Carb tuning and engine timing issues

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csd1982

csd1982

10 Year
Joined
Mar 26, 2012
Threads
94
Messages
554
Location
Chicago
Website
www.engusa.com
I have a 1975 fj40, 2f, stock carb. Originally I had a vacuum leak that I think I fixed so now I'm trying to get the rig running smooth again. However I have some issues. The carb was rebuilt by myself.

So when trying to tune the engine at idle I have both a tachometer and a innova 5568 gun connected up. The tachometer reads 700 rpm while the gun reads 1100. Which should I believe? Is the timing gun to new to work with my old car?

Furthermore my dam idle mixture screw does squat. I have good vacuum reading 18.5-19. But when I back off the idle speed screw down to 600 on the tachometer and 950 on the gun the vacuum drops to about 17 and the car will run for a bit then slowly die.

Also I cannot see the timing mark with the gun which I assume is because the gun timing is not working right. Or maybe it is working right and therefore the rpms are too high to see the mark which might mean the vacuum leak is not fixed and I have to keep the idle speed screw high to offset the leak and keep good vacuum.....

Don't know what to think. I have almost made my self sick blowing cigar smoke thought the intake manifold where the breakbooster hose connects. I did not see any leaks in the base of the manifold or where the header and intake connect to the block. I have a new header from marks off-road and one of those good gaskets.

Thoughts?

Why won't my idle mixture screw do anything? Even when all the way in the engine won't die. Figured it should.

What rpms are right? Believe the gun or the tach?
 
I like using propane. Adjust the idle speed down until the engine will just barely run. I put a 1/4 inch ID hose over the end of my propane torch after removing the nozzle and spray gas around any place the manifold might leak. The manifold may also be cracked under the carb and anything that connects to the manifold, like the brake booster can also leak.
 
csd1982 said:
What do you mean by no idea fuel? No fuel in the carb bowl? It's half full and the selinoid is new and working.
Click to expand...

I didn't say "no idea". I said no idle fuel.

That means that fuel isn't getting from the fuel bowl to the idle port under the primary throttle plate.

You could also have an intake manifold vacuum leak, so air is geting into the mainfold without going through the carb and picking up fuel.

Either way, there is not enough fuel to idle.
 
Y
Pin_Head said:
I didn't say "no idea". I said no idle fuel.

That means that fuel isn't getting from the fuel bowl to the idle port under the primary throttle plate.

You could also have an intake manifold vacuum leak, so air is geting into the mainfold without going through the carb and picking up fuel.

Either way, there is not enough fuel to idle.
Click to expand...
yes sorry, I had a typo. I did not mean to say idea. But you answered my question.

I think there is a leak on one of the exhaust header ports and one of the intakes mainfold ports as I was spraying carb cleaner around them and the rmp's spiked over 150 . I have headers as the rig came with them. However there were cracks in it so I got a new header from marks off-road. I also have a remflex header. Should I use some Permatex Copper COAT on the remflex gasket as well?
 
Well still no dam luck here.

I pulled the header, intake manifold and gasket off. There are no cracks in the header or manifold. I got a new felpro gasket. Loaded both sides with ultra copper sealant. Put it all pack together. Torqued to specs and in the instructed order. Let it dry over night.

Today the lowest I could get my engine to idle at was 1000 rpm on my timing gun. I loosened the idle speed screw so far it fell out. Would not get below a 1000 rpm and 21 vacuum. I still don't think the idle mixture screw is doing jack.

I have a flame thrower coil and electric ignition on the fj40. If that matters as to why I can't get the idle down.

Any thoughts? Is the linkage maybe out of wack on my carb? Do I need to adjust the other screws on the carburetor?

I also used a torch with a piece of vacuum hose and put it around the intake manifold were each of the 3 sections connects. I did no notice any change in the RPMs this time. Before I replaced the gasket I would spray carb cleaner and the RPM's would spike. I have not tried that now that I have the sealant as I dont want the carb cleaner to eat away the silicon sealant.
 
