Topic: Air screw to reduce decel popping?

[Deltarider]

I had issue with fuel hoses that were slightly kinked. It caused fuel starvation in higher speeds.
Where the fuel connection is, in wrong angle.

Yep, it is often overlooked. I have seen it more than once when softer aftermarket tubes were used. Best advice I can give: have tubes at the original length and diameter.
I've distilled the correct dimensions of my CB500 tubes, knowing: 17 and 28 cm resp., in the apropiate parts list: https://www.honda4fun.com/dwnload/Part-List/CB500/CB500-K2-76-Parts-List.pdf On p.32 #15 and #16 we have partnumbers: 95001-55170-040 and 95001-55280-040.
On previous CB500 models which had the bowltype petcock, partnumbers were: 95001-55180-040 and 95001-552300-040. I don't know if Honda has applied this way of numbering for tubes on other models though.
Adding inline fuelfilters in CB500/550 tubes brings a risk.

[Bigmant]

I had issue with fuel hoses that were slightly kinked. It caused fuel starvation in higher speeds.
Where the fuel connection is, in wrong angle.

Just checked! Lines are not kinked any where and they are all genuine Honda replacements.

[PeWe]

Which model of carbs? Stamped on carbs.
- Is it really stock needles?
- Not cheap not usable aftermarket that look totally different in both lenght and taper?  If thicker, it will run leaner.

My 086A carbs (stock K6)
Had needles at 4th notch from top with 836, 4-1 and pods

Those carbs later on my K2
Same needle setting to run well. Tried middle first.

Changed to 064A carbs where 4th notch was too rich. Middle (3rd) a must. (These carbs have different needle taper/thickness)
Air screws 1 turn out.

[Bigmant]

Does anyone know why there might be two small holes in the roof of the float bowl in one carb and only one in the other? And could this be part of my problem? It makes me think the carbs might be different…

The carbs are stamped behind the backing plate which I don’t want to take off, before someone asks hahaha

[PeWe]

Carb model stamped like these photos
086A
064A

Other versions
7A, 657A

[newday777]

Does anyone know why there might be two small holes in the roof of the float bowl in one carb and only one in the other? And could this be part of my problem? It makes me think the carbs might be different…

The carbs are stamped behind the backing plate which I don’t want to take off, before someone asks hahaha

To share the bowl vent with the outside carb bowl.
You have 2 vent hoses, both hooked to the 2 and 3 carbs, because of the slide going down through the center blocking a pathway to go straight across the body, so they just add the second bowl vent hole in the 2/3 carbs, it's the pathway to the outside 1/4 carbs.

[Bigmant]

Does anyone know why there might be two small holes in the roof of the float bowl in one carb and only one in the other? And could this be part of my problem? It makes me think the carbs might be different…

The carbs are stamped behind the backing plate which I don’t want to take off, before someone asks hahaha

To share the bowl vent with the outside carb bowl.
You have 2 vent hoses, both hooked to the 2 and 3 carbs, because of the slide going down through the center blocking a pathway to go straight across the body, so they just add the second bowl vent hole in the 2/3 carbs, it's the pathway to the outside 1/4 carbs.

Got it! So totally normal then!

[Bigmant]

Ok I’m back to the drawing board everyone. I need some more help.

I cannot possibly think of what could be wrong with the bike. My next step is to pull the carbs again and go back to 140s on the mains.

The bike stumbles in first gear and dies with any amount of throttle.

There are no air leaks or exhaust leaks. The fuel lines are routed properly through the holes in the carb rack and down into the nipples, with no kinks in the lines. Floats are calibrated to exactly 26mm.

Currently running
130 mains
40 idle
1.5 turns out for air screw.
Pods
4 -1 exhaust

It could be something simple, but I’m at my wits end as to why the bike has no power with this large of a main jet.

[scottly]

The larger measured distance meant a lower fuel level in the float bowls, causing a leaner condition, and may have explained the large main jets? I asked on the other thread in 2022 if you had performed a "clear tube" test to check the actual fuel level in the bowls, and I would recommend doing it now. Do check the spark plugs: if they are black and sooty or black and wet, the current setup is too rich.

