Husqvarna 550xp pop up

[WoodsliverDan]

I checked squish today, @.025". So a little shy of my .020" goal. That's ok, I'll check timing numbers today since I have to head to work now. Hopefully I'll get it started as well..

 

[WoodsliverDan]

Tomorrow *

 

[Farmchuck]

I forgot to include something about a 550XP. I built a 550 that was thrashed and it turned out pretty good.

I advanced the timing, cut the squish, muff modded it and mild porting. I didn't cut the base--no lathe.

If you want to solve/help the 550's heat problems, you gotta cater to what causes them. I believe it stems from the transfers.

The transfer lowers are ducted right around the exhaust outlet. Think about that for a minute....

A normal cylinder dissipates heat via the fins, whereas Husky 5-series dissipates directly through the transfer ports.

Essentially, you are getting the reverse effect of a radiator on a car. I theorize this is why the issue is a hot start problem.

What to do about it? It can't be solved, but it can be helped. As Scott said, simple mods are not going to make a difference in heat retention.

The problem is heat retention in the wrong places. I wouldn't worry about additional mods, until you've remedied the heat soaking issues.

IMO, the best mod to help is muffler mod. The more heat you get away from the cylinder, the better.

Also, eliminating the primer bulb seems to help. And depending on your model, mod the cover to allow additional flow.

Here is how I start to mod a 5-series Husky muffler. I don't think just poking a few holes in the diverter plate is enough.

I get rid of it completely and add another outlet.


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Hi guys, not trying to derail this but it sounds like a lot of 550 experience here. I have a 550xp which was ported by Randy & I love it, my only issue is that I’ve never owned a ported saw before & had no idea how LOUD they were. After running it a while I couldn’t handle the noise ( yes I do wear hearing protection) so I purchased a new factory muffler of Bob Spike60. I have had it on the saw for the last year or so, as you probably know it doesn’t run nearly as well as with Randy’s customized muffler.What I’m wondering is there an in between solution? Perhaps a way to modify the factory muffler to let the saw breath a little better but not be quite so loud. Also am I risking cooking my ported saw by running it with a factory muffler? Thanks guys.

 

[AlfA01]

Hi guys, not trying to derail this but it sounds like a lot of 550 experience here. I have a 550xp which was ported by Randy & I love it, my only issue is that I’ve never owned a ported saw before & had no idea how LOUD they were. After running it a while I couldn’t handle the noise ( yes I do wear hearing protection) so I purchased a new factory muffler of Bob Spike60. I have had it on the saw for the last year or so, as you probably know it doesn’t run nearly as well as with Randy’s customized muffler.What I’m wondering is there an in between solution? Perhaps a way to modify the factory muffler to let the saw breath a little better but not be quite so loud. Also am I risking cooking my ported saw by running it with a factory muffler? Thanks guys.

Have you had any issues with it not starting when it's hot? You can open the muffler a little bit to let some heat out without it being over the top loud.

I've never had one of Randy's 550's so I'm not sure how he mods the mufflers. Most of these saws don't cook themselves from heat.

The reason these saws had problems with scored pistons and cylinders were due to several factors.

Air leaks, lean condition, too lean of fuel mix and dull chains are the usual causers of scoring. If you are running by Randy's suggestion - 40:1 Only, you shouldn't have a problem there.

On another note. IIRC Randy drops the cylinder on those, which causes the exhaust not to fit just right. Make sure you elongated the lower bolt holes so you get a good seal at the cylinder.

 

[Farmchuck]

No hot start issues. Factory muffler seems to fit fine with existing bolt holes. Can you explain in a bit more detail about the muffler modification you speak of? I’ve never attempted to modify a muffler before & I’d hate to mess it up.Here are a few pictures of the modified muffler.

 

[Farmchuck]

Have you had any issues with it not starting when it's hot? You can open the muffler a little bit to let some heat out without it being over the top loud.

