carbs = brick wall

[Number Johnny6]

I have to say you guys seem to really know your Xs. I am at a brick wall with my carbs.



(PS - I read every post in the carbs category)

1981 X, 20,000 miles, 15 yrs ago it was set up w/ Kerker 6 - 2 and Dyno Jet kit. I never did get it tuned right before it went into storage. Just pulled it out sent it to a shop, now has cleaned carbs, Mac 6 - 2 and K+N single filter. They were supposed to tune the carbs, but they just put it back to where I started, (bleep), and it runs now just like it did then. It runs lean in the 1/4 throttle range, higher up its great. The tuning process was to lift the needles to the last (richest) notch. At every notch it was stronger and more responsive in the 1/4 throttle range. On the last notch (richest) something else (bad) happened, subtle, I can't quite quantify/remember it, (it was 15 years ago). I theorize that the needle has been lifted above its adjustment range.



So, where do I go next ???



SOME THOUGHTS.

I can't really see another bike I would prefer, so I'm stuck with the X.

I wonder if I have a stage 1 kit and need a different one? I called Dyno Jet Research, but I'm sure the fellow that tried to answer my questions was the janitor.

A very knowledgeable fellow at motorcyclecarbs.com was not particularly familiar with the Dyno Jet but suggested the best thing was to start with stock needles, as many aftermarket needles are too hard and not smooth enough that they wear out the jets.

Maybe I should try to find a set of 82 carbs which have a replaceable secondary?



I hope you guys can help me climb over the brick wall. I would find a good shop and pay them to do it, or go to one of your rallies, but I'm in Alberta Canada; the only thing I'm close to is THE CALGARY FLAMES and THE EDMONTON OILERS!

[Mike Nixon]

Okay, I will bite, although I am by no means the best around here on jetting carburetors. :) I think you are on the right track re getting things back to stock. The K&N replacement filter is a good one, but it doesn't really change things that much. Ditto the exhaust. Other than a good cleaning and inspection, in my opinion the only thing the carbs should need is the mixture screws turned out past the stock setting. (There is enough extra main jet already in the carb to handle the exhaust and filter.) Get back to us and we'll try to help...

[Number Johnny6]

The easiest/cheapest option would be to proceed from the current setup; I would not have to deal with all the issues of an unknown set of carbs, so I am going to explore that first. I'm a little surprised you think the stock setup could handle the headers; it was a long time ago, I have been assuming I got the kit because I had to. I certainly was not trying to hop it up - I was just tired of driving a sewing machine.



The fellow that installed them thought there was no chance they could be too lean. Comments in posts in this section say Dyno Jet's recommended setup is too rich. Your assessment was that stock carbs should handle the headers. Everything indicates that the carb kit should not be too lean. I can think of only 3 logical paths. 1> I've got it wrong/I'm doing it wrong, 2> there is something wrong with the current setup, 3> the installer put some incorrect parts in it.



I raced motocross, did all my own maintainance, and I think I have enough experience to tell lean from rich. The current setup seems to run smooth and responsive except in the quarter throttle range. But I don't know enough about carbs or this kit to decide what to start checking.



One thought was that the carb balance was grossly out. (This is my theorizing, not based upon knowledge) When the throttle is almost closed some carbs could be lean and some normal. At higher rpms when the throttle is further open, there would be less affect. I checked the butterflys visually, and they are not grossly out.

The older Xs were louder, sounded like motorcycles. The 82 sounded like a sewing machine. A carb kit for an 82, which has a much more restrictive exhaust system, would have to provide a richer mix than for a 79. Maybe the installer put a kit for a 79 model in there?



Your last suggestion was to adjust the air/fuel mixture screws. I have done that again and again; it doesn't do the trick.



I did learn some things about carbs. Check out this diagram http://www.motorcyclecarbs.com/keihin/j ... keihin.htm



Hey, should I be posting this to the main board ??

[broook]

Hey, should I be posting this to the main board ??

Welcome to the board. Sorry I can`t answer your carb questions but you are posting on the correct part of the board. Good luck with your project.

[Jeff Bennetts]

johnny6,

Well you only got a couple replies but you only need one good one to get help and Mike Nixon is about the best on this board when it comes to carbs, he just published a how to clean your CBX carbs instructional booklet, it sells for $29.00 and $4 handling, you may want to buy it and clean the carbs yourself.



He's correct about the Dyno Jet kit, its too rich the full range of the setup, clean stock carbs with a good accel pump with the stock needles shimmed 25 thousand is a good setup for a K&N and pipe.



