Topic: Can it be carb trouble or just bad carb settings?

[Jore]

Since I've owned my '75 400/4 has had it's carbs taken apart and cleaned 3 times. I've been trying to get it running before doing cosmetic stuff to it.

Now I have sorted out electrical and ignition gremlins. Last night I did a clear tube test, and all 4 carbs where about 5mm shy of where the bowls end, another member told me they where on the short side of fuel level.

So this is my problem, the outer cylinders are running rich, but the inner ones seem to run ok, I looked at the carbs and the airscrews on the inners seem to have about the same position (if it was a clock It should be pointing at around 1:35), the outer screws don't have a similar position with the other 2.

If I play around with the screw settings, can I get all 4 running correctly?

[750IV]

You can't tell by looking at a screw position. Lightly bottom out the screws then turn them out the amount the manual calls for, usually around 1 1/2 turns. I assume these are idle mixture screws and if like a car carburetor they affect the mixture at idle/low rpm's only and will make a difference at idle.
750IV

[flybox1]

Since I've owned my '75 400/4 has had it's carbs taken apart and cleaned 3 times. I've been trying to get it running before doing cosmetic stuff to it.

Now I have sorted out electrical and ignition gremlins. Last night I did a clear tube test, and all 4 carbs where about 5mm shy of where the bowls end, another member told me they where on the short side of fuel level.

So this is my problem, the outer cylinders are running rich, but the inner ones seem to run ok, I looked at the carbs and the airscrews on the inners seem to have about the same position (if it was a clock It should be pointing at around 1:35), the outer screws don't have a similar position with the other 2.

If I play around with the screw settings, can I get all 4 running correctly?

5mm sounds a little low.
what are you running for an airbox and exhaust? 
we can only assume you've done a full tuneup
did  you end with a vacuum sync?
are the plug deposits from running at WFO, mid throttle position, or at idle?

[Jore]

I'm running with the stock exhaust and stock air box but without an air filter.

Carbs where allegedly vacuum synced.

Mostly I've run idle and mid throttle I've done less than 5 miles at speed and WOT.

[TwoTired]

Are the emulsion tubes clean?
Are the emulsion tubes the same among the carbs?
Are the air jets clean and clear?

Have you found any corrosion inside the carbs?
Have you verified that the carb's air jet passages are clean and clear?
Are you certain the slide needles are all the same size and set in the same position among the four?

The O'clock position it not the setting.  It is the turns count from lightly seated that determines the setting.  (The carb bodies may not have been machined to high tolerance for the air screw bores, so the o'clock position is allowed to vary.)

Are there no bugs or dust for the engine to suck in where you run it?

Personally, I have a problem with "alleged" work performed.  But, I don't juggle jello well either, or tolerate missing rungs on a ladder.

Kinda normal to begin sooting plugs at idle and particularly with choke applied.  Mid throttle won't help clear the plugs unless the engine is making more power than to simply overcome internal friction.  The unknown here is time spent in the "sooting" mode.  A few minutes, shouldn't show sooting.  A few hours will.

A carb imbalance can cause cylinders to run differently among them.

Why aren't you driving the bike?

FYI: Cleaning carbs three times is not an accomplishment.  Cleaning them throrughly is.

Cheers,

[Jore]

Thanks TwoTired, I haven't personally taken the carbs apart, all that was done at the local honda shop, before I started working myself on the bike.

Every time I've emptied the fuel bowls, gas comes out clean, no debris or other foreign objects. Ridding time has gone down, since my work time has gone up, so most free time I have, I spend wrenching on the bike.

Can I set the screws all in and then back them out say 1 or 2 turns, and then see what I can get from there?

For start up I don't need to use the choke, unless the plugs are completely fouled, but at that point I'm running only on 2 cylinders.

One more thing if I give it some gas during idle say from 1200 RPM to around 3K, after letting the throttle go, the revs lower but to around 1600 RPM then I have to give it a little blip in order for the revs to drop back down to 1.2 K

[TwoTired]

Can I set the screws all in and then back them out say 1 or 2 turns, and then see what I can get from there?

Yes.  Book value is 2 turns +/- one half turn, (assumes stock, clean air filter.)

For start up I don't need to use the choke, unless the plugs are completely fouled, but at that point I'm running only on 2 cylinders.

If the outside air temp is warm, no choke might be ok.  But, if you are fouling plugs quickly, that indicates a problem to correct.

One more thing if I give it some gas during idle say from 1200 RPM to around 3K, after letting the throttle go, the revs lower but to around 1600 RPM then I have to give it a little blip in order for the revs to drop back down to 1.2 K

I've seen return to idle issues caused by poor vacuum sync alone.  Of course, there can also be other causes, such as air leaks between carb and intake valve pathways, to name one.

You are going to have to find out why all four cylinders aren't behaving the same, yielding identical plug deposits.  Something is different among them, if not carb sync then something else inside the carbs or air path runners. 
Have you done the tune up check list?  Tune carbs last.

Cheers,

[Bru-tom]

^^^^   always a pleasure reading your posts TT

[Jore]

Thanks again TT, i'll give it a try just with the screws and move from there.

This list you're talking about, is it the 3k mile tune up?

[mrrch]

Could it be ignition related? Are the 400's like the 750's where #1 & #4 cylinder fire the same and #2 & #3 are the same? Could point timing could be a culprit possibly?

[Jore]

Yes 1 & 4 are paired. I went through the wiring and even swapped sides on the condensers but I didn't check timing on them.

[TwoTired]

This list you're talking about, is it the 3k mile tune up?

Pretty much...

[lucky]

Since I've owned my '75 400/4 has had it's carbs taken apart and cleaned 3 times. I've been trying to get it running before doing cosmetic stuff to it.

