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I have a 96 slt780, with about 10 hours on a rebuild, 125 hours overall. It has been acting up, in part due to a bad fuel sensor. It has been replaced, but I am still having problems. It seems to pull well most of the time from idle, however if I hold it open, once it reaches around 6300 rpm it will die. It restarts easily, and will run at around that rpm fine, as long as I don't pin the throttle. I ran about 3/4 throttle for several miles, no problem. When I pushed it to the handle bar, it died again. I suspected a clogged fuel filter, but cannot find one. My dealer says it doesn't have one, other than the seperator. It will sometimes stumble or stall in a tight wide open turn as well. After my last test run, it even seemed out of power trying to get on the trailer under a load, then finally kicked in. These symptoms were starting to appear before the float in the fuel sensor failed. I can't tell if it is starving for fuel or spark. Any thoughts on this one would be greatly appreciated. Thanks in advance.
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The carbs have never been rebuilt. The dealer supposedly checked them when the engine was rebuilt, and that was july 2000. Do they need to be rebuilt a lot? -
They need to be rebuilt whenever you suspect debris in the internal filters, or after it has sit for more then 6 months with stabilized fuel, or 3 months with unstabilized fuel in them.
There is no way to 'check' carbs. If the dealer told you they did so they lied. You must open them up, clean them out and replace all the internals (rebuild them). Get some rebuild kits, download our instructions from the Tech section and go to town [img]smile.gif[/img]Comment
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So carburation is the most likely suspect? Any thing else that might be an easier first step as a test?
Also, does the 780 motor have the same fuel starvation problem that your web site notes regarding the Fuji 650 and 750? In other words, would I benefit from the additional fuel pump?
And, one more question. I am not sure which carb it has. Do I just need to look at the carbs, or do you know which one it used? THANKS AGAINComment
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That would be the first thing I'd do.
Luckily for you they are Mikuni SBN's - cheap kits and easy to work on. We have kits for $30 ea. if you need some, or your local dealer should stock them.Comment
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How long has it been since the carbs were rebuilt?Comment
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To answer your other question, no. The domestic motors do not have a starvation problem. The fuel pumps on those crafts were more robust. However, if it has been more than a few years, you might want to consider rebuilding your fuel pump. It is cheap and easy to do. Good luck on the carb rebuild. Your dealers are crazy, it is always a good idea to rebuild the carbs with any new engine installation.
[ December 18, 2001: Message edited by: tomsl750 ]</p>Comment
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So, the fuji 780 motor is domestic? Some have told me it needs the fuel pump too. I am thinking of trying a little fuel injector/carb cleaner to see if that does anything.Comment
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No, the 780 is NOT domestic, however it does use a larger fuel pump that corrected the problem with the 650/750 pumps. The 700, 900, 1050 and 1200's are Domestic. 650,750 and 780 are Fuji.Comment
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kennyh, From your description, it sounds like a classic lean condition. Wether it is caused by a clogged or dirty carb or just in need of proper adjustment is hard to say? The first step should be to rebuild the carbs and clean them out. Do not use carb cleaner. You have to dissasmle the carbs and clean them manually. Your engine most likely sustained some damage too from the constant WOT shut downs. The reason it shut down is because it had a minor seizure. The only way to rule it out is to inspect the top end by pulling the heads and possibly the cylinders to check for seizure marks on the pistons. No matter what you find, get it tuned properly because if I had to guess, I would say that your high speed circuit is lean on the carbs.Comment
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I forgot to mention that your stated max 6300 rpm is also kinda high for a stock SLT780 which leads me to believe that you are getting those numbers because of a lean condition. Under ideal conditions you can get 6300 rpm but if your carbs were dialed in under less then ideal conditions and when ideal conditions are present you run lean and seize. What I mean by ideal conditions are good air vs. bad air days and not water conditions.
Did this just happen recently with the cooler drier temps and colder lake water?Comment
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Since new, it has always topped out in the mid 6000's on the tach. I was testing this past week end, with temps in the upper 50's, water temp probably in the 50's too. I probably had 3 or 4 wot shut downs. The symptoms were worse, but I had seen some before I had the fuel sensor float failure. Looking back on that, some of those symptoms could have been the rev limiter cut out due to low fuel signal, but not all of them. At one point it was running poorly, and I put a fresh set of plugs in, and it instantly was better. The occasional stumble in full throttle turns started this fall. It has run no more than a few miles since that started.Comment
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From what you posted, it sounds like it's definitely running leaner with the cooler air and water and seizing. The other scenario could be a cold water seizure. You might have to restrict the exiting cooling line to let the water temp rise in the engine?
The fuel float is totally different issue. It does not cut out but limits your rpm to 4200. If you were shutting down before and thought it was the sensor kicking in then those 2 are not the same? I would also like to correct myself on the max rpm issue. I was thinking of the SLT750. Your 780 should be right around 6300.
I would definitely inspect the top end, rebuild the carbs and tune it so it is not running lean.Comment
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Sorry, I read it quickly and saw 700, but still typed 780. Been a Real Long day. It just has a bigger bore than the 750.Comment
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