Bike coughing at 2000-4000 RPM

[KeLL]

Hi All

Im having new bike troubles.

Bike starts with normal choke usage. Idle is normal at 1500 RPM. When I release the clutch and start rolling i then have the bike sort of 'coughing' as I am trying to increase speed (even if I am gradual). Once im at 6000 the bike is normal again and is cruising. It's sort of embarrassing in traffic because my bike takes a long time to speed up and it's coughing.

I don't know if this is what you would call 'bogging' or 'hesitating' - I dont know the difference..

When the bike is warm, if I turn the choke on 1/2 way the bike idle goes to a dangerously low RPM and the bike sounds like it is going to die. If I close the choke the bike resumes back to normal 1500 RPM. Does this symptom help at all? Also when I bleep the throttle there is great response.

The bike never used to act up like this, and I have done no changes to it's configuration since it was last running fine. I have cleaned the carbs twice in the past two months. I checked my spark plug colour and it seemed to be a healthy brown, but I did not check them at the time the bike was coughing.. the problem usually happens after a cold start and the bike is warming up for the first 3-5 kms.

What checks can I do to narrow down the problem?

Could it be anything to do with the thin spring air?

[MarkusN]

Are you talking about chugging, the motor shaking as if it wanted to throw you off? (High frequency, several blasts of torque a second.)

I have had that at much higher RPM than I can induce it now (she always does it when I'm lugging her) when my float height was off (fuel level in the carbs too high.) Bight be a stuck valve or eroded float needle.

[Toledo Jim]

-- snip -- Bike starts with normal choke usage. Idle is normal at 1500 RPM. -- snip --

Did you set the idle AFTER the bike was FULLY warmed up (ie: after you have ridden for 15 or 20 minutes) with the choke off?

-- snip -- When the bike is warm, if I turn the choke on 1/2 way the bike idle goes to a dangerously low RPM and the bike sounds like it is going to die. If I close the choke the bike resumes back to normal 1500 RPM. --snip --

That sounds backward to me, if I turn my choke on when the bike is warm or cold, the idle goes up, are you sure you are using the choke right?

[Savor]

The same kind of choke and acceleration problem happened to me as well.

Check the float height and the spark plugs. If the plugs are fouled, clean/replace them.

[3imo]

I agree with NSP, it sounds backwards to me too. hmmm. choke on bogs engine. wierd.
But the engine runs fine at higher RPMS?

rule out your electricals first.  ensure you have good  strong spark.  (which I bet ya do)

you mentioned you did some carb work recently, In that case I would ask you if you used any silicon based sealants?
Gas breaks down silicona and will gumm up the carbs.

other wise, If it were me I'd pull the carbs off, flip them upside down and pull the jets. just to be sure they are not clogging up, of have something hindering flow.

wish i could help. Let us know if you figure it out. 

[KeLL]

I did a compression test on my bike and the left cylinder was 110 and the right was 120. Is this okay? I wasnt sure if I did the test properly because I wasn't sure what a cycle was when firing the bike.

Float height is good and even with gasket. My left spark plug seems to be oil fouled.. no carbon present.. looks wet and never goes dry. What would this point to? (I have also replaced the spark plugs) My left cylinder seems to be firing less often than my right cylinder and some times doesn't work at all.. I think it has grown progressively worse.

I tried to view both sparks in the dark, and they seemed similar. I have not tried to swap the spark wires around yet. I am going to take the carbs off and clean them again with soapy water. I always pull them apart each time I clean them. Including removing the jets and cleaning them. I am going to try installing an inline fuel filter to see if this helps. I was going to check the clearance of the valves, and unscrewed the screws, but never took the top cover off yet. If I change my mind and decide not to check, can I just screw them back up tight again? or do I need to apply a seal to the gasket. I also used WD40 on my K&N air filter dual pod. So would this cause a problem because I didnt use "filter oil"?

When you asked about silicon based sealants, I used a bit of vaseline around the intake holes, would this cause a problem?

Also, I lost the damn tank rubber seating again! I will have to go buy another one. How do you keep the damn thing on? Previously I used liquid gasket tostick it on the frame but obviously this doesnt work. Anyone have suggestions?

[NiceGuysFinishLast]

I am going to take the carbs off and clean them again with soapy water.

Whoa whoa whoa.. maybe I'm just an idiot. But aren't you supposed to clean the carbs in Kerosene, or something similar? Not just plain ol soapy water? If I'm just being dumb, tell me.. it's late/early, and I'm studying for finals.. blah..

[3imo]

the compression should be between 142-199 psi.
CLymers has the service limit at 114 psi...which could explain one cylinder firing....

So to answer your question - - 110-120 is not ok

BUT.....I wouldn't guess you had a compression problem, just yet.

#1 - be 100% sure you are testing the compression and reading it correctly.
#2 - your left spark plug is "oil" fouled. are you sure its oil?   (could point to your piston rings, hence loss of compression)
#3 - swap plugs and see if symptoms change.

