fluctuating engine

[last]

I was out on a ride today and my bike stalled twice while rolling to a stop. I paid closer attention to the sound of my engine at the following lights and at our next coffee stop and noticed my engine fluctuating. Just wondering where I should be looking.

Thanks for you help

Wayne

2005 Nomad 1600

[caddman11]

Sounds like another case for "SEAFOAM"!!!!!

[ells]

A little faster than a SeaFoam treatment would be a thorough cleaning of the throttle body, Instructions in a recent thread with that in the title. Essentially, get a can of throttle body cleaner and spray and scrub with a tooth brush around edges of the butterfly valve under the right side intake cover.

[cactusjack]

Depending on what you mean by fluctuating, it could be a vacuum leak.

[ringadingh]

Id clean the throttle body, air filter, check the hoses, add some Seafoam to the gas tank and you should be right back on track.

[macmac]

Originally Posted by cactusjack

Depending on what you mean by fluctuating, it could be a vacuum leak.

Be my guess too.. If the bike is still stock I would be looking at a hard to reach hose tubing on the intake bore, located on the right side.

The best way to find it, is to raise the tank, and find the vacuum pod with hoses feeding the reed valve bodies. trace the smaller hose from the pod to the intake body, and pull that hose off and check both ends for being brittle, cracked or broken.

There can be other places for a vac leak, but that is the one i would start with.

[last]

Thanks for all the help. I'll take the tank off tomorrow check the vacuum lines. I did go for a 600km ride today and the bike didn't stall but still had the fluctuating.

[macmac]

I wrote this bit on vac leaks back in 03 for mcusa.
http://forum.motorcycle-usa.com/defa...x?f=18&m=13605

I did not write this just for you, and or just for a Nomad, but it applies and shows a way testing can be done with little expence.

.................................................. .................................................. ...

It seems to come up over and over again some problems just nag at bike owners.
So I guess this might be the first of a series of tech tips.
For those of you that don't know me, I was a foreign car tech, and was not ever a bike tech.............................................. ..................................


Many things work the same way more or less. To me pretty much theory just is.. By rights this should be the 4th in a series.


Compression is the first test of all tests...


Spark is the 2nd test


Fuel is the 3rd test, and each of the above has a routine in order to follow, so you are not guessing.


Vac Leaks:


A vac leak is unmetered air allowed in error to get by the intake. This effects carbs and injection equally bad....


You do not want a vac leak on any engine ever, but they are very common.


Sometimes you might not know it if the leak is small, and other times a engine won't start at all. So symptoms run a broad range of what a vac leak can do.


Some symptoms are a sudden lean condition, which can result in loss of power instantly and a matching increase in fuel consumtion.


This might be found to be true if heat cracked a vac line to the petcocks while you were riding, or the line just lifted off


Other types of symtoms cause what is known as "Hunting" Which is idle RMP that will not stay correct. The idle goes up to a given range maybe even to 2,200 rpm and then will drop to 600 RPM and go right back up as if a demon has the grips.. Or the bike might go to 2,200 RPM and stall forcing youi to restart.


Lesser leaks might effect idle, and what was correct yesterday suddenly is high today.


Turning down the over all Throttle linkage screw (THE ONE MAIN ONE MADE FOR FINGERS)
will work to lower idle sometimes but is a mis-adjusting when you should not do that..


If the leak becomes worse the idle will do what ever the leak demands..


The leak leans out the correct mix of 14% to 17% fuel to air and makes the mix undeterminable, ALWAYS lean...


On bikes each carb can have leaks, and manifold mount for any carb can have vac leaks.


Any throttle plate shaft can leak on either end. Any vac lines can leak on either end.


And any test port can have a bad cap, and so also leak.


Most bikes don't have vac operated accesories, with the one exception of vac operated petcocks. A vac operated petcocks WILL say, Pri = prime, On/Run, AND Res = reserve.


There is NO OFF setting..... Also the petcock will have 2 lines each... One line is for fuel and the other is a vacuum line telling the petcock the engine is MAKING vacuum, and to turn on the petcock diaphram to pull open the on off valve with in the petcock.


The way a internal combustion engine works creates vacuum. I have never seen any bike with a vac pump.


In my experience vac lines in general do not deal with heat and weather well. They crack, split, and become brittle, and should be replaced once a year, as well as gravity feed fuel lines.


To locate a vac leak you need a can of WD-40 which is probably the best thing you can use WD-40 for.


Also you can use WD-40 to test whether or not idle mix is right. This chemical beats ether hands down for use as a engine starter as well, and will not cause engine damage in moderate amounts.


WD-40 makes what you can't see, and probably what you can't hear findable.


You need to listen to know....


SO to tell if idle mix is right, Spritz a shot right at the intake with a running engine, and listen...


Does the idle go up? Or does the idle go down?


If things are correct the engine has all the fuel it wants and the idle will drop, as the engine wants no more...


If the idle goes up you are lean.......


If you have 4 carbs and all go down but one, then that one is lean.... Why it is lean remains a question.


Maybe the setting is wrong, and the pilot is in to far (mix screw on a car).


[ Often a book setting will say 2, or 2 1/2 turns out. That is a place where a fresh built engine should run to start, and IS NOT always the best mix for any given clyinder]


Or maybe you have a vac leak...and so adding fuel in the form of WD-40 causes the idle to jump to who knows what, and that depends on the unmetered air.


It is possible for a bike to run on 2 clys out of 4, and have the two dead clys fire up above idle speeds as the engine approaches mid range RPM.


So finding leaks becomes a bit of hit and miss, as you spritz about the carbs after a initial shot into the carbs.


Each time you spritz you must listen, so with a air cooled bike you might want a fan on the engine.


Places to spritz are the manifolds looking for loose clamps, throttle shaft ends, and any vac line ends and components vacuum operated. On injected bikes any Throttle body lines, and injector bases, also any vac operated components as you find them.


Often times vac leaks are mis diagnoised as clogged carbs, and bad plugs, wires, pick ups coils and more... Mac

[dogdoc]

if you said your engine just died at a light I would say mine does it on ocasion. Set your idle up a little will help.