83 Carb thoughts

[zore]

So while i'm waiting here for the 83 carbs to get here, I thought I might put some of my 20000 foot elevation thoughts on paper.  One thing I noticed is that the 83 carbs have a fuel return line going back into the tank.  My guess would be that the pump continues to pump fuel at the same rate.  When carb needs the fuel, the float lowers and lets fuel in, the remainder goes back to the tank.  I'm also guessin there is a regulator in there (in the fuel petcock?).

So here is my question.  Is that all really needed?  Could I not use the 82 fuel pump and bock off the return?

Again, I'm simply taking some educated/uneducated stabs at the problem.  If it turns out that this is going to turn into a science project, I may elect to save them until someone else needs them.  We'll see.

[Coil Coyle]

Yes.

[zore]

I just blew soda out of my nose.   ;D  Thanks.

[Walt_M.]

I thought the fuel return line on the '83 carbs was to cure vapor lock issues with the '82s. Don't know if it was effective as I've never been around an '82. I doubt you will see any difference in performance between the carbs otherwise. I did see a mod. someone did previously where he ran the return line to a fitting he plumbed into the underside of the tank near the fuel filler. Neat and it worked.

[Brian Moffet]

I'm not sure whether there is any regulating device in the 83 Petcock.  If that is the case, and the only thing that the return line is used for is to circulate the fuel, what would be the problem of putting a T-fitting in between the 1982 petcock and the 1983 fuel pump?  So you would effectively create a circular path, instead of going from fuel pump to petcock, you go from fuel pump to just below petcock. 

Now if the fuel pump return goes into the tank, so that it ends up going through the filter again, you might see a problem. 

I didn't rebuild mine, it was working just fine.

Brian

[zore]

My thought is that there has to be a certain amount of pressure in the fuel system, usually it's around 5 to 7 pounds.   On the 82, since there is no return, my guess is the pump can only produce so much pressure, my guess is there has to be something in the fuel system that keeps the pressure up before it goes back into the tank.  I am guessing again since  i dont have na 83. 

My hope is that the 83 carbs get rid of the low rpm stumble i have.  If the 83 carbs dont cure the visoin stumble than this experiment is pointless and I'll just throw them back on ebay at somepoint.

[Lucky]

there is no regulator in the 83 petcock, but there is a diaphram like the 82's, only double.  that's why it's impossable to rebuild except for a few of us who have the custom tools Jim made. the diaphram material is hard to find though.

what the return does do is circulate fresh fuel bringing in a constant supply of comparitivly cooler fuel, preventing vapor lock.  that said, when i had an 82 fuel system on my bike, i never experienced vapor lock.

i don't think there is much performance difference between the 2 carbs.  the pilot adjustments on the 83's seem more precise.

i have no plans to change over to 83's on Cafe Vision, no need.

[Brian Moffet]

That would be the push the old warmer fuel back into the tank method then, and draw cooler fuel into the pump.  The T-joint wouldn't do that.

Brian

[zore]

So the vision stumble still exists even in 83 carbs?  I have also not had any vapor lock and I ride in all temps so if I do try the 83 carbs, I'll just use the 82 fuel system.
'

[Lucky]

an 82 carb should not stumble. if you have the updated carb top, jets & airbox, then the carbs need to be balanced & the pilots set. 

[Tiger]

an 82 carb should not stumble. if you have the updated carb top, jets & airbox, then the carbs need to be balanced & the pilots set. 

8) Dead right...I don't have any stumble on my "82's  8)

[supervision]

  My wanting to use 83 carbs, was for the slight increase in size, should make slightly more power..  as far as needing the correct petcock for it to run on, I can't see the need.. The tops of the carbs are nothing special, they have two fuel lines that feed the needles from oppisite  directions, one side is slightly restricted,  I would either tee the two lines together, or block one off.  The only thing to beware of if you block one off, is not to run the one that is restricted, or you run the chance of starving the bowls for fuel at high speed.  I don't know if their is less stumble trouble with the bigger carbs, might be worse, because they are bigger.

[zore]

I've read of a few people glueing nickls to the air doors, i haven't done that but figured that would most likely solve my problem since the carbs are synced and it runs well otherwise.

[Night Vision]

can't speak for your carbs, but my brother has unmodified airbox, 130's top jets front and back, (2) nickels on the flapper... other jets are stock... and is right around 2.5 out on both pilot screws....

