Richness on suddenly open throttle

[Anonymous]

Is it normal for an engine running CV carbs to run rich and churn black smoke when suddenly opening the throttle? I know that suddenly changing throttle can create wacky vacuum problems. I have a suspi cion that I might always have richness on full throttle, sudden or not. But it's a little tough for me to see my exhaust as I have the throttle wide open... Much acceleration.

So is some richness to be expected or should I rejet?

Michael

[KEITH KRAUSE]

Suddenly opening the throttle when? After idling? While cruising 65 mph and suddenly opening the throttle?

[earlfor]

Re: Richness on suddenly open throttle

Its probably nothing more than burning out accumulated carbon build up. If the bike is running strong with good acceleration, I dont see how it could do that if the mixtures were so rich as to produce black smoke. If the mixtures were that far off, I doubt the bike would top out at anything over 40 mph. :-)
I would run it a while and give it a chance to clean itself out. Check the plugs off and on, that will tell you how the mix is burning.

I would not just yet consider any jetting changes.

Earl

Is it normal for an engine running CV carbs to run rich and churn black smoke when suddenly opening the throttle? I know that suddenly changing throttle can create wacky vacuum problems. I have a suspi cion that I might always have richness on full throttle, sudden or not. But it's a little tough for me to see my exhaust as I have the throttle wide open... Much acceleration.

So is some richness to be expected or should I rejet?

Michael

[Anonymous]

Suddenly opening the throttle when? After idling? While cruising 65 mph and suddenly opening the throttle?

Either. I can see that from idling on the sidestand to full open throttle causes smoke. I am also told that when a friend was driving next to me and I had it at 60 in second and gunned it, it also made a lot of smoke.

Michael

[Anonymous]

Re: Richness on suddenly open throttle

If the mixtures were that far off, I doubt the bike would top out at anything over 40 mph. :-)

Welp, I don't really know what my top speed is currently. Since I borrowed DEW's windshield I've been getting a nasty headshake at 103 or so... probably have plenty left.

Michael

[earlfor]

Re: Richness on suddenly open throttle

If it was going rich at full throttle, it would bog and acceleration would fall off.
If its still pulling hard, I dont see how the mixtures are going too rich.

Earl

Welp, I don't really know what my top speed is currently. Since I borrowed DEW's windshield I've been getting a nasty headshake at 103 or so... probably have plenty left.

Michael

[KEITH KRAUSE]

Well, sounds rich to me. A little black exhaust can be acceptable on sudden opening, but not a lot of it. Which bike is this? Is this the bike you said is running good? The one with the carbs synched and the mixture screws set correctly? What else have you done to try to correct the problem? Did it at one point not smoke? What's happened since that point?
When you suddenly open the throttle at 60 mph, as you hold it open and you're accelerating, does it pull a little harder if you back off the throttle just a bit?

[AOD]

something with the needles maybe? quick accel (unless it's wide open then its running on the main jet) is gonna pull fuel through there quickly...

i was told over time they can shake and waller out the area they sit in.

~Adam

[Detman101]

Re: Richness on suddenly open throttle

Is it normal for an engine running CV carbs to run rich and churn black smoke when suddenly opening the throttle? I know that suddenly changing throttle can create wacky vacuum problems. I have a suspi cion that I might always have richness on full throttle, sudden or not. But it's a little tough for me to see my exhaust as I have the throttle wide open... Much acceleration.

So is some richness to be expected or should I rejet?

Michael

Great way to beat the word-editor!

Dm of mD

[lhanscom]

When you first wack open the throttle, if anything, it should go a bit lean I thought, but the CV carbs are supposed to eliminate the problem. If you're not having acceleration issues, I would just run it up to redline a few times and check it again, it could just be clearing it's throat. Also check your plugs and see what they have to say, preferably right after it has the issue.
Good luck

[Anonymous]

My theory on the issue is the fact that the slides are vacuum operated, not mechanical. When the throttle is wacked open, the butterflies on the engine side come open, fuel is sucked up through the jets, and a split second later the slides open. I would venture that during this split second is when the bike goes rich.

Just a theory...

[lhanscom]

But if the slide is down, then the needle is down, and no extra fuel would be flowing, or is my logic flawed?

[Anonymous]

But if the slide is down, then the needle is down, and no extra fuel would be flowing, or is my logic flawed?

Might-be-wrong zone ahead:

As I understand it, the velocity of the air in the carbs determines how much fuel comes out the venturi, due to the Bernoulli effect. The cross sectional area of the flow chamber (as determined by the height of the slide) is what determines the volume of air in the mixture. So if the vacuum is high, the air velocity will be high, and there will be lots of gas, but if at the same time, slides haven't yet risen, there will only be a little air. Lots gas plus little air = rich.

Or I might be totally dead wrong. (Please tell)

Now leaving might-be-wrong zone

Michael

[earlfor]

Just some comments interspersed. :-)

As I understand it, the velocity of the air in the carbs determines how much fuel comes out the venturi, due to the Bernoulli effect.
************Thats right. Without sufficient velocity, there will be no fuel flow.


The cross sectional area of the flow chamber (as determined by the height of the slide) is what determines the volume of air in the mixture.
*************** The throttle plate being opened or closed causes a change in velocity/vacuum which causes causes the slide to move either up or down. Engine rpm and displacment determine the volume of air that will be drawn through the carbs.

If your engine processes 100 cu ft of air per minute at 1200 rpm, it will do so regardless of whether carbs are mounted to the cylinders or not. You could turn the crankshaft at 1200 rpm with an electric motor and the engine will pump the same 100 cu ft min of air.

Earl




So if the vacuum is high, the air velocity will be high, and there will be lots of gas, but if at the same time, slides haven't yet risen, there will only be a little air. Lots gas plus little air = rich.

Or I might be totally dead wrong. (Please tell)

Now leaving might-be-wrong zone

Michael

[KEITH KRAUSE]

OK. Now that we've got that scientific stuff out of the way, let's figure out why your needle and/or main circuit is rich.
How about my questions from my earlier post? Black exhaust can be just one carb too. It does'nt have to mean all the carbs are rich.