Topic: Terrible idle with Keihin idle jets?

[Buttmask]

So I wanted to test something out, my carbs on my 75 750F came with aftermarket kit idle jets marked 40. My buddy had a set of used 40 Keihin jets. The bike idled AWFUL with them in, anything below 1100 would just die out, sounded completely off too. The jet's are noticeably different, the diffuser holes in the top are clearly much larger

Is this because the jets are old? They look to be in good condition and not drilled out or anything(I cleaned them really well) Could a resync solve this? My bike idles well with the aftermarket jets in, but was just wondering what the deal may be since everyone recommends Keihin parts when possible.

[brewsky]

The jets may not be equivalent even though they are marked the same size.

See thread with this title
"Oem vs aftermarket jet testing"

[harisuluv]

How did you clean them?  Did you see perfect circles when you look through them into the light?

[Buttmask]

Oh I know the aftermarket ones might not be equivalent. That's why I installed the Keihin ones.

Harisluv- I shook them around in a mason jar of 50/50 hot water in simple green a little, used some brass wire and went through all the holes, and then blasted them real good in and out with a can of carb cleaner. And yes I can see perfect circles when holding them up to light.

Popped the old aftermarket jets back in and idles great again. So its definitely these jets. And theyre definitely the correct ones for the bike.

[harisuluv]

Ok, I'm not really sure what you're asking.  Kei Hin/Honda OEM jets are hands down the best quality, highest degree of quality jets available for these bikes period.  End.

Now, if yours don't work, it's not the quality of the jet, or the Kei Hin brand, or anything of that, it's totally irrelevant.  If your friend gave you a 2015 mercedes and later you find out that it had been in a flood and is totally water damaged, you would conclude that particular car has issues, NOT that Mercedes brand is a crap brand.

That being said, there are any number of reasons you could have issues.  And that's assuming that you didn't disturb ANYTHING while taking them off and on and everything is exactly as it was.  If you want, try and replace the jets back, you might even be able to do it on the bike, bowls pop right off, put the old jets back in. 

It could be that the OEM jets are right, but old jets were tuned/adjusted to compensate for them being non-OEM spec.

As far as your cleaning methodolgy, they need to be physically cleared, which sounds like you did with a brass wire.  Where did you get a 10 gauge brass wire from?  Keep in mind you have no idea of the history of the jets, or who cleaned them within the last 40 years.  Could have been improperly cleaned.

You can take some easy troubleshooting steps to try and definitely isolate the issue, but until you do that, you are just speculating.

[jonda500]

If you can get hold of an accurate size 0.4mm micro drill (you'll need a micrometer to check it is actually exactly .4mm) you could compare the jets by inserting the blunt end into the jets and noting whether it is a tight fit, snug slide in, or loose fit and gain more insight as to whether it's that your bike likes a non standard size or whether the oem jets have been cleaned too aggresively or drilled out to a bigger size, and find out if they're smaller or bigger than the aftermarket ones.
John

[flybox1]

The bike was probably tuned to the aftermarket jets change in fuel supplied.  Now, tune your bike to the oem jets.