Bing carb reconditioning job

[Bruce Tuncks]

While there is nothing wrong with the carb as far as I can tell, but it is getting old now and there are lots of rubber o rings etc which might have deteriorated over the last 20 years.

Should I be worried? If so, what should I do?

So far, I have just asked the Jabiru spare parts guys about a replacement carb or an overhaul kit .

[John Robert]

Rotax insist on all rubber replacement @ 5 years. Not only rubber but jets also wear as does the needle. The most important is probably the diaphragm. I would not like to be flying with a Bing carb that had 20 years since overhaul. The diaphragm is the reason for the Rotax directive to replace the fuel pump @ 5 years. My a*se is worth more than a Bing overhaul kit.

[Yenn]

I have an old Bing carby.

It started using excess fuel and giving black plugs.

I fiddled with it and eventually sent it to Jabiru.

They did an overhaul of it.

It still uses more fuel than it should and it starts best with plenty of throttle. Runs pretty well, better than before. I have changed main jet down 1 size and hardly any difference.

I am not really happy with it and keep intending to do more work on it. I have my doubts about sticking with Bing, maybe it would be better to change to the injector supplied by Sonex aircraft. The only thing stopping me is the change of controls required, but I am thinking about it. Bing spares cost excessive dollars in my opinion.

[facthunter]

They really shouldn't cost much. They are a pretty ordinary motorcycle carb basically, BUT when they are sorted they work (to a point) after the original LEANING effort that heralded problems. with Jabs The "ordinary bloke" should just leave well alone if it can be set up correctly. It's too much trouble to alter things. Nev

[Bruce Tuncks]

Yenn, why did you change down a size of main jet? was it to try and reduce the fuel consumption?

Years ago, I increased the size of the main jet by drilling it out just a bit. I did this to attempt to have cooler cht's at full throttle. It didn't work though and now I wonder if it was a good idea to drill out the main jet anyway.

[Yenn]

I wanted to get fuel consumption down from 150% of what it was originally to a reasonable figure.It still works OK and temps are good. Maybe I should have changed the needle jet, rather than the main jet.

[facthunter]

You should understand fully the principles of adjusting the mixture on these carbs and check your results by a proven and repeatable method. An exhaust gas analyser perhaps? Plug colour is too unreliable in normal operation. You have to cut the engine and not idle it. it's an OLD speedway motorbike thing Not good enough..Nev

[M61A1]

I have an old Bing carby.

It started using excess fuel and giving black plugs.

I fiddled with it and eventually sent it to Jabiru.

They did an overhaul of it.

It still uses more fuel than it should and it starts best with plenty of throttle. Runs pretty well, better than before. I have changed main jet down 1 size and hardly any difference.

I am not really happy with it and keep intending to do more work on it. I have my doubts about sticking with Bing, maybe it would be better to change to the injector supplied by Sonex aircraft. The only thing stopping me is the change of controls required, but I am thinking about it. Bing spares cost excessive dollars in my opinion.

It sounds like either the float level is too high, a common problem due to crappy floats or the starting carburettor may be leaking or not fully closing. A quick check for float level is to ensure the float bowl is full using your boost pump. turn it off and quickly remove the float bowl (quickly, because as you lower it away fuel will flow as the floats come off the needle), as a rough guide the fuel level should be about 1/2 inch from the top of the bowl.

Normally they won't cold start unless the throttle is fully closed.

The link below gives a good description of the starting carb. Apologies if you are already familiar with it.

https://electricmotorglider.com/wp-content/uploads/2017/10/CV-Carb-Part-2-web.pdf

[Bruce Tuncks]

thanks M6. That is the best thing I have ever seen on the Bing.

[M61A1]

thanks M6. That is the best thing I have ever seen on the Bing.

These articles I found very useful too....

https://bmwmotorcycletech.info/bingcv.htm

https://bmwmotorcycletech.info/bingcv-2.htm

[facthunter]

The choke method is a bypass thing and only works with the throttle closed. like the Solex carb. Nev

[Bruce Tuncks]

I got my small packet today. It had 2 rubber diaphragms, 2 cork gaskets , 10 o rings and one choke gasket.

I know that BMW motorbikes have 2 carbys, but I only expected one kit. There are parts for 2 except for a single small paper gasket.

I would have liked new floats and needle, I guess that these will cost heaps if the old ones are worn or lack buoyancy.

Has anybody done the replacement of rubbers and gaskets job?

[Downunder]

The diaphragms have a moulded "tab" on the side. Make sure this goes back on the same side of the slide. It fits into a groove in the carb housing.

