On the road and stumped: hesitation/lurching during acceleration (among other things)

[Guest]

Hey there,

Sorry, this got a bit long…
As some of you regular readers may know, I'm out on a big road trip and stuck in Flagstaff, AZ doing maintenance and trying to solve a problem that's preventing me from going further. I was also troubleshooting a problem of low power and an intermittently firing cylinder (see this thread for background).

I wanted to write with an update in hopes that someone may point me in a good direction. The bike runs, but not well enough for me to leave the city yet.

Here's the current situation: I adjusted the valve clearances (0.05mm-0.10mm on all valves) and synchronized the carburetors (I discovered after I synched them that the little ring clamps on the intake boots were not fully tight, and I'm willing to synch again with them tight if anyone feels like that would make a difference, it didn't seem like a huge deal to me, as they seem to seal well without the rings tightened down). I also checked compression (120psi on all 4 cylinders) and replaced the ignition coils and wires with Dynatek stuff. Spark plugs look good and all are sparking with the new coils/wires.

The issue I had previously with one cylinder not getting hot (thread above) seemed to disappear when I put everything back together and synched the carbs. I thought I was in the clear until I took it for a test ride. When idling the bike sounds nice, but when it is accelerating it seems to hesitate and lurch a bit, almost like I'm going over a series of small, random bumps. The problem varies in intensity as I ride, and the sound of the engine changes as I ride, too. I can only describe it as a sort of helicopter-like noise, choppy and intermittent, rather than the smooth purr that I feel it should be. Sometimes I hear a backfire, but I'm not sure if it's in the carbs or the exhaust.

After the incident with a cylinder exhaust pipe not getting hot, I've been checking them intermittently. At first #4 wasn't getting hot, then it was #3, then they all were getting hot, then #2, and now they seem to be all working.

Here's what I've thought could be causing the problem and what I've done to address each:

-Air leak somewhere: I have new intake boot o-rings, and I recently resealed the air box. I tightened everything down between the intake boots and the air box
-Carb fuel delivery issue: I rebuilt the carbs 4,000 miles ago, put Seafoam in 1,000 miles ago
-Carb synch issue: this seems possible given the loose ring clamps during synchronization, will address this tomorrow if anyone thinks it could be the issue
-ignition problem: I replaced the coils/spark plugs and am getting good spark on all 4 cylinders, compression is good
-ignition wiring: I haven't done anything for this, and I'm wondering if the problem could exist in my ignition wiring somewhere on the low-voltage end of the coils. Maybe I didn't properly crimp the primary wires down or there's a floozy wire somewhere?

Any thoughts? I am completely stumped, and fear that I may have to take it to a bike shop, which I loathe to do as I don't have a ton of money to throw at this.

Thank you so much.

[azr]

With everything you've done to the ignition, new coils and wires, I'm guessing your plug caps are new as well, if they're not get new ones. The issue has to be in your carbs if all of your plugs are getting a good hot spark, and you've verified this. Definitely resynch the carbs, those clamps not being tight will most definitely effect things. Now it could be a fuel delivery problem, ie the petcock is not working well, at idle where there is not much fuel demand the idle is good but once you start to ask for more fuel under a load things start to go wrong. The hesitating, lurching etc.. sounds like a fuel issue. After you re synch take it for a ride, but when you start it up move the petcock lever to the 'prime' settting and see if that improves things, that way you take the vacuum out of the scenario. Make sure your oil does not smell like fuel as well. Remind me again where your mixture screw is set at.

[azr]

Just a thought, but is your air filter clean and very, very lightly oiled? You would have to have a fairly severe air leak to be causing this much of an issue. And what's the voltage that is getting to the coils?

[azr]

Is there anyone near Flagstaff that could help this poor member out? crap if I had a known good rack of carbs for your 850 I'd be putting it in the mail tomorrow.

[Gorminrider]

JUST a thought but If you haven't already done it, Turn the petcock to Prime and see if that helps.

