Detecting Lean conditions on early 34mm carbs

xsjohn · Last edited by xsjohn on September 22, 2007, 3:30 am; edited 4 times in total

PM me.....after two years of work I have found the correct needles and learned how to work them............save the bike and a lot of time......

Thanks John Underwood

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

Ok John - I have a question for you.
I have an 81 with 2 sets of 34mm stock carbs.

The Yamaha factory manual says - set the floats so that when the bike is level and at rest - the gas level in the bowls is within 1mm of the top of the float bowls - using the clear tube attached to the drain nipple on the bottom of the bowl method - to see gas level while on bike.

If you do this - 27mm is WAY to LOW a float level.
The magic number is more like 24 to get gas near the top of the bowl

The Yamaha manual call for both a 27mm float level AND a gas level that reaches the top of the float bowl - IMPOSSIBLE!

Which is better - 27 mm with a half-filled bowl or 24 with a full bowl???

thanks
Jim

PS i noticed in one of your photos - in your other article- the plug electrode is clean - but the surrounding plug surface is ashy - mine are like this - they never used to get ash around the outer edges - is that normal? -

xsjohn · Last edited by xsjohn on September 22, 2007, 3:34 am; edited 1 time in total

Jim: Worked the situation out after pulling my hair out for 2 years....PM me and I will ship the correct main needles........dang these are good carbs except or the epa.........

John Underwoood

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

John - thanks for getting back so quick.
I wasn't questioning your methods ---I was questioning the stupid instructions in the Yamaha Service Manual (from Yamaha).
With the 34 mm carbs -
1981
They list 27.xmm as the float height.
But ALSO say run the fuel to the top of the bowl with the "clear Tube" attached method.

I SAY it is Impossible with Yamaha's methods!

Chilton lists 25mm for xs650H

As far as you believe - how high in bowl should the fuel be?

Also I noticed in your pictures - you are setting float height on older Brass floats - my 34's have smaller plastic/foam floats. (I believe they are lower)

I noticed your "mid-range" settings were done on a 38mm. (did I read it right?)

Would those mods work on my 34?

I would be interested in trying your mods on my extra set of 34s - just as long as they are for 34's not 38's.

Also could I use small brass washers as a spacer?

Let me know what you think.

About fuel depth in bowl -
and the mods.

Oh - and by the way - an old subject Idle mixture - 2 identical sets of carbs - rebuilt both - one likes 1.9 turns out for idle mix, the other likes 2.25 -
Any richer they stuble on acceleration, any leaner they die or idle poorly.
go figure.

Thanks
jim

xsjohn · Last edited by xsjohn on September 22, 2007, 3:35 am; edited 1 time in total

PM me for the correct needles........

John Underwood

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

Wow - a lot of information to take in!

I made the same mistake you did - only in the other direction -
I saw your brass floats and assumed that you had 38's because I thought all 34's had foam.

As far as the needles - .040 to .060 we are talking 4/100ths of an inch - correct? I don't have a micrometer - but I would like to try this mod.
I was thinking of trying a couple of small brass washers as spacers.
(I could add and subtract washers as needed - as long as I kept both sides even correct?)

I used to run my float level with the gas down about 1/4" from the top of the bowl - this is my first week running with them up to the top. The jury is still out.

One more question - I have something rattling around in my stock exhaust pipes - megaphone style - if I replace the factory mufflers - can I just cut the header pipe off of the muffler with a hacksaw - and and bolt on an aftermarket muffler? (the factory ones are welded together).

Thanks
Jim

xsjohn · Last edited by xsjohn on September 22, 2007, 3:36 am; edited 1 time in total

PM me.......

John Underwood

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

So far my bike is pretty much stock all the way around.
I have a rattle in my pipes - but other than that they seem fine.
I have hesitated in changing them for just the reasons you cite above.

I think I will hit the local Harbor Freight and get a micrometer - and give raising the needles a try.

I do mostly city driving here in buffalo, so the stock gearing seems fine.

actually most of the bike is just fine -

I am just a "tweaker"

When I get started on the mods I may drop you another line if I have questions.

Thanks again
Jim

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

Ok -
I spent the weekend doing a load of trial and error experimenting with both carb sets on my bike -
2 things I think I have concluded - and if you would please verify if my thinking is correct -

When the mixture is too RICH I get muffler explosion - and stuttering on acceleration - the muffler explosion is caused by the fact that both plugs fire at once on an 81 - and unburned fuel ignites on the exhaust cycle.

When it is too lean - I get hesitation on acceleration, and knocking - sometimes carb backfire.

(part of this is tied to my knowledge for when cars had carbs - backfire in carb = lean - muffler explosion=rich)

I tired rasing the needles with one washer - about .04 (I bought a digital micrometer!) And I got hesitation and muffler backfire - I assumed it was too rich.
So I put them back.

Float levels - with my new micorometer - I discovered - 25mm was too much - 22mm was right on the edge of flooding and 23-24mm was dead on with the foam floats.

The best I could achieve (it runs pretty damn good) was 2 turns out for idle mixture screws - 23-24mm on the floats - needles at factory.

When I tried 2.5 turns out, needles raised .040, and float at 25mm. I got muffler explosion at idle, and stutering on acceleration.

What are your thoughts on the symptoms of too rich or too lean?
At idle?
on accleration?

