Topic: Ideas for 400F performance modifications

[jonboycox]

  Hi, I am looking for ideas for modifying my '77 400F to run with a touch more power. I want to keep the look close to stock and I do not want a bigger bore. Also looking for ideas to improve handling from stock without changing the look too much. I have cleaned/rebuilt the bike from the ground up and it is running reliably. I have installed a Dyna electronic ignition and swapped out the coils for O.E.M. honda's with replaceable leads. It has a Mac exhaust with the stock headers. Everything else cleaned up well and is stock. Lets hear the ideas and lets keep them tasteful. I have to keep up with my little sisters 2009 GS 500 this summer. I want to keep up, likely a wheel or two behind, but be way more awesome

[RickB]

Jon,

I love that last line. 'keep up but be way more awesome'. That's my thinking with my CB400F too!

I had similar ambitions with my bike also. To keep the stock look but do some slight improvements where possible. Before too long Jesse will chime in with what he was able to wring out of his hopped up CB400F too. This thread might be useful to you also.

For some performance increases, the easiest thing to do is drop weight. Hard to do if you're keeping the stock look. So much weight is used in the battery and stock airbox area. Not to mention the rear fender and stock DID rims. If you don't want to rebore the engine, which is understandable, then would you consider boring out your carbs, porting the head, dropping in an aftermarket camshaft (webcam, cycleX etc), heavy duty valve springs.

Jesse rebuilt his suspension a hell of a lot more thorough than I, but I have had good results with just some 20mm preload spacers in my front forks. But you can get a set of progressive springs made up quite cheaply.

Well good luck with it all,
Rick.

[jonboycox]

I have a vintage aluminum D.I.D. rear rim that would fit this bike. I have had trouble sourcing a vintage aluminum front rim to match. Can anyone send me a link to an available cam upgrade? Is this a part that just sets right in?

[jessezm]

(Dutifully reporting, Rick!) 

I think the best bang for your buck if you're looking for increased power is the $110 466cc big bore kit on Ebay.  Like Rick said, if you're keeping the stock look, then you can't really do much else to lighten the bike, so engine work is the way to go. 

When I was contemplating how to unlock more potential, I contacted Rick Denoon who does the carb boring, and even though it cost him my business at the time, he steered me toward a displacement increase as the most obvious solution.  I eventually made other changes, included porting work from member Mike Reick, and I did get the carbs bored out as well and changed out the headers (a painful decision).  Added to that a cam with higher lift and longer duration, and I ended up with a bike that had more torque on the low end and that breathed much easier when getting high up into the revs. 

I could see a scenario where you kept the bore the same but had your head worked over and carbs bored out and installed a freer flowing exhaust and a hotter cam, as those changes would probably lead to a faster bike high up in the revs.  But the expense associated with all that gets out of hand pretty quick (trust me, I know!)

Tell me, why are you opposed increasing the displacement? 

[kyre]

I just bought one of those eBay bigbore kits. Slowly will be doing what you did jessezm. Might be picking your brain in the future.

Jonboycox I'd check those kits out, very good price. You'll definitely be spending some cash to make er go. Check out http://www.ttr400.com/ and http://www.denoonsp.com/ . Great inspiration, parts and service!

[Psychonaut]

More power with the same displacement means you are going to have to increase the peak rpm power, cam shorter stack, larger ports. I ride with a friend that has a Busa. He only rides casual 100% but even casual means faster than most cars accelerate. I keep up fine but I have to use the revs. Shift high and you will hang a GS fine. Put modern tires, BT45 or Avon and you will hang fine in the turns. If you want more torque, bore it but that's the only way you will get real lower rpm power.

[Bodi]

Without a piston kit you're limited to porting, a cam change, and bored carbs.
These will all help high RPM power but really do nothing for low/mid power. The bored carbs, I'm told, definitely make a big difference in top end horsepower as the stick oval throat carbs are limiting intake flow at high RPM and full throttle. I haven't sprung for this (yet?) since tuning the carbs for a 466 kit, pipes, cam, and pods is remembered as a long tedious chore and I don't relish doing it all again.
The 466 kit does a lot - the 16% displacement increase makes a very noticeable low and mid power boost. This is one hop-up I'd definitely recommend, why is it not on your list?

[hondamatteo]

not sure if you have heard this saying or not but "there is no replacement for displacement" and in the small 4's thats basically what your lacking. The 466cc will probably be the best bang for your buck.

[singedebile]

+1 on port and polish, carb bore, cam..  though I would also really consider a big bore kit as well (if you really want the power increase), then you can get it all done at once.

