1971 Kawasaki A7 Avenger

[iranana]

Thought I might just chime in cause there's a bit of stuff in this thread that kind of contradicts my understanding of two stroke tuning and I'd like to clarify a few things/contribute to the knowledge base (and I may very well be wrong... but this is what I learnt from tuning my RD). Jetting a smoker doesn't start at the main jet - the main jet is only ever really effective from 3/4 to full throttle (it does start to come into play at 1/4 but its effect is gradual). Before this, it's your needle jet/needle and pilot that do all the work. Jetting a two stroke should really start at the *pilot* jet (assuming your needle jet/needle is set up right - this is another matter). To do so, you warm the bike up to operating temp, then at idle you turn the air screw until you find the point of highest idle.

The air screw should be no more than 2 turns out and no less than 1. It varies a bit from bike to bike, but my RD, for example, should be set at 1 1/4 turns out according to the factory spec. You might find that with today's fuel and changes in altitude you might need to go up on the pilot jet a couple of sizes (I did). The point of this is to obtain the correct air/fuel mixture at idle, which will effect the running characteristic right across the throttle range. You can further tweak the air screw to get the perfect response when you crack open the throttle, too, just by riding and turning it an 1/8 of a turn.

Issues with low end running can usually be attributed to the pilot circuit and needle clip position... The main jet size should be determined *last* and the easiest way to do so is via the plug chop method, which should only ever be done with brand new plugs or you'll get an incorrect reading. If you change the main jet before you correctly tune the pilot/air/needle position, your main jet will be off... but, most importantly, before you do anything to the carbs, clean them *thoroughly* (and I mean thoroughly), or all your efforts will be in vain.

[Mike.Gayner]

Thanks Iriana, your experience matches the guidelines laid out in the workshop manual for this bike. All of this is why my efforts at diagnosing at idle were wasted - the pilot circuit and the air screw are set correctly, so the bike appeared to run just fine at idle. It wasn't until I got it on the road and opened the throttle that the issues became clear. The good news is that the bike is running 90% perfect now - I'll probably have someone cleverer than me set the points and do the final tuning, but it's ridable and very powerful right now.

[roogazza]

Eel will no doubt be a long soon to clarify but reading the manual to adjust air or mixture screws is all well and good if there is no fault in the bike like a blocked jet.
Warm it up yep and adjust to 1 and a quarter turns etc etc.

But if you want to jet the carbs, start at the main and work back thru. Otherwise you'll get all the slow running fine and then if the main is out and you change it the rest will change.

[iranana]

There's nothing quite like a properly tuned smoker! Bet that thing rips when it hits the power band... but the real question is: can it stop as fast as it can go?

[iranana]

But if you want to jet the carbs, start at the main and work back thru. Otherwise you'll get all the slow running fine and then if the main is out and you change it the rest will change.

The two circuits are more or less independent of one another, but they do 'cross over', so a correctly set up pilot circuit is important for a nice smooth response. A re-jet should always start at the pilot. If the pilot circuit is set up correctly, you could change the main jet to any arbitrary size and it would still idle and run fine at 1/4 throttle. The main jet doesn't come into play until the flow of fuel through the main jet is greater than that of the needle jet and needle. Work out the pilot circuit first, then the needle clip position, then the main.

[Mike.Gayner]

There's nothing quite like a properly tuned smoker! Bet that thing rips when it hits the power band... but the real question is: can it stop as fast as it can go?

HAHA I suspect you know the answer to that - this is my first old bike, so first experience with drums front and back. They're a little bit scary to be honest. For my own safety I had the mechanic give them a once-over and do a brake declaration when he put the new tyres on. Original shoes and un-machined drums, both in good condition, which is more evidence to suggest that the 12,000km on the clock is genuine.

[iranana]

HAHA I suspect you know the answer to that - this is my first old bike, so first experience with drums front and back. They're a little bit scary to be honest. For my own safety I had the mechanic give them a once-over and do a brake declaration when he put the new tyres on. Original shoes and un-machined drums, both in good condition, which is more evidence to suggest that the 12,000km on the clock is genuine.

I've only ever had to put up with a rear drum brake thankfully... and it was pretty bad. Luckily, my RD is one of the later models with front and rear disc brakes. I have heard, though, that the Yammy engineers designed their early disc brakes to behave a little more like drum brakes, for fear that their braking power would be too much for those coming from older bikes with drum brakes. Not sure about that, but my RD stops all right. The drum brake Kawasaki's make me feel a bit uncomfortable lol. 12,000km on the clock is really good, that crank will be happy. The main issue with old smokers, imo, is that their cranks are usually getting a bit long in the tooth. I'm thinking I'll have the get the RD crank rebuilt in a year or so. On the upside, everything else on these bikes is usually a simple fix. I'd personally love a 350 two stroke twin. I find the 250 can feel a bit under powered at times, but that might be remedied with a nice pair of Denco expansion chambers I just got my hands on.

[eelracing]

All good points Iranana and you can't fault your logic...but I disagree.
I guess it comes down to how you look at it re;two strokes.
For me they are and will always be about performance combined with light weight and simplicity...the perfect sportbike.

So with that in mind I always jet for top-end and i'll bet my left ball that when you fit those performance exhausts the first thing you change won't be the pilot or needle.

[iranana]

All good points Iranana and you can't fault your logic...but I disagree.
I guess it comes down to how you look at it re;two strokes.
For me they are and will always be about performance combined with light weight and simplicity...the perfect sportbike.

So with that in mind I always jet for top-end and i'll bet my left ball that when you fit those performance exhausts the first thing you change won't be the pilot or needle.

