issue when running warm

It began as an issue while the bike was warm: It wouldn't start easily, and ran rough when warm.

I checked and changed valve shims, and it didn't go away. So I checked them again, and then a third time. Still, not starting easily, and when warm the bike would lose power and run rough, like it was not running on all cylinders. Cylinder 1 and 2 had fouled plugs.

I synced the carbs, and have used colortune to tweak the idle mix, taken the carbs off and cleaned them, cleaned the tank. At the moment, cyl 1-2-3-4 idle mix screws are set to halfway between yellow and all-the-way-in, which is: 2.5-1.5-2.5-2.75 turns, respectively. And now it starts better (not perfect everytime). But it backfires like a mongrel. I say backfire, but it might be afterburn (in the exhaust rather than across the carbs).

The bike is stock, with these exceptions:
4-1 Pipeline exhaust.
Dyna coils

valves: 0.011 - 0.015, and 0.015-0.02 in/ex

So here I am for suggestions.

Anyone... ?

 

TCI

 

Definitely sounds electrical but I wouldn't jump to TCI immediately. Could be dirty/corroded connections. You should also ohm out the pickup and ignition coils to see if they are in range. You have a service manual? IT will have a good section on ignition troubleshooting.

 

I would........it's simple-----borrow and plug another one on and see if it solves it. It if does, you're done. If it Doesn't, then you know you are to try other electrical searches

 

Easy for you! You probably have ten of each TCI just sitting there ready to go. It'd be quicker for me to test components over trying to find another one to test with.

 

Fair enough

 

OK, I will get on to the electrics. One issue is: I don't know the Ohm specs for the dyna coils. Also, I don't think I have a TCI sitting around in my country town. I'll search, though!

 

If it won't run hot, and fouls plugs, it sounds like over fuelling. Have your carbs been to "the church of clean"
Unless on your bike a single coil feeds 1-2, I don't think so, I'd go for faulty/stuck choke. If it does, that coil is the culprit.
Hope this helps

 

^^^
There is great value in cleaning and reseating the many electrical connections...

 

UPDATE: the bike is rich on cyl 1 and 2. Colortune to blue on pilot, and increase the revs up to ~2500, the flame goes to yellow through the whole rev range and stays that way. The colortune book says this means the float heights are incorrect. I have opened the carbs (yes, zestfully clean), and checked the float heights, and I swear they're identical. I am going to do the fuel level test on them (carb bowl #1 has a broken drain screw, so I will do it by .. switching bowls amongst them, sadly). I will report back with the findings.

Is it possible that cyl 1 and 2 running rich (well, black soot on the plug) is a symptom of incorrectly sync'ed carbs?

Would two rich cylinders make all this fuss?

Stay tuned for tonights nightly fuel-level update.

thanks

m

 

The fuel across the bowls is within a millimetre of each other. Oh man.

 

The colortune is only tuning the IDLE mixture. Once you're rolling on the throttle you're running on the mixture set by the jetting

 

I would carefully check needle seat for ridge or leaking. Also try new mains, if they've been cleaned 100 times they can be reamed out to a larger size. Also be sure the slide needle is properly in the bottom of the slide and not hung up running rich.
Hope this helps

 

Replace the slide needle(s), mixture screws (springs and o-rings) diaphragms and enrichment plungers with new. Get rid of your old shit. It's worn out and will continue to haunt you.
I had done throttle shaft seals, new jets,vapor honed the bodies and emulsion tubes, carb intake rubbers, all new clamps, you name it. I dropped about $300 into this last ditch effort with my ongoing carb saga. The best chunk of cash I've spent on the bike by far. I'm easily into these carbs close to $1000 bucks but they aren't a mystery that causes problems any longer because they are "as new" as they can get.
✔️When I finally replaced my parts with correct new stuff my bike idled and returned to idle everytime.
✔️No more over or uneven fueling which resulted in consistent plug coloring.
✔️When going through the different throttle ranges all the bike would do is pull harder and harder in each gear.
✔️ The bike didn't feel labored while running as it did before.
✔️The bike noticabley ran much cooler and started without choke consistently.
✔️Colortuning and vacuum syncing then became a simple and quick step in tuning.

 

Only if the needles are worn (very rare).
It's more common (but still rare) for the needle jets to wear into an oval shape.
Your problem could have been that the wrong needles were installed by a PO.

 

I should have bought those Keihin CR Special carbs I had my eye one but wasn't going to let the Mikunis get the better of me.

 

Very true and valid point.
In my haste to rectify on going problems I never checked if they were the correct size. They (2) showed noticable ware. I just replaced with new correctly sized needles.

 

Take it easy following this advice - it'll cost you more than the bikes worth (itself a questionable motive I know, it should be "more than it would cost to replace the bike).
Anyway, I digress. Just be methodical, buy an eyeglass and inspect everything before condemning ANYTHING....

 

So much to reply to. Thank you for your interest in this saga!

