Rough Running advice needed -- at wits end

[paulbaker1954]

My 500 Four is running like a pig and I am at my wits end trying to fix it  !!

Symptoms are will not pull away from start properly and have to rev and slip clutch like hell to get going. It's so bad I cant ride it because it's dangerous when pulling in to traffic etc. I also think there is a lack of power overall, the motor just doesnt feel "zingy", feels really lumpy and feels underpowered.

Since my rebuild its got much worse. Things is have checked/changed

New Points
Timing spot on
New plugs
Good spark at all pots
Valve clearances spot on
Carbs well balanced
Float heights about 3mm below carb flange so also bang on
New pistons and rings so not a compression issue

I have come to the conclusion I have a carb problem but would like some thoughts and help. Other symptoms I have noticed are

Plugs 1,2 and 3 are very dark and sooty (rich) but plug 4 looks good
Advancing timing to nearly max advance point at tickover makes idle smoother
Moving air screw from 1/2 to 2 turns out seems to make absolutely no difference to behaviour

So bottom line she seems to be running very rich particularly at up to 1/2 throttle

When I did my rebuild I did not replace all the jets just cleaned them and replaced O rings so now I have ordered a full carb kit of all new jets, pilot screw, float valve etc so while i wait foe delivery I want to also to do more checks on the carb bodies.

Is it possible I may have a blocked idle circuit? If so how can I check there are no blocked passages anywhere in the carbs. I am not sure what hole connects to what as I cant find a Keihin eploded diagram. What holes should I squirt carb cleaner down to see if the passageways are clear and wher should it come out??

[LesH]

I'm watching this post with interest because that exactly mirrors my problem and I've not much hair left to pull out. 

[K2-K6]

It looks to me that you are on the right track Paul. The only thing I'd disagree with is balancing the carbs while it's not running correctly as you can very easily put in more error than you started with, balancing should really be the last ish tweaking to get it smooth.

If you look down the carbs and see much difference between slide height it's probably  better at this stage to make them all equal physically speaking to help you in sorting out the rest.

I do all sorts of carbs without knowing the passage directions but on the assumption it's got to come out somewhere. I mostly use carb cleaner and then blow them through with an airline which I use at about 90psi (use goggles as you always get a surprise direction) this will get through most gummed up holes but make sure to remove anything fragile that could be damaged first and do it over a big cardboard box to avoid anything important getting fired off somewhere you can't find it.

Failing this, I strip them  out and boil them if an old saucepan ( my alternative to ultrasonic cleaner!) and then blow them through. We always steamed everything in a chemical analytical lab to get all sort of residue off apparatus.

It does look like you just haven't got a flow though some of the small low speed jets and passages to prevent a even idle and transition up onto the bigger jets.

[paulbaker1954]

Hi Les
Glad you concur, anyone know where I can lay my hands on any data/diagrams/exploded images on the primary circuit routes inside the carbs. That would be a big help  in checking if things are flowing where they should

[Ashdowner]

Surely when you're setting off you're giving it some revs and the main jets should be coming into play. I had problems with the slow-running jets and my bike was rough as hell at low revs but recovered a lot when I opened the throttle. You've checked the compression? Are you sure all the valves are closing? Do all the pots get equally hot?

[paulbaker1954]

Progress update
Carbs stripped and figured out where air goes in the pilot circuit or in 3 carbs wasn't going as the circuit was blocked. Borrowed works ultrasonic cleaner and all are now clear (amazing tool - never used one before so regret not doing this on the initial rebuild )

Once new jets arrive this week will get all back together and hoping for big improvement in running

[AshimotoK0]

I Paul.... Gerben in Holland sell a full kit of Viton 'o'rings for the 500 four. Not particularly cheap but good quality and better than Nitrile and sourcing yourself individually.

[paulbaker1954]

OK I now have my carbs ultrasonically cleaned and fitted with a complete new set of jets, float valves, needles all of which ig got from Rocky Riders in teh USA ($40 plus shipping for 4 sets). Only complaint was one of the floats would just not seat properly so binned it and used on e of my originals that I knew was good.

