assistance about odd reving

Hi I've got my kz440 rebuilt. Now a new problem has arisen. I now have white smoke and stinks of fuel. And when started it idles fine then when revving up the revs drop and all by itself the revs pick up again. I'm confused
Any help would be hugely appreciated .

Was it running fine before? any changes made before the new problem? Is the stock airbox & air filter installed?

It was burning oil so was getting lots of blue smoke. So stripped cleaned and changed valve Stem seals. So I have no blue smoke just while and strong fuel smell from the exhaust. Its odd. I test rode it on the road outside the house was running ok then all of a sudden it started to hi rev out of the blue.

No stock filter its a bobber see picture

The air filter questions were asked because cv carburetors perform better with a stable air intake environment. Hi-revving is a symptom of a vacuum leak. Individual pod filters or no filters at all will flow more air & can act the same as a big vac leak. Free-flowing mufflers compound the problem. The carburetors probably need some re-jetting or tuning & the air filters probably need some attention as well.

A complete stock 440 airbox is going to be hard to find, so I would install some sort of extenders between the carbs & air filters, and use good air filters. extenders would act as inlet ducts to help stabilize the airflow. Also, the stock airbox provides support, so the carb holders may get stressed without it. so you should add a bracket or something to support the rear of the carbs, especially since it's a hardtail.

Any time the intake system is altered you can expect the need to rejet the carbs. Same goes for the exhaust but to a lesser extent. I'm not a jetting guy so I stay out of those discussions but you may want to see if any jetting kits are offered for your bike.

My two cents is that unless you want to mess with endless carb jetting woes and adjustments, and poor performance, at least put some kind of nearly stock air box and the stock filter back on it. I'm not a big fan of bobbers, but I see you have done a very high quality and well detailed build. It does look cool.

But you should still have some kind of quality air filters on it.

The revving up and dying problem to me spells intake vacuum leaks. Check your carb manifolds, the vacuum port plugs, the slide diaphragms, etc...

I knew some tuners who kept a hand pump spray bottle filled with gasoline for checking intake leaks. With the engine running (at the way too high rpm's you are trying to get rid of) they would spray a small mist of gasoline(!!!!) near the carb to engine junctions and see if the idle speed dropped back down to normal. If so, definitely a leak. Of course, this is extremely dangerous (insane?).

A better way is to spray a heavy water mist (same idea - less explosive) and see if it causes the engine to stumble and / or die. It isn't as effective or easy, but it is many times less likely to burn your bike to smoldering ashes...

A complete 440 airbox is going to be difficult to source. and the cap is even more rare. Some guys fabricate an airbox. or fab a cap if they have the rest of the airbox. One idea that almost worked was to get a Radio Shack project box (ABS), but the plastic wasn't durable enough & failed in no time.

I've fitted ram air filter socks to the carbs. Since doing this I'm getting smoke from the opposite exhaust now. I think I'm going to try one more thing and replace the carb boots amy other hints help thanks

pauld200281 wrote: I've fitted ram air filter socks to the carbs. Since doing this I'm getting smoke from the opposite exhaust now. I think I'm going to try one more thing and replace the carb boots amy other hints help thanks

I have a KZ650 I'm working on here and the carb boots were "workable" but I didn't like seeing the numerous fine cracks in the manifolds. Still, the carbs seemed to be working well enough. The bike idled, etc, but - noteworthy - I could not road test it as the brakes weren't working then and it was tethered to a large stationary battery pack.

Not wanting carburetion problems to develop later, I decided to replace all 4 manifolds with new ones despite the owner's opinion. Without any other changes, on first cold start up a few days ago, I had to back the idle speed adjuster off with the new manifolds, as the idle had increased from 1100 to 2400 rpm. At first this seemed counter intuitive, especially given my past experiences with cracked intake manifolds, but I theorize that it was the leaks in the old manifolds leaning out the idle mixture consistently[/]. With the new manifolds, all the air is now being drawn in through the carburetor throats and not cracked manifolds, thereby pulling more fuel into the mixture than before - it was acting like the cold start / high idle circuit was "on", I think. After it warmed up, I dropped the idle speed adjuster again and now think the pilot air screws need to be adjusted again, along with a final re-synch...what a difference!

Same here. New manifolds then I could work on the carbs themselves.
Steve