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Discussion Starter · #41 ·
Everything you need for that carb, to include tech support is here:

CV Carb Parts
It may be there, but apparently they are having some issues. There is no way to order from them online, and they are not responding to emails. A page says that due to a nationwide outage that the store is closed today. Has stated that for at least a few days now.

Pretty vague.

Very unprofessional, if my opinion counts for anything.... and, yes, I know it doesn't.
 

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Great thread. I have an FXR with a stock 80 in it. Im running a CV40 with the 1/8 hole drilled, lighter spring, 45 slow jet & 170 main. I had 2 shims under the needle clip. Idle screw 2 turns out. Factory exhaust & air cleaner. Ran good but fat IMO especially at idle. I put 155 highway miles on it during a trip & got 31 MPG. Steady cruising at 65-80 MPH. I messed with the idle screw adjustment & as the OP stated it didnt seem to make a hell of a difference & still smelled fat. I dropped the slow jet to a 42 & removed one shim from the needle. I will retest for mileage but during a road test it seemed crisper. Idle doesnt seem as eye burning. Bottom line is that i need an O2 sensor in this to be sure.

One thing i noticed Is that on mine is that much above 950 RPM, some fuel will draw from the needle so be sure that idle speed is kept in check during your adjustments.

Also mabye the experts can help on this, with air cleaner off during adjustments, if throttle is held at say 2500 RPM, i can clearly see fuel being siphoned from the accelerator pump nozzle...???? WTF Its a nice stream too, im holding the throttle dead steady, fuel is being drawn from the needle as it should but also from the accel pump.....if i plug the AP nozzle with my finger the engine sounds to smooth out nicely. How normal is this? Or not!
 

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So with that said, the only time you would play with the needle is if the scooter is fine at low speed, fine WFO, but stumbles or skips in-between.
Great advice, to maximize performance AND fuel mileage an on board air fuel meter would be handy. Probably never equal fuel injection but SO many carb'd harleys are running around pig rich.
 

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Discussion Starter · #44 · (Edited)
Before this thread gets sidetracked, I want to jump back in with a few questions/comments.

I have been away for a bit, working long, long hours, waiting on parts, waiting out the rain (seems like it's been raining for two weeks), etc. I got my layoff from the temp project yesterday though (vacation, woohoo) and am getting back onto my tuning project.

I did finally get the carb off of the manifold. Man, it was on there tight!!

I also am switching to Allen head screws all around, as the Phillips are just to easy to strip the heads on. That is all except the bolt that holds the throttle cable bracket on. Someone here ( thanks @Brand'd ) mentioned using a hex head there, which sounds like a great idea, with that location being so tight to access. My M5 x 10 for that is expected to be delivered tomorrow. It was a tough find in stainless. There was a guy on Flebay selling an Allen head set for the rest of the carb cap/bowls. Not that they were as hard to find, but it was just much simpler going to him for a completed set than it was going to home depot for a couple, and wherever for another, and yet somewhere else for another.

I also found a thread on another forum (fairly old) that has tons of info and tips on tuning the CV. I think the rules here prohibit me from linking to other forums, so I won't. It specifically gave me info on tuning the idle air mixture. I should re-read some of it before starting on this again tomorrow, but one of the general ideas I'm taking away from it is that it is often necessary to use a digital inductive tach to monitor engine rpm at those lower RPMs, rather than listening for the "idle drop". Especially with cam, intake, and exhaust mods. So, I did buy an inductive tach to help me see changes with the idle air mixture screw. I'm sure an A/F monitor could help, but I have not gone that route. There is just to much conflicting info out there for me to know what it should be reading when, so it would likely just confuse me and hinder my efforts.

Between our thread here and the unmentionable one, along with a couple of youtube vids that graphically display the operation of a CV, and Scooter Tramp Scotty's input... I have a much better understanding of how these CVs are supposed to work. There are sometimes things that seem to disagree with each other from the various sources, but then it starts to become clear with input from another source.