I have an idea (based on recent experience) that If the petcock is not delivering full fuel flow when the bike is moving, then even slight variations in carburetors (and their float needles etc) may cause the symptoms you describe...It's like running out of gas, except you never quite do- one going lean,another going dry,the others being "happy enough" because they are hogging the fuel available..and somehow incomprehensible (to me!) as a fuel starvation issue because the tank is full and bike idles ok.
It can turn up as an issue 3 miles down the road (because carb bowls start full but can't keep full) or halfway through a tank(because fuel "pressure" has dropped)

[klylor10]

Thanks for the support, everyone. It's a bit frustrating, but all part of the adventure. I added some seafoam to the gas tonight and will let it sit in the carbs overnight.

With everything you've done to the ignition, new coils and wires, I'm guessing your plug caps are new as well, if they're not get new ones. The issue has to be in your carbs if all of your plugs are getting a good hot spark, and you've verified this. Definitely resynch the carbs, those clamps not being tight will most definitely effect things. Now it could be a fuel delivery problem, ie the petcock is not working well, at idle where there is not much fuel demand the idle is good but once you start to ask for more fuel under a load things start to go wrong. The hesitating, lurching etc.. sounds like a fuel issue. After you re synch take it for a ride, but when you start it up move the petcock lever to the 'prime' settting and see if that improves things, that way you take the vacuum out of the scenario. Make sure your oil does not smell like fuel as well. Remind me again where your mixture screw is set at.

You called it, plug caps are new also. I'll synch the carbs again tomorrow and try a test ride in prime. I'll give the oil a sniff, too. My mixture screw is a bit different on each carb as I used the off idle method detailed on Bikecliff's site. Each one is a bit past 2 turns out from lightly seated.

Just a thought, but is your air filter clean and very, very lightly oiled? You would have to have a fairly severe air leak to be causing this much of an issue. And what's the voltage that is getting to the coils?

I peeked at my air filter and it appeared clean (I've got a K&N with 4,000 miles on it, very lightly oiled as per their instructions when I put it in) but maybe I should clean it just to be safe. Not sure what my voltage is getting to the coils. How should I go about testing this?

JUST a thought but If you haven't already done it, Turn the petcock to Prime and see if that helps.

Good idea, I'll try that tomorrow.

[azr]

The air filter will be fine then, the only thing you could have done wrong is to over oiled it, make sure that's not the case and if not leave it alone. I'm not 100% sure on your mixture screw setting but what colour were your plugs? To test the voltage getting to your coils you need a volt meter and test the voltage at the orange/white wire going to your coils while you have the bike running. Keep the connection connected, and stick your voltmeter probe into the connection somehow, and the other meter connector to a good ground. Anything above 11 volts is good, even 10 can work but anything lower than that and it could be causing an issue. But from what you describe I'm really thinking about fuel, not electrics, but a good thing to check for sure.

[klylor10]

The air filter will be fine then, the only thing you could have done wrong is to over oiled it, make sure that's not the case and if not leave it alone. I'm not 100% sure on your mixture screw setting but what colour were your plugs? To test the voltage getting to your coils you need a volt meter and test the voltage at the orange/white wire going to your coils while you have the bike running. Keep the connection connected, and stick your voltmeter probe into the connection somehow, and the other meter connector to a good ground. Anything above 11 volts is good, even 10 can work but anything lower than that and it could be causing an issue. But from what you describe I'm really thinking about fuel, not electrics, but a good thing to check for sure.

Thanks so much for your support, advice, and kind words, azr.

I followed the instructions from K&N when oiling it, half of their "pillow packet" and just enough oil to color the fibers.

My plugs are of what I believe to be a normal color (plug #3 was much less worn, which can be attributed to its lack of use due to it not firing for a while which I believe to be due to a faulty spark plug wire/coil) a bit of carbon deposit but in general light gray. Gaps are all good.

