Misfire after sitting a few months-not fixed...

Re: Misfire after sitting a few months-looking for suggestio

Got it! After three attempts with wire, drill bit, and Seafoam injections, followed by compressed air, she runs great. Thank you to all who made suggestions and helped me logic this thing out. It seems like a simple thing, but I never felt or saw what was causing the problem. Hence, the confusion. Thanks, again.

Re: Misfire after sitting a few months-looking for suggestio

Norton engine Problem Analysis is one of the three: Mechanical Electrical Fuel. Easy hey.

Re: Misfire after sitting a few months-looking for suggestio

needing said:

To clarify your 'float level' comment - the 'fuel level' should be 5mm from the top of the bowl when the float has full shut the float needle.

Ignore manliness comments but do make sure you unfetter your bike before you go for a ride.

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On a trip to Rabers a few weeks ago, I picked up a new set of floats. I thought mine were ok, but today I thought I would put them in anyway. Upon reading the Amal instructions, I found that Nortons from mid 74 on should have floats set at even with top of bowl. That is a departure from what I had previously read. Mine is a late 74 850.

Re: Misfire after sitting a few months-looking for suggestio

jamesp said:

needing said:

To clarify your 'float level' comment - the 'fuel level' should be 5mm from the top of the bowl when the float has full shut the float needle.

Ignore manliness comments but do make sure you unfetter your bike before you go for a ride.

Click to expand...

On a trip to Rabers a few weeks ago, I picked up a new set of floats. I thought mine were ok, but today I thought I would put them in anyway. Upon reading the Amal instructions, I found that Nortons from mid 74 on should have floats set at even with top of bowl. That is a departure from what I had previously read. Mine is a late 74 850.

Click to expand...

My rationale is that Amal float levels are set on the bench i.e. bowls level. Fitment to Norton Commandos places them at an angle.
Both fuel intakes, your pilot circuit intake and main jet, can only be uncovered when your bike is inverted (avoid this).
With prescribed settings, volumetric increase of hot fuel in carbys when parked (taps off) can/will cause flooding into the carby then head then cases and results in oil dilution. Persist with the conventional wisdom at your peril.
PS: Press to flood is a 3 second count for my carbys.

"Question everything. Learn something. Answer nothing." - Euripides
Oh well, 2 out of three aint bad!

Re: Misfire after sitting a few months-looking for suggestio

Yes, after trying the higher settings, I had to go back and lower one as it was seeping fuel between bowl and carb body, even with new gasket.

Re: Misfire after sitting a few months-looking for suggestio

My floats are set even with the top of the bowl and do not leak. Under extreme heat while shut off I suppose some expanding fuel could percolate into the combustion chambers in the same way it does when carbs are tickled. I have not experienced this as far as I know and at any rate the amount would be so miniscule it would pretty much evaporate from the oil when running. The seeping from the fuel bowl gasket is more than likely caused by the float bowl not being flat,,,very common. Because it is secured with only two screws they tend to 'pull' on these corners. If you have them off again in the future, invert them on a flat surface. You will see how they rock. It is easy to dress the bowls flat using a flat piece of glass with medium then fine emery cloth.
Glad you got the running issues sorted. The Norton community is a very helpful lot and I think we all feel a bit of accomplishment when a thread goes from the first "I got a problem"....To the "It's fixed!!!!".

Re: Misfire after sitting a few months-looking for suggestio

Thank you. This is a great resource. Its really cool to see help coming from all around the globe.

Re: Misfire after sitting a few months-looking for suggestio

glad to hear you found your problem. I haven't had a problem like that but am experiencing a problem like leanness above idle so will bare this in mind for next time I look at the bike. 0.16 inch = 4mm easy???

Dereck

Re: Misfire after sitting a few months-looking for suggestio

The setting of float level at 0 to -2mm to float bowl lip may have applied to upright Norton engines, Triumphs, BSA, etc but is carryover thinking for Commandos i.e. 'cos that's how granddad did it, it's good enough for me'.
Fuel is drawn through the Amall Mk1 pilot circuit and the main jet / needle jet circuit from the bottom of the fuel bowl -agree? A rationale for setting the float level at bowl lip or -2mm may have been to detect fuel leakage at the gasket as an indication for air leakage at the pilot circuit hole in rear of the gasket (on upright mounted carbys). As the carbys are mounted at a forward angle on a Norton Commando it is possible to have a good gasket seal at the front of the bowl yet still suck air into the idle circuit at the rear of the bowl.
At 5mm below bowl lip, extreme angles of lean when cornering will still not expose the main or pilot circuits (even if centripital forces did not help to maintain fuel level constant with bowl height setting).
Other than the oil dilution risk mentioned in my earlier rationale, a change of fuel state from liquid to vapour to separate it from your oil in the hot crankcases is NOT desirable as the fuel vapour will mix with the available oxygen to perhaps reach a 14.7:1 air:fuel ratio at which point it is most completely combustible i.e. your engine is now a bomb (in the literal sense) minus a spark for ignition.
Carbie - Just another reason for oil analysis and comparison!

