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Manta B Carb adjustment and hot start issues


Simon Dobbo
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Hi all

 

Some advice if possible please.

 

I took the Manta to a rolling road guy I have used before to tune the Weber carb etc.

He found it was running ok but pretty lean.

He increased the primary jet size from 115 to 125 and ran it again. Then he found it needed idle changing so he increaded idle jet by one size (55 i think)

Runs great, drives much smoother with no flat spots of hesitation. Drove it back 35 miles on dual carrigeway and loved it.

Then i stopped at the shops for 30 mins.

Car started again no issue - drove 1/4 mile then cut out and would not re start. Lack of fuel i think. After a bit of messing and leaving it for 15 mons it started again and drove another 12 miles great.

Then stopped it again and had same issue, starts, drives a small way and dies and wont restart.

 

ANY IDEAS PLEASE?

called the tuner and he said nothing he has done would cause the issue - but didnt have it before i went there.

Is it vapour lock? or fuel starvation as thing fuel filter was empty which i installed before the pump?

Guessing I need to go back to him but trouble is when its running its great.

 

If it is like a vapour lock - my brain doesnt understand why would get this by simply increasing jet size and the mixture.

 

Like i say it runs really really well - when it does

 

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I’m guessing 1.8? 
 

if the filter looked empty, then it’s possible that the pump isn’t pumpalating very well, or is starting to fail. I know the diaphragm inside can start to deteriorate with time, maybe drawing that small amount more is too much for it. You can run a small low pressure clicky clacky (electric pump) just to test it, and see what happens. 
 

how much fuel do you have in the tank? 
 

what fuel are you using? (E5 or e10?)

 

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Posted (edited)
27 minutes ago, Sutty2006 said:

I’m guessing 1.8? 
 

if the filter looked empty, then it’s possible that the pump isn’t pumpalating very well, or is starting to fail. I know the diaphragm inside can start to deteriorate with time, maybe drawing that small amount more is too much for it. You can run a small low pressure clicky clacky (electric pump) just to test it, and see what happens. 
 

how much fuel do you have in the tank? 
 

what fuel are you using? (E5 or e10?)

 

Hi

 

Yes sorry should have said - 1.8S

Fuel pump looks brand new - believe replaced by previous owner to get it running

I am running on E5 premium - did wonder if out of fuel although sender said half full, so i got 5 liters and put it in and eventually it started so took it to fuel station and filled completely - it only took 20 litres so was plenty in there.

Problem happened again after filling so rules that out.

 

Wondered if larger jets were causing a bit of fuel starvation but wouldnt that cause an issue at '70' on the dual carriageway?

Dont like the tank to engine bay 'plastic' fuel pipe so thinking of installing something a little larger in copper?

 

Edited by Simon Dobbo
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On the -u os, the spacers on the pumps are different between models, seen it previously where the spacer was too thick and it was not running on the cam lobe properly. also when it won’t start and fuel in the filter, definitely check the tank for vacuum, remove cap and see if it sucks. Could be slight vacuum is pulling fuel back. If so it might be check valve in the lift pump slightly leaking back. swapping to a different inline filter with check valve built in might resolve all the issues. 
Great info on jet sizes, hopefully that will help it’s running overall. 

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vacuum in tank is definately a possibility especially if theres an issue with any  breather pipes . the hatch shouldnt realy suffer as the breather is open and folded back to the rear of the tank . i suppose it could kink ? try blowing in it with filler cap off . 

on a coupe the breather is pushed into the chassis leg in the boot area . 

also check pump is working right by trying it into a container from carb end

 

also are we 100% sure its a fuel issue and not ignition related . when car dies try checking for spark .

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Might be worth pulling the sender unit out of the tank and check its condition. Is there a gause on the end of it? Could be blocked not pulling enough through. 

1 minute ago, cam.in.head said:

vacuum in tank is definately a possibility especially if theres an issue with any  breather pipes . the hatch shouldnt realy suffer as the breather is open and folded back to the rear of the tank . i suppose it could kink ? try blowing in it with filler cap off . 

on a coupe the breather is pushed into the chassis leg in the boot area . 

also check pump is working right by trying it into a container from carb end

 

also are we 100% sure its a fuel issue and not ignition related . when car dies try checking for spark .

Good shout there. Distributors do break down. Mine used to do 100 miles on the motorway then boom, pull up to a roundabout and cut out. Several sharp “WHACKS” with a metal billy bat got it running again. Ahh then we’re the days! 

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1 minute ago, Sutty2006 said:

Might be worth pulling the sender unit out of the tank and check its condition. Is there a gause on the end of it? Could be blocked not pulling enough through. 

