Cyl 1 missing

[sethhope]

Alright, I am fed up with this engine not running as it should. Since i got it 2 years ago it hasnt run perfect. I always had some problem or another. Ive been through the carbs 10 or more times, ive checked the electrical system several times, ive replace all the lines and rubber, and ive rebuilt the top end.

Im not sure where else to go with this. Cyl 1 is firing intermittently. Plug says its running rich, but lowering the float level didnt lean it at all. Main jet is the stock 137.5. Carbs are synched. Im getting a good spark to the cylinder and the 1-4 coil is reading proper resistance.

Where can i look next? Maybe replace the coil just to see? Im also thinking a new jet? Maybe its just worn?

[motoman]

Initially, I suggest cutting back that plug wire 1/4" and screwing plug end back on with it making a fresh new connection to plug wire.

[skids]

Initially, I suggest cutting back that plug wire 1/4" and screwing plug end back on with it making a fresh new connection to plug wire.

Agreed that could help. Also consider:

It could be the plug itself. Intermittant firing can foull a plug.
Low compression can allow a cylinder to fire at higher rpms and miss at lower.
A sinking float or dented float can cause high fuel levels.
A sticking spring pin in a fuel valve can cause issues.

[sethhope]

I already clipped the plug wire. As for compression, im showing 135ish. Plug was fouled, but after cleaning it didn't make much of a difference. The float is neither leaking or dented. As for the sticking spring, do you mean in the little valve under the float? As far as i can tell, that is also working as the other carbs are.

[DiverRay]

If the plug was fouled, replace it! the carbon from fouling give a path to ground without having to jump the gap. No jump, no spark.....

[sethhope]

Cylinder 1 still fires every few rotations. Would a fouled plug still exhibit those symptoms? Im not sure, but wouldnt a grounded plug be an all or nothing kind of deal?

Just to be safe ill go get a plug tomorrow and see what happens.

[skids]

[QUOTE=sethhope;506772 As for the sticking spring, do you mean in the little valve under the float? As far as i can tell, that is also working as the other carbs are.[/QUOTE]

There is a sping to cushion the tiny post in the needle valve that the float tyne sits on. I have seen a couple where they stick if you push them. When does the engine start missing? Idle, midrange?

Check the choke bar and make sure that it functions as it should. I think that each carb has seal gizmo. I “think” there is a set screw on each one to position it.

As maybe a last resort, you might want to adjust the “mixture” screw a little tighter to reduce fuel at idle and just off idle. Use a box fan. Lick your finger and tap the header to check for heat. I am betting that your head pipe is cool to the touch while idling...

[skids]

Another thing. If that carb is using the wrong piolt jet, it will cause an issue. If it is the stock sized pilot jet, consider either replacing it barring other possibilities. It looks to me like the brand new ones have a smaller outlet oriface. Maybe this is from wear of the stock ones with particles in the gasoline wearing over time. I do have a bike where one of the pilot jets is different from the other three and I will not be messing with that as it runs great.

[sethhope]

I checked that the pin doesnt stick. It pops right back up. The engine misses in all rpm ranges at all throttle positions. Seems to hit every 4 to 5 rotations. I tried playing around with the mixture screw with no results. As for the headers, ive been checking them with a spray bottle. 1 isnt cool, but it is certainly significantly cooler than the other three. The choke bar seems to be functional. The pilot jet is worn on the face so I cant tell what size it is. My guess is stock as it seems to match the rest in wear (visually anyway) and the rest are stock.

I should also mention that i did have all 4 cylinders firing properly and running well for a short time last year. Prior to this issue i hadnt changed anything since it was running well.

Next step ill replace the plugs and see if i can snag some good coils (i hear dyna yellows are what i need?). My plug wires are on their way out across the board anyway. And itll rule out electrical issues.

[MPittma100]

Pick up coil wires

Have you checked the pick up coil wires? Failure there is quite common and can be intermittent.

[skids]

I should also mention that i did have all 4 cylinders firing properly and running well for a short time last year. Prior to this issue i hadnt changed anything since it was running well.
(lots of snips)

Sometimes a good dose of Techron full system cleaner can dissolve congealed fuel from last fall.

[sethhope]

Pickup coil wires would cause a problem on 1 AND 4 I believe, so that can be ruled out, no?

As for cleaning, that was today. After the cylinder stopped firing that was my first order of business. I disassembled, cleaned, and reassembled with no different results.

[Radioguylogs]

Sync?

Carbs are sync'd?

[sethhope]

Carbs are sync'd?

Yep. Synched them this morning. It seemed to help a little bit, but it's still missing quite a bit.

[Ken Talbot]

If it was a coil problem, or a problem with a pick-up coil wire, it would be affecting two cylinders at a time. Similarly, it it was a petcock/fuel delivery problem, it would affect two at a time, but a different two than the electrical issues. If you are absolutely sure it is just one cylinder with a problem, my guess would be a dirty carb, i.e. one of more plugged passages, or something like the float chamber gasket sticking out just a hair and interfering with movement of the float, or an oddball jet, etc. Something in that one carb is not quite like the others.