Vtx Carburetor Guide
Fast Moving and. Carburetor and Fuel Systems. Part No.: 36634 (740061C). Description: Pre-Cleaner.
. Any time a change is made to the air intake/flow, fuel delivery, and or exhaust rejetting and carb tuning may be in order, usually these are changed with aftermarket or modified exhaust and intake. The exhuast may only require a simple fuel mixture screw adjustment on the carb, but an aftermarket intake or a modified stock intake requires more fuel to match the increased airflow which can only be corrected with a carb rejet. Pulling the carbs apart for a rejet, cleaning, or rebuild is something that gets easier the more you do it, and may seem scary or difficult at first but is a necessary task for keeping your VT750 tuned properly.
Below are a few pictures for reference to help you when working with the particular carburetor setup on your VT750. All CV carbs follow the same theory to operate. There is a pilot jet, a main jet, a needle, a slide, and a mixture screw. See the picture below to understand the parts and components of all CV Carbs including how fuel is delivered at idle versus at throttle. Based on throttle position fuel id delivered from different circuits within the carb. See the Chart Below for reference to see how each throttle position leads to fuel delivery overlap. Also see the Jet Needle diagrram which explains the needle clip position effect on fuel delivery, as well as the position of the needle at various throttle positions: Below are exploded diagrams of both the DC Spirit / CD Ace and the C2 Spirit / C Aero carb(s) included for reference pulled from the factory service manual.
This will help you understand the parts of your carburetors as well as your intake manifold and air box. VT750C2 Spirit and VT750C Aero If you have a single carburetor model VT750 pulling the carb for cleaning or a rejet is a fairly easy task requiring you to meerly disassemble and remove the intake, then disconnect the vacuum hoses and fuel line, and finally loosening the clams so you can remove the carb. From there the build will be similar to the pictures below of a VT750DC carb except there is only one of them.
Carburetor Diagram (right click images and choose to open in a new tab or window to see a larger version) for reference: Intake Manifold and Airbox Assembly diagrams for reference: VT750DC/CD If you have a dual carb setup model VT750 pulling the carbs is a little bit more difficult and requires a little finesse as it is a tight fit with limited space to operate in between the frame and the engine where the carbs sit. Diagram of the dual carb setup of the DC Spirt and ACE (right click images and choose to open in a new tab or window to see a larger version) for reference: The stock airboxes will differ between the ACE and the Spirit. Below is the DC Spirt Airbox for reference: VT750DC Carb Removal Summary The theory and similarities in steps between the VT750DC and other VT750 bikes are incredibly similar. The biggest differences are accessing and removing the carbs between models.
The single carb models have a more accessible carburetor while the dual carb models require a bit more effort to rejet or clean. Remove the seat. Remove the Gas Tank by unbolting and removing the speedometer, unbolting the underseat gas tank bolt, disconnecting the petcock fuel line (make sure petcock is set to off), disconnecting the right side rear air/overflow line, then sliding the tank back so it becomes free to be removed and placed somewhere safe. Remove the stock airbox or your aftermarket air intake by unbolting it, and then unclamping any clamps. On the other side of the bike remove the carb cover.
4.Remove the upper intake manifold by unscrewing the clamp screws and disconnecting the airbox vacuum line. Once the screws are loosened and the vacuum hose disconnected you will need to pop the intake boots off of the tops of the carbs and then slowly remove the airbox assembly turning and twisting it slightly when necessary to get it completely off of the bike. To make more room remove some of the decorative engine covers. Also removing the front cylinder coil from the frame also makes more room to work with. Remove any other items you feel may be in the way. Detach/unbolt the choke cable from the engine. Unclamp and disconnect the two breather tubes from each carb and disconnect the two throttle cables.
2004 softail deuce owners manual. The pull cable should be removed first and then the 2nd push cable can be removed to make it easier. Disconnect the fuel line from in between the carbs. This is tricky and may require some needle nose pliers to unclamp and disconnect the hose. Loosen the clamps on the carb boots connecting the carburetors to the engine. On the rear carb just loosen the top clamp that connects the boot to the carb. On the front carb loosen both the top and bottom clamps because this boot will need to be removed in order to get the carb assembly out.
