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cbmontgo
11-04-2010, 09:22 PM
Hey guys,

I just rebuilt my carb and reinstalled it on my stock 1976 FJ40. It drives great down the highway and shifts great, but seems to have a dead spot when starting off in first gear (when I first release the clutch) from a dead stop. I have to rev up the engine more than necessary to get it to accelerate without dying.

Also, I only have 10 hg of vacuum at idle. There must be a vacuum leak, but this may have been there before the rebuild. I have checked and can't find any leakage at the base of the carb or intake manifold so far.

Any thoughts?

Thanks--

rover67
11-04-2010, 09:50 PM
PCV circuit funkyness?

that's a big vacuum leak.

satchel
11-04-2010, 10:37 PM
I haven't dealt with carburetors since working on mustangs with Holley carbs so excuse my ignorance if the parts don't carry over to your application. It sounds like the accelerator pump nozzle or diaphragm to me. A carb works by using air flow and vacuum to pull gas into the engine and the problem is that when you accelerate there is not enough air flow yet to pull in the gas that the engine is looking for so an accelerator nozzle is used to push extra gas in to compensate until the air flow is sufficient enough to pull in what is needed. You should be able to check it out by pushing the throttle and looking for a squirt of gas into the carb. It would either be the nozzle or the diaphragm that pushes the gas that would be the culprit if this is the problem. Usually it is pushing too much through the nozzle if it causes the vehicle to die and not enough gas if it just doesn't accelerate fast enough.

A better and more thorough explanation of what I'm talking about can be found in this video: http://www.youtube.com/watch?v=k-Nx5HEzvlY

Again, I don't know if this necessarily applies to LC carburetors, but I wanted to share my thoughts in case it does.

RicardoJM
11-05-2010, 06:51 AM
On the rebuild, did you change the jets from what was in there? If you went smaller with the primary, it could be what is causing the slight stumble.

Do you have vacuum readings from before the carb rebuild? How does the current reading compare to them? The vacuum leak could be anywhere that is using engine vacuum; brake booster, emissions hoses, pcv system as well as the manifold connection to the engine block and carb. My initial guess would be that a vacuum line has become disconnected and or cracked.

cbmontgo
11-05-2010, 09:21 AM
On the rebuild, did you change the jets from what was in there? If you went smaller with the primary, it could be what is causing the slight stumble.

Do you have vacuum readings from before the carb rebuild? How does the current reading compare to them? The vacuum leak could be anywhere that is using engine vacuum; brake booster, emissions hoses, pcv system as well as the manifold connection to the engine block and carb. My initial guess would be that a vacuum line has become disconnected and or cracked.

Ricardo,

I did not run a vacuum check prior to the carb install, so I almost wonder if it already had low vacuum and that this is a separate carb issue. I kept the original jets, so no change there.

I put in a new accelerator pump that came with the carb kit, but swapped the old one back in thinking that it might have been the problem. It didn't make a difference at all. I do, however, need to make sure that it is pumping a visible amount of fuel into the barrel. I'll check that tonight.

Marco, what is the PCV? Does it have anything to do with this picture? This piece has been disconnected since I bought the 40...

AxleIke
11-05-2010, 09:30 AM
PCV is positive crankcase ventilation

On most, it comes off of the valve cover, and is just a pressure release valve. It can become clogged, and then the pressure vents at whatever seal is weakest.

rover67
11-05-2010, 09:36 AM
yep, that's the PCV hose (red thing)/valve (metal part in the hose and stuck in the rubber of the side cover tube).

make sure it is hooked up per the FSM. leaving it unhooked will certainly cause a big vacuum leak. Looks like yours might actually be broken since that metal piece has separated from the part in the side cover. Go to autozone or napa and see if you can find a new one and throw it on there.. make sure the hose headed to the intake manifold is nice and not broken and go from there.

here it is:

http://www.napaonline.com/Search/Detail.aspx?A=CRB29253_0182371191&An=599001+101976+50070+2070028

you may want to get a new grommet too, they are cheap:

http://www.napaonline.com/Search/Detail.aspx?A=CRB29122_0198984763&An=599001+101976+50070+2070028

the grommet holds it tight in the side cover tube

RicardoJM
11-05-2010, 10:58 AM
On the PCV valve and grommet. I've always picked mine up at the dealer. I have heard (but not experienced) that fitment with non-OEM has been an issue. Connecting the PCV will have a positive impact on your vacuum reading.:thumb:

cbmontgo
11-05-2010, 11:08 AM
Thanks, guys. I will replace mine. When the engine is running, it seems to have a little "spring" poke out the end. Does that make any sense?

