Topic: CB400F Re jetting and carb sync but still running bad. Advise please.

[harisuluv]

Looks like velocity stacks.  Why are we setting the carbs to OEM specs then?

It looks like the vacuum gauges are hooked up, yet they don't move when you twist the throttle.  In fact they don't seem to move at all, what's the deal?

[jonda500]

FWIW:
I had a CB400F in the early nineties.
I put foam unifilter pods on it and a muffler with no baffle in it fitted onto the standard 4 into 1.
It was perfectly ridable without changing the pilot jets or the needle clips - I only changed the main jets (I think I ended up two sizes bigger than standard).
John

[Jimbo]

Looks like velocity stacks.  Why are we setting the carbs to OEM specs then?

It looks like the vacuum gauges are hooked up, yet they don't move when you twist the throttle.  In fact they don't seem to move at all, what's the deal?

The vacuum syncs have small plastic air screws so you can control the flow of air into the dials. it helps prevent the needle from shacking around. I'm pretty sure its a new thing that they have included in the new vacuum syncs.

Each gauge has its own individual damping control and Calibration Control.

http://www.ebay.co.uk/itm/2FastMoto-Carburetor-Synchronizer-Vacuum-Gauge-Carb-Sync-Synch-Honda-/311525445358?var=&hash=item48885d0eee:m:mreYNZuhp4K2IvNPHv5N_4g

[Jimbo]

Looks like velocity stacks.  Why are we setting the carbs to OEM specs then?

I have both currently, pods and stacks i switched them up to see if they would make much of a difference so the stacks were on there the time i shot the video.

[Jimbo]

UPDATE !

Seemed to have turned a slight corner today. After cleaning the carbs again taking them apart completely and going over everything with a fine tooth comb (copper wires actually) put them back together new plugs, i also benched synced them a little more open than usual. I also took Flybox's advise from another thread about float heights being 24mm set mine to that.

Set up as follows

40 pilot jet
75 main jet
air screw 2 turns out
Needle on number 4 shim (1 down from the top)

Turned the bike over and it ran really smooth. As you can see from the video it actually idols so I'm guessing the next step is to start dialling it in, i started to do that but i ran out of fuel. The plugs are slightly black not carbon fouled but have fuel on them i can see slight patches of brown on them so I'm guess I'm getting close.

The bike seemed to idol fine but bogged down slightly when i got to half throttle. I guess a larger main jet will sort this out. What do you suggest would be the next steps and is there a certain way i should dial the carbs in, as in one cylinder at a time ?

Feeling a bit better about my progress and iv definitely turned a corner.

[flybox1]

Glad for ya Jimbo.
After it warms up, what is your idle rpm?  How low can it comfortably idle?
Can you throw in a set of NEW plugs in a hot engine, and let it idle for 3-4 minutes (please have a fan on the engine) and let us take a look at the plug color?

How did you settle on "Needle on number 4 shim (1 down from the top)"  ?
Was this what YOU set them at, or just stating what it was set at?

[harisuluv]

1 down from the top = 2nd needle position.

Stock position = 3rd (middle position).

The needle isn't really going to change much for your idle, although you think it's running good now, once you get out and actually ride it and the needle comes into play that can change.

[Jimbo]

Glad for ya Jimbo.
After it warms up, what is your idle rpm?  How low can it comfortably idle?
Can you throw in a set of NEW plugs in a hot engine, and let it idle for 3-4 minutes (please have a fan on the engine) and let us take a look at the plug color?

How did you settle on "Needle on number 4 shim (1 down from the top)"  ?
Was this what YOU set them at, or just stating what it was set at?

After it warms up i can get it to idol around 1400 - 1600 rpm

I will get some fresh fuel and put some fresh plugs in tomorrow morning and snap a pic for you.

When i put the carbs back to standard it was still running quite rich so i thought i would give it a try on a leaner needle setting, turned out ok for now but if mid throttle is an issue then i may have to re adjust 

[Jimbo]

1 down from the top = 2nd needle position.

Stock position = 3rd (middle position).

The needle isn't really going to change much for your idle, although you think it's running good now, once you get out and actually ride it and the needle comes into play that can change.

Position 2 Haris, apologise i thought it was the other way round

[flybox1]

Leaner needle will not change idle mixture, but as Harisuluv indicated, it will have an effect on 1/4+ throttle...confirmed by your The bike seemed to idol fine but bogged down slightly when i got to half throttle.post above. 
You WILL need to adjust these back to #3 position at some point (possibly #4 slots)but it can wait till after idle is dialed in and we are tuning that circuit.

