Strange observation about jets?

[michaelj]

I am running a 04 450R carb. on a highly modded 465EX. The carb. came with the stock jets and I took out the stock pilot jet and it is a 48keihin aprox. 23mm long. It has alot of popping on decel so I went to the Honda shop to get a 50keihin pilot and the one they gave me is like 28mm long, I question them on it and they said it should work fine. Well it makes my quad idle extremely fast- whats the deal??? Is it the wrong type of Keihin jet.

I have the idle turned down as far as humanly possible. As soon as I put the 48 back in it idles perfect but is way to lean and pops backfires...

[Sjorge450R]

Originally posted by michaelj
I am running a 04 450R carb. on a highly modded 465EX. The carb. came with the stock jets and I took out the stock pilot jet and it is a 48keihin aprox. 23mm long. It has alot of popping on decel so I went to the Honda shop to get a 50keihin pilot and the one they gave me is like 28mm long, I question them on it and they said it should work fine. Well it makes my quad idle extremely fast- whats the deal??? Is it the wrong type of Keihin jet.

I have the idle turned down as far as humanly possible. As soon as I put the 48 back in it idles perfect but is way to lean and pops backfires...

keep the 48 in there and then adjust the needle or the screw. That should solve your problems.

[d3ktrix]

The length of the pilot jets makes no difference. They both work the same, that's not related to your problem.

[GPracer2500]

d3ktrix is on the money. But in case anyone was wondering....



The 28mm pilot is a Series 21. The 23.5mm pilot is a Series 26. Keihin makes at least a half dozen "models" of pilot jet. Different carbs use different ones.

On the S21 and S26, they are identical except for the length from the threads to the slotted end. Some carbs (like the 04/05 450r and 400ex) are designed to use the less common S26. But as long as a S21 will physically fit with no clearance issues, it's likely to meter fuel nearly identically to a S26. S21's are used in place of S26's all the time, I'm sure. I know I've done it.

I can only imagine a very minor difference in the two. If the fuel pickup for the pilot is deeper in the bowl, it stands to reason (I think) that the differential pressure that pushes the fuel through the jet will be skewed slightly. But it would probably be something like: S21 size 48 = S26 size 47.5. That's easily absorbed by the fuel screw adjustment.