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07-05-2010, 3:17 AM nerdlinger Joined on 07-26-2009 Kansas City, MO Posts 23 Full throttle bog down 6000 - 8000 RPM, only when bike is hot... I've read a bunch of other similar posts, but they don't seem to address my problem. I've got an '81 Deluxe with about 17K miles. The bike runs great until it warms up - and it has to be hot out (over 85 degrees). After about 20 minutes of riding, if I give it full throttle, it will bog down as the engine approaches 6K on the tach. If I keep on the throttle and wait, the bike will accelerate (slowly) then when the tach gets to 8K - it takes off like a bat out of hell! It almost pops a wheelie! It won't happen at all when the bike is first started or on cooler days. Here's what I know.... 1. Probably not the carbs. I had 'em cleaned by Larry (man, he does nice work!) 2. I put on a new fuel filter (even though the one from last fall looked fine) 3. New spark plugs 4. Cleaned the vent in the gas cap 5. New K&N air filter 6. ONLY happens during full throttle (and only between 6K - 8K RPM). If I hold back a little I don't have this problem at all. Any ideas? Thanks! 1981 CX500 Deluxe    Report

07-05-2010, 1:19 PM l988justy Joined on 06-13-2010 Posts 27 Re: Full throttle bog down 6000 - 8000 RPM, only when bike is hot... have you balanced them on the bike? is it possible your fuel mixture could be off? this same thing happens on my dirtbike if i put too much oil on the k&n try hitting the kill switch while it is doing this and at the same time pull in the clutch and coast to your house and check the plugs that will tell you if its a mixture problem    Report

07-05-2010, 1:47 PM Blindstitch Joined on 03-14-2009 Greenfield Wisconsin Posts 9,863 Re: Full throttle bog down 6000 - 8000 RPM, only when bike is hot... I'm a fan of blame it on the carbs. But it seems to be isolated. The only thing that is really control when you hit rpms is your main jet. Yes all the additional fun too. But the main jet is the one supplying the fuel so if they aren't balanced and adjusted right then it would cause a low spot. Everyone likes to talk about throttle and how it relates to the carbs. Well here's the quick and dirty. Yeah after 1/2 throttle all the weight is on the bigger jet but in perspective the little jet runs out of snuff around 50mph in 5th and that's where they ease out and the bigger one takes over. This is why if you put your jets in backwards it won't break 50-55mph. So if you have all the tools try to adjust them accordingly. I have 3 sets of Larry carbs on 3 different bikes and they all act differently. 0-60 is great but after that they all preform differently. My main bike I'm playing with the jetting. I'm getting 42-49mpg with 90/120 jets 3 turns out and balls to the walls power. I just changed the jets down 1 to 88/117.5 and it rode fine but was blah. 0-60 was still great. After sucked. Now i'm running the 88/120 and with one person testing it was doing pretty good. Carbs/sparkplugs looked fine. But last night under load with a passenger it was rich but that could be due to idling in traffic maybe.  So I need another load test before I say screw it and go back. Lowest mpg was 45 with the smaller jet.  Oh yeah and this bike has a 2 into 1. Bike 2 has a stock exhaust and is a big questionmark  0-60 is great. Everything over is blah. Adjusted and rejetted several times and still the same results no matter the combination.  Don't know the mpg since I only test ride it. Bike 3 has the same exhaust and stock jetting and kicks bike 2's ass every time. But the over 60 is still a bit slow.  Seems to be hand tuned quite nicely but still needs to be gauge tested. What's this all say. Pretty much nothing. Find the gauges you need to check everything and also do the little tune up stuff as it does help. More history. Bike 1 has 60,000 miles and is the strongest of all in every spot. Maintained all the time. Bike 2 is the weakest off all of them and my least favorite for many reasons. Also has 35,000 miles and never had maintenance since my brother has had it unless I did it and forgot. Bike 3  has 18,000 miles on it and I did the tappets and cam chain as the engine which I didn't know if it ran was sitting in the back of my truck. Second strongest and can do a wheelie. Not as good as bike one but can still scare children. From what I here bike 2 can do a wheelie but only at high rpms. 1979 CX500 Supertanker ATGATT makes riding a bike like a sled easier. Quick Reference    Report

