motor as I said I just wanted to know more about the possibilities. Because I did a lot of searching on the forums and google and didn't see a lot of built up 400s to compare too. Where as its pretty well known what all you can expect from bikes like sohc 750s, gs1000s, etc. A couple of magazine reviews from when the 400 was new says it sort of flattens out after 8500 I was thinking the +1 camshafts available would probably liven up the top end and they don't require other heavy engine work.

[turboguzzi]

simon, is it a CBR250?

[lordmoonpie]

You want a challenge? I'm just tuning my 250-4 engine, who do you think will get more power? 

I'm not familar with a 250 four street honda so I assume its a race/GP style bike, I know they even made a 250 six. I'm sure if its full on race engine you'd win in the power department  I'm not going to go all crazy on my motor as I said I just wanted to know more about the possibilities. Because I did a lot of searching on the forums and google and didn't see a lot of built up 400s to compare too. Where as its pretty well known what all you can expect from bikes like sohc 750s, gs1000s, etc. A couple of magazine reviews from when the 400 was new says it sort of flattens out after 8500 I was thinking the +1 camshafts available would probably liven up the top end and they don't require other heavy engine work.

No - not a race/GP bike well not yet
It's a CBR250-4 engine. As a tock engine it's pretty well optimised anyway but I'm going to try and squeeze a few more HP out of it. I reckon it'll be fairly comparable power wise to a 400-4 by the end of things. Sounds like you're doing the right things though Jacksonc - the head is ahere it's all at so focus on cams, porting, flow and that sort of stuff...

Hey TG - yes it's a CBR250, do you have any experience of these engines?