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Old 03-19-2016, 01:51 AM   #1 (permalink)
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How Do I Fix & Preserve Carb Vac To Maintain CRX HF MPH?

Hi, I just bought a 1985 Honda CRX HF 1.5 with 3 barrel carburetor. Everything is original & stock. Only has approx. 125,000 miles. I bought as an alternative to a hybrid. I really appreciate this car & working on restoring everything.

I tried getting an answer from redpepperracing.com, then finally realized this is a Honda CRX Performance forum.

Any how, I bought this version for High Fuel Economy & not for performance. Fans of the HF say don't devac if you want to maintain or keep the same MPG rating. In other words keep it stock.

Presently the carb or insulator base plate gasket has a noticeable vacuum leak verified with carb cleaner.

When started cold it idles approx. at 2350 RPM then when it warms up kicks down to about 1350 RPM.
Now at what speed should the motor be idling at from a cold start & what idle speed when warmed?

Under hood says 650-750 RPM for HF

Do you recommend I have a professional smoke test performed on the engine to check for any & all vacuum leaks?

Note: It was recommended by Permatex & others to use Permatex Permashield Fuel Resistant gasket dressing (aka Hylomar Universal Blue( which is Non-Hardening & Non-setting as a solution for the carburetor insulator or base plate gasket. If gasket is salvageable then use together with the Permashield.

Please don't recommend devac or replacing with Weber as I'm not interested in performance. I do have a brand new Honda Service Manual for my 1985 Honda Civic CRX ( HF model). But I'm not mechanically inclined, but can read & follow directions.

Any suggestions for finding a capable or good Honda mechanic in the Pacific NorthWest? I live in the Seattle-Tacoma area in Puyallup by the State Fair.

However, I may be forced to learn this.

Any special tools I definitely need to get? I bought a carburetor rebuild kit, float kit & purchased the last Needle & Valve from Honda.

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Old 03-19-2016, 02:28 AM   #2 (permalink)
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Go ahead and use the nonhardening sealer. As a general observation, it is common for engines to idle about 750 rpm when warm and 850 to 1000 rpm when cold. You will get some specific data from other forum participants that are familiar with your car. When you seal the carb mounting leak, you may have to readjust the carb.

Don't tear into the carb yet. Wait until after you fix the vacuum leak. The carb may be fine. No need to go to the dealer to find intake manifold leaks; you already know how to do it with a can of carb cleaner.

More important, when was the timing belt last changed? It is to be replaced every 100,000 miles.

Good luck with your HF. They are a neat car.

Last edited by MobilOne; 03-19-2016 at 02:34 AM..
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Old 03-19-2016, 03:23 AM   #3 (permalink)
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Quote:
Originally Posted by MobilOne View Post
Go ahead and use the nonhardening sealer. As a general observation, it is common for engines to idle about 750 rpm when warm and 850 to 1000 rpm when cold. You will get some specific data from other forum participants that are familiar with your car. When you seal the carb mounting leak, you may have to readjust the carb.

Don't tear into the carb yet. Wait until after you fix the vacuum leak. The carb may be fine. No need to go to the dealer to find intake manifold leaks; you already know how to do it with a can of carb cleaner.

More important, when was the timing belt last changed? It is to be replaced every 100,000 miles.

Good luck with your HF. They are a neat car.
Thank you Mobilone, so you don't recommend rebuilding the carburetor, even after removing the carburetor from carb base plate to reseal?

