Keihin carb tuning

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57pan
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Keihin carb tuning

#1

Post by 57pan » Mon Aug 02, 2004 7:54 am

My 57 has a Keihin butterfly style (not CV) carb. It has a 100 pilot jet and 185 main jet and it is WAY too rich. If I put a brand new set of plugs in it and run it 10 miles (medium to low speed, just puttin') the plugs are black!
I put a 70 pilot jet in it but that seems to be way too lean (coughing and sneezing thru the carb).

So here are my questions:

* There are a lot of jet sizes between 70 and 100, and I don't really want to buy one of every size - how do I hone in on the correct size?
* Where can I get jets and/or a rebuild kit for this carb?
* Does anyone have any good tuning directions for this carb? (Most of the directions I find on the net are either too general or are specifically for the CV).
* Has anyone had any experience with the adjustable mainjet kit that is available for this carb?

I know someone's going to say just put a Super E on it, or put the Linkert back on it. The Super E is not in the cards right now - already way over budget on this project. I s'pose I'd be willing to try a Linkert if I could find a good one for cheap, but I hate to give up the accelerator pump.

Thanks for any thoughts, tips or suggestions.



Billy
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Joined: Tue Mar 23, 2004 6:57 am

Re: Keihin carb tuning

#2

Post by Billy » Mon Aug 02, 2004 8:01 pm

Any Linkert in usable shape is worth more than an S&S E. If you find one super cheap, expect to spend $$ to get it restored to operating specs.
Never cared for the Kehin butterfly. but if 100 is way too FAT & 70 is too lean split the diff. Try around 80-85 to start. That is a beginning .
This assuming your air cleaner is in clean usable condition.
Need more info: Is this carb New to your bike ??
Or did it just start doing this ?? Important!!

57pan
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Re: Keihin carb tuning

#3

Post by 57pan » Mon Aug 02, 2004 9:36 pm

Billy,

The bike had a Bendix on it when I first got it, and that carb was running rich. The local shop where I had it worked on put the Keihin on it and those are the jets that were in it, and it has run rich since it was installed last year.
I have done a complete top-end job on it since then and am just now getting it back into running condition and the over-rich condition still exists.
It has a foam air filter element - I'll try cleaning and re-oiling it to see if that has anything to do with it, but that element was cleaned/replaced at the same time the Keihin carb was installed.

Billy
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Re: Keihin carb tuning

#4

Post by Billy » Tue Aug 03, 2004 1:03 am

I'm NOT surprised that you had to do a Top-end. As an Over-rich condition causes the extra gas to wash the oil off the cylinder walls & thus creates pre-mature bore wear, pistons & etc...
That's the Seriousness of having it properly jetted.
I recently did a Top -End on a Brand New Sporty with ONLY 13,000 miles. It Had a Dyno-Junk kit put in it New, & was terribly Over-rich just washed the oil off & wore out the top-end out.... "TRUE" .....Just out of warranty.

Jetting is crucial in 2 respects:
(1) Too Lean = Overheating/holes in pistons
(2) Too Rich= Premature wear due to gas washing off the oil that protects the parts, bores, pistons & etc...

The Air cleaner I mentioned because, if it's clogged/dirty the motor can't get the deep inhale of air needed for proper fuel/air mix, causing Over-rich condition..
If it's been a Year without washing & re-oiling it.
Do it anyway...It's time..& Good maintenance.....
Try the 80- 85 jet & let us know how it reads. When you change jets, it's best to install new plugs to get a better "READ" off them. When you start it If you can, avoid using the choke as it will color the plugs & give a "False Reading"

Just needs dialed in...

Cotten
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Re: Keihin carb tuning

#5

Post by Cotten » Tue Aug 03, 2004 2:52 am

Linkerts don't need an accelerator pump.
They use a nozzle with a built-in reservoir to meter an extra charge of fuel upon the demand of accellerating.
No raw un-atomized fuel, no diaphragms to split, no linkages to get gummy, no tiny orifices to plug up, no waiting for the pump to re-fill.

haggis
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Location: Maine USA

Re: Keihin carb tuning

#6

Post by haggis » Wed Aug 04, 2004 2:48 am

Ah Ha.... were back on the Carbs again!!
Me I love a good Linkert..nothing works like it...the motor was designed to run it...why run anything else?
Give your Pan a Linkert...it;ll love you for it!! ;D Haggis

Cotten
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Re: Keihin carb tuning

#7

Post by Cotten » Wed Aug 04, 2004 3:19 am

And don't forget that a Linkert gives your right knee some room!
(Practicality, in my book. Especially in cold weather.)
A lot of Evil Manifold Leaks result from hitting extended aircleaners with the knee when kicking. Especially when fueled by alcohol. (The knee, not the carb.)
In a world obsessed with what their machine looks like, I am amazed that the the clean, tucked-in appearance of a stock assembly has been out of 'fashion' for so long.

57pan
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Re: Keihin carb tuning

#8

Post by 57pan » Wed Aug 04, 2004 9:57 pm

OK, you guys just about have me convinced to put a Linkert on it. I'll keep my eyes open for one.

In the meantime, though, I need to get the Keihin tuned. I took a 70 jet and opened it up to 80 - it was still too lean. I opened it up to 85 - no more coughing and sneezing thru the carb, so I think that must be about right. Haven't had a chance yet to put fresh plugs in it and run it for a while at 1/4 to 1/2 throttle to see what the plugs look like.
Just a word about the method used to open up the jets (before someone tells me that it can't be done accurately enough). I used a set of tapered broaches (reamers) that are part of my clock/watch repair tools. Using these reamers I can accurately open up the hole in the jet by any increment that I want - I don't doubt that I could hold a .0005 tolerance, and they leave a very smooth bore.

