FXR150 starting problems

**gijoe1313** · 6th February 2008, 14:09

Righto, working on the bike with Donor, found fuel in airbox (lots ... 100 -150mls worth!) .. Sprag sez "should there be fuel in there and can I light it?"

So ... why the hell is fuel spitting back from the carb into the airbox ... and discovered also that fuel was also in the vacuum tube. This could be due to it sucking it back from the carb.

Any ideas people?

**gijoe1313** · 6th February 2008, 14:38

Addendum : we have sorted out the airbox, on full choke will idle up to 5000rpm, using no choke and throttle cuts out around 2000rpm ... odd and odd!

**xwhatsit** · 6th February 2008, 14:39

Some bikes have a situation where when the carb overflows, the fuel can run into the airbox. Wouldn't have thought it'd work like that on a sloped single like an FXR, but who knows. Check the float valve isn't dirty and causing overflow. Or the float isn't sticking or something.

Some people talk about checking inlet valve clearances if the carb spits back, but I can't see how that'd work, personally. I am an idiot though. And that much fuel due to spitting back? Seems odd.

First thing I'd do is replace the sparkplug. You never know

EDIT: It was running right on the way to your house, Justin? Young Scorpio-killer wasn't red-lining it the whole way home and bent a valve or summat?

**EJK** · 6th February 2008, 14:46

I read FXRs can fit GN250 carbs?

FXR carb: 28mm
GN250 carb: 33mm

Edit: What about the spark Justin? would that ignite the 100-150ml fuel? lol

**deanohit** · 6th February 2008, 14:53

Originally Posted by EJKDDORAI

FXR carb: 28mm
GN250 carb: 33mm

If it fits on, there should be a slight increase in power with the extra fuel the GN carb should be pumping.

**T.W.R** · 6th February 2008, 15:01

Check your inlet valve clearance

**EJK** · 6th February 2008, 15:03

Justin is now saying its fixed???

**xwhatsit** · 6th February 2008, 15:07

Originally Posted by T.W.R

Check your inlet valve clearance

Yeah, I keep hearing that, why?

Unless I've got the Otto cycle completely screwed up, how is the charge going to be forced backwards, unless the clearances are so ridiculously tight that the machine wouldn't run at all when even slightly warm?

Considering the machine was running before as well.

These things do my head in lol. Confusing.

**deanohit** · 6th February 2008, 15:08

Originally Posted by EJKDDORAI

Justin is now saying its fixed???

Ummm, not quite.

**xwhatsit** · 6th February 2008, 15:10

Oh yes, I was reading a thread where the bucket racers fitted GN250 carbs to ye olde FXR -- but even better, XL250 carbs (same as CB250RS).

I've got two spare CB250RS carbs, if you want to go really fast, fit one of them. 33mm round-slide (none of this GN250 CV shit), accelerator pumper. The thing would have some snap

**EJK** · 6th February 2008, 15:13

Give em to me!

lol jks

Yep, the bike is now all fixed (According to words from Justin and Donor). He is now putting all the pieces and bits together. I'll go and pick it up later

I'll have a BBQ one day inviting all of you guys

**deanohit** · 6th February 2008, 15:15

Originally Posted by EJKDDORAI

I'll have a BBQ one day inviting all of you guys

Time and place man!

**T.W.R** · 6th February 2008, 15:17

Originally Posted by xerxesdaphat

Yeah, I keep hearing that, why?

Unless I've got the Otto cycle completely screwed up, how is the charge going to be forced backwards, unless the clearances are so ridiculously tight that the machine wouldn't run at all when even slightly warm?

Considering the machine was running before as well.

These things do my head in lol. Confusing.

Vacuum pressurization