The cork gaskets can be a pain to seat correctly as the want to keep falling out when trying to fit the bowl.

You can pinch them and they will leak.

When I had the carb out, I turned it upside down on the bench, put a very small dob of sealant in each corner ( really small), fitted the gasket and bowl.

Left overnight. Now whenever I remove the bowl, the gasket stays perfectly in place.

[facthunter]

That little TAB is the only thing that locates the dashpot in the correct place. Locating the "cork" gasket with a small amount of sealant on one face, not both, is a good idea. Leave NO excess as carbs don't like excess sealant. Check flotation of both floats. Needle wear raises float level.. (makes it richer) Bad flotation where the float sinks a bit also makes it richer or will even continuously flood if it's bad enough. Don't rush when you're playing with a carb of any kind.. Where the drain tube goes affects the mixture. .Nev

[Bruce Tuncks]

I got my small packet today. It had 2 rubber diaphragms, 2 cork gaskets , 10 o rings and one choke gasket.

I know that BMW motorbikes have 2 carbys, but i only expected one kit.

I would have liked new floats and needle, I guess that these will cost heaps if the old ones are worn or lack buoyancy.

Has anybody done the replacement of rubbers and gaskets job?

[Downunder]

sealant on one face, not both, is a good idea

Yes, I should have made it clear. Sealant on the carby housing only. None on the bowl.

[M61A1]

I got my small packet today. It had 2 rubber diaphragms, 2 cork gaskets , 10 o rings and one choke gasket.

I know that BMW motorbikes have 2 carbys, but I only expected one kit. There are parts for 2 except for a single small paper gasket.

I would have liked new floats and needle, I guess that these will cost heaps if the old ones are worn or lack buoyancy.

Has anybody done the replacement of rubbers and gaskets job?

Take great care putting the O-ring on the idle jet. A special tool is useful, I made one after breaking an O-ring.

The O-ring is very small but is required to stretch a fair bit, and when you that and slide it over the thread it, will often break with the combination of stretch and the thread nicking it.

 

There are also some good youtube videos about rebuilding Bings.

[OZJohn]

You check the Bing floats by weighing them. 3-4 grams is ok, over 5 grams replace.

[M61A1]

You check the Bing floats by weighing them. 3-4 grams is ok, over 5 grams replace.

I think the floats on the Bing 94s that Jabiru use have the floats as a one piece unit like the motorcycles use. I don’t think these suffer the same issues as the two individual floats as used on Rotax.

[Yenn]

The figure given for fuel height in a Bing carbie is not 1/2" down from the top of the bowl. I forget the actual figure, but when the bowl is removed, the float is no longer in the fuel and therefore its level drops. Using the correct figure will make the level be about right at the top of the bowl, when it is replaced.

[skippydiesel]

The cork float bowl gaskets are delicate and a pain to install - I have replaced mine with Viton ones that are more robust and should last for several service intervals. To hold them in place use a small amount of silicon grease.

[Bruce Tuncks]

At least I have a spare cork gasket skippy. If all goes well and I don't need it, I will have a spare kit ( one cork gasket, one paper choke gasket, one diaphragm and 5 "O" rings ) for sale. Already I have made a new choke gasket from gasket paper. This was easy since I have a real one to trace around.

Today I'm going to remove the carby from the plane and bring it home.

Thanks guys for the helpful comments. I think the floats are in a fixed pair. If so, I will be looking to find just what the pair should weigh.

[facthunter]

IF you have a figure for it. Floating it in petrol will provide some assurance. Keep away from Naked Flames. See how many giggles that gets. Nev

[Bruce Tuncks]

Good idea Nev. I will try and float them in petrol and if they both float the same then that will be good evidence they are ok. I wonder if the factory will reply to an email?

Well I have the carb at home now and taking it out was very traumatic on the plane. So I have been wondering just what would have happened if I had waited for a symptom before doing this.

For example, take the diaphragm. Any hole in it would start small and cause the engine to run rough I think. If the floats lost flotation it would start to run rich. Both these events would not be nice but they would not lead to a disaster either.

What wear and tear thing would cause a disaster? If the answer is not anything likely, then we are doing more harm than good by doing this job.

Maybe I should have installed a vacuum gauge instead of doing this carby job.

[Bruce Tuncks]

By disaster I mean a sudden engine stoppage. One thing that may do that is a crack developing in the rubber coupler which joins the carb to the engine. Strangely, there is no provision for safety wire to hold things together in this event.