End result WOW this is what a 500 four should feel like. Just feels like a different bike completely and what I would expect a 500 to perform like.

Just shows the effect that having 3 blocked idle circuits can have !!!

Good learning curve as I have also learned how these carbs work and where all the internal bores go to

Final job is to fine tune the idle mixture it's 2 turns out ATM and I think running to weak. But even with this setting I cannot believe the difference.

Lesson learned - When rebuilding these bikes spend a lot of time checking. cleaning and refurbing carbs. If I had just cleaned them properly in the first place and replaced jets etc I would have saved hours of back and forth to diagnose why she was running so badly

[gordo]

Progress update
Carbs stripped and figured out where air goes in the pilot circuit or in 3 carbs wasn't going as the circuit was blocked. Borrowed works ultrasonic cleaner and all are now clear (amazing tool - never used one before so regret not doing this on the initial rebuild )

Once new jets arrive this week will get all back together and hoping for big improvement in running

Could give a description of where to clean the idle circuit

[paulbaker1954]

The idle circuit consists of 3 holes and the pilot jet.

hole 1 can be seen on the carb wall on the inlet side throat at 90 degrees from the top before the throttle slide, this actually joins in to the hole from the air screw by the way.

Hole 2 is a VERY small one at the base of the throat on the exhaust side at 180 degrees from the top just in front of the throttle slide. This is where the idle mixture is fed in to the cylinder.

Hole 3 is where the air bleed screw goes in.

At idle air is drawn from hole one and the air screw then adjusts the amount of incoming air, this is then mixed with fuel from the pilot jet To provide the idle mixture.

The resulting mixture then squirts out of the very small hole (hole 2) at the front of the throat in to the cylinder.

I found the best way to check for blockage in the whole pilot circuit is to remove the pilot jet and air screw and blow down the air screw hole and at the same time cover the pilot jet hole and the other 2 holes with some combination of fingers and thumbs. You can then lift a finger or thumb from each hole in turn and hear if you get air blowing through.

It's a bit like mastering playing the bagpipes but an effective way to check the circuit for blockage.

This may sound complicated but if you find the holes and study the plenum chamber in the base of the carb it's pretty obvious how it works.

Hope this helps fellow owners with idle/suspected blocked carb issues.

I must apologise for my lack of foresight in that I should have taken some pics whilst the carbs were off. If I take them off again in the near future I will post pics to show where the relevant holes are.

Alternatively if someone else has a spare carb and can help maybe they could post some pics.

[Rob.b (Rob Birkett - RIP)]

Ok I'm on it, I had an old carb in the loft and I was wondering how they worked and prompted by the threads on the forum about the subject I thought that I would find out and share it here.

My initial examination has forced me to consider the existence of life on other planets, because what sort of mind is capable of coming up with all the little passageways and the like, let alone manufacture it, let alone do all of it in the 1960's.  I'll tell you how; its Alien technology FACT.

Another example is the Deltic engine.  look at this:

https://www.youtube.com/watch?v=6NdbonKRyKY

If you listen carefully you can tell its the Aliens because they synthesised the voice from a sat nav.

Anyway, Aliens or not and unless someone beats me to it I propose to figure out what is going on with these carburetors and will share my findings.

Here is part 1 'Dismantlement':

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Rob

[AshimotoK0]

The item on the RHS will give you a quick fix 

[gordo]

Cheers for that great description Paul, guess I'm in the garage this weekend.

[Rob.b (Rob Birkett - RIP)]

What happened to the float? looks to be only half there. I found one in an old tin earlier this week if it's any use, along with a complete slide, needle and arm. No idea why they were there.

The float was seized and broken when I was given the carbs, which is why they have sat around for so long, if I ever get to the position where I know how they work and want to reassemble them I may well take up your offer, but for their own safety your spares are probably best with you.  After all who knows what the Aliens are capable of once they know I am figuring out their technology. 😊

By the way there are two short perforated tubes that I think the parts list refer to as jets, are these also known as emulsion tubes, if not where is the emulsion tube (s)? Or is it that the emulsion tube is part of the jet.

Cheers Rob