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Decline In Engine Performance


Guest robbie

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Guest robbie

Having read other related topics on the forum I am unsure of the cause of my latest problem, so I turn to you once again for help!

 

As you may be aware I have managed to get the engine up and running and driving quite well until about 15-20 mins into the drive when she splutters, wont take the throttle and dies.

I have read about probs with air leaks and overheating causing the fuel to vaporise and it seems to run well until the engine is hot, or at least at running temp for a few mins, up to this point all seems well.

The twin carbs are probably running rich as I havent managed to fine tune them, perhaps this is a factor. The only other noteable occurance is a slight spit audible in the exhaust as though one cylinder is doing something odd!

Is there anything I can check to get by this next hurdle?

I really want to have a reliable car that can travel a fair distance with out me gritting my teeth the whole journey in anticipation of the next prob!!

Oh by the way, the car is only doing small run around house and garden and standing still for minor adjustments, perhaps this is a factor?

 

Thanks again lads

 

Robbie

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Guest Martin S

Hi Robbie

try checking the fuel tank breather, if the breather is blocked or not there then the engine will run untill there is a vacuum in the tank , when the fuel pump cant overcome the vacuum in the tank the engine will stop.

 

Hope this helps

Martin

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Guest Steve Allen

Hi Robbie

Yes could be the carb setup but just to let you know I have recently been suffering with the same problem, While the car was started cold everything was fine. 10 miles down the road and then no throttle, this got worse and worse until I was stopping every mile or two. The bad thing about it i was coming back from a rolling road session in hull (50 miles) and must of broke down 10 times.

whilst sat on the side of the motorway I rang the garage (had to blame someone)

and he said my coil might be over heating. Surpise spare coil in the boot, changed two miles down the road and then stop.

After further discussions I was told my petrol pump might not be supplying my new 45 side drafts enough fuel and that I should put an electric one in with a regulator. All weekend was spent doing this and adding a cut of switch etc.

Guess what ............... went 5 miles from my house and stop. managed to get home by tick over alone.

Moral of the story is this: One new coil, Electric pump and regulator. rolling road session, new plugs and leads just in case and the problem was:

Rubbish in the fuel tank blocking up the filter attched to the fuel gauge sender. Fine when cold because it settled and got worse as the tank mixed.

Always had a problem sealing the thing and should of never used a sealent.

Still leaks now. Steve

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Guest robbie

err.....fuel tank breather?

I mean ..of course............

eh......I'll go and check it's not blocked!

 

Seriously though I think I sealed this up (plastic tank from Fiat) and only left return on fuel sender uncovered, do you think this would allow air movement to the tank?

If not then we've certainly isolated a major problem.

I'll have a look see and get back.

 

 

Nice one lads.

Robbie

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Guest Mike Rhodes

Had 2 similar problems some years back, first was the car would run ok for a few minutes and then stop impossible to restart for 10 mins or so, cause;- the silicon I used to seal the tank dissolved in the petrol and deposited on the pickup filter.cured by flushing tank and making/fitting a rubber gasket. Second problem caused misfiring when hot with rev limiting at about 2000 rpm and random hunting between about 1500 and 2000 rpm, cause distributore.

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Guest robbie

Got a bit more info that I hope will help get a result with my twin carbs.

The car runs sweet from cold and drives quite well but after about 10 mins all of a sudden it got quite "lumpy" eventually stalling. Just before it stalled there was quite a bit of wheezing or suction noises from the first set of carbs. Imediatly after stalling the petrol just poured out of these two carbs. I left it for about 5 mins and up she went again as if nothing happened. Could it be a fuel pressure problem, (too much) or float problem that is rectified when the petrol drains out of the carb.

Remeber these have just been professionally rebuilt.

 

Over to you!!

Ta

Robbie

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Guest Steve Allen

Robbie.

I'm a fine one to give advise as my car is having a similar problem, now changed everything including the distributor, cap and rotor arm and still the same.

One thing i do know you should not have petrol leaking out of the carb, this makes me think that you have crap in the carb which one is making your needle valve stick open and if you do have debree in the carb this could be what's causing the running problem. worth taking the top off and clean out chambers and jets. I had a similar problem to the previous member were silicone from sealing the fuel sender had made it's way past 3 filters into the carb

Hope this helps

Steve

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Guest robbie

Took advise, cleaned out carb, there was a small amount of fine "gritty" stuff in the inlet filter (not beyond) checked the floats, seem to float! blew into inle to see that shut off valve works, seems to be ok too (though everything that i've eaten since tastes of petrol!)

Bolted everything back again, car ran for short time and again stalled. This time starting was a problem. The car would fire up and as the initial revs dropped she stalled again!

I'm sure you're getting fed up with this, I know I am! Thinking of changing to std carb system (38dgas) what do you all think? :(

 

Thanks for listening!

 

Robbie

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I have had sticking valves do something like you describe.

When head and valve cold the valve moved OK. As the exhaust valves warmed up the stem got bigger and the cam had to work harder to open valve, But the spring could not work harder to close the valve so the piston closed it. There were some interesting marks on the piston when I took the head off.

 

I also had inlet manifold gasket leaking coolant into a cylinder cause odd problems. The engine apeared to run OK cold but as the coolant warmed up and the presure climbed it got into one cylinder, on strip down that piston had a perfectly clean crown where the water had cracked all the gunge of the piston.

 

These were 2 cars about 20 years apart.

 

Ian

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Guest robbie

Hope it isn't the valves! Are there any ways of determining this before removing head?

I have got a fuel regulator but it is dated and there is no way of knowing how effective it is. It seems to be a simple restricting bolt! Is anyone running a system on full flow from fuel pump? (Facet) Someone has told me to look here first as the pressure of the unrestricted pump could lift the float valve and be part of the cause of my problems.

Keep it coming as I weed out the possible causes I will let you know

 

Thanks

 

Robbie

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Guest robbie

Think this might be it, I have a "regulator" but it is an old fuel king type with a simple screw which I assume screws in to restict and out to increase flow? Thing is I can't see any means of knowing how much (if any) I have altered the flow? :wacko: Total guess work!

I amy have to get a new reg with graduations on unless I can find some means of establishing pressure change in present system>

Heres hoping someone knows what I'm talkin about.

It's great havin so many heads under the bonnet of my car!!!!!

Thanks lads

 

Robbie :)

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Guest robbie

I've been turning wrong way for a start! Might go some way to explain why the engine won't take revs when warm and simply stalls after a period of time. I will investigate tomorrow. Still no way of knowing exactly where I am with pressure as the filter was never actually set for my engine so I suppose a bit of trial and error.

 

Thanks

 

Robbie

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