Running Rich

Okay, so I've finally got the monster running, took it out around the block a couple times, has great pickup at first, sounds a little clunky, but I'm not sure if that's normal or not for this bike. Anyways, The bike has been sitting for who knows how long, and after a little while it seems to bog down and not respond to well to the throttle, and the plugs foul up really quick. I checked the timing, it looks good, and the bike does great at first, but then it seems to lose it after about 15 min. I drained the oil and it also looked pretty brackish for being in the bike for only a couple of days, but as I said, the bike sat forever, and maybe this is normal junk coming lose from it sitting so long?

I think it is a carb jetting problem, everything is stock but I bought the carbs off of ebay and the jets might be different, I'll have to check. What are the stock jet sizes and what should I go to if I decide to put pod filters on?

Any suggestions would be appreciated. NO, I haven't checked valve clearances, but since the bike runs really strong I hope clearances are not the issue.

Oh yeah, the carbs are mikuni vm24's I think.

Maybe I should try lowering the needle?

Hey 77Davo. I have a 1977 650 C1 so I am familiar with the Mikuni 24's. If I am not mistaken the main jets should be 102.5's if nobody tinkered with the factory setting.

As far as sounding clunky, you might want to check the cam chain adjuster. In my experience, these motors are not known for any clunking noises if everything is tight and right.

Your clearances on the valves will tighten somewhat when the engine gets hotter. Are you getting any popping through the carbs or exhaust? This might indicate clearance issues but it might get you started down the right direction to zeroing in and ironing out the gremlins.

Here is what I suggest you might take care of since you said the bike has been sitting:
1. Drain and clean the fuel tank and fuel petcock.

2. Install a new fuel line and fuel line filter.

3. Pull the float bowls off the carbs and see what kinda crap (if any) you have in the carb bowls. If they are seriously gummed up you will probably have to pull the carb rack and throughly clean the innards.

4. Check the main jet sizes. As I mentioned earlier, they should be 102.5' or perhaps 100's.

5. Check your air filter.

6. Clean your current set of plugs and check each plug for a good solid spark. Cylinders 1 and 4 run off the same coil. 2 and 3 run off the other coil.

7. Lube the mechanical advance behind the points plate.

8. Find a secluded stretch of highway, install a brand new set plugs and do a plug chop. This will tell you if the motor is running rich or lean on the main jets at wide open throttle. If you need to learn more about the plug chop method do a search in the archives.

If you need some more info on the carbs check out Wired George's web site @ wgcarbs.com I wouldn't get into the carbs or pull the valve cover until I checked out the other items on this list. Hopefully this will get you started and rule out some simple to fix items.

I am confident that other members will chime in on some other areas to consider.

Cheers-Colin Firth-Ontario Canada
1977 Kz650 Custom with 14,000 miles. Newest reincarnation includes Wiseco 810 kit, Kz750 cams, springs, valves, milled, ported and polished 650 head, Dyna ignition and coils, WG Mikuni 28 carbs, velocity stacks, 14 tooth sprocket, braided stainless brake lines, 130 rear tire and other mods. Looks stock and runs like a scared cheetah.

Colin nailed it... not much to add except the principal when owning a non-runner and then getting it running is to do things in a certain order. The order ensures that time isn't wasted. If you haven't a lot of bike experience, what feels like a strong runner may actually be not so strong so don't go only on "feeling". Take the time to go through tune up steps already suggested in the order suggested by your manual. Valves and cam chain are FIRST as well as a compression check. If timing is OK, then look at the function of the plugs, points, condensor, coils, plug wires and power to the coils. Once you are CERTAIN these things are right, then move to carbs as an issue. The specs on the various VM24 assemblies vary all over the place. The mains vary about 10 points (92.5 to 102.5) and the jet needles/needle jets vary from econo oriented to performance oriented. Baseline the carbs a bit by reporting the specs but do this once you have the necessary tune up stuff looked after.