1991 Kat- need diagnosis help

[smallwwb]

First off, I have searched this and other forums for hours before making this post.

My bike: 1991 Katana 1100. D&D 4-1, K&N filter, Dyna DC-3 coils installed 12/1995, otherwise stock.

I got this bike in June '15. It runs great at low speeds with less than 1/3 throttle, but at about 3.5-4k rpms or half-throttle plus, it falls flat on its face and wants to die.
Acts likes it's starving for fuel or on the rev limiter.

I took it to the local independent motorcycle shop (the only motorcycle shop within 50 miles). They had it for 6 weeks, rebuilt the carbs, installed a factory pro jet kit with stage 3 mains (135 I think), adjustable needles, tuned, synched, and no change. At that point I took it back and am trying to diagnose the problem myself.
Here's what I have checked:
1. Coils. 3 ohms on primary (correct according to Dyna) Can't get a read on secondary. It will flash anywhere from 10k to 19k for a second, then go blank on multimeter. Wires do not come out of coils, boots do not detach from wires. Wires are Taylor and look great. Boots look great.
2. Completely removed and blocked off California AIS system. No change.
3. Fuel petcock. intank screen is clean, tank was cleaned and lined 2012, no gunk in tank.
4. Compression. Waiting for plug socket on order as the bike did not come with a tool kit. All 4 exhaust pipes get hot when running.

Other than checking the compression and trying to get a better read on the coils, I'm stumped. I'm trying to rig up a system to bypass the fuel tank altogether to make sure the petcock is operating correctly.

Any help or a nearby local mechanic would be greatly appreciated!

[92xjunker]

@3k rpm your carbs are bringing in the main jets. I would install stock air filter and stock jetting, leave the FP needles. K&N filter may be causing your issue. It's not as bad on the 1100's but, could be.

[Kreylyn]

They had it for 6 weeks, rebuilt the carbs, installed a factory pro jet kit with stage 3 mains (135 I think), adjustable needles, tuned, synched, and no change.

How did they "tune" the carbs after the mods if the bike is still running like crap?

Quick things to check...

Fuel line is good, no kinked, is real fuel re-enforced fuel line and not vacuum lines.

Take the tank off, set it on an elevated spot. Put the end of the fuel line going into a fuel safe container. Use a clean vacuum line on the petcock, use your mouth to apply suction on the vacuum line - while holding that suction kink the vacuum line. This should hold the diaphram open for at least 30 seconds, and fuel should flow freely and well from the fuel line. If that isn't happening, or you can't make fuel flow with applying suction, your petcock is faulty.

Run the bike in the dark with the tank off, check for any arcing from the plug wires, and look down into the plug wells and check there too. In the dark, you can easily see if there are arcs happening. If there are, that's a major drop on spark and will cause the engine to run like crap and have no power.

Finally... if the only variable is RPMs (no matter the speed, temp, or how long the bike has been running) it does the same thing, and it only does it under load... it "could" possibly be a CDI issue. I'd see if you can find/locate a good known one for swapping out to test by, as you can't really test the CDI.

Krey

[smallwwb]

With the consistency of the issue, and the amount of carb work that was done, I have reason to believe that the carbs are at least baseline in tune and not causing the underlying problem.

Did the petcock suction test, petcock is good.

I finally got a plug socket that would fit, and pulled the plugs today.
I discovered: Plugs are not the recommended plug (
#1 plug very black and has gas on the threads, exhaust pipe was warm but not hot on that cylinder after running for 10 minutes. All other plugs too black but tan around where spark occurs.
Based on this info, I think there is a low spark condition on #1, and either too rich mains in the carbs (135) or low spark on the rest.
I suspect electrical issue, either coils or CDI.
I'm not much of an electrical guy. Looking for any input or someone local to Puget Sound who could diagnose the issue?

Thanks!

[92xjunker]

Check the coil input voltage while running, it should be over 11v, for a hot spark.
Black is rich... I'm still going with my previous statement because, it's always the same problem when over jetting and a K&N filter. If the shop didn't change or check the plugs when they guess tuned the carbs, they surely didn't use a dyno to tune the CV carbs for a K&N filter and a jet kit.

[smallwwb]

Absolutely good point.
Will do check while running. Any thought on the #1 being fouled?
The plugs in it are ngk R series 7ea so hotter than stock.

However, Bike still had same condition before Factory Pro jet kit installed...??

[92xjunker]

With the K&N? Check the voltage, if it's good, change the plug(s). Check for spark cable dielectric failure (arching) with the lights off. Checks good, go for a ride ( long enough to fully warm the engine),then pull the plugs and recheck their color, black is a too rich tune. FYI.. It could be a bad coil or faulty CDI but, these CDI units are pretty tough, could be a faulty ignition pickup coil. start at the carbs, first.

[smallwwb]

Checked the input voltage at each coil- it fluctuates between 1.5 and 1.8 volts at idle. Voltage at battery is a consistent 15v at idle, so charging system is good.
Couldn't check for arcing as it was daylight, but it seems there is an issue between battery and coils? Don't know anything about that part of the bike.

Can't believe the "factory certified Suzuki mechanic" didn't check the plugs and find this issue when "tuning" the carbs!

Any ideas or further tests greatly appreciated!

