Engine miss - from good to bad to (nearly) dead

[4nRelations]

I've got a head-scratcher and am trying to narrow down the possibilities, hoping someone can help from prior experience. Fuel deliver problem the top pick by two of us who are reasonably good troubleshooters, but not quite sure where to start -- and electrical is also in the back of my mind. One thread on this forum suggests a carburetor rebuild is needed, while another points to the known spark plug gap problem. NT 2006.

Symptoms: After taking it out of winter storage (not warm garage) it ran great for 20-30 miles then started missing, rarely at first. Got progressively worse with each mile (vs. BAM!), and by 60 miles it barely ran (tow truck #1). Took it to a local guy who changed out a fouled spark plug (changed both) and it ran fine for 20-30 miles ... then same symptoms, starting with a miss/backfire and got progressively worse over the next 20 miles or so (tow truck #2). Next was cleaning out gas tank and lines but problem still exists. It's the progression from good to bad to (nearly) dead that confounds me. Ambient temp maybe 70F. Any takers? I'd love to know what I'm looking for before I start.

 

[mikesim]

I've got a head-scratcher and am trying to narrow down the possibilities, hoping someone can help from prior experience. Fuel deliver problem the top pick by two of us who are reasonably good troubleshooters, but not quite sure where to start -- and electrical is also in the back of my mind. One thread on this forum suggests a carburetor rebuild is needed, while another points to the known spark plug gap problem. NT 2006.

Symptoms: After taking it out of winter storage (not warm garage) it ran great for 20-30 miles then started missing, rarely at first. Got progressively worse with each mile (vs. BAM!), and by 60 miles it barely ran (tow truck #1). Took it to a local guy who changed out a fouled spark plug (changed both) and it ran fine for 20-30 miles ... then same symptoms, starting with a miss/backfire and got progressively worse over the next 20 miles or so (tow truck #2). Next was cleaning out gas tank and lines but problem still exists. It's the progression from good to bad to (nearly) dead that confounds me. Ambient temp maybe 70F. Any takers? I'd love to know what I'm looking for before I start.

The NT's that we are most familiar with are the 2010 and 2011 which were the only years they were imported to the US. These two years were also fuel injected. There is a Deauville forum from the UK and they have much more experience with the carbureted NT's. Having said that, I have been a forum member on that website since 2011 and have read many posts from the members there. I seem to remember that several of the folks over there had similar problems from time to time. One of the things that I recall was quite common was the fuel pump relay or in UK terminology "points". It seems that the bike would run OK with a nearly full fuel tank but when the fuel level ran low it would develop quite a miss and sometimes quit altogether. A new set of "points" or relay usually fixed it. The life of the relay wasn't very long so they added a diode to the relay to prevent arcing and burning up the "points". Another item that was quite prevalent was corrosion of the connectors due to the road salt used in the winter in the UK. Living in Sweden, you may have have the same issue. That's all that comes to mind. You said that you cleaned the fuel tank and lines, were they dirty? Did you remove the float bowls from the carbs and look for grundge in there? The one thing you mention is that it seems to run OK when cold but the misfire occurs after a complete warm up. That leads me to suspect something electrical. On our 2010 and 2011 NT's we have had some issues with the crankshaft position sensor that occurs when the engine is warm, but I don't know if this would apply to your bike. If you haven't yet posed your question to the guys across the pond, I would certainly do so as they are far more knowledgeable about your bike than we are.

Hope this helps!

Mike

 

[cliffh]

There is a chance that your tank vent has been blocked by an insect, rust or something. As fuel is used, a vacuum is slowly pulled until the engine starves for fuel. This may be unlikely, but it has happened to me. Just loosen the gas cap when the bike starts to run rough and see if it immediately gets better. This would be a free easy item to fix.

I don't know about your European model, but many bikes have a vacuum operated fuel valve. Make sure that the vacuum line is connected and not leaking.

Cliff

 

[ST1100Y]

.... another points to the known spark plug gap problem. NT 2006.

I'd start with replacing the spark plug connectors, it sounds heat related, possible they've corrosion/cracks on the resistor...

 

[DirtFlier]

A bad crank position sensor will keep an engine from starting when it is very hot - such as during a brief gas stop in hot weather. Once the bike's temp has returned to something closer to normal, the faulty crank position sensor will usually work again. It happened to me, and I continued that trip but replaced the sensor once home. And it only acted up twice.

