Mikuni CV BS34 lean but rich?

I would say so. At this point just leave the ignition alone.

jga2z wrote:

I rechecked the coils, 2.6-2.7 ohms primary 12.3K ohms secondary, batt voltage @coils, will jump 5/16-3/8 air gap on all 4.
Doesn't this seem like it should work?

Am I beating a dead horse?
To move on from ignition I need this question resolved.
Clymers says coil specs are 1.8-2.8 pri, 10.4K-15.6K sec, and I saw a post which said air gap test should be about 1 cm.
Can I move on to fuel/carbs?

Visually observed fat blue sparks across the plug tips likely evidences acceptable ignition. Am thinking the ignition timing isn't owner adjustable on this bike. However, may verify proper function of the timing advancer by watching the timing marks under a strobe-type timing light to confirm it's moving quickly back and forth as rpm is varied by blipping the throttle. The advancer might require lubing or both cleaning and lubing.

Should perform a compression test AND assure all valve clearances are within specs BEFORE addressing the carbs.

Good Fortune!

I definitely agree about making sure that your valves are adjusted properly. Your cam may be riding a bucket and therefore you have an open valve. Check the compression of all cylinders. What ever it is in one it should be in all four +/- a hair. (red preferably, they're the thinnest ):laugh:

I don't claim to be a 4 stroke pro tech but i have been wrenching at the "amatuer" level for the past 24 years and along the way I've tought myself a few good lessons when I develop an issue.

1)ALWAYS perform simple tests FIRST ! My #1 test is compression. You need all 4 cyl around 125 psi min and all within 10% of each other. You would be amazed at how many people think they have ignition issues when they really have a "bad hole" (low compression in one cyl)

2) Try to isolate weather you have an ignition problem or a fuel problem. Don't attempt to diagnose and or "guess repair" both systems at once.

No doubt running issues on older bikes can be a frustrating PIA, and I have had my share of ghost PIA issues, but my point is simply crack a beer, take a breath and try to systematically approach each diagnostic test.

OK the compression test shows #1 150, #2 155, #3 155, #4 150. on a cold (wet) engine
That looks pretty good.
I know that valve clearance will change cold to hot, but since it's not running yet It would have to be a cold check. Given the compression results I might skip that for now.

Back to the carbs?

jga2z wrote: OK the compression test shows #1 150, #2 155, #3 155, #4 150. on a cold (wet) engine
That looks pretty good.
I know that valve clearance will change cold to hot, but since it's not running yet It would have to be a cold check. Given the compression results I might skip that for now.

Back to the carbs?

Compression is good. Back to carbs. You comment you need to keep the choke on for the engine to run, and you also comment #3 and #4 seem to not be firing. Kawis fire 1-4 and 2-3 so with this i'm tossing out the idea of a bad coil. If you had say 1-4 cylinders not firing ,now that a good sign the approiate coil is suspect. I am really thinking you have a #3 and #4 fuel starvation issue. Simple test first crack the bowl drain for carbs 3 and 4, make sure you have a stead flow of fuel out the drain hose. It really sounds to me like you have a plugged #3 and #4 pilot jet circut...

It sounds as though your problem is fuel related. You may have Vacuum leaks around your intake manifolds, or dirty carb circuits. While some may disagree with a larger pilot jet, I can tell you I have the BS-34 Carbs with 40 pilots. They run much better and start easier than the 37.5's. All stock on 1 bike, 82 1100, and a 4-1 Vance & Hines on a 82 1000. Altitude of 6K plus. Never shows any rich conditions, great plug readings and the 1000 got 50 mpg over 3600mi trip. That's loaded with Vetter fairing and bags. Strange that every other thread recommends jetting increase through the range of the carbs with pods.
Have you properly set your fuel levels in your carbs with the clear tube method?
What about Sync, do it on the bench first using a round paper clip or wire for a gauge. Set all 4 butterflies the same. Turn your pilot screws the same # of turns out, like 1 1/2 for starters. Get it to run on all four, then a running dynamic sync once up to temp. You can make a Manometer if you don't have one, or maybe borrow one.
What does the plugs look like, wet on the cylinders that are not running, or dry?

jga2z wrote: ...I know that valve clearance will change cold to hot, but since it's not running yet It would have to be a cold check. Given the compression results I might skip that for now....

