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  #1  
Old 13th October 2007
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Lightbulb Carb Tuning, & the Andrews High Flow Accelerator Pump Kit

Carb Tuning, & the Andrews High Flow Accelerator Pump Kit

Unbelievable! The feeling, of riding this ol' girl when she is tuned up so well. I am so excited after this evenings ride i cannot sit still. Each time, over the past two years, that i have learned something and improved my tune up i have thought that was it. Well, it is so much better now.

I have been running it a little too lean for these past two years or so. Often i have seen the comment "IronHeads like to run rich". In spite of this i have always run mine with the plugs a light tan color - i learned that tuning some "foreign" bikes before i had my IronHead. Now it is running better than ever, and my plugs are a definite dark tan color.

First i set up the main jet better. Went from 165 to 175 to 185 then back to 175. 185 was way too much - it would not accelerate, just bog down. Perhaps 170 or 180 would be better than 175, but at WOT she runs better than before.

Then the slow jet: 52, then 55, then 58. 52 was definitely too small - it sputtered under steady throttle and light acceleration. Better with each change. The upper limit is when the pilot screw is out less than 3/4 turn. I have it at 1/2 turn out now so i cannot go to a 60 which would require a further bit of turn-in.

Tonight i installed the Andrews High Flow Accelerator Pump kit. Heh heh heeeehhh! If you have a 1980 to 1988 Keihin butterfly carb this you want. Around 20 bucks.

From the Andrews web site:
"For all 1980 through '88 H/D bikes with STOCK Keihin carburetors, this kit is an easy, inexpensive performance upgrade. Removing the float bowl and drilling one hole is all that’s required. The carb body does not have to be removed. On 1980-'88 carbs, the stock accelerator pump is restricted by eliminating check valves in the pump. A high flow accelerator pump puts them back. The result is increased fuel flow through the pump and greatly improved low end and mid range throttle response."

My suggestion is to be certain that you have it very well tuned up, as i did, before installing this kit. Then you get the best from it. Also, i think it is best to remove the whole carb from the bike and work on the bench. IMO it is a poor short-cut to work on the carb in the bike - delicate float adjustment for one thing.

EDIT: I have a 1986 version of the Harley Davidson Keihin Sportster carb on my 1980 XL. Hence, the smaller slow jet size. Stock 1980 carb uses a 68 slow jet.
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Last edited by IronMick; 13th October 2007 at 04:08..
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  #2  
Old 15th October 2007
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groovemeisterus groovemeisterus is offline
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Lightbulb Jet Needle...

Don't forget about the jet needle when tuning your carb.

You can raise it for a richer A/F ratio, lower it for leaner, or you can
buy a thicker or thinner needle for your engine combination.

I use a Mukini 42 carb, but still same generically some what
for tuning purposes.

0 to 1/4 throttle is just the pilot jet being used.
1/4 to 3/4 throttle the jet needle comes into play.
3/4 to wide open throttle is just the main jet.

Here is an A/F ratio example from my last dyno run to see the different
stages. Pilot running, then goes lean from jet needle, then flattin's itself
out using the main jet. Hope this helps. I need to raise my jet needle
or buy a richer one. I recently ordered a richer one since my needle
is almost raised as high as it can go. I raised it to maximum and noticed
seat of the pants difference in acceleration. I tried many combinations
before my dyno run though and learned a lot from tuning my carb
seat of pants before this run.

Still more tuning for me until my A/F is flat across the entire RPM range.

Also notice at 3000 RPM my TQ curve flattens instead of still rising.
And then notice that my A/F went lean with the jet needle at the same
3000 RPM, then started to rise again when the A/F flattened out using
just the main jet.



Just my 2 cents.

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Old 15th October 2007
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Quote:
Originally Posted by groovemeisterus View Post
Don't forget about the jet needle when tuning your carb ...
Thanx groovemeisterus. However, we are talking here about a butterfly carb. This is not a CV [Constant Vacuum, Constant Velocity] carb. No needle, no needle jet.