I haven't made it into the shop this morning to sync carbs or check voltage, but went out for a coffee and the overnight Seafoam treatment has done wonders! I need to ride it more to know for sure but it seems much better. I'm hesitant to say that this fixed the problem, because the whole thing wasn't too much of an issue before I took it apart and did this maintenance.

I had to crimp on new eyelets for the primary wires going into the new coils, and I wonder if those could be causing a floozy connection. I'll double check them in the shop today.

[OldVet66]

If Seafoam helps, You missed something on the rebuild or it has sat too much since. Seafoam worked on the injectors on my RX-8, but helps very little with carburetors. I would be using Startron for a stabilizer and help against alcohol in the gas. A 24hr soak in carburetor dip or ultrasonic is required to get a good rebuild. Keep it out of a shop and do it again. We can be real consistent with mistakes, and no carburetor kits!

[bonanzadave]

Fuel cap not venting ? Maybe that seafoam partiality cleaned a clogged filter screen inside the tank. Did it run any better with the petcock on PRI ?

[klylor10]

Fuel cap not venting ? Maybe that seafoam partiality cleaned a clogged filter screen inside the tank. Did it run any better with the petcock on PRI ?

Seems to run about the same on "prime" as it does with "on".

I won't be able to do anything until this evening, unfortunately. How would I be able to test for a non-venting fuel cap?

[eil]

Great to hear that things are turning around but I'm hesitant to give credit to the seafoam. If it does anything at all (and nobody has proven to me that it does), it's certainly not an elixer that you can just dump in the gas, dilute all to hell, and have it magically fix things.

If the bike idles fine, it's not a carb sync issue.

It does sound like a fuel/carb issue. Maybe there was some blockage that has now gotten dislodged. What's the condition of your gas tank? Are you totally sure it's completely rust-free? You can try draining the float bowls and see if there's anything in the gas.

Come to think of it, you've been travelling, are you sure you didn't get a bad fill-up of gas from some place with water in their tanks?

[eil]

Actually if there was water in the gas, it would be very hard to start and idle, so you can probably disregard that.

Another thought is that if the symptoms come back, try adding a bit of choke and see if that helps or makes things worse. That may point you to whether it's running way too lean or way too rich on acceleration, which will help narrow the cause down.

[bonanzadave]

How would I be able to test for a non-venting fuel cap?

Run it without the fuel cap....

Bring us up to speed on when this situation started. Somewhere between WA and AZ ?

[klylor10]

I'll address the questions, but first: after inspecting the petcock, inline fuel filter, and tank vent I saw no problems and decided that I would simply have to buy some carb dip, crack open the carbs and settle in for a good amount of work. I pulled the carbs from the intake boots and much to my surprise found that the connection point between the carbs and the boots was wet with gas on all 4 cylinders. Not a puddle, but there was definitely wetness. This seems abnormal to me. I pulled the plugs and #4 seemed like it may have been a bit wet but didn't smell like gas.

Before breaking apart the carbs, I decided to adjust the idle mixture screws again, and although I have a difficult time hearing the changes in idle as per the method on Bikecliff's website, they ended up being turned in a bit on all cylinders and still sounding great. I took it for a test ride and it seems much better, to the point where I'm unsure if anything is wrong. Perhaps I have just been running far too rich, since this problem began right after I synced the carbs (which included tweaking the mixture screws). I'm also at 7,000 feet elevation up here...

Does this sound plausible?

Now I gave the dilemma of breaking open the carbs to rebuild them while I have shop space, or trusting that they are okay and heading out, with potentially no place to work for 1,000 miles. What would y'all do in this situation?

On to the questions:
-I have gone to a few small town gas stations, so the bad gas is possible. I'm running an inline fuel filter and my petcock and filter seem fine.
-Tank has minimal rust, but a bit of gunk stuck to the bottom.
-This specific problem started right after the carb sync/valve adjust, but I've had a few intermittently firing cylinders before.