Progress - She runs at last! (75 CB400F)

[ManicGTI]

So, big progress for me.  After 20 odd years since it's last road tax, I have got her ('75 CB400F) started for the first time since my top end rebuild!  Thanks to all that have reponded previously.

IT STARTS!

Literally on the button, first attempt, with Choke open or closed.  Very happy about this! However I'm far from out of the woods.
- Appears to be running very rich (all plugs immediately / consistently blackened)
- Revs increase dramatically when I try to open the choke.

What's changed since my last attempt:
- Carbs stripped and rebuilt (again), bodies simmered in a pan for an hour or so with a dishwasher tablet, then recleaned with parts cleaner spray and went over all ports blowing and checking (concentrating on idle circuit).
- Re-Bench synced them, this time doing it in the 'closed position' rather than open.  Used a 4mm drill bit as it was what I had to hand, maybe I should have gone for 3mm as closer to the 'interweb recommended' 1/8".
- Also rechecked/adjusted Tappet clearances, Points Gaps, and Static timing.


So, any thoughts on what to do next?
- Check timing with timing light now I can run the engine.
- Redo carb Static balance?
- Idle screws?
- Try the OEM Idle jets back in there now the bodies are cleaned.
- Fit Hondaman transitorised ignition box (likely unrelated, but i'll fit it anyway)

Or is this likely to be something more fundamental, ie Rebuild kit jets not correct?  Carbs bodies still not clean?  REv counter isn't working, so not a clue what

At the very least this has renewed my enthusiasm so i'm keen to keep the momentum up!

Dave

For info, my previous thread:  http://www.sohc.co.uk/index.php/topic,9575.0.html

[Johnwebley]

glad its running,

  when I assembled my carbs and bench synced them ,I used a torch to shine through the carb ,and adjusted then so they all were
almost closed,I figured I could use the main throttle stop screw to open them as needed,

 are you sure you have the float heights set correctly? seems very rich ,so maybe levels to high ?

 

[Laverda Dave]

I've got exactly the same problem!  I started mine today after the rebuild.  I had the carbs ultrasonically cleaned, new jets, needles and float valves.  I set the carb floats using a 26mm gauge as recommended by Mr Haynes in his book and used a 3mm drill to set the slides.
When I turned the fuel on everything was fine for 5 minutes and carb no.4 flooded closely followed a couple of minutes later by no.1! When I connected the Morgan gauges only carb no.3 registered any reading, no matter how much I tried to adjust the settings on the screws and lockouts using a Honda tool nothing happened! The carbs are back on the bench and I'm scratching my head, I followed the carb rebuild instructions to the letter!

[mike the bike]

If I remember correctly,  the float heights are 21mm.

[Chris400F]

I agree, 26mm certainly doesn't sound right. This thread on setting float heights may help (people have been here before!).
http://www.sohc.co.uk/index.php/topic,7882.0.html

[Laverda Dave]

Thanks Chris.
I've given up for the day now, lesson learnt, try the carbs off the bike in future!
I'll try again on Saturday, work gets in the way for the rest of the week  .

[ManicGTI]

The float heights I did to 21mm, is that not right for the 400?   Bowls are are all filling fine, none of them are overflowing.

Sounds like I do the syncing in a slightly more closed position, but I don't see how that would help the richness?  I like the idea of adjusting to almost closed then using the main screw, I was just trying to stay as close as possible to the manual method.

[ManicGTI]

Oops, should have checked the subsequent posts.  Yup, 21mm.

I'm wondering if starting it in the garage doesn't help, always going to sound more 'dramatic'.

My plugs were like this:
https://goo.gl/photos/dF5kWjGSGkeJ6j3e6

Is there anything else I should be checking on top of the following?
- Bench Syncing (possibly have them too far open)
- Float levels
- Idle Jets?
- Idle screw adjustment?

I'm sticking with the idle at the mo, not touching the throttle really!

Dave

[Bryanj]

With a bench sync it is easy to get the slides so they dont close

first back off the idle screw till it falls out, then un adjust the carb slide adjusters so all slides hit the bottom pick one(on the 550 k3 its easy as one has no adjuster) and adjust the slide adjuster till it nearly moves, refit the idle screw and adjust it till the one you picked lets your prefered drill bit fit, 3mm is too big you need 1.5 if poss, then adjust all the others to the same. Finally undo the idle screw again and make sure all slides hit the bottom.

Run engine till hot ad ajust with gaudes AFTER you haveset tappets, cam chain and ignition timing

[ManicGTI]

Thanks for the run down Bryan, I'll redo the Bench Sync as suggested.

Cam Chain I haven't touched yet.

[Chris400F]

I had a rummage in my garage and found the tool I made when I did my float heights.
I can't remember whether I read about it on this forum or elsewhere, not that it matters - maybe it will be of help to others.
The tool was made from the lid of a tub of soft cheese (Philadelphia in this case; other brands are available).
Outer cutouts are 21mm deep (float height), inner cutout is as deep as it needs to be to clear the tube holding the main jet.
Working with the bank of carbs on end eliminates the effects of gravity - the height needs to be set with the float arm just touching the needle jet.
If the pivot pin is loose in the holes use masking tape or similar to hold it in place.
I have noticed that the text in the Haynes manual says set to 22mm. This is the 500/550 setting, 400 is 21mm according to the specifications.
I had never set float heights before but found this method worked well for me.

[Laverda Dave]

All very interesting info and unavailable in the Haynes manual.  I found the piece of card I used, it's 22mm, not 26mm as I stated in my earlier reply, two of the four carbs still leak though so I'm going with your idea Chris to make a proper 21mm gauge followed by the bench sync as recommended by Bryan.

[Laverda Dave]

Well, I made the gauge from some ali sheet to 21mm. All floats carefully reset and checked over and over just to be sure. I set the carbs using Bryan's recommended technique and all was good. I thought I'd bench test the carbs before putting back on the bike and placed them very gently in the vice, connected the bottle of fuel and waited. Everything as great for 5 minutes and then petrol poured from 2 of the overflows and also the central overflow pipes between carbs 3&4  . Am I doing something fundementaly wrong?
To cap a bad afternoon, I got that horrible feeling when one of the float bowl screws just kept turning, undoing the screw pulled out the tread with it! I need to get a 4mm helicoil kit now although opinion is timeserts are a better option (I've never used one). At least it's winter and I'm not missing out on any sunshine  .

[Bryanj]

 Not enough meat for a timesert as they are a lot thicker in the wall, Do the float needle seats have an O ring on them? Are the float bowls very full or could the internal standpipes be cracked

[K2-K6]

The float height would not usually alter how it shuts fuel off within reasonable range,  just the mixture when running.

If the valve seats are brass you can use something like a cotton bud with brasso or T-cut to spin slowly with a drill and get them smooth / polished. Needs thorough clean afterwards.

If the needles are plastic or rubber tipped, they can be hard to get to seal properly with just the float pressure on them. I know it's a slim hope, but the heat and engine vibrations do seem to assist this process when installed and running. I can see why you'd want to reassure yourself prior to install though.