Yamaha TRX850 Enthusiasts Forum

Hi all

Been fiddling on the bike two week ends ago (new throttle cables and TPS mod) and it has since decided to be awkward to start it in the mornings. I have to stay on the button quite a lot and play with the throttle a bit, it sort of half kicks in at times but dies when I'm off the button. When it finally decides to kick in, I can't open the throttle too much otherwise it chokes and dies. So I slowly ride down the road and after a few hundred meters, she clears her throat and then runs perfect. I can stop at the pump for fuel and it starts fine again. It seems the issue only appears when parked for a a few hours/overnight.

I first thought maybe the battery was weak so got a new one but the problem still remains.

There's a kind of whining noise under the rider seat when I start it the mornings and there is also a slight petrol smell when I take the cover off in the mornings. The oil level hasn't moved and the oil doesn't look runny or fuel contaminated.

Seems a lot of TRX's have had fuel tap/diaphragm issues recently but my symptoms seemed to be different and couldn't find much similar symptoms. Any ideas on what it could be and where should I start my further investigations? Fuel tap? Fuel Pump? Carbs?

Thanks in advance!
Adrien

Could be one of a few things.

What position is your fuel tap kept in?

Do you use the choke?

Does it operate ok? (the slider bar on the carbs can get a bit mucky/rusty so the choke doesnt operate right.

Try this: make sure fuel tap is left in the "on" position all the time. Then, before you start it, put it to 'pri' (prime) for a count of ten to let some fuel into carbs, then turn back to on and give her a whirl.

BTW the TPS mod wont do much at all if you've just got a standard motor with maybe a set of cans. Maybe swap it back and see if it helps?

I think the difficult cold starting could be down to the TPS mod. If you think about it, the spark is now happening earlier than it would usually with a functioning TPS.

Forgot to mention she has FCRs and cans.

It's a shame if the TPS mod makes cold starts difficult as she seemed to be running better up the rev range than before.

Tap is always on the "ON" mode, I'll try the "10seconds PRI" tip and see how that goes.

You have FCR's - that might explain it. Are you priming the carbs with a couple of twists of the throttle before starting? If not - you need to

NWS870R wrote:You have FCR's - that might explain it. Are you priming the carbs with a couple of twists of the throttle before starting? If not - you need to

It would also explain the smell of petrol (standoff) under the cover. And yes, prime the carbs first, there's no choke as such but twisting the throttle makes the accelerator pump squirt fuel down the carb bores

Gave it 4 twists this morning and the start up was less chaotic but not quite as it used to be before the TPS mod.

I didn't realise that having the spark sooner ment it needed more priming . I used to give two or three twists in the winter days and it started fine, didn't need any twists during "summer" until the TPS mod so I wonder how difficult it will be next winter.

I'll try the 10 seconds PRI thing tomorrow and see how that goes. Otherwise, I'm thinking maybe a switch button to easily siwtch from non TPS to TPS and vice versa... need to do a bit of digging on that one!

Cheers
A

Have you got TPS on the FCRs?

If yes, I'd use them. My bike runs better on the road with TPS and I certainly don't miss the 1 or 2 bhp that the mod brings about. (If I can be arsed, I'll mod it for track use.)

I don't see any point in doing the TPS mod unless you are forced to - ie you haven't got TPS on the FCRs.

I've got the tps on the FCRs and used it for approx 5,000kms just fine but I find the bike has more oomph with the mod.

Tried the 10secs PRI and three throttle twists which did the job. I'll see if I can live those starting procedures.

drix wrote:I've got the tps on the FCRs and used it for approx 5,000kms just fine but I find the bike has more oomph with the mod.

It doesn't - it must be in your head!

OK, it does add 1 - 2 bhp though the range on WOT but .....

phuk72 wrote:it must be in your head!

Could well be, god knows what happens in there really!


I'll try and do a test run with both configs, TPS on and TPS off and see how it feels. But at least for now, I know the reasons of difficult starts and can work around that.