Author Topic: My 1975 CB400F project: strange noises at idle  (Read 19777 times)

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Offline tsflstb

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Re: My 1975 CB400F project: Fork rebuild
« Reply #25 on: August 18, 2008, 09:54:54 PM »
I did the same thing with my "seal puller/gouge the hell out of fork lower tool"...smooth out the nicks with a dremel tool or something and then fill the low spots with JB weld. 

Offline Joel

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Re: My 1975 CB400F project: Fork rebuild
« Reply #26 on: August 18, 2008, 10:19:17 PM »
I did the same thing with my "seal puller/gouge the hell out of fork lower tool"...smooth out the nicks with a dremel tool or something and then fill the low spots with JB weld. 

Will I need to do any more smoothing after filling with JB Weld?

Offline tsflstb

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Re: My 1975 CB400F project: Fork rebuild
« Reply #27 on: August 19, 2008, 07:38:31 AM »
I used some 400 grit sandpaper to smooth it all out.  Just be careful not to enlarge the hole too much.

Offline kghost

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Re: My 1975 CB400F project: Fork rebuild
« Reply #28 on: August 19, 2008, 04:39:41 PM »
Told ya they were a bugger.... ;)

Seriously like everyone else said....bit of epoxy filler and sand to fill the gouges.

Just sanding to knock down the high spots.

Don't worry the dust boot covers most of the ugly  :D
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Offline Joel

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Re: My 1975 CB400F project: Fork rebuild
« Reply #29 on: September 06, 2008, 02:56:14 PM »
I took the ignition plate out to change the point and condensers.  I had to get new screws because a couple of the heads stripped during removal.  There are six screws, two of which are shorter than the other four.  Unfortunately, I didn't record where the short ones went.  Can anyone tell me?

Offline Joel

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Re: My 1975 CB400F project: Fork rebuild
« Reply #30 on: April 25, 2009, 06:01:06 PM »
It's been a while but I'm starting to make some noticeable progress again.  I've gotten the new seals put in despite starting the first one before reading the directions so I failed to coat it with ATF first.  I had to hammer it pretty hard to seat it but hopefully it isn't damaged.  Fortunately, this set of forks is a spare and I'll still have the originals if there's a problem.

Warm weather is finally here.  Hopefully to stay!  :)

Offline Joel

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Re: My 1975 CB400F project: Fork rebuild
« Reply #31 on: April 25, 2009, 06:41:43 PM »
Success!  A little bit anyway.  I've assembled the forks and filled them with ATF.  They should now be ready to mount on the bike when I get the time and figure out the best way to get the weight off the front.  Any suggestions?  I've got a floor jack and two jack stands as well as a center stand that needs to be put on soon.

Offline Joel

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Re: My 1975 CB400F project: Brake Help Needed
« Reply #32 on: May 03, 2009, 02:31:04 PM »
I tried to replace the brake pads while I was swapping to the stock length forks.  Unfortunately the pivot on the caliper swing arm is seized.  Is it possible to free it or should I just start looking for a replacement?  Also, there isn't enough space between the pads for the disc to fit.  The fixed pad is seated properly so it seems the piston pad isn't retracting.  Is this a problem somewhere in the hydraulics?

It seems everytime I get one thing taken care of, one or two more problems pop up.   :(

Offline Joel

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Re: My 1975 CB400F project: Brakes
« Reply #33 on: May 20, 2009, 05:06:08 PM »
Here's what I found when I finally got the piston out of the caliper cylinder.  Nasty.



Here's what the bike currently looks like.  Sucks since it's been sunny, cloudless and in the 70s and 80s here all week so far.


« Last Edit: June 06, 2009, 07:31:03 PM by Joel C »

Offline Joel

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Re: My 1975 CB400F project: Brakes
« Reply #34 on: June 06, 2009, 07:41:23 PM »
Ah, first rides of the summer yesterday and today.   ;D  It's been pretty fun.  I'm hoping the weather tomorrow is clear so I can ride again!

Once I got it back together on late Friday afternoon, it fired up in less than a minute with a little choke and throttle.  I do love the kick starter.  :)  I'll get some pictures of the headlight, brackets and turn signals tomorrow during the day.

