Symptoms of a cracked intake (1 Viewer)

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HemiAlex

Long live the 2F
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My truck started running poorly a few weeks ago. It had a fit and barely idled at lunch, I drove through the miss and then it started being normal again for a few weeks. In the last two days I really thought I got a bad tank of fuel. Found good gas, put some MMO in the tank and it seemed to get better. Then, the following morning it was acting up.

I can’t tip in off idle without the truck bucking and it feels down on power. Then randomly it will drive normal and pull solidly throughout the rpm range.

I’m caught up on all the maintenance, it’s got 20 in Hg of vacuum at idle, and it’s dead stable. The initial pump shot on the carb is working and there’s fuel in the bowl.

I’m starting to wonder if I’m chasing a temperature dependent vacuum leak. This intake has cracked before and i had it repaired when I redid the top end.

What have you all had happen when there was a confirmed intake crack found? This seems too intermittent to be a fuel or a spark related issue. The truck is desmogged so that’s not an issue that’s making things worse. I just think i need to keep chasing loose bolts and vacuum leaks before I do any parts swapping.
 
What kind of condition ( centrifugal advance, the little grommet that crumbles, allowing too much advance, free movement of the “point plate”, vacuum advance unit ) is your large cap distributor in?
 
What kind of condition ( centrifugal advance, the little grommet that crumbles, allowing too much advance, free movement of the “point plate”, vacuum advance unit ) is your large cap distributor in?
Pretty sure he had it rebuilt and curved by Jim so should be in good condition.
 
When you say it has 20, are you saying that because you put a gauge on it yesterday to verify that?
Could you run a vac gauge now and into the cab or are you already setup that way?
 
Battery cables are tight? None of the spark plugs show any bad signs? Intake is tight to the head?

Are you still running EGR? These symptoms could be related to a plugged or sticking EGR valve.
 
At 20 inHg stable vacuum, there is no vacuum leak. Also a vacuum leak is most detrimental at idle and less significant as the RPMs increase. You can't really "feel" a minor vacuum leak when cruising.
My guess: it's not a vacuum leak issue.

If a 2F idles fine but hesitates once the gas pedal is pressed down a bit- that's often a fuel delivery problem. Carburetor/fuel filter

Maybe there's some crap in the carb.
 
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That does sound like symptoms I had when my EGR was sticking. I hit the egr with a hammer while idling to break up the carbon. Then the carbon crud found its way to the bottom of the air cleaner. This resolved it.

Isn't 20 inHg a good healthy number for a 2f?

Make sure your fuel cut solenoid is clicking.
 
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Hey Alex, any chance it could be some garbage in your fuel filter? Only time I’ve been stranded on the side of the road (about 12 years ago) in a 60 was due to the filter. Similar symptoms you described as well. I’ve since learned the value of keeping spares :). If not hopefully you resolve this soon.
 
City Racer carb... how long have you been running it? Is it possible the o-ring at the FCS (fuel cut, idle cut, whatever it’s called) degraded at this point? Fuel at the sight window good?
 
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City Racer carb... how long have you been running it? Is it possible the o-ring at the FCS (fuel cut, idle cut, whatever it’s called) degraded at this point? Fuel at the sight window good?

Funny you mention. i just recently looked at a City Racer/Fuji carb and the fuel cut solenoid o-ring was not what I would call ideal for being new, curious if this is the case often
 
Funny you mention. i just recently looked at a City Racer/Fuji carb and the fuel cut solenoid o-ring was not what I would call ideal for being new, curious if this is the case often
I’ll be pulling mine off the truck soon to pull the head and I’ll be sure to take mine ICS out and check it.
Your not swapping to it are you Nate? Or just short term to try it out? Your fully smogged right?
 
What kind of condition ( centrifugal advance, the little grommet that crumbles, allowing too much advance, free movement of the “point plate”, vacuum advance unit ) is your large cap distributor in?

Distributor was a good core the was rebuilt by JimC and recurved. Distributor cap and rotor are 2016. I've driven with a broken vacuum advance diaphragm and it didn't cause these problems. It was slow-er than normal but not a drivability issue.

When you say it has 20, are you saying that because you put a gauge on it yesterday to verify that?
Could you run a vac gauge now and into the cab or are you already setup that way?

I put a large gauge on it and checked it in the driveway. No real movement in the gauge to indicate valves or anything RPM related. Actually higher than I expected it to be, but I've got a lot of initial advance in the motor right now. Maybe 12-14*

Battery cables are tight? None of the spark plugs show any bad signs? Intake is tight to the head?

I've got the Forerunner cables, plugs are about 3 weeks old and look good. Intake was resealed in December and I used OEM gaskets throughout. I did forget to put intake/exhaust block off plate in last time, so that is why cracking is a concern. This intake was cracked when I bought the truck and I had it fixed when I did the head 30,000 miles ago.


At 20 inHg stable vacuum, there is no vacuum leak. Also a vacuum leak is most detrimental at idle and less significant as the RPMs increase. You can't really "feel" a minor vacuum leak when cruising.
My guess: it's not a vacuum leak issue.

If a 2F idles fine but hesitates once the gas pedal is pressed down a bit- that's often a fuel delivery problem. Carburetor/fuel filter

Maybe there's some crap in the carb.

I know there are vacuum leaks that are small, but I've got a strong signal and I think I've just tuned around them for my idle. I thought that the biggest deal could heating and cooling of a cracked aluminum intake manifold causing issues based on load and temperature.