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One more note....I follow the manual and turned the idel mixture screw all the way in and then back 1.5 turns. In doing so I think I bent that tip of the screw. I took it out and I can see the end of the screw is straight and so is 90% of the shaft but part of it before the tip has a small bend. Will this effect the idel as well? Very minor bend
 
the idle mixture and idle speed screws are different. Try looking up the lean drop method for carb tuning unless you already did this after you rebuilt the carb. Is it timed right? maybe your running to advanced if you cant lower the idle. I am sure with pin_head here it will be sorted.
 
I have the timing set at 1000 RPMs. As the timing mark is lined up with the needle at this point. However I have not tried to set it with the vacuum advance yet. I figured its a waste to set the timing at such high RPMs.
 
Did you try backing off the idle speed screw? This is not the same as the idle mix screw. It is hidden behind the linkage facing the firewall and it is in the cast iron base. It is not one of the two screws on the linkage.

Note that the idle mix screw isn't supposed to do anything when the primary throttle is open and the engine is running on the main jet. It only works when the throttle plate is closed.

Look inside and verify that the primary and secondary butterflies completely close. You can use a piece of very thin wire or nylon monofilament to verify they are completely closed if you cannot see well enough.

Once you verify the the throttle plates are closed, then the idea is to adjust both idle speed and idle mix screws to get it idling smoothly at 650 RPM. Start with the mix screw two turns out from closed and then bump the speed up until it won't stall. Then alternate adjustments.
 
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You need ti take a step back at this point and breathe. I have been where you are, chasing my tail. Have you disconnected and plugged the hose to the carb vac advance?
Go back to zero and reset your dizzy, I would look at that idle mixture screw and make sure the tip isn't deformed because that will have an effect on adjusting the mixture.
Set your idle mixture screw out 2.5 or even 3 turns and you need to be below 900 RPM to be officially idling. If you have a vac gauge hooked up, it is a great help in setting timing and idle conditions.
Check timing throughout the process.
 
Pin_Head said:
Did you try backing off the idle speed screw? This is not the same as the idle mix screw. It is hidden behind the linkage facing the firewall and it is in the cast iron base. It is not one of the two screws on the linkage.

Note that the idle mix screw isn't supposed to do anything when the primary throttle is open and the engine is running on the main jet. It only works when the throttle plate is closed.

Look inside and verify that the primary and secondary butterflies completely close. You can use a piece of very thin wire or nylon monofilament to verify they are completely closed if you cannot see well enough.

Once you verify the the throttle plates are closed, then the idea is to adjust both idle speed and idle mix screws to get it idling smoothly at 650 RPM. Start with the mix screw two turns out from closed and then bump the speed up until it won't stall. Then alternate adjustments.
Click to expand...
So make sure both plates are closed all the way when my foot is not on the gas right?
 
Hi all,

Thanks for the info. I think I'm close. I got the engine to ideal between 620-720 rpm's. As well as good vacuum. However I do notice the vacuum will jump a bit every 30 seconds or so from 17 to 18 then 16 then back to 17. I have it timed right as well.

When I open the throttle the vacuum drops to 4 and the up to 27 then drops back to 17 which is good. Also when I drive it, it runs great! No problems anymore on acceleration, no sputtering at hi RPM's, good power.

So I'm not sure why I get the vacuum flux. Any thoughts?

Also my peddle sometimes sticks. If I hit it hard and release the peddle will return to full up position. Closing the throttle and idling at target RPM's. However if I lightly press the peddle and remove my foot the peddle will stay down and the engine idles fast, 1300 rpm's, because the throttle is not in its closed position. Any ideas? WD-40 on the linkage?

Thanks
 
There's always a bigger return spring. Pull the linkage off the carb and throttle the carb to see if is sticks with no linkage. Make sure that the linkage is adjusted so that the carb CAN fully close.
 
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