Bike runs rough under 5k RPM
 

Let's see if anyone on this forum can help me out.

I'll start with the symptoms.
The bike starts and idles fine.
With the throttle just cracked open and the engine RPM between 2k-4.5k or so it runs very rough. Throttle response is slow. I can hear the engine cough and sputter.
Once the rpm gets over 5k the bike runs great, power is smooth and predictable, and throttle response is sharp.
Fuel economy is approx 75-100 miles per tank (very low even for SH standards)
The spark plugs are caked with black carbon deposits.

Info about the bike.
1998 model.
I bought a few years ago with 9500 miles.
As of this post it has 64,000 miles.
There are a set of Two Brothers slip-ons, and the carb's where set up and dyno'd by Factory Pro. (I have the original receipt and dyno chart, it was something like $1500 for the full treatment)
The bike ran great for a long time.
Awhile ago I started noticing poorer fuel economy, and then this rough running thing happened it was gradual not all of a sudden.

I have read my manual, and talked to other people, and this is what I've done.
Valves are all within spec, and have never been adjusted!
APE CCT appropriately adjusted (I think:wink: )
Float height correct. Carbs cleaned out with compressed air. Needles show now signs of wear. Choke, or enricher, replaced, but old one showed no signs of wear. Air filter is K&N type recently cleaned(originally it was a stock filter, I aded the K&N).
TPS sensor says 910 ohms.

I don't get it.
I've checked everything I can think of.
Now I need things I can't think of.
Any help or advice would be greatly appreciated.

Thanks
-Mickey

Hey Mick-e

check out my post on bad fuel?????, we sound like we have the same prob or at least the same symptoms..

I have done a fair bit so far, have you played with or possibly tampered with the electrics under the seat? Thats where I am at, maybe a bad coil or a short in the system? keep me posted.

Good Luck

Ian

The carbon deposits and fuel range concern me. Start with a fresh set of plugs. Even though they're iridium, they will wear out, particularly on bikes which rev about twice what a car does. Also, the heat gets to the resistors after a while. The plugs are supposed to be self-cleaning, so if they aren't firing correctly this could be a cause.

If, after replacing the plugs, you're still getting carbon, this is a definite indicator of richness. If no changes have been made to the carbs, the only thing I can suggest at the moment is an air cleaner issue, or a birds nest in the airbox/intake.

Thanks for the reply.
I'll look into getting a new set of plugs and trying that.
I did some testing yesterday while riding with a friend.
I found that constant or nuetral throttle to be the biggest problem.
If throttle is applied from idle, and opened consistantly the bike will rev smoothly all the way through the rpm range.
If the throttle is opened and the bike revs to 4k rpm and then the throttle is left at a constant position to maintain 4k rpm the bike will sputter, and run rough.
Even worse is if the bike is rev'd out to 7-8k rpm and then the throttle is closed slightly and left constant allowing the rpm to settle down to 4-5krpm the bike will sputter, and lurch and try to die on me. If I snap open the throttle right here the bike gurgle, and want to stall then it will clear out and the power hits hard wanting to lift the front wheel.
At that point it sounds like it is flooding.
I filled up this morning after doing some mixed canyon/freeway.
90 miles, 3.5gal
25.7 mpg
ouch!
Any ideas on what to try next?

This concerns me more than anything else you posted. I made the mistake of hitting a carb (on a different bike) with compressed air once. The air went in some passage and bent the float adjustment tang causing the bike to flood constantly. If something like that is the case, the bike would get too much fuel unless you matched the amount of fuel with a BUNCH of air -opening up the throttle wide!

Compressed air with any more pressure than you might get in one of those cans of electronics cleaner is really bad to be hitting a carb with. You could damage seals, diaphragms, bend floats and lodge dirt in places you don't want it.

From the symptoms, my best guess at a solution would be to check/adjust/rebuild your carbs and see if that helps.

Interesting.
When I cleaned out the carbs I had mostly disassembled them.
The floats, main jets, pilot jets, diaphram, and needles where all out.
What could have been damaged?
However the bike ran just like it is now before the cleaning. That's what prompted the cleaning in the first place.

If the problem is actually in the carbs how likely is it that it's the same problem in both carbs?
You see both spark plugs are fouled.
What if I'm not getting enough air?
Any ideas on how or why?
The fairing is not stock.
It is a sharkskins street model. So I don't have any of the internal ducting.
Would that make a difference?

Nah, as long as you have the rubber snorkel at the steering stem and it is clear then you'll be fine with those fairings. So the air cleaner is fine then? How about TPS full check, not just at closed throttle. They have been known to go bad at certain points in the throttle range. That will throw off timing which will cause early/incomplete combustion and the symptoms you describe. Other than that, I'm stumped. I don't know any other wear-able part that will cause a rich condition or improper combustion based on throttle position. What I DO know is that something either broke or wore out if it just started acting up with no mechanical work done that would cause it.

