stock carb and pod filters

marcelm
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stock carb and pod filters

Post by marcelm »

Hi,

My friend has just bought a Honda CBX 650 E, 1986, 35.000 km.
Bike has pod filters and stock carb.
The engine is rev and sound like a swiss watch, but the problem is that has not enough power : in 5th and 6th gear, he cannot reach more that 5.500 rpm, even with full thruttle. Max speed is around 135 km/h (84 mph).

I know is a verry difficult engine to tune in case of using the pod filters, but he cannot go back to stock, due to frame mod.

Could you please give to me some hints, what he can do in order to increase the power ? jet kit ? increase the hole in the actual stock jets ? what size ?

Thanks in advance
Marcel

Edit : the plugs color is white and carb is Keihin.
Last edited by marcelm on Mon Nov 10, 2014 8:32 am, edited 1 time in total.

steve murdoch icoa #5322
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Re: stock carb and pod filters

Post by steve murdoch icoa #5322 »

Not positive but i think the bike/carbs are very similar to the 650 Nighthawk we got in North America.
There is a ton of carb info on this site for the Nighthawk.
http://paulsnighthawkpages.blogspot.ca/ ... -tips.html

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Gearheadgregg
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Re: stock carb and pod filters

Post by Gearheadgregg »

start with 1 step larger Slow Jet also called (Idle Jet) and then turn mixture screw out 1/2 turn for richer mix, Remember ONLY one thing can be done at a time then road test, if improved then go 1 step larger MAIN Jet, Then try moving Needle (UP) one notch, or use small washer if no clip or non-adjustable needle, Remember (SLOW JET ONLY FIRST)

marcelm
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Re: stock carb and pod filters

Post by marcelm »

Thanks,

I wil try study the site with the carb info.

Do you know the hole diameters for stock and 1 step larger ? for both Slow and Main jet ?
I have the posibility to drill the stock jets, at a tool shop for watches. Some friends did it with good results.

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Re: stock carb and pod filters

Post by Gearheadgregg »

not sure what the 650 has for size, If you have a Jet drill Index kit with assortments of Drill bits you would have to try to size the hole with fitment of the drill size, here is some help for drilling or Reaming slow and main jets, Look around on this site you may find a chart > http://www.hondachopper.com/garage/carb ... lots1.html

marcelm
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Re: stock carb and pod filters

Post by marcelm »

Still not sure how to go foreward .. Thank you very much guys for your willing to help.

As I have investigated, yesterday, more deeply, the problem :
1. If I twist the throttle, the vacuum pistons are lifting up just a little bit, but not even at half of their complete stroke => means not enough fuel mixture and from here it comes the less of power of the engine, that I have described in my first post.
2. I took off the pod filter and I have covered the entrance into the carb with my hand => If I let only a small gap between my hand and the carb body and restrict the air flow ...the vacuum piston lift up.

Before to increase the jet size, I'm thinking to put some tape on the pod filters, to restrict the air flow, then make a ride test.

Please tell me your opinion, or correct me if you think I'm wrong.

Thanks
Marcel

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Re: stock carb and pod filters

Post by daves79x »

Marcel:

You have to go up many sizes on the main to get your power back with pods. Don't know what size mains you have, but let's say they're 100. You would need to go up to at least 120 for the bike to run right. That's how much of a difference pods make. One size or two won't make any difference.

Dave

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Re: stock carb and pod filters

Post by marcelm »

daves79x wrote:Marcel:

You have to go up many sizes on the main to get your power back with pods. Don't know what size mains you have, but let's say they're 100. You would need to go up to at least 120 for the bike to run right. That's how much of a difference pods make. One size or two won't make any difference.

Dave
But, the problem is that the vacuum piston is not lifting up, at WOT it's less than half of its normal stroke. With stock airbox vacuum pistons were working well (at WOT they are at maximum upper position)
Even if I put bigger main jet, if the vacuum piston don't lift up, the problem will be the same, ..or ? This is what I don't understand, looks like more an air problem, the air flow/vacuum is not able to lift up the piston ..

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Re: stock carb and pod filters

Post by Gearheadgregg »

the only way the the Vacuum slides will go up is under "Load" that would require watching them on a Dyno under WOT or put a camera on the frame to watch them as you go through the gears, don't beat your self up start with with jetting, My 1978 CB 750 F would not hardly run with the stock air box removed they are already Very Lean from the factory for EPA reasons....My 750 F has stock Air filter and stock 4-1 exhaust and i still increased the Slow jet one step..and shimmed the needle, Cold start up is better and midrange has more punch !

marcelm
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Re: stock carb and pod filters

Post by marcelm »

OK. Thanks guys for the infos!

I will go foreward with the Slow jet and post back here, till ...end of project :)
So that everybody can use this as Leason Learned.

will continue ..

Marcel

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Re: stock carb and pod filters

Post by daves79x »

I'm trying to save you a lot of headaches, Marcel. If you don't go up on the main as I've suggested, you will never get to where you want to be. You're just nibbling around the edges with the 'slow jet', which your bike may not even have. Better yet, find a stock airbox and you'll have a much easier road.

Dave

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Re: stock carb and pod filters

Post by EMS »

daves79x wrote:I'm trying to save you a lot of headaches, Marcel. If you don't go up on the main as I've suggested, you will never get to where you want to be. You're just nibbling around the edges with the 'slow jet', which your bike may not even have. Better yet, find a stock airbox and you'll have a much easier road.

Dave
Yeah, but pods look sooooo much cooler... :mrgreen: :mrgreen:

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Re: stock carb and pod filters

Post by marcelm »

daves79x wrote:I'm trying to save you a lot of headaches, Marcel. If you don't go up on the main as I've suggested, you will never get to where you want to be. You're just nibbling around the edges with the 'slow jet', which your bike may not even have. Better yet, find a stock airbox and you'll have a much easier road.

Dave
Dave, I realy appreciate your help and thank you very much.

I just want to understand what is happening in the carb to chose the best way to go. But, it seems, as you said, there is only one way to go.

I will post the next step ... inside the carb ...:)

Thank you
Marcel

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Re: stock carb and pod filters

Post by EMS »

marcelm wrote: I just want to understand what is happening in the carb to chose the best way to go. Thank you
Marcel
Marcel: The fuel flow through the main jet in a CV carb is controlled by a tapered needle, that is connected to a slide which is raised by a diaphragm against a spring. Movement of the diaphragm relies on vacuum above the diaphragm.
The airbox contributes to the pressure balance in the carburetor.
If you don't have enough negative pressure above the diaphragm, the needle does not rise high enough. You either have to compensate by a significantly larger main jet or shimming (raising) the needle.

marcelm
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Re: stock carb and pod filters

Post by marcelm »

Thanks,

Now I understand deeper ... so, airbox has a direct effect into the vacuum above the diaphragm. And most important, the pods cannot have the same effect .... even I have put some tape to restrict little bit the air flow ..
As instructed, I will increas the jet size and post back here, after that.

Thanks a lot
Marcel

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