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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