Running on 7!

[Webby66]

I have a problem with my 98 Chimp. When she gets hot and the fuel level drops, she starts to feel as though she is running on 7! She also then starts to backfire on the overrun as well. I think it may be a fuel problem due to venting issues on the tank because I have taken the fuel cap off and there is a hissing noise as air is taken in, together with loud bangs as the tank expands.

I thought the the carbon canister may be blocked in some way or restricted, so was considering just running the vent pipe into the rear wheel arch without using the canister.

Any ideas?

[QBee]

Check your plug leads are on properly - sounds daft, but these cars are a little prone, with the extenders, to the leads just popping slightly off, especially when hot. The number 8 plug (nearest to the driver) is the usual suspect.

Might be worth popping the plugs out to check if you have one that looks different, and then diagnosing why. That can be the plug itself, leads, distributor, coil, you name it, it could be it. I use the Iridium 6 plugs, rather than the standard 7, recommended to me by a guy called Chimpongas, and they do seem to run better and stay good longer (but cost more in the first place (now just listen out for that well known noise of a can of worms being slowly opened )

They all suck air in when you take the filler cap off, but do be wary of the fuel gauge if you have done a long journey from brimming it - I ran out at 70 mph on the A1 alongside an HGV the other day, with the gauge showing 2 gallons left! Luckily I was wearing the brown trousers.....

You could have a carbon canister issue as you describe - worthwhile testing it.

Another issue is long hard left hand bends with low fuel - left hand because the fuel pickup is on the left hand side of the tank and the tank is not baffled, so the fuel all ends up on your side of the car. Most noticeable on track days, but the engine coughs to remind you, rather than feeling like it is running on 7.

[phazed]

It may be as simple as NOT calling it a chimp!

[Webby66]

Thanks for this. I will check the leads as the heads have recently been to replace the exhaust manifold after some bolts broke!! Still replaced the head gasket etc., and found that the bores looked pretty good as well. The plugs, leads and dizzie are all new but wirth a look.

When i first got her I ran out of fuel even though there was between empty and quarter full. The feeling was very similar!

[Webby66]

phazed said:

It may be as simple as NOT calling it a chimp!

Too true I am going to revery back to Chim or perhaps Stella as it is such a stellar car!!

[Classichims]

Yep, I had a misfire to find the plug shroud had spun round and shorting on the exhaust, as Qbee says it's the first thing to check.
Partially blocked fuel pipes or crud in the tank.
Mine runs like a Brabham on Super or 99
Like a Larousse on unleaded!

[QBee]

That's a fair point about fuel - mine much prefers super, runs a bit rough on standard unleavened.

[Webby66]

I always use 97 octane Super. Must admit though it's a b*****r to fill up!!!

[phazed]

Being a tight wad I run mine on ordinaire apart from TDs and even then often I don't

Can't say that I can tell the difference.

[Webby66]

Checking the plugs and found that one of the plugs didn't have a screw end on it which may explain my problem. Will try tomorrow to see whether it is or not. Fingers crossed!

[taylormj4]

I had lots of problems with extenders and shorting, tried new ones but they didn't last, so I got shot of them and put the leads straight onto the plugs and then covered them with the woven heat resistance socks. Fine since. You still need to try to keep a gap between the sock and the exhausts to keep the sock in good condition.

[Webby66]

Think have i identified the cause of the problem and it is the extenders so these will be replaced with a nice new set from Clevor Trevor.

Thanks for the help.