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Carburator Frezzing - Problem at High Speed


Well, in my introducing thread I spoke about my FXSTS which doesn't run normal for the moment. I will give you my short story and my question at the end.

In January this year I bought an FXSTS 1993 with 65000km (40300mi) on. The price here in Switzerland was a very, very good one ($10.500,-) I picked it up at my dealer arround 60mi away and wanted to drive home. It was in january and around 30°F. After 30mi there was bad backfire, coughing and spitting from exhaust and carb. Just to know the configuration it is with the Big Sucker Air cleaner and a Screamin Eagle Exhausts, as well a Thunderslide kit in the CV-carb. The dealer told me that the carb ist with a 45 slow jet and a 180 main jet. The jet needle clip is in the 4th groove from top. As it was also a little bit raining on this day and I didn't know at all the habbits of the "new" bike, I thought it will come from the humidity. After another 20mi I heard a big noise coming from the right side and I pulled the clutch and switched of immideatly the engine. This all happened on the highway at a speed arround 75-80mi/h. I was luckily because I stopped in front of a reststop. I called the dealer and they sent the truck to pick up the bike. Fortunatly I was with a friend of mine on the road and I could drive home with him. Two days later the dealer called me with the diagnose of a broken cam gear bearing and the parts were distributed all over the engine. The fixed it with a long list of new parts (including a new torrington bearing). They also had to split the crankcase, made new pistonrings and so on and on. After 10 days they brought my Bike and I was happy. Not very long. I took a ride and I had again to take the highway. While I was riding at arround 75-80mi/h it begann again with coughing and spitting. I turned back home and called again the dealer. He thought that this time he thinks it is the ingnition sensor. There is a well-known temp. problem. They sent the mechanician to me and in my garage we changed the sensor. After this, nothing was working. We found some electrical problem at this time and after 3 hours he just picked up again my bike. The next call was that they found the problem because the new sensor was broken as well. SO they ordered again a new one, installed it and fixed some other small things and brought the bike to me. The told me that they made a test ride of about 60mi and the bike is running great. Again once more happy with a big smile in my face I took the Bike for a ride. Arround 20mi, and again on the highway because I wanted to be on time at a meeting. Guess what happend? YES. The same problem. Well, nobody could hear me, and this was good, because otherwise They would have brought me to jail. I calmed down and wanted to know now if it is the same on the normal roads with less speed. And it was, but not sooo bad like on the highway. Again the call to the dealer. He was not really happy to hear me again, but the first thing he said was, that he will give me back the money and they will take back the bike. I was thinking to this, but finally I refused. At this time the bike ist going to be in a very good remanufacturing process, and I could not believe at all that the failure is not solvable. I told the dealer that there is only two more things to change. Either the Ignition coil or the blackbox and the spark plugs for sure. So they decided to send me the parts and I installed it myself. The agreed also on this procedure, to be save on my side for the warranty. After installing the parts I took a ride and on the highway the same coughing and spitting like before. Really pissed off, the call to the dealer. This time they will give me a bike for the meantime during they fixx the FXSTS. They think now it is something with fuel lining or carb.

This all happens during the last 5 weeks. The last interesting failure they found now when they checked again several times was a freezing problem in the carburator (CV with Thunderslide and 45 / 180 jets). It was on the highway with constant speed of 120km/h (74mi/h). Outside temperature arround 31°-40°F and a little bit foggy. Well I know this effect from flying, but not too much with bikes. I'm riding all the year until 14°F, except snow, but I never had this big problem.
Now they changed the thunderslide to the original Aluminium one, with no specially better results. They also changed now the jets to 42/180 and 42/175 with the Big sucker and with the original airfilter installed. There are no really better results. The carburator freez like a icecube mashine. Now they are really helpless. Me too, by the way. The last probosal was to change to the mikuni carb HSR42. I'm sure this is a very good carb, but in my opinion there are thousands of EVO Harleys on the road with a CV carb without htis problem, and they work fine. SO why not mine.
After all this problems and more than 5 weeks of searching, I'm almost at the point to give up and give the bike back. But I believe that there is only a small thing to fix. The only question is WHAT?

