kz900 a4 rejetting and adjustment

Hey everyone,
I'm new here and just got a 1976 kz900 A4 with 52000 miles for free from a buddy. I've been working on her for about a week now and have gotten her from rusty and not running to painted and running ok.

So for a quick run down of what I've done so far.

Taken off stock air box and put on pods(easier access to carbs), cleaned and synced the carbs and passage ways. changed the oil, gapped the plugs and points. everything seems to be running ok although it bogs down whenever I roll on the throttle hard. From idle to 4500 rpm there is almost no power and slowly gains it through the rpm rang. 4500-5500 it really picks up but I get a weird crackling sound and from 5500 through the rest it moves great. It's also running really ruff at idle.

I'm pretty sure it needs re-jetting but I'm not sure where to start on that. I'm pretty good with a wrench but this is my first time working on a bike, in fact its my first bike.

I live in Wichita KS elevation is 1,299 FT. I also have a non-stock 4-2 exhaust on the bike from PO.

I

Pods are a major pain to get running good Krusty. That's especially true when you have an aftermarket exhaust becasue fewer peopl will have the same reference point to give you advice from.

In general pods mean you have leaned your mixture so look to go up at least 10 on the mains and maybe 5 on the pilots. Those are total wags. You'll probably need to move your needle clip too.

There are endless threads on trying to get pods running right, make sure you LOVE your pods before goign down this road.

Taking out the stock air box, and putting on pods will make you into a carburetor tuning specialist in no time

By installing pod filters you have introduced a much larger volume of air to the individual carbs, effectively leaning out the mixture entering the engine considerably.

If you run the engine too lean, it can cause over-heating which will lead to engine damage.

Four seperate carbs is like having four small engines that must all be properly tuned and synchronized to work perfectly together. First thing is to check the fuel levels in the bowls while the carbs are installed. They must all be in spec, and exactly the same. Usually 3-4mm from the gasket is correct. Then get those carbs super clean and set them right back to stock defaults. Bench sync them.

If your not sure how to do this stuff, you can search around here. But I strongly suggest getting the manual for your bike. There is practically a novel of information to read. Its not really difficult, it just needs to be done right.

When it comes to jets, there is only ballpark figures that you can try, but they are not the correct jetting for your bike. You must expirement with many jets to get it just so. Again, there is ballpark settings and lots more info in the filebase here under KZ Information at the top.

I wish you the best of luck. You're going to learn alot

Cheers.

Krusty_47 wrote:

Hey everyone,
I'm new here and just got a 1976 kz900 A4 with 52000 miles for free from a buddy. I've been working on her for about a week now and have gotten her from rusty and not running to painted and running ok.

So for a quick run down of what I've done so far.

Taken off stock air box and put on pods(easier access to carbs), cleaned and synced the carbs and passage ways. changed the oil, gapped the plugs and points. everything seems to be running ok although it bogs down whenever I roll on the throttle hard. From idle to 4500 rpm there is almost no power and slowly gains it through the rpm rang. 4500-5500 it really picks up but I get a weird crackling sound and from 5500 through the rest it moves great. It's also running really ruff at idle.

I'm pretty sure it needs re-jetting but I'm not sure where to start on that. I'm pretty good with a wrench but this is my first time working on a bike, in fact its my first bike.

I live in Wichita KS elevation is 1,299 FT. I also have a non-stock 4-2 exhaust on the bike from PO.

I

You gapped the points but have you checked the timing? You need to start by checking the compression on this motor. Make sure there are no cracked intake boots by spraying them with carb clean. The points have to make contact electrically when closed. Check for pits them and run a clean peice of paper through them. Crackle at 5500 could be lean condition, or more likely spark. Check the voltage and you'll see you need to do the coil mod, this mod itself is going to eliminate alot of probs whith spark plugs fouling, hesitations, starting. You need to know what main jets are in there. 112 is the smallest you want to see in there and 112 is too small too. Changing to pods is not going to cause tuning difficulties since these are not cv type carbs. One quick test for pilot fuel, take off the pods, put a finger over the pilot air hole one at time on each carb. The location is on the mouth of the carb, one side is choke passage, the other is pilot fuel. Block it on a cylinder and the idle should drop/ if not, you have a plugged passage. Take note during warm up how fast each pipe gets hot coming right out of the head. You will be able to tie in compression, spark, carburation together. If compression is off you need to add oil to determine if it's valve related or rings. If it's valves, pull the cover and check valve clearance. On a high miles older motor it's possible the rings are stuck or broken, the oil test will reveal this. I have the same bike and with pods and 112 jet it ran fine. I went to 115 and it was fine. Wouldn't hurt to ohm test the coils they should be 4ohms. Check the points springs that they aren't too close to the timing plate, sometimes they get bumped and cause an intermittent shorting of two cylinders. A test light is the best way to set timing if u need to know how pm me. One last piece of advice test the plug caps to eliminate those as a potential ignition misfire cause. If you lived close to me i'd be right over there helping you whip that bike into shape in no time, free of charge. Keep us posted on everything so we can get you running asap. You have a good bike there and it will take you down a road because of the mileage but it's all worth it. My bike has a 1015cc kit, cams and it has a 155 jet now. Everything you do to these bikes makes a diff. And they're bullitproof! Any money that you spend will come back. :woohoo:

Thanks for all the advice. It's alway nice to have so many people will to help you out. I really wish I could find some people in my area that I could meet up with but alas I have yet to find anyone.

I'm going to head out to my buddy's later this week and completely redo the wiring on it. also going to put on new spark plug wires and the rest of it. It should be very fun. I pulled the carbs again and they have 17.5 pilots and 115 mains. hopefully it will be running much better once I finish cleaning everything. I'm pulling the boots off to clean them and check for cracks and damage. In the off season I hope to tear it down and and give it a good rebuild on bearing springs and whatever else the engine might require and I'm going to strip the frame repaint it and replace all the bushings. I'm hoping to have a very nice bike once this is all done. Still not sure if I want to sell it or keep it. I haven't put more than 100 bucks into it so far total so we'll see.

So I am an idiot....After finally getting new 120 main jets I discovered that I should have been paying way more attention when I was putting my carbs back together the last time. I was really wondering my my bike was running like a giant turd and come to find out I had installed one of the floats upside down. So once I fixed that rejetted and started her up I immediately heard a difference. I was running a cylinder short.

So I take off for a ride and almost soil myself at the amount of power she had. I was stunned. This bike is amazing. Now its time for all new gaskets, seals, a honing with new piston rings, and I should be good to go. Maybe a new exhaust when I can afford it.

Ahh... good...

now you feel the power of the dark side.

yes I do not know if I can resist it.

Hi from Aussie
It's not a good idea putting pods on unless you have a full on race motor.Most owners are scrambling to put the air box back in, not worth the drama's in tuning with pods. I recommend standard airbox with K&N air cleaner.Your troubles sound slide related.
Cheers Karl