The ports in the carb venturi are made active as follows as you open the throttle:
1. idle port, controlled by pilot screw, and 1st of 4 idle transfer ports are active at idle
2. next 3 idle transfer ports are exposed one by one as the throttle plate opens
3. mid-range port is next
4. main jet port is last.

Theoretically only one is active at a time, but there is some overlap.

All fuel is metered first thru the main jet, then either thru the slow jet or exclusively thru the main jet port depending on the throttle position; the latter basically at full throttle only.

To tune the main jet i made it bigger [160, 165, 175, 185] until it would bog down at full throttle [185], then went back one size. I ended at 175, although i have not tried 170 or 180. Perhaps the 175 is not perfect and either of the other two would be better; hmmmm, there is those adjustable mains; but i am good with it as it is now.

To tune the pilot jet i made it bigger [52, 55, 58] as long as performance was being improved and until the pilot screw was turned out only a very minimal 1/2 turn; this is with a 58. I suspect that if i go up to a 60 the pilot screw would have to be turned completely in, thus using only the 1st idle transfer port at idle. Perhaps this would be ok; maybe it would run even better with a 60 or larger, and perhaps even idle respectably with no further idle tuning possible. But i am good with the 58.

As a final step i added the acc pump kit. I believe this kit should not be used to solve an apparent problem; as in "my bike is not running well, maybe the acc pump kit will fix it". No to this. Get it running at its best first, then install the kit; then love it baby!

As a final check i examined the plugs after a full day 200 mile ride, ending with a short stint thru the city to get home. Nice medium to dark tan color on the insulator inside the working end.

Also, as previously noted, this is a 1986, not a 1980, Sportster carb. The 1980 carb uses larger slow jets, stock being 68.

Last edited by IronMick; 15th October 2007 at 18:00..
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Old 16th October 2007
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Question

Sorry for the confusion IronMick,

I guess I am not used to that carb. I've only used CV carbs and Mikuni's
that use Jet needles. I'm just a young pup.

What kind of carb do you have so I can do a google search and
learn more about it?

Thanks.

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  #5  
Old 16th October 2007
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If you want to feel REAL throttle response, you need to get a 2 barrel sidedraft carb like an old Mikuni-Solex or a Weber. When I first converted from the stock Keihin carb on my '77XLCH back in '77 to the Mikuni-Solex sold by Branch, I couldn't believe how responsive the carb was. Now, with my 'new' '78 that came with an S&S E I noticed that you had to crank the throttle a bit to get the carb to really kick in. I installed an old Mikuni-Solex just like the one I had 30 year ago and WOW! the response is instantaneous!! High velocity flow through two smaller venturis plus twin accelerator pump jets really makes the bike come alive. I also have a Weber 40DCOE with manifold that I'll install sometime this year for a comparison to the Mikuni. Guess I'm just a 2 barrel, sidedraft kind of guy after all!!

Eric
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Old 16th October 2007
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Quote:
Originally Posted by IronMick View Post
Carb Tuning, & the Andrews High Flow Accelerator Pump Kit

Unbelievable! The feeling, of riding this ol' girl when she is tuned up so well. I am so excited after this evenings ride i cannot sit still. Each time, over the past two years, that i have learned something and improved my tune up i have thought that was it. Well, it is so much better now.

I have been running it a little too lean for these past two years or so. Often i have seen the comment "IronHeads like to run rich". In spite of this i have always run mine with the plugs a light tan color - i learned that tuning some "foreign" bikes before i had my IronHead. Now it is running better than ever, and my plugs are a definite dark tan color.

First i set up the main jet better. Went from 165 to 175 to 185 then back to 175. 185 was way too much - it would not accelerate, just bog down. Perhaps 170 or 180 would be better than 175, but at WOT she runs better than before.

Then the slow jet: 52, then 55, then 58. 52 was definitely too small - it sputtered under steady throttle and light acceleration. Better with each change. The upper limit is when the pilot screw is out less than 3/4 turn. I have it at 1/2 turn out now so i cannot go to a 60 which would require a further bit of turn-in.

