Need jet suggestions for carb re-work.
Thread Starter
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Road Warrior
Joined: Dec 2006
Posts: 1,573
Likes: 138
From: StL, MO. USA
Need jet suggestions for carb re-work.
Hey all...
I was getting ready to rear into my carb to try and find whatever was causing a slight 'cough' when off-throttle at about 3500 RPM's.
Well...I found myself at a local dealer yesterday, and somehow I now have the Sreamin Eagle backplate and a Zipper air filter installed. After getting everything buttoned-up, I took the bike around the neighborhood to see how things worked. I can hear the difference both in the air flow (can actually hear the air being sucked-in), as well as in the deeper exhaust note...so I'm pleased with my purchase.
Since my carb is still stock - I can now obviously tell a lack of performance due to needed fuel not being there to compensate for the added airflow. It's not a HUGE lack of performance - but the kinda thing where I was like "OK - I know if this fuelgets right,it's going to make a noticeable difference". For those of you that have done similar mods - I'm am hoping you know what I am talking about. The bike doesn't run bad - it just suffereing from that 'untapped' power.
SO - how do i figure-out what jets/needles/shims I need for my set-up? I looked thru the 'do-it-yourself' section of the forum, and is looks like most of the topics are pointed at the addition of a SE air filter without exhaust mods. The Zipper filter I grabbed passes a LOT more air, and I also have Samson 'oval' slip-on's with the factory headers.
- Any suggestions?
I was getting ready to rear into my carb to try and find whatever was causing a slight 'cough' when off-throttle at about 3500 RPM's.
Well...I found myself at a local dealer yesterday, and somehow I now have the Sreamin Eagle backplate and a Zipper air filter installed. After getting everything buttoned-up, I took the bike around the neighborhood to see how things worked. I can hear the difference both in the air flow (can actually hear the air being sucked-in), as well as in the deeper exhaust note...so I'm pleased with my purchase.
Since my carb is still stock - I can now obviously tell a lack of performance due to needed fuel not being there to compensate for the added airflow. It's not a HUGE lack of performance - but the kinda thing where I was like "OK - I know if this fuelgets right,it's going to make a noticeable difference". For those of you that have done similar mods - I'm am hoping you know what I am talking about. The bike doesn't run bad - it just suffereing from that 'untapped' power.
SO - how do i figure-out what jets/needles/shims I need for my set-up? I looked thru the 'do-it-yourself' section of the forum, and is looks like most of the topics are pointed at the addition of a SE air filter without exhaust mods. The Zipper filter I grabbed passes a LOT more air, and I also have Samson 'oval' slip-on's with the factory headers.
- Any suggestions?
Road Master
Joined: Nov 2006
Posts: 808
Likes: 4
From:
RE: Need jet suggestions for carb re-work.
Banned
Joined: Jan 2007
Posts: 2,301
Likes: 4
From:
RE: Need jet suggestions for carb re-work.
Off thottle or off idle and 3500 rpms?
3500 would be 65-75 mph.
idle is about 900 rpm and off idle 950-1100 about.
and that would be where an off idle port would come in, depending on carb design.
I don't have any manuals on harley CARBS or replacement ones.
am I confused???
Never did much with HD carbs.
But normally an off idle (stumble) cough is normally (but not always) a little
to little fuel. But could be too much fuel too. Float level could be off also.
Too low starves, to high get over flow, depending on system design.
Remember ALL carbs are factory set for sea level.
Been a lot of years, but I believe it was one jet size larger for very 2000 ft rise in altitude.
But I would have to see if I still have a book on that fact.
Also, sometimes the idle speed could be set just a little too low.
Or the accelerator pump (if this carb has one) could be back flushing and not pushing
all the fuel forward though the acceleration ports (different carbs and different companies
call it different)
Most of my carb experience is on rochester, carter, holley, edelbrock etc. so may be a little different.
3500 would be 65-75 mph.
idle is about 900 rpm and off idle 950-1100 about.
and that would be where an off idle port would come in, depending on carb design.
I don't have any manuals on harley CARBS or replacement ones.
am I confused???
Never did much with HD carbs.
But normally an off idle (stumble) cough is normally (but not always) a little
to little fuel. But could be too much fuel too. Float level could be off also.
Too low starves, to high get over flow, depending on system design.
Remember ALL carbs are factory set for sea level.
Been a lot of years, but I believe it was one jet size larger for very 2000 ft rise in altitude.
But I would have to see if I still have a book on that fact.
Also, sometimes the idle speed could be set just a little too low.
Or the accelerator pump (if this carb has one) could be back flushing and not pushing
all the fuel forward though the acceleration ports (different carbs and different companies
call it different)
Most of my carb experience is on rochester, carter, holley, edelbrock etc. so may be a little different.
Banned
Joined: Jan 2007
Posts: 2,301
Likes: 4
From:
RE: Need jet suggestions for carb re-work.
Here's a couple links that might help you out.
http://www.harley-performance.com/ha...r-jetting.html
https://www.johnsmotorcycleparts.com...uning_tips.htm
Both appear to give the info you will need.