This is also a good time to remove the carb fuel heater wires form the terminals on the bottom of each carb. You will need to wiggle and pull the carbs to unseat them from the rubber boots. You may even need to utilize a flat head screwdriver to gently pry and separate them from the boots. Once the carbs have been unseated and separated from the front and rear cylinder boots remove the front boot from the bike completely and set it aside.
In order to get the carbs out you will need to lift and rotate them towards the front of the bike as you are sliding them out towards the right side of the engine. Gently maneuver the carbs around wires, hoses, etc. Once removed you will need to drain the fuel from each carb float bowl using the fuel drain screws to prevent spilling gas everywhere. Also rotate the carbs and pour out any remaining fuel from where the fuel line was disconnected.
Find an area you can work comfortably. Outdoors, I often utilize the bottom of a 5 gallon bucket as a simple 'work bench' setup. To change the jets for a rejet or to access the floats to change out the float valve when performing a carb rebuild you will need to turn the carbs upside down working on one at a time to access the float bowl. Stock there are 4 phillips head screws holding each float boal on. If you buy a Factory Pro jet kit it comes with stainless allen head replacement screws that are fantastic to prevent stripping.
Remove the 4 screws and then remove the bottom cover to expose the pilot and main jets as well as the floats. This is the Main Jet: This is the Pilot or Idle Jet: Replace each jet with the new jet or remove the jets to clean them and then put them back in place. Note that the carb with the throttle cabe assembly is the rear cylinder carb so it will take the bigger jet due to that cylinder naturally running warmer in a dual carb setup. Reassemble when done. To access the needle flip the carb over and remove 3 of the four screws from the vacuum side cover on the carb.
THERE IS A SPRING INSIDE, be careful not to loose it. Hold the cover in place as you remove the last screw and then slowly lift it once removed. Slowly lifting the cover relieving the tension of the spring: The cover removed: 16. Pull the slide out careful not to damage the rubber diaphragm.
Looking at the bottom you can see a plastic piece with a phillips screw head. Turn this to unlock it.
You can then remove the plastic piece with a tiny spring attached (do not loose) and then the needle. The factory needle is not adjustable, any jet kit will come with a replacement need that you can adjust by moving a clip. Once needles are changed out you will need to insert the plastic piece into the slide and lock it back into place so that the needle is now spring loaded. I find it is easiest to hold the needle in place with the slide upside down and then use my finger to lift the needle cover into place.
Once I have made it to the top, I flip the slide over and then use a screwdriver to lock it in place. Insert the slide back into the carb and gently re-seat the diaphragm the only way it will fit. Replace the spring and then gently put the cover back in place holding it while inserting all four screws.
Now is a good time to adjust the on each carb. The default setting is 2.5 turns out. You can go as high as 4 turns out to richen the mixture, or less than 2.5 to make it more lean. Once installed on the bike, you may need to pull the air box and carb side cover to adjust this further.
Once both carbs have been rejetted and reassembled it is time to put everything back onto the bike and then reattach all vacuum hoses, fuel line, intake manifold etc. In reverse order. You will need to insert the carbs at the same angle they were removed and then slowly rotate so they line up with the engine intake boots. Re-seat the front cylinder intake boot, then align both carbs so that are ready to be wiggled and pushed into both boots. This can be tricky to get both carbs to seat all the way ensuring the best seal. I have found that a small piece of 2x4 to gently push each carb all the way into the boot is a great tool. Prior to being able to use the 2x4 you have to have begun the seat by standing over the bike, and holding onto both carbs and gently rocking, wiggling, and pushing them into both engine intake boots.
Once the carbs are mounted back to the engine, tighten all boot clamps to lock the carbs in place. Then you can begin to reassemble everything in reverse order to removing it. Be sure to get a good seal on the intake tubes to prevent air leaks which can cause problems. Rejetting and tuning a motorcycle is a painstaking process that is often never perfect the first time, therefore, you may find yourself removing and reinstalling the carbs to change the jetting numerous times until you get it right. The more you do it the easier and quicker it becomes.
