Right Side Mixture Screw all the way in

[nishgriff]

Hi, I've posted here a few times before, and spent a bunch of time learning everything I can from the forum, it's gotten me through just about everything in bobbing this 81 650.

My problem is that after a full carb rebuild my right side will not run if the mixture screw is anywhere but fully in. When I begin to back it out, right side begins to bog. I'm looking for ideas as to what this is.

Here's what I've done so far:

New float bowl gasket, floats, needle seat, float valve needle, floats, floats set at 22mm from carb body. 144 main jet (xs pod filters and shorty exhaust), 40 pilot jet, new carb boots, new intake manifold gaskets. New mix screws with spring, washer, and o-ring, left mix screw set at 1.5 turns out dead cylindered. New fuel lines and inline fuel filter on non-vacuum petcock, air barbs capped.

I've cleaned the carbs as best I can, it runs well, kicks 1st or 2nd time, but seems a little boggy on right side. I have had problems with plug fouling so that's why I went down a notch on pilots. on dead cylinder right side fires but again doesn't idle on anything but mix screw totally in. It's not quite as strong as left side, and doesn't burn quite as hot.

Any ideas/thoughts? Somehow fuel is getting past the mix screw at idle. No problems running/cruising, etc, though maybe a bit boggy.

PS, Thanks to this forum I found and fixed the ZD4 diode problem in my stock TCI ignition, so no more mystery stalling

 

[nishgriff]

Just a note, both mixtures screws are now fully in, and the bike starts, idles, and runs fairly well, I am stumped here. I am sure the o-rings and washers are in there, but maybe they got damaged? I guess I'll check that. Also, pilot plug is in there too. Suggestions appreciated!

 

[Patches]

Just read second post, never mind.

 

[5twins]

Well, you're running way rich in the pilot circuit somehow. I would check the air jet and it's passageway leading to the pilot jet. If it's plugged, you would be getting all fuel and not a fuel/air mix through the pilot jet.

 

[gggGary]

Have the carbs been synched?

 

[gggGary]

Are the floats set correctly for the year? I am assuming BS 34 foam floats? First by float height, backed up by a clear tube fuel height check. And new parts aside it's possible a float valve is leaking.

 

[nishgriff]

Yes, I set the floats at 22mm measured from carb body (no gasket) to top of float. i have not done the site tube height check. They are BS34's from '81.

I thought I cleaned it well, but I'll double check the air jet/pilot circuit again and make sure I can get carb cleaner through there.

Are the floats set correctly for the year? I am assuming BS 34 foam floats? First by float height, backed up by a clear tube fuel height check. And new parts aside it's possible a float valve is leaking.

I had a float valve leak, that's why I replaced those, stopped the leak.

 

[5twins]

Exactly where did you measure to on the float, the top of the round "bulb" part or the flat area up by the pivot? Measurement should be to the lower top of the "bulb". Here's some set to 21mm .....

Although not totally accurate, a quick visual check can be made by observing the seam line on the "bulb" in relation to the carb body. It should run slightly uphill away from the pivot.

 

[nishgriff]

I measured to the top of the 'bulb' part, when I get home I'll measure again. If the floats are say, 2mm off, would that really affect the pilot circuit this much? And to be clear, when you adjust the floats, you just bend the metal piece slightly, right?

 

[bloodthirstysystem]

yes just bend the metal tab. it should be almost flush with the metal around it.

when checking float level i have read that you should hold up the float so the pin on the shut off needle is not being pushed down.. so the float is just touching the end of the pin. it will add another 1mm or so

i set mine this way and it runs fine, but they're 38's..

 

[5twins]

Yes, 2mm could have a major effect. The spec is 22mm +/- 1mm for your carb set. Remember, you're reading this measurement with the carbs upside down so a smaller number will translate into a higher fuel level once the carbs are right side up again. So, measurements lower than 22mm will give a richer setting. You bend what's called the "tang", the little tab your float needle hangs on with it's wire clip .....

 

[nishgriff]

Well thanks for the info folks, but I seem to have made things worse.

