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Discussion Starter #1 (Edited)
Hello, I have a 1988 Carbureted Prelude S. After several minutes of driving (around 12 miles) at high speed (about 75mph) the car will begin to hesitate(more like a buck) and gradually lose power until it stalls. When it happens the bucking starts out minor, then gets progressive worse. Once you shut it down it will run on for a few seconds. I have a spare carburetor and put it on, same problem. I've checked the fuel pump also, it is also fine. So, I'm thinking that its some sort of spark or timing issue. Does anyone know what could be causing this or something like this?
 

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*disclaimer: I know nothing about carbeurators.

I have one similar experience in my first car, which was a carb'd Accord. The car would do this thing just like you described, start up fine after a bit of a rest, and then do it again a little further down the road.

It was very cold out (-20 F) and I think there may have been water in the fuel, possibly freezing up in the carbs. This theory is based strictly on the temperature, the fact that I had just bought the car, and the fact that the problem went away after topping up the fuel, never to be seen again.

So, just based on my one experience I would pose you these questions. Is your weather cold right now? And is the tank completely full / do you trust the gas station you last filled up at? Hey, maybe it's worth the thought.

Beyond that all I can say is hopefully TripleLude swings by; he's kinda the forum's carb guru. The fact that you've already swapped carbs and checked the pump indicates that you're way more mechanical than I was when I owned that Accord. It also implies the problem has probably lasted longer than one tank of gas. :lol:

*edit: Also, your dieseling tells me I'm probably way off track with this idea.
 

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I would first put new plugs in and gap them correctly before you put them in. I would also consider inspecting the cap and rotor and just replace if you like. Lastly I would time it with a timing light. If you suspect bad fuel I think there should be a drain plug in the bottom side of the tank on the driver's side usdm. I know there is one on the fuel injected engines for the 3rd gen but they have a different tank that is baffled. What kind of transmission do you have auto or manual?
 

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I agree with Andrew. I've owned many carb'd cars in my life, including a couple of Prelude S models. One car in particular was really affected by moisture in the fuel. The problem went away once I started dumping in a bottle of Heet fuel system drier into the tank at each fill-up. This was only an issue for me during the cold wet months of winter. It never happened during warm weather.

joshuah459, does the problem go away after shutting it down for a couple minutes and restarting the engine? This was what I would observe, tell me if it's what you're seeing...
Car would run fine for the first 10 minutes or so, then would start to lose power. Continuing on the car would run worse and worse until it eventually died. After letting it sit for about a minute I could then start it and it would run fine for the rest of the trip, usually about 15 more minutes. This would repeat until the weather warmed up above around 45 degrees F. If this is what you're seeing then try adding a bottle of Heet to your fuel tank.
 

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...1988 Carbureted Prelude S. After several minutes of driving (around 12 miles) at high speed (about 75mph) the car will begin to hesitate(more like a buck) and gradually lose power until it stalls. When it happens the bucking starts out minor, then gets progressive worse....
This could be a partially blocked fuel filter; flowing enough fuel to keep the engine going at lower speeds, but not sufficient at higher speeds. As the carburettor float bowls empty, there will be gradually less fuel available so the problem will become more pronounced. If you back off and slow down, does the engine recover? When the engine does stop, if you give the fuel pump a few seconds to refill the float bowls, does the engine start straight back up?

Fuel filters
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf100/6-52.pdf


...Once you shut it down it will run on for a few seconds...
Carbon build up in the cylinders can cause your engine to run on (or diesel) after the ignition has been turned off. The flakes of carbon in the cylinders get very hot and can glow hot enough to ignite any fuel in the cylinder.

The traditional remedy is to take the cylinder head off and scrape the carbon deposits from the top of each piston and the inside of each combustion chamber; this is obviously time consuming, involves a lot of labour and new gaskets. However, there is a much easier method that simply involves squirting some water into the inlet whilst the engine is running. You can simply pour water a drop at a time into the inlet, but you might find the job easier using some sort of trigger spray; these two approaches are shown in the videos below:

https://www.youtube.com/watch?v=KFtp_jmLF3k

https://www.youtube.com/watch?v=eZDISp2pdSo

Because it is so quick and easy, I'd be tempted to give the water remedy a go before stripping the engine.
 