1400-1600 idle indicates the mixture is still off.  Idle plug chop will confirm. 
If the plugs are black from your last idle, warm up the bike, and adjust your mixture screws leaner by 1/2 turn before you put your next set of plugs in.

[Jimbo]

Leaner needle will not change idle mixture, but as Harisuluv indicated, it will have an effect on 14+ throttle...confirmed by your The bike seemed to idol fine but bogged down slightly when i got to half throttle.post above. 
You WILL need to adjust these back to #3 position at some point (possibly #4 slots)but it can wait till after idle is dialed in and we are tuning that circuit.

1400-1600 idle indicates the mixture is still off.  Idle plug chop will confirm. 
If the plugs are black from your last idle, warm up the bike, and adjust your mixture screws leaner by 1/2 turn before you put your next set of plugs in.

Will do Fly

Stay tuned

[Jimbo]

Ok guys

So i managed to get the bike idling really nicely, got her all warmed up and put some new plugs in. Started her back up and ran the bike for 10 mins (with fan in front) pulled the plugs and here is the results.

Weirdly cylinder 1 and 4 took a while to warm (don't think there firing)
Cylinder 2 was really hot
Cylinder 3 was hot but not scorching.

Pics to follow

[flybox1]

# 3 is great.  lets leave that one alone.
turn the air screws (richer) IN by 1/2 turn on 1,2 & 4.
Retest idle chop, and post pictures of just 1 & 4.
Lets just assume for the moment that #2 will behave similar to 1 & 4, but we'll want to check it once 1 & 4 start showing color.

[flybox1]

SO...is this an idle plug chop with your Delkavic exhaust on?

[Jimbo]

Yes

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[flybox1]

I think you might have got lucky as the decrease in back pressure leaned you out enough. 
Now, turn in those air screws until all are tan at idle like #3, then we can move on to needles/mains.

[Jimbo]

Lol. Well delkevic explained that the exhaust is set so no needle or jet adjustment is needed. The air flow would be the same as the standard exhaust... not sure how truthfull that is. I'll get those adjustments sorted tomorrow

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[Jimbo]

Here are the results from the plug chop today

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[DaveBarbier]

Here are the results from the plug chop today

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1 & 4 still cold, huh? Are the plugs wet when you remove them? With the bike off if you were to remove the #1 plug while still connected to the plug wire and hold it against the motor, do you see spark when you crank it over? Same for #4

You have a really shiny head. Your cabeza, not the bike's

[Jimbo]

Here are the results from the plug chop today

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1 & 4 still cold, huh? Are the plugs wet when you remove them? With the bike off if you were to remove the #1 plug while still connected to the plug wire and hold it against the motor, do you see spark when you crank it over? Same for #4

The plugs are slightly wet when i remove them and there also firing fine as well so I'm slightly clueless to why it won't fire.

Any help would be greatly appreciated

[b52bombardier1]

I'm curious what the compression on #1 is with vigorous cranking and the throttle held wide open? Could this simply be a lack of compression causing the no burn condition on #1?

Rick

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[flybox1]

#2 came along nicely 
bowl fuel level correct?  pilot jet fall out into the bowl?  improbable, but it has happened 
1/4 still white...coil?  Place one of these plugs against the head....getting good spark?
bad plug caps on 1/4?
yes, compression check

[Deltarider]

pilot jet fall out into the bowl?  improbable, but it has happened 

Happened to me, after I had it out for cleaning.

[flybox1]

pilot jet fall out into the bowl?  improbable, but it has happened 

Happened to me, after I had it out for cleaning.

#4 pilot dropped out on me during a tuning run after my 750 rebuild, and one was in the bowl of the 550 i just bought. 

[Jimbo]

#2 came along nicely 
bowl fuel level correct?  pilot jet fall out into the bowl?  improbable, but it has happened 
1/4 still white...coil?  Place one of these plugs against the head....getting good spark?
bad plug caps on 1/4?
yes, compression check

I know right.. #2 looking good

Ill check the pilot jets tomorrow along with the float heights, im pretty sure all cylinders were firing before i put the new plugs in ??

All the coils are firingwith good spark to all the plugs so there isn't an issue there, Compression check is the same as a vacuum sync ? or not