Engine Fluttering Sound

[SergeantChuck]

Both Friday and Saturday, I sprayed starting fluid all around the throttle body area with no reaction by the engine. I even expanded the spraying a little further than the throttle body and still nothing. Looking like it is not a vacuum leak. My next step will probably be to change the injectors and fuel rail.

 

[SergeantChuck]

I thought bad gas or a vacuum leak so I take out the air filter and there's a small gasket on both the top half and bottom half of the air box and part of it was out of place, lined it all up put it back together (did the EFI reset) and sure enough problem is gone.

It doesn't take much to make a noticeable difference on the NC apparently

I'll take a look at this. I have had the air box apart many times and could have missed that but I think it is good. I have also done the EFI reset. I did not try a reset after fixing the throttle body leak.

 

[SergeantChuck]

Hearing that the throttle body was loose is an odd problem but explains the symptoms. I remember reading this thread awhile back and recently had similar problems.
No noticeable power loss but it felt like riding something with a carburetor with the choke on our when it's cold.
Not noticeable (at least to me) at an idle or when above 4,000 rpm but under load (when riding) it was definitely not right.
I thought bad gas or a vacuum leak so I take out the air filter and there's a small gasket on both the top half and bottom half of the air box and part of it was out of place, lined it all up put it back together (did the EFI reset) and sure enough problem is gone.

It doesn't take much to make a noticeable difference on the NC apparently

Just wanting some clarification. I took the air box back out. You said something about a small gasket on both the top half and bottom half of air box. I see the gasket in the bottom half of the air box but the top half is supposed to have one too? I did not see one BUT I really did not look that hard. I will take a good look tonight.

 

[SergeantChuck]

I finally got around to swapping the injectors. What a PITA. There is no room in that area. The wiring harness clips to the fuel rail which complicates things and the electrical connectors have a large rubber cover which in my case made it hard to press the release lever hard enough for it to click so I could pull the connector free.

The hose between the throttle body and the intake could not be removed because of how they positioned the clamp. I cannot get a wrench, socket, or screwdriver on that fasteners to loosen it so wiggling the fuel rail past that was tough. I got the new injectors in place and will reinstall the throttle body tonight.

Cross your fingers. I hope this fixes my problem.

 

[rippin209]

Just wanting some clarification. I took the air box back out. You said something about a small gasket on both the top half and bottom half of air box. I see the gasket in the bottom half of the air box but the top half is supposed to have one too? I did not see one BUT I really did not look that hard. I will take a good look tonight.

There is two Part #4 one above the filter and one below (one for the box and one for the lid)

 

[SergeantChuck]

There is two Part #4 one above the filter and one below (one for the box and one for the lid)

I found the second seal/gasket the same day. Finally decided to remove the filter and look in that grove. Thank for the reply.

 

[SergeantChuck]

Well, if anyone is following this story, the injectors did not help. Still having the same issue. I post all this just in case someone else has the same problem in the future.

In my mind, this leaves one of two things. Just maybe, it could have something to do with the Throttle Position Sensor or it is a partially restricted fuel filter which is lowering my fuel pressure and it the engine is not getting supplied enough fuel. I'm looking into a way to test the fuel pressure. I spoke with a fellow worker and was told he might have a fuel pressure tester that has some sort of a "tap" that is used jump between the fuel line and the fuel rail. He is checking to see if he still has it.

I'm going to pull the new spark plugs and take another look since it has been ridden on those plugs for about 200 miles. I want to see if it is in fact running lean. I have a bad feeling I'm going to have to pull the tank and replace the fuel pump/filter. If/when I do this, I will try to take some photos since I'm not sure I have seen any posted on the site.

 

[Jt105]

You’ve done a lot of work chasing this problem. When you checked the valves, did you verify the cam timing to see if the cam chain skipped a tooth?

JT

 

[SergeantChuck]

You’ve done a lot of work chasing this problem. When you checked the valves, did you verify the cam timing to see if the cam chain skipped a tooth?

JT

Yes, I did check this. I wish it would have been that simple.

 

[MZ5]

Dang. I hoped you had it. :-/

 

[SergeantChuck]

Question for the those more mechanically smart than myself with motorcycles. My father-in-law and I just checked the compression of both cylinders. I ran the bike until it reached operating temperature and then pulled both plugs. I screwed the compression testers into the left cylinder, cranked the engine, and we got a reading just under 120 PSI. Did the same for the right side and got a littler over 120 PSI. Not a huge difference and probably off due to my not getting the valves adjusted perfectly. What I'm curious about is if 120 PSI sounds right? I looked up the compression information in the manual but they obviously tested them differently because it mentions 470 RPMs and 257 PSI.

 

[showkey]

The 470 rpm is the cranking speed. If you had a low battery it would slow the cranking speed which would effect the pressure achieved.