The CBX is rich enough stock on top but too lean off idle, with these simple changes you'll gain the richness and eliminate the off idle stumble.



I do carb rebuilds but I'm swamped and can not get to it for a couple months, it will only take you a couple days to pull off your carbs and clean them per Mike Nixons manual, you can PM him from his reply to your question and order the booklet .



jeff

[cbx6ss]

I tried my best to find needle shimming details on the site, unsuccessfully. I would be grateful if someone would provide a description of the procedure for shimming slide needles and leads for shim sources to improve throttle response.

TIA

Brad

[cbxtacy]

The elusive shim kit for CBX carb needles. I get my shims from Radio Shack. They have a small bag of small washers of various sizes and there's enough to do a set of CBX carbs in it. I don't remember the part number but I'm going there later today and will get a bag and will post the number. That's how I've always shimmed up my carb needles.

[daves79x]

Guys:

I've found that the washers that are on the pilot screws (the tiny aluminum ones on top of the spring) measure .021 inch and work perfectly for shimming the needles. They are the correct ID and the OD is perfect. Too many 3mm washers you buy have too large an OD and will hold the needle up in its seat. I rebuild lots of carbs and have saved all those old washers for that purpose. If you're buying 3mm washers, make SURE the OD is not larger than the head of the needle!

Keep in mind you have to 'pocket' the aluminum hold-down screw to regain enough room for the needle to float after shimming. You can also use teflon thread tape as 'interference' on the threads and only screw the caps down as far as you need to. Thanks Jeff Bennets for that!



Dave

[Mike Nixon]

I'm a little surprised you think the stock setup could handle the headers...

Well, I trust by now you have got this thing handled. Lot of knowledgeable people here. I thought however for the record I would respond to this comment. The best way is to provide the following link.



http://www.motorcycleproject.com/motorc ... tting.html



:)

[Mike Cecchini]

The elusive shim kit for CBX carb needles. I get my shims from Radio Shack. They have a small bag of small washers of various sizes and there's enough to do a set of CBX carbs in it. I don't remember the part number but I'm going there later today and will get a bag and will post the number. That's how I've always shimmed up my carb needles.

I know this is a long time coming.....but I'm going over two sets of carbs that I'm shimming the needles for this %&^%$ ethanol gasoline we have to deal with.

The Radio Shack package of small washers (100 in the kit) is catalog #64-3022 for $1.99. This is March 2011 for future reference.

Thanks.......Mike

[CopperCollar]

Interesting, What are the symptoms of a CBX carb running an ethanol mix of fuel? Is it boggy on the bottom end? Will shimming the needle help? Gotta ask as I have an inquiring mind when it comes to fuels and carbs.

Mike

[Mike Cecchini]

Considering the X carbs are pretty much set on the edge of lean-ness at the bottom and first 30% of the carb's range......right where the EPA tests them......then the rest of the carb's range is set nicely for the engine, the main effect of 10% ethanol is to further lean-out the overall mixture from top to bottom because ethanol has less energy than straight gasoline. Sooooo what happens is the lean areas become 10% leaner.......or 15% leaner.......or 20% leaner depending on the percentage of ethanol is in the gas you get.

Our government says we get 10%--15% ethanol......but recent tests across America by BMW owners nation-wide as reported in the BMWCCA magazine "Roundel' last month show some areas getting 18%--20% ethanol.......which means our fuel mixture is 18%--20% leaner. Many fuel injection systems can self-adjust for this.......but carburetors cannot........therefore very very lean mixtures result in those rpm areas where the fuel mixture is already on the edge....... like CBX carburetors.

The bottom line is the CBX engine will not run nicely at idle or low throttle positions. This can be compensated by 1.0 to 1.5 turns FURTHER out on your pilot jet screw adjustors and raising the needles by .020" to .025". The rest of the carb adjustment area (main jet) should be fine if your X is bone stock with the air-box and mufflers just like they left the factory.

My X has no airbox and I run three K&N filters http://tinyurl.com/4dxo883 which makes it a joy to see what's going on with my carbs and take them on/off in 10 mins. But because there's no airbox and I run PipeMaster's 6/6 exhaust http://www.pipemasters.net/cbx6.html I have to make major jumps in carb settings. The pilots have been opened up a couple of thousandths, the needles have been raised .040" and the main jets have gone from 110's to 120's with wonderful results...... but I've only lost 3 mpg over all for 39 mpg vs my buddy's 41 mpg on a 1000 mile run we did last year.

[markdam]

george you are my hero!!!!!!!!!!!!!!!!!!!!!!!