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Cv carb question

CUSTOMSPORTSTER

CUSTOMSPORTSTER

Member
Although this is my frist post i have been a lurker here for a long time!
everyone seems very knowledgable so here is my question.

I have a 2000 Custom Sportster with a 1200 kit. This motor was originally built in North Carolina by croft custom cycles along with all the other mods. problem is at about 60-70mph in 5th gear it cuts out, not a bog but just surges like crazy and wont accelerate. With very light throttle and i can cruise along fine, but twist on it at all and it surges liek crazy. downshift to 4th and it runs and pulls fine. I have changed everything from plugs to ign module, wires and whatever else you can think of. Pelkin fuel valve is fine, tank is clean too. The carb has a 45 idle jet and a 180 main jet. i was thinking maybe it is lean and changing the main jet to a 185 or 190 and see how it acts. the previous owner is gone so i can get no other info for him. I did talk to the shop that built the bike but the guy that actually built it for my buddy is gone to florida so all i can find out is they rebuilt the whole bike and added the 1200 kit. Was curious what ya'lls thoughts were on this. Idles absolutely perfect,starts fine and runs great in every gear until you hit 5th. Now if I run it wot thru all the gears when i shift to 5th it pulls fine. Just normal cruising and you shift to 5th it cuts out like crazy. Am i missing something? Appreciate any help ya'll might provide.
 
Welcome CustomSportster to HDTimeline, there will be plenty of info in the self help section (see the tabs at the top of the page). As for immediate help, a little info is required...can you identify what carb your 2000 Custom Sporty has?...stock Kehien (HD logo), Mikuni or S&S? Do you know if the needle/emulsion tube has been modified or "drilled" out? Was it running fine and just started acting up or has it been running this way since you got it? Engine 1200 mods only with full Stage I proven, before something done beyond?
 
I believe it is the Stock CV carb. I really cant tell if the needle\tube has been modded or not. I have had the bike for a while and it was like this when i got it. Runs perfect until 5th gear. I kinda inheirited this scooter, with limited info too. All i could really find out from the shop that built it was that there was a 1200 kit added when the bike was built.
 
I also for got to mention that this bike came from Bessemer North carolina and i am in NE texas. Elevation in bessemer is about 1000ft, here in NE texas my elevation is about 425. My original thought was jetting for the higher elevation was my problem but not sure if there is enough difference.

Bike also has the K&N filter and the Calibre 2-1 exhaust, with no baffels.
 
I am inclined to believe that you have an obstruction in the main jet, or carb bowl (drain it or pull off to see if gum, rust or varnish is in there)...you might also want to check the fuel level.

Here is a link to get you going on how to dissect the carb components and how they fit into the circuit at various throttle openings.

http://www.hdtimeline.com/fuel_and_carb_related_issues/1258-poor_performance_with_carb_models.html

Here is Glider's rough carb circuit chart

CVThrottlepositions1.gif


Here is an exploded view of the stock HD Kehein CV Carb:

cvbreakdownRPIC.jpg
 
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hmm...this is intesting, why only 5th gear? If it were a jetting/abstructed carb it wouldn't matter what gear you were in as it would act the same in every gear at that RPM. What are you turning for RPM/throttle input at 60 to 70 in 5th? I'd guess 3/4 throttle? Bad vacuum line somewheres? Not sure, just throwing things out there.
 
I have had the carb off and tore to pieces so many times, i am sure i could do it in my sleep!
Everything is spotless, no varnish, trash or anything, anywhere. I have replaced every fuel line, vaccum line and everything in between.Evan all the carb gaskets and the accelerator pump. Only thing i can figure about 5th gear is the load it puts on the engine. i would guess at maybe half throttle, but once it starts surging you can twist it wide open and it makes no difference. twist it very lightly and it goes fine, just wont accelerate. Like i said wind it thru 3rd and 4th gear wide open and when you hit 5th it pulls fine at wot. Try and cruise normal and it surges in 5th. i dont have a tach so not sure on RPM,, seems long legged though. This thing really has me confused for sure.
Several pics in my gallery if anyone wants to see how the bike is set up.
 
Never done much wrenching on bikes but, I've enough done on all sort of other combustibles. This sounds to me that your main jet might be a little on the small side.
If not enough fuel can be pulled through the jet by the vacuum created in the ventury you can get these symthoms. Our engines had an adjustable jet and when opening them a little the problem would disappear. I might be on the wrong track but this is how I see it.
 
That is what i was thinking although i am no expert. Figured i would get on here and consult with the real experts before i started rejetting.

bad part is i am not sure what exactly has been done to this motor before i got it. Best i could find out was they installed a 1200 kit before they put the motor back in the frame. The previous owner put 4500 miles on it in North carolina before it made the trip to texas. I have no clue how it ran before i got it.
has me puzzled to say the least.
 
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