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From what I have seen parts wise I think the carb may have two fuel filters. I pretty sure anyway that it has a small plastic one at the tank output.
 

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From what I have seen parts wise I think the carb may have two fuel filters.
Looking at the shop manual, I think you're correct.

The front filter appears to be in the engine bay between the left shock top mounting point and the brake fluid reservoir; should be pretty easy to spot.

The diagramme showing the rear filter isn't so obvious though. I'm guessing that the rear filter is hung on the left side of the fuel tank, but if anyone reading this knows for sure, please chime in.
 

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Confirmed. There is a filter mounted to the fuel tank. Remove the left rear tire and you can easily access it to replace it.

I'm smacking myself in the forehead for not remembering the problem I had with this filter. A previous owner had replaced the fuel filter in the engine bay, but didn't replace the one mounted to the fuel tank. I was only really seeing problems when going uphill though. On flat roads the thing ran fine.
 

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...Car would run fine for the first 10 minutes or so, then would start to lose power. Continuing on the car would run worse and worse until it eventually died. After letting it sit for about a minute I could then start it...
You could be onto something with carb' icing. I had a Kwacker GPZ550 that died every 10 miles in freezing fog, simply because the carb's iced up; only did it when the weather was cold and damp. But, when it did, the only solution was to wait for heat soak from the engine to thaw the carb's out again. The problem cost me a night of passion; girl invited back to her house, she was in her car, I followed on my GPZ but the carb's iced up and because I dropped out of sight she thought I'd changed my mind. :wzbigcry:
 

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Discussion Starter #10
*disclaimer: I know nothing about carbeurators.

I have one similar experience in my first car, which was a carb'd Accord. The car would do this thing just like you described, start up fine after a bit of a rest, and then do it again a little further down the road.

It was very cold out (-20 F) and I think there may have been water in the fuel, possibly freezing up in the carbs. This theory is based strictly on the temperature, the fact that I had just bought the car, and the fact that the problem went away after topping up the fuel, never to be seen again.

So, just based on my one experience I would pose you these questions. Is your weather cold right now? And is the tank completely full / do you trust the gas station you last filled up at? Hey, maybe it's worth the thought.

Beyond that all I can say is hopefully TripleLude swings by; he's kinda the forum's carb guru. The fact that you've already swapped carbs and checked the pump indicates that you're way more mechanical than I was when I owned that Accord. It also implies the problem has probably lasted longer than one tank of gas. :lol:

*edit: Also, your dieseling tells me I'm probably way off track with this idea.


Its actually not cold outside at all, its about 92 in my area right now. I'm beginning to think that the ignitor may be to blame.
 

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Its actually not cold outside at all, its about 92 in my area right now. I'm beginning to think that the ignitor may be to blame.
The symptoms you described are not common symptoms of a bad ignitor. Are you ignoring the fuel filter suggestion, or have you replaced them both already?
 

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Discussion Starter #12
The symptoms you described are not common symptoms of a bad ignitor. Are you ignoring the fuel filter suggestion, or have you replaced them both already?
The filter has been replaced, it seems to act like its losing spark. I actually haven't been able to get it to start today.
 

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The filter has been replaced, it seems to act like its losing spark. I actually haven't been able to get it to start today.
both filters?
 

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Lisle makes a spark plug wire inductive light tester. I have a pic of it in my oddball and large tool thread in the red F.A.Q. Lisle is available online like amazon and locally usdm sears and O'Reilly's. I think the online manual will show you how to test the igniter with dmm.
 

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Discussion Starter #16
Lisle makes a spark plug wire inductive light tester. I have a pic of it in my oddball and large tool thread in the red F.A.Q. Lisle is available online like amazon and locally usdm sears and O'Reilly's. I think the online manual will show you how to test the igniter with dmm.

Alright, Its now running again, It looks like the battery voltage was a bit too low to start. Anyway, the run-on is still happening, pistons didnt look that dirty. The bucking is still happening also, so id figure that bucking wasnt voltage related.
 

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Well tell us what you have done. You haven't been that forth coming so far so it is hard for us to help you. If the pistons didn't look that dirty does that mean you replaced the plugs with new ones and made sure they were gapped correctly? What about the cap and rotor, have you replaced them? What about using a timing light to set the timing? If it isn't bad gas I would suspect what I just mentioned will quite possibly fix it. What about testing the igniter with dmm if it has one. Do you have the inductive spark wire detector from lisle or another brand? They only cost about $10. Lastly I don't think you have told us if you have an auto or manual tranny?
 