When i re did the tank I fitted a second hand sender which was in ok condition.

Removed the gauze on advice from the tank refurb guy which is why i fitted a clear filter in the line in engine bay.

Am wondering if fuel starvation due to small plastic line but my brain doesnt get why it wouldnt be an issue at motorway speeds.

4 minutes ago, cam.in.head said:

vacuum in tank is definately a possibility especially if theres an issue with any  breather pipes . the hatch shouldnt realy suffer as the breather is open and folded back to the rear of the tank . i suppose it could kink ? try blowing in it with filler cap off . 

on a coupe the breather is pushed into the chassis leg in the boot area . 

also check pump is working right by trying it into a container from carb end

 

also are we 100% sure its a fuel issue and not ignition related . when car dies try checking for spark .

I will need to get it to do the fault again and then have tools with em and check spark etc.

I think i got a little vacuum when i took tank cap off so could be a vac issue but all breathers were renewed 8 weeks ago and seem ok at quick glance

Its just wierd it started when jets changed and carb tuned.

But he ia adamant what he did cant cause the issue.

Maybe fuel starvation due to needing more fuel with larger jets but wwhy only when hot and sat for a period.

 

Ill stick to boilers and air con 😩

17 minutes ago, Jessopia74 said:

On the -u os, the spacers on the pumps are different between models, seen it previously where the spacer was too thick and it was not running on the cam lobe properly. also when it won’t start and fuel in the filter, definitely check the tank for vacuum, remove cap and see if it sucks. Could be slight vacuum is pulling fuel back. If so it might be check valve in the lift pump slightly leaking back. swapping to a different inline filter with check valve built in might resolve all the issues. 
Great info on jet sizes, hopefully that will help it’s running overall. 

Maybe look at the pump and see if not working fully - does anyone have onfo on spaceers?

Suppose I could fit electric pump and blank off the mechanical one but the car is so original (apart from the carb)

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it wont be anything to do with the nylon supply line being small diameter . its perectly capable . ( unless its blocked) and the flow is only very slow anyway . it only keeps the carb topped up not like an injection system with flow and return pipes.

next time it happens is when you need to investigate at the roadside. 

and if theres any tank vacuum that wont help and could be your issue. 

silly comparison also but engine breather blockages can also create an issue but i doubt in your case . easy enough to check . blow into breather with oil cap off or dipstick out !

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If I have a vacuum in the tank when i try it why would this be?

I assume can only be due to breather pipe issue.

The pipe that vents open to rear is connected with a plastic valve I believe.

Could this be an isue?

I am also thinking - when car was in different garage last week for the gearbox - they mentioned possible small petrol leak where rubber outlet pipe joins the smaller nylon pipe.

Maybe drawing in air or they may have even tightend up the clip and possibly squashed the nylon pipe a litte.

But it was fine on way to the tuners for 40 miles and started fine when went onto the rolling road.

 

 

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For comparison, same setup as yours. I've noticed an absence of any vacuum on mine when removing the filler cap from tank. Having recently refurbed my tank and ancillaries, I was conscious of the nylon fuel pipe going into the rubber re enforced fuel pipe and not over tightening Vs tight enough to not leak. Just a thought

Could be that increase in the jetting has unearthed the problem, but is not causing is.

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the plastic valve on the breather is only to stop fuel going down it and fumes out but this is not where it vents . the pipe ( after various joints ) goes around the rear of the tank and folds back on itself venting open to the atmosphere . you should be able to blow into it and hear it through the filler neck. if you cannot then theres a blockage somewhere which needs investigating

Edited by cam.in.head
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46 minutes ago, cam.in.head said:

the plastic valve on the breather is only to stop fuel going down it and fumes out but this is not where it vents . the pipe ( after various joints ) goes around the rear of the tank and folds back on itself venting open to the atmosphere . you should be able to blow into it and hear it through the filler neck. if you cannot then theres a blockage somewhere which needs investigating

Yes mine has valve on spout that faces upwards on filler neck then a pipe onto the valve that simply goes down and to rear of tank and is open to atmosphere 

I will give it a good run when not pouring in rain and see if I get a hiss when removing filler cap

will also blow up the pipe from rear of tank and see what it’s like

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it sounds like your pipe configuration is not correct . that valve is not connected directly to the vent on mine . im pretty sure its as follows . 

the tank vent hoses around it all connect together via t piece connectors and then a hose comes up to the tank neck.this goes via a t piece to the plastic valve and also back down and then around the tank to the open end. 

