Low idle, no power with throttle

[dielman95]

Hey everyone.

I bought myself a ‘87 K75 about a year ago for a cafe project. I got it back together and running for a few weeks, but now I’m having some idle/power issues. I took her out for a ride, parked for a while, and then when I tried to ride home I get very little throttle response, can barely get over 4-5k rpm. I suspected a fouled spark plug because one of the cylinders was cold. I swapped in new plugs and that seemed to help a tad. All cylinders are firing, but now my Idle is still sitting at ~500 rpm, and still no power when I try to ride.

The list of stuff I’ve tried/replaced:
New fuel injector relay
New spark plugs (mentioned above)
Tried known good battery
Tried balancing the throttle bodies with a carb tune pro
New crank case hose (that Z tube that alway goes bad)
New fuel pump+filter (replaced 2 months ago)

Any thoughts? I’ve seen a couple other threads with similar issues that never seem to get a conclusive solution

[blackie1]

you could run your bike in complete darkness to see if you can spot any shorting from your HT leads just to double check if you have any leakage

[Scott_]

You say you 'tried' balancing the throttle bodies, how did you come out with that.
When was the last time the valve clearances were checked?
What did the old plugs look like when they came out, grey, black, wet, dry.....

Have you tried checking for other vacuum leaks around the TB's.
Have you measured the actual fuel pressure. (thinking pressure regulator)
Have you checked the actual fuel spray pattern from the injectors. (thinking partly plugged injector)

I'm sure others that actually have a 75 will chime in shortly with more suggestions.

[Laitch]

I’ve seen a couple other threads with similar issues that never seem to get a conclusive solution

That happens. I've also seen plenty of threads where the problem's source is discovered and a remedy found.

By the look of your attempted remedies, you seem to believe there's a fuel delivery problem. You need to be sure that all the fuel connections in the tank are tight and, as Scott_ indicated, check the intake manifold boots for vacuum leakage. You can use propane for that while the engine is idling. Change in idling while propane is being directed around a boot means leakage in the boot or its joint with the system.

You also need to explore other possibilities. Test engine response after each task so you'll know which condition might have been governing the fault. Check the plug wires to be certain their terminals are clean and that they are firmly seated on the plugs. Check them like blackie1 suggested, too. Check the coil wires to be certain their wire terminals are clean, the coil terminals are clean and that primary wires are firmly attached and not faulty. Check the output of the coils according to values in the troubleshooting guide on the site. One or both of the Hall sensors might be faulty so do the test in the guide for them too.

Get back to us with the results.

[dielman95]

That happens. I've also seen plenty of threads where the problem's source is discovered and a remedy found.

By the look of your attempted remedies, you seem to believe there's a fuel delivery problem. You need to be sure that all the fuel connections in the tank are tight and, as Scott_ indicated, check the intake manifold boots for vacuum leakage. You can use propane for that while the engine is idling. Change in idling while propane is being directed around a boot means leakage in the boot or its joint with the system.

You also need to explore other possibilities. Test engine response after each task so you'll know which condition might have been governing the fault. Check the plug wires to be certain their terminals are clean and that they are firmly seated on the plugs. Check them like blackie1 suggested, too. Check the coil wires to be certain their wire terminals are clean, the coil terminals are clean and that primary wires are firmly attached and not faulty. Check the output of the coils according to values in the troubleshooting guide on the site. One or both of the Hall sensors might be faulty so do the test in the guide for them too.

Get back to us with the results.

I’ve got a fuel pressure gauge on the way, I’ll report back the results when it gets here.

Would I be able to use starter fluid to test for air leaks around the boots, or do you have to use propane for this test? I’m not convinced it’s a fuel delivery issues, that’s just some of the first troubleshooting steps I’ve taken so far. I’ll double check the coil wires, but last I looked they were clean and secure.

You say you 'tried' balancing the throttle bodies, how did you come out with that.
When was the last time the valve clearances were checked?
What did the old plugs look like when they came out, grey, black, wet, dry.....

Have you tried checking for other vacuum leaks around the TB's.
Have you measured the actual fuel pressure. (thinking pressure regulator)
Have you checked the actual fuel spray pattern from the injectors. (thinking partly plugged injector)

I'm sure others that actually have a 75 will chime in shortly with more suggestions.

I’ve never personally measured the valve clearance, so I have no clue the last time it was checked. I didn’t know a bad clearance would effect idle/power like this. The throttle bodies were relatively balanced, but the output pressure was only minimally affected by adjusting the brass bolts. When “spray pattern” is mentioned, what exactly does that mean? I thought if the injectors were pulsing in general, that meant they were most likely fine.

[Laitch]

Would I be able to use starter fluid to test for air leaks around the boots, or do you have to use propane for this test?

Yes, you can use starter fluid. The reason for not using a volatile fluid like that is if excess fluid pools then a spark is generated, a fire can follow. Be careful with the spraying.

[The Mighty Gryphon]

Were the new spark plugs NGK's?  Did you put terminal nuts on them if they were?  NGK specs a plug for the K bikes that is correct in every way except that the terminal for the plug wire doesn't have the terminal nut that is necessary for a good connection.  You can get the nuts from NGK tech service in Michigan.

