Suzuki RF900 Flatspot

**Chookah** · 11th September 2006, 21:11

I am not particularly worried about this but I might just mention it as it may be abnormal.
I have recently bought a 2000 RF with about 22k (14 mile) on it, good nick and all the rest.
Goes well but it has a slight flat spot between 3 and 4 grand. This doesn't matter much as once out of town those rev's become immaterial, and it certainly goes well enough everywhere else.

Any comments or thoughts? It may just be that, as this is the smallest capacity bike I have ridden for years, I will have to get used to it.

**F5 Dave** · 12th September 2006, 12:14

As a starter I'd put a hotter thermostat in it which will help it warm up faster & further helping carburetion, but not decrease the ability to cool, ie: shouldn’t over heat any easier in traffic re last post. Do a search (also link in last post) & I have specified the thermostat I used & how to modify it.

Other than that RFs seem pretty touchy on float height. I raised mine so the bike didn’t stall up real steep low speed hills, but lowered it again in between as it was a bit rich.

I also run a Factory jetting kit which is quite nice for throttle response. But a 900 isn't an 1100.

**imdying** · 12th September 2006, 17:47

Originally Posted by F5 Dave

As a starter I'd put a hotter thermostat in it which will help it warm up faster & further helping carburetion, but not decrease the ability to cool, ie: shouldn’t over heat any easier in traffic re last post.

How would that help it warm up faster? And how would having a thermostat that opens later not decrease its ability to cool?

**Chookah** · 12th September 2006, 18:51

Thanks F5 Dave
Actually a good point about the float levels, I should check these.
I should have thought of that, but it is a while since I have owned anything with carby's

Also you say you have a Factory Pro jet kit. Would that be part no. CRB-S79-1.0?
If so does it have a noticeable effect in the low to mid range?

And... I think you mention elsewhere that you have installed an ignition advance kit. Can you tell me how effective that was (and what kit you actually fitted, i.e another of Factory's products?)

And.......where you bought it all from - direct from FactoryPro via the net?

**F5 Dave** · 13th September 2006, 09:35

1. The std thermo has 4 extra holes drilled right through it which means it takes forever to warm up & runs bloody cold. I think this is a crude attempt to get it to pass more water but it's just dumb. Once the temp is past the point where the thermo is fully open & they do distort quite a lot when they get real hot starting a little earlier will only give you as long as it takes to warm that temp diff extra, maybe 20seconds. Really the prob is the fan needs to come on in traffic, just like a car, not the thermo. Got the idea of changing the thermo from the Factory site.

2. I bought the std factory jet kit, whatever that was + some emulsion tubes as mine were worn slightly oval. Just called & gave my no. Pretty simple to deal with if you can understand the language. I understand it is close to english

.

What helped the most I don't know I had commited the sin of doing all (jet, emuls tubes & ign) at once. I advanced the ignition by slotting the pickup position & rotating it opposite to engine rotation. I intended to try it on the dyno but ran out of time & just worked on the jetting. May try it back std ign one day, it does pink a little under load in low revs, nothing to lose sleep over, just when you get lazy.

To be honest this is my touring bike so I aren't going to run 96/98 in it, I suspect the ig timing isn't worth changing.

**Chookah** · 13th September 2006, 21:52

I pulled the carby's out of it tonight with a view to having a go at the float levels.
However too my surprise it has got height adjustable needles already. which is quite possibly good news as I now, once I have checked the floats, have something to fiddle with.

These needles have stamped on them 5DV1 then a picture of a square within a square. Does this mean anything to anybody?

Further comment on the thermostats.
The suzuki factory sevice manual for an RF900 (94 to 98) says that the thermostat should open between 75 - 79 degress and the fan should on/off at 105/100.

By comparison a Hayabusa (again from a factory manual) has 82 degrees for the thermostat and 105/100 for the fan.

Both seem quite low to me, but the RF especially so.

**F5 Dave** · 14th September 2006, 09:17

Yeah if you search around the factory site (isn’t immediately obvious but in a questions area) he reckons Suzs of that era were too cool thermo.