I got some LED bulbs to replace the instrument lights.  Three of the four bulbs were burned out.  I used the BA9s-G-120 green bulbs from SuperBrightLEDs.com.  I'm curious to see what the blues would have looked like behind the green faces but I didn't want to buy two whole sets of bulbs when I only need one.  Here's a picture of what they look like.  They illuminate very well.

« Last Edit: June 06, 2009, 07:43:30 PM by Joel C »

Offline SOHC4 Cafe Racer Fan

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Re: My 1975 CB400F project: Brakes
« Reply #35 on: June 08, 2009, 12:00:59 AM »
Cool.  It reminds me of NVG's (night vision goggles).
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Offline Hush

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Re: My 1975 CB400F project: Brakes
« Reply #36 on: June 08, 2009, 12:12:13 AM »
You're doing great Joel, if you ever need to do fork seals again my tip is get an old cooking pot, fill with water and put the fork legs in upside down, heat to boiling (you wont hurt them) and the seals will come out real easy.
Something to do with aluminium expanding under heat and the old rubber seals softening. :)
I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline kghost

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Re: My 1975 CB400F project: Brakes
« Reply #37 on: June 08, 2009, 12:14:12 AM »
your getting it done  ;)
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Offline Joel

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Re: My 1975 CB400F project: Front Fender
« Reply #38 on: July 10, 2009, 08:46:29 PM »
Is a brace for the forks required?  I thought about running without the front fender but I figured the brace was there for a reason.  I even though about drilling out the rivets and running the brace without the fender but I didn't wanna mess up my fender since it's decent.

Offline Tim2005

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Re: My 1975 CB400F project: Front Fender
« Reply #39 on: July 11, 2009, 07:03:03 AM »
Yes, it does act as a brace- which is useful with the stock forks. As your fender is nice condition then you could ebay it (they sell well) & use the money to buy a proper brace.

Offline CBGBs

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Re: My 1975 CB400F project: Front Fender
« Reply #40 on: July 30, 2009, 06:14:39 AM »
Whoa! Joel! That ATF fluid is a bad idea. NO one should be using ATF fluid. Get some good for oil. I use Motul. Its a big bottle. You can do more than one set of forks with it. The ATF fluid has a modern additive that can swell the seal.
 I like the idea of LEDs in the gauges.
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Offline Joel

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Re: My 1975 CB400F project: Front Fender
« Reply #41 on: August 01, 2009, 08:03:37 PM »
Well, I drove it a couple times last Sunday and it ran well.  I parked it for the night and got it out on Monday to ride.  I started it with the choke as I always do and it seemed to idle the same as usual.  I got out to the highway and pulled out into traffic.  As I tried to accelerate up to speed, it would stop between 2 & 4k and hesitate.  It also seemed to want to die unless I had the throttle above idle.  I messed with the screws on the sides of the carbs and tried to readjust the cam chain tensioner.  Now it'll accelerate, albeit much slower than I think it should, and even under cruising throttle at the neighborhood speeds I was riding, I'll get a hesitation rather regularly, perhaps once every couple of seconds.

I don't know if this symptom is related, but it still seems to rattle at idle.  I've been assuming the problem is un-synchronized carbs.  I did notice that with the oil fill screw out, the noise is much easier to hear.

I'm going to try an oil change this week and see if that helps.  While I've got the oil drained, I may try to take the oil pan off and peek up underneath.  The only thing I can think of doing differently is adding Seafoam to the gas and oil but it was more than a couple rides before the symptoms appeared.

Offline Joel

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Re: My 1975 CB400F project: strange noises at idle
« Reply #42 on: August 14, 2009, 01:50:55 PM »
I did a bit more tinkering around with the bike idling.  I took the spark plug boots off one at a time.  When 1 or 4 were removed, the engine died immediately.  When 2 or 3 were removed, the idle dropped but it continued to run.

Is there a way to test the coils?  I don't think they're bad but I'm sure it wouldn't hurt to test them and be sure.

I'm going to put together a manometer with some clear tubing and synchronize the carburetors.  It may be that 2 & 3 are out of sync and aren't supplying enough fuel to those cylinders.