Popping and PAIR system

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Commando77
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Popping and PAIR system

Post by Commando77 »

I just put a couple of degutted etc cans on and it sounds nice after 2500 miles with stock baffles. Only problem is a gentle popping on the overrun which slowly pushes the front balance pipe off its stub. Well I realise it needs clamping on better but is this the PAIR system characteristic? It's notbad like a serious backfire more a pop, pop, pop, worse at lower revs and not noticed at higher rpms on overrun. Any harm if I just tighten down the vacuum pipes or should I do the PAIR mod? What do you guys recommend? Cheers.
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MacV2
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Re: Popping and PAIR system

Post by MacV2 »

Commando77 wrote: Mon Oct 01, 2018 8:54 pm I just put a couple of degutted etc cans on and it sounds nice after 2500 miles with stock baffles. Only problem is a gentle popping on the overrun which slowly pushes the front balance pipe off its stub. Well I realise it needs clamping on better but is this the PAIR system characteristic? It's notbad like a serious backfire more a pop, pop, pop, worse at lower revs and not noticed at higher rpms on overrun. Any harm if I just tighten down the vacuum pipes or should I do the PAIR mod? What do you guys recommend? Cheers.
You talking the front take off for carb balance ? Yes a small clamp will stop it coming off, try a zip tie first...

Then check all your exhaust clamps are tight as that can cause poppin on the overun...
Making up since 2007, sometimes it's true...Honest...
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Commando77
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Re: Popping and PAIR system

Post by Commando77 »

Thanks for that. Clamps are tight but old seals though. Still, no sign of leaks at idle. Awkward that front takeoff and i have the PAIR valve in the way. Will pull the airbox and do it right. Didnt think of a tie...that'll work. Any other thoughts on the PAIR assy? Cheers.
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MacV2
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Re: Popping and PAIR system

Post by MacV2 »

Commando77 wrote: Tue Oct 02, 2018 10:56 am Thanks for that. Clamps are tight but old seals though. Still, no sign of leaks at idle. Awkward that front takeoff and i have the PAIR valve in the way. Will pull the airbox and do it right. Didnt think of a tie...that'll work. Any other thoughts on the PAIR assy? Cheers.
Yeah take it off... either this... viewtopic.php?f=38&t=42705#p466942

Or early air box & rocker covers then the only thing needing blocking is the spigot on the carb...
Making up since 2007, sometimes it's true...Honest...
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Commando77
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Re: Popping and PAIR system

Post by Commando77 »

Thanks mr mac. Planning to pull the motor over winter and replace a noisy mainshaft brg. Runs fine as it is but i'm like that...love tearing stuff down to get it right. Ill do the PAIR mod same time. Cheers.
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Wicky
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Re: Popping and PAIR system

Post by Wicky »

Also check the vacuum hose for the fuel tap it could be damaged at the end. Trim a bit off and resecure.

Have you a balancing vacuum takeoff and hose on the front pot? Make sure it's securely plugged also. Any airleak in the exhaust/header/link pipes and in the intake can lead to popping so clamp (fully SS mikalor w4s) em up securely with new graphite seals and if required some supplementary hi-temp silicone.
It may be that your whole purpose in life is simply to serve as a warning to others.

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Commando77
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Re: Popping and PAIR system

Post by Commando77 »

Yes i have the vacuum pipes plumbed in and terminating by the battery. Both are plugged with golf tees! The popping only started with the modded stock cans. I bought them as stockers with the intention to modify but they turned out to have already been done. It looks like the external pipe has been removed from the internal baffle and then a larger bore piece welded in flush with the end face of the internals. This is only a short length though. I'll check the seals and try a temp bodge with silicone. The mikalors look new and clamp up tight but yes there could be a leak. Cheers.
tony.mon
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Re: Popping and PAIR system

Post by tony.mon »

Sounds likely that the popping and the vac line loosening are linked.
The vac pipe ages, hardens and cracks and as well as fitting too loosely allows air in and causes the popping
Just trim 10mm off the end.
Probably both ends will need trimming.
It's not falling off, it's an upgrade opportunity.
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Commando77
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Re: Popping and PAIR system

Post by Commando77 »

Oh yes sorry i didnt make it clear. I didnt phrase the question well. I meant was it an indication that the can change and having a PAIR system was the reason for the popping. Of course as pointed out it could just be a poor gasket and an airleak. On the vacuum pipes the problem one is a newish carbtune. Its soft rubber, an easy fit and great at being sucked bit doesnt like being blown :? Cheers gents.
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lloydie
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Re: Popping and PAIR system

Post by lloydie »

Get yourself a set of early cam covers and remove all the pairs crap
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