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Re: How to diagnose poor running?

To: Max Heim <mvheim@attbi.com>
Subject: Re: How to diagnose poor running?
From: Paul Root <proot@iaces.com>
Date: Wed, 25 Jun 2003 12:16:20 -0500
I found it with pictures on Skye's:

http://www.mgbexperience.com/service/su-tune.html

Max Heim wrote:
> I believe it is on the Scions of Lucas (SOL) site. Ah, yes, here it is:
> 
> http://www.team.net/sol/tech/su-tune.html
> 
> 
> 
> --
> 
> Max Heim
> '66 MGB GHN3L76149
> If you're near Mountain View, CA,
> it's the primer red one with chrome wires
> 
> 
> on 6/25/03 9:35 AM, Paul Root at proot@iaces.com wrote:
> 
> 
>>I spent a while this morning looking for it in the archives. Not so much
>>luck. I'm sure it's there, but without a time frame, it's very difficult.
>>
>>Any chance that any of our web guys (Paul, Barney, Paul, Skye, others?)
>>have this on their sites?
>>
>>Paul.
>>
>>Glenn Schnittke wrote:
>>
>>>Marc,
>>>
>>>You wrote:
>>>
>>>
>>>>I'm in need of some advice (how unusual...) to diagnose a problem I'm
>>>>having. My '80 MGB with the dual HIF setup I installed had been running
>>>>great. Over the last two weeks, it's gotten difficult to start when cold,
>>>>and runs rough, spitting and backfiring until it warms up really
>>>>throughly.
>>>>Then it runs mostly ok.
>>>
>>>
>>>I'll not claim to be an expert on HIF's. It's been a good ten years
>>>since the Maroon went under. But I found them to be very reliable when
>>>in good condition, and since my cars have always been daily drivers, I
>>>did like NOT having to retune for winter or summer.
>>>
>>>That said, has the ambient temperature just started to change in B'more?
>>>
>>>
>>>>I checked plugs, cleaned & regapped, swapped out cap and rotor with new.
>>>>After work today, I'll recheck the timing as well.
>>>
>>>
>>>Always a good place to start. As has been said - 90% of all SU problems
>>>are electrical.
>>>
>>>
>>>>I made sure that all manifold and carb mounting nuts were tight, and
>>>>checked
>>>>for leaks with carb cleaner. This is a fairly new installation that
>>>>had been
>>>>running really well.
>>>
>>>
>>>You didn't say how long you had the HIF setup on the car, but if they
>>>ran fine last summer, and you didn't really do anything to them until
>>>crap-out other than normal maintenance then that draws one conclusion.
>>>If you set them up over the winter and (etc) that draws another.
>>>
>>>
>>>>I was thinking I should just go through the whole set-up procedure
>>>>again. Is
>>>>that a normal occurance to have to do that?
>>>
>>>
>>>Not really but I can't tell you how many times I've done it anyway. Due
>>>to the nature of the cars, I would advise checking for vacuum leaks
>>>first. Check your throttle plates for poppet valves. If you have them
>>>they will tend to go bad or just not work and make your life miserable
>>>trying to find the problem. If you have them, my own advice would be to
>>>make them go away. I just did it to a very fresh complete rebuild on a
>>>set of HS4's and  NOW they work beautifully. (Drilled them out, filled
>>>the hole with Marine-Tex {I think it's better than JB Weld} and filed it
>>>down almost flat. Lovely).
>>>
>>>
>>>>Lacking experience, I'm not always sure that I'm doing these procedures
>>>>correctly. Seems it's more of an art than a science...
>>>
>>>
>>>Couldn't have put it better.
>>>
>>>Go to the archives. Pick up Roger Garnett's post on tuning SU carbs. He
>>>wrote it for HS's but they are basically valid for HIF's, too. When I
>>>first got into these cars I got the Bentley Manual, I got the Haynes
>>>Manual, I got the Haynes SU Manual. Then I found Roger's file and
>>>finally understood them. I still use it as a refresher course every fall
>>>and spring. Follow it to the letter (including the ale). Then you have
>>>done the complete procedure. You didn't say you'd adjusted the valves.
>>>
>>>
>>>>Also, I'm considering the purchase of a Gunson Colortune. Are these
>>>>useful,
>>>>especially for a novice?
>>>
>>>
>>>I use one on occasion. Rather than using it to actually find the right
>>>tune I use it to balance the front and rear carbs. I use it in the same
>>>context as the Uni-syn. Once I find the balance, I get rid of it and
>>>listen. Drive. Check plugs. Listen. Drive. Check plugs. Listen. Drive.
>>>Check plugs. Ad nauseum. I think it's more fun that way.
>>>
>>>Glenn

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