Oh absolutely - if you're jetting for top end performance then you can kind of disregard what's going on in the bottom end. Since I jet for the street (smooth, all round running) I like to start at the pilot for nice low end power and then move to the main from there - I barely ride wfo anyway. And of course, the first thing I do when the spannies go on will be richen the mains
I was just suggesting that perhaps it's best to start from the ground up if you've got carb issues - tis how I solved mine, though there is more than one way to skin a cat, so to speak

[Mike.Gayner]

Next hurdle is getting the bike registered. I'd hit a bit of a road block because we don't have old plates and have no other way of proving the vehicle was once registered in NZ. Heading down to the police station tomorrow, where hopefully they can check the background of the last registered owner (who I bought the vehicle off and have a receipt) and find out the old number plate. Once we have that it should be smooth sailing, because I've done pretty much everything else needed for registration.

[roogazza]

iranana, You may find this of interest.
I have a lot of guff here somewhere but couldn't be bothered searching.
However I did a quick google and this 'Factory Pro' site passes on some good info.


To properly tune, you MUST:

1. Have selected the BEST main jet for full throttle power (not just a "good" main jet - we mean "the BEST main jet" for power at high rpm).
That eliminates the common severe tweaking of the midrange and lower tuning ranges to compensate for a "wrong" main jet.

2. Then - select the BEST needle height / clip position for power at FULL THROTTLE / MIDRANGE after selecting the BEST main jet -
That almost eliminates weird problems at cruise caused by tweaked needle heights that were required because the main jet wasn't correct.......

3. Then, adjust the BEST Float Height for BEST FULL THROTTLE / LOW rpm (many Honda's excluded because floats are not adjustable) -
You should be able to apply FULL THROTTLE at LOW RPM in TOP gear without ANY misfire of bogging or stumble.......

If you follow that order, you will have:
1. Best topend.
2. Best midrange.
3. Best low rpm power.

Then - all you have left is dialing in the pilot circuit - i.e. mixture screw and pilot jet size - That's IT - Don't tweak needle heights and throw away full throttle midrange to try to fix a cruise issue!!! (Unless you want to!)

If you reach an impasse in steps 1,2 and 3 in the FULL THROTTLE tuning, STOP!!!!! and call TECH SUPPORT!!!

[Mike.Gayner]

I'm trying hard to get this bike registered but no one seems to give enough of a shit to help me. A guy at VTNZ suggested I called NZTA to try and get someone to look through the database and track down the bike's history, but unfortunately the person I got at NZTA was a complete asshole who obviously hated his job and his wife was almost certainly fucking the mail man. What an absolute prick of an organisation to deal with.

/rant

[iranana]

I'm trying hard to get this bike registered but no one seems to give enough of a shit to help me. A guy at VTNZ suggested I called NZTA to try and get someone to look through the database and track down the bike's history, but unfortunately the person I got at NZTA was a complete asshole who obviously hated his job and his wife was almost certainly fucking the mail man. What an absolute prick of an organisation to deal with.

/rant

I found that the NZTA was unhelpful as fuck when it came to getting my RD revinned, as was VTNZ. To make things more annoying, each place I talked to told me different things regarding the process involved, including shit like getting the old paperwork from their archives which would have taken weeks. However, I ended up getting in touch with a guy called Paul at VINZ on Carbine Road in Auckland. He told me everything I needed for the process, and it turned out to be very simple. I just took my bike to him with the old plate and a statutory declaration of ownership which I obtained from a JP (just went to a JP with a receipt from the last owner [who wasn't even the last registered owner] and told her what the situation was). He sorted everything else out for me, and the next day it was ready to pick up and road legal. I'd really recommend calling them up and talking to him, he will probably know what to do in your sitation. Out of the numerous people I talked to, he actually knew what he was on about.

In re:the jetting topic above, that's an interesting method, but it makes sense. Seems a little more involved, but I suppose it leads to the same place as jetting from the pilot up does anyway.

[Mike.Gayner]

The problem, Iranana, is that I don't have the old plates. I'm missing the one piece of documentation that you REALLY NEED to do this the easy way - proof that the vehicle was once registered in NZ. If I knew the old rego number I could go to VTNZ and get it registered this afternoon.

At this point it's looking like I have to get it VINned basically as a new import, which means complying with current regs to get through compliance - indicators, ensuring the frame is up to some bullshit standard, all that nonsense. All this despite two (of three) previous owners being absolutely sure that the vehicle was once registered in this country (and probably not that long ago).

[iranana]

The problem, Iranana, is that I don't have the old plates. I'm missing the one piece of documentation that you REALLY NEED to do this the easy way - proof that the vehicle was once registered in NZ. If I knew the old rego number I could go to VTNZ and get it registered this afternoon.

At this point it's looking like I have to get it VINned basically as a new import, which means complying with current regs to get through compliance - indicators, ensuring the frame is up to some bullshit standard, all that nonsense. All this despite two (of three) previous owners being absolutely sure that the vehicle was once registered in this country (and probably not that long ago).

If it's been unregistered for any significant period of time, the plates are probably dead, so you'd need to get it VINned anyway wouldn't you? My RD was last registered in '88, the plates were dead and there was no electronic record of it anywhere. Everyone I called couldn't find any record of it, the last registered owner was back in '88, and since then it had passed hands at least three times... When it was VINned they game me a new plate and VIN number.

The compliance test was pretty straightforward, and there's only a few things that you might need to tweak to make it compliant (reflectors in the rear brake light and that sort of thing).

Surely there must be some record that associates the VIN number with the last plate it was registered under? Like I said, it might be worth talking to Paul at VINZ, he can probably tell you more than most, and he might be able to find a record of it being registered somewhere.