Carb sync - 78 KZ750

I have been riding my KZ750 for a few weeks now, but it has a few problems with start and idle. When I get it started the idle is really high, about 3500 rpm. I have adjusted the fuel air mixture many times, but if I give the bike less fuel it will idle better but die at stoplights. I have cleaned the carb out thoroughly, but from what I have read online it seems like one of my carbs is delivering much more fuel/air than the other. How do I adjust how much each individual carb is sending into the cynlinders?

It's probably your timing advance weights hanging up used to happen to me all the time at stop lights. I would cracked the throttle and it would idle right. It has pads that it rides on they have to be cleaned and lubed

pazzadelivery wrote: I have been riding my KZ750 for a few weeks now, but it has a few problems with start and idle. When I get it started the idle is really high, about 3500 rpm.

That is a classic symptom of a vacuum leak, not sure but could be.

pazzadelivery wrote: I have adjusted the fuel air mixture many times, but if I give the bike less fuel it will idle better but die at stoplights. I have cleaned the carb out thoroughly, but from what I have read online it seems like one of my carbs is delivering much more fuel/air than the other. How do I adjust how much each individual carb is sending into the cynlinders?

You first do mechanical sync where the throttle bar is adjusted so both throttle butterflies open the same amount. You use a precise rod like a small drill bit to see if both are open the same amount very near to being fully closed where the bike idles.

The idle screws on the sides of the carbs adjust richness. gently turn them into bottom and then open about 2 turns as a starting point.

BTW: if you have the BS-38 carbs, increase the pilot jets to size #50 and the engine will run better. Stock is typically 45, but 50 will run better.

FYI: on the BS-38, the idle screws on the sides of the carb make it leaner as the screw is turned in, richer by backing it out.

Sorry I misread your post. I thought you stated the idle was high at a stop light

How do I check for a vacuum leak?

I suggest you try the following. Get the engine warmed up and temporarily set the idle as low as possible without killing the engine (lower than 900 rpm if possible). The lower the better because with the idle very low the slides are nearly shut and the vacuum inside the carb holders is at its highest. Then spray carb cleaner around the carb holders, especially where they mate with the cylinder head and where the carbs attach to them. Carb cleaner works best for this test as it doesn't leave an oily mess with WD40 or evaporate so quickly that it is not drawn into the leaks as can happen with propane or starting fluid (ether). If the engine dies or reacts to the carb cleaner, you need to replace the carb holders. Carb holder leak related problems are noticeable at idle but generally don't have much impact when riding because the throttle is open. If you find you need to replace the carb holders soak the screws with Kroil for a couple days before attempting to remove them, and use JIS standard, NOT Phillips, screwdriver bits, and this will greatly improve the odds that you will not break or strip a carb holder fastener as so many have done. Take a look at the link below for more info on JIS screws and Kroil. Ed

kzrider.com/forum/10-new-members/589649-...r-savannah-ga#594587

I just tried the carb cleaner spray a minute ago, and it killed my bike. Where do I find new carb holders?

pazzadelivery wrote: I just tried the carb cleaner spray a minute ago, and it killed my bike. Where do I find new carb holders?

That's a definite sign they need to be replaced - same thing happened to mine when my old ones leaked. Unfortunately Kawasaki has discontinued them, and I don't see an aftermarket equivalent on Z1E, so I suspect eBay is your best bet for new old stock (NOS) ones. Below is the Kawasaki.com diagram for the 1978 KZ750-B3 twin; it shows the part number. An eBay search using that part number did show some parts being offered (see link). Ed

www.ebay.com/dsc/i.html?_from=R40&_sacat...=16065-036&_osacat=0