Misfire- The lady that interrupts... ????

[hools100RS]

Ross. have you checked those needle jets yet? Mine were worn oval and caused overfueling at higher revs. Missing, hesitation...........thought it was electrical....changed gaskets and carb O rings.....PIA!!!! A change of needles and jets, a 20 minute job...no problems. Check those Jets!!!!!!! hools.

[Ross]

Ross. have you checked those needle jets yet? Mine were worn oval and caused overfueling at higher revs. Missing, hesitation...........thought it was electrical....changed gaskets and carb O rings.....PIA!!!! A change of needles and jets, a 20 minute job...no problems. Check those Jets!!!!!!! hools.

I can't get the needles out. The screw that holds each one is in seized tight. I have left them soaking in WD40 and still they will not undo.

[Ross]

I am still trying to get the carbs balanced. Doing it by "ear" but and not happy with the results so far. So will redo them with my Carbmate this time.

[Deleted User 72]

Ross. have you checked those needle jets yet? Mine were worn oval and caused overfueling at higher revs. Missing, hesitation...........thought it was electrical....changed gaskets and carb O rings.....PIA!!!! A change of needles and jets, a 20 minute job...no problems. Check those Jets!!!!!!! hools.

I can't get the needles out. The screw that holds each one is in seized tight. I have left them soaking in WD40 and still they will not undo.

Are you speaking of Bing carburetors? I've never had a set screw to loosen to get them out. Turn the needle 1/4 turn and pull it down, repeat until it comes out.

[Rob Frankham]

Fuel is the likeliest answer... but... don't discount electrics. A poor spark that will light the fires most of the time is most likely to fail under heavy load and cause exactly the symptoms you describe.

I would look at (not necessarily in this order):

• Float levels ,
• Fuel flow - check that flow isn't restricted by dirty filters or collapsing hoses. remove aftermarket filters,
• Fuel cap - air vent restricted,
• Coils,
• Plug leads,
• Plugs,
• External wiring to ignition system - many electronic ignitions draw more current the more revs you use (unlike a points system which uses marginally less) so a poor connection in the supply wiring to the ignition may cause a low voltage fault at high revs only,
• Ignition system earths (grounds) - same reason as above

Only then would I mess with main jets.

Rob

[Duane Ausherman]

I like doing the easy things first, even if they are less likely. I am lazy. First I would check the fuel flow rate. All riders should check this more often, as it really does cause trouble. Were you riding with a low level of fuel in the tank? Were you on reserve? The fuel flow is related to the level. You could have partially clogged filter screens and a low fuel level both. Filling the tank would make it seem like it was fixed.

Next I would swap in a pair of plugs, but only if you can repeat the symptoms. If you can't repeat the symptoms, then you could have had a plug problem that got fixed by that hard run. We used to fix many performance problems by changing the plugs. The bike actually only needed a hard run for 20-30 minutes on the freeway. These bikes like to run and tend to complain if not used.

It cost the customer more for us to run it and clear out the plugs than to just change them out. New plugs will last longer than older ones that would get fixed by a hard run. The customer use was the real culprit.

Rob's list is excellent.

[Jean]

native/5, BING changed the way the needle was intalled to have a screw and a "sleeve-like keeper on the needle. Then the needle is held with a clip. This is called the "new-style" and came on both 32mm (46-251 needle) and 40mm (46-371)needle carbs. This strated with the 32 series 64-32-335/336 and onwards, and 94-40-123/124 used on some R100 s (NOT only R100s!)
This info came out of the BING manual...

Ross, try filling the hole where the screw is with some PB-Blaster or KROIL if you have either, and let it sit at least overnight. WD-40 is not as good as these 2 liquids. I have always had best luck with KROIL, tho.

[blitz]

I had a similar experience recently while traveling through Indiana and Ohio, big ethanol states. 1978 R80/7 started to run poorly at high speed, big throttle openings, gradually getting worse. On a record-setting day in Southern Ohio, the bike refuses to run. Luckily, i run transparent fuel lines. Pull the lines, no fuel. Hmm. Pull bottom filter, little bit of gunk, not bad. Pull petcock, little bit of crud. But, I can't blow through petcock. Being who knows how far from any motorcycle dealer (funny, barely saw any on the trip), disassembled the petcock. bingo! The ethanol had swelled the internal 5-hole rubber seal to the point where turning the lever actually rotated that 5 hole rubber seal to the point where it was blocking the inlet ports. (The 5-hole seal is held in place by 2 cast bosses.) The bosses aren't full height/depth, which allowed the seal to rotate.

Reassembling petcock was enough to get me the 1200 miles back to Minneapolis, but i've ordered 5-hole seals.

[hools100RS]

Rob, I checked all of the possibles on your list !!! The problem frustrated the heck out of me. The needle jet ( not the main!!) wears oval with the continual vibration of the harder needle against the softer brass jet that it passes through. Whilst not as problematic with my freshly rebuilt RS, a change of needles and jets improved the fuel consumption by nearely 25% (no kidding!!!). Ross, native /5 is on the money! No screws to undo on Bings. Twist and pull to remove the needles from the slides! hools.

[Ross]

............... Ross, native /5 is on the money! No screws to undo on Bings. Twist and pull to remove the needles from the slides! hools.

Reading what Jean said wish it would just pull out. Jean I have never heard of this stuff in Australia.