Combustion Problem with 01' CR125s

[jaypro55]

I've been bothered by this ever since I found it on FMF's site.

NOTES: Stock bike needs at least 50/50 race/pump fuel to prevent cylinder head damage

That's in their jetting section under the 2001 CR125. I tried a search for specifics and couldn't come up with it so I'm wondering what the deal is.

I've been running my bike since April on 93 pump gas and for me, it's doing everything it should. I'm sorry but I will never spend a nickel on race gas, I just ride for fun and I'm on a tight budget as it is. Is this a legitimate concern? The specs of the bike on Honda's site say the compression ratio is 8.8 to 1, and from what I've read on here, pump gas should be good for at around 11 to 1. Other than the detonation problem with the lower octane which shouldn't apply here, what else could justify using the 50/50 ratio?

 

[Durt Cycler]

Wow I guess whoever wrote that must be the same idiot that handle's FMF customer service e-mails...

For one a stock 125 engine doesn't NEED any octane fuel over 91 but it is jsut wise to get 93 if you can. Race fuel will be better if you are trying to get the jetting absolutly dialed in because pump fuel is not consistant. But other then that running pump fuel won't harm a stock engine. Anything lower then 12:1 compression ratio will work fine up to 93 pump. And another thing...by saying a bike needs a 50/50 mix of race fuel and pump is retard because mixing race fuel with pump ruins the race fuels purpose. Sorry if FMF is now a DRN sponsor but I had to just state my opinion.

 

[jaypro55]

Yeah Durt, I was referring to your post when it said that anything lower than 12:1 is fine with pump gas. I think the reason they say 50/50 is because it's cheaper than straight race, but better than straight pump. I found the whole thing fishy to begin with because obviously Honda or someone on here would have made a big point about it.

 

[Durt Cycler]

Hmm another thing to consider if this was a guy who knew what he was talking about then why would he just say detonation only hurts the cylinder head? hmmm maybe it could hurt the piston, cylinder also.

 

[Rich Rohrich]

Originally posted by Durt Cycler
Hmm another thing to consider if this was a guy who knew what he was talking about then why would he just say detonation only hurts the cylinder head?

Because trace knock very often tends to show up initially on the edge of the cylinder head's squish band. This forum is quickly becoming a haven for bad advice, and you sure aren't helping matters Durt Cycler :|

If you want to run the bike with pump gas just run it a bit on the rich side. This should lower the combustion chamber temperatures enough to keep it from knocking.

 

[jaypro55]

Thanks a lot Rich. Yeah if I had the money, I'd be running race gas, but then again if I had the money, I'd have a team of mechanics working on my bike every day tearing it down and rebuilding it. So instead of 4 oz. to the gallon I might try to go a little more. I'll see if affects it enough to have to change any jetting I suppose.

 

[Rich Rohrich]

Originally posted by jaypro55
So instead of 4 oz. to the gallon I might try to go a little more. I'll see if affects it enough to have to change any jetting I suppose.

Adding more oil to your pre-mix MAY increase the tendency towards knocking on pump fuel. It depends pretty much on the oil you are using.

 

[Durt Cycler]

Rich I see your point, but I was only saying that not only that the cylinder head can be damage but the piston will be damaged and can cause a seizure in the cylinder. Maybe you misunderstood what I was trying to point out....

 

[jaypro55]

Rich I didn't know if you were talking about richer jetting or richer fuel mixture. I'm running Silkolene now at 32:1.

 

[Durt Cycler]

I beleive it was ment towards richer jetting but be careful you don't want it too rich.

 

[jaypro55]

Yeah of course not. I think right now I'm jetted pretty good. More towards the rich side if anything since it's stock.

 

[Rich Rohrich]

Originally posted by Durt Cycler
Maybe you misunderstood what I was trying to point out....

Yeah I'm sure THAT was it :silly: