ms290 fuel issues?

[dustyz]

(This post has been pulled from another unrelated thread. I'd like to delete it from the other location if possible.)

The saw will start and idle. It will not rev from a dead idle, but if I bump it, it will rev afterwards or from a higher RPM. The longer it idles, the more difficult to get it to rev. It will not start or run with a new or old air filter on, at all. (See video below)

I checked the plug(and replaced it), muffler, clear. I replaced the fuel/impulse lines, fuel filter, and cleaned the carb without a full rebuild first. I disconnected the tank vacuum and tested too, to make sure it wasn't clogged. I found a cheap aftermarket carb to test with, and adjusted both carbs per specs, no luck, same results. My compression gauge shows 120psi. After thinking I had a muffler issue, I opened it up. Same results. I finally rebuilt the HD-18c carb with a kit, cleaning all the passages thoroughly with carb cleaner & brushes. I did a vacuum test on the carb, and it held fine at 10psi. I pressure tested it with a regulated compressor @ 10psi and submerged it in water. No leaks. I've verified the carb needle lever is flush with the Walbro housing more times than I want to admit. It's good.

I do need to pressure test the saw itself, but I accidentally ordered the mv8000 vs the mv8500, so I didn't have that option. The 8500 is on the way.

Here's a poor quality video of how the saw acts: HERE

In the video I am adjusting the L&H back to the 1/4 & 3/4 recommended turns. I actually close them all the way, then open them back up WHILE the saw is idling. You can see it hardly had an impact. Air Leak? It just seems to have a lot of extra fuel blowing back out of the carb.

Thanks for any advice/help you can offer. This newb really appreciates it. ;-)

 

[Ozhoo]

Carb settings without limiter caps are 1 turn out on both H & L

 

[dustyz]

Carb settings without limiter caps are 1 turn out on both H & L

Good to know! I didn't realize removing the limiters changed that. It does make sense. Anything else I should inspect?

I tried adjusting them 1 turn out, and had the same results. It's practically identical results. As soon as I add the filter, it dies.... and is impossible to start afterwards.

 

[cus_deluxe]

Did you use oem fuel and pulse lines?

 

[dustyz]

I just watched your video. At the end when you put the air filter on, the very next thing you did was to choke the engine and pull the rope.

I pulled it a few times prior. It hit once, then nothing. I thought, although knew better, that it could be starving... and tried the one pull with a choke. Obviously that didn't help. With the filter on, cold, warm, or hot, I get nothing.

Yeah, on a good running saw you shouldn't need to do that. I agree. Any other direction? I'm eager to learn, and happy to be critiqued when it comes to troubleshooting techniques. Any advice helps.

 

[rd35]

Dustyz. I sent you a PM.

 

[dustyz]

Did you use oem fuel and pulse lines?

I did not. The 290 seems to put the fuel line in a bind back behind the carb. I've worried about that area, as it seems to crimp the line a bit when pushing it back. I replaced the lines because of the age of the saw, not because I identified a leak. I may try to check the old lines and swap them out to see if it makes a diff.

Are you thinking it's starving under a low vacuum @ idle, then opens up at a higher RPM? That doesn't seem like a crimped line tho. I'd think it would starve at a higher RPM if I had line issues. It really seems to be flooding at idle and with the filter on. Almost like it's creating too much vacuum for fuel via the carb. Once it starts revving up, the engine can consume the fuel, so it's less apparent.

I'm someone who likes to understand what each part does, and how it makes the engine run. At this stage, I don't understand everything, and that makes it difficult to troubleshoot.

 

[Old2stroke]

It will not rev from a dead idle, but if I bump it, it will rev afterwards or from a higher RPM.

Can you clarify this? What is the bumping stuff?

 

[cus_deluxe]

Yeah, that hard corner that the fuel line has to take is not something AM fuel lines do well.
Didnt notice the video, does sound like its getting plenty of fuel lol. You are sure the diaphrams are assembled correctly?

 

[dustyz]

Can you clarify this? What is the bumping stuff?

If I bump the throttle a little, and get the RPM's up, it will then rev fine. If I let it idle and hit the throttle, it bogs down heavy. If I slowly get into the throttle, it will eventually rev if I'm patient enough.

 

[dustyz]

Yeah, that hard corner that the fuel line has to take is not something AM fuel lines do well.
Didnt notice the video, does sound like its getting plenty of fuel lol. You are sure the diaphrams are assembled correctly?

Ha! It seems like it's getting plenty of fuel, based on the amount it throws out the carb. It really seems to flood at idle... and once I get the RPM's up to consume the extra, it will rev. I've gone through it several times, and there is a chance I could've missed something or assembled it wrong. I will check the fuel lines again, and when I do I will verify the carb.

 

[dustyz]

I sounds to me like it is starving on the "L" screw. If it were mine, I would try making the low circuit more rich (counter clockwise) about 1/8 of a turn at a time to see if you can get rid of that stumble on throttle-up.

In the video, I actually screw the "L" all the way down... and the saw doesn't change idle speed. That makes me think something else is going on. From my very little experience, there's usually a sweet spot for the "L" adjustment. Higher or lower, and the saw will die. I will definitely try it tho.

 

[HarleyT]

I watched the video.
That is an awful lot of spray out from the carb.
I would suspect the carb, or bad intake side piston wear.

 

[dustyz]

I watched the video.
That is an awful lot of spray out from the carb.
I would suspect the carb, or bad intake side piston wear.

Ok. When I pull the lines and the carb off this next time, I will inspect for piston wear.

That does make sense. I guess it would create more "blow-back" on the intake side... which would push the fuel out of the carb. Right? Is that the logic behind it?

 

[HarleyT]

Yeah, possible.
When you are adjusting the carb, do you have the limiters removed?

 

[dustyz]

Yeah, possible.
When you are adjusting the carb, do you have the limiters removed?

Yeah, they are removed. I set them both to 1 turn out, and had the same results.

Even with the sensitive carbs I've seen, the base settings will get one to start, or at least let it "hit" a few times. This one, with those settings and the air filter on, won't. It won't even try to start.

 

[HarleyT]

The air filter on must really piss off all of that blowback......

 

[heimannm]

In honor of HarleyT, the Double Taper...

 

[a. palmer jr.]

Compression a tad low @120 psi, 150 would be better..

 

[Old2stroke]

Sorry, I missed the video the first time through. There is WAY too much blowback through the carb. I suspect there is a basic engine fault rather than a carb issue. Do you know the history of the saw? Has it been recently rebuilt and did it ever run right? Porting attempt gone wrong or wrong piston/cylinder combo?