Do you know this for a fact or are you just listening to all the brain washed people telling you that OS plugs don't work.

All the guys at my track including me that run RB use OS plugs and they do not have a different taper than the RB, OD or Werks plugs, the OS is the most popular plug in the world and there is no way in hell that they have a different taper than the rest of the plugs out there.

I do know that I had someone stick an OS plug in one of my engines right before a qual started because I did not have any plugs in my pit bag. That button to this day will leak around the plug no matter how tight the plug is. To me they look different enough that I will stick with what is made for it.

I agree with you Chris, they will strip out the head button quickly also. They do not seat properly in the combustion chamber, for efficiency.

Yeah the distance from the small part of the taper to the large part of the taper on the OS plug is visibly shorter so the angle of that taper also has to be different... It may not be much but it can't be the same IMO.

I wonder if the displacement of the part of the plug that sits inside the head is the same or different between the two.

Meaning, would it impact compression at all?

It wouldnt impact compression, just the burn space would not be 100%, thus, less explosion in the combustion chamber, possible reduced power.

Hey guys
Just tried to begin run in and a have a few questions.
I pre heated the motor with my heat gun to 95 degrees celsius then turned on car and everything. I then blew in the air line to prime the motor and tried to start it. But everytime it starts the motor revs while the servo is at neutral and the carby isnt even moving. It revs pretty high for a few seconds then just drops back to an idle for 1-2 secs then stops. After this only way i can get it to start again is to prime once again and then it does the exact same thing revving high and then idles but stops.
I tried changing all the fuel and air line but it didnt change anything and also tried raising the idle a bit but that didnt help either.
any help would be much appreciated.
Mitch

There's more qualified guys here to comment but I'm on the thread so I'll try to help. It sounds like the low end is way too lean or it's sucking or blowing air. Maybe try this:

Have you had the head off? Make sure that it's tight and the glow plug's tight too.

Check the low speed (and all needles) are to factory setting.

Double check none of your hoses are leaking.

If you've got a fuel filter on it, take it off and see if that helps.

If you have a cigarette handy hold it around the engine and pipes to see if it's blowing or sucking smoke in anywhere. This always highlights an air leak.

I changed all the fuel line. but just looking at the motor then and the bolt that tightens the carby to the motor was loose so i just tightened it and hopefully that was the problem.
Thanks Mitch

Yeah, if she was sucking in air after the carby that'll do it.

That didnt change anything either. So i am back to square one. The head was tight aswell.

Ok, the height of the taper is different, but how does that affect anything? As long as the angle is the same it's should fine.

For me it's the only plug i am ever going to use cause it's the only plug out of RB, OS, and OD plugs that my LHS has.

if you look at the bod of the plug below the threads.. you will see the OS is slightly smaller also... hence the taper being shorter... so the angles could very well be the same...

just an observation.. i myself have been going back an forth with os and odonnels plugs in the past with out any issue

After you heat the engine you say that you have to blow on the line to get fuel there?? When you blow on the pressure line do you notice the fuel hit the HSN and sort of jump back toward the fuel tank? It sounds to me like your carb got really hot in the pre heat process and you are vapor locking. I have had this happen quite a few times when using heat guns to pre heat rather than the comp head heater. If this is what you are seeing you can blow thru the pressure line with the carb at full throttle until the fuel stays at the HSN and no longer jumps back away from the carb.... You should now be able to start it, but with the stock needle settings it may not just idle away on it's own, you may have to adjust some for your location.

If you do use a heat gun or hair dryer try to hold a thin piece of metal between the carb and the head while you pre heat.

What's happening also, you are burning only the fuel you forced into the the engine, and the engines has not ran long enough to create pressure to the fuel tank to draw into the engine, you can try to throttle some on the carb, like your pumping the throttle, to get the engine pressure going. Also, a finger on the exhaust pipe, while turning over the engine, helps force fuel into the engine, while holding finger on the exhaust, you can watch the fuel moving to the carb, when its to the carb, remove your finger, don't hold it too long, you can force more fuel than you need, and kill the plug, and hydro lock the engine with to much fuel.