1995 1FZ-F ....Slight Bucking and Hesitation At Low Throttle (1 Viewer)

[ASO544]

It was recommended to move this to the 60 forum as my 1Fz-F has a carburetor and more experience with this set up over here.

Just getting some miles on this new to me Series 70 JKZ73 and I have noticed I have a low throttle bucking and somewhat hesitant jumpy throttle response when initially taking off. The vehicle starts up fine and idles fine. I have to use a lot of clutch and throttle to get it rolling good when taking off, and then when I shift into 2nd, I have to do the same thing with the clutch and throttle. After driving it for 15-20 minutes it’s starts to get a little better but never perfect. Once it’s at cruising rpm it runs fine. It also hesitate initially if you floor the gas but then cleans up and takes off.

This vehicle came for Bogota which is at 9K above see level and the carb hasn’t been adjusted now that’s it’s a sea level here in Florida. Think that might be my starting point ?

From the looks of the engine, the fuel filter, dizzy, wires, ( possibly plugs) and fuel pump seem to be reasonably new. I leaning toward maybe needing a slight carb adjustment.

 

[g-man]

Sounds like a vacuum leak. Did you recently put a new carb on? Did you recently replace the intake/exhaust manifold gasket? What if anything did you change to make it act like this? Look at all your vacuum lines make sure none are loose. Spray carb cleaner around the base of the carb...carb to intake seal, intake to head seal. Maybe get under the vehicle and spray upward to check for an intake leak again between the head and the intake. If there is a crack letting too much air into the carb the engine will instantly rev up.

 

[Seth S]

The 1FZ-F is an aluminum cylinder head on a cast iron block with a cross flow design so you have an aluminum intake on one side and most likely a cast iron manifold on the other side. So....this is good because you are less likely to have the manifold leak problems that we see on older 2F engines.

You could still have a leaking vacuum line, a bad intake manifold gasket, or a bad base gasket for the carburetor.

A carb set for sea level that drives to 9000 feet elevation with no adjustment will become richer as the air gets thinner.

A carb dialed in for 9000 feet elevation that drives to sea level should get leaner as the air gets thicker (more air per volume). I don't know how the 1FZ-F compensates for either elevation or ignition advance.

So either rejetting or adjusting the carb as you guessed and also checking your base timing would probably be good places to start as well as verifying you dont have any vacuum leaks.

 

[bigboiimigel]

When my 2F used to buck I checked the timing and fixed all the vac leaks. My timing was at 14* base so I backed it off to 9*

 

[OSS]

Bucking (in my experience) when pressing down on the gas pedal is fuel starvation (running too lean).

Hesitation (in my experience) when first pushing down on the gas pedal often is caused by a malfunctioning accelerator pump in the carb. That too is a intermittent source of fuel starvation.

If an engine is dialed in to run good at 9000 ft, it'll run too lean at sea level and the timing will be too advanced.

 

[2mbb]

I think below is the vacuum piping diagram for your engine (1FZF). I originally thought the bleed ports on your HAC (high altitude compensation) Valve were inproperly plugged, but the diagram shows the two ports are plugged, so I guess it is as it should be. The fact you have an HAC valve may mean the previous owner was just "running it" with no modifications.

carburetor jets seem to still be available from Toyota, so you might try to replace yours assuming they really did something like change the jets.

 

[ASO544]

So with the HAC being properly plugged, it actually still in use in the system? I was concerned might be effecting my carb at sea level if it’s used to help carbs at higher altitudes Or if it’s actually faulty. Any reason to not just remove all the hoses and plug the ports to completely bypass the HAC?

 

[ASO544]

Little update.....

Did the Lean Drop Method today and got really decent results . I did this with the air cleaner assy hooked up and truck engine warmed up.

1. I zeroed down my idle mixture, then opened it up to 2 complete turns ( counter clockwise).

2. I hooked up my vacuum gauge to the port the runs the brake booster....

3. started up the truck and was getting about 18-19 on the vaccum.

4. Did about 1/2 turn counter clockwise ( rich ) and it moved up to 21-22 on vaccum. That was as high as it would go.

5. Then used white idle adjust to get at 650ish. Rev engine few times to ensure it returned to that same idle.

I took her for a ride and all the bucking was gone but had some hesitation / stumble with throttle when heavy on the pedal.

I stopped and moved the idle mixture 1/4 turn in ( lean) and adjust idle and went off again. It was worse. I stopped and went back a 1/4 and the another 1/4 ( rich ) and adjusted idle. It got better but still that heavy throttle hesitation/ stumble.... although a hair less

I repeated process 2 more times and got it where it runs the best I’ve had it.You can floor it through 1st with no issues . Once you hit 2nd - 5th, WOT will hesitate and stumble. If I back off throttle just a hair it cleans up and off she goes!!!

the good news is the bucking and jumping seems to be gone. Just have a little more to clean up on the upper side of the acceleration. To get rid of the heavy throttle hesitation / stumble.

this site has great info and help !!

 

[haryv]

It was recommended to move this to the 60 forum as my 1Fz-F has a carburetor and more experience with this set up over here.

Just getting some miles on this new to me Series 70 JKZ73 and I have noticed I have a low throttle bucking and somewhat hesitant jumpy throttle response when initially taking off. The vehicle starts up fine and idles fine. I have to use a lot of clutch and throttle to get it rolling good when taking off, and then when I shift into 2nd, I have to do the same thing with the clutch and throttle. After driving it for 15-20 minutes it’s starts to get a little better but never perfect. Once it’s at cruising rpm it runs fine. It also hesitate initially if you floor the gas but then cleans up and takes off.

