Sudden increase in idle speed and popping on deceleration

[Adski]

Took my 1641 type 3 for it's first decent spin yesterday - an hour each way.
Run brilliantly - but halfway home the idle speed increased by 100rpm for no reason and was also doing a bit of popping on deceleration.
I'm running dual weber ICT 34s. I checked the linkage, hoses, etc and everything visually seemed to be ok.
I'm wondering if an exhaust leak could be causing these symptoms?
Nothing appeared to have changed with the carb's and they still seemed to be opening at the same time. Not sure why this would happen all of a sudden.

Any suggestions would be appreciated.

[66brm]

Check for vac leaks, how was day of?
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Aust. RHD 66 Type 1
Aust. RHD 57 Type 1 Oval

[Adski]

Day of was dope!

Was thinking vac/exhaust leaks.
I'll have to give it a good once over on the weekend.
Had a quick look roadside and tightened up the carbs.

[fastfil]

Throttle cable freeplay? Intake leak? Tight valve?

Is it a new motor?
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[Frederik]

Also check distributor advance mechanism so that it isn't "sticking"

[Adski]

Thanks all for the tips.
I replaced the heads and cylinders recently with brand new ones. Also got new weber 34 ICT's.
It doesn't seem that the advance is sticking... but I'll have to check that on the weekend with a timing light - along with the valve clearances and for air leaks.

I checked the cable freeplay and that seemed fine. However just before the problem happened the throttle pedal got stuck about a 1/4 of the way down causing it to accelerate even when foot was off the pedal - a bit scary! I think it got stuck at the pedal end. I double checked the throttle stops were all the way closed and it was still idling 100 rpm higher than it was originally set.

I'll do some checks on the weekend and report back.

[nextgen]

I get the same problem with dirty jets. I clean the jets and it runs perfect.

Check your fuel filters. Clean the carb or Throw half can of Sea Foam or Barryman's B12 in the gas tank next fill up. Can't hurt. Sometimes after a 15 min run it will clear up.

That can be a symptom of Lean Mixture, that an air leak can also cause.
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[Adski]

So, upon further investigation, the only issues I found were that both valves on Cylinder #4 had tightened up a little, which was an easy fix.
The other thing was that both of the rubber boots where the pancake air filters sit on top of the weber 34 ICT had split. So, they were both sucking in air.
Pretty crap since it's about the 2nd drive I've had with these carbies on.

Instead of replacing them with more pancake filters, I got some of the sock type filters which shouldn't split and should still fit under the hatch of the Type 3.

I also re-balanced the carbies as they were ever so slightly out of balance.

Fingers crossed those little problems were what was causing the popping and high revs.

[66brm]

Another thing to have a look for that I forgot to mention was exhaust leaks, that'll cause the popping on decell also
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Aust. RHD 66 Type 1
Aust. RHD 57 Type 1 Oval