Ever get the feeling of de javu?

[Polly-Red7]

Hello! Apologies as this is quite a long post and it will also appear on the facebook page as well.

It would appear yet again that Polly my 82 2 ltr fhc is playing silly buggers and developed a misfire/lack of power around 2500-3000 rpm. It all started about 2 months ago when I was leaving work and accelerating down a slip road when the engine gave a distinct misfire and lost power. Since then I've tried numerous remedies without any joy.The car idles lovely and under light load behaves normally but once you reach the quoted rpm the car has a slight misfire and is almost holding back. Even dropping a gear the power continues to wain. This is especially annoying on any sort of gradiant.

At this point I have tried the following to cure it and on occasions I think I've cracked it, only for the problem to come back the next time I use the car.
Plugs,dizzy cap, points, rotor arm, condenser, air filter have been changed. I've also changed No.3 ht lead as it looked dodgy. I'm getting a good spark on all cylinders.
I've checked and triple checked the timing and I get a dwell angle of 40° and the dizzy has a new vacuum pipe on.
I've set and re-set the carbs using an airflow meter (the car passed emissions on MOT last week).
I've tried 2 different coils
The float chambers are at the correct height.
Dashpots are oiled and raising/falling as they should and the needles look ok.
The inline and fuel pump filters are clean.
I know my carb mounts are past their best and have caused me grief in the past, but normally as now a good smearing of high temp silicone does the trick while I source replacement ones.
I haven't yet done a compression test as I need an extra pair of hands.
I've hand cranked the engine and the valves appear to be working ok, although I haven't checked the clearances.
There is an oil leak but I can't tell if its the cam or cylinder gasket and I can't see anything when the car is running. I've no residue on the dip stick or filler cap to indicate its the cylinder head gasket that has blown but I'm running out of ideas! Any help as always greatly received.
Chris

[Hasbeen]

OK, you have done all the usual checks & replacements, I suggest the following in about this order.

Check the fuel pressure. Your symptoms are suggesting fuel starvation. Even if you have to go to a specialist to find a low pressure gauge. If this is impossible, set the thing up with a gravity fuel supply from a container on the roof, & check the result.

I have had these symptoms when the check valve in the fuel pump had a bit of rubbish in it stopping it sealing, reducing fuel pressure to about 1.5 PSI, & when I fitted free flow air filters without fitting rich needles.

Check fuel hoses. How old are they? Could one be breaking down internally?

Spray WD 40 or similar around the inlet manifold to check for air leaks. Use Beans method of clamping your carb mounts.

Check the valve timing.

Do that compression test

Just remember, YOU ARE HAVING FUN.

Hasbeen

[skertonman]

Does the lack of power continue, or is it just at that rev range.

I'm also thinking fuel starvation, it the tank breather blocked creating a vacuum effect?, whereby the pump isn't strong enough to suck enough fuel.

Crap blocking the pick up pipe in the fuel tank before it even gets to any other filters.

[littlepippin]

An easy one to rule out is to check and lubricate the bob weight in the distributor if you have one - does it advance the timing ? Think so.

[Polly-Red7]

Thanks for your replies so far. I shall add them to recommendations from the facebook page and let you know how I get on. It looks like a busy week!
A couple of follow up questions to individuals,
Hasbeen, what or how do I find the Beans method of clamping?

Skertonman The car accerates through the gears until I get to third as I change up in 1st and 2nd before reaching 2500 rpm under normal driving conditions. Its when I pass 2500 that the engine problems occur its almost the engine is being held back no matter how much I open the throttle. I can pull over and rev The car no problem at 6000 rpm when stood? Sometimes I can do this and continue my journey without further incident. Although I'm a little less lead footed under those circumstances. The tank is maybe a year old, how would I check the breather in situ? I don't fancy taking that out again lol

[busheytrader]

Has the fuel tank been replaced in the car's lifetime? They rust from the inside out. I had the exact same fuel starvation symptoms when superfine tan coloured powder (rust) clogged up the in line fuel filter.

The car idled fine and ran well under light load but trying anything at or above quarter throttle would make it misfire and hesitate. It would reset itself under light load and the process would start again.

[Polly-Red7]

Busheytrader the tank was replaced about 12-18 months ago. When I did that the flexible hoses were replaced and I added an online filter to supplement the one in the pump. Both filters are clear, although obviously I can't vouch for the metal fuel lines?

[busheytrader]

The note about the replacement tank beat my reply. I'd still check the fuel filter, pump and carbs for debris etc.

Cranckase breather hose? Mine perished and had cracks that opened up at high revs.

[Polly-Red7]

Will add those to those to the list Busheytrader. My breathers have perished a couple of times since I've had the car so definitely worth rechecking

[Hasbeen]

Obviously you do have a fuel starvation problem, if you can rev to 6000 under no load, but under load you lose power. It sounds intermittent, like a failing hose, dirt in a pump valve, or perhaps above the needle & seats in the float bowls.

I assume you have cleaned out the float bowls, & don’t have muck in there.

What fuel hose did you use. We will only use injection hose stamped “Made in America” as many previously good brands transferred their production to Mexico, & now produce junk. I had a “Gates” fuel hose split longitudinally in under 12 months, & leak 26 litres of fuel out onto the shed floor in 5 days. Check any new hoses for splits, & air leaks.

Hasbeen

[Polly-Red7]

Hi Hasbeen, The flexible fuel lines we're purchased from Rimmers. I will have to get under the car to see what's stamped on them. Yes floats have been cleaned but only a tiny amount of debris in the very bottom either side of the outlet. Before I changed the tank the car ran with tons of crap in there as well as water! I will remove the pump and see what I can see. Oh you didn't mention where to find the "Beans" method of clamping for when I check the manifold?
Cheers Chris

[Graham.Fountain]

Chris, Do you have a garage anywhere near with a rolling road? It's an expensive diagnostic, but it sounds like you've spent enough that it would be worth considering.

Graham

[Polly-Red7]

Hi Graham, to be honest I've never thought about it? But living in Sheffield I'm sure they're must be one about somewhere? Will have to Google it to see what costs are involved. To be honest I bought the car to maintain it myself and enjoy doing it, but like golf it can be very frustrating at times!

[saabfast]

There is a link to Beans blog at the foot of his posts. Basically its using large zip ties or jubilee clip type strip as a tie around the flat bar on the carb side of the rubber spacer and the inlet manifold to pull the two together and reduce the strain on the rubber and stop it cracking.

[skertonman]

If the car passed the MOT then I think it's safe to assume (risky I know) that the hydrocarbons are within range which would lead me to think that the valve clearances are OK, and if it is ticking over and revs up when stationary I think there's mo misfire.

The problem only comes in when under load, when the most fuel is needed, I'm wondering if the carb pistons/needles are moving freely up and down.