Topic: Another project CB400F

[Psychonaut]

How I happened to get the bike. I had been looking for a 88-90 GSXR for the last year to restore and found this CB400 about a 4 hour drive away. I had a 76' 400 in the late 80's and it's what got me hooked on light bikes. The bike started and ran but only with 1/4 throttle and only to about 5k.  I paid a little more than it was worth but that happens sometimes. I planed to just get it running and ride it. I got it running, put about 20 miles on it. July came and I tore it apart as it is hot as F in Az right now. I may as well make it how I want it now.

It looks way better in the pic than in person.

[Psychonaut]

It really only needed tires and 2 needle valves but I was bored and the little things like faded controls started to bother me.

[Psychonaut]

I hated the big turn signal so I cut the stock bracket up while I waited for the smaller ones to come in.

[Psychonaut]

I don't like how narrow the 400's rims are, 1.60/1.85. Even a 90/90 is too wide for the 1.60 rim according to Avon and Bridgestone so I am going to run a 2.15 rear and 1.85 front so I can fully use the entire tire. I'm using a GS550 rear wheel and putting the 400 rear rim up front. I know the angles on the holes aren't aligned perfectly for this but it should be ok.

I bought the zinc plated Ebay Taiwan spokes from vintage_001. Well worth the money.

I directionally sanded the hub with 320 and cleared it.

[Psychonaut]

The previous owner "rebuilt" the carbs. He had or someone had set the floats at 23mm, easy fix. Two of the float needles were intermittently leaking so I pulled them back apart and changed all of them.

[Psychonaut]

I've had this Super trapp for years. My dad bought it in 88 or 89  for a car and it's been on my shelf forever. Kind of sentimental. It's a little heavier than a stock pipe as it's stainless but it sounds great and is paid for.

[Psychonaut]

I'm going to modify the throttle to twist a little faster next.

[leogriss]

It's always nice to see a CB400F! keep it up, Psychonaut!!

[RickB]

Psychonaut,

On the 23mm float height, a member here, Timbo, had great results from setting his float height to 23mm whilst chasing down some carb issues. Here's his post on the Yahoo CB400F group. Take what you want from it, but I just thought I'd re-post it here in case your previous owner was trying to solve an existing problem.

Best of luck,
Rick.

Hi all, just thought I would post a message to another mystery being solved.

Its been a long journey getting my carbs running right, and I have finally solved the mystery to why #2 and #3 plugs have always been richer than the #1 and #4.

It all started when I was discussing the richness problem with my buddy and he kept on stating I should increase the float height 1-2mm (less fuel in the bowl, leaner mixture etc). Having read the forums and manuals (Honda, Haynes and Clymer), all state the float height is to be 21mm. However, the Jetting Instructions from Factory Pro does state that low end adjustment is done by changing the float height, so I decided to give this a go.

Right, float height makes a big difference. I adjusted the float height to 22mm, and immediately felt an improvement. More power :-), but still richness in #2 and #3 plugs :-( Knowing I was on the right path, I still needed to explain why factory settings are 21mm. I figure that floats that are 36 years old, must loose some of their floatyness? Comments?

Anyway, if this was the case, how badly do they go out of whack? Remembering some section in the Cylmer manual (p108, 109), I made up some adapters to test the float heights externally.



Now I have been very precise each time in adjusting float heights in the normal manner. Height is checked several times before putting the bowls on, so I am 100% positive that they are correct.

So while the carbs were still on the bike and having adjusting the bike so it was perfectly level, I dropped the fuel from the bowls, screwed in the external checking adapters and filled the bowls back up.



:-), look #1 and #4 are the same height, but #2 and #3 are out!!! I started the bike and while reving the engine, #1, #2 and #4 stayed constant, but #3 went up and down like a yo-yo!!! Ok, I now have 2 issues!!! The yo-yo effect on #3 was solved by replacing the float valve.

Removing the carbs, I was able to make final adjustments on the bench. Final readings were as follows
#1 - 22mm
#2 - 23mm
#3 - 23mm
#4 - 22mm

Here is a picture taken during that process



I am keen to get hold of a brand new float to compare. Maybe DSS has them? Comments?

So how did the engine run afterwards.

Initial ride, I set the air screw to 2 turns. Big improvement in power, but still felt a bit rich low end.

Second ride, I set the air screw to 2 1/2 turns. If dropping a wheelie up the street is any indication........

So fellow members, I am currently researching where to purchase Brass Barbed fittings off the shelf, as making these adjusters were a PITA. I found something that looks like it will work on eBay, and will post more details on findings as they come to hand.

Cheers

[Psychonaut]

Thanks for that. It's strange how well his runs at 23 mm though unless his pin height is not stock. Mine was really bad at 23mm. I wish I still had my wide band to know if I need to change mine. I'm not one for plug chops. Widebands only for me, it's the only accurate way to know the AFR. I might have to get another one.

[Psychonaut]

I chopped a stock seat down about an inch and recovered it.

[Bankerdanny]

Almost 2 years between posts. I can't help but feel like there is information missing.

[Psychonaut]

Almost 2 years between posts. I can't help but feel like there is information missing.

LMAO. Ya, I left a little out. I wish I took more pics up to this point. I am always messing with it when I have time and always intend to post but don't. I'll post some of the things I did and try to keep updating from where it is now.

[Psychonaut]

This is when I did my quick throttle. It is tight but does not rub. It is slightly under 1/4 turn.
 I drilled holes through from the outside, about 6 holes, 1/8" wide and used epoxy (stiff stuff in the tube) to pin them together and  keep the outer pieces from rotating. I don't have a pic of the drill and epoxied part. I also changed the throttle return spring for something about half as stiff. Feels like a modern bike throttle now.





This used up all the slack in my cable and caused the threaded part to rub. I trimmed them down a little.




I used pvc for these. I don't remember the size 3/4" maybe.



5/30, I have it a part again. This is how I attached the sleeve on the throttle with epoxy.

[Psychonaut]

I have a few more pics.

I wanted to blend the throat of the carbs a little better. My previous top speed was 94.3 mph. AFR was high 12's low 13. Pretty perfect
After I did the carbs I rode it for a while. I still had the throttle crack lean bog. The 1/4 throttle makes it more pronounced. After riding with it for a while I went with 80 mains.  This made the bike too rich every where but it no longer bogs on quick throttle snaps. My top speed after the carbs was 97.5.mph.  My afr was high 11's. If I left the stock jets I would have picked up more mph but it runs better and has more power than before even being too rich. I will drop the needles one notch when I pull the carbs again and see how that does.