Topic: Engine missing when hot?

[The Lone Builder]

I have a problem - “so what’s new” I hear.

Shortly, <50miles, after refuelling my bike started missing on one cylinder. I stopped for a while and when I set off again it was OK. After another stop and maybe 30 miles it started again. Next morning the problem resurfaced after about 25-30 miles.

I put some Seafoam into the tank, and that helped for a little while, or maybe it was the stop to buy the Seafoam.

Anyway, I then emptied the tank - fuel fine and no bits floating in it; same story with the float bowls. I also dismantled the pet cock and again all looked fine. I pulled out the jets and blew through them -  none appeared to have been blocked.

When I pulled the plugs, they were very clean save for No 3 which looked a little oily. Then I noticed that cylinders 1 & 2 had D8EA plugs while 3 & 4 had DR8ES plugs! Not sure how I let this happen, but there you are.

I got new plugs and after checking the HT coil resistance, I reassembled everything and set out on a 300 km ride. After 150 km the bike started missing again. At first it would still run, if badly, but then got so bad I had no option but to stop.

I pulled the plugs and they seem very, very clean, making me think the mixture is too lean. No 3 plug has brown marking on the earth electrode - see pic. I mistakenly turned the air screws in ⅛ turn which made this worse. I managed to get to a safe spot and now I’m waiting to see what tomorrow will bring.

Up until this point the bike had been running perfectly, just purring along at 55-60mph. Today’s problem started just after I had accelerated to maybe 70, plus a bit, to overtake a truck.

I recently carried out a 3000 mile service, doing tappets, points, cam chain, timing etc. Plugs were renewed at this point. I am in NC/GA/SC now where it has been very hot and humid and the engine runs very hot.

Any ideas / suggestions?

[scottly]

The plugs show you are very lean, as in dangerously lean!

[scottly]

Which cylinder did the upper one in the pic with the rusty ground strap come from? What do the other two plugs look like?

[The Lone Builder]

The others look like the lower one.

The “rusty” one came from No 3, which previously was the wet one.

That’s what I thought, but why would things suddenly change?

[scottly]

The rust was caused by the ground strap glowing red hot, with exposure to oxygen. It looks like it has a very large gap?
What was the last thing done to the carbs?
Try removing the float bowl drain plugs and turning the petcock on, with a catch pan underneath. Does fuel flow out of all four carbs, and does the flow sustain for any length of time? If the supply to the bowls seems adequate, do the "clear tube" test to verify the fuel levels in the float bowls. Also, make sure all vents and tubing are clear and open.

[scottly]

 I also dismantled the pet cock and again all looked fine.

Have you checked the flow directly from the petcock into a container? If that passes, move on to checking the flow with the drain plugs removed.

[newday777]

Sean
I'm sorry to hear that you are having problems again.
Did you gap the new plugs when you put them in?
I can mail you the set of clear tubes I have to check the floats are all set equally if you have found someone to bunk with down there? I agree with Scott it does look like a probable lack of fuel flow.
When you emptied the tank did you shine a flashlight in the tank looking for rusty surfaces? A light coating of surface rust can cause flow problems as small bits come off, but usually leave an orange sediment color in the float bowls. There wasn't any color in the bowls when you popped them off?
I don't think I looked in your tank when you were here in May....
Are you anywhere near Greenville SC? I have a good friend there that might have a place for you to stop at.
Stu

[newday777]

This tank had a light coating of surface rust that was leaving rust sediment in the bowls before I cleaned the tank out. His K4 was running poorly from it. I don't think though that it was running lean like yours though. I did an ultrasonic cleaning of his carbs along with derusting the tank.

[The Lone Builder]

I didn’t check flow directly, but all bowls were full when I removed them. There was no sediment at all in the bowls, nor in the petcock bowl. I’ll check it all the same when I now try to get to the root of the problem.

I have now turned the air screws out again, and then another ⅛ turn.

I also have another set of plugs so I’ll check the gap on those.

Failing that, I’ll have to take the carbs off and move the needle clip to see if I can make it run richer.

I’m not near Greenville, Stu, but sort of heading that way next

[newday777]

Let me know

[BenelliSEI]

Sean….. check your fuel cap? Are you sure the vent is clear and letting air into the tank? Running the bowls lower and lower after the tank pulls a vacuum will cause the “fake lean” condition and rough running. You say it clears after it cools, or is the tank slowly equalizing and letting the float bowls fill again? If in doubt, drill an 1/8” hole through the cap baffle plates until you feel the bit hit the underside of the  chrome cap. Try this before you pull everything apart, or just go for a ride and pop the cap when it starts to miss and fart. I’ll bet it clears in 30 seconds.

A good test is to put the hoses from the petcock directly into a fuel can and open it up (the petcock, leave the cap closed). If the flow slows to a trickle 5-10 minutes later, problem solved. Have a good look around at other things too. An internal carb problem should not “take 25-30 miles” to manifest itself.

Good luck and stay safe. What’s the prize, if I’m right?

[newday777]

Good point John

[Mark1976]

I have a problem - “so what’s new” I hear.

Shortly, <50miles, after refuelling my bike started missing on one cylinder. I stopped for a while and when I set off again it was OK. After another stop and maybe 30 miles it started again. Next morning the problem resurfaced after about 25-30 miles.

I put some Seafoam into the tank, and that helped for a little while, or maybe it was the stop to buy the Seafoam.

