Throttle issue when it warms up

So preface this with an extra thanks for the carb cleaning guide for my '86 700. And i am still trying to find the electrical "leak" but i haven't put much time into that...prolly this weekend if the rain holds off.

So, last year and more notably recently since bringing my bike home i have noticed an increasing habit of the throttle bogging down as soon as the bike warms up. Now i thought it was vapor lock/carb problems originally but now i am not so sure.

After warming up the bike from a cold start and heading out (anywhere, work, fun, etc) i get between 2-5 miles from start-up and the throttle boggs down and usually cuts out.

Sometimes it starts right back up. Sometimes i gotta wait a few minutes. Sometimes while moving i can ride it out while loosing about 15mph (usually takes between 15-35 seconds) before the bike comes alive again. Note that if i release the throttle or try to rev it it will kill it either way.

It usually happens ONE time and only once per cold start and warm up. As long as the bike doesn't completely cool i never have a problem for the rest of the day no matter where i go, how far or how fast. Sometimes it wont happen at all (about 1 out of 5 rides) but it is starting to worry me. It never did it in the first two years that i owned it.

The carbs are now CLEAN! There was a problem with clogged jets but that is a thing of the past.

I am not a pro but i have been trying to figure out what is wrong. I have been browsing the forums and it seems that there are a number of different things that can cause similar fun times for riders (fuel pump, regulator, vaporlock, sensor??) would anyone have a good idea of what the problem is and how i can fix it?

Admittedly, in an attempt to search the forums for similar issues i couldn't define the "technical" terms for these symptoms (my own limited shade-tree mechanic vocab) and finally just browsed by chronological order one page at a time by topic....not the best way to do it.

Suggestions of topic/threads to consult (like that carb cleaning guide!) would be great if anyone happens to know which ones should put me on track.

Thanks

 

Sounds like a carburetor issue--not getting enough fuel. You will have to ensure the fuel system is clean and functioning from the tank to the bowls and thru all the circuits. Pull the plugs to determine whether it is running rich or lean.

Did you verify that all the jets were clean and open to the correct diameter using steel pins or wire? e.g. A #38 pilot jet can look open and clean and even pass an 0.008" wire, but it should be open 0.014" (number 14 electric guitar string).

Did you check the float level setting; did you check the actual fuel level in the bowls to verify the settings are correct and that the inlet needle is working properly.

Do you have an inline fuel filter between the tank and the pump? It sounds like you have trash blocking the fuel flow, then when the motor is off the debris shifts and lets some fuel thru.

 

It's NOT vapor lock, so forget that !

 

as i am a shade tree mechanic and am still learning i will need some advice on how to determine the rich/lean by pulling the plugs. as for the carbs....i cleaned them to a faire-thee-well. i used a welding tip cleaning wire set to make sure all the jets were open and spray carb cleaner and compressed air to get the rest out.

The floats appeared to be functioning normally but there is always the possibility that is not the case. i removed the floats and inspected and cleaned during my carb-cleaning fun. the float inlet needles were also cleaned and removed as well as the inlet screws/screens. while i do not have the float gauge to use to measure for accuracy i did make sure they were all operating after re-install via a clear piece of tubing and some small glass jars. the amount of fuel drained from each bowl all came within approximately 1/16 of an inch in the small jam jars. i figured that was a good sign figuring any inaccuracies were due to remaining drops inside the tubing or the bowls.

I do have that clear plastic oem inline fuel filter on my bike and it will be replaced as soon as my order arrives unless the collective wisdom in these forums tells me to "screw that piece of junk" and get something else from another manufacture. (at this point i would be willing to bow down to said collective knowledge and keep the honda replacement fuel filter as a "spare"). Please let me know if you have a better idea for that fuel filter. as it is it does appear to be slightly discolored (yellow-ish) but i don't see any debris in it.

anyother ideas?

I have heard about the rectifier giving "warnings" of failure in that it seems to shut down the system mid ride but as i don't have a volt meter (also on the way) so at best i can simply stop, take out my multi meter and check the voltage (which seems to be "in range" at 14.3 at 5krpm). this scenario wouldn't surprise me but again i don't know how to test it, nor the possibility of early fuel pump failure.


thanks kenny and squirrelman for replying.

btw as a side note i took it out for a ride yesterday (wednesday) from my home to the beach/ferry terminals, about 19 miles and the bike ran perfectly, both ways, as well as a stop at 5 Guys Burgers and Fries =).... but the night before (tuesday night) i got 3 miles from home on my way to work and...bam... it restarted as soon as i hit the button and i was off again and bogged for about 20 seconds on my way home wednesday morning (without shutting down).

 

The only problem with the welding tip cleaner rods is they have burrs on the shank intended to cut and remove slag--they will also easily cut into your soft brass jets and open the hole diameter.

But it sounds like you have debris in your fuel system. Are you using some old gas? What was the condition of the carbs when you went to clean them--were they clogged and varnish-coated? The entire fuel system from the tank to petcock to filter to pump will also be coated to the same extent that you saw in the carbs. That old filter is suspect. Run a couple of tanks of fresh fuel and see how it runs after that.

 

Is the choke cable seized up or linkages holding choke plungers open ?? Bent plunger not seating ? Plugs will be unusually blackish if so.

Measure the float heights accurately, and check fuel levels with clear plastic tubes using the float bowl seam as the reference point with the carbs held level, not at installed angle. Proper float setting is confirmed if fuel level is even with seam + or - 1mm.







Since you had the bike, have you ever thoroughly flushed out the fuel tank, checking for dirt and rust ?

Problem might be related to fuel cap vent clogging, plugged fuel filter, kink in fuel line, debris in tank, bad pump relay.