Well, I thought to a lot of different things. We discussed with collegs also a lot of different things. I asked some other mechanician. Everybody thing to different failures. I also came to the altornator or regulator. I don't know.

What they did now is to take apart the whole carb and clean it in an ultrasonic bath. The y will chek every little pice of the carb. Also the Manifold and the VOES Switch. If this brings no results they will try a new carb or maybe the mikuni one.

Well until today no news.

What do you think? Did you ever heard of a problem like this? Well, I would appreciate your opinion to this. I am still full of hope that they will fix the problem. But maybe you got an idea which I can tell them.

Thank you in advance for your answer. Maybe you don't have any answer, but it helps already to wright the story down. If I will get the bike with the problem solved, I will tell you immediatly.

Bye ALex

From what you describe, to me it sounds like either an intake seal leaking or as you said the lining in the tank coming off.
Check the intake seals for leakage when the bike is hot.

Finding An Intake Leak - Harley Davidson Community

These guys aren't very good at pinpointing the problem based on what you have said here.

With the stock breather on it, you can rule out carb freezing I feel because it draws warmed air from between the cylinders.

Too many people change engine parts like carbs to get more power from the motor and end up with problems afterwards. The CV carb is hard to beat when set up right.
You mentioned fog. Humidity and cold weather are not a good thing with CV carbs. They have offered to replace the carb with an original part. You could try this or you may want to consider your money back and walk away. If your riding in an area with high humidity and cold temps consider an EFI bike.
I know it dosen't take long to get attached to a bike, but I kind of agree with stugotts. Baybe let the dealer take the back and but the money toward another bike.
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Well, just to update the Thread. They found finally the problem. It was the plastic washer of the Thunderslide Kit. Normally it is above the clip on the needle. But the one who installed this kit put under the clip. So this is why the carb was everytime Too rich and all this gas made the ice in the carb. Now it run great.

By the way, it was not me who installed this thunderslide. I installed a lot of this Dynajet, Yost and Thunderslide. But I never came to the idea to put something Under the needle. Stupid.

Bye ALex
Re: Carburator Frezzing - Problem at High Speed

As Hobbit say's works well with carbed bikes.

But cheaper still if you go to a chemist and buy some isopropyl it's about £12 for 2 litres.

Replacing your stock carb to a Mikuni HSR42 will stop carb icing without having to but a petrol additive in your tank weather you use 95 or 98 octane fuel, plus you get much better engine response and tuning options, all round a better option. If you have the money!

Carb Icing Explained
Just want to put the record straight on carb icing as there a few myths floating about.

Carb icing can occur at air temperatures between 0 decress and 23 degrees Celsius.

It cannot occur at temperatures below freezing.

Carb icing is worse in high humidity conditions i.e. Fog.

Carb icing is actually ice crystals forming in the low pressure areas of the carb, i.e. the venturi. Those of you who paid attention at school will know that when you put a gas under pressure the temperature will increase. Conversely when you drop the pressure of a gas the temperature will decrease.

This is whats happening in your carb. At low cruise throttle openings or when the engine is on the overrun, the pressure in the venturi drops. The drop in pressure will result in a drop in temperature. If the drop in temperature low enough and is sustained for long enough, ice cystals will form. These are what makes the bike run rough and in extreme cases will stop the engine.

Petrol additives won't help as these just stop the petrol freezing. The ice cystals don't come from the petrol, they come from the air and there's nothing you can do about that!

Piston engined aircraft suffer from this problem a lot and they get around it by directing warm air onto the carb. Other methods are electrically heated jackets or heated elements using warm radiator coolant.

The design of the carb and inlet tract are the main contibution to carb icing which is why certain carbs and air boxes are more prone than others. For info, Fuel injected engines don't suffer from carb icing at all, which is another good reason for buying a fual injected bike.