My first question, for @Thermodyne is clarifying the "1st hole" that should be uncovered. There seems to be one that is off by itself, directly above the idle mixture screw. This is the one that, I think, is fed by the pilot and adjusted by the idle air mixture screw. This is the one you are referring to as the first hole? Or are you referring to one of the four others that are grouped more tightly together, and kind of offset each other? Then there is one more, not grouped as tightly with the four, but still pretty close, but I would say it is by itself rather than overlapped like the other four. These are the staging holes as I understand it. Also fed by the Pilot Jet. Are you saying that none of those should be uncovered at idle? Or are you considering one of these as the 'first' hole. From what I see, how many of those are uncovered is originally adjusted by the the position of the idle speed screw, prior to any influence of the throttle.

Also, @Thermodyne What exactly are you referring to when you talk about drilling out the throttle plate so that only one hole is uncovered? I must be looking at this from a different perspective than you, as it appears to me that any drilling would only UNcover more holes?
 

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Before this thread gets sidetracked, I want to jump back in with a few questions/comments.

I have been away for a bit, working long, long hours, waiting on parts, waiting out the rain (seems like it's been raining for two weeks), etc. I got my layoff from the temp project yesterday though (vacation, woohoo) and am getting back onto my tuning project.

I did finally get the carb off of the manifold. Man, it was on there tight!!

I also am switching to Allen head screws all around, as the Phillips are just to easy to strip the heads on. That is all except the bolt that holds the throttle cable bracket on. Someone here ( thanks @Brand'd ) mentioned using a hex head there, which sounds like a great idea, with that location being so tight to access. My M5 x 10 for that is expected to be delivered tomorrow. It was a tough find in stainless. There was a guy on Flebay selling an Allen head set for the rest of the carb cap/bowls. Not that they were as hard to find, but it was just much simper going to him for a completed set than it was going to home depot for a couple, and wherever for another, and yet somewhere else for another.

I also found a thread on another forum (fairly old) that has tons of info and tips on tuning the CV. I think the rules here prohibit me from linking to other forums, so I won't. It specifically gave me info on tuning the idle air mixture. I should re-read some of it before starting on this again tomorrow, but one of the general ideas I'm taking away from it is that it is often necessary to use a digital inductive tach to monitor engine rpm at those lower RPMs, rather than listening for the "idle drop". Especially with cam, intake, and exhaust mods. So, I did buy an inductive tach to help me see changes with the idle air mixture screw. I'm sure an A/F monitor could help, but I have not gone that route. There is just to much conflicting info out there for me to know what it should be reading when, it would likely just confuse me and hinder my efforts.

Between our thread here and the unmentionable one, along with a couple of youtube vids that graphically display the operation of a CV, and Scooter Tramp Scotty's input... I have a much better understanding of how these CVs are supposed to work. There are sometimes things that seem to disagree with each other from the various sources, but then it starts to become clear with input from another source.

My first question, for @Thermodyne is clarifying the "1st hole" that should be uncovered. There seems to be one that is off by itself, directly above the idle mixture screw. This is the one that, I think, is fed by the pilot and adjusted by the idle air mixture screw. This is the one you are referring to as the first hole? Or are you referring to one of the four others that are grouped more tightly together, and kind of offset each other? Then there is one more, not grouped as tightly with the four, but still pretty close, but I would say it is by itself rather than overlapped like the other four. These are the staging holes as I understand it. Also fed by the Pilot Jet. Are you saying that none of those should be uncovered at idle? Or are you considering one of these as the 'first' hole. From what I see, how many of those are uncovered is originally adjusted by the the position of the idle speed screw, prior to any influence of the throttle.

Also, @Thermodyne What exactly are you referring to when you talk about drilling out the throttle plate so that only one hole is uncovered? I must be looking at this from a different perspective than you, as it appears to me that any drilling would only UNcover more holes?
All of those little holes are metered by the slow (pilet) jet. The first one, over the idle mix needle, is the idle port. If you look through the hole were the idle needle is, you are looking through that port.