Billy
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Re: Keihin carb tuning

#9

Post by Billy » Thu Aug 05, 2004 12:00 am

57Pan, sounds like you're close/ if not right there, on the slow-jet.
It's helpful that you can drill your own jets bigger.
It's a common practice when tuning & Cheaper, than buying loads of jets..
I drill mine as well, as needed. ;D Then when I'm where I need it to be, I scribe the 'New' size on it.
My uncle used to repair watches, I remember his tools.
I use micro-drill bits..

At least you're not Way Over-rich on the slow speed now. That's a good thing till you find your Linkert.
I'm Big on CV's & making them a 2 bolt pattern bolt-on.

57pan
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Re: Keihin carb tuning

#10

Post by 57pan » Thu Aug 05, 2004 3:33 am

I think I've got it. I blasted the plugs and got them nice and clean, then went for a 10 mile ride. Coming down the road to my house I pulled in the clutch, cut the throttle, killed the engine and coasted into the driveway. I pulled the plugs and here's what they looked like:

Image
Image

I think they look pretty good. It's hard to get the color to come out right on the screen, but the ceramic in the center is off-white. Maybe they should be a little more on the tan side? What do you think?

Billy
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Re: Keihin carb tuning

#11

Post by Billy » Thu Aug 05, 2004 6:44 am

57Pan, I think your pics are BIG enough !! :)
Seriously, your Rear plug is running Richer than the front. For only 10 miles & blasted clean-somewhat plugs. They show quite a bit of difference.
Look at them closely, You got a New top-end there.
Did you pressure test your intake after re-assembly ??

Cotten
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Location: Central Illinois

Re: Keihin carb tuning

#12

Post by Cotten » Thu Aug 05, 2004 5:20 pm

I see a slight difference, but not an alarming one.
I currently have one of my godchild Knucks in for service; Even with a drum-tight manifold, and the timing degree'd to where the images of front and rear timing marks (I use paint) are superimposed over each other with a strobe,....the plugs still burn with a minor difference.

Mr Ed
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2003 FLHTCUI

Re: Keihin carb tuning

#13

Post by Mr Ed » Wed Apr 01, 2015 11:44 pm

I read somewhere on this forum that there is no bad carburetor, just ill tuned. With that in mind I was determined to make a butterfly single cable Keihin work on my nearly stock 1964 FL which is .020 bored, and straight drag pipes. This is no small feat on a kick only bike. The Linkert was made for this because you can adjust the jets with the engine running and carb mounted. The Keihin is difficult because not only do you have to remove and disassemble the carb to change jets, but then you have to kick start after each adjustment. And it won't always start if the adjustment was too severe. But the Keihin flows a lot more and will perform better than a Linkert when tuned properly. So the stock carb from the donor 1977 FLH I think has a .72 low jet and a 170 (1.7 mm) high speed jet. I could not even get it started. This was a emotional low because the bike was new to me and I had to do the full tune monty to get to the point where I knew to up the low speed jet. So after pressure testing the intake, static timing the ignition with a test light and replacing the insulator on the points post I kicked and kicked with still no start. I was unable to find a vendor with a complete set of jets so I wound up buying what I could find piece meal until I could zero in. I decided not to drill the jets because they can be used on another application and you still have to disassemble the carb to change. I digress because no mention thus far in this thread about the idle mix screw position. I found it best at 3.25 turns regardless of low jet. The importance here is critical because it just won't start at 2 turns, but 3.25 is the sweet spot. I found a .80 and .88 low jet and a 1.75 high in the junk drawer at my local chopper shop. The .75 got it started but was lean and the 1.75 was lean also because it would bog really bad under high load. The .88 was way too rich made black smoke. Then I found a 1.80 at Barnett Harley. All through these adjustments I also played with float level and find that when viewing the carb upside down with bowl removed the float should be slightly up from level. Too high and you will be rich regardless of low speed jet and too low causes starvation up hill under load. I have settled on the .80 low and 1.80 high with idle mix screw at 3.25 to 3.5 turns and float as indicated above. It starts easily, the choke actually helps when cold, and the bike runs great. I am a working man and ride my Ultra Classic with my club frequently, plus I am old and can only kick a few times per day, so this process took over a year. I hope someone reads this and can cut that time down to a reasonable period.

UPSROD
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Re: Keihin carb tuning

#14

Post by UPSROD » Thu Apr 02, 2015 5:54 pm

The correct jetting depends on the model Keihin you are working on...they are not all the same!

58flh
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Re: Keihin carb tuning

#15

Post by 58flh » Fri Apr 03, 2015 1:53 pm

I was going to suggest opening the jet by 2-sizes each time until its correct.Seems your close--To me I think you should take a good ride like roll around for an hour /then check them.They looked LEAN to me /But your very close!--As long as the manifold has no leaks you can ADJ. it by hand to run a bit richer/Maybe a HALF-TURN out as Kehiens are Tempermental & A Half might be to much.I don't know which model you have.Some have a welch-plug that needs to be removed to get at the Adj.screw!-(another EPA Thing).Mine did & mine was a 3-jet kehign.---Respectfully---Richie---Sorry fellas--I didn't look & thought this was a new post!

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