over reving

[Keith.bryant]

I have a bmc 1.5 which is over reving in neutral when the engine is up to temperature it idles normal when cold also when engine is worm the engine will rev up then down without me touching the accelerator. fuel injection pump has been reconditioned and been bench tested and all is working A1. is it possible that the engine is burning engine oil?? on start up there is blue smoke but under load this dissappears.if engine oil is being burnt how would it be getting into the cylinders??

[RLWP]

That sounds like an air leak into the fuel system. It's an unexpected feature of those pumps

 

Richard

[bigste]

Deffo an air leak fwiw

[RLWP]

Deffo an air leak fwiw

 

Pretty surprising when you first experience it. You'd think the engine would falter

 

Ours was a loose union in the feed pipe

 

Richard

[cereal tiller]

That sounds like an air leak into the fuel system. It's an unexpected feature of those pumps

 

Richard

Sometimes Exacerbated by a blocked Pre Filter.

[Keith.bryant]

where am I looking for an air leak?? most common places would help

where am I looking for an air leak?? where's the most common place an air leak will come from??

[David Schweizer]

I used to get the same with the BMC 1.5 in our boat, it always happened when I had left too long a period between fuel filter changes. A new fuel filter always cured it

[MtB]

Fuel filter is the usual culprit. When did you last change it?

[Keith.bryant]

fuel filter changed a few months ago

[MtB]

And when did the problem start?

[Bee]

Anywhere at all from the tank to the injection pump, filters, lift pump, anything with a union, gently rattle the pipes as they go into a union, any movement and that's a likely leak, even if they all seem ok they have probably been made and re made many times and olives and washers hardened and scored, it can be tricky to find leaks. any little weep of fuel on a fingertip when you touch the underneath of a union is a likely leak.

[Keith.bryant]

problem started months ago and I've been trying to resolve it ever since.I did change the fuel filter and housing at the same time I can't see any leaks front the fuel filter so kind of counted that out.

[RLWP]

Anywhere at all from the tank to the injection pump, filters, lift pump, anything with a union, gently rattle the pipes as they go into a union, any movement and that's a likely leak, even if they all seem ok they have probably been made and re made many times and olives and washers hardened and scored, it can be tricky to find leaks. any little weep of fuel on a fingertip when you touch the underneath of a union is a likely leak.

 

I usually start at the tank with a set of spanners, then work my way along the feedpipe checking every joint to see if it is tight

 

Of course, you stand a chance of breaking a joint like this - which suits me fine. I'd like a joint to fail in a planned way rather than in a tunnel

 

 

Richard

[MtB]

problem started months ago and I've been trying to resolve it ever since.I did change the fuel filter and housing at the same time I can't see any leaks front the fuel filter so kind of counted that out.

 

I'd be inclined to count it back in then! Coincidences like this are are rarely that.

 

Did you check/replace the little O ring under the head of the bolt?

[Keith.bryant]

yes I checked everything but I will go back over it tomorrow

[pete.i]

When it happened on my BMC 1.5 it was a union on the output side of the fuel filter. Whilst the joint did look a bit weepy it certainly wasn't dripping fuel and if the engine hadn't started doing the up and down revs thing I wouldn't have bothered even looking at it.

[cereal tiller]

yes I checked everything but I will go back over it tomorrow

Had this same problem with my B.M.C. 2.5 3 Years ago,spent too much time trying to find the problem

 

I know the Boat well having built the entire thing from scratch,but could not work this intermittent fault

 

Then I removed the Half inch diameter Fuel tank Breather hose,it was blocked

 

Problem gone

 

CT

[Slim]

I once had a similar problem that went on for years ,literally. Every joint from tank to injectors checked and tightened without success. Thinking there might be an obstruction at the tank shut off valve I applied some fairly gentle air pressure to the feed pipe at the filter input point. Instantly bubbles appeared at a joint on an intermediate shut off value. Re-made that joint, problem cured. At no stage had there been ANY sign of a leak.

 

 

Frank.

[MtB]

I once had a similar problem that went on for years ,literally. Every joint from tank to injectors checked and tightened without success. Thinking there might be an obstruction at the tank shut off valve I applied some fairly gentle air pressure to the feed pipe at the filter input point. Instantly bubbles appeared at a joint on an intermediate shut off value. Re-made that joint, problem cured. At no stage had there been ANY sign of a leak.

 

 

Frank.

 

 

That's an EXCELLENT idea. Thanks!

[Tony Brooks]

 

I'd be inclined to count it back in then! Coincidences like this are are rarely that.

 

Did you check/replace the little O ring under the head of the bolt?

 

I know that is often the culprit but not all those CAV filter used O rings. The O ring ones have a taper at the top of the bolt hole. The soft washer ones have machined "disk" around the bolt hole for the soft washer seat.