Valve clearances are supposed to be measured when the engine is cold.
Because the clearance diminishes as the engine warms and attains normal operating temperature. The specs recognize and allow for this attribute.

Good compression on a cold engine may result when valves are just barely closed with minimal clearance. Then the compression suffers when the engine gets warmer, because the gap disappears and the valve fails to seal as it can't fully close.

Consider, even perfect carbs can't compensate for deficiencies in the other components. For instance, with leaking valves due to insufficient clearance, it's imo a waste of effort to address carb tuning.

Good Fortune!

Motor head....
I've checked for vac leaks around the intake boots many times with no leaks found.
I now suspect pilot circuits.
Can I replace the 37.5 non-bleed pilot jets with 40 bleed type? I tried to order pilots for these carbs and they sent me the bleed type. I read a post here that it wouldn't matter.

Yes I done the clear line fuel level test, #3 might be a bit high. Bench sync is/was perfect.
I have the plans for the homemade manometer, and will do that when I get it to keep running.

Patton....
I understand that the clearance decreases with higher temps. But this thing only ran real good when it was totally warmed up/hot. As a matter of routine I know the valve lash needs to be checked. I don't think it's an issue right now, but I'll bite the bullet and check anyway. Another potential problem I can't afford to fix.

On the pilot jet, bleed or non, they have the same size fuel flow if stamped the same. The bleed will change the the transition to the needle slightly. You may feel the difference and may not. You can try them since you have them.
Good that you have gone after air leaks already. Sometimes the leak is small and hard to find/ diagnose.
If it still does not run on a couple cylinders, but you show good spark on all 4. You can swap the coils if the plug wires are long enough, you can swap them just to see if the missfire follows the same plug lead.
But it really sounds as though with all the checks you've done that fuel would be the problem.

Be sure the passages from the pilot jets and the idle screws going into the carb bodies are clear. Squirt carb cleaner into them and then compressed air. Repeat 1000 times. Also the grease may be preventing air from going through the tiny passages, and no gasoline gets into certain areas to wash it out. The idle screws should have a spring on each one, then a tiny washer, then a tiny "O" ring. Be sure these parts are present on each idle screw.

The choke on these carbs is actually an enrichment circuit. Mine will not run well by tweaking it out just a small amount. It needs to be pulled out until it hits the first groove. Now if the weather is really cold, then pull it even further out.

This is a romote idea, but be sure the float vent hoses are properly connected. They are located on "T" fittings running between the 1 & 2 carbs and between the 3 & 4 carbs. On my bike, the previous owner had replaced the tubing and connected the two "T" fittings together with one hose. Nearly drove me to drink before figuring out that the bowls could not vent, and the fuel level could not come up to normal. I doubt this is your problem, however.

I have BS32 CV carbs on my 650 and I found that changing the pilot jets from 37.5 to 40.0 made a big difference in warm-up and low speed performance just above idle. My original main jets are 107.5. the bike runs quite well with these and gets great fuel mileage. 110.0 jets perform a little better, but mileage goes down about 5 MPG. I tried the 112.5 jets but the bike ran OK but "heavy" and mileage was terrible. By "heavy" I mean that throttle response was not crisp.

I agree with your analysis about the coils. They may not be quite as good as some after market ones, but unless there is something wrong with them, the bike should run reasonably well with them.

One more thing, for what it is worth. My bike would idle and run under very light throttle with the air box open, but would not generate any significant horsepower unless the air box had a filter and the screw-on nozzle on top of the box in place. Seemed to need some restriction to suck enough fuel to perform well.

Hope some of this helps. It took me 5 times to get all the passages clean in my carbs. My guess, is that something is still stopped up in yours. Good luck.

change the o rings p.n:16009a take the clips at down position(rich), and make adjust the air screw p.n:16014 i am adjusting air screws to looking at spark plugs burning color... it will be ok...
(p.n: part number)