1. turns out I had measured the float from the 'flat level part' not the 'bulb' part, and I had it around 18-19mm before.
2. I bent the 'tang' so that the 'bulb' part of the float was at 22mm, it sat significantly higher than before, and the tang was at least 7-10 degrees bent away from the surrounding metal.
3. When I connected back up, the fuel overflowed into the filter.

I notice that though the float theoretically would allow less gas in, the way the needle hangs on the tang means that the needle hangs lower, and as the float rises, it should push the needle in sooner.

&*$&%^!!!

so basically it's WAY richer now, so rich that fuel runs out of the carb... what am I doing wrong here?

Yes, 2mm could have a major effect. The spec is 22mm +/- 1mm for your carb set. Remember, you're reading this measurement with the carbs upside down so a smaller number will translate into a higher fuel level once the carbs are right side up again. So, measurements lower than 22mm will give a richer setting. You bend what's called the "tang", the little tab your float needle hangs on with it's wire clip .....

 

[angus67]

did you use replacement floats from mike'sxs?they lack the metal sleeve that the pivot pin slide in, and sometimes they hang up, get stuck, and stay open.

 

[gggGary]

This is my special harping point but I would remove and check the o-ring on the float valve. They can be (should be) a little reluctant going in and you might have a problem there. I like to lube them with a smear of grease. This problem is one carb or both? I haven't done this but will try it soon; While the carbs are upside down on the bench, put fuel or say paint thinner into the fuel line the weight of the floats should be plenty to seal the valves (at any setting) if they don't there's your problem.

 

[nishgriff]

Thanks for your help so far, gentlemen, but I have not resolved this issue. Here's what I've done since last post:

1. checked float needle seat o-ring: It's new, intact, and in place.
2. checked float height again: It's at 22mm measured from the 'lobe' portion
3. I did some rejetting, and seems to run decent at 142 MJ.
4. checked the slide diaphragm: slides slowly down when port is blocked.
5. cleaned and recleaned pilot circuit and air jets.
6. checked and rechecked valve clearances
7. checked cam chain tension
8. replaced mikes xs carb boots (that split) with JBM flanges, which are much more solid.

The right side mixture screw still needs to be almost the whole way in, and the right side has a definite different sound than the left. The ride side doesn't idle as solid, run as hot, or sound the same, and seems to make a different sound on decel. On accel it runs the same as left. The right plug also fouls.

I'm running out of possibilities here. I looked at the choke, but have not disassembled it, could that be a problem? These carbs did survive the right piston exploding on my last motor, i'm starting to wonder if this problem might be that piston shards gouged out some passageways in that right carb. Finally, I can't sync the carbs now that I have the JBM flanges as they don't have vacuum barbs. Can you sync without the barbs?

OK, thanks for reading, ideas?

 

[weekendrider]

Do you still have those size 40 PJ's in there? May be time to start at the beginning again?

 

[nishgriff]

BTW, here's a pic of my bike

 

[Q Tip]

Compression test?

 

[XSLeo]

Do you still have the stock idle mix screws? Try them with the new spring, washer and oring.
The seat where the air screw adjusts to may be damaged. A nick or crack. Someone over tightening the screw when seating for turns out will damage the seat. Any of these will let excess fuel/air mix past the idle mix screw.
The numbers you quote as main jet sizes sounds a bit off. The sizes are in 2.5 steps. As in 132.5, 135, 137.5 and so on.
Leo

 

[nishgriff]

I installed new mix screws, springs, washers, o-rings. I cannot see any damage in the screw seat, but I didn't look specifically. If it WAS damaged, is there any way to fix that?

The Main jets are Dynatune ones that my dealer tells me are compatible. They come in whole sizes unlike the genuine Mikuni ones.

Do you still have the stock idle mix screws? Try them with the new spring, washer and oring.
The seat where the air screw adjusts to may be damaged. A nick or crack. Someone over tightening the screw when seating for turns out will damage the seat. Any of these will let excess fuel/air mix past the idle mix screw.
The numbers you quote as main jet sizes sounds a bit off. The sizes are in 2.5 steps. As in 132.5, 135, 137.5 and so on.
Leo