Weber 40 DCOE, Spitfire Mk1 1147 and Standard Mechanical Fuel Pump

[Neil Clark]

When I went out on a test drive after the MOT with about 3 gallons (15 litres) in the tank, the car really struggled to catch when pulling away from uphill traffic lights.  No problem really on flat ground.  It was suggested to me that the Weber really needs an electric fuel pump anyway.  The Weber is inherited with the car and I've no idea if it was correctly specced but it does have the Moss manifold and a K&N filter.  I've topped the tank up to half full, but it still does it.

Does anyone have a view on this?

[Clive]

I think a manual pump should be fine , they are good for 100+bhp.

More likely is a jetting issue. Some tuners are naughty and sort WOT but don't pay attention to low rpm. Worth seeking out a decent tuner

[johny]

Dont know anything about Webers but I would have thought a good thing to check is its float height. This controls how much fuel sits in the float chamber reservoir and if low could cause starvation when on a slope but as Clive says with a non standard engine a specialist is probably required, at least for the initial set up ...

[Neil Clark]

Could it be that the carb is a bit gummed up?  Other than when I had got the car re-assembled and pottered along our road a couple of times, the carb has just sat for nearly 4 years now since the original accident and never been under load in that time.  The guy who helped today suggested I run it for at least a few hours before I do anything, and not in stop start traffic if poss.  i filled it with Shell V Power this afternoon.

[johny]

well you say it runs ok on the flat but not when pulling away up hills and I think gumming up would cause a problem all the time. However it is possible, like a few other causes, and you might stumble across the correct answer but I personally prefer a more structured approach to fault finding. This is even more important with a car thats new to me and I like to check each of the engine systems so I know theyre correct and can then be crossed off the list.... 

[Clive]

9 hours ago, Neil Clark said:

Could it be that the carb is a bit gummed up?  Other than when I had got the car re-assembled and pottered along our road a couple of times, the carb has just sat for nearly 4 years now since the original accident and never been under load in that time.  The guy who helped today suggested I run it for at least a few hours before I do anything, and not in stop start traffic if poss.  i filled it with Shell V Power this afternoon.

It could be one of the small passages has got blocked. Or a progression hole (though unlikely). Or it may be it has never been right. I parted with a set of Webers as they didn't work well on a particular engine, (I needed 5 progression hole carbs, the ones that came with it were 3 or 4 I think) amd that had a terrible flat spot. A change to Dellortos helped enormously, but they flooded on autosolos. Ho hum. 

Webers are not terribly complex, you could easily strip and check many jets/tubes etc. Google is your friend....

[Neil Clark]

Sorry, I wasn't stating it accurately.  It didn't seem to be happy after stopping at relatively steep uphill traffic lights, junctions etc.  I'll run it for a good while today around here and see how that goes.  Yes, I've got / found a lot of the Weber info thanks.

Will the original specification engine timing setting be affected by the Weber?  We're in my zero knowledge area here.

[johny]

If not done yet you could carry out a compression test and check valve clearances so thats two things off the list. They definitely should be as standard although I suppose the cam might not be🤔

[Clive]

7 minutes ago, johny said:

If not done yet you could carry out a compression test and check valve clearances so thats two things off the list. They definitely should be as standard although I suppose the cam might not be🤔

Aftermarket cams use different valve clearances, up to 22thou... but all dependent on the cam manufacturer.

Timing not affected by the weber, may be affected by a cam change. Best advice is to advnace until you get light pinking under load, then back off a smidge. After that it is a day at the rolling road with somebody who plays with springs and advance curves, or a 123, or mapped ignition.

[Neil Clark]

How do I tell if the cam has been changed?

[Pete Lewis]

well thats not simple, remove it and look see is one method  triumpmh cams have identification grooves on the front journal

other makes may have the type stamped in the shaft forging

a timing disc mounted to the crank and with a dial indiactor  on a rocker/pushrod/cam follower  measure the angles on the disc with the lift of the cam followers

as to when the lobe opens and closes 

Pete

 

 

[johny]

2 hours ago, Neil Clark said:

How do I tell if the cam has been changed?

