YD-100

[Dylan57]

Don't forget that the ignition plays a role in how well an engine runs, and often reveals it's weakness or other issues under load and at high RPM. Try an NGK plug from the parts store Part 3922 aka BR6HS. The plugs these engines come with are very iffy quality and often cause a lot of running issues. Your top speeds in each gear also indicate the engine itself is having problems going above about 5500rpm (22mph with a 44t and about 30 with a 36t) also making me believe your issue is ignition related more than fuel.

It may also be worth looking at your carbs float height and adjusting it as necessary. There should be a sticky in this section covering how to check and set the float height.

I have some new ngk plugs laying around from my last CG, will give that a go, was just hesitant since they are longer than the Z8C plugs, I’ve been trying to find one that matches better under NGK, Denso, or Champion to no avail. I didn’t know the float could be adjusted, I’ll most definitely look into that aswell, thanks.

 

[mony0_3]

Not yet, I figured I’d wait until 200 miles to do anything like that. Before you ported, what speeds were you looking at, and how would it behave when you hit those top speeds?

About 25 mph, also drilled 3 1/4" holes in exhaust cap and cut off the tube. Mine 4-stroked at WOT and I went down to a #62 jet and it screams now.

 

[ImpulseRocket]

I have some new ngk plugs laying around from my last CG, will give that a go, was just hesitant since they are longer than the Z8C plugs, I’ve been trying to find one that matches better under NGK, Denso, or Champion to no avail. I didn’t know the float could be adjusted, I’ll most definitely look into that aswell, thanks.

I like to run NGK BPMR7A plugs (Part # 6703) on my builds as they are shorter both at the threads and on the plug side. It's a common plug used on many Stihl chainsaws. Alternative option.

 

[wan37]

Something to try if posable. Try a different octane in fuel. I'm in a state, where non- ethanol gas is very hard to get. I have a gas station, 3 blocks from house. I will not run gas from there. So I go in town and only get Shell gas at 93 octane . Trust me it does make a big difference. Then mix with a good oil.

 

[francisjohn]

The yd100 won't be much faster than the regular CGs. They have more bottom end, but the internal geometry isn't good enough for them to have more top end

Exactly. On top of it, the timing on it is more meant for better low end. It always makes me sad to see people buy it thinking it's going to be faster.

Something to try if posable. Try a different octane in fuel. I'm in a state, where non- ethanol gas is very hard to get. I have a gas station, 3 blocks from house. I will not run gas from there. So I go in town and only get Shell gas at 93 octane . Trust me it does make a big difference. Then mix with a good oil.

No. Higher octane doesn't mean better. Octane is related to compression ratio and these do not make enough compression to run 93. 89 would be the highest I would go.

 

[wan37]

Here is why I used higher octane fuel
It actually says that mid grade 89 octane is suggested. This is because the oil that is added 2 stroke fuel lowers the octane rating of the gasoline. So a higher rating is needed to maintain the required level. Since the only difference the octane RATING makes is the fuels ability to resist detonation...

 

[DAMIEN1307]

t actually says that mid grade 89 octane is suggested.

No. Higher octane doesn't mean better. Octane is related to compression ratio and these do not make enough compression to run 93. 89 would be the highest I would go.

Hi wan37,

That "suggested" octane rating from the Chinese manufacturers is NOT based on the AKI method which is a combination of using RON and MON standards to measure octane as we do here in the USA as well as Canada.

The Chinese use a completely different method of computing their octane ratings that is not unlike how they use "Chinese Centimeters" on these motors of ours where they say it's an 80cc when in all actuality by our US measurements is only 66 to 69cc.

In China as well as in the rest of Asia and most of Europe, their octane numbers are higher because of using a different standard of measurement.

US & Canada uses AKI ratings numbers which is roughly 5 points lower than the equivalent RON rating used by other countries. 87/89/93 gasoline in the US are the same as 91/94/98 elsewhere. As a sidenote, only 98 RON is available in Hong Kong, when most cars on the road only require 95 RON or lower.

That being said, that means by USA standards, your motor would actually require only 84 to 85 octane using our octane rating method used here in the U.S., and Canada.

 

[DAMIEN1307]

So I go in town and only get Shell gas at 93 octane . Trust me it does make a big difference. Then mix with a good oil.

That 93 octane also has a higher amount of ethanol in to achieve that octane rating as well, which as we all know will eat out your crank seals as well as eat at your aluminum components inside the motor as well as the carburetor much faster due to the increase in ethanol used to achieve that octane rating.

 

[wan37]

That 93 octane also has a higher amount of ethanol in to achieve that octane rating as well, which as we all know will eat out your crank seals as well as eat at your aluminum components inside the motor as well as the carburetor much faster due to the increase in ethanol used to achieve that octane rating.

I‘m in Illinois there‘s a law that the states. That 10% or less if ethanol in any fuels here.The cheaper 87 octane has the most. So built 15 or more I’ve beat myself in the head trying to figure out why there where some wouldn’t run right Under load like riding but perfect idling.I fooled with port timing and ignition timing too. I switch to shell 93 they run perfect then.

 

[DAMIEN1307]

That 10% or less if ethanol in any fuels here.

Doesn't matter anymore what the states says, this year the Fed's, using an EPA "emergency"mandate for the rest of 2023 has now raised the minimal amount of ethanol to 15%.

The Biden administration is ordering it to come into full effect for 2024...Federal mandates and laws trump state laws on this.

EPA on Friday issued an emergency fuel waiver, allowing E15 fuel sales in Summer 2023. Generally, E15 is banned in summer months, but EPA flipped the script for the first time last year when it lifted the summer ban to alleviate high pump prices.May 1, 2023

Biden administration sees year-round sales of higher ethanol fuel by 2024

A U.S. plan for year-round sales of a fuel blend with more ethanol known as E15 in eight Midwestern states will likely go into effect in summer 2024, a year later than the states sought, the top U.S. environment regulator told lawmakers on Wednesday.

www.reuters.com