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Guest Message by DevFuse
 

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


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4 replies to this topic

#1 samneric

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Posted 03 July 2007 - 08:28 PM

: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

#2 aba4430

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Posted 04 July 2007 - 09:55 AM

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

#3 Skip

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Posted 04 July 2007 - 10:11 AM

"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.

#4 samneric

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Posted 04 July 2007 - 12:45 PM

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!

#5 samneric

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Posted 04 July 2007 - 01:53 PM

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




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