07-05-2010, 4:30 PM Harold Joined on 12-28-2006 Beside Washademoak Lake, N.B. Canada Posts 851 Re: Full throttle bog down 6000 - 8000 RPM, only when bike is hot... Does your bike have the vacuum petcock? I wonder if when the bike is hot the vacuum hose may be collapsing, or sucking air at the connections. "People are more violently opposed to fur than leather because it's safer to harass rich women than biker gangs." 1978 CX500 1980 CX500 Custom 1981 CX500 Custom 1982 GL500 Silverwing 1975 XL-100 http://www.myspace.com/downwiththebutterfly    Report

07-05-2010, 11:38 PM l988justy Joined on 06-13-2010 Posts 27 Re: Full throttle bog down 6000 - 8000 RPM, only when bike is hot... http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.aspx read the part about mid-range throttle, its exactly what you said happens    Report

07-06-2010, 2:23 AM nerdlinger Joined on 07-26-2009 Kansas City, MO Posts 23 Re: Full throttle bog down 6000 - 8000 RPM, only when bike is hot... Seems like everyone thinks it's a fuel/carb problem. No votes for coils? That was my next troubleshooting area. Blindstich- Thanks for all the info. Keep me posted on the results of your jet tests. justy- >have you balanced them on the bike? Not on my bike. I think Larry balanced them on his test bike. I'll have see to about doing that myself. Great link, very informative. Thanks! Harold- >Does your bike have the vacuum petcock? No, and the vacuum line from the carbs is sealed so leaks aren't an issue. 1981 CX500 Deluxe    Report

07-06-2010, 2:59 AM spanish bandit Joined on 02-12-2009 southern spain Posts 5,010 Re: Full throttle bog down 6000 - 8000 RPM, only when bike is hot... i vote coils,or something electrical.carb jets do not block and unblock themselves according to engine temperature. your gremlin is heat related,imho when i feel the need,i do it,llego,ve 60,s ----------------------------- 2008.1982 honda gli silverwing [uk model ] 2010.1981 honda gli silverwing [uk model ]    Report

07-06-2010, 8:41 PM l988justy Joined on 06-13-2010 Posts 27 Re: Full throttle bog down 6000 - 8000 RPM, only when bike is hot... ya but why would the coils work when the bike is cold? also if the main jets are 1 size too big they can work good cold and then when the bike warms up they become just slightly too rich    Report

07-06-2010, 10:58 PM spanish bandit Joined on 02-12-2009 southern spain Posts 5,010 Re: Full throttle bog down 6000 - 8000 RPM, only when bike is hot...  l988justy wrote: ya but why would the coils work when the bike is cold? also if the main jets are 1 size too big they can work good cold and then when the bike warms up they become just slightly too rich justy,coils can work fine when cold,then be tempermental when hot. coils generate high voltage electricity,maybe 20,000 volts.this in turn produces heat,which causes expansion,its this expansion that can make/or break a curcuit. when i feel the need,i do it,llego,ve 60,s ----------------------------- 2008.1982 honda gli silverwing [uk model ] 2010.1981 honda gli silverwing [uk model ]    Report

07-07-2010, 12:50 AM Shep Joined on 01-30-2007 UK.2x1980CX500A Posts 7,647 Re: Full throttle bog down 6000 - 8000 RPM, only when bike is hot... Like Bandit says.Coils can appear to be fully functional cold but then breakdown with heat if faulty.A common cause of this is a badly damaged or missing,"Air-Dam", My Music http://www.reverbnation.com/pauldouglas/ Join Just In Case :) http://globalcxglvtwins.hostingdelivered.com/ Id quot circumiret, circumveniat    Report

07-12-2010, 4:27 PM Chi-town GL Joined on 06-09-2010 Chicago IL Posts 62 Re: Full throttle bog down 6000 - 8000 RPM, only when bike is hot... I'm also on the blame the coils bandwagon.  This was one of the spectrum of problems I encountered working on my 82 GL500I.  Unfortunately I cannot give one specific fix as my bike was a lot of little things.  Of course the carbs were the main problem, but since you know those are good maybe take a look at the spark plug caps.  They could be damaged or, in my case, damaged due to a slight compression leak from my timid spark plug tightening-the right cap was actually popping off as the bike warmed up and ended up cracking.  The resulting symptom was what I thought to be random misfiring and even stalling once the bike was warm.  I also found a bad wire from the right coil to the cap.  Now that the wire and cap are replaced and the plugs tightened properly the problem is gone. 82 GL500I Silverwing 79 Yamaha XS400 Special "Everything worth knowing leaves bruises"    Report

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