Now I have sorted out electrical and ignition gremlins. Last night I did a clear tube test, and all 4 carbs where about 5mm shy of where the bowls end, another member told me they where on the short side of fuel level.

So this is my problem, the outer cylinders are running rich, but the inner ones seem to run ok, I looked at the carbs and the airscrews on the inners seem to have about the same position (if it was a clock It should be pointing at around 1:35), the outer screws don't have a similar position with the other 2.

If I play around with the screw settings, can I get all 4 running correctly?

IF you want your carbs to run properly ...set the float levels the way the workshop manual tells you.

The clear tube method is only AFTER....AFTER you have used a measuring device or float gage to set them. It even tells you that in the Clymer's manual.

Also it does no good to set old float needles. The rubber ones can have a pointed tip that is lop sided or not round and the rubber is hardened.
The metal tip float needles can have a shiny ring around the tip and if you look at them with a magnifying glass you will see that ,that shiny ring on the tip is a step worn into the tip.  they will never work right. You cannot polish them into working right.

[Jore]

I had some time off, and took the bike out after playing a bit with the airscrews, about 1 and 3/4 turns where the point the bike fealt better, got idling to about 1.5 K, took it for a spirited ride for about 20 minutes pull back in the garage, and it's starts acting up again, the revs climb, you have to blip it to take them back down. The It just stutters and dies, restart it, sounds rough disconnected #1 spark plug lead, revs don't change, reconnected it and tried the same with number 4, and the same story, take a look around the overflow tube from #2 is leaking, so that's that, I'm taking my carbs apart.

These are my questions:

With planning, how long will it take?
If something's missing can it be fabed?
Besides basic tools what else would I need?

Since my 2 inner carbs are working, can I just leave those 2 alone or do I have to take them apart?


Thanks!

[Bru-tom]

my thread i started, i will be updating this weekend with the assembly, if my o-rings arrive at my supplier in time.

http://forums.sohc4.net/index.php?topic=117658.0

[TwoTired]

With planning, how long will it take?

The better part of a day.  Consider 1-2 hour per carb.  Usually, twice that for newbs.  There's a reason why credible shops will often charge $400 for rebuilding the carbs.

If something's missing can it be fabed?
Loaded question.  Since, all the parts were fabed at creation.  So, yes anything can be fabed, its a matter of time, money, and skill.

Besides basic tools what else would I need?

Patience and a methodical approach.
A wood or nylon dowel to push out the emulsion tubes.
A set of manometers to set proper slide position.
A set of rubber parts to to replace all those that are hardened.  (Honda kit)
Carb cleaner.  I like the aerosol type. get two cans.
JIS tipped screwdrivers is a plus to keep the cross head screws in good condition.
Patience and thoughtful consideration.

Since my 2 inner carbs are working, can I just leave those 2 alone or do I have to take them apart?

  I would not make such an assumption, as they are all "working".  Because some are better than other does not eliminate impending problems with the others.  However, if the bowls are clean when you remove them and the emulsion tubes fall out and are also clean, I might be tempted to take a short cut.  Kinda depends on if you find something "wrong" in the outer suspected carbs, that you believe the inner carbs are immune from being effected. Like a jet falling out, for example.  Other wise, if it is gas gumming in the outters, the inners ought to be effected the same way.

What is worrisome is that, while possible, the carbs failing in the same positions as the coil cylinder boundaries deserves further scrutiny.  Are you certain you have eliminated the ignition system as contributary?  Replaced or swapped position of the condensers?  Set points and timing per book values?

FYI: Since the entire purpose of the float setting is to create the proper fuel level in the carbs.  The clear tube method supercedes the mechanical float setting.  Personally I don't care what the float needles "look" like, if it properly controls the inlet flow to the carbs, it's fine with me.

Cheers,

[Jore]

So I might as well, just take them all apart.

But coming back to the ignition side. Today after the fiddling/ridding, I noticed all 4 exhaust pipes where hot, but the inners where hotter than the outers. I did swap the condensers from side to side, but after that I didn't anything at all. Can 1 set of point be off timed ?

[Deltarider]

Yes.

[TwoTired]

Today after the fiddling/ridding, I noticed all 4 exhaust pipes where hot, but the inners where hotter than the outers.

That just says the hotter exhausts are from cylinders working harder than the others.  One possibility is that the carbs are telling some cylinders to work harder than others, such as from poor vacuum sync. (Some slide set to lift higher than others.)

Can 1 set of point be off timed ?

Yes, and if you rebuild carbs before doing the rest of the tune up check list, you risk having the same problem after rebuilding carbs due to other causes.

Carbs are last to address.

Cheers,

[Jore]

Well then should I start reading up on how to perform timing settings?

[Jore]

Quick question:

Can I check timing without a timing light? Also how can I check the advancer and all the other parts?

I'll have a got a spark and timing advance before going with the carbs

[TwoTired]

You can check static timing with an ordinary instrument 12v light bulb, and two wires with alligator clips.

Checking the advance function requires either disassembly of the advancer or a dynamic timing light.

[Jore]

TwoTired, can you please explain the process of checking the static timing? Thanks!

[TwoTired]

TwoTired, can you please explain the process of checking the static timing? Thanks!

I can.  But, I don't understand why the description and instructions in the Honda shop manual chapter 3 pgs 10-11 aren't understandable.
There's a similar process printed in the owner's manual, too.

Cheers,

[Jore]

Thanks! that's the guidance I needed.

I've just noticed something on the points, maybe it's nothing but still.

At low idle speed, you can clearly see both sets open and close, but once you get into it, say 3-4 K rev range, the points set for 2-3, seem static (like they don't move at all, but from time to time you can see a spark between them. Now the 1-4 set, seems to go wild you can clearly see it's movement, even shakier than the other set.

So can this point to something?