laser1 Posted August 2, 2009 Report Share Posted August 2, 2009 Anybody ever lean out the slide? Its hot and humid here in New England and my bike isnt picking up revs off the bottom like it did in the cooler months. I have the stock Dellorto slide (#60) and noticed that there isnt a bigger one offered. Does the PHBH slide fit? That goes to 70. Quote Link to comment Share on other sites More sharing options...
jse Posted August 3, 2009 Report Share Posted August 3, 2009 Anybody ever lean out the slide? Its hot and humid here in New England and my bike isnt picking up revs off the bottom like it did in the cooler months. I have the stock Dellorto slide (#60) and noticed that there isnt a bigger one offered. Does the PHBH slide fit? That goes to 70. I doubt the PHBH will fit the PHBL. The PHBH is the large body, oval bore used only one year in 1996 on the JTR370. Hot temps and humidity tend to richen the air/fuel ratio (Oxygen atoms are farther apart and the water molecules tend to take up space in the volume of air available) so you might look at a pilot jet/needle position change to compensate. The less dense air will also produce a slight lag in response if winter jetting is used. I'm assuming you have already adjusted the air/fuel screw for the ambient conditions. Jon Quote Link to comment Share on other sites More sharing options...
laser1 Posted August 3, 2009 Author Report Share Posted August 3, 2009 Thanks for the info about the PHBH Jon. The online documentation I saw on it was confusing as they had one drawing for both carbs and listed the part numbers like they were interchangable. When I set the fuel screw, and do quick WOT tests, it revs clean and quick - no bog, no sputter. If I ride it and give it slow 1/8 throttle tests, it feels rich. It also 4 strokes if ridden down the road at steady 1/8 & 1/4 throttle. Since the fuel screw is already about 3 to 3 1/2 turns out depending on temp/humidity, I didnt think the switch to a leaner pilot was in order. (I should test that logic) I can drop the needle one more notch and will try it next outing, but felt it wouldnt impact right off idle. Im thinking of buying another 60 slide and keep machining 2mm off until it revs up off better - or run out of slide....I do appreciate the physics of the summer, and that may just be it. Seems good on top though. (I did recently switch to a 112 main from a 115 in the cooler weather) Quote Link to comment Share on other sites More sharing options...
jse Posted August 3, 2009 Report Share Posted August 3, 2009 Thanks for the info about the PHBH Jon. The online documentation I saw on it was confusing as they had one drawing for both carbs and listed the part numbers like they were interchangable.When I set the fuel screw, and do quick WOT tests, it revs clean and quick - no bog, no sputter. If I ride it and give it slow 1/8 throttle tests, it feels rich. It also 4 strokes if ridden down the road at steady 1/8 & 1/4 throttle. Since the fuel screw is already about 3 to 3 1/2 turns out depending on temp/humidity, I didnt think the switch to a leaner pilot was in order. (I should test that logic) I can drop the needle one more notch and will try it next outing, but felt it wouldnt impact right off idle. Im thinking of buying another 60 slide and keep machining 2mm off until it revs up off better - or run out of slide....I do appreciate the physics of the summer, and that may just be it. Seems good on top though. (I did recently switch to a 112 main from a 115 in the cooler weather) As you've found out, the "off-idle to 1/4 throttle" is a very busy time for a carb. It goes from idle circuit, to pilot circuit, to needle draw, and all this is mitigated by the slide cutaway and the fine tuning of the air/fuel screw. The #'s on the slide generally correspond to the height of the cutaway, in that a #55 slide will have a cutaway height of 5.5mm. The higher the cutaway, the "leaner" the slide as it channels more airflow over the needle jet tower. I'm not sure what pilot jet you have in, generally a #36-38 works well. The pilot jet "pilots" the air/fuel ratio from idle to needle draw that would otherwise have a big gap until the air velocity/pressure drop over the needle jet reached necessary measurement. Flatslide carbs tend to channel more air over the center needle jet area rather than around it as a round slide would do. This provides better draw and throttle response. Jon Quote Link to comment Share on other sites More sharing options...
laser1 Posted August 3, 2009 Author Report Share Posted August 3, 2009 I'll try a smaller pilot 1st- certainly easier than grinding the slide. I always thought that 60 meant 6mm of cutaway like you said, but the cutaway looks bigger than 6.0mm on the Dellorto. I didnt measure it, so its probably just me. Your right about the flatslide, I always liked the keihin equiped bikes Ive ridden. Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted August 4, 2009 Report Share Posted August 4, 2009 Go back to basics, new plug spotless filter, strip and rebuild carb, q/a throttle super smooth little or no free play, then mess with pilotscrew and airscrew then pilot jets Quote Link to comment Share on other sites More sharing options...
