HIF6 bimetal failure

sdibbers

Well-Known Member
I have HIF6 carbs on my 2000TC (bored to 2200).

Recently I’ve noticed that my idle is jumping around with different heat conditions. When sitting in traffic it’ll go up to 1,000rpm. If I pull up after a higher speed run she stays at 700-750 rpm.

When in traffic it’s almost like a switch. All of a sudden the idle speed will change without me doing anything. The carbs are in excellent condition absolutely no spindle leaks or float issues.
I have noticed that she gets a little leaner when the idle rises and I wonder if the bimetal jet brackets might be on their way out causing them to jump instead of move gradually?

I’d prefer to have no bimetal compensation so I think I’ll try and make a simple replacement. Modern fuel has such different densities compared to what they were designed for I think they make things worse, especially with the amount of ethanol in New Jersey fuel.

Does anyone have have thoughts on my ramblings?

Thanks in advance,

Steven
 
Yes, i would suggest to try simple things first.
When you have the high idle situation, open the bonnet and try to push close the throttles, and see if with this the idle speed returns to normal. Sometimes they tend to stick a little.
If everything is OK there, i would suggest checking for a random vacuum leak, or have a look on the distributor side. Changes in advance could change the idle speed too.
In any case i doubt that the bimetallic strips are the cause of idle variations.
 
Throttles are closing fully, no change in idle if pushed closed (plus it returns to whatever idle speed it was at when throttle is snapped too suggesting it’s not a stop issue. No vacuum leaks around spindles I’ve capped the dissy line and again no difference, no vac leaks between carbs and intake manifold either (all leak tested with carb cleaner).
 
At the time you are suffering the high idle speed I'd make sure that it isn't the linkage sticking and causing it, or an air leak on the inlet side, and after that checks out OK you're probably right about the bimetallic strips.

PS did you centralise the butterflies when you fitted them?
 
At the time you are suffering the high idle speed I'd make sure that it isn't the linkage sticking and causing it, or an air leak on the inlet side, and after that checks out OK you're probably right about the bimetallic strips.

PS did you centralise the butterflies when you fitted them?
Already looked at linkages and tested for induction leaks. Yes, butterflies were centered after assembly and fit nicely. I think I’ll bite the bullet and just order new bimetals and fit them.
 
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