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Help! Dies At Low Rpm


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#1
Petros

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Hi All,

New to this forum but not to first gen CRXs. We have a '86 CRX with 1.5L and 3 barrel carb, all bone stock. I had recently replaced the long block with a rebuilt one, due to it being badly overheated. I swapped all the same external parts and accessories onto the new engine and got it running. I had to fix a few vacuum leaks I discovered in the lines.

Now it starts cold and runs great, it can be driven a few blocks, but when it warms up it cuts out and dies at low RPM. After it reaches operating temperature it refuses to stay running. Acts like it has no fuel because I can get it to run briefly if I spray starting fluid down the carb. I see no visible problems.

The auto choke starts out closed and slowly opens as it warms. It does not appear to open all the way, so I wired it open to see if that made any difference. It just ran crappy, so I took the wire off. I think this was how the choke worked before I swaped the long block, and I do not think that having it open 3/4 of the way will prevent it from running (or will it?).

Does anyone know if there is anything else that can cause this behavior. the fuel cut-off solenoid perhaps? Any other parts or systems to check? I even have a spare carb I can rebuild and install, but the old one was working fine before the engine swap.

I really need to get this car running reliably.

Thanks for any help.


#2
EuphoricBlue

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It's possible you accidentally turned the idle speed adjuster down while working on it and didn't notice it. Try turning up the idle speed while it is running cold, wait for it to warm up, and see if you can bring the idle back down to normal levels when it's warm.

If you can't get it to idle steady at normal RPMs, the first thing I'd do is pull the timing gear cover and double check the cam timing. It is easy to install these belts one tooth off.
Next guess would be that you haven't yet tracked down all the vacuum leaks.

Welcome to the boards.

#3
Bubba

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Is the carb's fuel level ok when you look at the sight glass on the driver's side of the carb (it should be in the dead center)?

There is a fuel cut off solenoid- it has the 2 wire connector. Make sure it is getting 12 volts to one wire when the ignition is on and that the other wire is a good ground. If the solenoid is bad, the car will still run OK as long as you give keep the gas pedal pressed down some.

Does the accelerator pump work after it dies? (take off the air cleaner and look for gas squirting down into the carb throat every time you open the throttle).

Double check your ignition timing and be sure that the vacuum advance diaphragm isn't busted (especially the inner one).


#4
Petros

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Thanks for the relpys.

I doubt it is the idle speed, I turned that in and out, left it at a high idle position just to make sure. And I doubled checked the cam timing (I have rebuilt similar engines numerous times, I always double check the valve timing by turning the engine over at the crank by hand several times, than double check my TDC marks).

Yes, when I have the aircleaner off and I pump the throttle I can see a stream of fuel going down the barrel.

I do not think it is a vacuum leak, I sprayed carb cleaner all over it when it was running and tracked down every leak. In fact I was wondering if it was running with the vac leaks before, and now that they are fixed it is giving me problems. Could it be running too rich?

Timing would not make it act this way, nor the vac advance diaphragm. I do not know if it is good or not, but typically if they are failed it will just run fine without the vac advance (all the vac advance does is advance the timing at part throttle conditions to improve economy at hwy speeds).

The fuel cut-off solenoid appears to be a good candidate to check.

Any other ideas?

Edited by Petros, 08 August 2011 - 02:02 PM.


#5
Bubba

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A busted dizzy vac advance would act as a sizable vacuum leak.

You stated that it ran bad when you wired the choke all of the way open- this would indicate that it is running too lean and a vac leak could cause this.

Is the fuel level in the carb OK?

#6
Petros

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I did not verify the float level, I assumed it was okay since there was fuel to the carb. the location of the sight glass is difficult to see buried under all the vac lines and such.

Which brings up another observation, when I had the fuel line off the fuel pump to change it out as a test, the fuel dribbled out of the line. It did not occur to me than, but the tank is lower than the fuel pump and that should not happen with the fuel tank low in the back, unless there is excessive pressure in the fuel tank. With all of the infamous heat in Texas right now, is it possible an improperly or faulty tank vent could over pressure the fuel system and cause flooding?

What should I check to see if the tank vents properly, what needs to be replaced or tested?

