am i running too lean?

[ianfotheringham]

so in the continuous battle to try and optomize fuel efficiency, i have been playing around with my carb fuel/air mixture...

i figured i had got it pretty much ideal, but the other day i was cruising up a fairly steep steady incline [in my 3000kg fj45] in third gear [3.73's, 31"tires] and i began to loose power pretty quick, and eventually the eingine began to hesitate, much like it would if it were running out of petrol...as soon as i threw in the clutch full power came back, and second gear allowed me to continue up the hill, but rather slowly of course...

is this due to me running too lean?

i assume so - but this is the only downside i have witnessed thus far...there hasn't been any pinging or knocking...could this be the only downside of better fuel economy?

thanks

 

[rockcrawler]

For quick diagnosis try pulling your choke out a bit when it happens next, if that makes it run better you'll know if its running lean.
Sounds more like low float level or low fuel pressure to me or maybe a sticky needle and seat. A motor running lean will also be harder to start and run hotter and even backfire.

 

[ianfotheringham]

For quick diagnosis try pulling your choke out a bit when it happens next, if that makes it run better you'll know if its running lean.
Sounds more like low float level or low fuel pressure to me or maybe a sticky needle and seat. A motor running lean will also be harder to start and run hotter and even backfire.

hmmm..run hotter? harder to start? backfire occasionally? i think we might just have our answer here....

ill try the choke idea...its funny how i never think of the things that make sense when they would really come in handy...odd...

the carb is an OEM...brand new...so i figure the float position should be good...otherwise, how does one check/adjust? there has always been fuel present in the window...so i always assumed it was ok...sticky needle/seat? how would one isolate that as being the issue?

if it is in fact lean, is there any serious downside to keeping it that way in the interests of improving fuel economy? so long as the temps dont get too out of hand?


hmmmm


thanks

 

[bsmith123]

power loss

#2 Eco-tune carburated V8's - fast and accurate - GoFastNews.com - All Racing News All the Time!

here's a good article on tuning for economy for what it's worth.

I was wondering if you might want to check your secondary and make sure it is opening under load

 

[Pighead]

.so i figure the float position should be good...otherwise, how does one check/adjust? there has always been fuel present in the window...

The next time your engine exhibits the symptoms, shut off the engine and coast to a stop...eyeball the porthole and check fuel level in the window. See if you have the usual level of fuel. Since you always have fuel present in the window (halfway up?) you float level is good. If the fuel level is low, or gone, you have a fuel delivery problem.

 

[ianfotheringham]

thanks for all the help guys - i'm fairly positive that its just a matter of air/fuel adjustment...as the carb was brand new - as is the fuel pump...and pretty much everything else mind you...i noticed my mechanic adjusting it the other day after i had blown the choke fuse without mentioning it - he thought it was adjustment....

anyway - im pretty new to carb tinkering...wrong generation i suppose...

what should be done?

should i turn the air/fuel mix screw all the way in till the revs drop then out a half turn or so? or is there a better way of getting the 'perfect' mix....fuel economy is of a fair concern as ill be putting some serious miles on it in the next few months....

or am i totally wrong here and i need to adjust the float level or something?.....

help!


thanks!!!

 

[Pin_Head]

The idle mixture screw only effects the mixture at idle and has very little influence on the mixture when the throttle is opened. To change the air fuel ratio at cruising speeds you would have to change the main jets and/or air correction jets (Toyota calls them slow jets). Changing the float level can also influence the mixture, but it has an optimal height, so it is better to change the main jets.

 

[ianfotheringham]

The idle mixture screw only effects the mixture at idle and has very little influence on the mixture when the throttle is opened. To change the air fuel ratio at cruising speeds you would have to change the main jets and/or air correction jets (Toyota calls them slow jets). Changing the float level can also influence the mixture, but it has an optimal height, so it is better to change the main jets.

so this is just due to them being worn? replacing them could solve the problem? is there no way of adjusting the mixture through the carb to avoid being too lean at speed?

its just that i have all the symptoms of being too lean...running hot, trouble starting etc...i figured it was a matter of mis-adjustment...

 

[ianfotheringham]

The idle mixture screw only effects the mixture at idle and has very little influence on the mixture when the throttle is opened. To change the air fuel ratio at cruising speeds you would have to change the main jets and/or air correction jets (Toyota calls them slow jets). Changing the float level can also influence the mixture, but it has an optimal height, so it is better to change the main jets.

also - the carb is quite literally brand new, OEM...would it be likely to have jet problems straight out of the box?

 

[bsmith123]

rusty bits and other gremlins

I had a newly rebuilt carb but the little rusty bits worked there way into the fuel inlet and jammed it---at some points it would fill slow and then finally no fuel would get in

I wouldnt necessarily assume new means ok---could of got some garbage in it

Have you tried doing the hand smack thing---with it running choke it off momentarily with your hand to create suction then lift off quickly to keep it running---do it a couple of times


hows your fuel lines ---no kinks?

 

[Pin_Head]

The chances of new carb being jetted too lean are slim to none.
The adjustment is only for idle mixture and has no effect at other speeds.
There is nothing to wear. The mixture is changed by changing the main jets.

I doubt that your problems are caused by the mixture being too lean, but you didn't describe the problems in sufficient detail to make a reasonable guess.


Read this for more info on how your carb works:
Cruiser Carb Info - Land Cruiser Tech from IH8MUD.com

 

[bsmith123]

throttle plates

PinHead

as far as the carb goes
What about the throttle plates opening too far for the amount of throttle, jamming open, or the secondaries opening too soon

any adjustments for that, chances of this?