Slight miss at idle with popping exhaust

sdibbers

Well-Known Member
#1
This is with a 2000TC running 9:1 2200 pistons with HIF6 carbs.

I had a great weekend up in Mass for the Nortb American Rove. Managed about 600 miles round trip with no issues.

Got home Saturday evening and noticed that she has a slight miss every second or so at idle with a popping at the tailpipe. I know I have to repair a crack on the exhaust manifold that I’m pretty sure got worse on the trip home. Could this be related? Power seems good still, idle is smooth apart from these occasional misses. My other concern is maybe this is the beginning of a burnt valve. I plan to whip off the manifold, weld the crack between the 2nd and 3rd cylinder pipes and try and anneal somehow

Any thoughts?
 

Demetris

Well-Known Member
#4
I always associated what you describe with a lean mixture. As you have HIF carbs, these lean out when hot.
If you do a CO check, you will find out.
 

sdibbers

Well-Known Member
#5
I always associated what you describe with a lean mixture. As you have HIF carbs, these lean out when hot.
If you do a CO check, you will find out.
I agree I've had that sort of experience too Demetris, although this time the idle seems steady when not missing (if that makes sense?). I have noticed that it only takes about two minutes of idling while warm to cause the bimetal strip to lean out the jet. However this time it's doing it from cold pretty quickly. I've even considered making a solid part to replace the bi-metal jet adjuster, seeing as modern fuel seems so different to the stuff available in the 70's.
 

sdibbers

Well-Known Member
#10
Update time. Exhaust manifold off. I’ll TIG the crack tomorrow at a friends house.

Bad news is I did a compression test. Not a happy camper:


Cyl 1 180psi

Cyl 2 175psi

Cyl 3 80psi

Cyl 4 170psi

Looks like the exhaust valve in cylinder 3 is the culprit. Oh well, head off later for an exam.
 

sdibbers

Well-Known Member
#13
Belated update to this thread. It was eventually found to be a bad piston ring on no.3 I replaced all of them to be safe than had a bad piston ring on No. 2! Fixed that and all good.

As for the popping, that was a closed up gap on one spark plug. I suppose I must have dropped it at one time and that caused the popping.
 
#14
If you ever need a shop for head repair (you said you're in NEW England, right?), River City Machine in White River Junction, VT and Dutcher engineering in western MA have both done right by me.
 
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