Yamaha TRX850 Enthusiasts Forum

Hello, I've changed the shims & they are within spec but after putting the top end back together it runs but not very well. Backfires a little through the carb but blows 4 inch flames out the pipe when you roll off the throttle. Has some trouble starting without starter fluid. I thought it may be the timing but I have triple checked this & have attached pics of the timing marks & they appear spot on.
Any advice would be great?

My TRX is basically bog stock with a Pipemasters 2 into 1. 65,000km & one of Cobba's ignitions. Other than check the fuel bowls for any sediment & the needles for wear I'm a bit stuck on why it won't run properly. I found an engine hoist much better to work on than crawling on the floor etc & you may have caught a glimpse of my wife's mighty CBR125 in the pics that is excellent at smokin Diavels down the back side of Glorious like last weekend.

Rotten ipad.

Rotten ipad.

Looks fine to me, have you checked the clearances with the new shims?

Thanks, have rechecked & attached my findings. The 2 middle inlets I could not check originally as they were too tight so I had to guess what size to replace them with but they are now at what the others originally were. I don't think these were checked or replaced over the 65k & I've only had it since 50k.
I'm starting to think its carbs or fuelling now as the timing appears spot on.

I have also balanced the carbs whilst it was barely running & that seems OK within a couple of inches of each other on my homemade manometer. That adjustment screw is in a bugger of a spot!

thats a huge change in your number 2 inlet valve on both cylynders, a 1.27 is a very thin shim. Is it a 96 model?

Nah it's a 99. .127 is final clearance but the shim's a 1.85. Can only get .05 increments from Precision Shims in Melbourne for this size. They were pretty good with a 2 day turn around.

I have a box full of shims in the garage. What size do you want that would be perfect?

I found when I checked my clearances I ended up going down to no shim and still had no clearance and concluded I needed new valves. Fortunately with new valves installed I was able to achieve ideal clearances. But what started as a va;ve clearance check has now turned to be a complete bike rebuild , so be careful.

Another question , to the forum as well, can you stack the shims? ie. use two shims to get to the size you want?

I don't think you can as they fit precisely inside the top of the valve. I'm thinking I will need a couple of 180's & a 165 to finish this off. I have the forks & shocks out at Suspension Improvements to get rebuilt & that's as far as this rebuild is going for this year . I've been really happy with it except for the crappy suspension.

devlin wrote:I have a box full of shims in the garage. What size do you want that would be perfect?

I found when I checked my clearances I ended up going down to no shim and still had no clearance and concluded I needed new valves. Fortunately with new valves installed I was able to achieve ideal clearances. But what started as a va;ve clearance check has now turned to be a complete bike rebuild , so be careful.

Another question , to the forum as well, can you stack the shims? ie. use two shims to get to the size you want?

No because the shims are held in place by the valve spring seat, if you had one on top of the other the top one would move, also given the vavles wear closed not sure why you would want to ....but then you could also grind down the back on you cams to get more lift and duration......probably not the best idea though

Con Rod wrote:

devlin wrote:I have a box full of shims in the garage. What size do you want that would be perfect?

I found when I checked my clearances I ended up going down to no shim and still had no clearance and concluded I needed new valves. Fortunately with new valves installed I was able to achieve ideal clearances. But what started as a va;ve clearance check has now turned to be a complete bike rebuild , so be careful.

Another question , to the forum as well, can you stack the shims? ie. use two shims to get to the size you want?

No because the shims are held in place by the valve spring seat, if you had one on top of the other the top one would move, also given the vavles wear closed not sure why you would want to ....but then you could also grind down the back on you cams to get more lift and duration......probably not the best idea though

Or just grind the valve tip.

Have you checked the clearance since you had the engine running?

Suspension improvement will charge an arm and a leg Jeff.
Wanted to charge me a grand to rebuild the R1 forks and I ended up going to MPE just off the highway near Coloundra .
Rebuilt the forks , revalving the cartridge and fitting gold valves for comp and rebound plus serviced the rear Ohlins and resprung all for the same price .
Just mention your from the Trx forum and a few of us have had rebuilds through him now and he'll do a good deal.

He'll rebuild and fit gold valves in the stock forks for about $250 .

Rod.s wrote:

Con Rod wrote:

devlin wrote:I have a box full of shims in the garage. What size do you want that would be perfect?

I found when I checked my clearances I ended up going down to no shim and still had no clearance and concluded I needed new valves. Fortunately with new valves installed I was able to achieve ideal clearances. But what started as a va;ve clearance check has now turned to be a complete bike rebuild , so be careful.

Another question , to the forum as well, can you stack the shims? ie. use two shims to get to the size you want?

No because the shims are held in place by the valve spring seat, if you had one on top of the other the top one would move, also given the vavles wear closed not sure why you would want to ....but then you could also grind down the back on you cams to get more lift and duration......probably not the best idea though

Or just grind the valve tip.

Have you checked the clearance since you had the engine running?

Ah yes, of course, I forgot the little seat they sit in. I thought about getting the ends of the vales ground down a touch but decided to just get new valves. I have run the engine yet. probably be about 2 or 3 months away I reckon as I work interstate during the weeks now so time is limited.