Topic: Replica Keihin jet measurements

[rosewood]

OK so purchased some replica Keihin jets from a retailer for my build to help with any tuning issues when I do finally get this bike running.

We have a OGP measuring machine at work so thought I would measure them to see how close they are.

Have read a lot about them not being very accurate and to not use them, but not being able to buy originals thought it was worth the gamble..

These are for a CB550F bike

I purchased 98, 105, 110, and 115's

Here are the measurements (all in millimeters) :

98's
0.9789
0.8941 - way off
0.9827
0.9792

105's
1.0701
1.0723
1.0708
1.0683

110's
1.1020
1.1008
1.1005
1.1001

115's
1.1532
1.1570
1.1382 - hole was not perfectly round, had a a couple of bumps around the edge which threw off the measurement. it would be closer to 1.15 if it was clean
1.1477


One of the 98's was way out closer to a 90 but the rest were pretty good
The 105's where actually closer to a 107 but reasonably consistent across all 4
The 110's were pretty damn close
The 115's where not too bad either with the exception of one not being a clean hole

Take from this what you will but I plan on buying a couple of extra's in the sizes that were out hoping I get something closer so I can then at least have consistent sets to use.

Will also measure some original keihin's next to see how accurate they are..

This was a pretty quick and easy measurement to do but obviously you need the equipment.

rosewood

 

[ekpent]

 Nice data you compiled. It will be interesting to see some actual Keihin and see just how close they really are. I have some Keihin cut-away pics on my other computer and will update later. May not only be the size of the hole but the way they are machined also.

[seanbarney41]

Also would be helpful if you could tell us what the source for these jets was or what aftermarket brand name these were sold under...there are at least 3 different company's manufacturing replica carb parts

[brewsky]

I did some simple flow testing on different brands and found significant differences especially in slow jets.

For example, a #40 aftermarket SCI supplied push in slow jet flowed much more than an oem #42 Keihin.

[seanbarney41]

that is a good point as I don't think main jets are gonna be an issue...surprisingly few ever really use 3/4-full throttle anyway, plus go ahead and swap those keihin 110's in place of some keihin 105's...not really an immediately noticeable difference, huh

The real issue is with slow jets, jet needles, needle jets, and air screws

[rosewood]

I'll pm you where I got these from, would rather not point the finger at any retailer/supplier in case its seen as questioning their quality etc...

This post was more to show that they could be measured to gain some confidence before using them... 

Also would be helpful if you could tell us what the source for these jets was or what aftermarket brand name these were sold under...there are at least 3 different company's manufacturing replica carb parts

[flatlander]

Have read a lot about them not being very accurate and to not use them, but not being able to buy originals thought it was worth the gamble..

nice research!
sssshhh... have you not hear of jetsrus.com?

[ekpent]

 As seen in the cut-away if this Keihin slow jet not just a simple hole bored through a piece of brass. Note the stylized 'K' insignia for people wondering if they have stock bits.

[seanbarney41]

Wow. That really shows how these get blocked so easily.

[PeWe]

I heard that Mikuni flow test their jets and stamp the value afterwards.
This might ensure the flow, not a specific diameter. Keihin do the same thing, if correct?
Correct flow of fuel or air is important.

Probably Mikuni only
http://www.jetsrus.com/FAQs/FAQ_mikuni_vs_dynojet_vs_keihin_sizes.htm

[rosewood]

I may be wrong but from what I gather their particular jets for the ones I'm referring to are not genuine...

http://jetsrus.com/a_jets_by_carburetor_type/jets_keihin_99202-601_main_secondary.html

Have read a lot about them not being very accurate and to not use them, but not being able to buy originals thought it was worth the gamble..

nice research!
sssshhh... have you not hear of jetsrus.com?

[Bankerdanny]

That is true, but unlike Keyster and some of the other options I would be inclined to trust JetsRus to have a reliable product.

[rosewood]

I've just contacted them and they confirmed theirs aren't genuine....I might try a set or two from them also if shipping is reasonable..

Also have some keihin with me today so if i have time will get them on the OGP..

My bike also came with keyster kits so will also try and measure these.

That is true, but unlike Keyster and some of the other options I would be inclined to trust JetsRus to have a reliable product.

[rosewood]

Ok I found time to measure some NOS Keihin 100's today I picked of a while ago if anyone is interested...

NOS Keihin 100's:

1.0065
1.0026
1.0074
1.0059

Small sample size but as you can see the numbers are very accurate....

I did try put some older used keihin on also but they were a bit knocked up and need a good clean first..

Also tried to measure some old slow jest but found it very hard to get the holes lined up and normal to the optics. This was a great tool to actually see how clean they were though as I've been struggling to see even with a eye glass with the lack of light..

What it showed was that not all the holes may be concentric with the rest of the jet and possibly not straight either which makes them even harder to see down if one of the outer edges is casting a shadow across the hole..

 

 

[HondaMan]

Boy, that's some nice equipment you've got there!
I used wire gages for years, but my ex-wife took them (didn't even know what they were... ) when she [was] moved out. The stated 'spec' from Keihin in the 1970s era was +/-3%, which fits pretty well with the numbers you have above. The US DOT/EPA made Mikuni and Keihin 'tighten up' on those specs circa 1976, to 1%, when they stopped offering them in "5" step sizes above 80 and went closer to "2.5" or "3" steps instead. It's been no secret that buying new jets of the same size for these bikes often altered their performance: for example, I have fixed some of the 750K3 bikes (more than a few) by doing nothing more than replacing (some or all) the mainjets with new ones of the same size. This stopped them from fouling sparkplugs constantly, suggesting the holes got a little 'off' once in a while?