[Doctorlumen]

Hey Jon,
If what you want is power specifically, then I'll cast my vote in the 466 camp. But I'm here to tell you that the 400f has plenty of go without the porting, boring and all. My little bike is alot like yours...Dyna S, 3-ohm coils, 17/30 sprockets. I also have bored carbs, am running pod filters, and stock headers with a marving "classic" pipe. That little brat throws 31hp to the road with 26ft/lb of torque. I have spent some time doing plug chops on and off the dyno to reach those numbers, and considering the 25hp she had when I got her, I'm pretty happy with my stock motor. Drill out the rotor, find a lighter battery (careful with the MOTY), loose the air box, swap the shocks and springs for something sprung for your weight, and pick up some aforementioned modern tires. Then keep those RPMs above 7k and see how well a 35 year old bike will do against the modern 500s.

[jamesv220820]

look at

http://www.ttr400.com/

they have alot of fun stuff but it does cost money

-James

[jonboycox]

Thanks for all the great information! It seems getting better airflow through the motor is all I can do until I want to spring for the big bore kit. I am worried about everyday starting and running if I remove the stock air system and mess with the carb. Lots of posts on here talk about causing all kinds of problems doing that. I wonder if my first step is to change the sprockets to better use the high revs and all those six gears. If anyone can send links to different spocket/chain sets that would be great.

[cgswss]

Most of the mods you will make will move the power up the rev ban.  Frankly, unless your racing, you really don't want to do that.  On the street you want more TORQUE   That means more displacement and higher compression.  Remember you have a very old single cam bike.  Your are not going to run with modern bikes.

If I were you, I would go up about 3 teeth on the rear sprocket.  You will loose about 10mph of top speed, but you will get a lot better pull at lower speeds.

If you must do SOMETHING to the engine, get a set of heavy springs and have a 3 angle valve job done.  You simply won't win any roll on drags, you need to use your revs and row thru that trans.  Of course the next move would be a big bore kit (which will also raise your compression normally)

I just would not waste a lot of money making a bike faster but less fun to drive (torque is fun!  high revving HP generates tickets)

If you were to go the whole way to get the most HP, you would spend enough to buy an older crotch rocket And there is about nothing you can do to that 400 to keep up with a box stock 600 crotch rocket.

[camelman]

Well, I agree with pretty much everything said above.  The best bang for your buck is the 466 kit.  It will increase displacement by roughly 16% and increase the compression ratio about a point (IIRC).  The next thing to do, which is actually the biggest choke point on your engine, is to increase the air flow through the carbs.  Have Rick Denoon bore them out, and you'll be shocked at the power increase.  Plus, you won't have to mess with your jets much if you stick with the stock airbox.  I went with a 466 kit and bored carbs with the stock airbox and ended up leaving the same jets in, or possibly one size up on the mains.  That stock intake will be fine for whatever you do too, unless you decide to go with velocity stacks, but it'll be a pain to tune.

After you make those two changes, you should consider your exhaust and a port job next since they will then be your limiting factors.  Another tip is to take one coil off the advance springs and change the stock "fire" setting, but I'll defer to Hondaman about that since he's the one who discovered it.

If I were you, then I'd consider putting money into the suspension after you bore the cylinders and carbs.  By the way, bored cylinders and carbs will effen shock you with the increase in power.  It is VERY noticeable.  So, suspension, get some decent rear shocks (hagons are totally fine, but get them for your weight and get the 13.1" bodies), send your swingarm to Hondaman for a rebuild, but put in tapered steering head bearings FIRST!!!!  Replace your fork oil too with 10 weight fork oil that you can get at any motorcycle store.
After all that, your next step should be a billet lower triple tree since the stock one is a flexy pile of poop, and upgrade your front suspension.  TTR400 makes a very nice aftermarket lower triple tree setup, and he is a super cool guy, so you'll be happy sending your business his way.  FYI, I just bought two triple trees, various adjusters and a pile of other goodies off him.
Front suspension can be improved with new springs, pre-load adjusters and emulators, although I have ZERO experience with emulators so I'm just going on what others say.

So, there you have it.  Power and suspension, but please keep it stock looking!  I just love seeing those old stock 400s tearing along in the twisties.  By the way, I've put my 350f through its paces, and I can tell you that keeping up with a GS500 should not be a problem on your 400.  In fact, I'd be willing to bet you'll dust your sister since those 500s aren't exactly handling majis!

Good luck and report back with progress please!

Camelman

[jonboycox]

This is turning into an awesome thread.... If only I could afford all this stuff! I rebuilt this bike from the ground up, using mostly the original parts, all without having a clue what it would be like to ride. I finally got insurance a few days ago and have been blasting about all over. What an amazing little machine! My first ride with my sisters GS500 should be next weekend, also with an Aprillia 750 and a '71 triumph bonneville chopper. We will see how things go, I find I can maintain 100+ kph(62+ mph) with no problem and lots of rev left in 4th and 5th gear. The handling feels good...I think at the bare minimum roller bearings are in order. To move to a 33 tooth at the rear, should I put on a new front sprocket and chain at the same time, or can I run with old front sprocket and chain and new rear sprocket with no issues?