Author Topic: Carb setting for pod filters etc  (Read 255 times)

Offline K2-K6

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Carb setting for pod filters etc
« on: May 10, 2019, 05:23:52 PM »
Found in an old magazine,  it's carried out on different engine but clearly shows what happens when removing the std airbox and then to compensate via rejetting to run correctly.

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Clearly shows with test data why it is difficult to sort out just by changing existing jets when it's really a response curve mismatch that is the root cause.


Offline K2-K6

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Re: Carb setting for pod filters etc
« Reply #1 on: May 10, 2019, 05:28:27 PM »
And the second page to conclude.

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Last two paragraph really do summarise what's needed to get out of situation created by using very different induction to std.

The manufacturer follows exactly this process in their research and testing to get it right,  which is negated when altered.

Offline Andych

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Re: Carb setting for pod filters etc
« Reply #2 on: May 11, 2019, 12:36:41 AM »
Looks like it would be a good read if it wasnt sideways.. You cant even click on the pic and bring it around the right way...
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Offline K2-K6

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Re: Carb setting for pod filters etc
« Reply #3 on: May 11, 2019, 05:07:47 AM »
Apologies as not scanning but using camera to capture,  trying to keep resolution enough to still read text ok on here with file size allowable.


I'll try to get something else up to correct it,  waiting for sun to rise and give enough light  :)

Offline K2-K6

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Re: Carb setting for pod filters etc
« Reply #4 on: May 11, 2019, 11:07:59 AM »
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Hopefully that's more useful.

Why I found it interesting is that it gives a formal illustrated view of the problem existing when asking the question of what jets to use in modified systems.

Clearly demonstrated is the classic increase in main jet size to cover one area,  which results in running rich in another.  At some point you get a flat spot or too weak a mixture which cannot be logically solved just by jet sizing alone.

Offline Andych

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Re: Carb setting for pod filters etc
« Reply #5 on: May 12, 2019, 01:54:20 AM »
That is perfect and a great read.... wouldnt it be good to have a Dyno in the back yard that allowed you to run full and part throttle :)
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Offline K2-K6

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Re: Carb setting for pod filters etc
« Reply #6 on: May 12, 2019, 09:34:11 AM »
It would be interesting to be able to test things like that on your own dyno if you run modded stuff.

I think that most bike riders can feel flat spots, hesitation etc as we're pretty well attuned to bikes that don't work well. It's the diagnosis of cause and coming up with something to correct it that's the difficult bit.

Or if it's a fault as opposed to setup/service problem.

Offline K2-K6

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Re: Carb setting for pod filters etc
« Reply #7 on: May 15, 2019, 08:35:23 AM »
Apart from sounding good,  there's an interesting view of intake stand off in this clip. The fuel when the engine is under full load is being pushed out above the intake bellmouths which you can see as a fine mist. It's a normal function of intake dynamics which you don't often see.

https://m.youtube.com/watch?v=y2iBbwocYZw

What relevance can it have here,  do I hear anyone ask?   :)

Well,  I've been reading a contemporary test of  Honda's 750 F2 that was "tuned" which they ran it on a dyno by removing the rear wheel and connecting directly with drive chain to dynamometer.

One of the problems it suffered was a huge flat spot in mid range revs, poor enough to prevent them from getting stable consistent torque reading from. It was fitted with bellmouths and they noted that during the flat spot it had a huge fuel standoff out where the airbox should be,  which is what you see in that video but of course you'd not be able to observe it while riding.

One of the things an airbox does is to provide a plenum isolated from outside atmosphere. The standoff in this is better ingested to help engine running and also promotes scavenging from one cylinder fuel to another dependant on firing order (cross talk). The mist is already well mixed and atomised so works well in helping promote good combustion and driveable engine conditions too.

Offline Greg65

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Re: Carb setting for pod filters etc
« Reply #8 on: May 16, 2019, 07:39:42 AM »
A very interesting article and the final nail in my podded Suzuki GS 1000 set up. When I brought it I found it had been up jetted by 10 stages, you could smell the richness. Settled on 3 steps up and it goes well under full throttle, but as the article suggests I have low end flat spots. So I think it will be a lot easier to return to original set up as that is what is was designed for, far better brains than mine have spent many hours on the problem and that’s their solution.
Keep smiling it makes the management nervous.
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Offline K2-K6

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Re: Carb setting for pod filters etc
« Reply #9 on: May 16, 2019, 09:50:49 AM »
It may be of interest for your application as the writer of that article, I think, is still in related trade http://www.emeraldm3d.com/about-us

As far as I know it's the same person,  journalist and tech editor at that time on motorcycle mechanics,  could be interested in a mod for your carbs and worth a question to them I suppose.

I've read alot of his projects and always they are very factual and honestly prepared, always reporting the downside as well while searching for improvements. A very informative writer.