Got my RV8 running now and it has issues. I think it's either running rich or somehow oiling up the spark plugs. Once the car is running it seems to be fine. However if left over a period of time, say a couple of weeks the plugs are black and wet. It struggles to start and one or more cylinders don't seem to be firing. The exhausts are cold. Take the spark plugs out of the offending bores and they are wet with black fluid. I don't know if its oil or sooted petrol. Clean then up and it'll fire and run happily.

I am new to building engines so (and I built this one) any advice is appreciated. I thought that maybe the valve guide seals were the offending problem but there seems to be differing advice on the net.

I don't understand how the plugs can get black and wet when the engine is just sitting there. My best guess is that it is running rich (hence sooty plugs) and maybe after switch off, it is continuing to leak petrol into the engine which then floods it at the next switch on?

What type of carburettors are you using? Or is it EFI? If carbs then maybe something like leaky needle valves on the fuel inlets to the float chambers?

btw, it's not uncommon to see sooty plugs on an RV8 unless you've been on a fairly decent length journey even if the car is running fine.

[Edited on 28/9/2015 by craig1410]

Well it seems to get oily as it sits there!!!

Things I should have already mentioned.

Just been through the IVA which it flew through the emissions test without braking a sweat.
It's a 3.9l Rover V8 with a Weber 500 carb. Carb bought known good from a locoster running a 3.5 engine. I would have though it would be running lean not rich.
Carb has recently been serviced.
I haven't done a compression test, just bought a tester now. On its way in the post.


Tried to start yesterday after a three week layup. No go. Chugging, sounding awful and even some petrol coming from the top of the carb. I had a feel of the exhaust headers, one stone cold. Whipped the plug out, black and wet. Cleaned it with a wire brush. Started straight away! Ran okay.

[Edited on 28/9/15 by Irony]

Okay, that info makes the carb less likely to be to blame.

What sort of crankcase breather(s) have you got? Is your crankcase getting pressurised and after switch off causing oil to be pushed through the valve seals?

FYI, on my RV8 I've removed the flame trap as it was fouling the bonnet and I've routed it to an oil catch tank with a K&N filter on top. I also swapped my rocker covers around so that the flame trap is on the rear of the left side and the filler cap is on the rear of the right side.

Edit: Is it always the same cylinder that fouls up?

[Edited on 28/9/2015 by craig1410]

If it's sat around dump the fuel and use fresh.

I have a little digger, parked it up maybe 2 months ago, would not start on Saturday fuel bowl looked like it was full of water, drained out the tank and it struggled to light with a blow torch !

Fresh fuel sorted me out, this new stuff they are selling does not last, next time I will drain it down when parking up.

Worth a shot but my RV8 sat all winter with about 10 litres of petrol in the tank and started first try in the spring. It's the same every year really.

Doubtful it's duff fuel, filled it up for my iva a month ago with premium unleaded.

Breather on the cylinder head goes to the pvc port on the card like so




Description

Just a thought, there were some plates in the cylinder head covers. Flat things that didn't seem to do much. When I had the covers cleaned they didn't come back with them so I left them off. What do they do?

[Edited on 28/9/15 by Irony]

When you say "cylinder head covers" do you mean the rocker covers? If so then maybe you'r talking about the baffles which try to prevent oil being thrown up into the breather pipe. Oil tends to splatter around due to the action of the rockers and ideally you don't want anything except fumes going into the flame trap.

Have a look inside the breather pipe for signs of oil and try to rule out something like a faulty PCV valve by venting the rocker cover to atmosphere and plugging up the pipe from the carb. You should see some oil fumes coming from the crankcase but not too much.

With a lot of fuel pump designs pump pump retains and deliver significant volume of fuel under pressure even when switched off. Fuel would appear to be leaking slowly past the float chamber valve when the ignition is switched off.

There are a couple of fixes you could try either fit a solenoid valve in the fuel line - Lotus did this on the 1970s -1980s models, the valves are sold by LPG conversion companies such as Tinley Tech or can be found on eBay.

