Backfiring thru carb

The EZ-Just should be slightly snug with tension against it from the spring inside. If it still seems loose a few turns of teflon plumbers tape on the threads will keep it snug. There have been rare instances of carbs with irregular threads from the factory and the EZ-Just feels sloppy in the threads.

Regarding the carb pop occurring off idle you can try turning the mixture screw out another 1/8th turn. Depending on how large the slide hole was previously drilled can cause the slide to open too fast. If you think that hole is larger than 1/8" (or 1/8" but elongated) I suggest using the stock length spring to compensate for the slide opening too fast. With modern fuel additives it is difficult to gauge plug color without putting at least a hundred miles on them.

change the slide.....about 25 bucks from the dealer.........problem should leave. the slide is working to quick.

use the spring that came with the kit.... have you checked for intake leaks??? very easy to acquire one when reinstalling the o-ring onto the manifold....just trying to help ya. the kits really do improve performance, but everything needs to be correct in the system. did you clean the carb. before installing the parts? there could be dirt in one of the passages. is the emulsifier tube installed correctly??? it can be installed upside down...what prompted you to install the kit? were you having issues with the stock setup???

EDIT: After typing the below possible causes I see you posted back here before I could click Submit. You mention that you have a clip style needle. That type of needle is not part of the CVP Tuners Kit and will not work with the provided emulsion tube and jetting. Clip style needles are specific to certain kits (Dynojet, Yost, SE, etc) and only work if you keep all the same parts together. Please use the needle provided with the CVP kit before proceeding with the below recommendations.

Let's see if we can get you back on track here. Note that I'm going to rattle off several things that can cause the trouble described and if you already did these things, don't take offense. I just want to cover anything that I've encountered that could cause an off-idle hesitation.

First install the kit as described, including the spring that came with the kit. If you mix up the springs the CVP brand spring is shorter than the original (unless someone cut the original). The needle gets installed first into the slide, followed by the plastic spring holder, followed by the spring.

Next make sure the needle jet (nozzle) is installed and installed in the correct direction. This is the stainless steel colar that protrudes up into the carb throat, and is held in place by the emulsion tube. When looking into the front of the carb you can see this piece where the tip of the needle passes down into the bottom of the carb's throat. The nozzle has two very different ends; the widest open end with an inside bevel faces up toward the needle, the end with a smaller hole flat end mates to the end of the emulsion tube. Installing this piece upside down (or not at all) will result in a hesitation and poor midrange as the needle lifts.

Accelerator pump: Check that when you crack the throttle open (engine off) that you see a small amount of fuel spray into the throat from the accelerator pump pedestal/nozzle. If no spray check that the accelerator pump rod is in place and that the accelerator pump diaphragm is in place and the small spring is on the bottom wetside of the diaphragm.

Check the 2 front air bleed jets for clogs. These are the 2 small holes at the front/bottom of the carb opening facing the air cleaner. Inside those holes are brass jets pressed in. Using something fine such as a sewing needle or wire bristle from a wire brush, gently pass into these jets to dislodge any debris. Follow this with compressed air.

When the mixture screw was removed and replaced, make sure that the packing (o-ring, washer, and tiny spring) were put back in or not accidentally lost. A missing o-ring can cause erratic behavior since the mixture may not always be spot on with these parts missing.

As mentioned by Chuck one of the more common causes following a rebuild is an intake leak. This would also account for the need to have larger jets to compensate for the excess in intake air being drawn in.

Float level: Not very common but occasionally the float level can become disturbed while working on the carb by inadvertently pressing against the float thus bending the tab. If you replaced the float needle plunger as part of your rebuild be sure to check float height as the manufacturer has made multiple variations of the float needle of the years. Some are a fraction shorter or longer and can cause a change in float height. If you don't have the factory shop manual for your model (highly recommended) I'll attach a diagram of the float setting here.

The kit has worked every time (never had a return) so I'm sure we can get you running smooth.

here it is..........

http://bike-talk.com/forum/tech-tips/11942-setting-float-level-cv-carburetor.html

Typically a backfire is timing related

Popping through carb is fuel


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When you press the carb back onto the manifold, does it fit snug (takes effort to fully seat) or does it press on easy? It should take some effort to seal correctly.

Just a hunch, try switching the manifold boot gasket with the old one. You can probably do this without removing the cables and hose, just pull the carb forward, reach behind and remove the boot from the manifold, slip the new one onto the manilfold. What has been described still sounds like an intake leak or the mixture screw being too lean.

When you put the mixture screw back in, how many turns out from seated did you turn it? Turning the screw out another 1/8th turn will richen up the idle and off-idle transition.