EXUP Worldwide

I posted this on the YZF sub-forum, but no responses to date. Maybe someone here can advise me?

I recently had to ride my 1996 YZF750SP up a steep drive-way. Very steep: 30 to 35° I guess. Anyway, my bike almost didn't make it. I had to rev the bike to about 5000 and slip the clutch horrendously in first and paddle with my feet to get to the top. Since then this has happened several times, always on a very steep uphill, although the bike makes good power in all other situations.

This is obviously not the way it should be, and my first thought (my only thought!) is that the float heights are wrong. So I've read up the procedure in the Haynes manual: fit clear tubing to the drain plug and measure the fuel height using the dot on the carb body.

My first question is: am I really on the right track in solving this poor steep-uphill performance problem? I am aware that in some instances the fuel height should be increased to first 10mm and maybe 14 mm.

My next question is: is that the only way to measure the float height? Can't I come right by removing the float bowl and measuring there? It would be a lot easier than bowls off, adjust, bowls on, measure, bowls off, adjust some more, bowls on again, next carb etc. etc.

Finally, if I do raise the fuel level, what other side-effects can I expect? My thinking is that the bike will run richer every where - is that so?

cheers
Thomas

Interesting problem Thomas, so i guess it seems like is running out of fuel/power on the incline, or is it running rich?

On the FCR raising the float levels will richen through the running range. If you are going to make changes, make them in small increments.

I don't know that much about the FCR's, though I plan to become acquainted in the future!! If your going to make adjustments, pull them off and do it on the bench. While your at it give them a good clean and check everything! Once they are off and prior to cleaning you can simulate the angle your trying to have them work at. Needle and seats could be worn/dirty and sticking at the angle you are trying to ride up etc. Check everything, clean everything! Keep us posted

Here's a page that may help in understanding the carbs.

http://www.factorypro.com/tech/carbkei.html

Thanks Spook.

I've raised the fuel level to 12mm and we'll see what that does.

I also tried to synch the carbs but that's a lost cause: the engineer who determined where the vacuum guage adapters are to be located must have been an exceptionally cruel bastard. There's no way I'm going to be able to get my bloody fingers in there... and I'm fairly normal in the fingers department. I reckon when Yamaha built these bikes they synchronised the carbs on a flow-bench.

However I have another plan for measuring the manifold vacuum up my sleeve... watch this space!

Yes please do Thomas. There are quite a few of us here 'interested' in FCR's. Photo's are always good! Cheers

A couple of months late, but I'm here less now the SP is gone, but I had 10" lengths of fuel hose blocked off with bolts, so you just unblock them & plug em in to the gauge.

I've had to raise fuel levels for steep conditions (on CV carbs), but I'd not compromise a good setup for this, only enough to get it usable up hill. My SP never had problems with the FCRs up hill (there was a snotty 1st gear clutch riding hill I knew) so it should be possible.

F5 wrote:A couple of months late, but I'm here less now the SP is gone, but I had 10" lengths of fuel hose blocked off with bolts, so you just unblock them & plug em in to the gauge.

I'm not sure why Yamaha did this in those particular YZF's and FZR's but the Ace has those hoses already set up, and the hardest part of a carb sync is propping the tank up!

Now that's a little creepy. I looked at the pic and said "hmm... I don't remember taking that pic."

I have the same ring, watch (mines black and silver), hairy arms, and I've taken the same pic a couple of years ago.... The biggest tip off was the blue fairings.

FZRDude wrote:Now that's a little creepy. I looked at the pic and said "hmm... I don't remember taking that pic."

I have the same ring, watch (mines black and silver), hairy arms, and I've taken the same pic a couple of years ago.... The biggest tip off was the blue fairings.

Hahaha, funny, I thought I was the only gorilla on the forum! The ring was designed by the wife, so probably a little different (pilot sport tread pattern!) But everyone's got a timex ironman don't they?