Dark Posted November 7, 2008 Share Posted November 7, 2008 I had a previous thread regarding my '74 TX500 and some issues I was having with it. Well, now it's pretty much road worthy with the exception of a slight idling issue. The bike starts up fine (on choke or without when cold, no choke when hot) and idles great when it's cold. Once I take the bike out and it gets warmed up it always feels like it wants to die when I let the rpm's settle back down to idle (just above 1k). It use to die like this all the time until I restricted the intake filter a bit (wrapped some cloth around it somewhat decreasing breath ability) and this seemed to help. I have figured that it is probably just running lean at idle/under 4k rpms (pilot jet) and that restricting the filter somewhat helped. It doesn't like it when I abruptly give it a lot of throttle from idle (chugs or dies). Is there anything I can do before I resort to swapping out the jets that might get the mixture a bit more rich? The carbs are clean, floats are spec'd, etc. The bike is 100% stock. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted November 7, 2008 Moderator Share Posted November 7, 2008 Are the idle mixture screws set as per spec for your bike? You could try turning them clockwise by the same amounts (that is of course if its a multi cylinder), this will richen the mixture at idle. Link to comment Share on other sites More sharing options...
Dark Posted November 7, 2008 Author Share Posted November 7, 2008 Are the idle mixture screws set as per spec for your bike? You could try turning them clockwise by the same amounts (that is of course if its a multi cylinder), this will richen the mixture at idle. I have yet to touch the mixture screws so I am unsure if they are at oem specs or not. I can check to see where they are set and try a turn or two clockwise to see if that helps. The engine is a 500c inline twin. Two (absolutely horrible) Keihin carbs. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted November 7, 2008 Moderator Share Posted November 7, 2008 I have yet to touch the mixture screws so I am unsure if they are at oem specs or not. I can check to see where they are set and try a turn or two clockwise to see if that helps. The engine is a 500c inline twin. Two (absolutely horrible) Keihin carbs. I didnt realise that keihin were fitted to yamaha's, usually the choice of honda, anyway Keihins air bleed (mixture) screws are nearly always set between 1 and 2 turns out from gently closed Link to comment Share on other sites More sharing options...
Dark Posted November 7, 2008 Author Share Posted November 7, 2008 I didnt realise that keihin were fitted to yamaha's, usually the choice of honda, anyway Keihins air bleed (mixture) screws are nearly always set between 1 and 2 turns out from gently closed I will verify where they are set and compare them to that setting (as a reference). I would prefer mikuni carbs but at this point in time I am not up for the hassle of a conversion. Link to comment Share on other sites More sharing options...
Dark Posted November 7, 2008 Author Share Posted November 7, 2008 Alright. One carb was set about 3.5 turns out and the other was wayyy out at around 5-6 turns. I took out anything I had covering the filter so that I could get the fuel set properly. I started the bike, let it warm up and used the idle set screw to get the idle around 1750-2000 rpms. From there I adjust each 'air screw' out (from a gentle seat) until I reached the highest idle that I could notice and then turned it in a 1/4 turn. As soon as I let the idle screw down the bike would hover around 1000-1100 rpms and eventually die after a few seconds. If I leave the idle screw set just high enough to keep the bike running the rpms want to hang for a little when I give it gas. The 'chugging/stalling' feeling when I begin to use the throttle from idle is still there and this is somewhat magnified when there is load on the bike (i.e moving from a stop). Anything else I should check? I've changed the plugs with NGK's, the points look great, but I never touched the wires...would that be causing a similar problem? Link to comment Share on other sites More sharing options...
JimR Posted November 8, 2008 Share Posted November 8, 2008 I had a previous thread regarding my '74 TX500 and some issues I was having with it. Well, now it's pretty much road worthy with the exception of a slight idling issue. The bike starts up fine (on choke or without when cold, no choke when hot) and idles great when it's cold. Once I take the bike out and it gets warmed up it always feels like it wants to die when I let the rpm's settle back down to idle (just above 1k). It use to die like this all the time until I restricted the intake filter a bit (wrapped some cloth around it somewhat decreasing breath ability) and this seemed to help. I have figured that it is probably just running lean at idle/under 4k rpms (pilot jet) and that restricting the filter somewhat helped. It doesn't like it when I abruptly give it a lot of throttle from idle (chugs or dies). Is there anything I can do before I resort to swapping out the jets that might get the mixture a bit more rich? The carbs are clean, floats are spec'd, etc. The bike is 100% stock. Hi I would guess you still have some drillings in the carbs blocked, I guess you have done the norm, tappits, dwell and timing, if not I would make sure they are correct first, then hit the carb area, pull them off and run carb cleaner thro every hole you can find (Yamaha did some real good stuff in the middle 80's got rid of all the green gunge out of the carbs on modals that the factory had not crated correctly). when the carbs are stripped make sure the progression holes (the drillings I mentioned earlier) are clear Regards Jim Link to comment Share on other sites More sharing options...
Moderator Airhead Posted November 8, 2008 Moderator Share Posted November 8, 2008 I agree, it seems that you are compensating for blocked pilot jets or passages by opening the throttle stop screws to bring in the fuel through the main jet, so it looks like further cleaning of the carbs and their passageways, make sure all the tiny little holes in the needle jet emulsion tube and the pilot jet are not blocked, soak them in carb cleaner as well as the carb body, compressed air is useful to blow out the carb passageways Cou could also consider a rebuild kit Here Link to comment Share on other sites More sharing options...
JimR Posted November 8, 2008 Share Posted November 8, 2008 Alright. One carb was set about 3.5 turns out and the other was wayyy out at around 5-6 turns. I took out anything I had covering the filter so that I could get the fuel set properly. I started the bike, let it warm up and used the idle set screw to get the idle around 1750-2000 rpms. From there I adjust each 'air screw' out (from a gentle seat) until I reached the highest idle that I could notice and then turned it in a 1/4 turn. As soon as I let the idle screw down the bike would hover around 1000-1100 rpms and eventually die after a few seconds. If I leave the idle screw set just high enough to keep the bike running the rpms want to hang for a little when I give it gas. The 'chugging/stalling' feeling when I begin to use the throttle from idle is still there and this is somewhat magnified when there is load on the bike (i.e moving from a stop). Anything else I should check? I've changed the plugs with NGK's, the points look great, but I never touched the wires...would that be causing a similar problem? just read this part of the thread (sorry for missing it) have you run some vacuum gauges on the bike yet ? with a mixture screw so far out of spec the carb balance is well worth a look.. if the one cylinder is well down & the other high try to sync them with the screw between the carbs , if the engine idle increases when correct adjustment is achieved and set back to 1100 rpm if the bike then dies suspect the valves !!! in the UK TX500 was called XS500 our(UK) early XS500 had a 2 piece cylinder head and was prone to problems I'm not sure if the TX was the same motor as the early XS500 here (but I guess it was). but I must add this bike did always run better with the Dwell set (22.5 %) rather than just gapping the points !!! Regards Jim Link to comment Share on other sites More sharing options...
Dark Posted November 9, 2008 Author Share Posted November 9, 2008 I did rebuild the carbs when I got the bike but the kit I got through S&S did not come with new jets. I dropped the bare carbs off at a local shop to have cleaned (they put it in some machine that vibrates the part in a solvent). The points look great and last I checked the timing was spot on, I'll check the dwell. Just an FYI, the engine has just over 700 miles and it starts and idles just fine when it's cold. Link to comment Share on other sites More sharing options...
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