My oil in frame A65T spits flames or raw fuel back through the carb when I blip the throttle. It runs perfectly well when cold, when hot, under load but when at idle or occasionally on overrun it will do it, especially slowing down after being at speed for any length.
The bike is a 1972 Thunderbolt, and I've checked the timing which is set with a strobe light as per the w/s manual, the valve clearances as per the w/s manual. The carb is an Amal R928/17 Premier which is set as per the w/s manual, and is new (4 months old). In terms of carburation, it's not running rich or lean, but also still spits when adjusted (for test purposes only) to run rich or lean. Electrically, it's got new spark plugs, Pazon ignition fitted which appears to be working well, and advancing as it should. I have a Sparx voltage regulator and new alternator, both charging and keeping battery voltage above 12.5 volts with high beam on. The spark plugs aren't being fouled or coked up, nor are they coming out oily. I almost forgot to mention, I've removed and checked the exhaust/balance pipe, resealed then checked for leaks. Plus the exhaust is not blued. The intake side has also been checked for vacuum leaks, and I've had the manifold off and resealed it (new gaskets against the head and 'o' ring against the carb), then checked again.
The bike has been doing it for a year and a bit now, which is over 3000 miles. Over that course, nothing I've done has remedied it. Overall, the bike certainly does run nicely in all other aspects.
I had this once when someone had removed the original bell mouth.
Due to the valve timing and overlap degrees , the inlet air speed had been upset by the removal of this bell mouth and spat back.
Replacing it was instant cure
sounds like the jet needs to be bigger or air reduced or theres a bit of a leak on the intake side but just remember i know nothing. i'm just plucking wabbits out of a hat
Hi,
Do you have the filter fitted? Standard jetting is for the filter being fitted.
Dave.