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Unregistered. You may have just purchased a new exhaust and/or air intake and are wondering how you should 'tune' the carburetor. First off if you just 'fire the bike up' with the new parts installed, THE BIKE WILL RUN. Depending on how 'free flowing' the aftermarket parts are that you installed the bike will run anywhere from 'pretty good' to 'pretty lean and very nervous', but it will run. So now the bike has to be TUNED. The easiest, least expensive, quickest, most predictable and fool proof method of rapidly tuning it would be to ADJUST the stock parts that are already in the carb. Some people venturing into the 'mods' game want to do them all at the same time.
This has OFTEN been proven to cause problems for the neuvo MC 'wrench'. DO NOT remove the PAIR system during the same session that you are tuning the carb., it is common while working with the PAIR removal to 'miss' something in the process and have an open vacuum line or 'other' air leak. Many who have done both of these mods simultaneously have ended up fiddling with their carb for days/weeks on end chasing their tails looking for what went wrong with the carb tuning while all the time it was an error in the PAIR system removal. There have been some war stories spread about how difficult it is to tune a carburetor. The most difficult part of tuning a carb on a VTX 1300 is removing the fuel tank for the first time and figuring out how to disconnect the electrical connectors under the tank. So, what comes first eh? REMOVE THE FUEL TANK.
Follow the directions in the service manual. Everyone should have a service manual. The money you save in THIS carb tuning process alone will pay for a service manual. The money you save doing your first valve adjust using the service manual would buy a nice set of tools that can be used in OTHER money savings projects. EVERYONE needs a service manual. Next REMOVE the air filter and backing plate. I won't 'get into' hooking and unhooking the hoses attached behind the backing plate, they are pretty straight forward and will become part of your 'learning process' of the easiest ways to rapidly navigate through assembly/disassembly.
NOW the carburetor is EXPOSED. Sitting on top of the carb you will see the vacuum chamber cover. Remove the cover and then remove the compression spring under the cover. Now gently grab the diaphragm/piston rubber and pull it out. The Vacuum piston (slider piston is what most old timers call it) is attached to the diaphram and the whole package will come out with it.
Vtx Carburetor Guides
YOU ARE ALMOST DONE AND READY TO PUT THINGS BACK TOGETHER. See, I told you. Removing the tank was the most difficult part of the process.
Unscrewing the 4 vacuum chamber cover screws was no big deal, right? Look at the slider piston and you will see a tappered 'needle' sticking out the bottom of it, that is the jet needle. Look inside the slider piston and you will see the Jet needle holder. The jet needle holder is next to be removed. You will see in the center of the holder it will accept a Phillips head screwdriver which can be used to 'unscrew' the cam locks, BUT the 'best' method is to use a small socket and fit over the head of the 'cap' and unscrew the cap. I'm thinking it's an 8mm.
Difficult to recall those things sometimes at my age, but you'll discover the correct size. Twist the cap counter clockwise just as tho you were unscrewing any 'standard' nut or bolt and you will feel a 'pop' after making a very small motion. That was the cams unlocking. The cap can now be removed, it is 'unlocked'. Under the needle holder cap there is a small spring 'screwed' onto a plastic 'tit' protruding from the bottom of the cap. Well actually the 'tit' has no threads, so the spring is not 'screwed' on, but consider it so.
Instead of 'pulling' the spring off and distorting it's shape, give a 'light force' pull on the spring while unscrewing it from the 'tit' and set the spring aside. The 'tit' does not protrude very far, but it must be 'trimmed' for 'heavy breather' mods, so go ahead and trim it now even if you are doing a 'light breather' tune. Take some TOENAIL clippers (those are the large ones, not to be confused with fingernail clippers) and 'snip' the 'tit' in half.
That should be enough for heightened needle raising and still provides enough remaining 'tit' for the small spring to be screwed back onto. Set the needle holder cap aside.
Remove the needle from the slider piston. Place your shims into the needle 'point' and make sure they slide all the way to the needle head with the washer/shim hole big enough so free movement along the needle is achieved. Hold the slider piston in your left hand and turn it at an upwards angle and insert the needle INTO the slider piston hole, passing through the CENTER hole in the slider piston (this process will not work for 'left handers', you will have to purchase a Yamaha carburetor).
