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How Do I Fix & Preserve Carb Vac To Maintain Crx Hf Mpg?


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#1
ascendedmind

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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 realize this is a Honda CRX Performance forum, however 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.

 

 

 

 

 



#2
shuttlecraft

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Welcome to RPR.  85 CRX HF, Awesome!  Normal cold start rpm should be up around 2.5-3K for the first few minutes depending on ambient temps.  Carb linkages work against the fast idle cam to gradually step rpms down to around 750 at normal operating temperature.  If it idles at anything more than 750 rpm, or is hunting, somethings up.  The systems that control the carburetor devices are electro-mechanical and vacuum driven.  They are numerous and take a little patience and experience to understand.  I highly recommend FSM over the Haynes or other knock-offs.  FSM are your best documented source for knowing as much as you can about how these systems work.  Also, recommend finding a local mechanic that can work with you if your new to Honda engines.  You will just have to keep looking and anticipate that a lot of them will tell you that they don't work on carbureted vehicles.   When it comes time to removing the carb, take copious notes and photos at each step so that you'll have a record of where things go during re-assembly.  This is a good time to inspect all vacuum hoses.  There should also be a vacuum line diagram sticker on the inside of the engine hood.  You will need to drain a little more than a quart of coolant from the system before removing the carb, otherwise you'll dump coolant into the intake manifold.  Don't waste your time attempting to seal or repair the insulator plate.  Get a new one (they're available) and install it (dry) using the factory torque specs.  I think it's 17lb-ft for both the plate and carb bolts.  You want an even, uniform seal.  Don't over-tighten.

 

I wouldn't be so convinced that the carburetor needs rebuilding.  Fixing that major vacuum leak could be all that's needed.  It's your choice, but if were me, I would take on one issue at a time.  Dido on aftermarket carbs.  They don't quite run as smooth with the CVCC head configuration.  Good luck.



#3
ascendedmind

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Thank you Shuttlecraft, I appreciate that you took the time to answer my question.

 

Any idea where to buy the insulator plate from? What keywords would you use to find the carb insulator? I'm assuming 1984-1987 CRX HF insulator would only work?

 

However, if the rubber insulator is notorious for vacuum leaks, why not use a fuel resistant sealant like Hylomar Universal Blue together with the insulator for reinforcement?



#4
GeezRX

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Any idea where to buy the insulator plate from? What keywords would you use to find the carb insulator? I'm assuming 1984-1987 CRX HF insulator would only work?

I used the search 1985 CRX carburetor insulator and got a good selection of hits... this one:

http://www.autoparts...html?redirect=1

was cheapest of those I looked at and said it was in stock for immediate shipment.


"Old and usually in the way" - Check out my '86 3G build in "VIEW GARAGE"


#5
ascendedmind

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I used the search 1985 CRX carburetor insulator and got a good selection of hits... this one:

http://www.autoparts...html?redirect=1

was cheapest of those I looked at and said it was in stock for immediate shipment.

 

 

Wow, thank you, I really appreciate this find, I just assumed it was no longer available because virtually everybody told me so. Bad mistake.



#6
shuttlecraft

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I don't know where you were told that the insulators were "nortorious for leaking" and don't forget that these vehicles are 30 years old.  I will agree with most that the entire system is prone to vacuum escape because there are so many opportunities for this event to occur on these engines.  If you keep with it, this engine will train you become "mechanically inclined".  I don't blame others for devacing, or likewise seeking alternatives and there are some pretty clever means out there for doing so.  Which is exactly why I prefer RPR because the membership base is so broad and there are multiple examples of modes, swaps etc.

 

It might help you to think of this engine as having many of the same systems and sub-systems as modern computer controlled fuel injection engines with the difference being that on the early carb'ed, Hondas, the engine management systems are doing the same job using early some say primitive technology.  Ok, fine. but when a cold engine starts, it asks for a rich fuel mixture, for example, regardless of how technologically advanced it might be.  This engine will force you to think vs. the convenience of a CEL code.  My EW keeps me on my mechanical toes.  I read a thread recently about a chap that was explaining the emotional satisfaction lets say, after performing some repair that allowed his Honda to survive for another day.  That's it in a nutshell.  I too, dig that feeling and to think that anyone can also achieve it with a pair of pliers and a 10 mm box wrench is Honda's genius.  I digress.



#7
ascendedmind

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I don't know where you were told that the insulators were "nortorious for leaking" and don't forget that these vehicles are 30 years old.  I will agree with most that the entire system is prone to vacuum escape because there are so many opportunities for this event to occur on these engines.  If you keep with it, this engine will train you become "mechanically inclined".  I don't blame others for devacing, or likewise seeking alternatives and there are some pretty clever means out there for doing so.  Which is exactly why I prefer RPR because the membership base is so broad and there are multiple examples of modes, swaps etc.

 

It might help you to think of this engine as having many of the same systems and sub-systems as modern computer controlled fuel injection engines with the difference being that on the early carb'ed, Hondas, the engine management systems are doing the same job using early some say primitive technology.  Ok, fine. but when a cold engine starts, it asks for a rich fuel mixture, for example, regardless of how technologically advanced it might be.  This engine will force you to think vs. the convenience of a CEL code.  My EW keeps me on my mechanical toes.  I read a thread recently about a chap that was explaining the emotional satisfaction lets say, after performing some repair that allowed his Honda to survive for another day.  That's it in a nutshell.  I too, dig that feeling and to think that anyone can also achieve it with a pair of pliers and a 10 mm box wrench is Honda's genius.  I digress.

 

 

Yes, this car has forced me to become mechanically aware, & learned how to screen out other so called Honda mechanics who have proven not to be qualified regarding this carburetor system. Most will simply decline as they don't want to think.