avramd

Hey Everyone,

I just put the original carbs back in my bike after a fairly extensive overhaul. These carbs had sat for a long time (2 yrs) with unstabilized fuel in them before I bought the bike. I cleaned them as well as I can imagine, including the passages machined into the carb body, and just to be safe, replaced the jets and emulsion tubes (all stock) with brand new ones.

Now my bike has a really hard time starting. The choke doesn't seem to have the right effect, it seems like it has an even harder time firing when I put the choke on. Once started, it will not idle whether the choke is on or off, I have to keep the throttle on until it's up to at least 140 degrees. There is no point at which the choke helps it keep from stalling. Once it is up to 155 degrees, it seems to run fine. It sounds nice, and pulls about the same as the eBay carbs.

The carbs are synced. I have very few changes from stock. They are:

• .040" shims (2x #4 brass washers)
• TPS set to 490
• pilot jets 2.5 turns out

The bike ran fine on the eBay carbs. Their settings were:

• .060" shims
• TPS somewhere between 500 and 600 (didn't have as precise an ohm-meter at the time
• pilot jets unknown (prior owner of these carbs had jetted them; I went back to stock jetting, but don't know if he had changed the pilots or not).

Another detail worth mentioning is that the diaphragms on the bike right now aren't the originals, and the seemed to have shrunk a little; at first they would not seat all the way around - some part would always pull in. I stretched them a bunch and got them to barely stay in the seat all the way around. I am not 100% sure they stayed that way as I fitted the vacuum chambers.

I'm wondering which direction to go to sort this out. Does this sound like something that could be fixed by adjusting the pilot screws? The setting I have now is something I read here suggested as a baseline. I don't know whether in or out makes it richer or leaner, and I don't know if it would have any affect on the choke seeming to not have the right effect when starting.

I'd appreciate any advice.

shayne

Sounds to me like you have a problem to be found. You may be on to something with the diaphragms, or perhaps a manifold leak.

avramd

By the way, if you're wondering why I changed the carbs when the bike was running fine, it's because after shimming to .060, I was getting horrible fuel economy (33 mpg on easy highway rides, 20 mpg around town, not very hard riding). Mostly it's because I just thought (hoped) it would be easier to use the other carbs I had lying around, get them set up the way I wanted, and then just do a quick swap, rather than go into the carbs while the bike was open. But partly it is because I'm being stubborn and insisting that I get the original carbs running right "just because."

residentg

These are tough to diagnose without seeing or hearing the bike. Based on what you wrote I have two thoughts, and I stress thoughts.

1. The carbs are still not clean, in particular your pilot jets.
2. The diaphrams are not sealing. I have a an unpopular suggestion on that. CAREFULLY use a little permatex form-a-gasket 2 (non hardning) to hold, not seal, hold the diaphrams in place when reassembling. Also, spray the diphrams with silicone to restore the rubber a bit (do this first)
3. Check your choke cable routing and connections. Check to ensure proper fitting at the carbs.

What are the jet sizes? Turing the pilot screw out (counter clockwise) = richer.

avramd

Hey Res,

All of the jets and emulsion tubes are stock and brand new.

I am sure the choke connections are good. However I never know what is the proper routing for the rear choke cable. That is another difference - before I had it behind the rear carb throat. This time I have it just in front of it.

What kind of silicone spray are you suggesting to restore the diaphragms? I apologize if this sounds like a dumb question - I seem to find that the word "silicone" has many different meanings.

residentg

Just the basic autoparts store spray lube. It is a clear mist. As for the cables, be sure that they are not kinked and that they are seated in the connections.

Did you check the float heights? Is gas spilling out? JB

steve29

Good way to check if the diaphragm is seated properly is to open the slides and let them go. If they don't make a kind of sucking noise and they slam shut, they are damaged or not seated properly.

comedo

Do the enrichener valves retract fully when you pull out the choke ****? It might be worth taking a look. I had to lube the choke cables and junction box on mine to get them to do so. A bit of corrosion caused the problem.
Choke cable routing is shown in the manual. It's probably not critical as long as the bends aren't too tight.

avramd

I did not check the float heights, and yes, in fact, gas was spilling out when I first got it started after the install. However it was only that one time, it hasn't spilled since. I was guessing that it was a side effect of the very long process of getting the bike started the first time.

Both float valves are brand new, and the floats themselves ran properly in the other carbs. My understanding from the manual is that float valve height isn't something you can adjust - it's either right or you replace the floats, correct?

sunnovabich... I just remembered... on of the problems with this carb set was that when I originally refurbed it, one of the float valves was seized from some kind of corrosion. It was very difficult to get out, and even a new float valve did not operate smoothly in its fitting. I smoothed out the corrosion inside the fitting myself with some fine-grit sandpaper until the assembly seemed to visually operate identically to the other one.

Maybe that is the answer. Maybe these carbs are un-refurbishable.

avramd

Steve: Thanks for the tip on checking diaphragm seating.

Comedo: The choke cables operated fine with the other carbs.

residentg

See page 5-13 of the Honda Service Manual which is available in the KB section. The float level is at least measurable. I have not taken the SH carbs apart, this is the first carb that I have seen where the float level is not adjustable - seems odd, but that is what is written.

shayne

In regards to the diaphragms, I replaced mine when I did my rebuild. Mine seat easily. Perhaps new ones might help your cause.

residentg

You can boil the old ones before you install, sometimes that loosens them up.