1981 KZ 550 LTD Engine hop up

This is a short question but I will take any advice possible. I have the above bike and I would like to know what mods I should/could do to increase the engine output. More precisely I would like find the engine mods that yield the most bang for the buck or the most power for time spent.

Thought you guys could point me in the right direction.

Thanks
Krok

Krok18 - (Moderator Hat ON!) - Please edit your profile to put your bike year/model in the signature. You might also consider putting your location in the signature to allow local members to help you out or you could help other local members (if they knew you were local). (Mod Hat OFF!)

Anyway, there isn't a wealth of hop up that can be done on a KZ550 without some serious knowledge. You can remove the stock airbox and replace the airbox with pod filters. You will need to rejet. You can replace the stock and heavy exhaust with an aftermarket exhaust.

Once you have done this stuff, you will gain about 5 hp. If you have the money, consider a larger displacement piston kit. There might be cams for your bike that will drop in and change the power band a tad.

All in all, you didn't pick a great model to want to hot-rod. I suggest it might make more sense to go with a larger displacement bike as more options exist for the 73-80 903/1015cc family of bikes. These bikes have much more potential for hot-rodding as there are many more aftermarket hot-rod parts than there are for the 550.

Probably the cheapest performance you could get would be to change sprockets and change the effective gearing.

Post edited by: wiredgeorge, at: 2007/03/07 14:12

Hey George! Would you still rejet if you had CV carbs like his 550 when you put on pods?

Rejetting is absolutely needed whenever installing pod air filters; CV carbs are especially sensitive to the need to rejet; probably even more than VM carbs.

what about if you only changed the exhaust to 4-1, and kept the airbox?

My bike has stock jets and airbox, but a 4-1 exhaust. Would I be better off with different jets? If so - which ones would work with my TK26s? The jets are apparently the only ones available.

FYI - I have 120 mains, 32 pilots, and clip 3 on the needle.

If memory serves there is a stage one and and stage three jet kit. Stage one for aftermarket exhaust (with maybe a drop-in airfilter for stock box) and stage three for pods and an aftermarket exhaust. The need to rejet comes with the increased airflow. They are typically sold together so you can upgrade as needed. At least I believe my kit came with both sets.

Bdog

Well, this thread is moving to the carb related... If anyone has any carb related questions they want to pose at me specifically, catch me at my Vintage Bike Carb Forum via our website.

FWIW: I don't recommend Dynajet jet kits. There are three general circuits on any carburetor they build kits for. Pilot, mid-range and wide open. They don't address the pilot circuit. Bikes that have pods/pipes generally require larger pilot jets. They supply jet needles for the mid-range component but unfortunately, these jet needles are the same ones used in MANY different kits. One size doesn't work any better for jet needles than it does for buying a suit. If everyone bought a 42R, perhaps a few folks would have a suit that fit but most would not... too big, too small, too short, too long... well you can see where this is going; Last is the wide-open part... performance drops off at wide open throttle most particularly when the main jet is too small. Dynajet main jets tend to be on the largish side and work fine.

If you need to use pods/pipes on your Tekei carb'd bike, use Keihin small head mains (same sizing and thread) and reclip the stock jet needle down a slot. It is far better matched to the Tekei needle jet. Any more carb talk and this will go to the carb section, I guess...

Yes, you can always buy a faster bike, but so can anybody with a fat checkbook. Making your outdated machine faster is a challenge and is much more rewarding.

You can convert your 1981 550 C2 ltd into a 1981 550 D1 gpz by changing the pistons and cams, but since you want "power versus time-spent", you can just swap in the cams and end up somewhere in between.

You can find pistons, blocks and heads for the D1 pretty cheap on ebay.

I would recommend the gpz oil pan for use with an oil cooler if you convert to a gpz motor because it will produce a lot of heat.

There is Wiseco 615 kit for the 550 engine displacement, but I haven't had any experience with it.

You may also want to get D1 advancer springs for the ignition, in case they are different from the C2 springs.

For the carbs (which are not CV), you only need #94 main jets to make them the same as the ones on a D1 motor. The #94 mains work well with the airbox and stock exhaust or even a mild Kerker exhaust. #96 would work better with the Kerker, though. If you use a Mac 4-to-1 exhaust, you'll need #98 jets, or possibly #100. The Mac flows more, but the Kerker seems to make as much if not more power, but these are just seat-of-the-pants opinions, which can be wrong.

The dynojet kit is very good if you are going to use pod filters and, of course, a 4-to-1 exhaust. The needle will work better than stock in the lower rpm range, and it's adjustable. It also comes with several jet sizes (for four carbs). (I don't shim the needles because it causes them to lock up and they don't float properly in the hole). The Dynojet recommended slot in the needle works best. There are adjustable versions of the stock needle available in other brands of rebuild kits. These can be made to work pretty well and may save you some money over the Dynojet kit, but you'll need to drill the jets.

link to dynojet kit details

I like to keep the airbox which gives better low end pull at stop lights, especially with a passenger. In that case you can stick with just a jet upgrade to 96 or maybe 98. The Mac exhaust is definitely more finicky than a good kerker and requires more tweaking.

I've never had to mess with pilot jets with the Kerker with or without the airbox. The Mac is only a little rough when it's cold. After it warms up it runs totally smooth. I may drill the pilots for use with the Mac as an experiment to see if smooths out the cold running off idle.

Of course, all of this tuning takes a huge amount of time if you want to do it right. You have to start with the engine.

Compression test
valve adjustment
Valve timing verification

Then ignition timing and advance

Then verify the carbs are working 100%.
Set Fuel level
Set vacuum balance
Set Mixture using lean-drop
I use an EGA to verify the settings, but it's really not essential, and the idle mixture screws should all end up in very similar positions if everything is right on.

Post edited by: loudhvx, at: 2007/03/08 21:01