Diablo runs but sometimes needs choke??

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bottomsupduckclub
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Diablo runs but sometimes needs choke??

Post by bottomsupduckclub » Sat Jan 28, 2012 8:57 am

I've got a problem with my 503 that Bruce went thru a couple years back. It starts & idles fine but when I drive it alittle then slow down & go to give it some gas & drive again it seems to want to die off. This is where pulling the choke alittle brings it back around & off we go again.
I will be installing a new plug for sure. The gas is mostly fresh (there was some old gas in tank that I added to) I am getting fuel to the carb no problem there.

Why is this happening? What should I be looking for or at to resolve my issue?

BOTTOMS UP from Horicon, WI
69 Diablo "503"
72 Kitty cat
74 JD 295s (1 1/2X)
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81 Spitfire
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Go Go Diablo
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Re: Diablo runs but sometimes needs choke??

Post by Go Go Diablo » Sat Jan 28, 2012 10:29 pm

Dang carbureation. It's always a challenge. I presume you tried adjusting your high speed jet, so I won't even suggest that.

We know this motor is tight in regards to seals and stuff, cause we checked that in the Diablo shop. I would try to remove the diaphragms from the carb and just ever so slightly bend the fulcrum arm for the needle and seat outward just a tad and see how it affects performance. With care, you can do this without removing the carb from the motor.

Any other suggestions from the rest of ya?

Bruce
Too many Diablos and parts to count.
Yamaha 600 SX

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snocatpete
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Re: Diablo runs but sometimes needs choke??

Post by snocatpete » Sun Jan 29, 2012 12:06 pm

I have been thinking about your problem and here are some of my thoughts, right or wrong. To me it sounds like you have a problem with your intermediate discharge port in your carburetor. The reason why I think this is because you say it will idle but then hesitates when you try and rev up the engine and once it is up to speed and running, past the intermediate stage, it seems to run fine. It sounds like the idle port is fine and your main jet discharge port is fine. I therefore suspect the intermediate port could be plugged, causing the hesitation or dying out. By choking it, it causes your carburetor to pull the fuel through the main jet and main nozzle to get the engine up to speed.
A couple of things you can try - as Bruce mentioned adjusting your inlet needle lever , make sure you are getting the right amount of fuel in the carburetor chamber. At the same time you have the carburetor apart, checking this, I would spray some carburetor cleaner to make sure all three ports are clear.
Anorther thing I always preach is make sure your gas tank vent is operating. Over time, even if the fuel line looks like it has fuel in it, the fuel pump is still pulling hard against the fuel tank vacuum if the vent is blocked. I don't think this is the problem if you pull the choke and you get the engine up to speed - it seems to run fine. It just sounds like to me like the transition from idle to off idle.
You could try if you have a spare diablo or carburetor - switch carburetors from one diablo to the other. If the problem moves too, then for sure it is your carburetor (Maybe you have already tried this). If the problem does move or if another carburetor works on your machine, you have 100% isolated the problem if it is carburetor or really an engine problem that seems like a carburetor problem
In Bruce's Diablo Information package that he has available for sale, there is a Tillotson service manual. In this manaul there is a really good explanation of the intermediate operation of the carburetor. And on the last page of the manual, there is a really good troubleshooting chart. And a section pertaining to "engine will not accelerate".
If you don't have this, I could scan it and email it to you. Maybe some of these ideas will help you out.
Peter

ljhuuki
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Re: Diablo runs but sometimes needs choke??

Post by ljhuuki » Thu Feb 02, 2012 4:18 pm

Hey Pete, I agree totally with you on this. I deal with 7 Hus skis and a diablo and I have dealt with some type of carburator issue with each and every one of them.

I do have a question for you that I hope you can throw some input to. I have a HL 167A for a spare that I can not get high end out of. The carb is completely clean, all ports work properly with carb cleaner being sprayed through. The best I could ever get out of it is a little more than half throttle. At one point I bent the lever control arm way out and had high end but of course I could not get low end. With lever in proper position machine starts with one pull and idles all day long but starves for gas on high end. I was thinking check valve? But carb cleaner flows through fine??? Any ideas?

Thanks for anything.
John

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snocatpete
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Re: Diablo runs but sometimes needs choke??

Post by snocatpete » Sat Feb 04, 2012 2:04 pm

Hi John, I haven't been ignoring you but giving your question some thought. I am going to assume alot of things which I probably shouldn't do. I am going to assume that it's a fixed main jet carburetor and I am also going to asssume that all your gaskets are in good condition or new. And i will assume that both base gaskets are in good condition. Having said that we are running out of possibilities here. When you adjusted the fulcrum arm to let more fuel into the carburetor base chamber you got full throttle - lots of power but then no bottom end. Does this mean it won't idle or idles high? For me with a fixed high jet carburetor with the jet tight ( I assume that it is tight) there is really nothing you can do to adjust high end therefore I would be looking at low end - the only part you can adjust. I am also assuming that the low idle mixture screw has a good rubber seal or o ring around it and it is not leaking air. My first inclination is that it is a bad ball check in the main jet circuit. This ball check prevents air from being pulled into the carburetor when the carburetor is in idle position. You say when you bend it back to its optimum position it will idle fine. I also know your internal passages are all clear so I will assume that your atmospheric vent for your metering diaphram is also clear and unobstructed. Another suggestion is have you tried to get a happy medium on the fulcrum arm where it will let enough fuel in to get high performance on the main jet and also where you can lean it out with the low idle mixture screw and get idle. Also it is a bit of a balancing act between your idle mixture screw and your idle stop screw. These both have to be adjusted pretty precisely to get good idle.

Now you mentioned this is the spare carburetor so I will assume you have tried this on other engines with the same results and vice versa so you are 100% sure it is the carburetor and not an engine problem.

Is this an original hus ski carburetor? My 444 and my 600 engines both have a 186A carburetor... Don't ask me what those numbers mean! Maybe it could be the difference as to why this carburetor isn't working well on your JLO engines.. Just a thought Does your 167A have that balance tube infront of your choke valve at the mouth of the carburetor? If it does, make sure it isn't blocked as that will affect your high end performance.

That is all I can think about for now but will keep thinking about it as I work along here. If you can provide any more info or if you want to PM me to discuss further, I will be happy to try and help out a fellow enthusiast if I can. Please bear in mind though I am no expert! If I have a eureka moment I will post it on here. Maybe Barrie could shed some light on this problem as well.....
Peter

ljhuuki
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Re: Diablo runs but sometimes needs choke??

Post by ljhuuki » Mon Feb 06, 2012 8:19 pm

We have a few of the 167A carbs on our Hus skis and they work fine. This carb does not have the tube in the mouth. It also does not have a fixed high end jet it is manual. I had it almost hanging out and still no high end. Barrie thought the main high end check valve was stuck but it isn't. I don't want to give up on it because low end idle is perfect and not hard to get. When I bent the lever control arm out enough to get high end out of it the machine would flood out on idle. It's mind boggling. All new gaskets, clear ports. I have messed around many HL carbs and one has never beat me but this one is Definately doing it.

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