Project: 1990 ZR550 Zephyr (yes, another one)

Your third wire is a straight ground (which may not have suited the relay you had) so if it works ok without having this wire connected to the relay you  are using now -  happy days 

I took the bike out for a ride today. Only ten miles, very conservative, about 45mph top speed. Tried to focus on slow movements and just really feeling everything. 

With the throttle open past the idle jets it feels smooth, relatively linear predictable power. But below 2k rpm’s it’s like the tach has a mind of its own. From one stop light to the next it might decide to idle higher or lower. And the throttle feels like it has heaps of mushy free play despite being adjusted to spec this morning. 

My theory is that the PO rejetted the carbs for pod filters. This is an easy assumption because when I got the bike there was a lot of parts in bins, including the carbs, and they were fitted with pods when I found them. There was also a Factory Pro jet kit in there. 

So I think the obvious thing to do is see if I have the original jets and get them back in there. It looks like maybe I do, but im not entirely sure how to identify OEM versus aftermarket jets, and where to purchase replacement OEM jets if I need them. 

 

Keihin jets will have a "K star" and some type of number on them.  At least the ones I have seen did. As to locations to find real jets, I am sure others will chime in, but there are several online locations one can find them. You might try jets r us for starters and check other locations as well.

If you don’t mind pods, the Factory Pro stuff is high quality.

I’m kind of neither here nor there about pod filters. I’ve seen them look good on some bikes, but just an eyesore on others. Some CR carbs with velocity stacks on the other hand… 

Yesterday I took the carbs out, and found that it had the needles and main jets from the Factory Pro kit installed. I put the OEM ones back in, and readjusted the pilot jets to 2-1/2 turns out. 

While I had them out, I took the time to install a manual cam chain tensioner. 

Overall I feel like this made a difference in stabilizing rpm’s in the low range. However it is still prone to idling too high, and when I adjust it lower, it goes back up again. And when I do get it down around where it should be, it has a galloping kind of gurgle, almost like it’s running on three cylinders. I am wondering if maybe I need to install the proper spark plugs. The PO put in NGK D8EA’s but the stock should be D9EA’s. 

Also I still feel like the throttle has that mushy unresponsive sort of feel. Is it possible to dial out the throttle free play entirely? 

 

With the stock mains and needles are you still using pods, or did you install air box and filter?  I would think with pods and stock settings it would be lean, as pods should flow more air than the stock air box/filter will.

I’ve got the stock airbox in. 

I’ve been riding the bike a bit, it’s now got about 60 miles on it since I got it running. It’s very cold-blooded and takes longer to warm up to a smooth idle than my other bike. But eventually it does feel like things are running smoothly. However there’s still a few things that need ironing out, and I have some concerns. 

Here’s a strong vibration that I only feel at about 6100 to 6600 rpm’s. It does it in every gear. I have no idea what would cause that, other than maybe some kind of resonant frequency thing. But my other bike doesn’t do it, so I am curious. 

I’ve got an oil leak on the left hand side. I feel like it’s probably just a bad gasket. Perhaps the previous owner installed a non-OEM cheap-o gasket. I know for sure the cam cover gasket is crap as I installed that myself (bought it from eBay listed as OEM, but I’m pretty sure it’s not, already bought a replacement). While it does seem like some of the leak is coming from there, I think there may be another coming from under the cylinder block. 

And finally, I am perplexed by the manual cam chain tensioner. I have manual cam chain tensioners installed on both bikes, but one sticks out with room to go in way further than the other one. I followed directions for installation to a T, but given what I’m seeing I feel like one of them has to be wrong. 

Photos just because. 

The cooling fins on your Bronze / Gold  Zephyr cylinder head look uber cool!

H.

Any tips on where to start chasing down these leaks?

 

Start with a clean .. really clean bike/engine and pay really close attention?