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V8 on Carbs - Few questions for knowledgeable folk..


tommobot

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I've recently purchased a Land running with a V8 on carbs...

Problem is I know nothing about carbs at all.... So after a bit of advice / few questions..

I've probably done around 1000miles in it so far, and apart from running out of petrol a few times no issues at all!

Every other 3.5 V8 I've seen on Google images however seems to have a different layout of piping entirely.

WP_001079_zps574086fc.jpg

- Firstly, flame traps? As far as I can see it doesnt appear to have any?

- There is a small breather towards the back, at the centre on the top of the engine that constantly produces a high pitch whistles when running.... When covered it kills the engine? Should this be connected to something - or even put a small breather filter on top of it?

Anything else pointed out that looks a-miss on the photo would be greatly appreciated

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Hi, welcome to the forum.

It looks like you have some K&N filters fitted directly to the carbs. This is common on retro fitted v8s, as the standard pipe and filter setup doesn't fit with the engine close to the bulkhead.

The other questions, not so sure, but there are plenty of people on here that know.

We want more pictures of your truck! There is a special members vehicles section for this.

Daan

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Hi, welcome to the forum.

It looks like you have some K&N filters fitted directly to the carbs. This is common on retro fitted v8s, as the standard pipe and filter setup doesn't fit with the engine close to the bulkhead.

Ah, thanks for the input.. That makes sense..

I'll upload some a bit later, its a Series 2 Hybrid I believe with a RR chassis and obviously a V8... :)

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There is a flame trap on the front of the left hand rocker cover with a black poor coming out of it leading to the carb. This pipe provides vacuum to take fumes from the rocker covers. The other vent on the back of the other rocker allows air in to the rocker covers and crankcase. There should be some sort of filters on it to stop dust and grit getting in. In an original setup, there would be a pipe connecting to the main air filter so filtered air gets in that way.

Real Steel and others sell little filters that should just push on the breather pipe.

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Throw away the awful k&n filters and fit the correct v8 elbows and air box. The breather pipe that is down the back of the engine then connects to a fitting in the standard air box.

This then gives proper pcv where just fitting a filter on the end doesn't.

I don't get why people feel the need to fit k&n filters like these, the standard airbox is far superior and will fit into a series conversion quite happily. I used the oval shaped one that came out of the same Range Rover that the v8 did in mine and it fitted without any clearance issues whatsoever.

Jon

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Small whistle breather thing is likely the port to the 4x4 vacuum switch on a classic rangy. That should be blanked off, or connected to the vacuum switch/plunger on an LT95. If it is like mine it is; on the inlet manifold at the back, off to the RH side a bit and is a banjo fitting.

You will need to change the carb mixture to allow for blocking it off. Which is a bit of a fiddle at first..........

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Mine isn't LT95 either. That's why the 4x4 vacuum pipe terminates in a number plate bolt :) I endeavour to tidy up my younger self's work...........

I would think it has been 'tuned' to run with that line open. The question is; do the plugs look that nice light brown colour? If they are white I'd block the fitting and wind up the tickover.

My minor concern would be that the leaky fitting is at the back, so it will be making only some cylinders lean on the mixture, not an even 8.

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  • 2 weeks later...

The problem with K&N's is the carbs need to have the right needles for them.

You have there a set of twin SU carbs, parts and service kits are available from Burlen Fuel Systems http://burlen.co.uk/

They can offer advice on the right needles likely to work well with K&N (or copies of them) air filters.

My experience with K&N's was I (young & stupid) stipped the old airfilter box and elbows out and put a pair of K&N's on, and found that my top end went to ....! well not very good! I suspect that this was to do with the vacuum that had been lost given I had gone from a high pressure resistance air filter system (STD 90 v8) to a low resistance system, thinking power would increase (young + stupid). The way the SU's work is they have a single needle which is drawn up the dash pot (aluminium lump on top of the carbs, held on by 4 screws), the needle is tapered to a specific profile to match the vacuum (engine load).

