Saw Tuning Issues- Moto-Mix vs. Non-E 89 Pump Gas?

[SteveSr]

Hello,

Working on a bit of a mystery here. Saw is an 026 Pro with the Wt-394 carb. I believe that the Wt-394 is the same as the Wt-194 but with the compensating "snorkel" top cover.

The saw was rebuilt and tuned with pump gas and used extensively this past winter and spring. The saw was then transferred to a friend who complained that he couldn't get it to start. I took the saw back and had no problem getting it started but it would stall at idle and sounded pig rich at WOT.

Thinking that this was old/bad fuel I dumped the fuel tank and put in fresh pump gas. The saw ran much better! It was a little bit rich at the top end since it was originally tuned when the temperatures were 30-40 degrees cooler and it didn't stall at idle.

So I asked my friend what kind of fuel he was using. He said Stihl Moto-Mix! So I am wondering if any of you have seen any weird issues / tuning issues related to using Moto-mix. I don't know what the chemical differences are between Moto-mix and pump gas but it would appear that older 2-cycle engines can tell the difference!

Can anyone offer any insight?

Thanks,
Steve

 

[mdavlee]

Motomix is higher octane. Needs to be leaned out to run right on it

 

[1Alpha1]

I've switched back & forth between pump gas and canned fuel.

If there was any difference in performance, I didn't notice any.

 

[SteveSr]

Motomix is higher octane. Needs to be leaned out to run right on it

This sure sounds like the way it was acting. What happens if the saw is tuned for Moto-mix and someone puts in pump gas? Lean seizure?

 

[mdavlee]

This sure sounds like the way it was acting. What happens if the saw is tuned for Moto-mix and someone puts in pump gas? Lean seizure?

Possibly if the tunes are that different.

 

[SteveSr]

Possibly if the tunes are that different.

Good experiment... He will be running Moto-mix exclusively so will be bringing some fresh fuel to use when I retune it. I'll check the WOT tach changes just by swapping the fuel mix.

I think I have also seen running issues in temperatures around freezing when abruptly switching to Moto-mix. The issue was extreme cold-naturedness and barely wanting to run at all. I put this down to Moto-mix not wanting to volatilize at these lower temperatures. Has anybody else seen this behavior?

 

[mdavlee]

I've never used motomix. Used VP and Trufuel. If I remember there was a good 1k rpm or so from VP to 87.

 

[Van462]

Could be a factor of lower compression in an older saw combined with the higher octane. It may be starting its burn cycle a bit later than with lower octane pump.

 

[Ted Jenkins]

Saw motor should be adjusted EVERY TIME there is a significant change. A small screw driver and maybe minutes to get peak performance. Thanks

 

[Mad Professor]

Not surprising.

I use 100LL in my saws and tune is different than pump gas.

I need to make a log as non-corn 91 pump gas is now available nearby, so I can just set Hi/Lo when I switch mixes

 

[SteveSr]

I've never used motomix. Used VP and Trufuel. If I remember there was a good 1k rpm or so from VP to 87.

1K is definitely significant. Have you seen similar changes when going from winter to summer ambient temperatures?

 

[SteveSr]

Saw motor should be adjusted EVERY TIME there is a significant change. A small screw driver and maybe minutes to get peak performance. Thanks

This is true. However, our user base are volunteer trail maintainers whom I don't want messing with carb adjustments. My job is to try to come up with a compromise tune that won't result in a lean seizure in cold (30-40 degree) temperatures and will still run fairly well in 70-80 degree temperatures. Looks like this is a hard bill to fill.

 

[mdavlee]

1K is definitely significant. Have you seen similar changes when going from winter to summer ambient temperatures?

They never get left alone that long. I tune almost every time out

 

[lone wolf]

I've never used motomix. Used VP and Trufuel. If I remember there was a good 1k rpm or so from VP to 87.

What octane VP ?

 

[SteveSr]

What octane VP ?

Based on the websites VP small engine is 94 while Motomix & Trufuel is 92. Anyone know if Motomix and Trufuel are the same thing i.e. come from the same packaging plant?

 

[Rockjock]

I sell a great deal of Motomix and have never run into that issue. I also sell a fair bit of Aspen as well and have never seen that as well. The saws are mostly unadjusted homeowner and semi pro saws and those saws are tuned pretty safe. For the Emergency services they are all tuned to stock setting and they have never, thankfully, had an issue.
My experience is that the saws run better on the Motomix and it certainly better for the bloke that keeps a saw on standby.

 

[Rockjock]

Based on the websites VP small engine is 94 while Motomix & Trufuel is 92. Anyone know if Motomix and Trufuel are the same thing i.e. come from the same packaging plant?

I think they do come from the same plant, packaging is the same for the trufuel motomix and the VP. But I am sure the formulas are quite different.

 

[SteveSr]

I sell a great deal of Motomix and have never run into that issue. I also sell a fair bit of Aspen as well and have never seen that as well. The saws are mostly unadjusted homeowner and semi pro saws and those saws are tuned pretty safe. For the Emergency services they are all tuned to stock setting and they have never, thankfully, had an issue.

As I mentioned in my original post the 026 was designed long before Motomix and other synthetic fuels ever existed. The full range adjustable carb on this saw offers wide latitude it makes precise changes difficult due to the highly sensitive screws. The newer equipment that you mostly deal with has limited adjustment range and caps on top of that.

My experience is that the saws run better on the Motomix and it certainly better for the bloke that keeps a saw on standby.

I haven't had much running experience with Motomix but I am sure that it works better for storage.

 

[Little Al]

Have no Idea if your problem is the same. A while back a guy in the village brought a saw to me complaining it wouldn't run properly A lot of Fiddling around & drain & refilling with 32/1mix had it running good, some days later he was back with same bother he brought the fuel he was using Motor mix4T uuuuuggggghhh Said he'd asked the shop for a premixed fuel for an XYZ chainsaw & that's what they sold him "just wondering "

 

[mdavlee]

What octane VP ?

94 from a can