It doesn't start up so easily... but boy does it run good... pulls strong throughout the rpms even with a pillion, "no" stumble, gets better gaz mileage than I do too.... and I never dipped or rebuilt his carbs.. just sprayed 'em.

if you have spotless carbs, the modified airbox, try a 130 front 135 rear on top, one nickle on the airbox.... you'll still need to adjust the pilots screws...

and no matter what anyone says.... they all stumble once in awhile... but not constantly if you have 'em tuned good. some days they run like 750's... once in awhile, not so much 

[supervision]

 I think the biggest improvement I noticed, is when I realized my yikes was leaking between the two chambers Now that I have that corrected, I'm a firm believer in that function of vacuum reserve, helping low speed pick-up.  Also I think that made the difference in why my bike is starting better from cold.

[zore]

It doen's stumble all the time, just every so often and only when i'ts fairly warm out.  I'll try adding some weight to it.

130 135 upper, what are you running for mains?

[Night Vision]

It doen's stumble all the time, just every so often and only when i'ts fairly warm out.  I'll try adding some weight to it.

130 135 upper, what are you running for mains?

122.5/127.5 (stock)
about 5.25 / 2 out on the screws
Unifilter... one nickel on modded flapper

you have macs (my brother has your chromes) so all bets are off!
a 1/4 turn on the pilots can make all the difference

[Rick G]

Properly tuned and setup '82 carbs  work just fine. Mine do not stumble at all . The problem stemmed from  The fact that bikes in general and visions in particular were selling poorly  at that time . The bikes that sat in crates and on dealers floors , suffered from the gas evaporating  and gumming up the carbs . Many dealers and mechanics , didn't read the YIC service bulletin, or just ignored it , outlining the procedure to bring these bikes up to spec.  So they had a stumble and a bad reputation.
My opinion is that the '83 carbs were an attempt to correct a problem that didn't exist!   I have yet  to have it vapor lock , not at 98 deg. and 98% humidity in MN. or 106.deg. and 40 % in OR.  And especially not here in AZ.  at 120 deg  and 15% .

[h2olawyer]

My 82 carbs will run rough and stumble when the bike is vwery warm - hot.  I found one cause was the fuel line.  I have one of the small plastic 90 deg. fuel filters.  The fuel line from the petcock to the filter made a pretty sharp bend.  As the heat got to the line, it would soften & restrict the fuel flow.

After replacing the line with a slightly longer piece of fuel injection hose (which made the bend smoother), the rough running problem decreased significantly, but did not go away entirely.  Still get a sporadic stumble once the bike gets hot.  Not there any other time.

Tractor has some amazing carbs.  That bike has more low end grunt than I've ever felt on my V.  Before I get the 83 fuel system swap done on Silver V, I think I'll try the Tractor carbs on it to see if it is the carbs or other problems causing Silver V's slight low end power issues.  Tractor had the great low end with the rotted stock exhaust & kept it with no noticeable change when I swapped to the MACs.

Silver V may need another good carb cleaning.  After all, it has been several years since I did anything but adjust them.

H₂O

[jasonm.]

My thought is that there has to be a certain amount of pressure in the fuel system, usually it's around 5 to 7 pounds.   On the 82, since there is no return, my guess is the pump can only produce so much pressure, my guess is there has to be something in the fuel system that keeps the pressure up before it goes back into the tank.  I am guessing again since  i dont have na 83. 

My hope is that the 83 carbs get rid of the low rpm stumble i have.  If the 83 carbs dont cure the visoin stumble than this experiment is pointless and I'll just throw them back on ebay at somepoint.

Zore, The pressure in the fuel system is 2 or 3 psi at best. I can end all the quesions. Just put in an electric fuel pump. Works like a charm. Mine is off a Virago 535. I got tired of waiting for the pump to do it's thing while cranking the engine. Some days were better than others. Now I just turn the key and the pump is on, carbs are full. I capped off the "return" to the tank and used fuel hose to connect the not needed 2 extra connections at the carbs. These are self regulating pumps. Just 2 wires + and -...Also the '83 carbs will only get ride of the stumble if you have '83 front head pipes or MACs. The '83 carbs are matched to the pipes ! especially the front.  If you get a stumble when the bike is hot...then your too rich. You can adjust the low speed screws or open the flapper a bit. Yes, it's adjustable with the 2 screws that secure the vacuum diaphragm.