Anyway, I then emptied the tank - fuel fine and no bits floating in it; same story with the float bowls. I also dismantled the pet cock and again all looked fine. I pulled out the jets and blew through them -  none appeared to have been blocked.

When I pulled the plugs, they were very clean save for No 3 which looked a little oily. Then I noticed that cylinders 1 & 2 had D8EA plugs while 3 & 4 had DR8ES plugs! Not sure how I let this happen, but there you are.

I got new plugs and after checking the HT coil resistance, I reassembled everything and set out on a 300 km ride. After 150 km the bike started missing again. At first it would still run, if badly, but then got so bad I had no option but to stop.

I pulled the plugs and they seem very, very clean, making me think the mixture is too lean. No 3 plug has brown marking on the earth electrode - see pic. I mistakenly turned the air screws in ⅛ turn which made this worse. I managed to get to a safe spot and now I’m waiting to see what tomorrow will bring.

Up until this point the bike had been running perfectly, just purring along at 55-60mph. Today’s problem started just after I had accelerated to maybe 70, plus a bit, to overtake a truck.

I recently carried out a 3000 mile service, doing tappets, points, cam chain, timing etc. Plugs were renewed at this point. I am in NC/GA/SC now where it has been very hot and humid and the engine runs very hot.

Any ideas / suggestions?

   Don't get me wrong, but neither plug is a particular poster child for internal combustion. The plug on the left is seriously over heated, the discoloration goes almost halfway up the threaded portion of the plug, it almost looks like the ground strap has rust on it.... And backing out that mixture screw isn't going to change anything beneficial to this situation. It's looks seriously lean, might be plugged vent, but whew.

[BenelliSEI]

Will be interesting to see what Sean discovers?

[The Lone Builder]

So the prize and my thanks go to Scottly

The issue was simple; a kinked fuel hose supplying No 3 & 4. Bike now running fine again.

But what do folk think of my plugs now? The first pic is before the fix and the 2nd after +/- 100 miles of fairly straight fast roads.

Air screws are all 1 turn out, but maybe it’s still a bit lean. Another ⅛?

[HondaMan]

They look OK if you're running 55 MPH or higher. They do look a little uneven, though, with 1-2 leaner than 3-4.
Do you know what your jetting is? (If you told me already, I forgot...).

I've often 'adjusted' the plug colors on long trips by using different octanes in different areas. For example, at (or near) sea level you can use more octane to darken them a little, and use less octane as the altitude gets higher. Here in Colorado, if I I/we are heading for the high country, everyone will fill up with the lowest octane we can get locally. Then when you're at higher altitudes the fuel burn rate was already adjusted by the refiners for that area: then we go back to [whatever] normal [is] for the bike. When we're coming back down the hills there is much coasting, which tends to burn the plugs cleaner, too.

[The Lone Builder]

The main is 110 with 40 slow jet. The needle clip is in slot 2.

I did think about using a higher octane. I’ve been using 87 up to now; maybe I’ll try 89 next time. I’ll tweak the air screws for 1 & 2 also.

Anyway, problem solved and the show is back on the road! 

[newday777]

Good to hear that you have it figured out.
Add a couple oz of 2 stroke oil to the gas to help slow the burn at altitude.

[BenelliSEI]

Well done. Smoother times ahead!

[Deltarider]

Good to hear that you have it figured out.
Add a couple oz of 2 stroke oil to the gas to help slow the burn at altitude.

No oil in the fuel tank! Never! Can soot like hell!

Good to hear that you have it figured out.
Add a couple oz of 2 stroke oil to the gas to help slow the burn at altitude.

I was warned: never add oil or diesel to the fuel tank. It can soot like hell.

[bryanj]

Then how do pre mix two strokes run?

[newday777]

Good to hear that you have it figured out.
Add a couple oz of 2 stroke oil to the gas to help slow the burn at altitude.

No oil in the fuel tank! Never! Can soot like hell!

Good to hear that you have it figured out.
Add a couple oz of 2 stroke oil to the gas to help slow the burn at altitude.

I was warned: never add oil or diesel to the fuel tank. It can soot like hell.

It works anyhow. You can do as you will.

[PeWe]

Kinked fuel line has tricked me and my K2 jetting stock carbs last year into this year.

The soft not braided fuel line do not need much bend to reduce fuel to carbs.
Acted as lean main jets in higher speeds.

A curvy route from dual piped petcock on right side  to 1-2 and 3-4 carb T pipes.

!! If the T has a little wrong angle....
Easy to move when adjusting fuel screws.


I got thoughts about stiffer lines with 90* hose bends where needed as my Mikuni TMR got.
Braided hoses for fuel injection + plastic 90* fuel hose bends.

Worked fine since spring 2015.
Lean only caused by the jets and fuel screws

[scottly]

But what do folk think of my plugs now? The first pic is before the fix and the 2nd after +/- 100 miles of fairly straight fast roads.

The #1 and #4 plugs look to be a bit on the lean side, but #2 appears to have at least some color on the porcelain? I would check the fuel levels in the float bowls with the "clear tube" method to see if those 3 cylinders have lower levels than #3, and adjust the floats accordingly.
Run the higher octane fuel, but don't add oil, as it can actually reduce the octane.  

[scottly]

Then how do pre mix two strokes run?

You mean two smokers?