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RPM's stuck at 3000

  • Thread starter Thread starter Buster-boy
  • Start date Start date
B

Buster-boy

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Ok guys, I've been here before and have asked a billion questions, but each day it seems to be something just a little different. When I start outfirst thing everything is fine. But, after riding for a while (15-20 minutes) everytime I pull in the clutch to either shift, downshift, or stop, the R's shoot up to a steady 3k rpm. Many of you have told me it's an air leak. Ok fine. BUT WHERE?

I've replaced all eight boots, all eight clamps, all four O-rings, (all with OEM parts) cleaned the air filter and oiled it, all new fuel and vacuum lines, brand new OEM petcock. I had the carbs disassembled and cleaned with new jets/needles installed. What am I missing? Where else do I look? I haven't got a clue on what else to do?

I play with the adjusting screw on #3 carb almost daily and try to set the ile to around 1100-1500 rpm. Everyday it's a difference scenario. Just for hoots and hollers I even plugged the two breather hoses coming from the carbs. That did nothing.

How finely tuned were these engines (81 GS850GX) to where you can't allow even ths slightest air leak.
 
So, are you getting the idle down when you adjust the idle set screw, then it shoots right up??

Have you synced the carbs? Maybe you cranked all of them up too high
 
Are the carbs synced and where are the idle mixture screws set? Sounds like they are too lean. Standard procedure is to set the mixture screws until you achieve the highest idle speed - typically in the range of 2.5 to 3 turns from lightly seated. Of course, this depends on if the bike is stock and if the jets are all the factory parts, which apparently they are not. It's easier to give advice when the parts are factory mikuni stuff, sometimes the aftermarket carb kit parts are junk.
 
Well, the FIRST thing you need to do is to unplug those breather hoses. :eek:

After that, determine how far out your mixture screws are set. If they are anywhere near the stock settings of 1.0 to 1.5 turns, move them out to 2.5 or so. You will likely have to re-adjust your idle speed (again), but the bike should run better. Once you get it to run at something lower than 3000 rpm without using the 'choke', slowly tweak each of the mixture screws, listening carefully for highest rpm on each one. Readjust the master idle speed screw, if necessary, then continue to the next mixture screw.

When you are all done, the bike should be able to start with only half 'choke', you should be able to ride it within a minute, and turn off the 'choke' by the time you get into second gear. The idle speed should then remain somewhere near the suggested 1050 +/- 50 rpm.

If none of this works, it just might be time for a total carb cleaning session.
It might be that there is a small passage that is clogged just enough to give you problems.

Let us know what you find.

.
 
Hey guys thanks for your replies. My first thought was the carbs needed sync'd as well. I brought it into the shop to have that done and they said #1-3 carb were perfect and #4 was a hair's width less than center scale. So to answer your question yes, they're sync'd.

I unplugged the breather hoses back when I did it. I only put a piece of black tape over them just to see what'd happen. Sorry for the confusion.

Personally haven't messed with the carbs at all. I hired someone to clean/rebuild them. I wouldn't know what to do with them anyway. I have removed them though to replace the O-rings and I can tell you the screwdriver slots on the pilot jets are at about 1:00, but how far in or out I really couldn't say.

When I start it first time for the day, I pull the choke on full until it fires, then I drop it to about half. In the time it takes to put on my helmet, gloves, and finish my smoke I take off the choke completely. It'll idle around 1000-1100 +/- or so, then down the road I go. It seems like it runs normally until it gets warmed up, 15-20 minutes or so. That's when the 3000 rpm at a stop comes into play.

Now let me ask you this - I have a secondary fuel shutoff and filter on the fuel line as well. It's clear tubing and I have seen little tiny bits of crud, no bigger than a flake of pepper, in the line. Would this likely be a major contributor to my problems? On a scale ferom 1-10, what would this be?


It's emabarrassing to pull up next to someone with their window down and my bike is screaming away like I'm waiting on the Christmas tree at the drag strip. I ended up just shutting it down when at a stop light and restart it when the light turns green.

I'm more than likely to just take it back to the shop and have them mess with it. It'll cost a me few bucks more than I wanted to spend, but I think I've done all I can do. I know the difference between a cam shaft and getting the shaft, but I'm no bike mechanic.
 
Ok I'm back. I had the carbs sync'd (again) and it runs 99% perfect. It's still a little sluggish below 3K but 400% better than it was. I can FINALLY ride it since buying it in May.

Next question - Why did gas flow out of the airbox? I parked it after riding about 17 miles, and I left it on the side stand. When I came out of work there was gas all over the ground and dripping from the airbox. I have the Petcock at 3 o'clock which is the PRI position. I thought in this position it needed the engine running to pull gas from the tank?

This has happened before, but doesn't happen all the time.
 
If I understand correctly, Prime is for when the carbs are dry and you need to get some gas into the system. You definitely don't want to be on Prime all the time. This allows gas to flow into the carbs constantly and possibly into the cylinders maybe even diluting your oil. Use the On position on the petcock.
 
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Check your oil for gas.If there is gas in your oil change it and your filter. It will ruin your motor if you dont.
 
Buster-boy said:
Oh...maybe I have it backwards then?
Click to expand...

Yes. There will be ON, RES, and PRI. ON and RES allow fuel to flow only when the engine is running, but PRI (prime) is the wide open position that's used to fill the bowls when it's off. It shouldn't be used more than a few seconds, and never longer than a minute or two. When PRI is on, fuel just flows and flows, until you get gas everywhere like in your case.

Always use ON or RES, and only use PRI when you've drained the carb bowls for some reason. Like kparkfan said, you should change your oil now, lest you harm the motor, or worse, yourself from having gas in the oil.
 
Ok, I'll change oil/filter today. Thanks guys for the tips. What's the purpose of the PRI position anyway? Why would I want to use it at all, AND only for a few minutes - just to fill the bowls quickly when dry or something?
 
The PRI position, is only for after you have the carbs apart, or you have drained them, or they have sat a week or so, fuel has evaporated away from the bowls, they need to be primed, or refilled. Only use it for the time it takes to fill the bowls, less than a minute or so. I only use PRI for a few seconds while I back the bike out or whatever and go back to ON before starting the engine so I can't ride off and forget it in PRI.

Adjust your idle speed screw (the big one underneath that moves all the throttles together) for the correct idle speed (1,000 or so RPM) when the engine is fully warmed up. It will idle slower while the engine is cold, or maybe not idle at all at first, that's normal and OK. The oil is thicker, it just runs slower. You can use a little choke to keep it at a decent idle speed or just use your throttle to keep it running. Ideally don't idle it at all, just get on and ride gently until it is fully hot and idles normally.
 
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