Faulty petcock?

Hey guys, new to the forum, new to motorcycles in general. About 3 months ago I bought a 78' kz650d2. Its in great condition and I'm in love with it. Anyways, 2 days ago I noticed some fuel dripping out just behind the center stand. I figured out that the fuel was coming from the overflow tube connected to carb 1 so i blew some air up there to see if that would fix the problem, check on it yesterday and there wasn't any fuel on the ground. However, when I tried to start it, the engine kicked on and then died a few seconds later. So now I figure that the engine is flooded and drain the oil out of her (which did smell like it had fuel in it). Before I closed it up, I set the petcock to prime to see if anything would drip out and it did not.. Even still, I decided that I wanted to take float bowl off to inspect it and when I opened drain plug with the petock set to "on", the fuel would not stop coming out for some reason and yet its not just pouring into the engine. If my understanding is correct, since this is a vaccum petcock, this should not be happening?

When you first noticed fuel on the floor it probably came from the overflow tube. You may have left your bike on the side stand, or you may have an improper float level. If possible the bike should be left on the center stand so that the float bowl level is even. You need to check your floats to ensure you have the correct level.

You're correct that the fuel should not flow if the engine is not running and the petcock is in the on position. You probably need a rebuild kit.

I've been in this situation with my kz1000st ,firstly it does sound like the vacuum part of the fuel tap isn't doing its job, honestly forget the nice and cheap fuel tap rebuild kits out there, I tried two and you can rebuild them as carefully as you like under a magnifying glass with tweezers and they'll either let fuel through or shut it off too much, my advice is do what ever it takes to find a complete new old stock tap and pay what you have to pay then fit and forget, my tap came from Germany when I tracked one down and it cost £85 .
Second you should never have fuel coming out of the overflow pipes even if the tap has failed, more than likely the little needles have worn sharp and or developed ridges in them as they vibrate a lot in their brass seats, to fix that you can track down genuine mikuni seats and needles but these are usually insanely expensive, in the UK they're £46 for EACH needle and about the same for each brass seat... luckily there's a good Japanese company called tourmax who sell sets and the quality is perfect ,impossible to tell the difference between tourmax and mikuni really, again fit and forget, mine have been In the bike for about 8000 miles and not a single drop of fuel out of the overflow pipes finally I always recommend a good carb set up on vacuum guages after having them apart and the bike should run and go great oh in the carb kit pic you just want the two little bits bottom right, you can fit the other parts of the kit if you like but the main thing is the needle valve

Just after I posted the last post I saw hardrockminers post, he brings up two good points ,these bikes should always be on the centrestand (especially when running for any length of time) or atleast put a piece of wood or something under the side stand to get it a bit more upright and yes float heights are very important and again followed by a good vacuum Guage balance

Thanks guys. I always use my centerstand. Ive been having a hard time finding a rebuild kit for the petcock and will probably just replace it. I really want a manual one from a 77', but that's even harder to find. I do have a question regarding the failure, why does the fuel flow freely when the drain is opened but doesn't overflow out of the overflow pipe?

I think that's probably because the fuel is escaping so fast it can't activate the needle valve, it must be normal for it to do that though because every few months I take all four drain screws off my carbs and run a little bit of guttering under them then I take the fuel line off the tank and blast carb cleaner down the fuel line, it gives the carbs a really nice clean

Price wrote: Hey guys, new to the forum, new to motorcycles in general. About 3 months ago I bought a 78' kz650d2.

I hate to tell you but there's no such thing as a 1978 KZ650-D2. The KZ650 D models began production in the 1978 model year, so all 1978 KZ650-D models are D1 not D2 models. If your bike is indeed a D2 then it is a 1979 KZ650 model. Keep in mind, just like cars production of bikes of a particular model year is begun a few months before January of the model year. So if your bike was built in late 1978 it is in fact a model year 1979 bike. It may seem like I'm being a bit anal about this, but you will find that this information is quite important when you need to order parts for your bike. Ed

I'm sorry for that. I am embarrassed, as it is in fact D1. As in a 78' kz650sr. I am certain about it now after double checking. I must have missed that when I was trying too hard to sound like I'm not totally winging it.

If you want an easy method to check your floats....read this link carefully.

www.kzrider.com/forum/forum-index/3-carb...n-setting-fuel-level

Thank you all for your input and thanks to hardrockminer for the link. This is a useful resource and I will certainly be using it as a reference for the foreseeable future.