Carburetor Mystery (To Me)

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Joined
Nov 22, 2015
Messages
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Location
Lenexa, KS
My Bike Models
2003 Honda Valkyrie
Well, I've been rehabbing my '77 and wondering why it only has 13K miles on it. I don't know how many owners it's had but more than likely there have been quite a few hands laid upon it to excise the demons. Now it's my turn.

I've been through the bike from front to back and sorted out most of the usual things that need to be addressed. As far as the engine goes I've replaced the timing belts , valve seals and set the valve clearances all to 0.004". I went through the carburetors and inspected all the brass to be sure that everything is as it should be (and is in the correct location) and blew cleaner or air through all the ports to ensure they're open, and set the float levels to 21mm. I also checked and set the static timing of the Dyna S module. I also modified the air bleed orifice to be 0.038 using a #62 drill bit as per the recommendation of Randakk's site. I have aftermarket Emgo coils with new spark plug wires and 5K resistor caps that are all in great condition.

A test run demonstrated a very soft engine performance around 1-2K rpm with the engine being slow to return to idle @ 950. It idles great but is slow to rev and slow to return to idle. My trusty Champion neon spark tester shows that all cylinders are getting spark without obvious missing or weakness.

I checked for air leaks using propane and found none. The carb balance has also been adjusted to spot on. Checking the plugs reveals that cylinders 1,2 and 4 are very lean with snow white porcelain. Cylinder #3 looks much more normal with some black/brown on the porcelain but no soot or wetness.

Sooo, I pulled the carbs to have another look at them. I drained each bowl in turn and weighed the gas and found them to all hold about 27 grams of fuel. I flipped the carbs over and removed the bowls for an inspection. I see some differences between the four carburetors that I can't understand so I'm hoping that someone here can help me with what I see.

I have circled two orifices that are common to all carburetors. I'll call them orifice #1 and orifice #2. Orifice #1 is round and orifice #2 is oval. The mystery is that they're not all drilled the same in each of the four carburetors.



Here's what I have (X = not drilled, O = drilled):

Carb.......Orifice#1......Orifice#2
#1..............X................O
#2..............X................X
#3..............O................O
#4..............O................X

I'd love to know if this is common to GL1000 carbs and what the reasoning is for the hit-and-miss condition of the orifices shown. Ideas anyone?

(Oh, and yes, I know that there are parts missing off of the carb jets, plug etc., I pulled them out for measurements.)
 
I get that that the casting is intentional. Look at these pics to see that one carburetors port was never drilled and another carburetors port was.



 
I have checked and cleaned the caps and slides using crocus cloth and WD-40 and ensured that they're all free moving and sealed up. They respond freely and easily to a vacuum.
 
Usually a vacuum issue when it's slow returning to idle. Those may be drilled for the air cutoff valves. Not certain. I think the 1000 carbs have two.
 
Just looked at mine. Only one round one is drilled on the carb closest to the one cutoff valve. So the second drilled one may be a replacement carb or mis drilled. None of the ovals is drilled on my rack.
 
Try a temporary plug of some kind in the oval drilled hole and check the air cutoff valve. If that fixes the issue put in a permanent plug.
 
Interesting, And thanks! I'll be plugging the errant holes with some old gasket material and some Permatex fuel resistant non-hardening sealant so I can back out of this if I want. This is going to take a few days as I'm replacing all the o-rings and will be closely inspecting every nook and cranny, washer and cotter pin to be sure everything is exactly as it should be. I'll follow up. :thanks:
 
Check the fuel pump pressure, and the fuel passages in the plenum. The #3 carb is the closest to the fuel inlet on the plenum, and you say it's running normal while the other 3 are lean...could be fuel delivery.

Ya might want to do a compression test also.
 
The drilled holes lead to the carburetor throat. I closely examined the the gasket and bowls to determine the internal path when the bowl is attached. There is a cutout in the bowl gaskets to connect these holes to internal pathways. That said, I determined that the round holes (orifice #1) lead to nowhere in all cases. They simply deadhead into the bowl flange. The oval holes (orifice #2) are different. Carb #1's hole goes from the engine side of the carburetor butterfly to the air cut valve. However, carbs 2,3 and 4 bowls don't have air cut valves so their respective bowls aren't drilled, so in the end, the extra oval hole doesn't go anywhere. I don't know why the extra holes exist. It may be like Slabghost said that they were either misdrilled or exchanged over the years.

Anyway, I'm leaving the holes alone for now and renewing the rubber for another trial. The changes between the previous trial and the next will be:
1) rebuilt air-cut valve
2) new o-rings in the main jets
3) new vacuum hoses and air cut hose
4) new OEM style air filter
5) new bowl gaskets

I also recently acquired an ignition timing window adapter so I can see my ignition timing advance in action to make sure its working correctly.
 
I have a parts rack at home. I will give it a look to see what all those orifici look like on it so we can get another survey. I too would think that perhaps the slides are not returning correctly or quickly if its a return to idle issue. Replacing all of the rubbery parts is a must on a stock rack IMO. You mentioned polishing the slides with cloth and WD. Make sure you get inside the cap as well where the piston goes. The slides must function flawlessly or it just wont work correctly. Also, after polishing clean everything with a parts cleaner, like brake fluid for example. You want something that will evaporate and leave no residue. WD if left will leave a sticky mess that will slow the pistons in both directions. Usually they will respond and move up quickly but may "rattle" on the way down which will screw the idle all up. Its not as much the lift that has troubles as the return. The internal of the cap has a brass sleeve. Brass is kind of a "sticky" metal that can easily bind the return of the piston.

Here is a video I made that shows my method of ensuring this movement is perfect. That part starts at about 6.5 minutes into the video.

https://www.youtube.com/watch?v=D3zLIUQzYJQ

[video]https://www.youtube.com/watch?v=D3zLIUQzYJQ[/video]
 
Thanks for the info and advice Bronko. Your video is great and I compared my slides to yours and have the same free movement. Before reinstalling I'll double check their cleanliness. The carbs go back in tonight and I'll report on the outcome. :thanks:
 
She's running much better now. Finally! After reinstalling the carbs and warming her up she was running better but not great. Snapping the throttle still gave me a soft response. Higher rpm's were just fine.

I remembered reading a warning somewhere about setting the idle too high. Previously I had set the idle up a bit to try and avoid the primary chain rattle. So I lowered the idle screw and throttle response got better. I lowered it some more and things got better still. I've never experienced such a thing and I'm no Spring chicken! At this point I'm very pleased with the throttle response from idle to redline. I'm letting things cool down to see how it behaves from a cold start. Right now I'm darn pleased with the carbs. :Egyptian: :music:

Finally, I used my sight glass tuning adapter and strobe light to time the engine while running. I couldn't really see the marks clearly enough to make sense of it. I was in a pitch dark room and using a powered strobe - to no avail. Is this typical?
 
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