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9 minutes ago, cam.in.head said:

it sounds like your pipe configuration is not correct . that valve is not connected directly to the vent on mine . im pretty sure its as follows . 

the tank vent hoses around it all connect together via t piece connectors and then a hose comes up to the tank neck.this goes via a t piece to the plastic valve and also back down and then around the tank to the open end. 

May be the issue then 

I re connected them as I found them but with new T pieces etc.

So 3 of mine connect together via a T piece

Then another 3 connect together via a different T piece

Finally the one on filler neck has the valve straight onto the filler neck spout and the other side goes down and to rear of tank to atmosphere.

So thinking about it - 6 of the vent spouts simply connect across the tank and only vent to atmosphere is the filler neck spout via the little black valve

1 minute ago, Sutty2006 said:

Someone put a schematic on here if all the hatch breather pipes didn’t they? 

That would be really helpful

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image.thumb.jpeg.d87cb955321a757e97406292a8986a88.jpeg

image.thumb.jpeg.6c33ea8210138631e80d9866f8562360.jpeg

Tried to mark up the tank - pic was before refurb

3 sets of connections marked in different colours across both the pics

 

Please forgive the poor editing and IT skills - ha

The Blue line is the valve connection that runs to the rear of the tank and vents to atmosphere

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16 minutes ago, Simon Dobbo said:

image.thumb.jpeg.d87cb955321a757e97406292a8986a88.jpeg

image.thumb.jpeg.6c33ea8210138631e80d9866f8562360.jpeg

Tried to mark up the tank - pic was before refurb

3 sets of connections marked in different colours across both the pics

 

Please forgive the poor editing and IT skills - ha

The Blue line is the valve connection that runs to the rear of the tank and vents to atmosphere

Good enough that 👍

Does the vent to atmosphere have a check valve fitted I see? Guess it is -ossicle that it could block/degrade or be fitted the wrong way ? 

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16 minutes ago, Jessopia74 said:

Good enough that 👍

Does the vent to atmosphere have a check valve fitted I see? Guess it is -ossicle that it could block/degrade or be fitted the wrong way ? 

Yes there is some kind of valve.

I will give it a Blow test up that pipe when i can get to it - probably the weekend now sadly as working away

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the plastic valve has a ball in it which could become stuck i suppose ( or it could be fitted the wrong way round .) im pretty sure its purpose is to prevent fuel going down and out the vent if you overfill or car is overturned. either way there should never be a vacuum ( or pressure) in the tank . 

this may or may not be your issue here but it certainly needs sorting anyway .

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  • 4 weeks later...

Spent ages on the car yesterday

new fuel lines installed and runs beautifully for 10 miles

stop it and leave 20 mins then starts and dies after 1/4 mile

believe it’s down to an ignition issue now - basic tests 

good spark with spare plug direct from coil

weak spark or non existent on plug leads so I’m thinking it’s ignition module or distributor

module is new - fitted just before I bought the car - but think a cheap Chinese one

 

Need to get it right before Thursday so need to hunt down parts now

 

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if you are getting a good spark from coil centre terminal then theres nothing wrong with ignition coil or module . its getting lost after there 

so either of the below .........

lead to distributor 

rotor arm

distributor cap

leads from cap 

if you have a multi meter you can test the leads. if they are the resistive type then expect a few k ohms ,increasing with the longer leads .

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56 minutes ago, cam.in.head said:

if you are getting a good spark from coil centre terminal then theres nothing wrong with ignition coil or module . its getting lost after there 

so either of the below .........

lead to distributor 

rotor arm

distributor cap

leads from cap 

if you have a multi meter you can test the leads. if they are the resistive type then expect a few k ohms ,increasing with the longer leads .

I guess so

leads and cap are new

rotor arm new ish but has some marks on it

meters out ok according to maters autodata book.

i will get a new cap and rotor arm anyway.

could it be distributor?

so confusing that drives for miles and miles fine then park and leave for 20 mins

then it starts fine - pulls fine for about 1/4 mile then lose power and dies and won’t restart for half hour

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it doesnt sound like a distributor issue itself(main unit)but i mentioned the arm ,cap etc  because you say you have a good spark to the main ht lead .  its a strange issue indeed .  when the car stopps running after a while you definately still have good main lead spark but very poor spark coming out of ever cap plug lead ? is this correct .

cannot see how it would run for miles up to this and then only do 1/4 mile and fail ? 

very strange . 

so logically if theres a good spark going into cap but not coming out changing the rotor and cap is a good place to start !

and not ignition related . we dont have any tank vacuum now ?

 

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