Having fitted a wideband lambda sensor on mine, I found that land rover had got the needle selection spot on.

Given that yours is a convesion you cannot just use the standard landrover needles as the compression ratio + cam profile also comes into the needle selection, hence it's best to get some details from your engine

1) engine number on side of the block, forget which side, between the two central cylinders (2&6 / 3&5)

2) compression ratio from below / above the engine number

3) carb needles (if you carefully remove the 4 screws, you can lift off the dash pots and inspect the needle which should have 3 letters on it (may need to remove the needle as it may be on the top face, from memry there is a flat headed screw that is undone and it slides out).

4) suggest you get both needles as I've heard of someone putting different needles in both dash pots.

I'd suggest on reassembly that you put oil in the top of the dashpots (undo the black nut and lift out the damper, and add a little oil to the center of the dash pot where the damper came out of) the oil is usually the same as the engine oil, it acts as a damper to smooth the speed the damper responds to engine load.

Then give Burlen a call and explain what you have and what they'd suggest needle wise to see what you've ended up with as it may need new needles.

edit-

The air vent at the rear of the engine (top of the belhousing / block) is the fresh air port, and is normally connected onto the air filter a distance away from the rocker cover vaccum ports, or where they connect onto the carbs (as mentioned above) the rocker ports are crackcase scavenge ports so pick up on the gases that blowby the piston rings. Given you are using K&N's i would suggest (as stated earlier above) that you put a small air filter on the port hose, but you may also benefit from putting a patial restriction in the hose too (think of an 8mm bolt with a 3mm hole in the middle of it) so that the block is always under vaccum from the carbs (this principle is used on the LS engines). Given the fresh air port was oriiginally connected onto the engine side of the air filter it would have always had some negative pressure / slight restriction.

The reason why when you block it off the engine stalls is because the carbs are tuned to let by that leaking fresh air supply, so when you block it off the mixture changes and it stalls (you;ll probably find the mixture goes rich, given the carb needle is lifted with the extra vacuum in the dashpot.

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Had K&Ns on the SUs on my 101 for a short time while I sourced the correct airbox. They sounded good for ten mins then the induction roar just became tedious and I'm sure you could hear the petrol gurgle in!

Sold them on for what I paid for them.

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  • 7 months later...

Bit of a bump here.. still struggling on with this. Left the project dormant for a while but now back on it.

To further add to my confusion, the car is rocking a series 3 bulkhead with series 3 pedal box and servo. The servo previously wasnt working. Brakes are still good, but firm and obviously MOT fail without servo working properly. Theres a vac hose going to I believe the previously refered to open breather at the back of the engine, but when its all connected the revs drop to around 200/300rpm.

With a bit of throttle its fine but it barely idles as is.

I assume that its that the idle needs adjusting on the carbs (no idea how to do this) an would assume that for some unknown reason the car was setup to run without the servo?

Any advice / input welcome :)

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Bit of a bump here.. still struggling on with this. Left the project dormant for a while but now back on it.

To further add to my confusion, the car is rocking a series 3 bulkhead with series 3 pedal box and servo. The servo previously wasnt working. Brakes are still good, but firm and obviously MOT fail without servo working properly. Theres a vac hose going to I believe the previously refered to open breather at the back of the engine, but when its all connected the revs drop to around 200/300rpm.

With a bit of throttle its fine but it barely idles as is.

I assume that its that the idle needs adjusting on the carbs (no idea how to do this) an would assume that for some unknown reason the car was setup to run without the servo?

Any advice / input welcome :)

I had a bit of a play with the idle adjustment last night, but could only get it to idle with the servo plumbed in at silly revs...

You could get the idle set perfectly, then give it a rev and the revs wouldn't return back down.

Strangley, post adjustment to idle speed, the moment you take the servo hose off it runs perfectly everytime.

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  • 3 months later...

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