Running lean, how bad is it?

[Burque73]

I replaced the carb boots and orings and have a recently rebuilt set of carbs but still have lean running issues. Airbox is sealed, boots are nice and soft too. The engine starts right up with the choke but revs pretty high if you're not feathering the choke control to keep it under 2k. Once it warms up it's fine and runs great. After cruising at highway speed for ten minutes or so, come to a stop and the engine revs to 3k, unless I slow it down by engaging a gear and letting the clutch out a bit. The idle comes down eventually at first, but longer rides and it takes longer or just doesn't come down. Could this be some orings on the carbs them selves, maybe around the choke plunger? And how bad is it to run this way?

I need to head out of town about 200 miles and the wife needs the truck here so I was thinking of riding unless this lean issue could cook the valves or warp the head or something bad! I could take the work van but ugh, 200 miles with all that rattling crap bites!

Any thoughts or advice would be much appreciated.
Thanks

[tkent02]

I have an 850 piston with a nice round half inch hole in the top of it.

[Burque73]

I have an 850 piston with a nice round half inch hole in the top of it.

Burned through, or hit a valve?

[tkent02]

Burned through, from running lean.

[Burque73]

My short term solution, take the truck and the wife and make a weekend of it! Ill figure this out eventually

[Nessism]

Where are the pilot screws set? Any mods in the intake system or exhaust? Are the carbs vacuum synced?

[Burque73]

Where are the pilot screws set? Any mods in the intake system or exhaust? Are the carbs vacuum synced?

No mods to exhaust or intake systems. I'll have to check the pilot screw settings. I dont own a sync tool. How often do they need syncing? I guess I could pick one up but it may be a couple of weeks.

[bobgroger]

You need to sync first. They need syncing if you make any changes like valve adjustment, pilot screws, basically whenever you have problems. Set the pilot screws at 2.5 turns out and sync. Report back....

[Burque73]

You need to sync first. They need syncing if you make any changes like valve adjustment, pilot screws, basically whenever you have problems. Set the pilot screws at 2.5 turns out and sync. Report back....

Thank you. Will do!

[Doug]

Running lean - How bad is it? So, how bad is it? Have you checked the exhaust pipe temps and tell us what they are?

Harbor Freight has temp guns on sale if you don't have one.

[Burque73]

Running lean - How bad is it? So, how bad is it? Have you checked the exhaust pipe temps and tell us what they are?

Harbor Freight has temp guns on sale if you don't have one.

Well the temperature varies so much with that laser type temp gun i figured it to be unreliable. Not sure if the shiny chrome surface on the headers throws it off or what. I was getting between 150 and 280 degrees F. But that changed drastically with the angle and even an inch or two. Checking the exhaust bolts was pretty consistent 305 degrees F. Does any of that make sense?

[Steve]

I replaced the carb boots and orings and have a recently rebuilt set of carbs ...

Where are the pilot screws set?

I'll have to check the pilot screw settings.

Seriously? You just rebuilt the carbs and don't know what your pilot screw settings are?

Did you even remove them from the carbs?

.

[Burque73]

Seriously? You just rebuilt the carbs and don't know what your pilot screw settings are?

Did you even remove them from the carbs?

.

I didnt say i rebuilt them, but they were recently done. I would have obviously known the settings if i did the rebuild.

[roeme]

Not sure if the shiny chrome surface on the headers throws it off or what. I was getting between 150 and 280 degrees F. But that changed drastically with the angle and even an inch or two. Checking the exhaust bolts was pretty consistent 305 degrees F. Does any of that make sense?

It's noted in the manual of each and every temp gun: Shiny surfaces warp the readings drastically. Broadly speaking, laser temperature measurement relies on the shifted reflection of the laser - but shiny surfaces bring it all kinds of out of wack (This is why plates used for calibration are matte black).

Also, in the manual, the measured surface area (the laser dot is just a visual hint where the center of this area is located) in relation to distance should be documented as well. Basically, there is a cone outward from the laser diode, hence the shifting readings when changing the angle.

[gs11ezrydr]

Lean enough to hole a piston, Sounds like a massive air leak or pilot jet stopped up, Head gasket, excessive carbon build up. or mixture screw turned off on that cylinder. Timing should have holed both pistons running on that coil if it was timing. Maybe a wrong plug installed in that hole also. Extended tip, heat range out of this world . Insects, tar or something blocking that air flowing through that cylinder. Or just flat out lack of fuel in the cylinder. Thinking, Just weird dude.