archie Posted December 15, 2010 Report Share Posted December 15, 2010 When I am going downhill, the engine revs tend to drop slightly (and it is less responsive) and occasionally it coughs and dies as I open it up. I have the float height set accurately at 18mm. This is not the more common four stroke cough as I have spent a great deal of time optimsing the carb settings. It runs fine on the flat or uphill at low revs and picks up cleanly from low revs without any hesitation. The problem is ONLY when the bike is going down a drop. For your info I have the 17.5 pilot jet. Mine runs best with two turns on the fuel screw (it is sensitive to even a 1/4 turn). I have found that three turns as recomended by others is way too rich. If the bike has a tendency for the revs to drop slightly and occasinally stall when going downhill, is this a float height related issue? What is happening and should I try to increase the float height? Any thoughts would eb gratefully appreciated. Quote Link to comment Share on other sites More sharing options...
godzilla Posted December 16, 2010 Report Share Posted December 16, 2010 Mine did that when it was low on fuel. Quote Link to comment Share on other sites More sharing options...
archie Posted December 16, 2010 Author Report Share Posted December 16, 2010 Mine did that when it was low on fuel. Quote Link to comment Share on other sites More sharing options...
archie Posted December 16, 2010 Author Report Share Posted December 16, 2010 Mine did that when it was low on fuel. Thanks for the reply. Mine does it regardless of the level in the tank, and I've checked the breather also. Any more ideas ? Quote Link to comment Share on other sites More sharing options...
godzilla Posted December 18, 2010 Report Share Posted December 18, 2010 Its clearly shagged, but all is not lost as i will take it off your hands.. Quote Link to comment Share on other sites More sharing options...
archie Posted December 19, 2010 Author Report Share Posted December 19, 2010 Thanks for your generous offer Quote Link to comment Share on other sites More sharing options...
copemech Posted December 21, 2010 Report Share Posted December 21, 2010 Possibly that is why the recommendation of running the fuel screw out further? Quote Link to comment Share on other sites More sharing options...
archie Posted December 21, 2010 Author Report Share Posted December 21, 2010 I know that Birks recomends starting at 3 turns out with a 17.5 pilot, but on my bike 3 turns is way too rich. At three turns the plug goes really sooty and it becomes less responsive. You can hear it too as the exhaust note softens. I have found my bike really likes to run on the lean side. The throttle is more responsive and it feels alot more powerful. When it was warm it would run really well on the highest clip (leanest) on the needle. Now it's so cold it runs better on the middle clip. I run a 100 main jet now having experimented with 100, 102.5, 105 and 110. I was originally thinking that the problem was carburation, but I have also lightened the flywheel, and I think now that may be the problem. It may be it's just me stalling it as the tickover is too low? I'm going to try running it with a higher tickover to see if that helps and failing that I'm going try it with the orginal flywheel back on (I bought one to lighten off ebay for Quote Link to comment Share on other sites More sharing options...
copemech Posted December 25, 2010 Report Share Posted December 25, 2010 Not going to hurt anything by playing with the float level a bit. I have had similar situations with the kiehins and oko carbs on the 2T bikes, and another 1.5 mm drop in float height helped a lot on downhill situations with no other problems. Jus got to play a bit! Quote Link to comment Share on other sites More sharing options...
archie Posted January 9, 2011 Author Report Share Posted January 9, 2011 Since my original post I have been trying to figure out the cause of the problem, and I now seem to have it solved. Although I had the float height set accurately at 18mm, I wondered if this was anything to do with the problem. The float hinges from the back of the float chamber, and when going downhill I reasoned that the relative fuel level in the float chamber would be lower when going down hill as the float would cut it off earlier and I wondered if this was anything to do with it. I tried increasing the fuel level by setting the float at 17mm, and I am pleased to say that the problem seems to have been cured. If any other lurkers are interested in some other development work which I have done. I had the head off to check the condition and de-coke. Most of you will know about the miss match of inlet manifold and inlet port (there is a nasty step where the two faces meet), and (with the head off and using a die grinder) I gently removed quite a bit of material to match the inlet manifold to match the inlet port which is now really nice. With the valves out I also noticed that the steel valve seat inserts were also rather a Quote Link to comment Share on other sites More sharing options...
copemech Posted January 16, 2011 Report Share Posted January 16, 2011 Since my original post I have been trying to figure out the cause of the problem, and I now seem to have it solved. Although I had the float height set accurately at 18mm, I wondered if this was anything to do with the problem. The float hinges from the back of the float chamber, and when going downhill I reasoned that the relative fuel level in the float chamber would be lower when going down hill as the float would cut it off earlier and I wondered if this was anything to do with it. I tried increasing the fuel level by setting the float at 17mm, and I am pleased to say that the problem seems to have been cured. If any other lurkers are interested in some other development work which I have done. I had the head off to check the condition and de-coke. Most of you will know about the miss match of inlet manifold and inlet port (there is a nasty step where the two faces meet), and (with the head off and using a die grinder) I gently removed quite a bit of material to match the inlet manifold to match the inlet port which is now really nice. With the valves out I also noticed that the steel valve seat inserts were also rather a Quote Link to comment Share on other sites More sharing options...
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