Doh! Okay then, I'm not sure what the problem could be. I have an XR600 that behaves similarly when my floats are out of adjustment and the air compressor incident happened long ago on a CR250 with an assembled carb. I was just putting those thoughts together. I do have an issue on the 600 where the floats go out of adjustment randomly, but that is a tough one with two carbs...

It is possible it's an air thing. It's something to check at least.
Check all your ignition related goodies.
It might be nothing, but I think I'd be checking timing too. If your timing chain slipped a tooth one direction or another I could see something like this happening too.
It sounds like it is going to be a hard one to nail down. I'd probably just start checking everything related to air, fuel, spark and timing.

I think it would be helpful to hear how the problem started. And BTW, I'm sticking with my original diagnosis for now.

:confused:

Well the problem has been gradually getting worse.
I think over a year ago I noticed fuel milage going down, but nothing bad.
It seemed like it was running more and more rough. I just sort of lived with it for a long while and only now am I doing something about it.

Has anyone tried running without an airfilter?
I know when diagnosing this problem I ran without the airbox on at all, and the bike ran fine below 5k rpm, but once it got into the higher rev range you could hear it struggle. I assume it wasn't getting enough air.

What else can I look at?
Let's assume for arguments sake that there's nothing wrong with the carbs.
Would a run on a dyno tell me anything?

Mick,

i had the exact same problem...

your factory pro jet kit has titanium needles in it... those needles are way more abrasive than aluminum ones on the brass jet at the bottom of the carburetor throat that it sits in to meter fuel... your brass jet has been egged out by the huge pulses of air rattling it around in the jet and it's richening up your midrange.. this is why it's gradually gotten worse than suddenly.... take the slide out and examine with a flashlight the jet the needle rides in (needle jet) and look close at the engine side of the hole... you'll notice it's been ovaled out... i havent replaced mine yet but i found that if you take the snorkel out of the airbox it will temporarily help the problem (more air)... i havent found a way to replace it yet, call factory pro (800-869-0497)and see if they can help you. i've heard that you may not be able to replace that jet, and havent really looked yet, but if i do, i'll let you know or you can call me..i'm currently rebuilding my 98 SH, and will have to address my problem at some point...

your struggle to run with the airbox off was the lean condition, the dyno crew put the perfect jets in (with the airbox) so without it, it runs way lean, consider going up a size in main jets if you take the snorkel out..

When I spoke with some mechanic friends of mine they had suggested that the "emulsion" tubes where worn. That being the part of the main jet assembly where the needle slides into. When I took my carbs apart I saw that the needle did not directly interact with the main jet holder, instead it moves adjacent to it. Very different from what I thought so I assumed there was nothing wrong with that area. When I looked at the needle there didn't appear to be any wear so I didn't even think to look at the brass bowl. OK so the needle slips down into the long brass bowl that does not appear to have any threads on it. How the hell to I get that out?
Is it pressed in? :confused: :evil: :confused:

your guess is as good as mine, somewhere along the line i heard "carb replacement".. but call around, dynojet (www.dynojet.com) or factorypro and see if they can help... check your carbs first by looking directly down in line where the needle would be... and see if it's worn.. maybe you can take the emulsion tube out and tap the brass needle jet out from the bottom up... i'm not sure.. i'll explore my carbs as soon as i can (being their in a box next to my tools) and let you know what i find..

did you get it fixed??? mine is still playing up and the dyno today showed it was extreme lean at 2-5k, like no fuel lean...back to the parts cleaner.

I have not taken the carbs apart.
I did speak with a Honda dealer, and the piece of carburator that I want to replace is not a part. I can't order it. So truely if I want to fix it I have to replace the carbs. I haven't spoken to Factory Pro yet,

I'd be keeping an eye out for carburetor prices on ebay. I think I've seen them a few times recently for between 75 and 200. Not sure about the final selling price. Good luck though.

I have the same problems.
Have you fixed it now?

Not yet.
once the sparkplugs foul it makes things even worse.
So my bike runs like complete shit at low rpm

Hi, just joined the forum...

I wanted to let you know I am having a similar problem. I have Factory Pro kit as well as high miles (56,000 miles).

My mechanic suggested the emulsion tubes might be worn. I will be taking apart the carbs soon and will let you know what I find.

It's positively not the emulsion tubes.
I know.
I bought new tubes thinking this same thing.
How disapointed was I when I discovered the needle does not make contact with the tubes at all.
In fact the needles run perpendicular to the emulsion tubes.
However I have two brand new ones still seeled in the factory Honda baggies if you want them.
The only thing the needles make contact with is a little brass bowl and that bowl is pressed in, and not a purchaseble part.
I'm about to bid on a set of carbs on ebay as I write this...
I hope I don't steal them from someone on this board.

Got 'em.

