Yamaha TRX850 Enthusiasts Forum

FCR Question

Sunday was FCR day for me I headed down to the garage around 8:00am and started stripping things down, at 11:30am I was off to Bunnings looking for a Torx set for the TPS bolts (that was a surprise), which turned out to be a waste of time as they just stripped out anyway (nothing WD40 and Vise-Grips couldn’t handle though) and by 1pm the bike was back together and it was time for a test ride that lasted about 2 minutes as I’d left way too much slack in the throttle cables. After flooding the carbs adjusting the cables it was time for a proper test.

The first thing you notice is the induction noise (I know a lot of you have been there and done that – but this was a huge moment for me) the best way to describe it is like having a Labrador on your tank panting. The grin factor is off the chart (and this with the standard air box). The test ride left me wanting more but the roads were wet and I’d already ignored the misses for most of the day so it was time to put the bike away and smile at my achievement over a beers .

And now for the question,

Has anybody noticed a lack of response when opening the throttle wide from around 3500rpm in third (17 – 41)?

The old carbs would pickup well from here but the fcr’s seem to bog-down for a split second before sparking to life. From 4000rpm it’s all go but it just seems strange to me as I was under the impression that they would increase power across the range but I seem to be having to down shift to find the power now.

I’m wondering if I have the tps adjusted wrong as I took a shortcut and installed it in the same position as on the standard carbs without going through the TPS setup sequence in the Haynes manual.

And the snap-crackle-n-pop rolling off the throttle was more than I expected

Anyway does this all sound normal to you guys and I just need to re-educate myself on how to ride with more rpm's or does it sound odd

Cheers in advance

Nick, not knowing much about FCRs on TRXs, but I had a set of FCR 41 horizontals on the Guzzi and yes they do tend to bog down a bit when the throttle is opened wide. It tends to make you a bit more precise with the right hand Probably a bit of fiddling with the clip and needle might cure it.......hard to say. I just used to ride around it in that rev range.

My bike used to pop and fart a bit with the FCRs but no more than a Guzzi usually would.

Yes..... isn't that induction sound wonderful !

Bob

Whacking the throttle wide open is not recommendable with FCRs. The vaccuum carbs open the throttle smoothly for You, even when you twist the throttle wide open. That's the 'vaccuum' part, the driver let's the vaccuum increase, and it causes the throttle to open up. You can compensate a bit by increasing the accelerator pump, but generally speaking You'll have to be a bit more sensitive with the throttle control. I am pretty certain You'll have more power throughout the whole RPM range anyhow.

Yep, agree with Hans: don't give 'em a big handfull, they don't like it. Doesn't mean you have to be limp-wristed either though.
...and sort this out! Will make a difference...

...or go down the 'bypass' route for another added pony or two.

Gotta say, now that mine are just about sorted I've no complaints at all - can't say I've noticed any bogging, but that could well be down to needle position (was it Billy or Steve who posted something a few weeks ago..?) Having said that I've only got the deedly widdle 39s on mine, but my balls are still only the size of peanuts...

G

I never noticed mine bogging down infact I found them far better all round than standard set up only bogged down if in the wrong gear

this is good to here as i have just got some from trixynut,, they are 41s with 155 main jets running pod filters,,ive just give them a good clean but to be fair i didn't find any shite in them at all,, the fuel screw is set at 1/2 a turn out and most others seem to be running at 1 turn but iam not sure if this makes any difference ?? is there likely to be any worn parts to fcr,s ?? as this is all new to me

steve speed wrote:this is good to here as i have just got some from trixynut,, they are 41s with 155 main jets running pod filters,,ive just give them a good clean but to be fair i didn't find any shite in them at all,, the fuel screw is set at 1/2 a turn out and most others seem to be running at 1 turn but iam not sure if this makes any difference ?? is there likely to be any worn parts to fcr,s ?? as this is all new to me

I would just second the sentiment that bogging on WOT is normal behaviour for flatslides, which is one reason why they weren't routinely put on road bikes in the days of carbs. If you whack the throttle open on the stock factory set-up YZF750SP (4xFCR) at low revs, it will warble and choke pathetically until it gets to about 6,500 rpm, when all hell breaks loose.

So, while I'm not suggesting it can't be fixed with the right bore carbs and the right setup, I wouldn't assume your FCRs are broken.

Thanks for the replies.

Turned out to be the TPS. Although I could not get the taco to read 4000rpm (kept pogoing between 1000 and 8000) I tightened the tps into position during this pogo stage as it was the only reading between the two extremes. Took her for a good run and the bogging down is not noticeable now

Still seems to be running a bit lean or pop and fart as wombat would say which makes me wonder what adding more air to the mix (pod filters) will do

Anyway - all smiles now