 

[4nRelations]

Many thanks, guys, but none of the above reflect what I'm experiencing except possibly spark plug connectors? Once it starts clogging up it doesn't get better when the bike cools down. Nor is it a tank vacuum problem though it certainly acts like it could be. My friend who cleaned the tank saw a little minor white gunk but nothing that he thought could cause the problem I'm experiencing (he's a prize winning racer and knows his stuff). Mike, thanks for deeper insights, I didn't realize the NT was only imported to the US in 2010-11. I'd seen elsewhere in this forum that someone had tipped another person to the UK forum and now I understand why. I started here as I'm originally from CA and thought there'd be a bigger universe of experience here (my profile photo is from 1971, me on a CB350 in the middle of the Mojave Desert). Thanks again for the input - if my additional comments here trigger anything, bring it on.

 

[mikesim]

Hmmmm.... each time it acts up and gets progressively worse until it will no longer run.... then you find fouled spark plugs, replace or clean them and then all is well for a while until the problem repeats itself... correct? This sounds very much like you have a float or floats sticking in the carburetor causing fuel flooding, or the needles in the carbs have deteriorated to the point where they no longer seal.... ethanol fuel is wonderful stuff....
I think it's time you take the carbs off and check them..


Good luck!

Mike

 

[Hondafan]

Since it is only fouling one plug, a float problem or leaking float needle seems like the likely culprit.

 

[junglejim]

Do the carburetors have overflow tubes? Your bike is probably new enough to be without them. And that would surely cause your problem if the float was stuck open or leaking.

 

[mikesim]

Do the carburetors have overflow tubes? Your bike is probably new enough to be without them. And that would surely cause your problem if the float was stuck open or leaking.

Another thought occured to me that if the float was stuck open or leaking the excess fuel could be washing down the cylinder and diluting the oil with gasoline. You may want to pull the dipstick and sniff the oil and see if it has a raw gas odor. I have heard of very rare cases of a crankcase being filled with gasoline when the engine stops with the intake valve opened and the bike is oriented in a nose down attitude the overflow from the float bowl travels down the intake manifold into the engine.

Mike

 

[Phil Tarman]

I had something somewhat similar. When my bike got to about 120K miles, it would miss and slow down. Opening the throttle caused it to slow down more. My dealer here has a guy who is a Honda specialist (but he's gone during our coldest months). I had decided it was probably a fuel pump issue. He tried several different things and nothing made any improvements. He'd work on it when he didn't have anything pressing...he probably put 5-6 hours into it with no luck. Finally tested the fuel pump. It had normal pressure, but when he tested the flow it was at about 50% of what it should have been. We replaced the fuel pump and it was running fine when I traded it for my 2nd '10 NT. #1 had 139K miles by then and #2 is up close to 30K miles.

 

[4nRelations]

Thanks again, guys. I think Mike and Hondafan have nailed it... float problem, likely needles. Mike, I've checked the oil and so far so good. A friend of mine here in Sweden had a Gold Wing and also suggested the needles could be a problem. Mike, when you wrote ethanol it triggered a vague memory of the Swedish gas stations switching over last summer to a new blend with a higher mix of renewables. And then I didn't put it in a warm garage, which I certainly will do next winter (never had a winter problem here over 18 years but most of that experience with Beamers). Thanks again for weighing in, I'll stick with the Yanks going forward and let the Brits keep their bloody little island

 

[mikesim]

Regarding the ethanol mix, Hondas on this side of the pond are designed to work OK with up to a 10% ethanol mix. Anything over that can be problematic. I would suspect the same for bikes sold across the pond, but I can't be sure on that. Even with the allowed 10% mix, ethanol laced fuel is nasty stuff. In the presence of moisture, phase separation occurs and corrosion and an ethanol/water sludge can form clogging jets and tiny ports in the carb. The float needles are usually Viton which is designed to handle the 10% solution but once phase separation occurs, all bets are off. Over here, there are still some gas stations that still sell 100% pure gasoline. If you can find 'em over in Sweden, I would most definitely use them due to the long layover you have during winter. If you can't find pure gas, then I would use a fuel stabilizer. Hope you get your problem resolved quickly.

Mike

 

[ST1100Y]

Regarding the ethanol mix, Hondas on this side of the pond are designed to work OK with up to a 10% ethanol mix.

Over here most Honda model production years from '89/'90 onward only... studying their list unvails some restrictions though:
RC47 Deauville NT650 2002 onward... (the 650 was build from 1998 till 2005, so only the last 3 model years can handle E10)
RC52 Deauville NT700 year 2006 onward...
RC59 Deauville NT700 year 2010 onward...

And despite the fact my SC26 ST1100 (produced 1990 till 2001) is listed as "all years" I avoid that ethanol by all means... especially before grounding the bikes during winter...
Premium fuel gives better performance and range anyway, I also avoid discount stations and use brand ones only...
(the owner of the Toyota workshop I have my trusty '96 Carina estate in service, told me a lot about engine failures due to cheap, contaminated fuel on old and current models...)

