Rough Idle - Dirty Carb or Something Worse?

[l008com]

Yup I cleaned the carb the other day, took it all apart, sprayed everything. The tank looks totally clean and has seen several tanks of fresh gas so theres no old fuel anywhere.

Would a dirty carb cause backfiring out the exhaust?

 

[GearHead36]

Yup I cleaned the carb the other day, took it all apart, sprayed everything. The tank looks totally clean and has seen several tanks of fresh gas so theres no old fuel anywhere.

Would a dirty carb cause backfiring out the exhaust?

Doubtful. I don't recall... have you checked the flywheel key? Backfiring would make me suspect the key.

 

[l008com]

I didn't check the key yet no. It seems strange that it would be that though. The machine ran - not perfect - but pretty good for an hour straight and suddenly it forgets how to run. I'll see if i can check the key Friday just for the hell of it. And I'm thinking ill replace the plug too since theyre only a few bucks. But I don't expect either thing to work :/

 

[l008com]

Did some poking around tonight.
Double-checked the spark plug. Either this plug is mint, or I don't understand spark plugs. So I'm assuming its not the plug.


Then I finally got around to popping the flywheel off. The key looked perfect, no sheering or gaps or looseness or anything like that.


On to the muffler, I wanted to make sure there wasn't a screen in there that was somehow clogged up. There was not.


Then while that was off, I figured I might as well take the cylinder head off. It was a little dirty in there but I didn't think it looked TOO bad. Like not too bad to run. But looking closer at the pic, one of the valves DOES look open! And with it pulled that far off the block, the rods should be a mile away from being able to push it open, right? So the springs should absolutely have closed it? That's what I'm thinking. I couldn't get a great view of it or play with it because the carb was still on there so I couldn't pull it off very far.

The port thats open, is that the intake or the exhaust? If it's the exhaust, could it just be jammed up from a piece of carbon breaking off and getting in there somehow? If thats the case, how do you fix this? Just take it all again and manually push it back and forth until it frees up?

 

[bertsmobile1]

Flip it over and check the height of the top of the valve relative to the floor of the head
The valves and the springs are the same length so the valves should protrude the same distance
IF not them either there is crud stuck under a valve or the guide has shifted in the head
The latter happens when the head overheats which is usually from having crud in the cooling fins or a defective blower housing

 

[l008com]

It was running on and off for a over an hour the day this happened, however there is zero crud anywhere, so it seems very unlikely it would be overheating. I'll have to take the carb off again, then I can take the head off completely and take a closer look.

If it is just some crud, do I just clean with carb cleaner?

 

[bertsmobile1]

Depends where it is
Baked on carbon gets removed with spraying water into the carb with the engine running flat out
Use a misting sprayer because too much water = cracked head
Search decoking with water lots of videos showing it done, mostly on 2 stroke mowers & motorcycles .
You can measure the valve heights just by removing the rocker cover
While you are there measure how far the rockers move the valve stems as well.
The grind on the cams is identical but it is not unknown for one lobe to wear almost round , or a follower to break
Also make sure both valves have their lash caps on

 

[l008com]

Ok I took the valve cover off and the problem became very clear. One of the rockers fell off. I was able to press down the valve by hand and snap it back in to place. But how did this happen in the first place I wonder? I did JUST adjust the valves, they seemed too tight, so by internet specs, I loosened them using a feeler gauge. But now one fell off. So maybe the internet doesn't know shit and I should have kept them nice and tight?



What would cause a rocker to fall off the valve like that? Is there anything besides being too loose that could cause it?

 

[l008com]

So it felt like the set screws had loosened up a lot, even though I had tightened them good and snug with my T10. I re-tighten them after I readjusted them, squeezing as hard as I could with my T10 driver but no luck. Is there a trick to this? The first T10 (bit) I used snapped when I was trying to initially loosen them. I can't get them back that tight, not with my hand driver anyway.

 

[l008com]

Another thing I don't udnerstand. I was able to pull the cord and get the machine to fire a few times before it died again.
If the intake vale is stuck closed because the rocker isn't touching it, how was the engine able to run at all? That doesn't make sense to me?