At idle, the throttle blade must not be open so far as to uncover and draw fuel out of the second hole. If it does, you loose the ability to adjust idle mixture.

The little hole in the pictured throttle blade is an idle air bypass. It gives the motor more air, without adding open angle to the throttle blade. So the throttle can be closed a little, to cover the second transfer port.

269579


Adding those holes to blank throttle blades was tuning black magic back in the late 60's early 70's

269580
 

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Discussion Starter · #46 ·
All of those little holes are metered by the slow (pilet) jet. The first one, over the idle mix needle, is the idle port. If you look through the hole were the idle needle is, you are looking through that port.

At idle, the throttle blade must not be open so far as to uncover and draw fuel out of the second hole. If it does, you loose the ability to adjust idle mixture.

The little hole in the pictured throttle blade is an idle air bypass. It gives the motor more air, without adding open angle to the throttle blade. So the throttle can be closed a little, to cover the second transfer port.

View attachment 269579

Adding those holes to blank throttle blades was tuning black magic back in the late 60's early 70's

View attachment 269580
That is what I was thinking, on the holes in the body. Thanks for confirming that I was following you and the other info sources correctly.

WOW!!! This drilling you show here looks to be a pretty extreme move.
 

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@Thermodyne Any thoughts on the siphoning of fuel from the accelerator pump snout off idle?
@journeymanjohn I had read & read & re read the manual trying to figure out why i couldnt stall the bike with the idle screw. Someone had been in my carb before & drilled the slide & i thought mabye some other passageway was modified, i looked at all the transfer holes & thought mabye something was added but there wasnt. Like you said when you research & stare at enough pictures things become clearer. When my bike is at 850-900 the one lonely transfer port is exposed (engine side) along with the idle mix port. If i close the blade anymore in attempt to block the one transfer port hole it just plain will not idle....i had the carb off many many times thinking it through. Good luck!
 

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Discussion Starter · #48 ·
@Thermodyne Any thoughts on the siphoning of fuel from the accelerator pump snout off idle?
@journeymanjohn I had read & read & re read the manual trying to figure out why i couldnt stall the bike with the idle screw. Someone had been in my carb before & drilled the slide & i thought mabye some other passageway was modified, i looked at all the transfer holes & thought mabye something was added but there wasnt. Like you said when you research & stare at enough pictures things become clearer. When my bike is at 850-900 the one lonely transfer port is exposed (engine side) along with the idle mix port. If i close the blade anymore in attempt to block the one transfer port hole it just plain will not idle....i had the carb off many many times thinking it through. Good luck!
I want to say that upon pulling my carb, the idle mixture port was exposed, and maybe the first one or one and a half transport holes. That is why I was wanting confirmation from @Thermodyne that none of the transfer ports were supposed to be exposed at idle, and only the idle air mixture screw/port should be in use at idle. I'm pretty sure that is what he said, so am going to experiment some today.

I really don't like the idea of drilling out the throttle plate. It seems like it probably sounds easier than it is. I mean... choosing the size of the bit, where exactly to drill, etc. It seems to me that drilling that MAY be something for the drag strip rather than for the street. I'm just learning and really don't know though. Either way, I expect drilling that plate will be a last resort for me though.
 

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That is what I was thinking, on the holes in the body. Thanks for confirming that I was following you and the other info sources correctly.

WOW!!! This drilling you show here looks to be a pretty extreme move.
Na, carbs are pretty simple. You just need to be patient and take your time. If the math says you need a .200 inch bypass, drill a .100th and see what it does. Then enlarge it a little at a time. Back when we did a lot of this stuff, it wasn't really a big deal. If you made a mistake, you could just buy a new blade and start over.
 

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Discussion Starter · #51 ·
Bad or missing check valve.
I'm wondering if a bad check valve might be contributing to my issues.

I'm getting a slow leak from the accelerator pump standpipe port, which allows fuel to slowly accumulate at the air intake ports to the left of it, at idle. It could be worse at throttle, but I can't really see it while riding to check.