#7
EuphoricBlue

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QUOTE (Petros @ Aug 10 2011, 10:53 PM) <{POST_SNAPBACK}>
I did not verify the float level, I assumed it was okay since there was fuel to the carb. the location of the sight glass is difficult to see buried under all the vac lines and such.

Which brings up another observation, when I had the fuel line off the fuel pump to change it out as a test, the fuel dribbled out of the line. It did not occur to me than, but the tank is lower than the fuel pump and that should not happen with the fuel tank low in the back, unless there is excessive pressure in the fuel tank. With all of the infamous heat in Texas right now, is it possible an improperly or faulty tank vent could over pressure the fuel system and cause flooding?

What should I check to see if the tank vents properly, what needs to be replaced or tested?


Some fuel will dribble out of the line, there is a check valve that keeps the line from emptying back into the tank when the engine is off. So if the line is unplugged, and is below the where it was, at the very least the fuel in the line would drain, if it's below the pump, the fuel in the pump would drain too. It is normal for gas tanks to build pressure, I highly doubt that's your issue. And if it was, your symptom would be fuel leaks from the charcoal canister or carburetor and very rich mixture due to flooded float bowl.


How you described vacuum advance is not how it works on our cars. The vacuum advance is connected to manifold vacuum, and is activated during high vacuum conditions (idle, steady cruise) When accelerating vacuum drops to near zero and the advance is released.

If you hook the line up to a ported vacuum source your idle advance will be way too low. You can then advance the timing to get your idle advance back, but your total advance at some points will be way too high as it will combine your static advance+vacuum advance+centrifugal advance. This can cause issues of its own.


Double checking the vacuum advance. Make sure the diaphragm is not leaking. If you have an inner and outer pot, make sure the inner (closest to distributor) port is connected directly to manifold vacuum (the vacuum tree on the back of the manifold) With the vacuum advance hooked up, and the engine warmed up, set timing so that the red mark lines up with the timing tab (insure your timing light is set to 0 advance, if it is adjustable). Your timing should now be properly set.

If you have a dual port vacuum advance, the upper port is an additional advance for cold operation. When active, it will provide an extra 4 deg advance. So long as neither the pot nor control circuit are causing a vacuum leak, this port can be ignored as it will not affect anything enough to worry about.

#8
Petros

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The distributor has two vacuum ports. Both are connect I believe to the correct port.

I do not understand what you mean by I did not correctly describe how the vac advance works; when at cruise speeds (part throttle) as you describe, the vacuum is high and it advances the timing. this has the effect if improving fuel economy at part throttle conditions since the flame front moves slower through the combustion chamber at part throttle (high manifold vacuum) conditions. The reason to advance the timing make the peak combustion pressures occur more optimally in the cycle, improving economy a bit. If it is not working it only means you miss out on the part throttle advance, it will not prevent it from running. Unless of course if it is so badly ruptured that it acts like a large vacuum leak.

All vacuum dances work this way and many cars from the 50's 60's and even the early 70's had no vacuum advance at all. I have owned a number of them. the other vacuum port on most vacuum advances from the 80's was to retard the timing during certain driving conditions to reduce emissions, and it too does not prevent it from running if it is not connected.

And when I meant fuel was leaking from the fuel line, it was not just a few drips. It continued to flow out from the supply line coming out of the fire wall and would not stop until I put a plug in the line. It was acting like the tank had pressure in it. The tank is supposed to be vented through the carbon canister to atmospheric pressure, it is blocked it will build pressure since the cap acts like a one way valve, allow air in to vent the tank, but not out.

#9
Bubba

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It is very normal for the tank to build some pressure from gasoline evaporating (this causes the hiss when the gas cap is removed when you fill up). This pressure pushes the gas out of the gas line even when the engine is off.

I always seem to make the mistake of not removing the gas cap when I change a fuel filter- what you describe happens every time (even on may fuel injected vehicles)- fuel flows from a line higher than the tank and keeps flowing until I run around and remove the gas cap/vent the tank, then it stops immediately.

If one of the dizzy advance diaphragms is busted, then it would cause a vac leak which may result in the symptoms that you described (running lean). If you do not have a vac pump to test them, you could suck on each fitting to test them (usually the inner diaphragm goes bad) or you could remove both vac hoses temporarily and plug them then see how it runs.

