1985 Nissan 720 bad bpt valve?

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Jm350521
Posts: 3
Joined: Sat Jul 17, 2021 12:02 am
Car: 1985 Nissan 720 2.4

1985 Nissan 720 bad bpt valve?

Postby Jm350521 » Sat Jul 17, 2021 7:04 am

Screenshot_20210716-233033_Chrome.jpg
Hello there I had a question hopefully can get a thorough answer on what the cause is? So, a small hose that connects to the intake manifold and connects to bottom of the bpt valve is shooting out hot high pressure, and keeps blowing off the hose from bottom of the bpt valve. I understand it's supposed to blow from intake manifold through the bpt valve then through egr valve. With recently removing the engine and completely cleaning it up, changing gaskets, new exhaust system, seals, water pump, new plugs and wires basically an overhaul. I never really noticed before the overhaul if that much pressure was coming out of the intake manifold. Is it just a bad bpt valve that's not allowing high pressure from the intake manifold to travel through bpt valve correctly? What could be causing that much pressure to continue blowing off the small hose from bottom the of the bpt valve? And is that much pressure supposed to be coming from the intake manifold through that small of a rubber hose? It's a stock Hitachi rebuilt carb, all stock motor 2.4 but in process of cleaning up air the lines, and maybe deleting unnecessary hoses for emissions. Thanks
Attachments
IMG_20191005_111802400~2.jpg
Side view if bpt valve hose thats blowing off from bottom. Why??
Screenshot_20210716-233033_Chrome.jpg
This hose here from intake manifold to bottom of bvt valve keeps blowing off from bottom of valve from high hot pressure. Why is that?
Last edited by Rogue One on Sat Jul 17, 2021 6:26 pm, edited 1 time in total.
Reason: Revise title


mdmellott
Posts: 726
Joined: Mon Sep 02, 2019 3:32 pm
Car: 2002 Pathfinder SE, 3.5L, AT, P/4WD
2013 Kia Soul+, 2.0L, AT
Location: SF Bay Area, CA

Re: 1985 Nissan 720 bad bpt valve?

Postby mdmellott » Thu Jul 22, 2021 8:46 pm

That hose feeds exhaust backpressure to the BPT. The pressure should not be high enough to blow the hose off the nipple unless the hose is worn out or there is serious exhaust restriction creating excessive backpressure. There was no hose clamp originally installed since it should not be necessary but installing one now, if the hose is worn and loose, might just resolve the problem.

Jm350521
Posts: 3
Joined: Sat Jul 17, 2021 12:02 am
Car: 1985 Nissan 720 2.4

Re: 1985 Nissan 720 bad bpt valve?

Postby Jm350521 » Thu Jul 22, 2021 9:33 pm

@mdmellott thanks man for reply I changed out hose didn't blow off even replaced with another bpt valve might need to replace carb with a webber have complete new exhaust down pipe straight pipes with cherry bomb so no restrictions there. Fires up but doesn't stay running have to consistently press gas pedal to stay running then dies out so carb might need to be upgraded.

mdmellott
Posts: 726
Joined: Mon Sep 02, 2019 3:32 pm
Car: 2002 Pathfinder SE, 3.5L, AT, P/4WD
2013 Kia Soul+, 2.0L, AT
Location: SF Bay Area, CA

Re: 1985 Nissan 720 bad bpt valve?

Postby mdmellott » Thu Jul 22, 2021 10:00 pm

It's been longer than I can remember, in detail, but when I ran a straight header exhaust on my old ride back in the early '80s, I had to re-jet my carb with a larger main jet to handle my new exhaust because it ran too lean after the exhaust install and I too had to give it more throttle at idle to keep it running. The new jet fixed that issue but then it was a bit too rich until I slapped on a hot coil. It roared like a lion after that. Good times. A Webber or Holly carb would be good choice.

Jm350521
Posts: 3
Joined: Sat Jul 17, 2021 12:02 am
Car: 1985 Nissan 720 2.4

Re: 1985 Nissan 720 bad bpt valve?

Postby Jm350521 » Thu Jul 22, 2021 10:28 pm

Yeah have the stock hitachi carb had rebuilt a while back ran good decided to pull motor clean up installed new gaskets, water pump plugs, wires distributor, new exhaust etc went to put in and seem lime running too rivh/lean but first issue was bpt hose blowing off threw me for a loop. Its pretty consistent pressure changed tighter hose hasnt blown off but seem like air coming out somewhere literally sounds like a turbo blowoff valve thought was bad exhaust gasket and getting slight air leak where exhaust manifold and down pipe connect but figure even with slight leak should not be enough to keep it from running. So next is Carb setup and see if that will adjust the way its running. You know how it is start rebuilding a ride and more crap pops up.. lol. When so close


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