Thanks
Jim

Oh yes - having the factory air boxes on improved accleration.

And I did a little trick to sync them -
Started with a visual sync when the carbs were off (butterflies in same position)
Then - with the bike running I pulled each plug wire and compared the drop in idle - until the rpms on each cylindar alone matched.
Then used the vacum gauge to fine tune and match them.

It seemed more accurate in balancing the cylindars than using the vacum gauge alone.

Jim

xsjohn · Last edited by xsjohn on September 22, 2007, 3:37 am; edited 1 time in total

Got the right needles.........

John Underwood

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

Maybe I have the only 650H built - that actually runs best at the factory settings!

If I pull the air cleaners - I don't get a huge difference in performance - sometimes it may develop a hesitation or pop at around 3-4K.

The timing is not adjustable - it's factory TCI.

What do you think about my symptoms of too lean or too rich?
Is my thinking right?

Have you heard of this?

I don't doubt your system works well - I have seen too many people sing the praises of richening up the 650.

I just have the exception to the rule.

I do know that on my bike - too rich makes it run like garbage. And I want to stay away from too lean.

Thanks
Jim

xsjohn · Last edited by xsjohn on September 22, 2007, 3:38 am; edited 1 time in total

Got the needles.........
John Underwood

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

Yes in my early adventures with my xs650 I had an intermittent dying problem. Would die - but start right up. Found 2 things - copper wires going into aluminum spades caused a die-electric corrosion - even WITH die-electric grease on them -
So I soldered all the wires to the spade connectors - cleaned the connectors and again used die-electric grease on them.
THEN - I tore open the TCI box examined the circuit board and found 4 or 5 bad solder joints on the circuit board - repaired all of those and BINGO!
y problem went away.
(What I won't do to save a few hundred bucks!)
y timing is dead on, and so is my advance.
y spark caps are all new at 5K - and I have even added a higher output coil from Mikes.

I am sure there is some little difference in the passage of the carbs or the casting - like I noticed before - even between my two sets -
One likes 2.0 turns out - one likes 2.5. On paper it shouldn't be different.

What about symptoms for too lean or too rich -
What do you see as signs a bike is too lean?
What about too rich? (other than plugs)

Thanks
Jim

xsjohn · Last edited by xsjohn on September 22, 2007, 3:39 am; edited 1 time in total

Like my 18/29 and the right needles

John Underwood

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

xsjohn

Great post. Now we have something we can talk about. You do have to give the plugs some time to develope the color you would hope to expect. Funny thing with my 80 is that it never misses no matter what settings I have decided. It is like it is begging me to set it right and giving me all the leaway to f it up or get it right. Runs like an old GM 283 now. Good thing I have the experience to not go off waco. What carbs are you running as I am trying to understand the 38's. Seems they have none of the same problems that the 34's have. My friends both have the 38's and I am to dumb to help them. One revs high at an idol and the other runs rich but ok. Guess you have to own it and ride it a lot ot really get into them. That I havn't done with the 38's. Thank god sinc the 34's were bad enough. It is much easier to richen than to lean out a carb. As you described changing your clip toward the rich and the plugs started to blacken. The right place was most likely in between the clips. Grab the caliper and you will be there. Thanks for adding to this post. Let me know how things proceed. Old Yamaha Mechanic John Underwood

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

xsjohn

One is a 78-79 as you described above that we will copy. The other is the pain in the a 77 that spits and the idle raises when it feels the urge. We have checked the advance on it and it is lubed through the cam and I think it is working right. My guess is the choke on one of the carbs is goofed. Timming is good so I don't think it is electrical.
I doesn't spit all the time at idol and it doesn't always rev. We have checked for vacume leaks. None. Crazy.
We have cleaned them twice. Havn't rehabed the choke mechanism or taken it apart there..

I run 135 mj in my 80 model. 137.5 eats to much gas the way I have mine set.. Don't hold it wide open much anyway.

Thanks John Underwood

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

xsjohn

Thanks and I will pass this great information on to my buddies. Have you kept a tab on your mileage. Rich is 52mpg. Meduim is 55 and lean is 60mpg on 1980.
John Underwood

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

Alright - in the "I'm going crazy book", with my carbs REBUILT AND set damn near factory - I am still getting the a pretty good coating of dry fouling after driving my bike for a week or two. (right up and over the electrodes) The floats are not set as rich as the Yamaha manual, calls for - but pretty damn close to what they were when I bought the bike 22 years ago.
(gas level is about 5mm (1/4") down from the bowl gasket.
Idle screw is about `1.9 turns out from seated.

As the plugs start to foul I get the rich stumble - 5 twins described above.

Ok - I am trying one hear range hotter on the plugs to see what happens - I moved up to a NGK6es (it calls for a 7es).

ANY Dangers here with a 1_step hotter plug?

The bike has 11K on it - and I am the original owner.

Let me know your thoughts on a hotter plug.
thanks
Jim

jimdi · 650Rider Supporter Joined: Oct 27, 2005 Posts: 512

Oh, one more thing - my milage at last check was a little less than 50 (maybe 45-50) but to be honest - I probably wasted a lot of gas when I pull the carbs on and off - So I will have to run a couple of weeks to get an accurate reading on mpg.

Thanks
jim

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

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Yamaha xs650