550xp port job is running weird on 1st start….. help

[dangerousatom]

Ok after the bone stock 550xp tossed a ring and chunked the piston and jug I bought a new jug and pop-up piston. I did an extensive port job without any timing changes and a gasket delete and rebuilt the carb. Before I did the muffler mod I decide to run the saw with muffler to see if it would start n idle without any issues….well it’s ridiculous!

It will start and run but only at full throttle and it’s barely running then. It will wonder up n down like 500-700 rpm ( by ear haven’t put a tac on it ) and only get up to 5-6k rpm at full throttle. I assume the wondering is the carb trying to make sense of what happed from last time running. I have ported both my 562xp and 565xp without issues and retuned the carbs via the let idle and then continued cut method with great success. I have also ported 7 other non electronic carb saws without any issues. This is just weird, any foresight advice or experience with this would be appreciated.

I do not believe there are any issues/vac leaks with the bottom end as the saw was running great until it just stopped as I let off the throttle while cutting.

 

[huskihl]

If the idle is changing while it’s sitting still, you probably have an air leak somewhere. The O-rings in the transfer caps can leak, the base gasket area can leak if you deleted it, and obviously the bearings/seals are a bit of a known weak point. There could also be fuel system delivery issues but it’s hard to say

 

[dangerousatom]

If the idle is changing while it’s sitting still, you probably have an air leak somewhere. The O-rings in the transfer caps can leak, the base gasket area can leak if you deleted it, and obviously the bearings/seals are a bit of a known weak point. There could also be fuel system delivery issues but it’s hard to say

Yup considered all that, I did high temp RTV everything in lieu to prevent air leaks but ya never know. It will not stay running when off throttle. Ill have to give it the once over when I get t a few hours.

 

[Ketchup]

Maybe a free-port issue?

 

[huskihl]

Yup considered all that, I did high temp RTV everything in lieu to prevent air leaks but ya never know. It will not stay running when off throttle. Ill have to give it the once over when I get t a few hours.

The cylinder extension might be bottoming out in the case or on top of the bearing pockets. I can’t remember in a 550 if I have to clearance for that or not for port work

 

[dangerousatom]

Unsure as I didn’t look, but I didn’t lower the ports or even widen them. My work was all in the smoothing out of the beginning lower split going into the strato channels and working in the channels themselves. I polished the exhaust side and did a gasket delete. I’m leaning toward an air leak.

When I get back into it I’m going to check the squish and compression.

Only other idea I had was the charge is getting into the chamber so fast that it needs a trimming advice but I can believe that’s the case when the entire intake run is only like 4” long. I’ve done porting on 4 cylinder heads & intake manifolds and a steady decrease in the runners volume after the throttle body will increase air flow velocity if you have long runners ( Subarus ) and that’s basically how I worked the strato channels. Can that even happen in a 2stroke?

 

[huskihl]

Unsure as I didn’t look, but I didn’t lower the ports or even widen them. My work was all in the smoothing out of the beginning lower split going into the strato channels and working in the channels themselves. I polished the exhaust side and did a gasket delete. I’m leaning toward an air leak.

When I get back into it I’m going to check the squish and compression.

Only other idea I had was the charge is getting into the chamber so fast that it needs a trimming advice but I can believe that’s the case when the entire intake run is only like 4” long. I’ve done porting on 4 cylinder heads & intake manifolds and a steady decrease in the runners volume after the throttle body will increase air flow velocity if you have long runners ( Subarus ) and that’s basically how I worked the strato channels. Can that even happen in a 2stroke?

When you deleted the gasket, that’s what I was talking about. I don’t know if there is clearance for the extension down into the case and above the bearing pockets without the gasket

I think you’d have to get in there pretty far and change the strato openings a bunch in the cylinder for that to make it run that poorly

 

[emanuel]

Pressure and vacuum test the engine and the lines. A tester is around $60, if you use it even once, it paid for itself.

 

[srcarr52]

This must be a MK1 550 as the MK2 comes with pretty tight squish and the gasket is very thick to where you couldn't delete the gasket.

Most MK1's are around 0.031" squish, so deleting the gasket is probably going to get you down to 0.018" squish, which will be ok at this bore size.

The MK1 has almost a full circle extension (cut out only at the lower transfer feed) which could hit with just a gasket delete. Since the skirt extension hits flat you wont notice it when bolting down as it wont rock or cause too much of an odd feeling when tightening down the bolts. You'll only find it by mocking up the cylinder and shining a light across the gasket surface.

 

[dangerousatom]

So ur saying the jug maybe hitting the bottom of the crank by a few thousands…..?

 

[huskihl]

So ur saying the jug maybe hitting the bottom of the crank by a few thousands…..?

This area…all the way around

 

[dangerousatom]

Yup gotcha

I’ll check it when I’m back in it

Thanks!

 

[dangerousatom]

Finally got back into the saw last night.

-No cylinder/crank contact
-Compression before start up on new cylinder/pop-up-piston and caber ring w/gasket delete is 135psi and thats with a decomp valve and a 18" long rubber hose and quick disconnect in the middle of the hose.
-skim RTV the intake boot to cylinder

It runs but will not idle at all. If I keep my finger on the throttle maybe 10% it will, but its hunting terrible and will stall out otherwise. The autotune is trying, as I gingerly lowered the throttle over a 2-3min idle and it does slightly compensate, but still eventually stalls out. At high rev is seems to be learning as well, at first it had no rev at normal full throttle like the previous try 5-7k but after few cuts its near +9k This is all by ear as I have not put the tac on it yet.

As emanuel said Im leaning toward a vac leak and I dont have plugs or plates to seal everything off so ill have to make some up and pull out the mityvac. ............... I really dont want to have to replace the crank seals

 

[dangerousatom]

OK Vac/Presure test done and no issues. Holds +/-8 rock solid at the crank seals and cylinder. Hum?!?

 

[FederalQ]

At this point possibly a leak between the carburetor and that boot? I had the cylinder off my 550xp this summer and now have the stalling during idle. I have found the leak to be between that boot and carb and in the process of redoing that. Also, I know I saw a YouTube video some time ago where the guy drilled a larger hole in the carb throttle plate to solve a failure to idle issue on a 550xp. IIRC enlarged it to 3/32“.

 

[dangerousatom]

Was thinking the same thing about drilling a hole or putting a notch on the butterfly.

I have a Husky Diagnostic Tool and cleared it to factory new settings. Ran the covered air bleed screw in and out at 1/2 turns about 5-6 different positions with little difference.

Im going to put it on the Engine Diagnostic Tool and see what I says again.

 

[dangerousatom]

No codes, Will a software update make a difference?

 

[Canadian farm boy]

I had a 550xp I ported that came back with a hard start and stalling at idle condition. I found that the FW side crank seal had failed. I ended up rebuilding the saw with new crank bearings with the seals already installed. After the rebuild I had to do both a low speed and high speed reset to get the saw running properly.
I’m not saying this is your exact problem but trying the reset is worth a try before sinking any more $ into the saw

 

[dangerousatom]

I’m under the impression that you can’t do a high reset until the low has been done…?

That’s were I’m stuck it won’t idle so I can’t do the reset. I can cut as I mentioned above but it still isn’t right in the cut IMO either.

There are a few other things I’m going to try. I have a second carb that I’m going to swap over to see if it’s same/same. That would lead me to believe it’s still an air leak somewhere before the intake side of the cylinder. If it’s way different then it’s the carb or the firmware

 

[Fullkip]

Do a carb pressure/ vacuum test.
The main jet on these are a weak point.