Tonight i installed the Andrews High Flow Accelerator Pump kit. Heh heh heeeehhh! If you have a 1980 to 1988 Keihin butterfly carb this you want. Around 20 bucks.

From the Andrews web site:
"For all 1980 through '88 H/D bikes with STOCK Keihin carburetors, this kit is an easy, inexpensive performance upgrade. Removing the float bowl and drilling one hole is all that’s required. The carb body does not have to be removed. On 1980-'88 carbs, the stock accelerator pump is restricted by eliminating check valves in the pump. A high flow accelerator pump puts them back. The result is increased fuel flow through the pump and greatly improved low end and mid range throttle response."

My suggestion is to be certain that you have it very well tuned up, as i did, before installing this kit. Then you get the best from it. Also, i think it is best to remove the whole carb from the bike and work on the bench. IMO it is a poor short-cut to work on the carb in the bike - delicate float adjustment for one thing.

EDIT: I have a 1986 version of the Harley Davidson Keihin Sportster carb on my 1980 XL. Hence, the smaller slow jet size. Stock 1980 carb uses a 68 slow jet.
Well, Mick , you've convinced me now....that's the very next thing I'm buying for my ride...as everything you've told me about tuning the 88 keihin butterfly on my 75 has made it run better, then I believe ya when ya say this will, too...My bike is starting to scare me in quickness......And this will make it faster? I'll have to have my Dr. Up my blood pressure pills a bit!!
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  #7  
Old 16th October 2007
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Quote:
Originally Posted by groovemeisterus View Post
... What kind of carb do you have so I can do a google search and learn more about it? ...
The original design is by Keihin. I understand that at some point in the later history HD bought the design etc and redesigned & manufactured it themselves. Most people refer to it as a Butterfly carb, referring i assume to the choke plate [pics of choke plate in my gallery].

Years ago Haynes published a book "Motorcycle Carburettor Manual" [note the British spelling] authored by Pete Shoemark ISBN 0-85696-603-7. It has been out of print for a long time, but i got one from an internet bookstore a few years ago. Might have been Amazon or AbeBooks, or eBay or whatever. He refers to them as Fixed Venturi or Fixed Jet carburetors. Very good reference on carbs.
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Old 16th October 2007
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For you guys with CV carbs, especially Keihen, i believe Andrews has an accelerator pump kit for those also. Check out their web site.
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Old 19th October 2007
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Quote:
Originally Posted by ericfreeman View Post
If you want to feel REAL throttle response, you need to get a 2 barrel sidedraft carb like an old Mikuni-Solex or a Weber. When I first converted from the stock Keihin carb on my '77XLCH back in '77 to the Mikuni-Solex sold by Branch, I couldn't believe how responsive the carb was. Now, with my 'new' '78 that came with an S&S E I noticed that you had to crank the throttle a bit to get the carb to really kick in. I installed an old Mikuni-Solex just like the one I had 30 year ago and WOW! the response is instantaneous!! High velocity flow through two smaller venturis plus twin accelerator pump jets really makes the bike come alive. I also have a Weber 40DCOE with manifold that I'll install sometime this year for a comparison to the Mikuni. Guess I'm just a 2 barrel, sidedraft kind of guy after all!!

Eric
If anyone wants to buy either a two-throat Mikuni-Solex or a two-throat Weber (as mentioned in post #5) with o-ring intakes, I have one of each on Ebay for the next week. Check them out and see if they are something to make your Ironhead kick it. I also have a couple of S&S Two-Throat carbs that I may sell later on.
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Old 19th October 2007
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Hey Mick,
Ponder this... A 1000cc Ironhead sporty will religiously pull 40 to 45hp on the dyno, line 20 of them up & thats what you'll get. My 1000cc Iron pulled 60hp day in & day out with stock cams. First off, an S&S "B", will get things started in the right direction. I loved my Keihin until I found my "B". Food for thought.

Red
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