Yamaha TRX850 Enthusiasts Forum

Just wanted to give a heads-up, in case you have flat-slide carbs, a well-oiled foamfilter on the velocity-stacks and tight (no) clearance on the inlet valves, this is what can happen...




Engine back-fired, lit up the filter, and whoops, there i was running around in the pit, screaming for a fire-extinguisher. Ignored by everyone, but luckily, the fire stopped by itself, without causing anything else to start burning. Wipe off, start up up, and another track-day had begun:)

Once i got home, i noticed all inlet valves had minus clearances. The engine was hard to start in the cold morning, and i guess the acceleratorpump squirted a surplus of fuel into the carbs, and then when it back-fired, all hell broke loose.

If i have the time to go to the garage, i will give another heads-up this week. That one concerns those with a YZF750 swinger, rear-sets and an "active ride-style".

Way ahead of you Hasse

scary but not un-heard of.
Apparently the trick is to keep cranking and get it started, the fire then being dragged into the bits that should be alight on the inside.
I live in fear, the way mine backfires and carries on.

Hmm, I've never heard of this before. Thanks for the warning Hans, especially since I have the same setup (TDMR's trumpets, foamfilter) and a trackday coming up on friday!

As the man said - no inlet valve clearances are the problem - not the filters/carbs

dandywarhol wrote:As the man said - no inlet valve clearances are the problem - not the filters/carbs

Correct. What puzzles me is that when i restored the engine, i put in new inlet valves. These should have been the 2nd generation, presumably sturdier and not resulting in tight clearances. Will have a look at them this winter.

In any case, a small fire extinguisher is high on my purchase list. There are many other cases in. A pit, where it could be handy...

Hans - do you remember if the part number on the valves suffixed with -01? Maybe you were sold a batch of new original valves suffixed -00

dandywarhol wrote:Hans - do you remember if the part number on the valves suffixed with -01? Maybe you were sold a batch of new original valves suffixed -00

I believe i ordered those, that's why i refer to "2nd generation". But i'll have to double-check that.