[seanbarney41]

lets see your plugs

[Bigmant]

lets see your plugs

Are we implying that I pull the plugs even when the bike won’t run in first gear? Not sure what the plugs will say when there is a more obvious issue.

[Bigmant]

The larger measured distance meant a lower fuel level in the float bowls, causing a leaner condition, and may have explained the large main jets? I asked on the other thread in 2022 if you had performed a "clear tube" test to check the actual fuel level in the bowls, and I would recommend doing it now. Do check the spark plugs: if they are black and sooty or black and wet, the current setup is too rich.

Scottly, are we implying that the float bowl level could be the cause of no power in first gear?

[seanbarney41]

lets see your plugs

Are we implying that I pull the plugs even when the bike won’t run in first gear? Not sure what the plugs will say when there is a more obvious issue.

the plugs are not the issue...but looking at them will tell you what your issue is.

[scottly]

The spark plugs show what is actually happening in the combustion chambers, and are the first things to check when trouble shooting.

[Bigmant]

The spark plugs show what is actually happening in the combustion chambers, and are the first things to check when trouble shooting.

First picture is cylinder 4. Second picture is cylinder 1. If we think I need to grab the harder cylinders i can do that haha.

[Oddjob]

Very rich by the look of those.

[Bigmant]

Very rich by the look of those.

So could my lack of power actually be flooding?? Maybe I need to bring the mains down to 120?

[Oddjob]

It could be flooding, it would depend on how wide open the throttle was when you did the plug chop. You could clean those up, refit and don’t exceed 3-4 thou and remove and inspect again. If they are still black then it’s most likely down to flooding. If not then it’s possible the mains are far too big or the needles are raised to high.

Personally I’d suspect flooding, those are really black and also look wet. Indicates so much petrol that it can’t burn it all, it would also get in the exhaust and detonate if conditions are right causing backfires etc. Would really bog down at low throttle openings.

[RAFster122s]

Are those iridium plugs? They aren't great in a carburetor motor unless it is properly tuned...

[scottly]

Those spark plugs are fouled, and once fouled will misfire even after the carburetor problem that caused it has been corrected. Do you have any standard plugs on hand that aren't fouled? If not, sometimes you can burn the black off the the central porcelain with a propane torch and re-use a fouled one. Also, the gap on those plugs looks big?
Yes, try installing the 120 mains; as I mentioned before, the improper float levels that you corrected would have made 130 jets too rich.

[Bigmant]

Those spark plugs are fouled, and once fouled will misfire even after the carburetor problem that caused it has been corrected. Do you have any standard plugs on hand that aren't fouled? If not, sometimes you can burn the black off the the central porcelain with a propane torch and re-use a fouled one. Also, the gap on those plugs looks big?
Yes, try installing the 120 mains; as I mentioned before, the improper float levels that you corrected would have made 130 jets too rich.

I do! I just bought some Denso x24es-u plugs to replace these just in case. I’ll go down to 120s, start with fresh plugs and see what happens!

[seanbarney41]

Those Iridium plugs seem like they have no ability to endure incorrect mixtures.  It seems like even once the mixture is corrected, they won't self-clean like a regular plug.  They were factory spec for an 07 CRF450 I had.  If you left the choke on too long they would foul, and not be able to clean themselves. Even after correcting the choke situation, they would just get worse and worse until no spark.  And they are expensive!

[Deltarider]

In general and without having read all the above. When plugs are sooted like yours, I'd look at the air intake first of all. Is the intake free of obstruction, meaning: no forgotten cloth near the aircleaner opening, no chokeflaps remaining closed, etc. Is the airfilter element itself still OK? Does your model happen to have a recircl blow-by gas breather fitted, which possibly could have fouled the aircleaner element? Has the latter been wet or moist? Any chance there's water in the fuel? I agree that fitting new plugs is best. After a cold start, reopen the chokes asap and let a somewhat raised idle prevent the engine from stalling.

[scottly]

In general and without having read all the above.

If you had bothered to read the last few posts, you might have noticed the mention of huge 130 main jets to compensate for low fuel levels in the float bowls, which have been corrected.

[Deltarider]

That's why my reply said: in general. It was meant tio help against tunnel vision, which often occurs. Moreover I myself clearly said: without having read the above. See, I anticipated your reaction, so to speak. But thanks anyway! You were great help.