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v1nn1e

Ring-Ding-Ding after throttle blip and hunting idle

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Just want some other opinions to check my thinking on this...

After having the carb flood on me a couple of times, I removed it and took the float bowl off to find a too large float jet. There was also some greeney-grey crud in the bottom of the float bowl that I scraped out. After a thorough rinsing and checking the floats were good, I replaced the 250 float valve with a 200 and re-assembled with new float bowl gasket but everything else left untouched.

No more flooding but now, when I blip the throttle, the engine Ring-Ding-Ding's for ages and won't settle down to a smooth idle. Also, if I do get it to slow down, adjusting the idle mixture screw appears to make little difference.

IMHO, i think there may be some crud blocking the idle jet. Ho, Hum - looks like another carb strip down will be required to flush this through.

Any other thoughts?

 

Cheers

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If you lower the fuel level in the bowl you reduce (albeit only slightly) the pressure pushing the fuel through the jet.  Your symptoms sound like you're lean at idle which would correspond to the change in fuel height/pressure so it sounds like you need to step up your pilot jet a size to compensate.

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The numbers on the float valve assy( often referred to as the needle and seat Assy) refer to the actual size of the hole .So if you reduced the size of the hole from 2.5 mm to 2 mm that is a 25 percent reduction in the fuel flow .

what you describe is a engine running lean so before trying to tune for this condition check to make certain the correct float valve Assy is in the carb.

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Hello,

One thing u should verify is that the needle in the slide is positively held in place. if the hold down clip is incorrect or missing the vacuum of the engine will lift the needle in the slide at idle and supply extra fuel thru the main circuit causing uncontrolled idle issues . the needle should not be able to move up in the slide. another member here referred to this condition as hunting and hanging of idle. may not be your problem but worth a check.

happy new year,

Maxwell

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I've never heard of anyone changing their float valve size as an engine tuning procedure. Typically the float valve is sized to be large enough or larger. It looks like the parts manual for your bike does call out the 200 float valve and someone may have upped it to handle a fuel starvation issue. On the larger Betas with the Keihin the valve size is actually too small but it only manifests during long high speed runs when at full throttle the bike will starve for fuel after about a minute. The Keihin valve seat is just drilled into the body so there's no way to replace it like the Mikunis and Dellortos. The float valve is a conical valve with a similar seat shape. It only needs to be open a tiny amount for full flow so a nick or fleck of grit on the seat can hold it open. You probably fixed the flooding problem more by cleaning than changing valve size.

As you have figured out already what you have that causes the run-on is a lean condition which is usually caused by a blocked pilot jet, too small a pilot jet or an air leak. You can check for an air leak by spraying starting fluid around the intake manifold while the bike is running. There should be no change in the engine. This is a procedure that can be dangerous so only short bursts in targeted areas. Have a fire extinguisher handy and do it outside where it is well ventilated. Jets and passages are best cleaned with compressed air. Again in a well ventilated area since you may be spraying residual fuel. Be careful of pressure as you can damage seals in the carb with too much. Some will advocate running a wire through a jet to clean it. Don't. If you change the diameter of the jet by either abrading the hole larger of leaving residual material in the orifice you lose any reference point for jetting. That you change the idle air/fuel mixture screw position and hear no change would point to either a way off pilot jet or blockage in that circuit. Since you didn't change the jetting I think you are in for a disassemble and clean of the carb. The DellOrto uses a fuel circuit for the idle adjust so it's possible though unlikely that is blocked. The only other thing I can think of because I've seen it on Keihins is a situation where the choke circuit doesn't properly shut leaking air into the pilot circuit. 

In any case a clean carb is a happy carb so it's always reassuring to know you've gone through the carb and it's in top form. Good luck tracing it down.

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Ultrasonic cleaning and close attention to original manufacturers settings should see good results. Checking for air leaks in the induction system is better carried out with WD40 or similar maintence spray, less chances of fire especially if using starter fluid. If there is an air leak...usually at a flange gasket, then the engine will draw in the liwuid and evidence itself as smoke from the exhaust...do this outside in a well ventilated area?

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Regarding the float valve size, there was an article on the SplatShop web site for the 2011 290, which uses the VHST carb, that suggests for some reason known only to the author to replace the 200 with a 250.

I can only guess that maybe someone read that article put 2 and 2 together and got 5!

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1 hour ago, v1nn1e said:

 

Regarding the float valve size, there was an article on the SplatShop web site for the 2011 290, which uses the VHST carb, that suggests for some reason known only to the author to replace the 200 with a 250.

I can only guess that maybe someone read that article put 2 and 2 together and got 5!

When you put 2 and 2 together you end up with 22?Seriously though agree with your theory on float valve size?

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OK, got the carb apart and checked everything through. Given pilot jet a good blow through and it looks clean.

However, noticed that it's a 35 size, where as in my user manual the spec section at the back says it should be 30.

That sounds like a not insignificant size bigger. Slide and needle are as spec'd, and of the four grooves in the needle, counting down from the top of the needle, it is in groove 3. The spec sheet says  '3rd + 1 clip 0.5' which I don't quite know how to interpret. Perhaps it just means 3rd groove with one circlip of size 0.5...?

Should I hold reassembly and order a size 30 pilot jet? Hmmm....

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OK, quick chat with the helpful chappie at SplatShop and he reckons the 30 size was too small and not uncommon to up. Thinks it may have been related to squeezing through emissions regs or somesuch - can't honestly see how a smaller pilot jet is going to fool anyone, with all that oil smoke belching out, but  who knows... Certainly, a 30 seems to be the smallest size available.

Anyways, reassembled, smeared some silicon grease around the carb rubbers to assist with air sealing, and fired it up. Left it to warm up and it seems to have cured the issue, idles reliably and after blipping, on the over run, it settles down nicely.

Thanks all

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