cut-outs after reving above 4500rpm

[GinettaG15]

Dear Alec, i dont get what you want to tell me?

i just checked again the history of the car:

the engine is definately a genuine PI engine, converted to carbs.

[Alec]

Hello Ginetta,

I think we are getting a bit confused with all the inputs.
You now say it is a pi engine not just that it has a pi cam.(I.e. with the higher compression ratio). There is a difference between carburettor engine and pi engine distributors, does yours have the pi distributor, from memory, carburettor has have more advance at higher engine speed.
However pis fitted with carburettors were a common 'repair' for pi troubles so the information anbout which needles match should be available. Have you spoken to Burlen Services?

Alec

[GinettaG15]

sorry for my late reply.

yes its genuine PI saloon-engine,non-recessed block, incl. its PI-dizzy, it was converted to carbs using a TR6 long intake manifold.
during refurb of the engine an early TR6 PI camshaft (par number 308778) fitted, 270degres duration, 0,232" Lift


what i can say is: the cut-outs do NOT happen when i slightly pull the choke....so it should be fuel related.
(some months ago a had a longer motorway trip and was wondering why i had no cutouts when driving home at night with a quite high speed and constant revs around 4500rpm....next morning it was clear...the choke was still slightly pulled out...)

[johnnydog]

Looking back through your replies, you mention BDN needles, and in a later reply BDM. Is this correct, or a typing error? I referred to BDM needles in my otherwise standard S, which have been great, so I just wondered....?
You state your car doesn't have butterflies fitted - it must have, or are you actually meaning 'poppet valves'?
Individual deviations from standard engine spec will always be prone to experimentation, but not always with any great benefit.

[GinettaG15]

BAM´s are fitted and i tested BDN (very bad running).....rest was typing mistake

as said i would need needles which are identical to BAM´s until ~4000rpm and after became richer.

[johnnydog]

sorry for my late reply.

some months ago a had a longer motorway trip and was wondering why i had no cutouts when driving home at night with a quite high speed and constant revs around 4500rpm....next morning it was clear...the choke was still slightly pulled out...

I'm intrigued about what speed this is happening at - my S at 2750rpm (albeit in overdrive top) is doing about 75 - 80 mph from memory!
Is the PI engine fitted the 132 bhp or the 125bhp? There were noteable differences, and also in the factory settings for example.
I take it the coil has been included in the list of changed / tried good used components..?
In the absence of any other faulty components, I think I would put it back to points, doing away with the Accuspark, purely to see if any there is any difference.
I appreciate what you are saying about the problem only developing over 4500 rpm, and it doesn't seem to occur with the choke pulled out slightly, so the only reasonable cause is either the fuel delivery at that speed (fuel pump, pressure, mixture) or an ignition related issue, which in my opinion, could be the coil whilst under load, the needles delivering an incorrect mixture above 4500 rpm indicated by the use of the choke, or an ignition issue.
Is the 'cutting out' hesitant, a violent cutting out / misfire, or more gradual (as if were brakes were applied whilst still under power)?
You say the carbs have been refurbed - have they been properly set up / balanced, including the throttle / choke linkage operation? I would like to think so, but I have seen some supposedly set up professionally, but probably by (as someone recently said) 'a blind and deaf man with no fingers'.
In an ideal situation, in the absence of any obvious reason, the ideal would be to put it back to original (obviously keeping the PI engine as I know from personal experience that they run very well with the recommended BPZ needles fitted), and if it runs ok then, change it one by one back to the components you have fitted to hopefully establish the individual problem.
I don't what else to suggest being honest.
Changing anything from original can lead to issues, and a degree of experimenting to overcome them. Car manufacturers spend large amounts in the development of their engines, and any alteration from 'factory' can sometimes produce headaches....

[sprint95m]

i can drive the car all day long, no matter if outside-tempeatures are 10 or 35 degrees, it runs well and troublefree....but once i rev it over 4500 it starts to cut-out (from the sympthoms it sounds /looks more fuel related)...it recovers after a few seconds and runs normals again when keeping the rev´s below 4500.