I've never had one of Randy's 550's so I'm not sure how he mods the mufflers. Most of these saws don't cook themselves from heat.

The reason these saws had problems with scored pistons and cylinders were due to several factors.

Air leaks, lean condition, too lean of fuel mix and dull chains are the usual causers of scoring. If you are running by Randy's suggestion - 40:1 Only, you shouldn't have a problem there.

On another note. IIRC Randy drops the cylinder on those, which causes the exhaust not to fit just right. Make sure you elongated the lower bolt holes so you get a good seal at the cylinder.

Forgot to mention I do run @ 40:1 am soil saber & 90 octane e free fuel.

 

[Farmchuck]

Forgot to mention I do run @ 40:1 am soil saber & 90 octane e free fuel.

Not that I am trying to start an oil thread here or anything but if anyone has any better suggestions I’m all ears. Seems a while back I read Randy was going to try some am soil dominator, wondering if that is better than the saber?

 

[Farmchuck]

If these questions need to get moved somewhere else I understand. Not trying to derail but since we were on the subject of 550s I figured what da heck.

 

[Farmchuck]

Perhaps these are better photos. I do love the way the saw runs with this muffler. Much Much better than with the factory one . Just wondering if there is some middle ground.

 

[Backtroller]

I know what you mean about the loudness. It bothers some worse than others. These and the 562 seem to get loud with any muffler mod.

I had a 2252 with a big 1” pipe and it ran great but using it for extended periods bothered me. I ended getting a new one and just opened it up under the factory baffle....but this was on a basically stock saw. Performance was a bit less in this situation.

Now on a mmws I’m betting that performance is going to take a big hit without a free flowing muffler.

Maybe foam plugs under muffs?

 

[Farmchuck]

I know what you mean about the loudness. It bothers some worse than others. These and the 562 seem to get loud with any muffler mod.

I had a 2252 with a big 1” pipe and it ran great but using it for extended periods bothered me. I ended getting a new one and just opened it up under the factory baffle....but this was on a basically stock saw. Performance was a bit less in this situation.

Now on a mmws I’m betting that performance is going to take a big hit without a free flowing muffler.

Maybe foam plugs under muffs?

That’s what I wear for protection when I run it. For me personally one or the other alone isn’t enough.
Can you explain in more detail what you mean by”just opened it up undythe factory baffle”
I’ve never attempted to modify a muffler before.

 

[Backtroller]

I cut the baffle a little on each side with a dremel and bent the baffle open. I then grinded to make the “hole” as large as the area that the baffle had covered. So I basically made it open around the “tube” under the baffle. I then folded the buffle down and welded the cuts that I had made.

 

[huskyboy]

Try two 3/8 holes on either side of the one under the deflector. They get louder when you open the big internal baffle/diffuser whatever it’s called inside.

 

[Backtroller]

Or that

 

[Backtroller]

That is probably the total area that I opened up. There isn’t much real-estate under the baffle since I didn’t totally cut off the baffle

 

[Farmchuck]

Try two 3/8 holes on either side of the one under the deflector. They get louder when you open the big internal baffle/diffuser whatever it’s called inside.

Is the deflector the thing that sticks up on the muffler with the screen inside?

 

[huskyboy]

Is the deflector the thing that sticks up on the muffler with the screen inside?

Yes, make sure whatever you grind/drill is under the deflector. I just used pliers to lift it up to get room to work and then I tapped it back down with hammer. Make sure u get all the shavings out.

 

[WoodsliverDan]

Muffler

 

[WoodsliverDan]

Got the wheel on it tonight, came out with 106-115-78 and stratos at 79. Figured that is an ok start, so I put new ring in piston and put carb back on. Popped after 6 pulls. Haven't put a bar on it yet, and since it was about midnight, it will have to wait til later this week. So far I'm impressed with the snappiness and compression.

 

[Chainsaw Jim]

Got the wheel on it tonight, came out with 106-115-78 and stratos at 79.

Stock numbers?