Carb. Float Height

Bruce Woodrow · Posted: Thu Aug 29, 2002 5:27 am Post subject: Carb. Float Height

Does anyone know what the correct float height setting is for the Dellorto VHSB34?

The repair manual only mentions that the float arms should be aligned and parallel to the carb. base when held upside down. it doesn't give any dimension.

I am pretty sure that I have too much fuel in my carb since the overflow tubes always seem too have fuel in them. I have cleaned the needle valve, so I'm sure that isn't the problem.

Bruce

phil feigel · Guest

you can start you motor on the stand,with the air cleaner off,but do not rev it up on the stand,hold a little braking and gas it on the stand,but do not zing the motor look to see if it is shooting fuel out of the front hole in the venturie,i would say the float is a little high and lower it just a bit,the bottom end will be really clean coming out of the turn no more bog,thats what i have found and it works great,and yes they say level when carb is upside down,but you also have the tang at the needle,you can tweek it alittle also but do not do both at once or you can really screw it up best to have a spare arm to look at,you can email me at pbf1@airmail.net phil

Charles Pou · Posted: Thu Aug 29, 2002 4:47 pm Post subject: Carb. Float Height

Bruce, I was told by a Dellorto expert that the float height is not critical. Maybe that's why the manual does not specify this dimension.

As I understand it, with Dellorto carbs you change to a different size/ weight float to make this adjustment. As we all know, with the RMax this is not allowed.

Without changing floats, I think you can adjust the float height slightly and I think it does make some difference. That is, if the float is too high, the carb will tend to run rich and if too low tend to run lean.

So, make sure the float arms are both even and parallel with the float base. Then, if your engine is not running well, you may want to try different float heights by adjusting the float arms and testing, as Phil describles above.

Anyway, it sounds like your floats are maybe a little high, but you never said how the engine was running. If running good, don't worry about some overflow. :-)

Bruce Woodrow · Posted: Fri Aug 30, 2002 8:42 am Post subject: Carb. Float Height

Phil/Charles,

Thanks for the pointers. My engine hasn't been running right - suffering from a curious, intermittent lean misfire at about 11,500 rpm. This is despite running a larger main jet than others. The other odd thing about the misfire is that, if I stay on the gas, I can drive through it and the motor runs fine again up to peak revs. To add more confusion, at Camden, OH, this would only happen on the S/F straight and not the back straight! I do also suffer from 'bogging' despite being an avid trail-braker and rarely completely releasing the gas pedal.

My current theory is that due to the high fuel level in the carb., the vent pipes are filling with fuel and causing a vapor lock. This causes reduced fuel delivery into the carb. leading to the lean misfire until the vent pipes clear.

Anyway, I'll set the floats a little lower and see what happens.

George Grenier · Joined: 23 Jul 2001 Posts: 105

Bruce,
I would try two things:
1. Vent the carb to the air (no catch can) for one session and see if it is better.
2. Add a couple of teeth to the rear sprocket. Maybe you are catching the weird spot in the ignition curve at bad time on the track.
Also, you are not using the same catch for the water, oil and fuel, are you?
George

naveen_rao · Joined: 17 Jul 2002 Posts: 18 Location: San Jose, CA

WE HAVE HAD THE EXACT SAME PROBLEM!!!! We just couldn't get the jetting right; it just seemed to be VERY sensitive. If it was off just a bit, the engine would cut out down the front straight and we didn't know why (we'd run rich, lean, couldn't get it to run some times).

Anyway, this problem was solved! We finally got frustrated after 3 months of botched races. We took our engine to the Rotax service center for them to look at. They found out that there were 2 base gaskets on the thing (I guess they stuck together during assembly) which caused the squish and exhaust port to be WAY off spec. Once this was corrected, they engine responded to jetting changes normally and no longer cuts out on us for no reason.

I hope that helps! Rotax really needs to get their quality control in order.

Naveen

Bill Wright · Posted: Fri Aug 30, 2002 11:22 am Post subject: Carb. Float Height

Naveen,

It is common to use a .3 and a .4 base gasket together to get the squish within spec.

What was the squish when you took the motor in? What is it now?

Bill Wright
"Get on Course!" with FK www.formulakart.com

Michael Horley · Posted: Fri Aug 30, 2002 1:14 pm Post subject: Carb. Float Height

quote:
Originally posted by Bruce Woodrow:
Does anyone know what the correct float height setting is for the Dellorto VHSB34?

The repair manual only mentions that the float arms should be aligned and parallel to the carb. base when held upside down. it doesn't give any dimension.

I am pretty sure that I have too much fuel in my carb since the overflow tubes always seem too have fuel in them. I have cleaned the needle valve, so I'm sure that isn't the problem.

Bruce

The Dellorto manual that I have gives a dimension of 3.5mm from the float bowl joint face to the underside of the float arm. (With the carb upside down). It also says the float arm must be parallel as you say. I queried whether this dimension was with the needle valve spring compressed or not and they said not compressed. This came from the UK importer of Dellorto products.

Hope this helps.

naveen_rao · Joined: 17 Jul 2002 Posts: 18 Location: San Jose, CA

Bill,
I realize that they use multiple gaskets to get the squish IN spec, but ours was very far out of spec. I think the spec range is .09-.15 and ours was .26 (those numbers are off the top of my head so don't quote me). Anyway, the rotax guy fixed that and changed the piston ring (the motor only had about 10-12 hours on it) and all was good.

I guess the other variable is the piston ring. It could be something to do with that, but he thought that the squish be so far out was our problem.

Naveen

Bruce Woodrow · Posted: Sat Aug 31, 2002 5:45 pm Post subject: Carb. Float Height

Cheers Michael,

Exactly what I wanted to know. BTW, where did you get your Dellorto manual from? If it is a UK source - no problem, I have visitors/family over from England regularly. I usually get them to pick up some parts from Dartford Karting - can't beat sprockets at £5 ($7.50) in comparison with about $20 here!

Bruce