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Vitesse - loses power when hot


OB96
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Hello all,

I’ve recently bought a 1965 Vitesse 1600.

After taking it for a run a few times, I’ve noticed a problem:
- It runs pretty well for the first 10/15 minutes or so, but sometimes when warmed up, it loses power. This is especially noticeable at speeds over 40mph or when going uphill. The engine feels a bit juddery, like it’s starved of enough fuel.

I’m thinking it might be something to do with the fuel supply? I understand it wasn’t used much in the past year or so, maybe there are some deposits causing occasional blockages? 

However, might the fact that the issue seems to be associated with engine temperature suggest maybe a problem with gaskets/oil/cylinder compression? 
 

It’s running Solex carbs. I’ve taken the air filter connection system off when the car was losing power, immediately after stopping. The butterfly valves were working fine and the jets were still both spraying fuel and in time with each other.

Any suggestions would be very welcome

Oliver 

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Is it solex or stromberg carbs? (I have zero knowledge of solex)

Does it only do it on hills? I remember my dads MGB had a fuel issue, that would be ok until sustained at over about 2500rpm, when it would loose power and die, but pop it out of gear (while still moving) for a few seconds, and it would be OK again. That was faulty electric  pump, slow fuel supply. Also if the car is rested for a couple of minutes at idle, is it ok again for a short time? 

The choke-pulling idea is one that reveals a weak mixture, so first, simple port of call, at least with strombergs (no idea about te solex, is that a real choke as opposed to fuel enrichment?)

Ifnot, have a look at the ignition system. Remember the old saying, 9/10 of fuel systems are down to ignition. Some modern points/rotors/condensors are very poor. And check that the distributer is advancing correctly with rpm.

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solex also  can suffer form rubber slivers blocking the float needle if any hoses have been disturbed then refitting a hose can breed the little devils

solex has a a starting valve enrichment device not a simple choke flap , so a pull on the choke may give some limited gain 

there are jets main idle and compensating  they all need to be removed and cleared if you remove the top cover you can purge the fuel line into a jar 

to see if you catch any rubber tiddlers 

all the jets unscrew and can be blown or carefully poked with fine wire to clear them 

do you have accelerator pumps  these were discontinued also rimmers still have low speed imrovement choke barrels on sale ( another late modification)

accelerator pumps did over rich and cause poor running hence their disappearance , they were just replaced with a blanking plate but you coud just disconnect the levers 

I would place a bet on debris blocking the back of the needle valve 

do check robs suggested pump filter 

Pete

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Thanks for all the replies, very helpful stuff! 

It’s running the later Solex carbs without the accelerator pumps.

I’ll take a look at the fuel pump and will sample the fuel from the carbs next time the issue crops up.

It did seem to pick up when it was running poorly if I pulled the choke out a little.

Unsure if it’s connected, but I just took a look at the plugs and they seem to have some dry sooty carbon fouling with oil on the threads. Had the carbs tuned but maybe not set properly and running too rich?

Oliver

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you cant tune a downdraft for its main running is pre determined  you can only alter the  idle speed and idle mixture with the two screws 

the idle mix is just turn the  mixture screw to best idle and turn in a small amount so you are at the weaker end of nice 

the idle mixture will only work if the idle is set at around 700  rpm any higher and the idle circuit is closed as soon as you open the throttles 

the idle mixture jet is the small brass hex headed jed on the side of the carb ,take it out make sure the small hole in its end is clear

Pete

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Hi Pete,

I took off some of the fuel from the pipe supplying the carbs after it was running poorly. No contamination as far as I can see.

Also checked the mesh filter on the fuel pump, which again looked clear to me.

Its currently set up with Champion N9YC plugs, I have got some equivalent NGKs to replace them if I can figure out why they’re blackening. May well be as you say: not running for long enough for them to burn off, most of the trips have been fairly short 10-15 mile distances with choke starts.

As I say, with the air cover off I can see the jets which supply fuel towards the butterfly valve, these both seem to be working and in sync.

Taking it to a local garage tomorrow to see if they have any bright ideas.

Thanks for all the suggestions so far!

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do check the hose clips are really working on the short hose from top of the tank to the main fuel pipe 

its a good place thats ignored as not easy seen , but can be loose and all you do is suck air not fuel  its a cheap fix too.

have you changed the air filter ???  or even checked the timming , set it to 10 deg btdc  and use super 97 + fuel 

nothing wrong with champion N9YC.

a word of caution on timing the older the car the worse this can happen the crank pulley  damper ring bonding breaks down and the damper ring with its timing marks all moves round so a simple check of top dead centre is as the marks define ,,   it can be way out 

Pete

 

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Haha I’ve already bought a set of cd150s plus manifold, need a bit of restoration though.

Interestingly, I just checked the cylinder compression pressures and there is a defect there 

1 = 8.4

2 = 7.8

3 = 7.1

4 = 5.4

5 = 6.0

6 = 7.4

May be a head gasket issue? Though not sure if this would fully explain the variable power loss? 

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youre right doenst correlate to odd power losses  ,there would be a consistent  misfire all the time

the 1600 has a steel shim gasket its not prone to failing , but a loss of torque is often found  might be worth a retorque 

most suffer from head nut washer deformation which drops the clamp load 

before you get thoughts of heads off   have a read of Paula's recent troubles with a 1600 head gasket and solved with a  retorque 

do check the boot tank hose

check the coil HT lead is not green inside 

if plug age is unknown then replace to test the variance  plugs  life and soul of the engine performance 

the air filter age is unkown then thats the first over rich contender  replace to eliminate it 

pete

 

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  • 3 months later...

Re torque the head, then repeat the compression test.  I would second Pete`s advise about the Air Filters too. Something easily overlooked but can underly similar issues.

Did the early 2L cars have the damper as well?. (it was 1980`s, so the memory is a fading event).

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Sad to see it go back when.

Pete

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