Topic: Air Fuel Ratio for 836 engine?

[eurban]

For the acel pump the best check is with the carbs on and the airbox removed.  On the bottom of each intake throat is a small brass nozzle next to the choke plate.  With the carbs gassed up, when you whack open the throttle you should see a squirt of fuel shooting from each nozzle towards the engine.

[scondon]

Idle mix screws can now be adjusted for max idle speed at a given throttle setting (turning the screws should make a difference!) I also "tested" the performance with various mix screw settings and the max idle screw setting seemed to work the best.. . . . .

   Just got back from my ride. I started by turning only one mixture screw 1/2 turn in either direction and hopping on for a run down the road. Better?worse? adjust that screw and hop back on. No change? adjust leaner until it did change. After about 10 trips up and down the road I was at a point where I could turn any screw 1/4 turn and hear the difference in the engine. Adjusted by sound and test rode. Minor adjustments from there and it's pretty good now.

   Remember that #2 bowl that had 1/8" lower fuel level? It's at 3 turns and is difficult to find the sweet spot. Much richer and it doesn't burn well, much leaner and it makes my exhaust sound like a popcorn maker when I decellerate. The others are at approximately 2- 2 1/8 turns out and are easier to tune.

   Gonna take this one step at a time and the first step is to raise the fuel level in #2. If that doesn't help then I'll pull the jet and clean the crap out of the circuit.

   After todays carb synch and this last tuning run the bike runs real quiet at 900rpm

For the acel pump the best check is with the carbs on and the airbox removed. On the bottom of each intake throat is a small brass nozzle next to the choke plate. With the carbs gassed up, when you whack open the throttle you should see a squirt of fuel shooting from each nozzle towards the engine.

     Thanks for the reminder, it's been a couple years since I checked this function

[upperlake04]

great listening in on your learned chat with Eurban, Scondon   I've gleaned some valuable nuggets  that can be applied to my own 78F carb problems.  Question - with the clear line attached to the bowl drain nipples on 1-3-4,  where is the  fuel level relative to the bowl/carb body joint?       please carry on with your discussion

[scondon]

great listening in on your learned chat with Eurban, Scondon I've gleaned some valuable nuggets that can be applied to my own 78F carb problems. Question - with the clear line attached to the bowl drain nipples on 1-3-4, where is the fuel level relative to the bowl/carb body joint? please carry on with your discussion

  Jump right in,upperlake

  Here's the fuel level measurements I got using the clear line:

   Measuring from the bottom of the carb body(slight gap between float bowl and carb body so these are from the carb body, not the top of float bowl) the fuel level is 3/8" down on 1,3,4. On #2 it is 1/2" down.

   Checking my parts carbs I see that the pilot jet tip is 5/8" lower than the carb body. This tells me that 1,3,4 are emersed in 1/4" of fuel and #2 only 1/8"

[upperlake04]

thanks for checking that   I found, as you did, that even though the floats measured the same when assembling the carbs ( mine were measured with a micometer) , the actual levels when verified with the clear tubing showed differences, from each other, and yours.  Hmmmm...

[scondon]

thanks for checking that I found, as you did, that even though the floats measured the same when assembling the carbs ( mine were measured with a micometer) , the actual levels when verified with the clear tubing showed differences, from each other, and yours. Hmmmm...

   Don't keep me in suspense What did you find when you measured yours?

[upperlake04]

They were adjusted to 14.5mm which  filled the bowls  1/8" to 1/4" below carb body. 

[scondon]

cool From what's happening with mine I'm willing to gamble that my fuel levels are low and that your 1/4"-1/8" is more desirable. Possible my float measuring technique could use some fine tuning since I was shooting for 14.5mm alsol. Having the levels even seems to be key as well.

[mrbreeze]

Sean,when I built my carbs and during all of my experimenting (main size,needle position,etc.),I decided to check my bowl levels.When I assembled the carbs,I set all float heights to spec.Anyhow,I checked my bowl levels differently than you. I drained each carb seperately into a baby food jar.I drained #1 and made a mark on the jar. #'s 2 & 4 were spot on with #1 but #3 was lower. I pulled #3 bowl and readjusted the float till it gave me a fuel level to the line on the jar. That fixed her right up and I haven't had any other troubles with it.Matter of fact,I haven't even been back into the carbs since then!!!!

[sparty]

Oh, my head hurts from reading all of this carb tech stuff.  The next thing that I am going to do with my terrible '78 carbs is toss them up in the air and hit them with a baseball bat.

Sparty

[scondon]

Sean,when I built my carbs and during all of my experimenting (main size,needle position,etc.),I decided to check my bowl levels.When I assembled the carbs,I set all float heights to spec.Anyhow,I checked my bowl levels differently than you. I drained each carb seperately into a baby food jar.I drained #1 and made a mark on the jar. #'s 2 & 4 were spot on with #1 but #3 was lower. I pulled #3 bowl and readjusted the float till it gave me a fuel level to the line on the jar. That fixed her right up and I haven't had any other troubles with it.Matter of fact,I haven't even been back into the carbs since then!!!!

    I looked around the house for a jar small enough to measure the gas coming out of each carb but couldn't find anything. Next time I go on a baby food binge I'll remember to save one.

Oh, my head hurts from reading all of this carb tech stuff. The next thing that I am going to do with my terrible '78 carbs is toss them up in the air and hit them with a baseball bat.

Sparty

  Would that be aluminum or wood bat, Sparty? And, if you no longer need the tool after your carb "correcting" procedure then how much, with shipping to 94611?

[Hockers Choppers]

I'm getting my 78 750f with k topend, ported head, bigbore, cam, etc. back together. I'm running the stock carbs with pods and 4-1. I had it running good before the rebuild. What jetting did you end up with? needle setting, idle setting? Anynore dyno runs? Need a set of braided steel  brake lines? I have an extra set for the 77-78 super sports.
Thanks a ton!!!!

[Sam Green Racing]

Thanks Sean, top of the morning to you and the page.

Sam.

[JohnG]

I have enjoyed reading all of the posts in this thread greatly.  Every now and then I think I might get carb tuning down yet...

I have a very side related question I hope you don't mind me asking.

Back in the late 70s it was suddenly the "hot setup"  to drill out the back of your airbox and remove the lip on the bottom, for better air flow, at the expense of some intake noise.  I vaguely recall having to go up a couple of main jet sizes  to accomodate the increase in air  (also had put in a K&N).

The question I have is:  does anyone know if removing the bottom lip of the box does anything good or bad??  It seems pretty clear the holes help but what about the lip??  I can think of reasons to keep it since it helps direct more air into box as it flows underneath but lacking time on a dyno to compare, what do I know??  right now mine is removed but I have another one intact.

Thanks for your thoughts and please keep up the great thread!

          John