smart51
Established member
Most of you will have followed my journey working on a 500R I bought last year. It has a 594cc 126.A5 engine with a 28IMB carburettor. I bought this version deliberately so that it would have a little more go than a 499cc car, but everything I've done so far has drawn a blank. The car has a top speed of 60 MPH as measured by GPS.
The fan is solid and blows air well. The air intake tinware is clear and in good condition. The air filter was new less than a year ago and has about 500 miles on it. All the ducting and carburettor is clear. The throttle opens fully. The cylinder head has the 30mm diameter inlet port and the cylinder head looks good.
I have a fuel filter in next to the tank which is full of fuel and looks very clean. The fuel pump is new, the carburettor was stripped and cleaned meticulously. I've tried various jetting combinations and the standard ones work best.
The engine has 130 PSI of compression on 1 cylinder and 120 PSI on the other - fair figures.
The exhaust ports on the head have been lightly opened up - mostly softening the inside of the curve where there was quite a lip. The exhaust elbows have had similar light treatment. I have a sports exhaust which is new.
It has a 126 wasted spark ignition system. The coil, ballast resistor, distributor, condenser, HT leads and spark plugs are new. The points are gapped and the timing set with a strobe.
It has a new 35/70 cam, new followers, new timing chain and gears. New gaskets everywhere except the front of the crank shaft. I've had the sump off and inspected the inside - all good. I've had the flywheel cover off and inspected - all good.
The brakes don't drag. The gearbox has oil in it and changes gears smoothly. It sounds good and drives well.
Yet on a level road, it will not go over 60 MPH according to the GPS app on my phone, which is just short of 110 km/h on the speedo. It suggests that the engine is making about 17.5 BHP at 4200 RPM. The 126.A engine should make 22.8 BHP at 4800 RPM and give a top speed of about 67 or 68 MPH in a 500. Is there a difference between the 126A and 126A5 engines that I have missed? Is there something about the engine I've not checked? I can't think of any reason I've not checked why my car is underperforming. Any ideas?
The fan is solid and blows air well. The air intake tinware is clear and in good condition. The air filter was new less than a year ago and has about 500 miles on it. All the ducting and carburettor is clear. The throttle opens fully. The cylinder head has the 30mm diameter inlet port and the cylinder head looks good.
I have a fuel filter in next to the tank which is full of fuel and looks very clean. The fuel pump is new, the carburettor was stripped and cleaned meticulously. I've tried various jetting combinations and the standard ones work best.
The engine has 130 PSI of compression on 1 cylinder and 120 PSI on the other - fair figures.
The exhaust ports on the head have been lightly opened up - mostly softening the inside of the curve where there was quite a lip. The exhaust elbows have had similar light treatment. I have a sports exhaust which is new.
It has a 126 wasted spark ignition system. The coil, ballast resistor, distributor, condenser, HT leads and spark plugs are new. The points are gapped and the timing set with a strobe.
It has a new 35/70 cam, new followers, new timing chain and gears. New gaskets everywhere except the front of the crank shaft. I've had the sump off and inspected the inside - all good. I've had the flywheel cover off and inspected - all good.
The brakes don't drag. The gearbox has oil in it and changes gears smoothly. It sounds good and drives well.
Yet on a level road, it will not go over 60 MPH according to the GPS app on my phone, which is just short of 110 km/h on the speedo. It suggests that the engine is making about 17.5 BHP at 4200 RPM. The 126.A engine should make 22.8 BHP at 4800 RPM and give a top speed of about 67 or 68 MPH in a 500. Is there a difference between the 126A and 126A5 engines that I have missed? Is there something about the engine I've not checked? I can't think of any reason I've not checked why my car is underperforming. Any ideas?