This vehicle came for Bogota which is at 9K above see level and the carb hasn’t been adjusted now that’s it’s a sea level here in Florida. Think that might be my starting point ?

From the looks of the engine, the fuel filter, dizzy, wires, ( possibly plugs) and fuel pump seem to be reasonably new. I leaning toward maybe needing a slight carb adjustment.

Check the accelerator pump. Grab a flashlight and look down the Venturi of the carburetor and push the throttle body forward. You should see to Jets of fuel in being injected I'll buy the accelerator pump. It's a very common problem on carbureted vehicles. If you have a throttle body sensor like a TPS sensor that's also a very common cause of a lack of fuel but it doesn't necessarily happen at idle it can be at higher speeds jelly where the wiper arm spends 80% of his time on the carbon track which is variable resistance carbon track Aloha wear a where spot into it and send the wrong postage to the ECU which will reduce the fuel dwell frequency into the cylinder causing fuel starvation

 

[ASO544]

I went on and pulled my carburetor today to send it off to Jim C at TLC Performance to have it rebuilt. I got a temporary one to hold me over till my OEM one gets back. What I did find once I got mine off was a mess. It appeared the metal gaskets attached to the insulator had some what deteriorated and had some gasket maker on them to get a solid bond to the intake. Now most of the LCs from Colombia just use water in the radiator and you can see the rust. I had to flush out my system, and add antifreeze....I also have new radiator and water pump I’m going to install.

im going to order a new insulator which has the metal gaskets attached as one piece. I did try to mount my temporary carb with the current insulator and gaskets but I was getting a coolant leak from the Under the isolator. No doubt these gaskets have seen better days and not sure if the intake surface has a marred Issue as there was gasket maker between the insulator and the intake.

I did clean it off as best as I could.

Even when I get a new insulator/gasket set.....is there something I should put under the gasket to help insure a solid seal???


now my temporary carb is of course a China built one.....guess I’ll see if it was a waste of money. Tim C said his backlog of rebuilds may take 5-8 weeks so I wanted something to get me around if possible.

It seems to be decently built. Once I get the new insolator /gaskets I’ll try to install it again and see how it perform. On my initial install, it started right up and the choke was working properly but I did get a couple of times the throttle was sticking when I reved it up. So there may be a few bugs to work out.

just had a few questions....

1. idle Adjustment
2. idle mixture
3. ???????
4. Hose???? This was not on my OEM carb...it was plugged

is the last screw pictured the fast idle ( choke speed set screw) ???

Thanks for any help or guidance.
aso544

 

[snapdragon]

3 is fast idle, only works on cold days and only idles up a few seconds. well that is what I noticed on mine.
Ja, I have no idea about that pipe, maybe for auto transmission?

 

[snapdragon]

How did the China carb run?

 

[Seth S]

I'm just going to toss this idea into the fray...but I bet Holley Sniper would be great addition to a carb'd 1FZFE

 

[FJ40Jim]

#3 is AC idle up.

The weird hose is going from venturi vacuum to a vent port in the air horn. That's... Weird.

The open vac fitting on the air horn is HAC. Can be capped below 4k ft.

ASO544's OE carb is going back together now. It was missing a jet, 2 springs, an emulsifier sleeve and a critical O-ring. Surprisingly, it still ran.

 

[snapdragon]

I'm just going to toss this idea into the fray...but I bet Holley Sniper would be great addition to a carb'd 1FZFE

Had a friend who replaced the OEM carb on his 1fz-f with a holly, or another aftermarket, cant remember what.
Was a complete mess, it would cut out on steep angles and struggled to start again, the original ones work well at angles.
Because of the age of the carbs they are getting harder to find replacement parts and knowledgeable people to fix them, just familiarize yourself with the repair manual and keep your eye out for replacement parts, I find to be the best way to keep her on the road.

 

[Seth S]

Had a friend who replaced the OEM carb on his 1fz-f with a holly, or another aftermarket, cant remember what.
Was a complete mess, it would cut out on steep angles and struggled to start again, the original ones work well at angles.
Because of the age of the carbs they are getting harder to find replacement parts and knowledgeable people to fix them, just familiarize yourself with the repair manual and keep your eye out for replacement parts, I find to be the best way to keep her on the road.

The Holley Sniper is not a carb. It’s a standalone efi unit that bolts on in place of the stock carb. You have to install an electric fuel pump and an O2 sensor in the exhaust...it comes with the O2. The unit self programs but does allow you to fine tune. Very popular with Fj60 owners and much improvement over the carb.

 

[ASO544]

The China carb works great. I had to adjust the AC idle up with directions from JimC but overall it has run well and tied me over till I get my carb back from Jim.

 

[snapdragon]

The Holley Sniper is not a carb. It’s a standalone efi unit that bolts on in place of the stock carb. You have to install an electric fuel pump and an O2 sensor in the exhaust...it comes with the O2. The unit self programs but does allow you to fine tune. Very popular with Fj60 owners and much improvement over the carb.

Oh ok, I haven't seen one here in South Africa, how reliable are they?

 

[snapdragon]

The China carb works great. I had to adjust the AC idle up with directions from JimC but overall it has run well and tied me over till I get my carb back from Jim.

Good to know, thank you

 

[Seth S]

Oh ok, I haven't seen one here in South Africa, how reliable are they?

So far they have proven to be reliable and improve hot and cold starting and overall drivability

Sniper EFI 2300 2BBL

www.holley.com