MDH33
11-05-2010, 11:25 AM
Did you end up finding the jets you needed? I actually brought a pocketful to the meeting last night in case you were there. :hill:

RicardoJM
11-05-2010, 11:56 AM
Thanks, guys. I will replace mine. When the engine is running, it seems to have a little "spring" poke out the end. Does that make any sense?

Are you talking about the metal piece of the PCV valve coming out of the red hose?

As Marco indicated, it appears your PCV valve has broken into two pieces. I've not ever seen the inside of a broken one, but it would make sense that something inside there moves.

As I understand it (someone will chime in if I am way wrong) the PCV valve is in a "closed" position at rest. With engine vacuum sucking on the end (red hose end) it opens and allows stuff (unburnt fuel, emission gas) that was not purged via the exhaust valves to be "pulled" up into the intake manifold and back into the combustion chambers. Without it being in place, that stuff builds up pressure which is not good for the engine.

rover67
11-05-2010, 12:19 PM
Thanks, guys. I will replace mine. When the engine is running, it seems to have a little "spring" poke out the end. Does that make any sense?

Yeah, it's broken into two pieces. there is a spring and a weight in there that acts as a valve to only allow a certain amount of flow to the intake. THe goal is that the manifold pulls a vacuum on the crank case, but dosen't suck too much air to act like a big vacuum leak. that's why with a good setup, removing something like the oil cap allows more air in and the idle increases.

throw a new one on there and see us in the mornin' :)

cbmontgo
11-05-2010, 01:43 PM
Thanks, guys.

Martin, I kept the stock jets; it sounded like the consensus was to not fix what wasn't broken. It may run a little rich, but it hasn't been as issue so far at this elevation. The real test will come in the mountains, which I hope to do soon.

I hope to actually make one of these meeting; Wednesdays are always hard for me. If any of you guys down this way get together for lunch or beers, let me know!

subzali
11-05-2010, 02:51 PM
We have the DTC lunch club every week or two...:) typically Friday lunch. Check the Event Staging Area.

I'll have to look into getting a PCV at the dealer - the one I got at Autozone or someplace might have something to do with some of the PCV issues I've been having...thanks Marco and Ricardo for your input!

MDH33
11-05-2010, 03:15 PM
Since we're talking about PCV's, what would cause oil to back up into the hose? mine is pretty messy.

satchel
11-05-2010, 03:34 PM
That is typical, especially when your cylinders age and wear. As you get blow by through the cylinder it picks up a little of the oil vapor and that vapor travels along the PCV line back into your intake so it deposits the oil vapor along the whole pcv system usually. Your intake will probably have some oil in it as well. Some people create catch cans for this reason so that the oil collects in a container instead of getting sucked back into the intake.

cbmontgo
11-05-2010, 05:00 PM
A couple of other things that have come to mind:

*I adjusted my idle mixture screw out at least a full turn to where it seems to idle smoother. Could leaning out the idle mixture at least cause the hesitation to go away? Seems logical since it only happens when I go from idle to first gear, not second through fourth gears.

*I removed a "cap" on the pipe (pictured below in the circle) to the carb and replaced it after the rebuild with a temporary cap to test vacuum. What is this thing? Part of an EGR system?

rover67
11-05-2010, 05:11 PM
I honestly think it is running lean and that's the hesitation. Fix the PCV valve and go from there.

As far as that pipe, I am not familiar enough with the older setup to know what it is. Maybe somebody else can chime in?

subzali
11-05-2010, 05:27 PM
I know my carb has that, but I'm pretty sure I have it plugged. It must be an EGR thing and I haven't had that hooked up since I drove it home from the emissions place over 5 years ago...:D

You need it plugged though or hooked up to whatever it's supposed to be hooked up to. Definite source of vacuum leak.

cbmontgo
11-06-2010, 08:34 PM
Well, I installed a new PCV today with new hoses. I also leaned out the idle mixture screw...we are back in business. It runs better than it did before the rebuild and the hesitation is gone; thanks so much for the help guys.

The only thing I have left to do is fix my choke. The "sleeve" right behind the dash knob is disconnected; I need to figure out a way to undo the nut behind the knob. This thing is really hard to get to. Is there a way to do this without removing the heater?

rover67
11-06-2010, 09:10 PM
SUH-WEET!!!

Congrats! :)

RicardoJM
11-07-2010, 08:01 AM
That is very good news to hear. Good job!!!

I'm no help on the other pipe.