Certainly if youve changed to a Weber then a different cam, head skim and porting would be sensible to make any use of it....

[Neil Clark]

30 mlles of running around this morning, open road and traffic, and the hiccups have disappeared, running better and better from the cold damp start this morning to the warm summery day now.  And now the gear selection has gone very loose and imprecise - that's about the only part of the transmission I didn't remove or fiddle with in the rebuild!

[Clive]

24 minutes ago, Neil Clark said:

30 mlles of running around this morning, open road and traffic, and the hiccups have disappeared, running better and better from the cold damp start this morning to the warm summery day now.  And now the gear selection has gone very loose and imprecise - that's about the only part of the transmission I didn't remove or fiddle with in the rebuild!

Good news. Guess it may have been ignition, now drying out.

Not so god on teh gear linkage, but cheap enough to sort if a faff. Canleys are probably teh best source unless you find genuine NOS

[Neil Clark]

2 minutes ago, clive said:

Good news. Guess it may have been ignition, now drying out.

Not so god on teh gear linkage, but cheap enough to sort if a faff. Canleys are probably teh best source unless you find genuine NOS

I've ordered the Canley's kit after I remembered reading about it in the posts by Rich Tea Biscuit

[DanMi]

probably just needed an Italian tune up (thrashing) after years sitting Idle. The problem with modified cars is that you have no idea what has been done and to what standard (unless you modified it). The weber would indicate that more has been done as the twin SUs work well on the mk2 (hotter mk3 cam), but the only way to tell without documentation is to strip the engine, well I guess you could measure with dial gauges to see if the cam is stock but if it isn't you still will need to know who made it to find the correct valve clearances. 

[Neil Clark]

Having fitted the radiator deflector boards and radiator grilles the temperature now sits steadily in the middle of the gauge at last, at all times.  The car is running really beautifully except but stutters starting from stop at traffic lights or uphill.  Tickover is fine at all times and just now is adjusted to 1000rpm.  When I press the accelerator to pull away promptly as I say it's only a stutter but needs care to get the revs going.  

Am I way off the right answer here to think it might be a fuel supply issue?   I've fixed the fuel leak on the input side of the carb.  Never having had a Weber before all my experience was with SU's.  I imagine that the mechanical fuel pump needs to be operating to feed the initial head of fuel to the Weber?  So while there is probably some fuel there (which is why it doesn't pick up strongly), perhaps it needs a couple of seconds of turning faster to boost the amount of fuel the Weber wants? 

[johny]

Well you could try a replacement pump as theyre not expensive, are easy to change and always handy to have a spare as they can pack up with little warning....

[NonMember]

1 hour ago, Neil Clark said:

So while there is probably some fuel there (which is why it doesn't pick up strongly), perhaps it needs a couple of seconds of turning faster to boost the amount of fuel the Weber wants? 

It may well be the opposite. The Weber is likely to be even worse than an SU at delivering the right mixture at idle, so the engine's probably even richer than a standard one would be. That cokes up the plugs, and when you pull away you get poor spark and misfires, until they've had a chance to clear out.

[johny]

7 minutes ago, NonMember said:

It may well be the opposite. The Weber is likely to be even worse than an SU at delivering the right mixture at idle, so the engine's probably even richer than a standard one would be. That cokes up the plugs, and when you pull away you get poor spark and misfires, until they've had a chance to clear out.

I suppose that could be tested racing car style by revving up the engine a few times before pulling away in the hope that the plugs are then clean.... 

[Neil Clark]

So at the lights boy racer I must be again?  Awesome.  Just entered my eighth decade.  Yee hah!

[johny]

You know it attracts the girls!

[Pete Lewis]

sounds more like the accelerator pump is lacking and its flat spot on rapid throttle opening

take care a fast idle setting will often overule the slow run ciruit and the idle mixture screw have little effect 

as the slow run circuit is already bypassed by the overly open throttle plates 

common error on fix jet downdrafts 

Pete

[Neil Clark]

Now that it's running well overall I'll try that Pete.

[Pete Lewis]

slow the idle then set the mixture screws to best    readjust idle after if needed 

Pete