You say you balanced the throttle bodies.  Did you start with all the mixture air screws about 1 1/2 turns out?  When you are done, all the air screws should be open about the same amount.  If you start from the same point, you shouldn't need more than a half turn either way to balance the vacuum on a cylinder.

Proper spray pattern from the injectors should be a fairly narrow stream.  A fine mist indicates a plugged nozzle.  There are inexpensive injector cleaning kits that have a plastic fitting that allows you to connect he injector to a can of carb cleaner and a wire to connect it to a 9v battery to open it.  They can be had online for under 10 bucks.  There are also rebuild kits that have new o-rings, filters and pintle caps that will rebuild all your injectors for 5-6 bucks.

A quick test to see if the problem is in one cylinder would be to start up the engine and let it run for a couple seconds.  Shut it down and feel the header pipes close to the head.  They should all feel equally hot.  If one is colder or hotter than the others, that is where the problem is and where you should concentrate your attention.  If all are the same, the problem is more likely to be in the engine control system or one of the sensors for ignition, temperature or air flow.

Last, as mentioned earlier, double check the hose connections to the fuel filter.  You will not be the first to have had a connection slip off the filter and leak fuel back into the tank.  This can be best seen by running the engine with only a gallon of fuel in the tank.

[dielman95]

Were the new spark plugs NGK's?  Did you put terminal nuts on them if they were?  NGK specs a plug for the K bikes that is correct in every way except that the terminal for the plug wire doesn't have the terminal nut that is necessary for a good connection.  You can get the nuts from NGK tech service in Michigan.

I just checked, my NGK plugs are missing the terminal nut. I'll start by snagging some and see if that helps!

[blackie1]

you said "throttle bodies were relatively balanced, but the output pressure was only minimally affected by adjusting the brass bolts"

I assume you are aware that only the air mixture screws are to be adjusted and not the screws that have a blue dab of paint on their heads, which are set at factory and should be fiddled with at your peril.

read this

http://www.motobrick.com/index.php/topic,364.msg576.html#msg576

[dielman95]

you said "throttle bodies were relatively balanced, but the output pressure was only minimally affected by adjusting the brass bolts"

I assume you are aware that only the air mixture screws are to be adjusted and not the screws that have a blue dab of paint on their heads, which are set at factory and should be fiddled with at your peril.

read this

http://www.motobrick.com/index.php/topic,364.msg576.html#msg576

Haha yes I’ve heard many a horror story for those who dare touch the blue painted screws. It was the air mixture screws I was messing with

[blackie1]

good to hear.

and although possibly unrelated to your current problem you should check your valve clearances. very simple job to check at least.

a little more involved if adjustment is required.

should really be done PRIOR to throttle body balancing to get best results.

it makes a hell of a difference I found and guards against possibly burning your valves.

good luck

[Laitch]

When “spray pattern” is mentioned, what exactly does that mean? I thought if the injectors were pulsing in general, that meant they were most likely fine.

There's always more to learn. All the injectors in this video are pulsing.

[stokester]

good to hear.

and although possibly unrelated to your current problem you should check your valve clearances. very simple job to check at least.

a little more involved if adjustment is required.

should really be done PRIOR to throttle body balancing to get best results.

it makes a hell of a difference I found and guards against possibly burning your valves.

good luck

Yes, easy to check, and only requires a couple of fairly inexpensive tools to change the shims which are readily available at the local Kawasaki/Yamaha dealer.

I found the first indication was a long warm-up and a valve adjustment took care of it.

[dielman95]

So I finally got spark plugs with the terminal nuts, but they didn't seem to make much of a difference. I did spray some starter fluid on each of the throttle body boots. I saw the RPMs jump by about 100-150 momentarily when I hit the center clamp. That's enough of a jump to indicate a major air leak, right? If so, can I take the K75 plenum chamber off without removing the whole frame (thats what I did the first time around)?

[Laitch]

That's enough of a jump to indicate a major air leak, right? If so, can I take the K75 plenum chamber off without removing the whole frame (thats what I did the first time around)?

If it jumps, it leaks. Leaks—major or minor—will affect performance. Furthermore, look at the throttle cable mechanism at the throttle bodies. It's possible that one of the clamps on the rubber hoses is interfering with the mechanism and could be the cause of the engine's failure to accelerate past a certain point. If so, you'll need to rotate the clamp sufficiently so it doesn't obstruct operation.

You can remove the plenum without removing the engine from the frame. When you reinstall it, mind the clamp positions and be certain they're tightened sufficiently.

[dielman95]

wow realized I posted this reply on the wrong one of my threads lol.

Sorry for the delay in updates, Boston winters and a busy schedule have put a delay in working on the bike. I did swap out the throttle body boots out for a fresh set, added some RTV to take care of what I thought was an air leak, yet no change. The RPM is steady at ~500. I believe my next step is to check the fuel pressure to see if the pressure regulator is bad. I'll post when I get around to checking this.