Face the slider piston DOWN and the needle should be hanging from the bottom of the slider piston and sitting 'on' the shims/washers INSIDE the piston. Take the SMALL spring that was unscrewed from the underside of the needle holder cap and screw it back onto the shortened 'tit' under the needle holder. Put the needle holder cap into the slider piston with the small needle spring tensioner sitting on top of the needle head.
(If the 8mm socket is placed onto the top of the needle holder cap 'nut' the tension is enough to hold the cap. The needle cap holder can be easily inserted into the slider piston with this method utilizing a socket extender). Twist the needle holder cap clockwise (even the left handers) as tho 'tightening' and you will feel the cams lock into place. That's it, the needle holder is locked. If enough of the 'tit' was trimmed, this should be a relatively easy 'twist'. Hold the slider piston with one hand and 'wiggle' the needle with the fingers on the other hand.
The needle should 'wiggle' (movement), this assures true alignment into the emulsion tube. If the needle is 'stiff' and won't 'wiggle', then the 'tit' was not trimmed enough. Go back and trim more from the tit until free needle movement is achieved. (If you are using a DJ needle, the tit must also be trimmed for the same reasons) Replace the diaphragm spring onto the needle holder cap and replace the vacuum chamber cover. NOTE: There is an irregular 'shape' in the cap that must be matched to it's mating surface when remounting, this is what the manual calls the 'tab and air passages'. 'Snug' the vacuum cap screws and continue reassembly.
Under the carb is the A/F screw (see manual), the stock screw head requires a 'D' type tool for adjustment. If you slightly dent the end of an empty.22 shell casing, this will fit into the hole and can be used to unscrew the 'D' screw. Take the 'D' screw completely OUT. On the top of the 'D' screw head will be a spring followed by a washer and then an 'O' ring.
Save these parts and reassemble in the same order when putting the A/F screw back in. While the A/F screw is OUT, use a hacksaw blade or some similar device to cut a thin channel into the head of the top of the 'D' screw. This slot or channel should be wide enough for a flathead screwdriver blade to fit into for A/F adjustment. Once the slot has be cut into the screw/needle head and the screwdriver blade fits, replace the spring/washer and 'O' ring and replace the A/F needle into the needle jet hole and screw IN. Take your screw driver and screw in the needle until it LIGHTLY seats or stops turning. Don't get anal about this and over tighten or damage could be caused to the needle/jet mating surfaces. If you error on 'seating', error on the LOOSE side, final tuning will not be affected by a minute discrepancy of 'seating' at this stage of tuning.
Turn the A/F screw OUT 2 1/2 turns with the screwdriver. Reassemble the airbox and fuel tank. Before firing the engine, look at the CHOKE KNOB and push it in all the way. Any flexing of the carb while working on it will flex the choke cable and pull the choke out. It will not run properly with the choke pulled out AT ALL and final tuning cannot be achieved. Shim heights: 'Open' style airbox and aftermarket 'free flow' pipes. Usually about 2or 3 shims.
Airbox flowing more air than stock design, but not in the 'heavy breathing' class and/or pipes either free flow or somewhat restricted. Usually about 1or 2 shims Stock airbox (K&N filter in stock box is still 'stock') and after market pipes. Usually 0 or 1 shims Stock airbox and stock pipes. Tune the A/F screw for maximum performance. A/F settings: While determining proper main jet circuit settings the A/F screw should be set at 2 1/2 turns and NO adjustments made to it until the high speed circuit has been properly tuned - Turning the screw IN leans the mixture.
Turning the screw OUT richens the mixture - Fine tuning the A/F screw should be done in no more than 1/8 turn increments. Very fine tuning will be even less.
It is highly recommended to 'slot' the 'D' screw and tune the A/F screw with a screw driver. A 90 degree drive is useful if you have one. SLIDER PISTON SPRING: That's what I call the big spring directly under the vacuum cap and sitting on the needle holder cap.
Most tuners that have springs of the type found in the VTX carb shorten the spring for faster throttle response. This is not necessary for the bike to operate, but you will shorten the response time if you shorten it. I would not recommend shortening it past 5 1/16'. That is the lenght of the shorter DJ kit supplied spring and is a proven entity. The Keihin spring is of slightly larger diameter wire so a 'safe' fudge factor is built in if you cut it to 5 1/16', most do. You can cut it less than that if you are nervous, but you shouldn't have any problems with 5 1/16'. Place the cut end DOWN into the slider piston and resting on the needle cap.