Remember loss of compression will require opening the engine to repair, be sure to rule out everything else first.

BTW- WD40 will not be a problem, just don't do it again 
and whats with the vasaline?
for the valve cover do not apply a sealant, just tighten it down, it is made to be serviced and doesn't require any sealant.

Good luck

[LimaXray]

Yeah I don't think soapy water is the best thing to use to clean your carbs.  I don't know if it's a bad idea, but you would probably be better off with a stronger solvent, like carb cleaner. 

You compression sounds fine, at least fine enough to run.  A compression test is easy, just put the thing in the spark plug hole and crank the engine for a couple seconds.  I'm sure you did it right.

When the engine is running is there blue smoke billowing out of the exhaust?  If not that means its running to rich, or in your case would most likely indicate an intermittant misfire.

A misfire points to an electrical problem.  Check your ground wires coming from the battery.  There have been many reports of losing one cylinder when the auxilary ground wire (the smaller of the 2) goes bad.  Make sure the connector it goes to is connected, clean, and free of damage.

I don't think cleaning a K&N filter with WD40 is a good idea.  You can go to any autoparts store or even Walmart and pick up a K&N filter cleaning kit for $~10 IIRC; it includes the cleaning solution and filter oil, and it will last you several cleanings.

I'm sorry if you already mentioned this, but did you rejet for the new filters?  If so, you should try getting a set of Champion 809 sparkplugs as there have been complaints about the stock plugs being to cold for the richer aftermarket jetting.

[3imo]

oh yeah, soapy water leaves a residue and is not recomended.

I think LX is right the bike should at least run,  but you said you checked both sparks.

anyway, check again and recheck. rule out everything else first.

do you have any experience cracking open engines? 

[TragicImage]

uhhh.... what RPM are you at when you release the clutch?

[veeref]

My bike did the same thing (bogged ~2-4000rpm).  Some suggested that I wind the motor out, and that I was in too high of a gear, but I still didn't think it was running right.  When I checked my valves clearance, I sprayed some carb cleaner in my intake and black smoke started coming out of my exhaust.  My bike has run fine ever since.  My RPM's exhibited the same symptoms of idling somewhat low at half-choke (~1000rpm), but other than that, it's fine.  You mentioned you cleaned your carbs twice, already, but I would try the carb cleaner in the intake as well, just to see what happens.  Best of luck,

Randy

[KeLL]

Hi all,

Firstly thanks for responding! I need to clear a few things up. I do use carb cleaner on the carbs before I wash it with soapy water, i then rinse the carbs as well. But I am going to clean them again in case something got blocked again (as I dont have a fuel filter but this is going to change). Secondly, I know how to use my clutch and I am familiar with the gear/speed ratio. I have been riding bikes since I was a kid.

No, there is no blue smoke coming from the exhaust.

So what does a compression test rule out anyway?

No one has answered my question about undoing the screws to my engine. Can I just do them tight, or do I need to apply liquid gasket around the gasket now?

Also, I lost the damn tank rubber seating again! How do you keep the damn thing on? Previously I used liquid gasket to stick it on the frame but obviously this doesnt work. Anyone have suggestions?

[3imo]

The compression test rules out bad rings and such.  if you can run the engine I wouldn't worry about that until you've exhausted all other options.

I mentioned that the valve cover gasket doesn't need any liquid gasket. it is rubber and is designed to be opened and shut for routine maintanence.

for the rubber tank seat, I think epoxy might work. I just used a rubber hammer to tighten the metal clamp under the tank then wedged it up there. never lost it.

dunno. might work for you, too.

[LimaXray]

3imo beat me to it but here you go:

You need 3 things for an engine to run: fuel, spark, and compression.  The compression test mostly rules out compression as being the cause.  While your numbers are a little low, they are even and *high enough*.  If one cylinder was 120 and the other was 70 then you probably have bad rings, a bad head gasket, or your valves aren't seating properly. But this is most likely not the case so you shouldn't worry about it.

If there is no blue smoke in your exhaust that is a very very good sign.  The fouling you're seeing in that cylinder is do to either too rich, a intermittent misfire (which would be hard to detect by eye), or your plugs are too cold of a heat range.   

[3imo]

sorry LX... I'm bored at work. 

did I mention you should try reseating your ignition module connectors?    MAn, I wish I had the bike in front of me.

[LimaXray]

It's ok, I know your pain 

[TragicImage]

I'm telling you... if you're letting your clutch out at 2k rpm, its gonna doing a "Chugga Chugga".

[3imo]

Secondly, I know how to use my clutch and I am familiar with the gear/speed ratio. I have been riding bikes since I was a kid.

he knows 

[TragicImage]

well, just to test my theory, I went out and from a dead stop trying to roll off at 2k I got the chugga chugga.