Another rarely mentioned point: if the bike was run a lot with the years of MTBE fuels we had in the 1980s (which mine was), the brass got really badly etched, inside and out. New jets made my own bike run much better (hey, RXman, remember when you sent me those new jets? You started it...).

[Jerry Rxman Griffin aka MuthaF'er]

Yep, always glad to help HM 

Now you have me wondering what a needle jet new vs used vs off brand (if available) comparison looks like. Keep up the good work. We've bashed Keyster for years. I'm also wondering now what manufacturer JetsRUs uses??

[david 750f]

About 10 years ago I compared a needle jet to the Keyster equivalent on an Optical Comparator. The Keyster taper was about 8% greater than the OEM. I used brand new Honda needles in the test.
This would mean the Keyster would run richer than OEM at the same clip setting.

This was for a 76 750F.. I believe the K needles have a different taper as they are different part numbers.

https://en.m.wikipedia.org/wiki/Optical_comparator

[DaveBarbier]

I'll pm you where I got these from, would rather not point the finger at any retailer/supplier in case its seen as questioning their quality etc...

You’d withhold this info from us! Seems like it’s better to get the word around here for who stocks/makes quality jets instead of not making a company feel bad. Just my opinion but I wouldn’t care what a company feels if they’re not making great products.

Edit: Very nice measurements by the way. I love that we have people on this forum with access to different equipment. I may have some spare nice new genuine keihin jets for my CR26 specials if you’d want to measure.

[rosewood]

Fair call Dave I guess its no secret any replica parts are not going to be as precise as the originals....

The jets i purchased are from 4into1..

The important thing from my perspective is that all 4 should be consistent and you know what actaul size they are. If one is way off it could be a headache down the road for tuning.

I am happy to use these replicas if i ever do need them but will make sure they are all close in size and have clean holes, if that means buying a few spares to achieve this then so be it.

Happy to measure your CR26's but I am in New Zealand so logistically not practical to do..

When I do have time ill measure my keyster jets and needles and compare to the originals..

rosewood

I'll pm you where I got these from, would rather not point the finger at any retailer/supplier in case its seen as questioning their quality etc...

You’d withhold this info from us! Seems like it’s better to get the word around here for who stocks/makes quality jets instead of not making a company feel bad. Just my opinion but I wouldn’t care what a company feels if they’re not making great products.

Edit: Very nice measurements by the way. I love that we have people on this forum with access to different equipment. I may have some spare nice new genuine keihin jets for my CR26 specials if you’d want to measure.

[TwoTired]

I wonder if you are forced to use aftermarket jets, you might be better off to buy undersize and drill them all to next size so they will all be the same.

Cheers,

[robvangulik]

I wonder if you are forced to use aftermarket jets, you might be better off to buy undersize and drill them all to next size so they will all be the same.

Cheers,

That is exactly what i did for my 400/450, no worries about jetsize, and didn't have to buy loads of jets, just upped the size carefully until i was happy with it. Kept a good administration about what i did and what the results were, worked out fine! Started at 86 and ended with 98, i even marked the jets with the final size so i couldn't forget and for a possible next owner

[DaveBarbier]

Fair call Dave I guess its no secret any replica parts are not going to be as precise as the originals....

The jets i purchased are from 4into1..

The important thing from my perspective is that all 4 should be consistent and you know what actaul size they are. If one is way off it could be a headache down the road for tuning.

I am happy to use these replicas if i ever do need them but will make sure they are all close in size and have clean holes, if that means buying a few spares to achieve this then so be it.

Happy to measure your CR26's but I am in New Zealand so logistically not practical to do..

When I do have time ill measure my keyster jets and needles and compare to the originals..

rosewood

I'll pm you where I got these from, would rather not point the finger at any retailer/supplier in case its seen as questioning their quality etc...

You’d withhold this info from us! Seems like it’s better to get the word around here for who stocks/makes quality jets instead of not making a company feel bad. Just my opinion but I wouldn’t care what a company feels if they’re not making great products.

Edit: Very nice measurements by the way. I love that we have people on this forum with access to different equipment. I may have some spare nice new genuine keihin jets for my CR26 specials if you’d want to measure.

I don’t need them measured, but was offering if you didn’t have new jets in stock. Yeah, NZ is a bit far just to send jets, haha.

I definitely would be great to have a sticky on “Why you want to buy OEM jets” with actually data and images instead of people just saying the QC on these aftermarket jets is minimal.

[DaveBarbier]

I wonder if you are forced to use aftermarket jets, you might be better off to buy undersize and drill them all to next size so they will all be the same.

Cheers,

Maybe drilling and reaming to the size. I just feel the nature of drill bits won’t get you as precise a hole but I’ve never drilled a jet.

Anyone have any links to good jet drill/reamer kits?

[Deltarider]

I wonder if you are forced to use aftermarket jets, you might be better off to buy undersize and drill them all to next size so they will all be the same.

Cheers,

That is exactly what i did for my 400/450, no worries about jetsize, and didn't have to buy loads of jets, just upped the size carefully until i was happy with it. Kept a good administration about what i did and what the results were, worked out fine! Started at 86 and ended with 98, i even marked the jets with the final size so i couldn't forget and for a possible next owner

Man, you're in business! What machinery did you use? BTW, what bike is '400/450'?

[robvangulik]

A simple set of jet reamers, and a cb400 bored to......why else would i need to rejet?