When done get a shop to run you an O2 exhaust test see if lean or rich or midline
http://www.harley-performance.com/ha...r-jetting.html
https://www.johnsmotorcycleparts.com...uning_tips.htm
Both appear to give the info you will need.
When done get a shop to run you an O2 exhaust test see if lean or rich or midline
Thread Starter
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Road Warrior
Joined: Dec 2006
Posts: 1,573
Likes: 138
From: StL, MO. USA
RE: Need jet suggestions for carb re-work.
ORIGINAL: choochoo
Off thottle or off idle and 3500 rpms?
3500 would be 65-75 mph.
idle is about 900 rpm and off idle 950-1100 about.
and that would be where an off idle port would come in, depending on carb design.
I don't have any manuals on harley CARBS or replacement ones.
am I confused???
Off thottle or off idle and 3500 rpms?
3500 would be 65-75 mph.
idle is about 900 rpm and off idle 950-1100 about.
and that would be where an off idle port would come in, depending on carb design.
I don't have any manuals on harley CARBS or replacement ones.
am I confused???
I have removed the accel pump and cleaned it up pretty well...and still experience the problem. Now that I have changed the air filter - I have different symptoms in addition. But those can be attributed to to added airflow & will resolve themselves after I go to a bigger jet & shims.
Having not worked with carbs too much myself in the past - I was hoping there would be an 'easy button' for figuring jet/needle configuration for my current set-up...guess that isn't the way it works.
One thing of note - the bike sat for about 2-years prior to me geting it and doing the rebuild. So I am assuming the 'cough' issue is a result of varnish accumulation. This is the last issue that reamins & once worked-out I'll be a happy guy.
Banned
Joined: Jan 2007
Posts: 2,301
Likes: 4
From:
RE: Need jet suggestions for carb re-work.
Ok as I said I'm not much on HD carbs
and 3500 yes depends on gear ratio.
But off thottle vs off idle.
Now i think you meant when you let off the throttl, in which case that is different.
Now a pop back through the carb can be caused by numerous thing.
Cams with a higher lift and longer duration, loose valve guide causing a valve closing
problem, weak valve spring, poorly seating valve.
Engine not thoroughly warmed up timing a little too advanced.
I remember reading something on this problem somewhere, or someone talking about it.
didn't pay much attention at the time, guess I should have.
But your middle circuit could need fine tuning also.
did you study the links I sent you? I haven't yet, just a brief glance over.
which carb do you have?
Remember do only one change at a time.
Get a spray bottle of water, with engine running and raising rpms and letting off
spray the intake seals.
A leak here can also cause some popping. allowing a momentary lean condition.
and 3500 yes depends on gear ratio.
But off thottle vs off idle.
Now i think you meant when you let off the throttl, in which case that is different.
Now a pop back through the carb can be caused by numerous thing.
Cams with a higher lift and longer duration, loose valve guide causing a valve closing
problem, weak valve spring, poorly seating valve.
Engine not thoroughly warmed up timing a little too advanced.
I remember reading something on this problem somewhere, or someone talking about it.
didn't pay much attention at the time, guess I should have.
But your middle circuit could need fine tuning also.
did you study the links I sent you? I haven't yet, just a brief glance over.
which carb do you have?
Remember do only one change at a time.
Get a spray bottle of water, with engine running and raising rpms and letting off
spray the intake seals.
A leak here can also cause some popping. allowing a momentary lean condition.
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Cruiser
Joined: Oct 2007
Posts: 122
Likes: 0
From: lynn ma
RE: Need jet suggestions for carb re-work.
I went with a #48 pilot jet an #195 main jet,after installing big sucker air filter ,wild pigs slipon mufflers that had 1 3/4 baffles.My bike seem to lack power in the mid range,Its alot better now. Some put shims [washers]under the needle to raise it up.Easy to change the jets ,4 bolts in bottom of carb.Have fun'.
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Thread Starter
|
Road Warrior
Joined: Dec 2006
Posts: 1,573
Likes: 138
From: StL, MO. USA
RE: Need jet suggestions for carb re-work.
I am a happy fella.
I'm sure there will be a bit of tweaking that I need to do - but the bike runs a TON better than it did since I put the new breather on.
I went to the local sho around lunchtime and grabbed a #45 slow jet. Came back to the house (I work from home a couple of days a week) and installed it. Whole process took about 25-minutes - It woulda been done in 15 if the stock jet woud have played nice - I ended-up having to bend a screwdriver so i had enough leverage to break the jet loose. It DID NOT wanna come out.
SO.. screwed the new jet in place - and ran the bike up the street for a quick test (less than am mile total) and I am now smiling as I am printing my reports.
It's the little things that really can change your day.
I'm sure there will be a bit of tweaking that I need to do - but the bike runs a TON better than it did since I put the new breather on.
I went to the local sho around lunchtime and grabbed a #45 slow jet. Came back to the house (I work from home a couple of days a week) and installed it. Whole process took about 25-minutes - It woulda been done in 15 if the stock jet woud have played nice - I ended-up having to bend a screwdriver so i had enough leverage to break the jet loose. It DID NOT wanna come out.
SO.. screwed the new jet in place - and ran the bike up the street for a quick test (less than am mile total) and I am now smiling as I am printing my reports.
It's the little things that really can change your day.