 

[4nRelations]

He's back. Me that is. Digging yet deeper (Mikesim, mine's a 2006 NT700). Ha! I don't have a carburetor, it's fuel injected. Got my hands on a tech manual and the symptoms that come closest to the troubleshooting guide point to "IACV circuit malfunction - Loose or poor contact of the IACV connector, or its circuit malfunction", leading to "Engine stalls, hard to start, rough idling". Still, no mention of the progression I've experienced from Good to bad to (nearly) dead. I'll check in with the Brits' forum to see if they've had any experience here. Thanks again, guys.

 

[mikesim]

Well, that paints a different picture indeed. Not having any experience with the NT prior to the 2010 made me think/assume that it was carbureted. The IAC valve (Idle Air Control Valve) is certainly then something to look at but I don't think a malfunction would cause a no start or poor driveability at higher RPM's. The air intake on the engine is primarily controled by a butterfly or slide valve in the throttle body.. On fuel injected vehicles the IAC valve is used to control air intake at idle speeds independent of the butterfly or slide valve. The IAC valve is a small pintle controlled by a small stepper motor. The IAC valve input is controlled by the engine ECU which accepts inputs from the CTS (coolant temp sensor), O2 Sensor (oxygen sensor), MAF (mass airflow sensor if equipped), MAP (manifold absolute pressure sensor if equipped) and TPS (throttle position sensor). The IAC valves principal job to to keep the engine at the target idle speed and stabilize the idle. You will note that when you start the NT when cold, its idle RPM is somewhat higher than normal. This is the IAC doing it's job. It is setting your target idle at a higher speed during warmup up based upon input from the CTS. Once the engine reaching the proper temp it will return to the lower target idle speed. The IAC really doesn't do much at 2K rpm and higher that's why I'm suspicious that your problem lies elsewhere. If you have the tech manual, see if you can find the procedure to read any fault codes that may be stored in the ECU. There may be codes stored in the ECU that haven't caused the check engine light to illuminate yet. These are "pending" fault codes.

Sorry for the lengthy treatise on the IAC but many times its helpful to understand how stuff is supposed to work. If you already knew about the IAC, I apologize if I wasted your time. Once again, good luck!

Mike

 

[Hondafan]

I thought it was a 650 carbureted model. I would try swapping the spark plug caps and see if the problem changes cylinder.

 

[4nRelations]

No apology needed, @mikesim, very much appreciated. Am a bit embarrassed about having led you and others down the carburetor road but got thrown off by another thread on this forum, which led to my leading you guys down the wrong road. I should know better after 5+ years as a factory troubleshooter for Deere!!! (admittedly 40+ years ago, however). But alas, getting lazy in my old age when we don't have to check the oil every other fill-up. Your IACV explanation was great, thanks. Since the connectors have been flagged as a problem elsewhere and they're easy to check, I'll start there of course. Yes, even swapping the spark plug caps a good idea, @Hondafan. So many (potential) fixes, so little time...

 

[Coyote Chris]

There is a chance that your tank vent has been blocked by an insect, rust or something. As fuel is used, a vacuum is slowly pulled until the engine starves for fuel. This may be unlikely, but it has happened to me. Just loosen the gas cap when the bike starts to run rough and see if it immediately gets better. This would be a free easy item to fix.

I don't know about your European model, but many bikes have a vacuum operated fuel valve. Make sure that the vacuum line is connected and not leaking.

Cliff

a malfunctioning poppet valve in the Kawasaki gas gap was famous for fuel starvation. The bike would stop after a long ride, you would get off the bike, look in the tank, lots of fuel, and the bike would start right up, especially if you put the manual/automatic petcock to reserve. Dont know a thing about the Deauville but the English have a great forum about it....dont know if the D has trouble codes but the forum is the place to start.

 

[4nRelations]

a malfunctioning poppet valve in the Kawasaki gas gap was famous for fuel starvation. The bike would stop after a long ride, you would get off the bike, look in the tank, lots of fuel, and the bike would start right up, especially if you put the manual/automatic petcock to reserve. Dont know a thing about the Deauville but the English have a great forum about it....dont know if the D has trouble codes but the forum is the place to start.

Thanks for writing. While the progression from Good to Bad feels a lot like it could be a vacuum problem, it isn't improved by opening the tank. Once it's progressed to Bad, the next stage is Nearly Dead. I've joined the UK group now. There seems to be strong consensus around the spark plug caps, though the IACV circuit also remains suspect.