My email to Carbjetkits

[Gene]

Problem: My bike idled fine but stumbled just off of idle to approx 3000 RPM. After that, it ran fine.

I decided to rebuild the carbs.

I have a 1985 Honda 650cs Nighthawk
Carbs: Keihin VE54ABWK. According to the service manual, I have a 49 states '83 – '85 carb, not a California carb. The carb for my 650 is not listed in the factory service manual which stops at 1984.
 I ordered your jet kit to re-jet the bike and help to eliminate the stumble.

The main jet, according to the factory manual: is a #115, and there is a 115 installed.
 Slow jet, according to the manual: Not specified, but it is a 38
I received the following;
Replacement jets:
Main jet: 120
Slow jet: 35

It seems that the slow jet is too small, and would not fix the stumble. The main jet size is larger, which might mean the carbs would run a bit too rich.
 
using your calculator, this is my results:
Your bike is a Honda CB650SC 1983-1985
Selected riding altitude is between 0 and 100 Feet.
Average temperature you are riding in is between 60 and 80 degrees (F)
Selected Modification:
Exhaust System: All Stock Exhaust system
Air Intake: Stock Air Filter Box with improved air filter such as K&N
Timing: Stock Timing


What do you think?

[Pete in PA]

You can go to the parts sites also to find what jets are original.

I looked it up.  Both Cali. and 49 state bike came with #35 pilot.
Someone put in a 38.  Too rich  with your stock bike.

All carburetor bikes are lean from the factory. Fact.

I used Carbjetkits on my otherwise stock 92 750 Nighthawk. Main went up 1 size (2 sizes from Cali. bike). Washer under needle, pilot remained the same.

Bike runs great! More power, no hesitation. Did have to find a happy pilot screw setting.

Their calculator is interesting to play with.  Especially inputting different elevation.  Past 8k (I think)feet it says no change.

I'd trust them.

Make absolutely sure all passage ways are clean, I'd seperate carbs and replace fuel tube O-rings, bench test for leaks, then reinstall.

[Gene]

 Thanks Pete, I feel better now. My next question, I have planned to dip my carbs in Carb Cleaner, the old type, (which is outlawed in Calif) I wonder what it will do, (if anything) to the shaft seals for the butterflies.

[Pete in PA]

I just used spray carb cleaner. Be sure to blast out every passageway in each carb.

[mollusc]

The shaft seals are probably brass.  There are plenty of other rubber seals and o-rings that will be degraded by the soak in cleaner solution though.  If you're going to do this, get a couple of rebuild kits and do a full teardown and soak the disassembled carbs for at least a day.  Make sure you keep the parts for each one separate.
Spray cleaner doesn't do a great job of getting rid of lacquer buildup.

[Gene]

 Thanks Mollusc and Pete for the help. Mollusc, I used to clean/rebuild Mikuni 2-stroke carbs in the early 70's, soaked them in the aforementioned carb cleaner and never had a problem. I'm learning that the Keihin CV carbs are a lot more complicated. Mollusc, I have 4 complete rebuild kits, so I am ready.

[Northern Rider]

Good luck in your carb cleaning! By the way has anyone viewed a how-to video for changing jets and adding the washer on a 1996 NH 750? If so, I would appreciate viewing one before I started the project. Thanks!

[Pete in PA]

Youtube is full of videos for the carbs of the 92-2003 750 Nighthawk.

Watch them all.

[Northern Rider]

Thanks Pete for the info. Guess I'll spend some time on the PC.