120psi sounds low........but two questions: was a quality trusted gauge used ? Was the throttle held open during the test.

Have not done a compression test on a NC
257 sounds high but have seen similar values on other Honda’s witha 50 HP engine.
NT650 and Transalp has compression spec 225 psi
XR 250 spec 213 Psi
TRX300 spec 210 PSI
ST1300 spec is 199 psi

Edit.......my curiosity was peaked, plus cold and snowy and already skied 6 days this week.

Both plugs out, fully charged battery, throttle Wide open.....Snap On gauge:
Compression done on a 40* engine was 150 psi
Fully warmed up to operating temp, same parameters just a few pounds short of 250 PSI



Think you maybe on to the root cause of your problem. Cylinder leak down testwould be more informative on the cause and might determine a valve or ring problem. Assuming your gauge and test procedures are OK.

 

[SergeantChuck]

The 470 rpm is the cranking speed. If you had a low battery it would slow the cranking speed which would effect the pressure achieved.

120psi sounds low........but two questions: was a quality trusted gauge used ? Was the throttle held open during the test.

Thanks for the reply. I think the battery is good. It was cranking over quickly. The quality of the gauge? Well, I can't speak to that. It is my father-in-laws gauge. He typically buys good tools but I have no idea the true condition. As for the throttle being wide open. I must have missed that part. I did nothing with the throttle. I only cranked over the engine. Looks like we need to do it again with the throttle wide open.

Thanks for the info and reply.

 

[MZ5]

Yes, you’ll want to re-do. A closed throttle will throw your reading way off from what the book says. I hope this is _not_ the problem, and I kinda sorta think it is not, but you’ve done so much with this that everything needs to be checked.

 

[rippin209]

I had similar conditions possibly a lighter version of it. This started around a month ago, I've ridden around 500 miles sense then (much less then usual) due to travel or weather I tried checking the air filter, I tried using a fuel injector cleaner, through all of this it felt like my NC was running at 95% not terrible but definitely not right.

yesterday it through an engine code for the first time sense this started (85 or 96) not sure if the first blink counts. Either way the code didn't even seem relevant to my engine issues (gauge cluster) so that was annoying, after some web searching the consensus appeared to be, use connector cleaner on the connections like the ones going to the air box sensor (recently changed) and I also cleaned the plug for the water temp sensor (also recently changed)
because my motorcycle has sat in cold weather longer then it has as long as I've owned it and I don't have a battery tender, I pulled the battery out to hook it up to the charger that I do have (charger said battery was in perfect condition, charged and no problems) the positive side was slightly loose. So whether it was cleaning the connectors or it was tightening down the battery connections, my NC us back to 100% [emoji1360]

 

[SergeantChuck]

I had similar conditions possibly a lighter version of it. This started around a month ago, I've ridden around 500 miles sense then (much less then usual) due to travel or weather I tried checking the air filter, I tried using a fuel injector cleaner, through all of this it felt like my NC was running at 95% not terrible but definitely not right.

yesterday it through an engine code for the first time sense this started (85 or 96) not sure if the first blink counts. Either way the code didn't even seem relevant to my engine issues (gauge cluster) so that was annoying, after some web searching the consensus appeared to be, use connector cleaner on the connections like the ones going to the air box sensor (recently changed) and I also cleaned the plug for the water temp sensor (also recently changed)
because my motorcycle has sat in cold weather longer then it has as long as I've owned it and I don't have a battery tender, I pulled the battery out to hook it up to the charger that I do have (charger said battery was in perfect condition, charged and no problems) the positive side was slightly loose. So whether it was cleaning the connectors or it was tightening down the battery connections, my NC us back to 100% [emoji1360]

I'm willing to try anything at this point so I'll give it a shot but I'm not very hopeful. Mine is running much worse that a 5% loss. The entire engine shakes under a heavy load. I do appreciate the suggestion.

 

[rippin209]

I'm willing to try anything at this point so I'll give it a shot but I'm not very hopeful. Mine is running much worse that a 5% loss. The entire engine shakes under a heavy load. I do appreciate the suggestion.

Good luck man, sorry to hear you still haven't found that gremlin.

When you get a chance list everything you've done sense the trouble started, I know you've done this once before but if anything has changed[emoji848]

Maybe someone will have an insight

 

[showkey]

I'm willing to try anything at this point so I'll give it a shot but I'm not very hopeful. Mine is running much worse that a 5% loss. The entire engine shakes under a heavy load. I do appreciate the suggestion.

Did you retest the compression ?

 

[Jt105]

Here’s a straw to grasp at...

Have you replaced the clutch before or had the right engine cover off? Isn’t there a crankshaft position sensor on the engine cover? If that is loose or if the connection is intermittent it would cause a problem.

JT

 

[SergeantChuck]

Did you retest the compression ?

I have not. Probably this weekend when I can get my father-in-law to bring back his compression tester. I'll post the results.