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Fuel/oil ratio


mazda13bbpt
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I don't know what most people would mix a Sherco 50, but if it's like any other trials bike, it's 80:1. The problem isn't your mix ratio as much as it's the oil you're using. Motul 800 has one of the highest flash points you're going to find in a premix oil. It's made for guys on big bore enduro bikes going through the woods with the throttle pinned. Try Motul 710. Much better oil for a trials bike.

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For the better part of 2 years, I was using Silkolene SX Pro2 (higher flashpoint than Motul 710 2T) at 80:1 and kept struggling to get good spark plug readings using 95 to 98 octane equivalent with mix of 1 to 2 parts 108-110 Octane leaded race fuel with 3 parts 91 octane non-ethanol pump gas in Trials bike. I recently switched over to Motul 710 2T pre-mix at 80:1 and now find it much easier to get the carb jetting dialed in and near perfect spark plug readings on my Trials bike. I'd prefer to keep using around 64:1 on my 250cc 2T Woods bikes that are typically run at much higher engine rpms, but 80:1 is best for Trials bikes as heffergm mentioned above.

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1 hour ago, heffergm said:

I don't know what most people would mix a Sherco 50, but if it's like any other trials bike, it's 80:1. The problem isn't your mix ratio as much as it's the oil you're using. Motul 800 has one of the highest flash points you're going to find in a premix oil. It's made for guys on big bore enduro bikes going through the woods with the throttle pinned. Try Motul 710. Much better oil for a trials bike.

Will give the 710 a try this weekend at 80:1, kids are riding very easy at the moment with minimal wide open throttle!!  

Thanks for that 

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3 hours ago, wheelieman14 said:

For the better part of 2 years, I was using Silkolene SX Pro2 (higher flashpoint than Motul 710 2T) at 80:1 and kept struggling to get good spark plug readings using 95 to 98 octane equivalent with mix of 1 to 2 parts 108-110 Octane leaded race fuel with 3 parts 91 octane non-ethanol pump gas in Trials bike. I recently switched over to Motul 710 2T pre-mix at 80:1 and now find it much easier to get the carb jetting dialed in and near perfect spark plug readings on my Trials bike. I'd prefer to keep using around 64:1 on my 250cc 2T Woods bikes that are typically run at much higher engine rpms, but 80:1 is best for Trials bikes as heffergm mentioned above.

What ????

 

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You say your 50 is rich - rich means too much petrol for the air. An engine will happily run and stay clean with a fuel to oil ratio of 25:1. I have lost count of the number of time riders think they are putting too much oil in when the real problem is too much fuel due to incorrect carb settings / jets.

Before you decide on the oil ratio for your 50 check what the bore material is. Some 50s have cast iron liners, I do not know about Sherco.

A problem that can give rise to false assumptions about oil ration / carburation is the fact that many trials engines spend much of their time running below proper working temperature. Use an infrared thermometer to check the temperature where the plug enters the cylinder head. It wants to be a minimum of 88 Deg C. 94 to 98 Deg C being much better. If its over 105 Deg C then detonation and piston damage is a possibility. 

If you engine is being frequently  stop / started and pottered about it might only be getting up to 65 or 75 Deg C which will mean it looks rich or oily when in fact its the way its being ridden is the problem.

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25 minutes ago, dadof2 said:

You say your 50 is rich - rich means too much petrol for the air. An engine will happily run and stay clean with a fuel to oil ratio of 25:1. I have lost count of the number of time riders think they are putting too much oil in when the real problem is too much fuel due to incorrect carb settings / jets.

Before you decide on the oil ratio for your 50 check what the bore material is. Some 50s have cast iron liners, I do not know about Sherco.

A problem that can give rise to false assumptions about oil ration / carburation is the fact that many trials engines spend much of their time running below proper working temperature. Use an infrared thermometer to check the temperature where the plug enters the cylinder head. It wants to be a minimum of 88 Deg C. 94 to 98 Deg C being much better. If its over 105 Deg C then detonation and piston damage is a possibility. 

If you engine is being frequently  stop / started and pottered about it might only be getting up to 65 or 75 Deg C which will mean it looks rich or oily when in fact its the way its being ridden is the problem.

Thanks for that. I would say the putting around is certainly an issue as my kids are 9, 7 and 5 plus only riding for a year so full throttle is really visited! 

Its s good point you made about the temperature! I pulled the exhaust of last night (repacking) and so much oil had accumulated in the low point on the pipe. 

Great advice thanks!

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50:1 is very good works with all type of bikes you might go a bit less of oil for trials riding 75ml for 5l gasoline is my mix, (which is around 66.67:1). I am using 50:1 for my 89 KTM 500 cc 2 stroke enduro/MX bike works flawless.

I use Ipone or Putoline half synthetic with a low burning temperature as oil.

Gasoline is Aral Ultimate 102ROZ without ethanol or Aspen fuel.

My tip: You might stay away of any fuel with ethanol very bad stuff depending your climate the storage of a fuel mix with ethanol can be very short.

 

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3 hours ago, pschrauber said:

50:1 is very good works with all type of bikes you might go a bit less of oil for trials riding 75ml for 5l gasoline is my mix, (which is around 66.67:1). I am using 50:1 for my 89 KTM 500 cc 2 stroke enduro/MX bike works flawless.

I use Ipone or Putoline half synthetic with a low burning temperature as oil.

Gasoline is Aral Ultimate 102ROZ without ethanol or Aspen fuel.

My tip: You might stay away of any fuel with ethanol very bad stuff depending your climate the storage of a fuel mix with ethanol can be very short.

 

Thanks for that! I have stepped up to 60:1 using Motul 800 and had the kids really hang off the throttle today. No issues other than a lot of oil at the exhaust tip on all three bikes! 

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Motul 800 has a high burning point. When the oil is coming out of your exhaust it did not burn, I think the engine is running not hot enough for Motul 800 you might try out Motul 710 which birns up easier due to the lower flame point.

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For explanation Motul 800 is made for road racing and the oil has a flame point of 252 deg. Celsius.

 

While Motul 710 has a flame point of 94 deg. Celsius. This oil will burn up easily at suits much better to your needs.

Even in my 500cc KTM 2stroke bike from 89 which is a monster I would not use Motul 800 too high flame point even for that high performance engine as the motor uses around 5 to 10l am hour!

 

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51 minutes ago, pschrauber said:

For explanation Motul 800 is made for road racing and the oil has a flame point of 252 deg. Celsius.

 

While Motul 710 has a flame point of 94 deg. Celsius. This oil will burn up easily at suits much better to your needs.

Even in my 500cc KTM 2stroke bike from 89 which is a monster I would not use Motul 800 too high flame point even for that high performance engine as the motor uses around 5 to 10l am hour!

 

I was talking to guys at the bike shop and they said no difference between the 800 and the 710. Reason I stuck with it as I didn't want to buy more oil. He didn't mention anything about the flesh point between the two. So this is interesting as I noticed my youngest daughter who is 5 was still only putting around and her bike was way more oily at the tip then the other two who were riding a lot harder! 

Pulled the plugs and all looked ok but will see how we go tomorrow up at the Trials park. 

A bit of trial and error with these bikes I think. Thanks for the help all the advice is much appreciated 

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