Flat Spot

[LORENZO73]

Many thanks for your information that you gave me David Painter.
I print everything that you send me in the forum, and i gave it to my mechanic.
I hope that the fist step pass, change distributer, i put 1.8 super like her camshaft, and make all settings, if no, i don't have an alternative, i change camshaft and distributer TC'S

Many thanks
Renzo

[david painter]

Before buying anything go though the checks I have listed this will establish where your problem lies. It is possible that the distributor weights and springs have been changed to Marina items but a simple check of the advance curve with a strobe light will confirm. If still Mini advance curve I wold 45d MGB distributor and install a Pertronix ignigtor electronic ignition. The last thing you need to worry about is the camshaft as this will alter your power band and if correctly timed will not be the cause of a flat spot
Dave

[LORENZO73]

Hi Dave,
My mechanic set it with the strobe light for advance curve and he told me it is good i see it.
Then he check the no 1 with colour tune and we go for a ride together,
The car still make flat spot, and he told me that there is nothing to do now.
I told him, so i leave it like that? He told me, change cam and distributor, but no me i am 65 years old, i don't have health to take engine out. I close my garage and i go home like a donkey. Sorry for the expression.

Thanks
Renzo

[david painter]

I is very difficult to give you a specific answer to your problem. If however you follow the diagnostic procedure I have described you will find out what the cause of your problem is.

I would not be to concerned what numbers are stamped in the distributor body as 40 years later the internals may well have been changed. This will show up when the Mechanical advance check is carried out.

What RPM and throttle loading does your flat spot occur? when it does occur , does the engine spit back through the carbs ? Is there any improvement pulling out the choke when it occurs?

The Carbs do not know what camshaft is fitted in the engine But supply air and fuel dependent on the engines volumetric efficiency. Within reason Variable Venturi carbs are self tuning the more air drawn the higher the piston rises the bigger the hole in the jet to allow fuel in. This Air fuel ratio is trimmed by altering the needle tapper at specific points. Hence differing needle numbers.

You should concentrate your fault finding arround the point when the flat spot is present. Is the ignition timing retarded to the figures I supplied at the specific RPM.

Are the spark plugs equal colour on all cylinders or weak on either front or rear carb.

Camshaft Duration I am unable to find any specific duration figures for Marina 1800 SC or TC engines but on the MGB duration was gradually dropped from 264deg in 1965 to 244deg by 1980 as emission regulations started to take hold. The majority of MGB engines had twin SU Carbs in either HS or HIF types the only exception being the single Stromberg CD175 used in California. A typical Fast Road performance cam is specified at around 270deg Duration. As the figures show TC carbs can be used with a wide range of camshafts.

Even Back in the Day ( not a phrase I like) but it was very common to go the scrapyard on a Sunday morning unbolt the Twin carbs bolt them on your car in the afternoon and go to work on Monday morning without changing anything else.

Dave

[LORENZO73]

Good morning Dave,
Many thanks, for your replay, and for your help.
I understand what you write, but i have to show everything to my mechanic, because i am not technical.
I think that i am in trouble with this engine, because she didn't have the right things in it.

I am confused because i spent about 2000 euro to rebuild that engine [parts and labour], and now, is to much for me to open in it for second time. If i am a mechanic is not a big problem, just buy parts and finish, but to do it by mechanics, i now that i want more money for labour, and the big problem is our mechanics today he didn't want work on it, so for sure have to wait to many days or months.
I try to do the best things,and i put my health on it, because i love Marina so much.

Good Day
Renzo

[LORENZO73]

Hi Guys,

Thankyou all for your help. The problem that I had was that I had the distributer of the mini clubman. He was more advanced and we changed it with one 1.8 super marina. After, it worked perfectly. But when I went for a ride and had to stop in the traffic with the engine still working for about 20minutes, then when I drive she misfired and I smelled petrol. From the information I have from Mr. Chris Weedon and Mr. David Painter, is likely the cause is fuel vaporisation. They told me it can be improved by fitting stainless steel heat shield stain steel over braided fuel hose a electric fuel pump SU type not facet as pressure to high
also lagging exhaust manifold and down pipe.
Best Regards
Renzo

[locost_bryan]

Good to hear that changing the distributor solved your flat spot.

Chris and David are worth their weight in gold.

[MarinaCoupe]

It was my old Super distributor.

[LORENZO73]

. I find this broken, when i do clean up and change fuel filter, maybe that is a cause of misfire as well, when i stay in traffic. Thanks Renzo

[david painter]

I would change both floats for the ones I sent you the picture of along with the needle and seat kit the seat part of the valve is adjustable with various thickness washer supplied in the kit with new float fitted turn housing upside down so float uses gravity to rest on needle valve you should be able to pass a 1/8to 3/16 inch drill bit between top of float and chamber lid as per the Moss Video.
Dave

[LORENZO73]

Hi Dave,
I try to change it yesterday, but i think that i fix it something wrong, because the engine give me much Flat spot like before.
Maybe i find someone to fix it properly.

Many thanks for your help
Renzo

[LORENZO73]

Last chance next week with another mechanic if she continue disturb my brain, i put that.

[LORENZO73]

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[LORENZO73]

Hi Guys,
Finally the engine is ok, we change the Dashpots and dumpers of carbs, and he works like a clock.
Is not easy to errange engine, when have parts from an other engine not marina, i want to tell a big thanks for chris weedon and David Painter, for his help that gave me everday and weekend by messanger and whatsupp.

Many thanks
Renzo

[SLOW ITAL]

Hi Lorenzo,
Glad you have now got it fixed & running well.
Yes Chris & David great technical advise & help when your'e in trouble.
Gil ...