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Suzuki LT4WD - Carb Question


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I have been rebuilding a Suzuki LT4WD. I have replaced the valves, guides, seals and honed cylinder and replaced the rings. I have measured the timing chain and set the timing and adjusted the valves. This machine would run for about 30 minutes and continually get harder and harder to start and would smoke out the valley. I have corrected the smoking problem but have not corrected the starting issue. I need Ideas

I have done resistance checks on the pick up coil and the voltage checks on the stator and all are with in specifications according to the manual.

The machine will start up cold almost instantly. She will run for about 15 to 20 minutes and then start to fumble and die. At this point its almost impossible to get her to start again. The Plug is black with soot. Which tells me to much fuel (RICH) I have rebuilt the carb and reset the floats and check it several times now. I can not seem to find anything wrong. The diaphragm has no cracks or holes and seems to work fine. I have adjusted the floats to spec and no change.

I read a motorcycle thread that had a similar problem and it turned out to be the main needle Seat. They said it was worn to the point that it was oval and would not allow the needle to close it off and it was acting like the choke was constantly on. To much fuel.

Has any one encountered this. Carbs seem to be my nemesis and I always have problems when I mess with them


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I hear you. I have ordered the new Needle jet and Jet Needle that are the proper sizes. I believe this it the root of the problem I am having. I read for about two hours last night about Mikuni Carbs and this surely sounds like what I have going on. All the other parts have been changed but most kits do not have the needle jet and you have to order that separate. I will post once I change it out and see what happens.

From what I read last night this problem arises with machines with some mileage like this one. Thanks for the help

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You were Correct Oxidized_Black. The seat or Needle Jet emulsion tube was the culprit.

I searched and could not find any threads about this on ATV sites but what I did find is that Harley Davidson use the Constant Velocity (CV) Mikuni carburetors. What happens is the seat or needle jet emulsion tube will become oval inside allowing the fuel to pass at all throttle stages. One of the indicators is if you do not need to utilize your choke on colder days. Basically it causes a rich condition like having the choke on all the time. This is a slow process and according to the web site it occurs with the use of stainless needles and also Harley attributes it to vibration imagine that.

Anyway my Needle Jet was oval and causing the rich condition. Thank you for the input and I would tell anyone rebuilding a CV type carb to buy the Needle Jet emulsion tube (seat) and replace it. I did not find this jet in any of the carb kits and had to purchase it separately. This surely cured my problem and the machine runs like a top now.

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