How is the cars on climbs?

I had an early Dolomite 1850 in the 2000s.
When I got it it was running fine but a problem appeared on climbs or when driving into strong head winds, it would miss badly and lose power.
After slowing down and it was okay again.
Eventually I discovered it had an air leak at the inlet manifold/cylinder head. I had been suspicious of the visible orange instant gasket and
fitting a new pair of inlet manifold gaskets solved the problem.


Ian

[GinettaG15]

sorry for my late reply.

some months ago a had a longer motorway trip and was wondering why i had no cutouts when driving home at night with a quite high speed and constant revs around 4500rpm....next morning it was clear...the choke was still slightly pulled out...

I'm intrigued about what speed this is happening at - my S at 2750rpm (albeit in overdrive top) is doing about 75 - 80 mph from memory!
Is the PI engine fitted the 132 bhp or the 125bhp? There were noteable differences, and also in the factory settings for example.
I take it the coil has been included in the list of changed / tried good used components..?
In the absence of any other faulty components, I think I would put it back to points, doing away with the Accuspark, purely to see if any there is any difference.
I appreciate what you are saying about the problem only developing over 4500 rpm, and it doesn't seem to occur with the choke pulled out slightly, so the only reasonable cause is either the fuel delivery at that speed (fuel pump, pressure, mixture) or an ignition related issue, which in my opinion, could be the coil whilst under load, the needles delivering an incorrect mixture above 4500 rpm indicated by the use of the choke, or an ignition issue.
Is the 'cutting out' hesitant, a violent cutting out / misfire, or more gradual (as if were brakes were applied whilst still under power)?
You say the carbs have been refurbed - have they been properly set up / balanced, including the throttle / choke linkage operation? I would like to think so, but I have seen some supposedly set up professionally, but probably by (as someone recently said) 'a blind and deaf man with no fingers'.
In an ideal situation, in the absence of any obvious reason, the ideal would be to put it back to original (obviously keeping the PI engine as I know from personal experience that they run very well with the recommended BPZ needles fitted), and if it runs ok then, change it one by one back to the components you have fitted to hopefully establish the individual problem.
I don't what else to suggest being honest.
Changing anything from original can lead to issues, and a degree of experimenting to overcome them. Car manufacturers spend large amounts in the development of their engines, and any alteration from 'factory' can sometimes produce headaches....

ingniton parts have been re-newed without any difference. ign. timing can be set from 8 to 16 degrees advance....the cut outs remain identical. the car had a mechanical fuel pump and now an electric...both the same....i can drive with open fuel-cap on tank or closed (to exclude that the tank is not properly vented)...problem remains the same...

i have replaced the accuspark module against another one (i think it was powerspark)...problem remains.

the cut-outs come smooth...like somebody is pushing the brake...its definately fuel-related.....rev-counter still works properly during the cutouts (if it would be ignition related the rev-conter would play-up)

so, again: i just need a needle which is richer above 4000rpm compared to my BAM...but i´m struggeling to find one.
so the only "help" i would need is to find a suitable needle.

whatever combinations i try on mintylamb..i do not find anything

[johnnydog]

I think we are all at a loss, made even harder to diagnose distantly.....
Relative to the conclusions you have arrived at, as Alec previously suggested, speaking to Burlen Fuels or any other SU specialist may be your only option, as you need a conversation with someone who actually has expertise in the various SU needles relative to your desired increase in mixture above 4500 rpm. What other option is there?
I still fail to see how your engine is so greatly different that makes finding a suitable needle is so difficult...?

[GinettaG15]

to exclude also the Dizzy: i replaced my PI dizzy (converted to Petronix) with a S dizzy (converted to petronix).....problem remians identical...so another "prove" that it must be fuel related. (the S dizzy came from a mate´s car)