The symbol you describe is Mikuni ie: std. it’s the shape that could be better not the adjustment up or down so much. Also check your emulsion tubes (that the needles slide into) for ovality, if that’s a word, and Bill Gates spell checker doesn’t agree with me it appears . Doesn’t take much to affect them.

**riffer** · 14th September 2006, 11:32

What's the URL for the factory site Dave?

**F5 Dave** · 14th September 2006, 11:45

factorypro.com

**Chookah** · 14th September 2006, 21:35

Riffer, It appears that you have an RF there.
Do you have I slightly “off song” spot between 3 & 4k?

**Chookah** · 14th September 2006, 21:56

F5 Dave,

Everything looks in fine shape, though I still haven’t checked the float levels yet.
The “oviality” or maybe the “ovalacalityessness” or otherwise of the emulsion tubes looks just fine to the extent that I would still call them “round”

**riffer** · 15th September 2006, 09:28

Originally Posted by Chookah

Riffer, It appears that you have an RF there.
Do you have I slightly “off song” spot between 3 & 4k?

Not at all. It's a bit buzzy at 5-6000 rpm though.

Try this neat trick on an RF900.

Accelerate in first up to 7,000rpm. Shift back on the seat as you do this until your bum is up against the back of the front bit of the seat. Now close the throttle and push down. As it gets almost to the bottom of the suspension travel open the throttle wide open. Change up at will.

Clears the carbies nicely (and the cobwebs from your brain too.)

**Chookah** · 17th September 2006, 11:53

The float levels were all over the place, but on average about 1.5mm higher than what they should have been.
Further to that the pilot screws were all over the place as well.
To give you an idea one carby had just 3/4 of a turn out while another had 2 turns out.

I reset the floats to 6.9mm and the pilot screws to 1 1/4 out, gave the whole show a good blow out and balanced them.

No fluffy spot between 3 and 4k now and the idling, though pretty good before, is now incredibly smooth.

Hard to say which was the main culprit, probably a bit of everything, but it is a good example of the wisdom of checking the basics first.

And just in case anyone is interested the carby's on mine are stamped with ID No. 31EA which means that they are for the UK, Netherlands and Italian market. Other markets with different ID No's have different pilot screw settings (though I see that all the float levels are the same)
This info comes from the Suzuki factory service manual.

**WINJA** · 17th September 2006, 18:01

Originally Posted by Chookah

I pulled the carby's out of it tonight with a view to having a go at the float levels.
However too my surprise it has got height adjustable needles already. which is quite possibly good news as I now, once I have checked the floats, have something to fiddle with.

These needles have stamped on them 5DV1 then a picture of a square within a square. Does this mean anything to anybody?

Further comment on the thermostats.
The suzuki factory sevice manual for an RF900 (94 to 98) says that the thermostat should open between 75 - 79 degress and the fan should on/off at 105/100.

By comparison a Hayabusa (again from a factory manual) has 82 degrees for the thermostat and 105/100 for the fan.

Both seem quite low to me, but the RF especially so.

I HAD A 98 ZX9 WITH A SIMILAR FLAT SPOT , WORKED OUT IT WAS LEAN FOR EMMISION OR NOISE TESTING , I RAISED THE NEEDLES AND RICHENED IT UP , WITH A BACK TO BACK DYNO RUN IT GAINED 12HP IN THE MIDRANGE AND 6 UP TOP,I KNOW WHAT YOUR THINKING HOW CAN THE TOP END GET BETTER , WELL IT WAS SLIGHTLY LEAN AND NEEDLES DO HAVE A SLIGHT EFFECT ON TOP END AS WELL, PLAY AROUND YOU CANT LOSE , ALSO BE WARNED ABOUT YOUR ARSE DYNO CAUSE WHEN YOU TIDY UP THE MIDRANGE IT CAN MAKE THE TOP FEEL FLATTER SO USE A MATES BIKE TO DO RUNS OR A DYNO