Re: Misfire after sitting a few months-looking for suggestio

For all practical purposes, I don't it makes a lot of difference one way or the other whether the floats are set level with the edge, as mine are, or 5mm below as you have yours. I did just do a very cursory experiment with water, a float bowl and float, no needle.... Water added until float 5mm UNDER edge, and with the bowl level, equaled about the same liquid level at the BACK of the carb as when water added until float LEVEL with edge but with bowl tilted as would be on a Commando. The jet area had equal levels and of course the front of the tilted bowl with level floats had a higher level of liquid at the front. And that's why I'm more comfortable with a higher float level.

I hope you can follow this post, It was a head scratcher to compose. :lol:

Tonight was first time I've had a chance to ride it. It starts easy,idles great, but starts misfiring above 4000 rpm, closer to 4500. Also ran uneven at part throttle. Danged.

Wow that must be frustrating. Can you isolate one side from the other and tell if only one side is missing or are both sides misfiring? I haven't had a chance to really read through all of your posts but just to be sure and have you double checked your valve adjustments? Also what kind of gas do you have? Is it possible that its fiberglass and it or some liner is coming off & gumming up the intake/valve train?

jamesp said:

Tonight was first time I've had a chance to ride it. It starts easy,idles great, but starts misfiring above 4000 rpm, closer to 4500. Also ran uneven at part throttle. Danged.

Click to expand...

OK. Good comment about the fibreglass fuel tank - although 850 should be a metal tank ?

Next then.
With it running, can you tug on the individual throttle cable to each carb, in turn,
and verify that each cylinder is capable of revving up a bit, and indeed is revving up a bit.
Give it a decent amount of tug, although on one cylinder at a time it won't rev too much anyway.

It would be a little odd for this problem to be in both cylinders, unless the carbs were equally gummed up ?
Have you strobed the ignition timing, to be sure the timing is still correct and advancing with revs like it should.
Have you checked the fuel flow out of the fuel tap(s), just in case its not flowing enough fuel to keep the engine happy.
Wouldn't be the first time only a trickle of fuel was all that could flow, which plays tricks on figuring what is going on.

That's a very good point Rohan, especially since the problem started after it sat for a while. It's possible the seals in the pet Cox have swollen and are not flowing much gas. Personally I think there's still something wrong with the carbs like a clogged passage,

jamesp said:

Tonight was first time I've had a chance to ride it. It starts easy,idles great, but starts misfiring above 4000 rpm, closer to 4500. Also ran uneven at part throttle. Danged.

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Just to clarify, This is just about the RPM where it ran fine before, correct?

Under pretty heavy throttle while accelerating, does it run ok at through this 4000-4500 RPM range or misfire here too?

Uneven at cruise/part throttle can still be the pilot/idle circuit, but if it starts well and you have a nice idle, I doubt if those passages are still plugged.

Try this. With transmission in neutral,the bike on the center stand, gently bring the rev up to that RPM range. (Hang on, it may want to walk backwards out the garage door.) If you encounter a misfire here, and I'm guessing you will, turn each mixture screw in 1/8 turn and check again. This richens the pilot circuit. If this helps, but misfire not completely gone, turn the screws in a bit more and recheck. As you do this you'll find the idle quality and speed will drop some. Simply increase the idle speed to what you want by equally turning in the idle speed screws.

To answer previous posts, it has metal tank, fresh gas.

Original problem was poor idle combined with misfiring at part throttle while revving motor. Now, it idles well and accelerates well up to 4500 rpm, then starts misfiring. Also, runs uneven at part throttle. Probably one cylinder, but need to try to isolate.

I checked the main jets when bowls were off, they looked clear. I will try some of the other suggestions tonight when I get off work. Thank you.

Fire it up in total darkness and rev the motor to see if the plug wires are leaking. You can also get an unsuspecting helper to hold the plug wires one at a time to see if they FEEL any leakage. Just make sure it's someone with a good sense of humor.

Danno said:

Fire it up in total darkness and rev the motor to see if the plug wires are leaking. You can also get an unsuspecting helper to hold the plug wires one at a time to see if they FEEL any leakage. Just make sure it's someone with a good sense of humor.

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And good heart function to boot (pun intended).

How are the plugs looking now. One might think light, my guess is dark.

Dark.