The 2nd owner never changed Timing belt & they bought it when it had about 105,000 miles. So I purchased a new Gates Timing Belt (EPDM) kit & a new Aisin water pump. However Gates still recommends changing per Honda specs at every 60K. 100K sounds reasonable since the new EPDM timing belts are typically known to last this long.
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Old 03-19-2016, 08:12 AM   #4 (permalink)
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Mobile one is recommending addressing 1 thing at a time. Once your are sure the gasket leak is fixed, it can be fixed again for the few dollars a gasket and tube of sealant cost. changing gaskets, rebuilding the carb, changing timing belt all at once can lead to more issues and then you aren't sure what job caused the new issue. Doing things 1 job at a time is how you keep from getting swamped in the project and lost in why it's not running properly after the car is back together.
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Old 03-19-2016, 11:03 AM   #5 (permalink)
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You said you have a carb rebuild kit, you can do the work with the carb on the car and most of the vacuum hoses left in place, I'd repair or replace the base gasket at the same time.
The accelerator pump wears out over time and leaks, so a rebuild might fix multiple problems you didn't know about.
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Old 03-19-2016, 01:45 PM   #6 (permalink)
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Quote:
Originally Posted by Ryland View Post
You said you have a carb rebuild kit, you can do the work with the carb on the car and most of the vacuum hoses left in place, I'd repair or replace the base gasket at the same time.
The accelerator pump wears out over time and leaks, so a rebuild might fix multiple problems you didn't know about.
Thank you Ryland, rebuild the complete carb? Or just repair/replace base gasket & accelerator pump?

Now if you are going to repair/replace base gasket this would require removing from the car. What I'm I misunderstanding?
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Old 03-19-2016, 03:15 PM   #7 (permalink)
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Quote:
Originally Posted by ascendedmind View Post
Now if you are going to repair/replace base gasket this would require removing from the car. What I'm I misunderstanding?
The carb is built as two halves, the top half has most of the vacuum hoses and is a pain to remove, the bottom half has the float bowl, jets and is what mostly gets rebuilt, if you want to completely remove the top half and reinstall it for your first time set aside at least 4 hours otherwise it's about 4 to 6 screws to remove the top half, flop it aside leaving everything you can still connected, should take ten minutes.
At this point if the base gasket wasn't an issue you'd rebuild the lower half while it's on the car, the accelerator pump is the only part that's hard to reach, but your base gask leaks so pull the bottom half the carb off, 3 to 5 minutes.

Check and clean, replace jets and gaskets, 20 minutes.

Read the repair book again, ten minutes.

Read the book again, 5 minutes.

Put it back together, 15 minutes.

Wash the gas smell out of your hands and change clothes, 20 minutes.

If you've done it before it might take half as long.
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Old 03-19-2016, 04:19 PM   #8 (permalink)
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Ryland, this is very helpful information as you have inspired confidence within me!

So if I remove the bottom half to replace carb insulator gasket, would I need to completely remove the top half of the carburetor instead of flopping it aside?

Are you aware of any carb adjusting tool for easily adjusting the Honda Keihin Carburetor w/o removing the air cleaner?

I was not able to find the Schley Products Unit P/N 87100 recommended for adjusting the Honda Keihin carburetors.

Quote:
Originally Posted by Ryland View Post
The carb is built as two halves, the top half has most of the vacuum hoses and is a pain to remove, the bottom half has the float bowl, jets and is what mostly gets rebuilt, if you want to completely remove the top half and reinstall it for your first time set aside at least 4 hours otherwise it's about 4 to 6 screws to remove the top half, flop it aside leaving everything you can still connected, should take ten minutes.
At this point if the base gasket wasn't an issue you'd rebuild the lower half while it's on the car, the accelerator pump is the only part that's hard to reach, but your base gask leaks so pull the bottom half the carb off, 3 to 5 minutes.

Check and clean, replace jets and gaskets, 20 minutes.

Read the repair book again, ten minutes.

Read the book again, 5 minutes.

Put it back together, 15 minutes.

Wash the gas smell out of your hands and change clothes, 20 minutes.

If you've done it before it might take half as long.
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Old 08-19-2016, 09:33 PM   #9 (permalink)
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Just letting you know, my carburetor was completely rebuilt & reinstalled with new carburetor base plate. The 1985 Honda CRX HF runs like new now with absolutely no idle or vaccuum leak issues.

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