Or you could fit a switch in the fuel pump feed and switch off the pump before stopping the engine.

quote:

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Originally posted by craig1410
When you say "cylinder head covers" do you mean the rocker covers? If so then maybe you'r talking about the baffles which try to prevent oil being thrown up into the breather pipe. Oil tends to splatter around due to the action of the rockers and ideally you don't want anything except fumes going into the flame trap.

Have a look inside the breather pipe for signs of oil and try to rule out something like a faulty PCV valve by venting the rocker cover to atmosphere and plugging up the pipe from the carb. You should see some oil fumes coming from the crankcase but not too much.

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The consensus on the V8 forum is that it's just running rich and possibly the float levels are not set up correctly. I am going to take the carb apart and have a look to see what jets are in it. The carb was originally used for a 3.5. Mine being a 3.9 i thought the last thing would be it running rich. Apparently this is not always the case.

Yeah that was my first thought but it sounded less likely when you said the carb was a known good carb, recently serviced and that it had passed emissions on your car.

I still think the most likely cause is a leaking needle valve on the float chamber inlet possibly caused by incorrect levels as you say. Also, I know that some carbs are sensitive to the angle of the carb itself (eg. holley 390) and require adapter plates to level them up to avoid issues. Hopefully it will be something simple like a piece of debris in the needle valve seat keeping it open and bleeding down the residual fuel pressure after switch off. Could also be some heat-soak from the engine evaporating the fuel in the float chambers but that usually just causes hot starting problems not so much 3-week-later starting problems. You can get heat insulating adapters to help with this if necessary.

Let us know how you get on and good luck.

[Edited on 29/9/2015 by craig1410]

Does the carb sit level when mounted on the engine, have a vague memory of having problems with a RV8 running a Holley and there being 2types of carb spacers? One was tapered , the other parallel . Worth checking the float heights and possibly the auto choke if it has one , maybe even securing the choke flaps in the off position just to check

The engine does sit at a slight angle. But from memory I can't remember how much. The SWMBO is going out tonight so I shall get a full night in the garage. I shall report back with all my findings!

Took the carb apart last night and it was way easier than I thought. I watched a couple of videos on the net and it seemed to go okay.

1. I think the float heights are way out. By at least 3 or 4mm. I don't have a handy 7/16 drill bit but they are still out. Am I right in thinking I just bend the metal as per the manual?



2. Found a tiny sliver of metal that shouldn't be there.


3. How do you measure the jets accurately? I found the hole in the jet to be 2.1mm and about 2.4mm



4. Rods: As image





I took the car out before doing this procedure and it did run okay. By the time the gentle 15min run came to a end it was beginning to cough out a bit of black smoke and small backfires. This has happened before and if I clean the plugs it will no doubt run fine.

I whipped all the plugs out on one side and I have photographed them. They pretty much look like this



I made a tedious video of the whole thing if more info is needed. The video was to help me put it back together. I am not a good camera man




Any help would be greatly appreciated.

I'f I'm not mistaken, your float heights (assuming 7/16th is what you are aiming for) are too low because in the photo they are upside down and the float arm is prematurely touching the needle valve. So I don't think adjusting the floats will make the car run any leaner, possibly the opposite.

That said, maybe the floats are just fine and you have debris in the seat where the needle valve seals. That might be due to swarf as you found elsewhere. That would make the float level appear to be low when it fact it's fine but at the same time it might cause the needle not to seal properly. It would only need a 0.5mm or so piece of swarf to cause an apparent 3-4mm float height error due to the leverage ratio between float arm and where you are measuring from.

So, if you've not already done so, please check and clean the float needle valve seats with an air line or something soft like a toothpick. Don't scratch the seat with anything metallic if possible.

HTH,
Craig.

ps. I can't help you on the specifics of this carb as I don't know much about it. I've got twin SU's on my RV8

pps. if the car is running progressively richer as it warms up then that's no surprise as effectively it's like having the choke stuck on. As someone else mentioned, check that the choke is not in fact activating when you don't want it to. My RV8 only needs manual choke for the first few mins and then it will run fine without it but I'm on much different carbs to you.

[Edited on 1/10/2015 by craig1410]