laser1 Posted August 4, 2009 Author Report Share Posted August 4, 2009 Im there and back. Thats good advice and the 1st thing I do before any carb changes. Bike runs very good - just wanted to know if there was hot setup for the mid summer solution. (pun intended) Tried a 36 pilot, seems about the same other than needing the fuel screw out more. Will be very hot & humid here tomorrow, so will check again before trying any slide mods. Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted August 4, 2009 Report Share Posted August 4, 2009 Im there and back. Thats good advice and the 1st thing I do before any carb changes. Bike runs very good - just wanted to know if there was hot setup for the mid summer solution. (pun intended) Tried a 36 pilot, seems about the same other than needing the fuel screw out more. Will be very hot & humid here tomorrow, so will check again before trying any slide mods. Funny thing is and I wonder who is right but over here very few mess with jets and slides yet in the states its almost the opposite? Is this because thats the normal thing with MX's? Occasionally pilot jets but slides hardly ever. Quote Link to comment Share on other sites More sharing options...
laser1 Posted August 5, 2009 Author Report Share Posted August 5, 2009 I heard that too, and that your bikes were spot on over there as delivered. Too rich on the main and needle here - need to drop the needle as a minimum. Something about the difference in the gas??? Dont know, maybe its a tuning conspiracy. I kinda figured they were break in settings. My personal reason is probably more due the fact that im an engineer and can't ride worth a darn - so Im left with experimentation and crashing. My current setup (that works pretty darn good on my 250 in New England) is: Main = 112 (just switched from a 115 now that its summer) Plug looks like the color of cardboard with W/O plug checks. Pilot = 38 (trying a 36 right now) Fuel screw = just under 3 turns out (almost 3 1/2 with the 36) - not static settings Needle = D36 (stock - no other needle looks very close) Clip = 2nd from top Atomizer = 270 (I think - stock ) Slide = #60 (stock and largest avail) Fuel = 50/50 93 pump/110 Race gas Oil = 100:1 Amsoil Quote Link to comment Share on other sites More sharing options...
motomerlin Posted August 5, 2009 Report Share Posted August 5, 2009 Definitley try smaller pilot jets & needle clip position before you butcher slides! Get a range in & a spare few hours for testing... On my 300 (dellorto) I've gone smaller pilot & droped needle a groove for the humid English summer, it was blubbery low down on std Uk settings. Much cleaner running now. & yes I tried Keihins etc, but whilst they carburate superbly - I can't handle the superb power. I had good results using the VHST on the 250 Pro. Can advise (VHST) jetting if needed. Quote Link to comment Share on other sites More sharing options...
laser1 Posted August 5, 2009 Author Report Share Posted August 5, 2009 Today will be a good day for testing. I have a range of pilots and will try the clip in the very top position as well. Thanks for everyones sound advice. MotoMerlin - I do have access to a VHST (My Dad has one off a 03 GG I believe), so would be very interested in your recomendation regarding setup for my 250. Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted August 5, 2009 Report Share Posted August 5, 2009 Wonder if the consistent petrol europe wide 95/98 octane may help us? Perhaps race gas is exaggerating the problems? Quote Link to comment Share on other sites More sharing options...
laser1 Posted August 5, 2009 Author Report Share Posted August 5, 2009 Wonder if the consistent petrol europe wide 95/98 octane may help us? Perhaps race gas is exaggerating the problems? I agree - anytime one introduces more variables, the outcome is bound to contain more uncertanty. Unfortunately, My bike seems to prefer higher octane than the straight pump (in the USA) can provide. I dont like the smell of straight race gas, and is more expensive, so I cut it 50/50 and always use the same supply. Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted August 5, 2009 Report Share Posted August 5, 2009 perhaps if you aimed for 25/75 would that give you 95 octane? Quote Link to comment Share on other sites More sharing options...
laser1 Posted August 5, 2009 Author Report Share Posted August 5, 2009 I had a slight pinging issue when I was running 75/25 in my old bike - so went to 50/50. This bike would probably be OK. Quote Link to comment Share on other sites More sharing options...
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