[92xjunker]

There is no way you got 1.8v and the bike was running. My bad, I gave erroneous test info. It would give an abnormal reading if it were running. Test the coil input voltage while starting, cold motor no choke would give you more test time as actual starting would be delayed. 11+v is ideal. I'm shocked nobody caught my incorrect test procedure, there you go, maybe nobody really gives a shit.....

[smallwwb]

7.4 volts at each coil, cranking over with spark plug wires disconnected.

[92xjunker]

That's not good. What is the battery voltage when starting? If the battery shows good (12v)......Well......the best thing you could do to help that issue, is to clean every connection, including the hand controls then follow up with a dab of dielectric grease. (The entire bike electrical connections) the whole bike isn't necessary but, why only maintain part of the loom?. Reseat all bolted grounds and + battery connections also.

[smallwwb]

Yep, the battery is fine.
I read another post that suggested following the current back from the coils to every connection, and finally back to the battery, however on my bike the wires for the coils come out of the loom just before the right side coil. Guess I'll need to study the wiring diagram a bunch.
I'm sure there is a way to test other parts of the system?

[92xjunker]

Just do the procedure I discribed. You don't want to have to unwrap the loom unless completely necessary. Should take 2hrs at the most and the loom will now be maintained and weather sealed. Find a good electrical cleaner, dielectric grease and Q-tips.

[smallwwb]

Still Working on the loom. Haven't found any bad looking connections yet. A friend said it could be the stator/regulator but from what I have read that would either cause over charging or no charging. The battery reads a good 14+ volts when running so it seems the stator is good?
About ready to send this thing to the local auto electric guy...

[Kreylyn]

Still Working on the loom. Haven't found any bad looking connections yet. A friend said it could be the stator/regulator but from what I have read that would either cause over charging or no charging. The battery reads a good 14+ volts when running so it seems the stator is good?
About ready to send this thing to the local auto electric guy...

Let me simplify the connections to check for you.

These are the connection points.

Coils, ICM (2 points, out to coils, in from key switch), key switch connector, the key switch (don't forget the switch is exactly that, a switch with multiple connectors inside), battery.

So I would suggest a good digital volt meter. You want to check power before the connection, and after.

So for example:

Check your power reading on the battery post. (lets say hypothetical it reads 12.2 volts).

Then, check the power reading on the wire at the battery post. (lets say hypothetical reading 12.1 volts)

Here is an example of a connection power loss. Clean up the battery post, check the connector end is clean, that it's tight on the wires, that you don't have head damage to the wires at the connection point, that a mis-crimp didn't happen at the factory causing only partial of the wires being actually included in the connector crimp... and so on.

Every connection having a .1-.3 volt drop, and then having 10 different points or more that this can happen... means you quickly add up to 1-3 volts total drop by the time you get to the coils. And that means a no or hard start issue.

That said, if you check and clean and fix all the issues you can, but find you still don't stop the drop in voltage from between the battery to the coils, you can do a simple modification that costs less than $10 on average to completely bypass all the bad points. It's called the "coil relay mod". Done right, it's simple, safe, and completely reversible.

Just fyi. Your bike has an alternator, not a stator. It's a full on real alternator. The regulator is build in. Together they are a pretty solid build component, and very rare for them to go bad unless something has out right damaged them (like someone screwing with the wiring and causing an actual major issue that fries them). General use and age doesn't lead to failures there very often if much at all. Where an issue is common, is the wiring harness that feeds the alternator with it's information on how much power is needed for it to charge the system.

Simple of how that works... the regulator adjusts the output of the alternator based upon how much power is fed back to it, after it runs through the entire wiring harness. If, like above described issue I was describing how to track down, you have power dropping through the wiring harness... that means you could have a situation where the voltage being fed to the regulator is much lower than the voltage at the battery. Ultimately, you don't want the battery to over charge, so if your getting voltage drop that puts voltage at the regulator at 14v, but the battery is getting 16v... your gonna have a fried battery eventually.

The voltage input for the regulator is an orange wire, on the alternator. So when you do voltage tests, you will want to eventually check 3 key points.

With the bike at 3500 rpms, check voltage out of the alternator, battery voltage, and voltage into the alternator (orange wire, with it still connected) to check variances between all those points. Again, if there is major differences, your going to need to start checking/cleaning connections. You could do another mod just like the coil relay mod, running a power wire directly from the battery to the voltage regulator (replacing the orange wire from the harness basically) if needed, but I highly recommend trying to fix the issues with the OEM equip first... THEN do the relay mods only if your unable to resolve or to fix the issues means complete replacement of a wiring harness. I'm not gonna replace the entire harness when the relay mod would resolve the issues. I'd not jump to it first either, might be just 1 -2 connection points that are simple to clean up and or repair.

Don't forget heat will effect wires and how electricity flows. So electrical issues that are "random" may not be as random but are heat effected. So I suggest if you have any electrical concerns, check the bike when cool and first started... Then do the same checks again at the same points, when the bike is hot and ridden a while. So check it, then go for a nice ride, then come back and check it again. This will help narrow down more issues for you.

None of these steps would require you "open up" the wrapping on the wiring harness, unless you find a problem in a wire between connections. Then you might need to track down damage, but you will have a very specific section of known wire to track down then.

Krey