Slight problem needing help with

Ran my bike today at highway speed - 55mph for only about 1 mile then had to slow for a turn and as soon as I slowed down to turn, the engine quit on me.

I suspected fuel starvation so I rotated the petcock to prime and cranked it over some and it finally started after choking.

It also runs a bit rough in the 2500-3000 rpm range when accellerating but not when stationary and flicking the throttle up.
Low speed mixture screws are currently set at 2 3/4 turns on all carbs.
Carbs recently cleaned out.
Bowl fuel levels are within specs.


My Colortune came in so I am going to use it tonight to set low speed mixture.
I am going to run the bike to speed with the petcock on Pri to see if the problem duplicates.


Any other suggestions on what to check and try would be very helpful.

Thanks

 

What was the tempature and humidity? Going from highway RPMs down to an idle can cause fuel starvation due to carb icing.

If this is an ongoing problem disregard tempature/icing questions.

As the bike works fine at throttle, I'd be surprised it was a petcock failure... from the posts I've seen they tend to fail by supplying too little fuel at higher rpms... unless it was on the vacuum side of the petcock I guess, in which case your prime test is a good one.

Woot.

 

I'm not trying to be a smart ass, but is there gas in the tank?? My old XS400 and my fathers Cb750 both sputter and spit before they run out of gas (before switching to reserve) My Maxim does not, I'm driving along fine come to the end of the off ramp pull in the clutch and it dies, same thing too I put on prime and it will start ( and run on reserve)

 

Thanks for the input!

No icing, temp was a nice 50 degrees.
Has 1/2 tank of gas.

I don't know, maybe the engine just needs to be shown who's boss since this bike has not been run at these speeds is a long long time.
Maybe I'll talk sweet to her before I start out next time.

I'll do the Colortune thing and the petcock prime test again then let you know what happens.

Thanks!

 

BTW- I'll also run some Seafoam thru too and see if that helps.

 

You'll probably be fine after doing the ColorTune. You're likely to find yourself adjusting the Pilot Screws out considerably more than the 2.5 Factory set-up, the 2.5 > 3.25 above Factaory set-up everybody adds for idle and just off-idle tuning.

I've done two 750's, so far, with the ColorTune. Both needed coming-out closer to 3.25 and more for a predominantely "Bunsen Burner" blue.

For decent Cold Starting and low-rev performance; I'd guess you'll need a solid blue. Slightly Rich being a good thing; anyway.

 

Don't know about the 550 but my 650 needs to go on RES when it appears to be 1/2 full. Remember, a lot less fuel in the bottom half of the tank because it straddles the frame.

 

MiCarl,
Good point. I never thought about that.

Well, I colortuned and she is running better.
Ended up at 4 turns on all carbs then went an extra 1/2 turn for good measure - 4 1/2 turns toatal on all four carbs.
Runs alot smoother now with no hesitation in the 2000-3500 rpm range.
smooth all the way to red-line under load.

Also, did a diagnostic on the petcock and while looking at the clear fuel filter, with the position "ON" after a few minutes, I can actually see the fuel level dropping, looking like fuel starvation. Then, when I flip over to "PRI" the level increases.
So- Either I need to put more fuel in tank or the vacuum part of my petcock is fried..

Carb mixture question. Does ambient outside temp affect this adjustment?
Tonight it was approx. 40 degrees.
If I had done this when it was 80 degrees what would change, if anything?

 

Ambient temps above 40-Degrees?

Technically. Splitting hairs and getting deep into the Physics ... Yes.

Practically. Not enough to worry about. Glad your bike's got the whole power band going for it.

 

ooooooh, someone in the Texas area with a colortune. Wanna loan that sucker out?

 

I don't mind loaning it out. However, there was some talk of a possible CarbClinic this fall season in the Dallas Area. ShadowHawk may have some info.
Personally, I would prefer it to be in Ft.Worth but beggers can't be choosers.
Do you ever get to Granbury or surrounding area?
PM me.

 

So far, in the almost 9 years that I've lived in Texas, the closest I've gotten to Granbury is Glen Rose, down at the Dinosaur State Park.

I got the email a while back about a possible CarbClinic, but haven't heard anything more.

Did you happen to get your colortune locally or did you have to buy it online?

 

I am only about 15 minutes from GlenRose. Glen Rose is a great place to visit. Granbury is a nice place too.
I bought mine from etoolcart.com on line.
Had paypal dollars I wanted to use, they take paypal payments.

 

Did you buy the single colortune or the "professional" kit (with 4 colortune plugs) and if I might ask, how much did they nick you for it?