Not a Zook, but looking for help

[rudy]

I just posted this on sohc4.net.


Well, first post and I'm already asking questions! I'm getting an 82' 650 engine running for a guy. I have CV carbs from an 81' that I've taken apart and dipped overnight and cleaned with aerosol carb cleaner and compressed air. All looked good when I was putting them back together. The carbs weren't in bad shape, but where fairly dirty. Bought the new "T" vent fittings between 1 & 2 and 3 & 4 for an arm and a leg from Honda, but don't really have anything to connect them to, so they sit in the air pointing up (as per part fiche).

Anyway, on to the problem. First of all, all four carbs overflow right out the throats as soon as I crank the engine and the vacuum operated fuel valve opens (amazingly doesn't leak!). Ok, I can deal with that. Just fill the bowls and then shut off the fuel to see if it will run. Well, no dice. Fires here and there a little, backfires out the carbs and pops pretty nasty randomly out the exhaust. All four pipes will get warm if you crank long enough. Spark is great, as I have ignition directly wired to a switch on my engine stand. Seems to have pretty good compression, but I don't have the 12mm adapter for my compression tester or leakdown tester (waiting for them to arrive). I've checked valve clearances as well, all are good. Tried adjusting ignition timing while cranking, but this changed nothing from retard to advanced. Tried adjusting idle screws as well, and playing with the throttle while cranking. Throttles are bench synced.

How picky are these carbs? Do they really need to be cleaned out with wire in all the little holes even if it's soaked overnight in full strength kleen-flo? I should get some kind of firing with the main air box, but no air filter, right? I've tried putting my hand over the inlet to the air box to provide some restriction, but no change. I've tried choke, I've tried partial to full throttle. Tried pumping the throttle to squirt fuel with the accel pump. One or two fires, then nothing. Even if I keep pumping.

Fires a bit if I spray aerosol carb cleaner in the airbox opening, so that leads me to believe that the carbs aren't putting fuel in the air at all. Plugs smell a little like fuel, but are dry for the most part, but sometime randomly damp and never soaking wet.

Now to address the overflow problem. All floats (plastic ones, non-adjustable) are perfect. No holes or damage in any way. Tested in a bucket of water, no air bubbles and they float forever. Tried squishing a bit under water, still no leaks. Inspected float valves. Needles look new, and are viton tipped, so they must seal pretty nice. Not cracked or worn. Checked to see if the valves will actually close when float is up. They all do. EVERYTHING moves freely and is clean. Is there some other place that the gas would be flowing from and into the carb throats? It's not just a little leaky, it's full bore POURING out of all 4! These are my first Keihin's, and I can't really say I'm impressed yet.

One other thought. Would it make a difference that my auxiliary tank is maybe two feet above the engine? Could this create enough head pressure to flow past the float valves?



If anybody's got any ideas, please let me know.

Rudy

 

[Suzuki mad]

Sounds like you may have rebuilt them slightly wrong. Can't help much from there.

Suzuki mad

 

[Guest]

not really familiar with keihin carbs... but some general tips would be:

lower that aux tank as low as the original tank would be, that should tell you if the float valves are indeed working or not

even if you soaked the carbs for a long time they may still be clogged internally, in the tiny passages
use the carb sprayer to shoot through those passages to confirm that they are open
pay spec attention to the choke circuit as with that not working the bike wont start even if all the rest of the carbs is clean

make sure you have no air-leaks in the intake system

keep us posted on what you find

 

[Zook]

Keihin carbs suck. Period.
Some have float needle seats that are not replaceable.
Your problem is likely bad float needles. Do not buy aftermarket units, they will not work. OEMs will work, but they are spendy, and still may not fix the problem.
I went through this on a Concours and wouldn't wish it on anybody.

 

[buster]

I found on the Honda's that I had the Keihin's where very picky. I did the same as you the first time. Just soaked and put back together, then had to take them apart and run a fine wire through every port. I was suprised that I still got more gunk out of those little passages.

My floats also "tested" o.k. no leaks or air bubbles, but when I had gas pouring everywhere I went ahead and replaced them and it fixed the problem. The old guy at the Motorcycle Junkyard says "If they sit too long they get heavier than they should be" I don't know how that works if they still float, but whatever I bit the bullet and replaced the floats and needles and the issue stopped.

Good Luck!

 

[rudy]

Agreed, Keihin is synonymous for "junk". If you want quality, get something that starts with M. I don't know how some Honda nuts think these things are good. Not user, tuner or rebuilder friendly at all.

Anyway, took the carbs apart again last night. Stripped everything down and ran a wire in everything except for one of the three tubes that stick down into the float bowl (one has main jet, other has pilot, last is choke?). Don't know for sure where it goes to, or what it does, but it's plugged SOLID in all 4 carbs past where it takes a turn to the outside of the body.. After I ran wire in everything (was all pretty clean still) I boiled each carb body in plain water at a RAPID boil for about 10 minutes each. I've read that this is good to soften up the varnish. Well, it worked! I got all the passageways for the idle circuit to blow completely clean. Then blew some carb cleaner through them just for fun. Put them all back together, no more flowing from bad floats, but no starting either.

Tried torching the old plugs and getting them nicely cooked out. Cleaned and gapped them (weren't bad) and put them back in. Closest I got to starting was all four cylinders fired consecutively....... once. Then back to sputtering.

Original coils were about 2.5 ohms on the primary and about 12k ohms on the secondary. I don't have anything that will hook up to those coils though, so I'm using the original ones from the GS as they have boots that are in one piece and attached. These are 4.5 and 22k ohms. They still spark decently, but should I be using the other ones? I REALLY don't want to pull out my nice new green Dynas and wires for this POS.

I'm gonna pick up some new plugs tomorrow in hopes that they are the problem. I noticed that all four pipes were getting hot after cranking for a while. This is good. When I pulled the plugs afterwards, 1 and 2 were wetter than the others. This says to me a problem with spark. But I've plugged an extra plug into all wires and it never misses a fire.

I'll keep plugging away (pun intended) and see what I come up with. Hopefully I'll have good news for you guys tomorrow afternoon. And maybe I'll be a few hundred bucks richer so I can turn around and drop it all into the GS.