85 GPz 750 Cafe Project

ayeckley wrote:

loudhvx wrote: Because coils take time to charge, and they get less time to charge as RPMs go up, ignition electrical load decreases as RPMs go up. The duty cycle stays about the same (after a certain RPM regarding the factory electronic ignition), so the coils are charging for the same percentage of time and resting the same percentage of time regardless of RPM. But as the RPMs increase, even though the time percentages stay about the same, the actual time of charge decreases, so the average level of charge reduces.

Hmmm, I might have to concede your point there. Makes sense if the inductance of the coils is relatively high. I should probably break out the scope...

I built a makeshift digital scope out of a laptop to capture the signals if you are interested.
I also designed a special regulator to apply voltage to the coil such that the switching transistor's voltage drop is out of the measurement, to get true steady applied voltage to the coil. (Normally, the switching device will have an increasing voltage drop as the current increases, so you don't have a steady voltage on the coil. This regulator corrects for that.)

s3.amazonaws.com/gpzweb/Ignition/Ignitio...s/IgnitionCoils.html

ajsfirehawk wrote: I removed the inline filter, It is now a one piece clear 5/16 inch fuel line. Choke is off when riding and testing in neutral. I fire it up with the choke on, work the choke down until it will idle on it's own with the choke off. Give it another couple/three minutes to heat soak, Then start taching it up in stages, 3K, return to idle for a few seconds, 4K, etc.

I would try it with the choke on and see if you can get to redline. If so, then you know it's not enough fuel getting to the motor via the jets (but enough is getting into the carbs).

Interesting thought Loud, I'll give that a shot.

I can't seem to quit acting like Don Quixote charging at windmills. I pulled off the carbs, rechecked fuel bowl levels, all good. Pulled the needle valve assembly out to find #1 needle valve base screen had come off. That is two of those miserable pieces of garbage. So I removed all of them in all four carbs. I put in 135 main jets just to see how the bike responded. It will now slowly run up to 8K rpms. To me that suggests it is not a matter of the fuel bowls being drained and not refilling. Nothing was done to change anything that would affect that since it would only run up to 6K. So if it will slowly accelerate to 8K but bog if you stab that throttle at anything over 4K there has to be some issue with the needles/sliders, right? If the exhaust events were opening a bit early (cam timing) would that affect vacuum? The bog doesn't exist with the bike in neutral and I can watch is go rich/yellow on color tune whenever I stab the throttle.

I've ridden several GPz 750's and above 6K rpms when you stab the throttle they just about jump out from underneath you. 7K to 9K happens so quickly you have to pay close attention to shift in time. I'm finally giving in and going to swap in a different carb bank. Uncle! If the bike behaves the same that eliminates the carbs.

I've got 135s in it now which seem silly big. I think I have 142.5's, why not. I have not run it without the K&N's on it. I was thinking I would do that just to see the sliders operate dynamically. Although I expect them to behave with no load.
I had a local buddy ask me about slider springs. As I don't know a lot about the carbs history, I pulled out the ones I have for the BS34's. I found two different sizes, see pic below. The larger springs where in it and I thought AHA! No, behaves slightly better but if I was to characterize the high rpms performance, I'd say it runs like $hit. Tomorrow is shot with chasing down the CSR. I'll be back at it Saturday.

I'll watch the sliders with the filters off running. I'll put boots on it and see how it performs. If there isn't a breakthrough I'm going to break down and try the other set of carbs I've been threatening to put on.

I'm struggling to connect the ignition issues to running lean, and it is running lean. See pics below.

No change in symptoms or performance with the lighter slider springs. Today I tried removing the K&N filters, installing the stock airbox boots and running with those uncovered like velocity stacks. Same, maybe even worse performance. Short vid of the bike running in neutral while watching the sliders.

For some reason I thought you were running a stock airbox. With pods you might have to make some pretty large changes in jetting. I would search for a Dynojet kit for your bike, known to work with pods. They usually have radically different metering needles.

Have you changed needle positions? (Sorry if this is stuff you already mentioned. I didn't go back through all of the pages.)

I've messed with the needles a bit. With 120 mains I raised the needles all the way and got another 1K rpms out of it. I put it 135s with the needles on the 3rd notch from the top. Almost no difference. (Much bigger jet, dropped the needle two slots)

You have your work cut out for you trying to make the CV carbs work as well with pods as they do with the stock airbox since a lot of engineering went into the design of the airbox to tune it to make the carbs work well. Take a look at the video in the link below; it shows how CV carbs work. Notice at time 1:20 when the throttle is opened the throttle vacuum passage opens and the throttle vacuum passage retracts. This causes the throttle slide and jet needle to rise. The amount of air that is drawn through the main intake is critical in that the more air drawn through it the less vacuum is available at the throttle vacuum passage which in turn affects the opening of the throttle vacuum passage. At time 1:56 with the throttle wide open the vacuum at the vacuum passage pulls the diaphragm and jet needle all the way up.

As I see it the difficulty in getting pods to work well on the CV carbs is dealing with the fact that the resistance to air flow through the main intake is reduced which in turn reduces the vacuum available to pull the diaphragm up. Consequently, tuning the carbs so the engine runs great at wide open throttle will normally be detrimental to the way the engine runs at other throttle openings and vise versa. This may not be of any importance to a person using the bike on the track since he will not necessarily care about how the engine performs at moderate throttle openings, but for street use this can be an issue.

In any case, you may find the video interesting and informative. Ed

I'm following Ed and it is very interesting, expands my understanding. Are there modern carbs which are not CV carbs? Buying new carbs may be preferred versus a complete redesign of the bike. The real estate that used to be occupied by the air box now houses the electrical components and battery. All would have to find new homes and there is no room at the inn.

You could always just do the old cardboard flap test.

Take all four filters off.
Cut a rectangle of stiff cardboard so that it's wide enough to cover all four intakes.
Start the bike and let it warm to where it will idle.
Then slide the cardboard over the intakes, but leave it held open at an angle, sort of like a trap door, so you don't cover up any breather ports etc.
Then try revving.
There will be a position for the cardboard such that you will get full RPMs available to redline.
If this does not work there may be a more problems than just the jetting. Like clogged mains, or ignition, etc.
This has always worked. By restricting the opening, you restore vacuum to the main throat.

In your video, I see the slide blip open, but I don't really see any fuel spray out of the needle jet. When the slide first opens there should be a pretty good spray visible (but it might not show up on video very well).

NEVER LOOK DIRECTLY INTO THE THROAT OPENING WHILE RUNNING. Flames can shoot out 3 to 4 feet, and douse you with flaming gasoline.

I'll see if there is a video online.

Somewhere after 3:30 ish, you can see the fuel spray.

I'll do that today Loudhvx. Yesterday I took a step back to verify some basic items. I checked cam timing. Some have suggested it may be off one tooth. Once assembled I'm going to put another bank of carbs on it off of an 82 GPz750 I have to see if that changes anything. I'll do the cardboard test then. Cam timing shown below: