Different slide needle tips?

Differences in ignition timing can give similar symptoms to changes in jetting.

I lined up several used 2-groove standard needles for comparison.
You can see minor differences in the machining at the tip of the needle.
The two on the left have a more blunt cutoff than the others with more of a tapered end.

Is this what the original poster was concerned with?

Bob Z. said:

I lined up several used 2-groove standard needles for comparison.
You can see minor differences in the machining at the tip of the needle.
The two on the left have a more blunt cutoff than the others with more of a tapered end.

Is this what the original poster was concerned with?

Click to expand...

Yes that is the issue with my needles

I wouldn't think the tip of the needle made much difference. The end of the needle doesn't come out of the needle jet until about 3/4 open throttle, so it's only going to be a short period of time that the end of the needle passes in and out of top of jet. The rest of the time the mixture is controlled by the taper or once out by the main jet. Unless you just happen to be riding around at near 3/4 throttle position most of the time.
I would hazard a guess that the difference in the pipes blueing is at the other end of the scale and has more to do with the idle mixture.
If you are running a wasted spark ei, theoretically advance should be the same on both sides.
My bike has a left pipe bluer than the right. Someone on here has mentioned Commando's seem to run a little hotter on the left. If the bike runs good and the plugs look okay I wouldn't lose any sleep over it.

A quick way to compare needles is to stand the tapers of two needles in the jaws of a vernier calliper at various finely adjusted settings in the tapered range of the needle. then check to ensure that the circlip grooves line up with each other. The tip of the needle will be relative to the machine that produced the blank needle before grinding and of no relevance to the final needle profile.

gripper said:

A quick way to compare needles is to stand the tapers of two needles in the jaws of a vernier calliper at various finely adjusted settings in the tapered range of the needle. then check to ensure that the circlip grooves line up with each other. The tip of the needle will be relative to the machine that produced the blank needle before grinding and of no relevance to the final needle profile.

Click to expand...

That is the idea i had (after i had ordered new needles and needle jets of course :roll: ) and won't you know it all the needles matched up. Well they are not expensive an now i have a spare set for when time comes to replace them.

Also give me chance to reroute the cables yet again and that has improved things so not just a waste of time and money.

The tip of the needle should never come out of the needle jet. If it does, it can hang the slide up and give you a quick trip into the boon-docks. There is a problem which can occur especially if you use methanol fuel - it is when metering occurs off the tip of the needle instead of the main jet. So if you increase the size of the main jet and don't get a darker plug reading when you do a plug chop, you know you have got this problem. It can cause burnt valves and pistons if not corrected. With petrol as fuel, increasing the needle taper can correct this condition. With methanol a different technique must be used - recess the needle jet and meter lower down. In any case the tip of the needle must always remain trapped.

Here is the data I took 15-20 years ago.
The 2 ring and 4 ring are incredibly close and I have often used them interchangeably. The combination with the cut away spray tube is probably the biggest difference.
Toppy the needle problem you "supposed" is more a problem of the mind than of hardware. :mrgreen:
The different tip performance you perceived is completely nonexistant IMO. Acotrel is correct for the most part. The main jet takes over before you get to the needle tip so the needle tip is almost nonfunctional.
click on pix to see the whole thing

My brother races 500cc and 750cc two-stroke triples in historic sidecar races on speedway using methanol fuel. We have almost come to blows discussing how to jet the bikes. If we get it wrong, it costs a big dollar.