Topic: 81 Cb650 revs in neutral, won't under load, shuts off after 10 mins of riding

[dfoxengr]

fuel tank is fine, i added an inline filter too.

[grcamna2]

It would be nice if there was a test for you're Electronic Ignition Unit...

[dfoxengr]

I used this and things checked out fine.

http://www.electrosport.com/media/pdf/fault-finding-diagram.pdf

[thrutheframe]

try posting at http://www.hondacb650.com/.  There are a couple of really helpful guys over there.

[grcamna2]

I used this and things checked out fine.

http://www.electrosport.com/media/pdf/fault-finding-diagram.pdf

That test will work for the Charging System...;I don't believe there is a test for the Electronic Ignition "black box"...aside from installing another one from the same year/model CB650 w/ the exact same #'s on the box, that would be my next course of action after confirming that all the other components are in good working order..the "process of elimination."

[thrutheframe]

I could be wrong but I believe the CDI igniters either work or they don't do anything.

[scunny]

I could be wrong but I believe the CDI igniters either work or they don't do anything.

that's my belief also

[grcamna2]

When they're beginning to get weak & die they do just what he is experiencing..it gets hot and dies, but it could also be other components as well;at this point it would be good to test the spark strength of the coils.

[dfoxengr]

What gets hot and dies? The igniters or the engine?

[phil71]

you can keep messing with everything if you want to, but it's still a fuel issue.. and you drilling out those jets was a mistake. YOu say you drilled them to 120.. what did you base that on? That number is completely arbitrary.
Have a look at this> http://faq.ninja250.org/wiki/Dynojet_-_Mikuni_-_Keihin_jet_sizes_conversion
and you'll realze you may have goofed.
you say they were 78s, 78 WHAT? Somewhere, somehow, your carbs are running out of gas faster than they can refill. Keep searching.

p.s. don't #$%* at people who are trying to help you get that old dog of a motorcycle running again FOR FREE because you don't have the experience to diagnose it.

[grcamna2]

What gets hot and dies? The igniters or the engine?

The inner electrical components of the igniters.When the engine is running for a while they give up.I have only seen that happen 2 times..they usually just die completely.If it is them it'll get worse. I'm sorry I brought them up though because they can't be tested at home & even most dealers don't have the testers to confirm their condition...& especially now as it's an older bike.I think you could ask someone that is close to where you live if you could borrow theirs for one ride..a friend maybe.

I think it's good for you to download the Factory Honda Service Manual to use as the Clymers is limited in certain things.

[tomkimberly]

you can keep messing with everything if you want to, but it's still a fuel issue.. and you drilling out those jets was a mistake. YOu say you drilled them to 120.. what did you base that on? That number is completely arbitrary.
Have a look at this> http://faq.ninja250.org/wiki/Dynojet_-_Mikuni_-_Keihin_jet_sizes_conversion
and you'll realze you may have goofed.
you say they were 78s, 78 WHAT? Somewhere, somehow, your carbs are running out of gas faster than they can refill. Keep searching.

p.s. don't #$%* at people who are trying to help you get that old dog of a motorcycle running again FOR FREE because you don't have the experience to diagnose it.

This fairly why I no longer get into these dicusions. Many a third party think they are owed a clearcoised response while not havinhg any skin in the game.

[BeSeeingYou]

Sounds like the classic restricted fuel flow and then flooding it on trying to restart.  It may idle fine and even run at low rpm but the fuel flow can't keep up at higher rpm and slowly lowers the level in the bowl.  You try to restart but with a low level in the bowls no go and as they fill you flood the engine.  Been there done that with my XS650 with vaccum petcocks.

[cb650]

Maybe you gas cap isnt venting.   Also for the reving try to run it without the filter cover.

[dfoxengr]

i'll make sure to keep an eye on the gas cap, but last I tried, I had it removed. also, I have K&N dual filters.

hopefully I can mess with it soon.

The mains are now 1.2mm, which I thought was a 120 size. if Keihin doesn't follow that standard rule, then I am still slightly undersized, but still much closer than before when they were 0.78mm.

thanks.

[phil71]

"The mains are now 1.2mm, which I thought was a 120 size. if Keihin doesn't follow that standard rule, then I am still slightly undersized, but still much closer than before when they were 0.78mm."

Are you actually absorbing any of this? the stamped jet# is NOT correlated  to a ruler measurement. There's no way any PO scaled the bikes jets down THAT FAR and rode it. Which means you opened them up so much you're going to drown the engine, assuming you ever get everything else to a base-line for testing.
    Having a gaping main jet on an engine that small can ACT like a lean condition in some ways.
You really need to get back to stock or you're going to keep fighting a losing battle.
 I promise you, 1.2mm is waaaayyy too big a hole for a stock 650, even if you have some bull$#!t pods on there.

[scunny]

1.2mm is the keihin 120 jet size. that's what I'm running now on my 650 with individual pods. I drilled mine in increments up from the 98's that were fitted to get me close to the sweet spot then bought 3 sets of jets around that figure for a bit more uniformity than drilling. a vacuum sync has to be done as well.

