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MG MG Y Type - Max.power not at max.throttle

My YA runs ok and is no more gutless than most I think, but when pulling up hills, maximum power is not at maximum throttle opening. As revs increase, the amount of throttle needed for max. power increases, but never quite reaches full throttle.

Mixture is about right (milk chocolate coloured plugs): compressions 150 to 160 lbs/sq.in but tested cold I must admit: carburetttor piston runs freely in bore, and dashpot has correct oil (genuine SU).

Help please.

Michael Nicholson

If the plugs look good ie correct colour for the correct mixture then I would leave the carburation alone - try looking at the timing or check the throttle spindle - oiling it occasionally is well worth while - I use engine oil in the dashpot for summer and top up with a thinner oil in winter when using the car. Cleaning the air filter may help possibly. Good luck.
David Mullen

It could be that you camshaft is worn. Unfortunately the YA/YB camshaft is a pethetic thing with a far less lift than the TC. It could be that your one is strangling the combustion chambers even more. I should think fitting a TC or TD shaft should brighten things up.
Bryan

As a long time owner of a YA [since 1960] I have pondered why the car is so low tuned being some 5cwt more heavy than the TC. My conclusion is that it would have competed with the TC & TD for speed, and that would have been bad for sales of the sports cars. I refer you to Wilson McComb where he describes that in 1950 at Jabbeke a Y type fitted with a low pressue Shorrock supercharger driven by Gardner exceeded 104 mph before loud noises came from under the bonnet. One can only conclude that the YA/YB with the TD tuning and correct gear ratio would have been a very fast car for its time.
Bryan

Interestingly to note I took my YA to Park City, Utah this last summer for GOF West. Had a great time in the famous Winter Olympics area despite the heat!! Part of the week was a scenic run and the YA acquitted itself perfectly sailing passed a TD on one of the many uphill sections in third gear! No idea if the TD was 'gutless' or my car had had Shredded Wheat for breakfast, but I think I was doing about 35 mph at the time, and the slope was pretty fair!

I do love my YA!! (Single Carb!)

Paul
Paul Barrow

Set the static timing with a 5 degree advance.
Scott Barrow

By the way Michael if you remove the rocker cover and hand crank, each valve should move 6.5 mm full travel.
Bryan

I have observed the same phenomenon right after my engine overhaul (including camshaft) and so far I have not yet been able to track down the cause. This winter I will install the Dutch "123" electronic ignition and hope for an improvement.
Remo Peter

Michael,

I have two questions,
1. Does the power decrease when you give full throttle or does it improve when you go from full throttle to less?
2. Have you tried without the air filter? Even if our filters only serve to filter out large rocks, maybe due to a blockage the amount of air through it is insufficient?
Willem van der Veer

Willem
The power decreases at full throttle and increases when throttle is reduced.
I have cleaned out the air filter with petrol. If it were this, then lots of people would have the same problem wouldn't they?
Michael
Michael

Back in January I had the very same problem in my single carb YA.

While climbing a long hill , about 25km, I too noticed that the easing of the throttle to 50% produced more power on the climb than a flat out throttle.

Now I had only serviced the car the day before and the only thing I changed from previous practice was the dashpot oil. I had purchased a small bottle of the correct labeled "SU Dashpot Oil" and filled it to the level as discribed in the manual.

So I decided halfway up that long climb to test if the oil was the problem. I pulled off the road and using some paper tissue, I "drained" the dashpot oil from the carb.

The change was amazing. the pickup returned and I could apply almost 80% full throttle to get maximum power.

Now, about 2 months ago I decided to find that last bit of throttle power and changed to a "lean" carb needle - now maximum power is at full throttle.

So my suggestion is you have a combination of too heavy oil in the dashpots (I now only use SAE10 motorcycle fork oil or "Sewing Machine Oil"), and a needle too "Rich" for modern fuel.

Think about your symptoms - when you ease the throttle you increase the dashpot lift and richen the mixture, while when you open the throttle, the mixture is too lean to produce any power.

What you need is the optimum air/fuel ratio over all throttle openings, and I have found that light dashpot oil and lean mixture needles give the desired result.

Also remember that the mixture adjustment and described in the manuals, only adjusts the mixture at idle, not across the RPM/throttle range.
Tony Slattery

Max TORQUE is need to climb a hill, not max power ( bhp) The best torque figures are at about half way up the RPM scale. So a Y type oulls best at about 30-35mph in 4th gear. Opening the throttle any more will do nothing other than make more intake noise, and weaken the mixture. The reason the best 'pulling' power is half way up the rev range is due to the fact the camshaft timing, valve openings, port sizes, carburetter choke, are all at their best at one speed only; all other speeds are a compromise. Just look at any torque graph to show this effect. The BEST mpg is at the highest torque speed as well.

NC.
Neil Cairns

This thread was discussed between 29/10/2007 and 04/12/2007

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