Topic: Intro - 77' CB400F "Give Up"

[PHeller]

I call it "Give Up" because this is my second stab at classic motorcycles. The first, my 75' CB360 I gave up trying to figure out why it was constantly stalling and surging at stops. I sold it at profit and still regret it, because the bike was so cheap.

I owned a pretty boring, reliable, 1999 Yamaha XT225, but sold that because it was boring.

I longed for classic cool.

And so I found this. The iconic exhaust and sound of the CB400F.

Only mine is a pile. MAC Exhaust. K&N pods. Spraycan Black. Previous owner had it running perfect last summer, then decided to scrap the stock exhaust, put on the pods and MAC, and did something to the carbs and timing that has the bike running like complete hell. He lost patience...I hope I can keep mine.

The wiring is cut up, nutted up, taped up, and a general mess.

The paint is horrible.

The lights are in disarray.

The jetting is ?

The timing is ?

BUT

I've got a spare tank, spare rearsets, newly reupholstered seat, new fork seals, rebuilt head, new tires, and a host of other parts that would cost a fair amount to replace.

Now all thats left is labor and love.

and it's telling me "Give Up". Good thing I like a challenge.

[flybox1]

i hope the additional parts include an airbox and some stock jets.

good luck with your project.

[PHeller]

Nope.

Original airbox, yes, but I'm not sure I want to go back to the airbox when I've already got a higher flowing exhaust on it.

I'm thinking 90's for tuning during the winter of Pennsylvania will be a good starting point.

[PHeller]

TIMING

Lets say the PO didn't time the engine/cam chain correctly, how would I know? The bike does run, just doesn't idle and no power.

Which would be better - Pay local shop to time my bike, or buy Dyna DS-1 ignition? It's my understanding the electric ignition is pretty much "set and forget", which is appealing.

This is all assuming that timing is my problem and not the jetting.

[jessezm]

Soooo many other things to check before you decide how to prioritize your spending.  Have you confirmed that all 4 cylinders are firing both at idle and under load?  That would be the first place i'd look to diagnose an underpowered bike that wont idle.

You need to start with a full tune-up and also check your charging system.  I would not pay a mechanic to do anything to this bike--isn't that what your "labor and love" is all about?  You can do it!  

Save your $150 at the moment and go spend $20-$40 on a timing light and have at it yourself, it's easy.  The first money i'd invest would be in a shop manual, or just download the free one you can find on the forums here.

I truly doubt the timing is your main issue here, but probably is one of them.  I would do the following to get a good starting point and go from there:

1.  Clean the carburetors and determine what the jetting is and that all passages are clean and clear.  Get some extra jets in different sizes from stock to 2 or 3 steps up (175's, 180's, 185's, and 190's maybe).  Bench sync the carbs and make sure the air screws are set evenly to each other and to factor specs, or just a bit rich.  Also make sure your throttle adjuster screw on the carb rack has enough play in it to both open and close the slides after bench the bench sync, and set it just a bit open.  Check and make sure the clip position in the needles is in the middle.

2.  Start over with the stock airbox and a new, clean airfilter.  Jet the carbs almost stock, maybe one or two steps up to compensate for the pipes

3.  Adjust valve clearances (with a cold motor)

3.  New plugs.  Test all 4 cylinders for spark.

4.  Inspect your points, and if OK, gap them, then set your static timing with a 12v test light or a voltmeter/ohmmeter (this is a few bucks at the auto parts store)

5.  Make sure your battery is good and has a full charge, and fire her up to see if she runs.

6.  If so, set the timing with your new timing light.

7.  If running at idle now, adjust the camchain.  You'll probably want to go back and readjust the valves at some point as well.  Ideally, you'd do the camchain tension first, but without a bike that idles, that's sorta tricky...  Oh, and BE GENTLE with the adjuster nut, they are well-known weaknesses in this bike!

8.  Oil and filter change.

Now, if you did all that, and now have a bike that runs relatively ok, you're in pretty good shape.  If you get stuck along the way and still can't get it to idle, check back in and tell us what's happening.