If you remove the air cleaner, you will be able to see the sight glass on the driver's side of the carb without too much trouble- you may need to push a couple of hoses aside. There are some good pics of the bare carb in the devac thread of the carbs section of this website.

#10
EuphoricBlue

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QUOTE (Petros @ Aug 11 2011, 11:04 AM) <{POST_SNAPBACK}>
I do not understand what you mean by I did not correctly describe how the vac advance works;


QUOTE (Petros @ Aug 8 2011, 11:59 AM) <{POST_SNAPBACK}>
all the vac advance does is advance the timing at part throttle conditions


This is what I'm talking about. It's not just part throttle conditions. On our cars vacuum advance is fully engaged at idle.
But regardless if it works or not, so long as the timing is at the red mark at idle you should be idling fine (unless there are leaks, or improper mixture.)

If your advance pot is ruptured enough not to work, it is ruptured enough to cause a vacuum leak that will effect idle.

All "modern" fuel tanks build pressure and vacuum, it is normal. It is why your filler cap is tested to make sure it holds pressure where emissions tests are standard.
There is a valve that vents the tank to the charcoal canister if it exceeds a set pressure, and a fresh air line if it builds too much vacuum.

Since you seem to be sure it's not in the advance or vacuum leaks, start messing with your fuel mixture since it's the only thing left and your description with the choke points to an overly lean mixture.

#11
Petros

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QUOTE (EuphoricBlue @ Aug 11 2011, 10:35 PM) <{POST_SNAPBACK}>
Since you seem to be sure it's not in the advance or vacuum leaks, start messing with your fuel mixture since it's the only thing left and your description with the choke points to an overly lean mixture.


not certain it is not a vacuum leak yet, but reasonably sure it is not, I will keep checking for that, and the vac advance. by passing it is a simple enough test.

Not to be a PIA, but how do I "mess" with the fuel mixture on this car? From what I recall there is no easy mixture adjustment, the carb is sealed I thought.

Could a bad fuel cut-off solenoid cause this behavior?


#12
Bubba

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There is a low speed mixture adjustment screw on the base of the back of the carb, but it is covered with a tiny plug type seal that would be hard to remove without removing the whole carb. The high speed mixture is not adjustable.

One thing that would affect mixture greatly is the fuel level in the carb. I think you should verify the level of gas in the carb shortly after the engine dies and refuses to restart. It should only take 5 minutes to remove the air cleaner and check the sight glass. A low fuel level in the carb would tell you that you have an issue with the fuel pump, clogged filters or even a clogged intake in the gas tank.

Even if the fuel cut off solenoid is bad, the car will still start and run OK as long as you give keep the gas pedal pressed down some. One time I accidentally pulled one wire out of that connector and was still able to drive the car a few miles to get it home. It was very annoying because it would try to die at every stop sign unless I feathered the throttle. I plugged the wire back in and all was well.

#13
Petros

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Thanks for the reply.

You know now that you mention it, last year my daughter ran the car out of gas just short of the gas station. Someone helped her push it to the pump and she filled it up. just a few miles later it stalled out and died, and would not restart. She had it towed home, and the next day it started and ran fine. I told her it likely had some crud in the tank and it plugged the rear filter (which I had replaced for her just six months before). We put a new one in and did not have a problem since.

But that might mean the intake line is plugged with crud from the tank. I put a new filter in next to the carb, and tried swamping fuel pumps with a spare used one, no change. It seems odd however that it would be starved of fuel only after warms up, it needs more fuel when it is cold.

I will check the float level next time I get a look at it. I also have a spare carb I might rebuild and just swap out. I will also check the function of the fuel cut off solenoid.

#14
Petros

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If I completely replace the carb with another one (that checks out), what are the chances that will fix what ever is causing the stalling out?

That would mean working needle valve in the float bowl, new fuel cut-off solenoid, clean inteiror ports, jets and passageways, etc.

Or could the problem be caused by something outside the carb?

#15
Bubba

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Yes- even with a new carb you might have the same issue if it is being caused by a bad fuel pump, clogged filters or even a clogged intake in the gas tank.

Checking the sight glass when the car is acting up would be pretty easy (5 minutes of work) compared to changing out the carb.