Hi all. Ever since i got my 550 running.. Stanard or tuned (stanard with 3in1) I can only get a steady idle at around 1800-2000rpm... Im beginning to suspect that my pilot system is not correct..
I can get lower steady idle when the bike is cold, and using the choke. But it smokes alot though..
Adjusting the air screw dosent really make any difference... Carbs have been carefully cleaned and has the same amount of throttle opening on idle... When i hit the throttle at idle , when warmed up, it somewhat lags a bit and bogs too..
All 3 plugs seems spot on and exactly same colour
Crank has been rebuild.
Main 105 jet on all 3 and running new original air filters.. It pisses me off a bit, because im running jemcos and they make alot of noise at 2000rpm.. The dingding noise seems to dissapear at below 1400rpm wich would be perfect for my neighbours
Any suggestions?
2-strokes are full of speed,
4-strokes are full of parts!
Up one size on the pilot jets just might cure your idle problem and bog when tweaked. Main jets have no play under 3/4 throttle so they are not the issue here. It sounds to me like the idle circuit is starving for fuel. That's why it falls off and dies. The bog is caused by insufficient fuel instantly available.
I was born with nothing and still have most of it left.
Check your float heights. If they are too low there won't be enough fuel in the bowl for the pilot system to work properly. The engine will run lean and die at idle.
+1, check float heights. Most important aspect. If not to spec. Other aspects will be clouded by float levels not being correct. If making an adjustment to air screws makes no difference. Sure sign pilot jets need to be changed for a different size ( if float height is correct. ) Bogging out and low on power when you hit the throttle because it is too rich. Same reason why it will only idle at 2000 rpm. Because you induced enough air to try to accommodate that it's getting too much fuel. Induction of air caused by one of several ways, increases idle speed. Increases power. But, puts liability of a motor at risk depending on how lean mixture is. Risks of over heating, seizure or holed piston if a mixture is too lean. Richer improves longevity of a motor. But, looses power and creates flat spots in throttle response. Depending how drastic the rich mixture is. Beyond a 1/4 turn of throttle. The fuel/air mixture is adjusted by a combination of the diaphragm needle clip position and main jet size. Loss of power or idle, too rich. Too much idle, over heating, hanging throttle. Too lean. I would triple check all 3 float heights and perhaps raise the needle clip 1 notch to lean out the fuel mixture if floats don't improve the situation. You have to be very careful and watch that the top of the floats don't hit the ceiling of the float chamber when adjusting float level. Otherwise, the fuel will not be completely shut off by the needle valves. If this happens. You need to check that the float arms are not tweeked and drop the float level until there is about 1 mm in between the top of the floats and float chamber ceiling. This may be happening. As a result, you're getting slightly too much gas. Idle speed is very dependent on how much air/fuel you induce. Adding more fuel will drop idle. Adding more air will raise it. You have to find the mixture of both that makes idle correct.
Allan,
In UK, I use these guys:
Motocarb jets are genuine Mikuni http://www.motocarb.co.uk/default.htm" onclick="window.open(this.href);return false;
Order by email through 'contact us' tab, or call (+44)151-924-5383.
Genuine Mikuni mains are N100.604-size and Mikuni pilots are VM22/210-size.
Size of pilots may be as small as 25 and as large as 30 depending on your carb model. Mains may be as small as 97.5/95/97.5 and as large as 105/102.5/105 again depending on your carb model. What are your current sizes? I have found the reference sources quite confusing for GT550A/B carbs! My UK GT550B has the larger sizes.
Cheers,
Mike
Too bad shipping would be an obstacle. I can get genuine Mikuni jets for around $12 per pack of 4. I can get them in 2 or 4. Not sold in packs of 3. What's a triple??
I was born with nothing and still have most of it left.
The pilot jets are standard whatever that is..? But i will check when i take the carbs off the bike.
But is it normal the the pilot jet is too small all suddenly? Both my sets of carb had 105, 102,5 , 105.
And im now running 105 on all three, wich seem to work fine. I did try 110 mains, but this was too much.
The engine is rebuild, portet and runs with jemco's... But the idle problem was also there when the engine needed a rebuild and had a 3in1
Thanks for all the help, this sure gave me something to work with..
2-strokes are full of speed,
4-strokes are full of parts!
Its probably obvious but in case not...the main jet size has nothing at all to do with whether it idles slowly...thats mostly or all down to pilot jet size, cleanliness of the pilot circuit and also pilot air screw settings. Assuming all is well elsewhere in and beyond the carbs!
Throttle balance, and float heights may already have been mentioned, if they're out, it still won't behave
Cheers,
Mike
I'd focus on being sure float height is accurate and needle valves are ok. Before installing any other jets. With float height you can test that it's not to high by gasoline over flowing out the tubes and you can check needle valves shutting properly by simply leaving the petcock on for longer than several minutes. It no fuel comes out over flow tubes the needles are shutting off fuel properly. If those things check out ok, move on to the pilot jets. I had a near identical situation to yours a couple of weeks ago. I checked everything. My new battery wasn't holding a charge due to a new rectifier I installed. I swapped that out for an old rec/ regulator off another bike. From that point on, the bike would consistently idle where ever I wanted it to. Before I fixed the charge issue, it ran perfectly fine at higher revs. But, would not consistently idle where I wanted it to. Until the charge issue was fixed. Something also worth looking at. Idles like a dream now.
Good stuff to know, & especially read thru the low-speed circuit description on pg 2 & FIG. 3. Those small ports in the body casting on the engine-side of the slider are where the air/fuel for idle is pulled into the engine. They are about the diameter of a straight pin & get plugged with deposits over time. I found a couple of mine (GT550) plugged & had the same problem you describe (although mine would idle at about 1400 rpm).
Hey there. Just checked the float height. Carbs held in 45degree, removed the gasket. The floats were only off by about 1mm. Standard 25,7mm. The float were slightly bend, so one was a bit under and the other slightly over.
Pilot jet is #30.
2-strokes are full of speed,
4-strokes are full of parts!
yeadon_m wrote:Allan,
In UK, I use these guys:
Motocarb jets are genuine Mikuni http://www.motocarb.co.uk/default.htm" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
Order by email through 'contact us' tab, or call (+44)151-924-5383.
Genuine Mikuni mains are N100.604-size and Mikuni pilots are VM22/210-size.
Size of pilots may be as small as 25 and as large as 30 depending on your carb model. Mains may be as small as 97.5/95/97.5 and as large as 105/102.5/105 again depending on your carb model. What are your current sizes? I have found the reference sources quite confusing for GT550A/B carbs! My UK GT550B has the larger sizes.
Cheers,
Mike
Pilot jets are #30
Main jet is 105 on all 3
Have just ordered 32,5 pilot jets, and 3 carb rebuild kits to be sure it all works
2-strokes are full of speed,
4-strokes are full of parts!
