Engine and Transmission Tech

tips, technology, tools and techniques related to vehicle driveline components

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bsa_m21
Martin Rothman
Vancouver, Canada
(216 posts)

Registered:
01/06/2009 11:41AM

Main British Car:
1980 TR7V8 Rover 3.9L

authors avatar
Engine Suddenly Won't Idle
Posted by: bsa_m21
Date: August 13, 2015 02:47PM

Hi all,

I have a TR7 with a breathed on Rover 3.9L with an Edelbrock 1404 carb on a spacer and heat shield. The fuel pressure is a steady 4-5psi. For the past year she has run just fine. Two weeks ago after being on the highway, she suddenly wouldn't idle. Back off the throttle and she'd instantly die. She would start right up and run fine under throttle, but would not idle, even when cold with the choke on.

I took the carb apart, gave it a good cleaning, put in all new jets and needles, reset all settings and reassembled. She ran great for the first few days then lst Sunday after being out cruising backroads for several hours, it happened again.

I mucked about, checking all the external connections, and finally raised the idle screw until she would idle at 1200rpm. However, even then she kept hunting and sounded very uneven.

I checked the dist (stock Rover HEI) and timing, all fine. Changed coil and ignition amp (mine is remote), to no effect.

Before I take the carb apart again, does anyone have any suggestions (other than buying a Holley!)?

Thanks.
M.


DiDueColpi
Fred Key
West coast - Canada
(1365 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

authors avatar
Re: Engine Suddenly Won't Idle
Posted by: DiDueColpi
Date: August 13, 2015 04:50PM

Sounds like your idle jets are plugged up Martin.
They are the small tubes on your primary boosters.
Probably some trash is floating around in the booster wells.
So pop the carb top off, remove the boosters and blow everything out.
That'll probably fix you right up.

Cheers
Fred


pcmenten
Paul Menten

(242 posts)

Registered:
10/08/2009 10:40AM

Main British Car:


Re: Engine Suddenly Won't Idle
Posted by: pcmenten
Date: August 13, 2015 05:54PM

Could it be a wicked vacuum leak?

If it's not the idle jets, you might consider the failure of something like the PCV or even the brake booster diaphragm. (I had a mysterious idle problem on my stock MG that turned out to be a bad brake booster. I could diagnose the booster by disconnecting and plugging the vacuum line.)


88v8
Ivor Duarte
Gloucestershire UK
(1041 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: Engine Suddenly Won't Idle
Posted by: 88v8
Date: August 14, 2015 05:56AM

I have an intermittent problem with my Rover V8. In a couple of days the mixture goes from 4% to 10% CO to unmeasurably low. It's been this way for five years but has recently got a lot worse. Some days it starts up and runs fine, next day it won't idle and runs rough at low throttle openings.
I have SUs, I've rebuilt them, and subsequently changed the floats again, the needle valves again. Changed the fuel tank, the pipes the filter the pump wrapped the pipes in heat sleeve, I have a Filter King the pressure is good.

I think there s a vacuum leak, I plan to pull the inlet manifold but where the engine is sitting it's hard to access the rear fixings and I have other things to do.
Grrr.

You could also look at the rocker breather system that can create some lovely air leaks.

Ivor


Nexxussian
Erik Johnson
Alaska
(62 posts)

Registered:
04/20/2015 10:32PM

Main British Car:
1974, MGB, Citroen Color Rover V8

Re: Engine Suddenly Won't Idle
Posted by: Nexxussian
Date: August 14, 2015 09:28AM

Martin, I agree with others that you should [re]verify you have no vacuum leaks.

In addition to what was mentioned check for leaks between the carb and your spacer / heat shield as removing the carb would disturb them, although I suspect you put fresh gaskets on them while you had the carb off.

Also check for any vacuum caps or plugs suddenly missing as it will take a fairly large vacuum leak to cause it to suddenly not idle at all.

However it sounds like you found your issue earlier, if a dismantle and cleaning fixed it before.

As it had that issue before, check your fuel filter as it sounds like it may be passing trash through to the carb.

You mention a trip on the highway, did you buy fuel somewhere you haven't before?

By any chance did you park it anywhere some low life could have put something in the tank?

Alternately you might have a corrosion issue inside the carb (ethanol in your fuel?) or you run it infrequently enough your gasoline is decomposing in the carb.

Any of these would suggest junk in the idle circuit as your current problem, but it's a symptom as opposed to the real problem.


My first suspect after vacuum leak is a full or otherwise failing fuel filter, with trash in the tank being a possible aggravation of the potential filter issue.

I would change the filter if cleaning the carb fixes it again, even if it was changed with the last cleaning.

Verify something between the carb and fuel filter isn't disintegrating and putting trash into the carb.


The corrosion and decomposition issues are long shots as I would hope if your carb was corroded the last time you dismantled it you would have mentioned it, also it sounds as if you drive it enough (especially with a heat shield) that you shouldn't be having an issue with decomposition either.



Edited 1 time(s). Last edit at 08/14/2015 09:50AM by Nexxussian.


bsa_m21
Martin Rothman
Vancouver, Canada
(216 posts)

Registered:
01/06/2009 11:41AM

Main British Car:
1980 TR7V8 Rover 3.9L

authors avatar
Re: Engine Suddenly Won't Idle
Posted by: bsa_m21
Date: August 14, 2015 11:39AM

Thanks everyone.

Will check it out all of your suggestions tomorrow morning and let you know what I find.


You take the carburator off.
You put the carburator on.
You take the carburator off.
And you shake it all about.

You look for the leak,
You can't be meek.
It's only your idle.
So don't be suicidal.

It's not that severe,
There's time for a beer.
So don't be a dufuss.
Pray to George Lucas.


smokekit.jpg


DiDueColpi
Fred Key
West coast - Canada
(1365 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
I really thought that I'd be an action figure by now!

authors avatar
Re: Engine Suddenly Won't Idle
Posted by: DiDueColpi
Date: August 14, 2015 12:32PM

What model SU's do you have Ivan?



bsa_m21
Martin Rothman
Vancouver, Canada
(216 posts)

Registered:
01/06/2009 11:41AM

Main British Car:
1980 TR7V8 Rover 3.9L

authors avatar
Re: Engine Suddenly Won't Idle
Posted by: bsa_m21
Date: August 17, 2015 10:50AM

Well I checked for leaks around the base of the carb, but it was fine. I then took it all apart, but couldn't see any dirt in it. So, I blew out every passageway with compressed air, checked every setting, reassembled and remounted it. I also changed the fuel filter by the pump and added a 2nd one in the engine compartment.

Seems to be runing fine at the moment. Will have to wait and see if the problem re-occurs.

Thanks for the advise.


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