Plugs backing out

[dajogejr]

put some plug locks on ther untill the next rebuild, which won't be long

 

That is the funniest thing you've ever written...I had to laugh at that one.

 

Plugs back out for two reasons.

Deto or Fubar threads. And as said, they don't have to get hot to deto.

 

What is your squish band and thickness at first off. I saw that was already asked but never answered. This could be as simple as the wrong domes. If that's the case, no amount of timing is going to help you. Since it's together, you can't measure the UCCR (Uncorrected compression ratio) but you can get the cranking compression. Measure that as well.

 

If the squish is ok, then look to an air leak/and or fuel issue.

I know you said you don't want to run race fuel...but I can promise finding 5 gallons of race fuel to test out vs. buying a new top end or more is cheaper in the long run.

Try good race fuel and eliminate if AV Gas is the issue.

 

I don't think AV Gas is hurting you....but when you have an issue like deto you cover all your bases, even the ones you're pretty positive aren't the problem.

[dajogejr]

Second...

You shouldn't have to gap your plugs at .022 for gas.

The only way you should have to gap them that small is if the ignition is failing, or if you have too much compression.

 

Back to the domes. Check 'em out AND get a cranking compression reading...sounds like your problem lies there.

 

If your domes check out and you still have to gap them at .022...try race fuel as said.

[Profilact]

I tried measuring the squish last night but all i have here is .038 solder and didnt get a reading. Ill get some thicker solder today and try again.

 

Compression is 185-190. I ran a stock setup last year at 185 and had no probs with avgas which is why i dont understand whats happening.

 

I started this year with c-12 and THE DAY i put avgas into the mix a plug backed out. This leads me to believe that compression is the culprit, along with having to gap the plugs so close. leakdown test was good before the motor was installed into the bike.

 

On a side note: I guess deto is a sneaky thing. You dont hear it, but its happening? Detonation and pre-ignition are two different things?

 

Thanks guys - once this issue is resolved I will be good to go for the rest of the season!

[jbooker82]

Yea they are different.

 

Detonation is like a Hard Explosion. Where preignition is just the air fuel igniting to soon due to a hot spot.

 

http://en.wikipedia.org/wiki/Detonation

 

http://en.wikipedia.org/wiki/Engine_knocking

[AKheathen]

yah, avgas is some awesome gas, even in 2 strokes, lol. now, this is a prime example of why cr is stressed over psi. 185 on stock, vs 185 on 4mill. the asme thing would be true for 185 on stock porting vs 185 on dune/drag port, for example. so, you are wanting to keep the best midrange, i assume by looking at your avatar, so dropping compression will be the least harmfull, and also allow more overrev. the timing, i think, is a bit more valuable to have. and, as for getting custom domes cut, wildcard is almost 1/2 the price, lol, last i heard

[dajogejr]

I think you answered your own question...

Lower the compression or buy C12.

The 100octane AV gas is rated at is NOT the same octane regular fuel is rated at.

I think 100AV gas on the same scale as car gas is only low to mid 90s.

They don't use Research/motor octane numbers on average.

[06specialedition]

I'm no expert but I've heard your plugs can back out from a bad gas cap....i dunno just saying.

[SAVAGE420]

I'm no expert but I've heard your plugs can back out from a bad gas cap....i dunno just saying.

[dajogejr]

I'm no expert but I've heard your plugs can back out from a bad gas cap....i dunno just saying.

 

I heard if you put 5 monkeys in a room with a typewriter, eventually they will write Gone with the Wind.

[WINDYCITYJOHN400]

I think you answered your own question...

Lower the compression or buy C12.

The 100octane AV gas is rated at is NOT the same octane regular fuel is rated at.

I think 100AV gas on the same scale as car gas is only low to mid 90s.

They don't use Research/motor octane numbers on average.

 

 

Not to step on any toes ....(In the past I have argued that "100 low lead AV gas" was not a 2 stroke fuel) BUT!....Once Tim at Titan Racing told me directly, that I could run 110 race fuel or AV gas and almost not even have to re-jet, I had to rethink my stance. Your right, they don't have the same octane rating system for Av and auto. But the AV low lead is actualy high in lead compared to the Research/motor fuels. Lead was the best product in the past for preventing detonation and increacing the octane of a fuel. Now his problem MIGHT just be that when he switched from the C12 to the AV gas the weather might have required a jetting change. I'm not saying don't try running race fuel. But I AM saying that when Tim cut my custom domes he told me that he thinks motors run BETTER and CLEANER on the AV gas. But if your racing at a track your going to have to pass a fuel check, so for his track motors they end up running the race fuel. But he was specific when he said I could jump from 110 to AV gas and not re-jet. That's my 2 cents....not trying to be the smartest guy in the room...just passing on info from one of the Nations Top Builders. Free.

[firebanshee]

I heard if you put 5 monkeys in a room with a typewriter, eventually they will write Gone with the Wind.

[bode1]

I heard if you put 5 monkeys in a room with a typewriter, eventually they will write Gone with the Wind.

 

Yeah, but there's no way they could write War and Peace

[sandman81]

Let me see if i can explain it.

 

The three different octane numbers that are used in gasoline are Motor octane Number (MON) Research Octane Number (RON) and R+M/2.

 

MON is tested to meet the demands of wide open throttle, high rpm's and heavy loads. Which is important for race engines due to them being at those levels. To get MON the fuel is tested in a single cylinder engine were they change timing and compression ratio.

 

RON is tested to meet part throttle. To get RON the fuel is tested in a single cylinder engine almost like the one used to get MON, the difference is that the timing is set to stay at a specific number.

 

R+M/2 is simple, RON+MON/2. The average. This is what you see when you go to the pump. The daily driver doesn't need to know about MON since it usually is not used for race engines.

 

When buying race fuel the octane number that is MOST important is MON.

 

C12 has a MON of 108.

 

Avgas is tested different. They use what is called Aviation Lean along with other test, but for the octane numbers we are looking for ill stick to the aviation lean. Aviation lean is the same test as MON.

 

So 100ll is actually close to a MON of 100.

 

Hope this helps you guys when buying gasoline.

[BigRed350x]

Yeah I know about the whole avgas thing - i ran it all last year. Im not switching fuel as it would cost me a fortune to ride all season on c-12. Its either domes or timing, but one of these if not both have to change. I just want to know which one will make me lose the most power, that way I will do the opposite.

 

Too low of an octane rating for your compression and timing, too much timing, or improper dome design.

[Profilact]

I am convinced that my compression ratio is too high for avgas. Im gonna go from 20's to 22's, and keep the timing at +4. Sound about right?