[flybox1]

yep 

[PHeller]

Ok, so I got the carbs off tonight, which was pretty easy, and I was disappointed at what I found.

The bowls must have been leaking on the previous owner, so he used some sort of sealant to seal them...only it didn't harden and turned to a gooey mess inside my bowls.

So here's the run down:

External Condition: Good, most screws come loose pretty easily. Everything seems to be there including hoses. Discovered PO must have switched the throttle because it only had one cable. There is no return cable on the carb.



Bowls: Gunky with gook. Drain screws were extremely tight (probably because of gunk), and one I couldn't get out...I actually rounded a flathead screw...


Main Jets: Marred and gouged, clogged and two had really messed up seals. They don't appear to be drilled, but who knows.

Pilots: clogged, but otherwise fine.

Carb body (inside bowl): I'm seeing some pitting on the #4 jet holder thing. Is this a problem?


Floats: Here is where I noticed a big question. The float has a nick in it. Are these solid floats? Does this nick keep it from floating?


Throats and slides: Both look good. Some little nicks on the slides, but nothing serious...I think.

[jessezm]

Off to a good start.  Those carbs look totally serviceable, though you're probably best off just buying a set of carb kits.  Stick with your stock needles if they look okay (round, smooth profile, not oblong or notched/worn).  But you're probably best off with new slow jets, mains, needles and seats, as well as the gaskets that come with the carb rebuild kits (they also come with air screws and springs so replace those too, and blow out ALL the passages).

You can try to be cheaper and salvage your jets, but you'll need o-rings and gaskets and it'll probably cost the same, plus buying the float needles and seats on their own is too expensive if those are warn.

The corrosion on the main jet tower shouldn't be a problem.  Make sure to take out your emulsifier tubes.  I find the easiest way to do this is to take out the slide and tap them out from above with a gently tap from a hammer on the end of a phillips screwdriver or other tapered tool that you can center over the top of the tube.  Clean those well--lots of tiny holes to clear of gunk.

Not sure what to say about the float, but I'd be looking for a new one on ebay.  There's a set on ebay right now but it's for all 4 at $100...   You could probably get one from a dealer for $25 or $30 maybe.

Also, get a new "push" cable.  It's kinda important, even if you can do without it.

Once you get those puppies rebuilt and back together I think you're going to be pleasantly surprised.

[PHeller]

Run right how? I've read plenty of posts from people who run open carbs with stacks and exhaust.

Problem is going back to stock would cost even more on top of the parts I'll need for the carb.

I'm broke and unemployed so I need stuff as cheaply as possible.

Will the float work for the time being?

[Tugboat]

The inside of my carbs on my 750F looked similar to yours when I first took them apart. The PO had even used some gasket goop around the float bowls that had gotten everywhere. Used a dremel with a wire brush on it to remove all of the sticky mess off the bowls. Give them a good soak in some Simple Green or carb cleaner too - that'll help loosen everything up. The pitting on the main jet tower never caused me any problems either - just make sure the o-ring inside has a firm seal. As to your float, pop it in a cup of water and see if it floats, or if one side sinks. If it floats, it's probably good enough to at least get you running (though you'll want to replace at some point). Good luck!

[PHeller]

Thanks Tugboat. Good info.

[PHeller]

Last night:

Put carb back together without new jets (crappy seals), without new float bowl seals (let them soak in brake fluid) and aside from a good cleaning, pretty the way it came to me.

Today:

Beautiful morning, so I set off to get some spark plugs.


Get back to the shop, pull the plugs...and find this...

On the left, you'll see a D7EA, D8EA, and then a DR8EA. On the right are the new plugs after idling the bike and running for about 5 minutes with a quick trip down the block.


Yes, you read that, the bike IDLED for a few minutes. I tried running up the street, but it was really bogging. However, it did rev past 6,000 rpm, so this is IMPROVEMENT.

The bowls didn't leak, the bike didn't smoke much considering it condition, and it actually revved like a normal bike.

After running for about 10 minutes the bike wouldn't start again, I think I either flooded it or the jets got clogged again.

So the carbs will come back off, get recleaned, and new jets will be installed. Then we'll try again.