372XP ported and muffler modded too rich running

[aaares]

Hi guys,

I have something for you specialists and tuners here.

On my older Husky 372 XP I did some mild porting and later some muffler modding.

What is REALLY ODD - it seems that I had to gradually LEAN the carb as my porting and muff. modding continued. (I made my second muffler outlet bigger gradually - in two parts). Now I have H-screw on the carb turned 0,7 turn out from fully closed position. Saw is turning 14.000 and still slightly four-stroking. I run 95-octan fuel (European number) in ratio 50:1 with "MOTUL 800 2T (Off Road)" oil. My muffler is "Jungle" type = small tube on right upper side and it's baffled inside - if it does matter. I didn't gutted it out - the baffle inside has some approximately 23 mm hole (0,9" ??) in the right bottom corner - I didn't change it. I just made some 14,3 x 20,3 mm hole in the front bracket. The ported jug is OEM Mahle 70,2cc (50 mm diameter) and it is just really slightly ported -widened exhaust to 64% of the bore diameter (chord measured), I didn't even widen the intake-just changed it's shape of "tubing". I polished the lower transfers. Didn't mess with upper transfers. There isn't any gasket under the jug - squish is still around 0,03", compression around 150 PSI.

I measured (degreed) ports (I left them OEM) - so numbers are (durations in degrees):

Exhaust: 158°
Transfers: 120°
Intake: 150°

So guys, what's up with the carb tunning ?? Why only 0,7 turns out on the H-screw? Please don't tell me that I messed something in big picture

Thanks aaares

 

[mtngun]

If it runs and cuts well, I wouldn't worry about whether you had to tune it richer or leaner.

 

[HiOctane]

At 3/4 out,its still pretty normal,i would say.Its not necessarly your porting that cause that.Dirty air filter,worst if you use a flocked one or damaged inlet tip or inlet lever not adjusted correctly.But at 3/4,i would enjoy it without worrying at all.

 

[aaares]

OK,

saw runs pretty good and cuts really fast. And that throttle response.....

So you guys think that it isn't problem at all. I think I could be fine with it

Just if somebody could explain me what phenomena could cause that after so "much" muffler opening the saw wants LESS fuel than before. I have always read here that after porting and muffler modding you have to RICHEN the carb. I'm pretty sure that carb condition (leaking inlet valve,.....) haven't changed in few minutes as I did the muff. mod. Air filter is clean.

aaares

 

[timberwolf]

Some times with muffler mod the LS needs to be opened so much that it actually puts enough fuel in that the HS needs to be closed down a little. This is because the LS makes up about 25% of full throttle fuel.

Seen it a few times mostly on non ported saw with fairly open mufflers.

 

[pioneerguy600]

Would it be where the engine is ported, the ports made larger, that there now is actually less velocity running through the carb at idle, therefore more fuel needs to be dumped into the airstream at idle and then when the volume increases as the saw nears WOT that it can now pull more fuel from the carb than it could before porting. If the L S has been opened already then the H may just have to be closed slightly and the carb is still providing enough fuel to 4 stroke out of the cut. Just my thoughts on the subject.
Pioneerguy600

 

[aaares]

Today I checked setting of L carb screw - it is set to 1 1/4 turns out. So I don't think it's somewhere extraordinary opened. But you guys have some really good ideas what could cause it. I think just other lesson learned.

When I'll find tree of appropriate size I'll try tune the saw in the wood (as I learned here). I will see what I can get. If I remember I can give here some video to show how it runs (my first port job - so I think pretty much :newbie: ) :hmm3grin2orange:

Thank you

aaares

 

[subhunter]

I checked the tune on my 372 today as the weather is not near as hot as the last time I cut with it. ANd my carb adjustments were almost same as yours. 1 1/4 turn on L on 3/4 on H. And it sure seemed to sound nice 4 stroking. I am cutting with it tommorw and see how she does.

 

[aaares]

I checked the tune on my 372 today as the weather is not near as hot as the last time I cut with it. ANd my carb adjustments were almost same as yours. 1 1/4 turn on L on 3/4 on H. And it sure seemed to sound nice 4 stroking. I am cutting with it tommorw and see how she does.

OK, thanks verymuch - that is some info what I was looking for. I thought that these saws are ment to be run much richer than this (somewhere 1 3/4 turns out on the H carb screw - on ported and muff-modded saw). Is your 372 XP also ported and muffler modded?

Thanks once more

 

[subhunter]

Yes it has a muff mod and has some minor porting done to open the exaust.
I ran mine today and it was definitely turning some serious rpms in the cut but it was still 4 stroking just a bit in the cut when you didnt have any pressure on it. I am not going to lean it out any more until I get a tach.

 

[Husq445]

Some times with muffler mod the LS needs to be opened so much that it actually puts enough fuel in that the HS needs to be closed down a little. This is because the LS makes up about 25% of full throttle fuel.

Seen it a few times mostly on non ported saw with fairly open mufflers.

Good call Timberwolf

I have also run into this on a couple of saws, seems like with everything opened up (exhaust and porting), low side has to be richened up quite a bit to have a good response off of an idle in turn requiring the high side to be leaned up a little.

First saw that this happened to me on I thought I really messed up the porting or something but it turned out to be quite a runner, still is.