I just bought a GPX750, has K&N clip on air filters (possibly not re jetted though).
It ran fine, then I had problems with No 1 cylinder, checked everything and ended up at the carbs.
I stripped, cleaned, & rebuilt the carbs after cleaning out loads of silt & varnish (Yes I did put them back together right, with all the seals etc)
Now the bikes tick over is eratic, and sometimes the revs climb, if you rev the bike the revs do not come down, and sometimes the bike revs out of control.
I removed throtal cables to eliminate this (still no change) checked for air leaks the best I can. The only adjustment seems to be the Idle jet (Haynes says 2 turns out, they were 2.5 but it wont run at any of these, its now set to 1.75 turns out and it runs, in a fashion)
I was going to try balancing the carbs, but cant do this if it wont tick over, and I am rapidly running out of ideas now.
The ONLY thing that was touched was the carbs, so nothing else has been tampered with so I dont understand how it ran when it was full of crap on 3 cylinders, and after a clean it runs on all 4, but has the problems I mentioned earlier.
Anyone have any ideas before I take the bloody bike to the scrap yard???
Thanks for the advice... I have checked them, and even disconnected teh cables completely and even working the carbs directly by hand I still have the same issue, so its definately a mixture issue rather than cable... Hay it was worth a try, and I appreciate you taking the time to reply..
Do you know that if the rubber O ring on the Idle jets was sticking to the jet, so when I unscrew the jet the O ring came down with the screw (ie letting in air) would this possibly have the effect of revs not dfropping??? I just thought of this while I was typing..Thanks for the advice... I have checked them, and even disconnected teh cables completely and even working the carbs directly by hand I still have the same issue, so its definately a mixture issue rather than cable... Hay it was worth a try, and I appreciate you taking the time to reply..
Do you know that if the rubber O ring on the Idle jets was sticking to the jet, so when I unscrew the jet the O ring came down with the screw (ie letting in air) would this possibly have the effect of revs not dfropping??? I just thought of this while I was typing..
This should make the idle setting use more fuel, as the mixture at the correct idle would be lean(Too much air in the mixture) So it is more likely to be allowing in too much fuel this could give you the symptoms you are getting. The thing you have to consider about following the Haynes manual is that it only covers a standard setup. With K&N's it would flow more air so it would need more fuel to attain the correct fuel/ air ratio for correct running. The correct (Most accurate) way to setup carbs is with a rolling road or vacuum gauges. A rolling road session will set your engine up to run as it is- not the way a manual thinks it is. Well worth the time and effort.This should make the idle setting use more fuel, as the mixture at the correct idle would be lean(Too much air in the mixture) So it is more likely to be allowing in too much fuel this could give you the symptoms you are getting. The thing you have to consider about following the Haynes manual is that it only covers a standard setup. With K&N's it would flow more air so it would need more fuel to attain the correct fuel/ air ratio for correct running. The correct (Most accurate) way to setup carbs is with a rolling road or vacuum gauges. A rolling road session will set your engine up to run as it is- not the way a manual thinks it is. Well worth the time and effort.
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Hi Thomas only thing I can think of is that its not getting enough air is it the right filter as it may be not be allowing enough air through. As you probably know if you don't get the right amount of fuel & air it won't run right. Hope it helps cheers Paul
Wouls not run at high speed, kept bogging down. Bought the carb adjusting tool and set the high speed jet and ran as it was suppose to for a few days and started the same thing. Contacted Echo had they are having a lot of problems with the carb on these machines, they sent out an updated carb and it runs fine for now.
The symptoms would seem to indicate a blocked air filter. Just because the fuel filter is showing fuel, doesn't mean it is getting to the jets. After a complete fuel system clean it could be something as simple as some dirt in the jets of the carb. When you clean something as thoroughly as that you can still miss something.
If this one is with a Carb. then sometimes the idling jet washer gets loose after getting worn out or compressed and with vibrations the jet rotates and looses its ideal place. Check for jet on lower side next to throttle wire under the air filter housing. Tighten the same fully and loosen 2 threads. If the thing starts, replace the ring washer which can normally be bought from the dealer with carb. kit.
Your lower rpms are controled by the mixture screw, pilot jet, accelerator pump and the slide needle. So your problem is probably in one of these-though racing 4 strokes are known to have a little stumble at the bottom, but not what you're describing. I'll have to assume the shop has the pilot jet clean and the mixture screw adjusted properly.(roughly 1.5 turns out)
First, check your accelerator pump. Remove the carb enough to be able to look inside the throat, but leave the cables hooked up. Work the throttle a few times and make sure that there is a small squirt of fuel in the throat of the carb each time you twist the throttle. If not, your accelerator pump is clogged or damaged.
If everything is fine there, the next likely problem is the needle adjustment. It's mounted in the slide. Once you remove the needle, you'll see a small clip around it. Try moving this clip up one notch. This will lower the needle and slightly delay the fuel feed from the main. If this fuel comes in too soon, it will cause a way rich condition and cause a bog off idle.
Outside of carb issues, valve adjustment(too tight) can make for a rough idle and hard starting.
Does it have a fuel pump or is it gravity fed? If gravity fed, when you rebuilt the carb, did you make sure that the main (power) jet orifice was totally clean? No varnish or residue in the hole. Pressurized air or carb cleaner spray into the jet is a good way to test flow restrictions. It sounds like a clogged main jet or a vacuum leak at the carb to manifold gasket. You might want to flush the gas tank and replace the gas cap also, as evaporating fuel over time will leave behind varnish deposits if the cap doesn't seal, even though it is a vented cap.
You shouldn't notice a difference if you remove the air filter. So I would replace it. Also if you are using compressed air to clean or blow-out the carb. Be careful, its not recommended and could make it worse.
Sometimes it is hard to tell at low speeds if the fuel mix is too lean or if it is too rich. Simple to work at though. Let's say the mix is too lean. Remove the slide from the throat of the carb then move the clip on the jet needle down one notch. This richens the low end mix. Try it out. If it is better then try another notch. Choose which is best.
Now lets say the original mix is too rich. Remove the slide from the throat of the carb then move the clip on the jet needle up one notch from the original clip position. This leans the low end mix. Try it out. If it is better then try another notch. Choose which is best.
The rebuilder may have move the jet needle position clip. Take the top off the carb and pull out the slide. Remove the needle and then move the clip to position 5 from the top. Try it noe. What you did was to provide a richer mid-range fuel mix. Hope this helps.
Thanks for the advice... I have checked them, and even disconnected teh cables completely and even working the carbs directly by hand I still have the same issue, so its definately a mixture issue rather than cable...
Hay it was worth a try, and I appreciate you taking the time to reply..
Do you know that if the rubber O ring on the Idle jets was sticking to the jet, so when I unscrew the jet the O ring came down with the screw (ie letting in air) would this possibly have the effect of revs not dfropping??? I just thought of this while I was typing..
This should make the idle setting use more fuel, as the mixture at the correct idle would be lean(Too much air in the mixture) So it is more likely to be allowing in too much fuel this could give you the symptoms you are getting. The thing you have to consider about following the Haynes manual is that it only covers a standard setup. With K&N's it would flow more air so it would need more fuel to attain the correct fuel/ air ratio for correct running. The correct (Most accurate) way to setup carbs is with a rolling road or vacuum gauges. A rolling road session will set your engine up to run as it is- not the way a manual thinks it is. Well worth the time and effort.
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