Fuel pump is a recent piece from last year, fuel filters get replaced every 3,000 miles because my tank is old. Replaced in 1991. I've got solid fuel in the bowl at idle, the pump shot works when the truck is revved and I've got no issues starting it.


That does sound like symptoms I had when my EGR was sticking. I hit the egr with a hammer while idling to break up the carbon. Then the carbon crud found its way to the bottom of the air cleaner. This resolved it.

Isn't 20 inHg a good healthy number for a 2f?

Make sure your fuel cut solenoid is clicking.


I'm completely desmogged. No EGR left. The motor is running great and has great numbers for a 312,000 mile short block with some refreshing.


Hey Alex, any chance it could be some garbage in your fuel filter? Only time I’ve been stranded on the side of the road (about 12 years ago) in a 60 was due to the filter. Similar symptoms you described as well. I’ve since learned the value of keeping spares :). If not hopefully you resolve this soon.

Fuel filter looks clean, but I'm throwing another filter at it tonight as well as my back up carb. I want to narrow down if my tank is just contaminating past the filter and gumming up the carb. It ran great for me and @gregnash had it on his truck for a while. I'm not going to do anything but bolt it on and see if that fixes the problem. I hate to be the guy to blame the carb when I've not done my due process.

City Racer carb... how long have you been running it? Is it possible the o-ring at the FCS (fuel cut, idle cut, whatever it’s called) degraded at this point? Fuel at the sight window good?

I put in on in Jan 2018. FCS clicks and works right. Fuel at the window is present while running and the truck keeps fuel for several days in the bowl.



I borrowed a smoke machine, I'm going to fog it tonight and see what I find. Then I'll replace the carburetor.

I'm worried that it's going to lead to a fuel tank being the issue. That would mean that I have three options:

1. Pull what I've got, try to get it restored. Some have warned against this because I may end up stranded if something goes wrong or the tank is overly rusty or thin.

2. Find a good used tank. Restore if it needs work.

3. Buy a LRA tank. A ton of money, but I gain capacity and I can have a module installed for EFI later down the line.

I want to do the last option, but Ive been in a very happy place with the truck being very fault free for 35,000 miles of daily driving that I don't want to spend money that isn't needed. I've know this could be a place I get stuck at for a while. I've already got a tire carrier bumper so a big tank would be a hassle free ordeal.
 
I’ll be pulling mine off the truck soon to pull the head and I’ll be sure to take mine ICS out and check it.
Your not swapping to it are you Nate? Or just short term to try it out? Your fully smogged right?

I’m not, no. Was doing a desmog locally for someone and he brought in a new Fuji from city racer. Didn’t see anything wrong other than solenoid o ring, he’s running it currently and very smooth with the oem solenoid and o-ring to make it easy to ground temporarily while I rebuild his OEM carb, he’d like to maintain the HAC and fuel cut solenoid functionality since it worked.

I’m currently full desmog with oem carb and runs great. I was bouncing between desmog and full smog between tests but now staying desmogged.
 
Find a good used tank.
Years ago when I had my first truck I bought a used tank from CruiserParts. Granted their rep isn’t so good, it came and was in great shape. I paid maybe $250 but that was back 10ish years ago. What does your filter look like now?
 
Years ago when I had my first truck I bought a used tank from CruiserParts. Granted their rep isn’t so good, it came and was in great shape. I paid maybe $250 but that was back 10ish years ago. What does your filter look like now?

The filter looks pretty clean. I’m changing it tomorrow anyway.

I did some work this evening, and I swapped to my oem aisan carb. Then I swapped it back off because it looks like the accelerator pump is dead. No fuel was flowing through it when the throttle was bumped at idle.

So I tore down the city racer half way and put a few cans of carb cleaner through it. Nothing was scary dirty but I did see very fine silt in a few places.

I let it get up to temp and drove it around. It feels about 95% Better. It’s not bucking and stumbling any longer, but it does feel a little sloppy from primary to secondary.

I’m going to get a bucket of carb cleaner and find an ultrasonic cleaner this weekend and just soak the whole thing.


This means I need to plan the next steps to make this right. I’ll be thinking hard about a jimc carb, dropping and fixing the tank and whatever else it takes.

I bought a 40 micron in-line filter to put between the fuel pump and the carb to catch some of the other debris. That’s the first step.
 
Did u do a paper clip test to see if the 2ndary open is working?
 
Did u do a paper clip test to see if the 2ndary open is working?
Haven’t got that far into it yet. I’ll check tomorrow. Thanks for the idea.
 
find an ultrasonic cleaner this weekend
In a pinch if you have a palm sander, you can put the carb body into the can of cleaner and strap the sander to the tightly closed lid, then secure that to a table or chair and let it go to town for a hour or so. Preferably in a garage behind a closed door as it is noisy as heck.
I pulled my city racer off my truck yesterday and checked the condition of the o-ring on the FCS and it looks pretty good. No obvious cracking. Maybe your friend got a used one that was sitting around, @mattressking?

FB23D3AF-8BC2-46D0-A5D3-B39C99D04779.jpeg
 
In a pinch if you have a palm sander, you can put the carb body into the can of cleaner and strap the sander to the tightly closed lid, then secure that to a table or chair and let it go to town for a hour or so. Preferably in a garage behind a closed door as it is noisy as heck.
I pulled my city racer off my truck yesterday and checked the condition of the o-ring on the FCS and it looks pretty good. No obvious cracking. Maybe your friend got a used one that was sitting around, @mattressking?

View attachment 1978476

Yea that one looks the way it should, I was thankful I had oem spares floating around for this.
 

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