[dfoxengr]

"The mains are now 1.2mm, which I thought was a 120 size. if Keihin doesn't follow that standard rule, then I am still slightly undersized, but still much closer than before when they were 0.78mm."

Are you actually absorbing any of this? the stamped jet# is NOT correlated  to a ruler measurement. There's no way any PO scaled the bikes jets down THAT FAR and rode it. Which means you opened them up so much you're going to drown the engine, assuming you ever get everything else to a base-line for testing.
    Having a gaping main jet on an engine that small can ACT like a lean condition in some ways.
You really need to get back to stock or you're going to keep fighting a losing battle.
 I promise you, 1.2mm is waaaayyy too big a hole for a stock 650, even if you have some bull$#!t pods on there.

Phil, your comments are ridiculous. the manuals say stock is a 120 jet. You just posted a link saying that a Keihin 120 jet is somewhere close to 1.2mm (by extrapolation of shown the Keihin 110 jet size). I measured the size that was in there. the stamp on the jets was 78 which measured out to be 0.78mm. I did that myself.

Again, both manuals I have say 120 is stock size. my research and scunny's confirmation that 120 Kehin jet is 1.2mm shows that what I did by drilling them back out to 1.2mm is close to correct (much closer than the 0.78mm that was in there). you guys might think I don't know much just because I am new to this particular bike, but please think again. obviously this proves my point.

Trust me, don't go off what the PO had on there. The carbs were a wreck when I got them. Everything possibly had been fiddled with and was not in spec. Even the acceleration pump rod was replaced and was incorrectly installed. You should have zero faith in what was on there when I bought it. I know I do and I wouldn't put it past them to have screwed it up that badly.

[w1sa]

1.2mm is the keihin 120 jet size. that's what I'm running now on my 650 with individual pods. I drilled mine in increments up from the 98's that were fitted to get me close to the sweet spot then bought 3 sets of jets around that figure for a bit more uniformity than drilling. a vacuum sync has to be done as well.

Hey Scunny,

What year/eng no/carbs type/vin is yours?....

The earlier 650's used non-CV carbs, IIRC. So any tuning (for pods etc) to those carbs would most likely be different to tuning for the later CV carbs..... You can't just assume that CB650/pods/120mains is going to be successful/oem (or even close) for any year.......the OP states it's an '81 CB650 (which came with CVs)........If it's meant to have Keihin 120 mains, that's fine............... with pods, you would expect they should probably be bigger... but it doesn't necessarily work that way with CVs........You can (most likely) get them to run richer or leaner on the mains, by careful selection of the needle/jetting, while retaining the stock air-box/filter........but, .........If you run with pods on these carbs, it can be a total crab-shoot.....

[dfoxengr]

With CVs, the size is 120. This is what the manuals, both, state.

[w1sa]

With CVs, the size is 120. This is what the manuals, both, state.

Yes.....but that only applies (per oem spec) in unison with the oem standard air-box/filter.....these carbs can work beautifully, if you set them up correctly and only depart from standard spec where absolutely necessary.

[phil71]

you reading comprehension is what is ridiculous. How on earth did you take this >
 "DynoJet jets are marked according to the diameter of the hole in the jet .. ie: DJ150 = 1.5mm and DJ175 = 1.75mm.
This is not true for Mikuni or most other OEM equivalent jets. This size Mikuni jet, (N102.221 Super BN), is marked according to its' flow rate, ie: 150 = a rating of 150 cc of fuel per minute. "

to mean that a 120 is 1.22mm? That would only be true if it were a dynojet.. and you're saying they're oem.
 You know what, do whatever you want.. 

[scunny]

sorry, should have stated mines a 79. have a head and set of carbs off a 81 in the garage and the main jet in those is 78. ?
pods are always a crap shoot, I just need to shim my needle now if possible(winter project)

[dfoxengr]

you reading comprehension is what is ridiculous. How on earth did you take this >
 "DynoJet jets are marked according to the diameter of the hole in the jet .. ie: DJ150 = 1.5mm and DJ175 = 1.75mm.
This is not true for Mikuni or most other OEM equivalent jets. This size Mikuni jet, (N102.221 Super BN), is marked according to its' flow rate, ie: 150 = a rating of 150 cc of fuel per minute. "

to mean that a 120 is 1.22mm? That would only be true if it were a dynojet.. and you're saying they're oem.
 You know what, do whatever you want..

First off, I was under the impression that a 120 was standard at 1.20mm, not 1.22mm (not sure where you saw me write that number). That may be slightly off based on your link. This is my thought now (again based on your link).
Keihin 105=1.02mm, 108=1.04mm, 110=1.06mm, therefore 120>1.06 and through extrapolation is probably around a 1.16mm

I also never said my jets were an OEM jet. Again, Not sure where you got that from.

The point is that you said I was making a "huge" jump. Which is false. I just proved to you that I am pretty close in jet size and that the #78 that was on the bike was way off.

[dfoxengr]

sorry, should have stated mines a 79. have a head and set of carbs off a 81 in the garage and the main jet in those is 78. ?
pods are always a crap shoot, I just need to shim my needle now if possible(winter project)

So the set of 81 CV carbs have a jet with a 78 stamp on them? Could you measure the diameter with a drill bit?