Harley Davidson Forums banner

1 - 13 of 13 Posts

·
Registered
Joined
·
40 Posts
Discussion Starter #1
I have a 1991 Fatboy, with Arlen Ness big Sucker I kit on CV carb and Thunderheader exhaust. Carb Gurus, what would be a good jet combo?

Thanks
 

·
Super Moderator
Joined
·
12,743 Posts
I'm no guru, but if it were me, I would buy a complete jet kit. When you pull your current jets, there will be a number. I wouldn't jump up to the highest number on the first go around. Go up a number or 2 and try it. You may have to try a couple combinations before you hit it just right.
 

·
Registered
Joined
·
3,736 Posts
Get the engine warmed up real good.
Give it a good hard run for about 3 to 5 miles.
Immediately pull over to the side of the road and pull the plugs while they are still hot and check the color.
Kinda of a light brown is O.K. frosty white is dangerous.
Install richer or leaner jet to compensate for what the color of the plug is.
Give it another run and look at the plugs again.
repeat these steps until you get the desired color.
Here`s a chart for a good general description.
http://www.theultralightplace.com/sparkplugs.htm
 

·
Registered
Joined
·
39,558 Posts
To add to what Marty is explaining, its called a "throttle chop". What you want to do is use the kill switch after your run and coast to a stop.

Probably a bit difficult to find a suitable location to do this in NYC.... pretty easy in Kansas and Montana.

Try starting out with a .165 Main jet.

Heres a tuning manual for Mikuni HSR carbs. Some good info in there.
http://www.mikuni.com/pdf/hsr_tuningmanual_021003.pdf

Best way to tune is on a load dyno (dynojet 250i), you can get all your jets spot on.

Next best would be to make runs at a drag strip, but adjusting jets to get best ET only gets your main jet right. Still would need to do throttle chops to get your intermediate jets right.
 

·
Registered
Joined
·
87 Posts
What Marty & Kainam said. Keep in mind that 5R6a is hot as hell so don't make the determination based soley on the tip of the electrode & insulator, look down inside the base of the plug. I think 45/190 or 200 would get it close. You can also shim the needle to perfection after you determine the proper jet.
Jets cost $7 from the Stealer but if you ask for cv jets for a FatBoy they give you deer in headlights look & say they don't carry jets, unless you act like you know what you're doing and say "Gimme a 27105-88" then they go in the back & get you one.
Hope this helps.
 

·
Registered
Joined
·
40 Posts
Discussion Starter #7
Thanks for all your help guys. I put 45/180 combo. So far everything seems to be in order however it is overflowing somewhere. I have adjusted the floats and checked everything and can not figure out where. I am borrowing a carb from a friend of mine and will give it a shot. Take it from there.
 

·
STAND AND FIGHT!
Joined
·
13,194 Posts
Thank God for fuel injection.

I hated working on carbs. All carbs. They truly suck.

Holley made generic throttle body fuel injection for cars, the technology should be pretty mature, since it's been available for 20 years, does anybody make an aftermarket throttle body fuel spitter for HD?
 

·
Registered
Joined
·
3,736 Posts
Thank God for fuel injection.

I hated working on carbs. All carbs. They truly suck.

Holley made generic throttle body fuel injection for cars, the technology should be pretty mature, since it's been available for 20 years, does anybody make an aftermarket throttle body fuel spitter for HD?
I do`nt know about an "aftermarket" fuel spitter for H.D.
A friend who is building a SHOP bike is expirmenting with installing Ford injectors and brain box,etc. onto a shovelhead using ford components.
I had a very small turbo for a Ford{EXP or something like that}1.9 liter engine laying around so I donated that to the cause.
Seemed like a good idea at the time any how.:)
He has`nt got it up and going yet but last time I stopped in for a visit the bottom end was together and the jugs,head were on it.
 

·
Registered
Joined
·
87 Posts
<<<it is overflowing somewhere. I have adjusted the floats and checked everything and can not figure out where.>>>
I don't know how you adjusted the float but if it's leaking from the overflow tube rather than the bowl o-ring my WAG is that the needle valve is not closing between 0.413-0.453 on the float height with the carb @ a 15-20* tilt. Put a piece of tubing on the fuel inlet & blow thru it to tell exactly when the needle valve closes.
If that's the problem you need to check jetting again because a flooding carb creates a rich fuel/air mixture.
Hope this helps.
 

·
I {Heart} Hookers.
Joined
·
31,321 Posts
I don't know how you adjusted the float but if it's leaking from the overflow tube rather than the bowl o-ring my WAG is that the needle valve is not closing between 0.413-0.453 on the float height with the carb @ a 15-20* tilt. Put a piece of tubing on the fuel inlet & blow thru it to tell exactly when the needle valve closes.
If that's the problem you need to check jetting again because a flooding carb creates a rich fuel/air mixture.
Hope this helps.

Agreed.

The carb needs to be off to correctly adjust the float level and be held at a 15-20 degree angle. The float gets adjusted 7/16" from the top float ledge to the carb bowel deck.

If you have too high of a float level, the needle won't reach up into the seat far enough, and fuel will flow constantly.

Also, take a look at the Viton tip of the needle, and look for damage or a worn "Ring" where the needle seats.

I've not seen many, if any floats go bad in these carbs. They're a solid, buoyant plastic material and in almost all cases, turned out to be the float adjustment of a bad needle tip.

Here's a link to adjusting the float if you need some visual help.

http://www.hdtalking.com/fuel_and_carb_related_issues/981-cv_carb_float_level_adjustment.html
 

·
Registered
Joined
·
40 Posts
Discussion Starter #12
Thanks, I am a member on HD Talking as well and have both Harley and Clymer manuals. I pretty much followed instructions to the tee and it is still overflowing. I will re-check again, I may have missed something or did not adjust the float correctly.
 

·
Registered
Joined
·
87 Posts
The manual says something about a restricted gas tank vent will cause carb overflow but I didn't go there because 9 out of 10 times a new problem is caused by the last thing you fixed.
I clamp a carpenter's speed square to my bench then clamp a steel rule on the degree mark and once for smoe retarded reason after completely rebuilding my carb I clamped the top edge of the rule to the degree mark instead of the bottom edge, which actually had me setting my float with a 9*-12* angle and my bike ran like crap.
That had me scratching my head for a while.
 
1 - 13 of 13 Posts
Top