Skip to content
View in the app

A better way to browse. Learn more.

Ultimate Subaru Message Board

A full-screen app on your home screen with push notifications, badges and more.

To install this app on iOS and iPadOS
  1. Tap the Share icon in Safari
  2. Scroll the menu and tap Add to Home Screen.
  3. Tap Add in the top-right corner.
To install this app on Android
  1. Tap the 3-dot menu (⋮) in the top-right corner of the browser.
  2. Tap Add to Home screen or Install app.
  3. Confirm by tapping Install.

'85 Brat - Cold start - Rough Idle & Stalling - Fixed!

Featured Replies

:headbang:

 

Faulty HAI motor wasn't holding a vacuum and letting hot air into the carb on startup....

 

These later year carbed cars are fascinating to me :)

 

I remember my old '78 Ford Escort which drove off a throttle cable turning a butterfly valve letting more air into the mix.... That was it!

 

Those EPA regulations certainly threw a spanner -er wrench in the works. The solution of numerous mechanical carb choke levers and vacuum driven bits and bobs is definatley intriguing....

 

I hope they all keep working for a while longer :grin:

 

I'm begining to understand a little more of what lies behind the decision to move towards computer controlled fuel injection - definately cuts down on the number of springs, sprockets and gizmos surrounding the good old carb throttle and (if you were lucky automatic) choke plates...

 

Steve

In my opinion, the system is supposed to let in hot air during cold start-up........ Anyways, happy you got your issue resolved.

"vacuum driven bits and bobs is definatley intriguing...."

 

 

 

Having the pleasure??? of working on some late eighties

Honda's

 

The magic black box on the bulkhead had some serious

framous-dingles inside

and about thirty (30) vacuum lines to it.

 

There should be a thermo-switch in the aircleaner

to control the "furnace".

It was reported that the carb jets are tuned to provide

the proper mix when the air temp going in is

100 deg F.

 

As we know, air density (02 content) is a function of temp.

  • Author
In my opinion, the system is supposed to let in hot air during cold start-up........ Anyways, happy you got your issue resolved.

 

Sure, bad English - my bad. I had been juggling around with the grammar and for some reason that sounded like the right sentence to land on :confused:

 

Lemme try again....

 

"Faulty HAI motor wasn't holding a vacuum hence not letting hot air into the carb on startup...."

 

There we go!

  • Author
Having the pleasure??? of working on some late eighties

Honda's

 

The magic black box on the bulkhead had some serious

framous-dingles inside

and about thirty (30) vacuum lines to it.

 

Damn, now THAT sounds like fun! Lots of doo-haa's to firckle with there!

 

There should be a thermo-switch in the aircleaner

to control the "furnace".

It was reported that the carb jets are tuned to provide

the proper mix when the air temp going in is

100 deg F.

 

Yeah, Haynes mentioned that the thermo valve regulates the air temp to 100-130 F (think?) so even when the engine reaches running temperature, the exhaust duct valve is constantly adjusting to maintain those inlet air temperatures.

 

As we know, air density (02 content) is a function of temp.

 

Not sure about math functions - I'm a programmer so my concept of the word goes more like: Let variable = Function_Name(parameter list).

 

Applied to our world of engines (now this IS gettting fun :)):

 

Let liAirDensity = lcSizeOfAirIntake ' e.g. liAirDensity = 100

Let liAirDensity = Adjust_Air_Density(liAirDensity, Get_Ambient_Temperate()) ' liAirDensity = 90 (its damn warm down here!)

Let liAirDensity = Adjust_Air_Density(liAirDensity, Stuff_Air_Through_Intercooler(liAirDensity)) ' liAirDensity = 200 ! Damn!

 

Let liAcceleration = Make_Car_Go(liAirDensity, Add_Fuel())

 

Damn, liAcceleration is an amazing 0-60 in 5.6 seconds!

 

Just imagine if we took the "Stuff_Air_Through_Intercooler" Function out...

 

Now liAcceleration is now a measly 0-60 in 12 seconds....

 

Or if I think I have the idea down right (without the archaic DOS Basic!)..

 

The colder the air molecules - the smaller they become:

the more you can get in the chamber:

the more fuel you can add without the mixture becoming too rich:

the bigger the explosion:

the more force pushing on the piston/conrod/crankshaft:

 

We go DAMN fast indeed!

 

Steve

Please sign in to comment

You will be able to leave a comment after signing in

Sign In Now

Account

Navigation

Search

Search

Configure browser push notifications

Chrome (Android)
  1. Tap the lock icon next to the address bar.
  2. Tap Permissions → Notifications.
  3. Adjust your preference.
Chrome (Desktop)
  1. Click the padlock icon in the address bar.
  2. Select Site settings.
  3. Find Notifications and adjust your preference.