Uncut end UP against the vacuum cover. That is the 'common' practice (and no bannanas on boats either). Most any needle design or jet design will work with the Keihin carb as long as they are set to the proper height and have the correct diameter. It has been my findings that the stock Keihin needle and jet work more 'smoothly' if properly shimmed than some other designs because of the needle design and large diameter jet size. The Keihin design is just more forgiving and not as 'touchy' as some other designs and need I say you are not required to remove the float bowl cover to change main jet sizes?
The Keihin 195 main jet suits most all purposes. If you require more than that you are past the 'beginning' tuner stages and in that case you might think about a Keihin 200 or 205 (DJ equivalents of 213 and 218). I don't think more than a 205(/218) would be required by anyone unless cam, piston, valve and porting changes have been made. In which case I would like to communicate with you on your engine mods and findings.
You most likely won't require any 'advice', but I would like to hear about extensive engine mods. Mine will retain the stock configuration.
I have a 1200cc street fighter for speed. Have fun and if I am 'not around' to answer any possible questions (I have a somewhat irregular schedule at times), I would recommend asking Retro Rich. He has a mechanical mind and a healthy grasp on the tuning philosophy. Radio Shack Shims: Radio Shack Part # 64-3022 Package of 100 Steel Flat Washers 20 each: #2, #4, #6, #8, #10 They are in the Hardware section of the store - In the plastic pull out trays that are divided into sections.
Looking at the bag I would say we are using the #4 washers. Anyway it is the second from the smallest. We 'miched' em several years ago and can't recall, they are like 0.019 or 0.020 or pretty close to that neighborhood. Oh yea, they now cost $1.99/pkg - inflation. Any 'washer/shim' of similar thickness (0.020') with a hole big enough for the needle to comfortably slide through and small enough for the needle head to sit on will work just fine. I could write another entire page on 'tuning techniques', but it has already been done in what I consider a comprehensive and accurate manner.
Use it as your tuning Bible - Factory Pro Don - AKA 'Scars' Last edited by Big-X; at 02:17 PM. I have a 2005 1300r in the shop and i can't figure it out. It idles fine, even revs up fine. When i put it in gear and throttle up it falls on its face. The bike has a hypercharger and v&h longshots. I called kury akyn and jetted to their specs.any help would be appriciated. ScottForget the Kuryakyn jets.they're all wrong.
You'd be better off with stock carb parts. Just set the A/F at 2-1/2 out, and stick a couple (2-3) shims under the needle. Stock slow - 55 Stock main - 195 Stock needle If you want to get fancy - you can experiment with larger Keihin jets.but that setup will be a much better starting point.
I have a 2005 1300r in the shop and i can't figure it out. It idles fine, even revs up fine. When i put it in gear and throttle up it falls on its face. The bike has a hypercharger and v&h longshots. I called kury akyn and jetted to their specs.any help would be appriciated.
Scott Howdy Kuryaken to prevent being sued seems to jet every thing fat. We could not get over 40 MPH and found out that we did not have the seal on the slider installed correctly. Then it did all kinds of weird stuff but would ran better. So off to the Honda shop and found out that the choke was stuck in the closed position. I assume that my partner jamed the cable when he took it off or put it on. Got that fixed, leaned the jetting ( we are at 6000 ft above sea level) runs like an ape about to get raped.
I had already had the dealer put a dynojet stage 1 in the bike with my pipes. After putting on the Hypercharger I figured it was a simple a/f adjustment. Nope and the dealer swapped out the pilot to a 62, told me to pick it up and it ran great. I hit the throttle and all sorts of hesitation and it fell over on its face at wide open throttle.
To avoid more charges I decided to use the garage and thousands of dollars of tools where I store it, at my buddies. I now understand and have no fear. I actually put back in a 185 at 2 1/2 turns and clip 4 with one shim and it runs excellent. It does feel like it has a slight flat spot. I am going to a stage 3 kit but wanted to have a base to be able to go back to if I ran into trouble.