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
/// or try http://www.team.net/cgi-bin/majorcool
/// Archives at http://www.team.net/archive
|