Engine not revving properly

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Joe98
L-Driver
Posts: 4
Joined: Thu Jan 10, 2019 1:25 pm
Drives: 1985 Mk2 Golf GTI

Engine not revving properly

Postby Joe98 » Thu Jan 10, 2019 1:27 pm

I’ve recently bought a 1985 Mk2 and I’m having some troubles. The car from the factory came with the 8v engine however it has since had the 16v engine dropped in, its also got KJet injection.

The problem is that when I’m driving and I go near 4500-5500 rpm or above, the car will stutter and cut out. (The engine will still run but a drone sound comes from the engine when the accelerator is pressed)

It doesn’t happen all the time and it’s not always at the same rpm but around that area. The cars had a new alternator and battery and it has made it a little better but the problem persists. A local garage thinks it could be due to me having 3 standard plug leads and 1 BMW performance lead (came with the car when purchased). When the engine jerks and cuts out near the rpm range I can hear a relay (or a number of relays) clicking underneath the dashboard. When the engine jerks, it’s possible to slow the engine down, shift down a gear and the car will make it past without jerking all the way to red line.

It’s hard to explain what’s happening but basically when the revs get near 4/5k the car will suddenly start to jolt instead of accelerating. The car won’t stall out but I have to let off the accelerator for it to stop. This will happen either at WOT or just gradually building up speed.

What could be causing my problem?

Any help is greatly appreciated.
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eddypeck
Supercharged
Posts: 8953
Joined: Thu May 23, 2013 1:29 pm
Drives: 1986 MK2 Golf GTI 8v
Location: Bristol, UK

Re: Engine not revving properly

Postby eddypeck » Thu Jan 10, 2019 2:46 pm

Before you trust any garage with your car ask if they have the equipment to work on k-jet. Just this, say nothing else.

The length of the pause they give you will be the indication of if they even know what k-jet is.

By their comment about the HT lead this already tells me they have no idea and are already guessing, they'll do more harm than good... run, run away now!!!!

Many high street garages binned their testing equipment years ago and a decent garage will be honest about this. Basically you can't do anything on a k-jet without first testing the fuel pressure under certain circumstances.

The whole system is based on fuel pressure and vacuum. The pressure is high compared to modern cars! even half a bar too low and you'll never it get it running. Likewise, the vacuum is massively important, a small air leak from 30 year old perished rubber can give crazy problems that you'll chase for ever. Start with air leaks and move onto pressure.

What you are describing sound like a symptom of either low fuel pressure and/or air leak. The pressure is adjusted by the warm up regulator so you'll often see different result from cold, and once warm - as you say it's not doing it all the time.

Also things like is the pressure maintained after shut off, if not you'll have starting issues.

Loads of K-Jet info here: viewtopic.php?f=37&t=41350 and scroll down about half way and there's a troubleshooting table. It's dead handy to get you going in the right direction.
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Joe98
L-Driver
Posts: 4
Joined: Thu Jan 10, 2019 1:25 pm
Drives: 1985 Mk2 Golf GTI

Re: Engine not revving properly

Postby Joe98 » Thu Jan 10, 2019 2:54 pm

Thanks for the reply.

After you mentioned pressure I realised the problem began after I blew a mixture screw. At the moment, a bolt is just screwed in. Is it possible my engine is running badly because there isn’t a mixture screw in place?

The mixture screw is just after the air box but before the actual engine.

I’ve also been told the hall sender could be on its way out, is that a possibility as well?
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eddypeck
Supercharged
Posts: 8953
Joined: Thu May 23, 2013 1:29 pm
Drives: 1986 MK2 Golf GTI 8v
Location: Bristol, UK

Re: Engine not revving properly

Postby eddypeck » Thu Jan 10, 2019 7:32 pm

Do you mean the idle screw in the throttle body on top of the inlet manifold at the rear of the engine, Just below where the throttle cable sits? If so, that's a definite culprit. There should be a rubber o-ring on that screw. Without this the it will give problems. (forgive me if description isn't quite right. I'm doing it from memory and am more familiar with 8v k-jet than 16v.)

The mixture is on the metering head, the bit on top of the airbox with all the fuel lines coming out of it.
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Joe98
L-Driver
Posts: 4
Joined: Thu Jan 10, 2019 1:25 pm
Drives: 1985 Mk2 Golf GTI

Re: Engine not revving properly

Postby Joe98 » Thu Jan 10, 2019 7:56 pm

That’s 100% what I mean. The car used to idle really rough before it blew out. I bodged it with a bolt and it sorted out the rough idle but now it jerks as I Rev high.

Know of anywhere I can find this screw?

I’ll post a picture tomorrow of where I mean but I’m pretty sure we’re talking about the same place.
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Pootz
VW Bug
Posts: 1065
Joined: Sat Jul 13, 2013 3:43 pm
Drives: A 5 door Shed

Re: Engine not revving properly

Postby Pootz » Thu Jan 10, 2019 8:35 pm

There are a couple of idle adjustment screws on eBay but whether they're the correct ones I don't know.
Type in "K JET IDLE ADJUSTMENT SCREW" into the eBay search and scroll down.
Most say Honda but there are some with no manufacturers name, just numbers
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Joe98
L-Driver
Posts: 4
Joined: Thu Jan 10, 2019 1:25 pm
Drives: 1985 Mk2 Golf GTI

Re: Engine not revving properly

Postby Joe98 » Sun Jan 13, 2019 1:47 am

https://www.youtube.com/watch?v=xC0WcegpaGI

This is what I mean. It gets to a specific RPM and will just stop revving. My foot was held in the same position so it just bounces off the RPM and won't go above it. The end of the video shows that if you rev it hard enough it will go past the problem and continue revving.

Could this be down to the idle adjustment screw not having a rubber seal on it?
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