the mystery un folds

[gravelman]

hi guys gravelman here.well i found something intristing on my 77 650 today.i was having problems trying to get the bike to run correctly wouldnt idle very good and broke down on the midrange .anyways i tore the carbs apart clened and cleaned then i checked all my jetting and needles which was all correct except the pilot jet it was a 45 and the manual calls for a 25 so trying to set air screws with 45 pilot at 1.5 turns made it run horriblethen i looked little deeper and noticed the pilot and float bowl was from earlyer modelswith the different metering orfice .so my question is the only i can cure this is to find 77 bowls and change pilot or is there any other choice .probly not but just thought i would ask thanks joe

 

[DirtyErnie]

That's a thinker... I'd say go to the Tech section and do as much reading about carburetors as you can stand... then a little bit more.
Find the 'Carb Guide', it's in there somewhere and has a bunch of model ID pics. Once you get all that straight and know what you have it shouldn't be too big of a chore to get the right parts and start tuning.

Good Luck.
E

 

[XSLeo]

I have a set of 76-77 carbs with all the brass parts out of a 74 in them. It took me a long time to figure out why things were not working right.
The pilots will be ok if they are the right size to match the float bowl.
With the 45 pilots try .75 turn out on the mix screw.
If you look in the carb guide, scroll down to the last pages you will see pics of the float bowls. The first is the 76 -79 style float bowls. They use the VM 22/210 pilots.
The second is the 70-75 style float bowl these use the BS30/90 pilots.
Note the way the air bleeds feed air to the pilot jets, one feeds the top, one feeds the bottom of the jet.
When you feeds the bottom of the jet it needs to be bigger because the fuel is mixed with air before it passes through the jet. When you feed the top of the jet the pilot is smaller because the air is mixed after the jet.
They both feed the same amount of fuel, they just mix in the air from different places.
You can't swap the jets from early to late bowls and have them work right. You can swap the bowls and they will work. You just have to use the proper jets and set the mix screw to match the jets.
In the carb guide is a chart that shows the years and mix screw settings. The 74-75 carbs used the 45 pilot jets with a .75 out smix screw setting. The 76-77 carbs used the 25 pilot and the 1.5 mix screw setting.
So with your 45 pilots, if they are in the early bowls will work, you just need to set the mix screw to match.
So be sure you have the bowls and jets match and the mix screws matches them.
Leo.

 

[grizld1]

Uh, Leo, ever look at where the choke pickup pipe and choke fuel reservoir are located on the Solex stamp carbs versus later versions? You're not gonna get a mix-and-match there.

 

[XSLeo]

I have both a 74-75 set of bowls and a 78-70 set of bowls they both fit on my 76-77 carb set. Both run fine.
The 78-79 bowls are marked with a letter E, the 74-75 bowls I have are marked with a Letter H. My 72-73 set have A marked bowls, they fit on the 76-77 carb set too.
The only difference I see in any of these bowls is the 78-79 bowls don't have the over flow and the air feed is on top of the pilot.
I don't have a set of 76-77 bowls Or I don't think so. From the pics I have seen the 76-77 bowls have a metal over flow port on the bottom of the bowl. The over flows I have are plastic.
None of them are marked as Solex carbs. The 72-73 set have chromed smooth alloy diaphram covers. The 76-77 and 78-79 set are marked MIKUNI KOGYO CO, LTD
On the 72-73 carbs the enrichener pipe where it comes out of the carb body is only about half as long as the other carbs.
I can't say I have had the experience of you on these carbs but the ones I have work with any of the bowls I have.
Leo

 

[gravelman]

thanks guys i just got a set of 79 bowls with the air feed on top and ordered the proper 25 pilots so hope fully it works the bowls look identical to me other then the air track and like leo says no overflows so i see what happens thanks again joe

 

[gravelman]

hi guys i got some 79 bowls and proper jets number 25 i will give it a whirl thanks joe

 

[DirtyErnie]

Keep us posted, always nice to know when another one gets running.

 

[gravelman]

hi guys no problem i will let u know how i make out.my parts should be in to day with the rite size jets .i just cleaned the carbs in my ultra sonic cleaner got everything spotless .i will let you guys know thanks for all ur help joe

 

[grizld1]

That "overflow" is what keeps the float chamber at atmospheric pressure. 78-83 carbs vent through the intake bell.

 

[gravelman]

so does that mean they wont work kinda lost now thanks

 

[gravelman]

ok i understand what u mean now but my carbs also have the vent line on the side of carb body which dumps in to float chamber? i blew through that line and it blows air in to float chamber so i think i should be ok for presshure
any more input welcome thanks joe