View Full Version : 503 performance problem

keith_b - n/a
15-Apr-06, 12:05 PM

Was giving my 503 Storm a first run yesterday on the beach, a bit too windy but didn't sink in the sea and I only fell out once.

After about 30 mins of use the engine would not get up to maximum revs - sitting on 5000 max (been happily revving to 6500) - the engine was not "bogging out". So I had to call it a day.

Anyone got a view on what to check?

I think this is a fuel feed issue.

I have come up with:

1) Carburettor blockage

2) Fuel pump failure

3) Fuel pump heating up too much and reducing fuel pressure/creating vapour lock.

The twin outlet Mikuni fuel pump is mounted under the carburettors on a 20mm * 40mm length of steel box. This assembly is bolted direct into the engine casing in the proper Roatx threaded holes.

There was still loads of fuel in the tank. The spark plugs are showing a "light brown" so i think the mix is OK. Unfortunately I didn't get a chance to cool off and try again.



Ian Brooks - n/a
15-Apr-06, 02:37 PM

I had this issue - are you using K&N airfilters? If they get soaked, you can get the symptoms you report. The solution for me was using foam air filters from Ken.


keith_b - n/a
15-Apr-06, 03:15 PM

Yep - they were wet

That's probably it then