When I get the new carbs. I'll post up what the difference is.

could it be the "choke", or enricher circuit being stuck open? If I am not mistaking, its effect will be most noticeable at lower rpm and will decrease as engine speed rises. I do recall an incident where a buddy left the choke partially on on his Yamaha RX-1 snowmobile (essentially a pre-2006 FZ1 engine) and the engine ran like crap and fouled the plugs like crazy. May be worth a look.

Good luck

Mikstr

Thanks for the note. I'lll be curious to hear what you find out.

The saga continues.
I now know for sure what the problem is.
It has everything to do with the needle being Titanium.
It's not the brass bowl that the needle sits in, but the brass fitting that the needle passed through in the body of the venturi.
It really is oval shaped.
That would explain all the extra fuel. It's as if the needle where part way open all the time.
So the post about the choke being open is somewhat correct. The ovaled hole is acting like an enricher, just not when I want it too.

So onto the solution.
As far as the second set of carbs goes I really messed that one up. They where completly stock, and in the process of removing the factory air screws I damaged one of the screws, and had to drill it out. Now I'm waiting for a 6m x .5m tap to open it back up.
So now have the problem diagnosed, but I'm still waiting on the cure.
Anyone got half a set of carbs?

I assume you are referring to the main jets that are oval? All you need to do is replace them - like $5 in parts. Those are what meter the fuel.

There's nothing wrong with the jets.
The needle does not make contact with anything except the brass fitting in the center of the venturi. It passes perpendicular to the main jet.

I know what you are talking about, I had a similar problem, vtr wouldnt accept open throttle till 5k and then all good, after many carb pulls I saw a slightly ovaled needle jet (this is what the needle goes into and is in the venturi), saw at the factory web that you can buy new ones...rang honda and they said ok we'll order it for you...started trying to pull the needle jet out...pulling...tapping from the float side...really pulling now w/pliers cause hey I can buy a new one if it gets damaged...then honda ring and says i will need new carbies as the needle jet is pressed in at the factory and cant buy new ones....aarrgghhh. I was very pissed. Anyway the bike didnt run any worse for my hancking at it with pliers.. Fixed (my) problem as the filter (unifilter foam type) was dry and I was mega lean untill 5k when the main jets come in.
So oiled the filter as directed, done! Then went and got larger mains (180,182 Keihin jets)(keihin are bigger for the same no. as dynojet), pulled out my mains to compare and the previous owner had drilled out the std mains and were way larger than 2xoversize jets I had just bought....

Installed new jets ( now leaner up top) drilled the slide holes to be the same size as the hole that the needle goes through ( just a bit bigger to lift the slide faster) and the bike is awesome, acept throttle anywhere and is very keen and much less hesitant.

moral of story...there isnt one, but check your filter too.

if you want more info on this or some other things I have done to make the storm better for tiny dollars then check:

http://ozfirestorm.proboards34.com/i...ead=1158797056

Cheers
rufion and good luck!!

Same problems
 

Hello everyone. My name is Eric, I am new here to, I came accrost this searching for possable sollutions to my VTR's problems. I have been tearing my head off the last few days also. I have had my carbs on and off about 20 times, playing with the jets, fuel, everything I can think of aswell.

Im starting to lean towards ignition instead, I have missing problems and once I hit 4K to 6K rpms, I loose power, its always had a slight hesitstion from 2k to 3k, but now its worse. And It will run great for about 2 minutes, then it has an airy sound, then cuts off. Its been doing it alot lately, and usually on the freeway or at higher rpm's, but now its all the time. It seems to me like it is starving for fuel, but its always in the filters (I installed glass filters)

Whatever I find out, Ill post up. Here's a pic for now.
Attachment 31706

Is your carb' stock?

I finally figured it out I think, I have been pulling my head off all week long, and weekend. Lastnight and todya I havnt had any problems with it so I think Its good again.

First whoever had the bike before me had the fan hot wire grounded and a wire to the fuse block from the ground:confused: It ended up burning my wire harness and exposing wires all along the front of the engine including the front coil wire. The power wire had a bare spot very close to the frame, probably causing it to arc and short out the front coil, I fixed the wires and now the fan works properly, on and off when it should.
I also had a pet cock problem, it wasnt letting enough gas through to the back carb. and I took out the aftermarket needles and installed the stock back in and re did my jets to only one size bigger than stock. The Bike shop who did my carbs for me last C-Mas never tightened the front carb down so it was leaking air through the manifold causing it to back fire constently, and throw flames every time I let off the throddle. and I had alot of corosion in the connector to the converter unit.

So Im not sure if it was all or part of it, but its running better than it has in a long time, I am suppost to ride to Atlanta tomorrow, so its cutting it close, but its been good for two days now, so well see.

And yes, the carbs are stock, but have been jetted.

Running badly
 

My two cent's worth..
..Just got home from the hospital..yukky flu..but brain a little foggy. If you did this forgive me..didn't catch it..Replace the jets with the same size that's in there now...I've seen aftermarket needles hammer out main jets... escpecially with those miles...I've seen it on two twins...with CV carbs... Try it.

Dave