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Discussion Starter #18 (Edited)
Well tell us what you have done. You haven't been that forth coming so far so it is hard for us to help you. If the pistons didn't look that dirty does that mean you replaced the plugs with new ones and made sure they were gapped correctly? What about the cap and rotor, have you replaced them? What about using a timing light to set the timing? If it isn't bad gas I would suspect what I just mentioned will quite possibly fix it. What about testing the igniter with dmm if it has one. Do you have the inductive spark wire detector from lisle or another brand? They only cost about $10. Lastly I don't think you have told us if you have an auto or manual tranny?
OK, The car is a manual. The engine runs at about 1500 RPMs idleing (which is a bit high, but I haven't figured out whats going on with it. its not a vacuum leak) Timing is good, I took it to a shop to have the timing checked and corrected if necessary. The car does have continuous spark, so the ignition system is fine. This is this cars second engine. The first one had a couple bad piston rings. The old engine didn't have this problem, this engine always kinda did. It has gotten worse. I have just replaced the plugs, the new ones are gaped properly, but the old ones were a little bit off. I "think" its a B20A3 engine. The run-on is also lasting longer, sometimes it can go on for 30 seconds...its really worrying me.

This is the carb setup:

https://drive.google.com/file/d/0B0V79280n1j-d01YbDdqeFNwbGE5WjE3NkFGeDVYU0lZdEo0/view?usp=sharing


https://drive.google.com/file/d/0B0V79280n1j-WEszNUQ0WDJjRHZlTWx4RWwxeWNEeUtkbE1n/view?usp=sharing
 

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...The run-on is also lasting longer, sometimes it can go on for 30 seconds...its really worrying me.
Something is igniting the fuel after you have turned the ignition off. In my experience, this is either:
a) Spark plugs continuing to fire.
b) Carbon build up in the cylinders.

TEST
Connect up a timing light.
Start the engine.
Timing light flashes and indicates that the ignition is firing.
Turn the ignition key off.
Timing light should stop flashing immediately.

When the engine is running on, is the timing light still flashing?

RESULT
a) Timing light stops flashing when ignition is turned off. Run on is being caused by a build up of carbon, see post #5.
b) Timing light continues to flash after ignition is turned off. Run on is being caused by a faulty ignition system.

If the plugs continue to fire after you have turned the ignition key off, then the ignition coil is still being erergised somehow. Looking at the wiring diagramme, there are two items directly connected to the ignition coil; the igntion switch and the igniter.

a) When the engine is running on, try wobbling the key, does this cause the engine to stop? If yes, you may need to replace the ignition switch.
b) Replace the igniter.


Item locations
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf100/16-51.pdf

Wiring diagramme (page 16-55)
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf100/16-52.pdf

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Other items to check that may be causing, or contributing to, the problem:

Were you supplied with the correct spark plugs? I have read that if the plugs are too hot they may retain sufficient heat to cause or contribute to run on.
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf100/16-65.pdf

Is the engine using oil? What is the compression like? Worn cylinders can allow oil into the combustion chamber and contribute to the carbon problem.
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf100/5-4.pdf

Check the crankcase ventilation (PCV) system is okay.
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf100/6-74.pdf

The high idle can exacerbate the run on problem, because it continues to draw air and fuel into the hot cylinders. This article explains.
http://www.badasscars.com/index.cfm...duct_id=94/category_id=13/mode=prod/prd94.htm

Adjusting idle.
http://media.honda.co.uk/car/owner/media/manuals/PreludeManual/62sf100/5-10.pdf
 

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^^Good stuff there.

Another method of removing carbon build up in your intake and combustion chamber is to do a Seafoam treatment. If you're not sure what that is just google it. Tons of you tube videos out there because one of the side effects of this treatment is the huge amount of white smoke which your car emits during the treatment. Pretty entertaining I guess. :lol:

Disclaimer: As with any liquid that you introduce into your intake, you'll want to make sure that you add it slowly. Too much at one time can be detrimental to your engine.
 
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