missing with 87

[The motor guy]

I've always run either 89 or 93 in all my ope. I decided to run the recommended 87 in my ztr for once. I noticed it had a bit of a miss at idle. I know my echo equipment will run like [censored] on 87 and stall randomly, but those are higher compression motors. I was surprised that my mower kind of ran [censored] too. Sounded like it wanted to die at idle. I believe it's 8.1:1 compression ratio so not high. Been running 89 or 93 since and it hasn't done it. Any ideas?

 

[andyd]

Yah. go back to high test if it runs better on it. Modern OPE is set way too lean. I have tried 93 mostly because I am trying to clean out the carb on the 4 stroke Suzuki on my Toro and to give my mix a little more zap. No noticeable difference in performance. I suspect it is slowly strangling from varnish in the carb. After a 1/4 century of much work and little maintenance, the GTS needs a shot of carb cleaner to coax it into starting. The crazy thing is that it runs fine when mowing. But runs like a hit and miss motor in no load conditions. I totally destroyed the 'Zuki 2 stroke when I blundered through an attempted carb cleaning. So I think I will first get a later model OHV Tecumseh? 4 stroke powered Lawnboy that has been stored since '09 going before I attempt to tune up the 4 stroke.

 

[supton]

Hard to argue with empiracal data.

How much gas do you have un in a season? I have to think the extra cost is meaningless.

 

[oldhp]

Try 110 octane race fuel, might not run any better, but it sure smells great!

 

[The motor guy]

Originally Posted By: supton
Hard to argue with empiracal data.

How much gas do you have un in a season? I have to think the extra cost is meaningless.


I go through a tank a week when the grass is growing good. Burns about a gallon an hour.

 

[The motor guy]

Originally Posted By: andyd
Yah. go back to high test if it runs better on it. Modern OPE is set way too lean. I have tried 93 mostly because I am trying to clean out the carb on the 4 stroke Suzuki on my Toro and to give my mix a little more zap. No noticeable difference in performance. I suspect it is slowly strangling from varnish in the carb. After a 1/4 century of much work and little maintenance, the GTS needs a shot of carb cleaner to coax it into starting. The crazy thing is that it runs fine when mowing. But runs like a hit and miss motor in no load conditions. I totally destroyed the 'Zuki 2 stroke when I blundered through an attempted carb cleaning. So I think I will first get a later model OHV Tecumseh? 4 stroke powered Lawnboy that has been stored since '09 going before I attempt to tune up the 4 stroke.

So you're saying it runs a bit hot for the 87 causing the mis?

 

[artificialist]

Originally Posted By: oldhp
Try 110 octane race fuel, might not run any better, but it sure smells great!

Many OPE engine manuals say "unleaded fuel only" even though those engines have no cats and no oxygen sensors.

 

[andyd]

Yah, heat is caused by the lean running carb. Some guys open up the jets by drilling them out. I am just using a couple cans of carb cleaner every season instead of fixing the root cause

 

[mk378]

There is such a thing as unleaded racing fuel. NASCAR and some other racing organizations require it in the rules.

But what you really want is an alcohol-free gasoline, since alcohol requires a richer mixture. You don't need high octane in a low compression engine. Alcohol-free 89 is sold at a few retail gas stations in my area.

Governor hunting / misfiring with no load is usually a problem with the idle circuit in the carb. A few carbs still have a needle valve to adjust the idle mixture though the high speed mixture is pre-set.

 

[Trav]

Do you have any idea what the actual misfire count is? Its not uncommon for the engine to run a little rougher at idle until the ecm re-calibrates.