If I cover the port with my finger, the accumulation/leak stops. Uncover, and it begins again.

I had a spare bowl with standpipe available, so moved all my new accelerator pump parts to it an installed. Still I have the leak. So I either have a bad check valve on both, I've missed something somewhere else, or they all do this.

I did set the float level correctly.

I did install the o ring/ diaphragm, and spring correctly in the accelerator pump.

What else could I be overlooking?

And yes, I asked this in the carb forum, but there has been little response, and it seems the FXR guys are more willing to help other FXR guys, so I am continuing the question here.
 

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I'm wondering if a bad check valve might be contributing to my issues.

I'm getting a slow leak from the accelerator pump standpipe port, which allows fuel to slowly accumulate at the air intake ports to the left of it, at idle. It could be worse at throttle, but I can't really see it while riding to check.

If I cover the port with my finger, the accumulation/leak stops. Uncover, and it begins again.

I had a spare bowl with standpipe available, so moved all my new accelerator pump parts to it an installed. Still I have the leak. So I either have a bad check valve on both, I've missed something somewhere else, or they all do this.

I did set the float level correctly.

I did install the o ring/ diaphragm, and spring correctly in the accelerator pump.

What else could I be overlooking?

And yes, I asked this in the carb forum, but there has been little response, and it seems the FXR guys are more willing to help other FXR guys, so I am continuing the question here.
Only cost ya $15 to find out.

Check Valve Upgrade
 

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Discussion Starter · #54 · (Edited)
Am getting frustrated. I've got it installed but get no output.

Dropped the ball in first, then the spring. Was no need to drill the housing, as it pressed in easily enough with a c clamp. Snug, but nothing extreme.

Yes I've got the other accelerator pump components correct.

Is installed with the pushrod, but no output.

Checking manually, it seems to be directing fuel back inti the bowl, rather than up and out the nozzle.
 

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Checking manually, it seems to be directing fuel back inti the bowl, rather than up and out the nozzle.
The only thing that could be is the ball check.

Sent from my SM-G965U using Tapatalk
 

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So it went in the hole as ball - spring- nozzle? And you mad sure the nozzle was clear? And the oil check valve is on your bench?

All I got is take it apart and see if you can blow compressed air through it.
 

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Discussion Starter · #58 ·
So it went in the hole as ball - spring- nozzle? And you mad sure the nozzle was clear? And the oil check valve is on your bench?

All I got is take it apart and see if you can blow compressed air through it.
If "oil" check valve is meant to be "old", then yes. Oddly, there was no spring in the old one, just the 4 sided needle one (kinda like the fuel float needle, but smaller).

If I pump the throttle hard a few times, I'll get a little squirt thru it on maybe the third pump. Like it has to build up pressure to overcome the spring tension.

I read on another forum where a guy had the same issue and ended up trying various combinations of the original valve combined with either the spring or ball from the new kit. He ended up, suposedly, without a spring, but used the original needle with the ball as a weight. I tried that...... ended up with a bunch of fuel dripping from the carb.

I just don't have the patience to try to tune a check valve spring. Am not sure what to do. Maybe just run it as plugged with a sportster needle designed for the carbs without an accelerator pump.
 

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Discussion Starter · #60 ·
I have no idea what's going on with that carb. But I know how to fix it once and for all.

Boyesen
I thought you were gonna link a Mikuni.

Although that looks nice, my first thought is, "Where is the overflow?".

I've actually made an appointment with a mechanic, as I'm wasting too much valuable riding time dicking around with this. Ya, I wish I coulda learned to tune it myself, but I just don't seem any closer, and that's after buying and installing jets, and o rings, and rebuild kits, etc. Along with hours of reading how to do it, and fiddling with it, and cussing it.

I don't imagine throwing more money at new fangled parts will help any. It sure hasn't helped with the last purchase.... well it stopped the leaking, I guess, at the expense of stopping the flow entirely

I think one (at least I do) needs to be "shown" how to do this properly, rather than trying to learn it by reading.
 
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