Firstly: I have fixed the problem. It was electric. Short version: new plugs and leads.

Longer version:
I have within the last 12 months updated the carby kit. So its all new stuff, which is great. I gave the carbs one more inspection, and reassembled. I thought I might switch the plug leads around (after market dyna coils with removable leads), and one of the connectors to the dynacoil end was busted. So: new plugs and leads and the bike was suddenly tuneable. A quick colortune and sync and bob's your uncle.

It didn't 100% get rid of a flat spot in the throttle response and the occasional backfire, which lingered and threatened to upset me. But I have been able to et rid of that problem by changing to lower octane fuel (previously 98%, I am now running 94% with 10% ethanol) and now it sings like it never sang before.

A note on the colortune plug to hogfiddles. Like you said, I used the plug to set the idle, but there are a few more diagnostic tests you can do per cylinder, and the colour shift in the combustion flame can be used to diagnose engine/carb tuning issue with other jets (at least, according to the colortune manual, which I would link here, but I am not allowed to link... bummer). The two tests are quick rev and long slow rev up to ~3000rpm. You can identify issues here, but you're right: to rectify them, you normally have to pull off the carbs etc. as the problem is not with the idle jet.

 

I also did that

 

Slide needles aren't nearly that expensive.
Based on his avatar photo the bike is worth a hell of a lot more than the U.S. $80 that a set of slide needles curently costs.

Still, no need to change them without inspection being done first.

 

If I recall, and can't be bothered to check, the list was more than just needles. I think the total cost was 1000 usd, hardly trivial.

 

My experience with my carbs is that if the bike is stock, valves in spec, and the carbs are thoroughly cleaned and floats properly set, then using the colortune to set the pilot screws at idle solves the problem throughout the throttle range. My process for using the colortune plug is to start from a lean setting with new plugs and then do a series of rides and adjustments until the plugs have a nice light tan or gray color. Specifically, I use the colortune plug and close the pilot screw until until I get a white (lean) flame and then open the screw just until the white disappears. Repeat for all cylinders. Then install the new plugs, ride 15-20 miles and take a look st the plugs. They will probably be all white and if so open the pilot screw no more then the width of a dime. Repeat for all cylinders. Ride and check again. Continue this process until all plugs have a nice light tan or gray color. You may be surprised where the pilot screws end up. Mine are set between 1 3/4 and slightly over 2. I think you will be happy with the results.

 

I suppose that's a matter of perspective. Even spending three times that is much cheaper than buying a new motorcycle, and any used motorcycle is going to need some work no matter the price paid for it.
Even so, there's no need to replace anything that isn't worn out.

 

Exactly kmoe, that's why I suggested to buy an eyeglass, inspect all the bits carefully before spending. Then, there is also the issue of buying bits - you need to know they are genuine, but of course for stateside you have the ideal vendor.
On the value of your bike thing I'm more positve than most on this, but comparing a 30 year old design to a new bike, with makers warranty, better handling (you'de hope), better spares availability (for the near future anyway), better ecomomy - Ok, I give up, but you see what I mean.
The real value of course is somewhere between what a similar one would cost to buy and what the owner values it at - and that can be influenced by emotions.

 

I confess.
I'm emotionally attached to my motorcycles. When they don't run correctly or I can't figure out the problem that attachment is similar to how I feel about my ex-wife. I through money at her, like my carbs, trying to fix her.
"Things get just plain worn out and need to be replaced with new or they will continue to be an issue and haunt you."

 

I bothered to check for you.
My suggestions based on my personal carb problems totaled $300 USD. That address the final issues that made the carbs pretty much new.
Anyone who has comitted to making these old bikes dependable and perform as they should has invested countless hours and easily between $400-$800 bucks into just the carbs.
I've bought cheap parts for them and that was wasted money. I then would purchase from Len, he has the best stuff and you get what you pay for. A deluxe rebuild kit that covers four carbs is $280. That's the starting dollar amount.
Add the other parts that are gone from age, that many can't come to terms with, and we be have broke the $700 mark. Easily.
Go ahead and fiddle with those old parts and maybe, possibly, you'll get to ride a few rides. That's great but very temporary because those parts will cause issues guaranteed.
I'm not trying to be an ass clown just sharing the shitty experience I had with these carbs at first. I hated them. Over the years I've came to understand what it takes to make them reliable well operating assemblies.
Quality new parts = dependablity/ no headaches.
That's significant, not trivial.

 

Well I bothered o check toooo

So that figure has magically reduced now..
I reiterate my original statement - replace worn with original new. And actually, now I need to change something - I should have also suggested - where it affects one cylinder fuelling over another, replace all four cylinders (carbs) bits, that way at least they are all the same.
I have to say though, coming from an SU background, where you have a needle, jet and spring, these carbs are a pain in the butt. No wonder they don't like pods, they're not too keen with a std airbox and filter!

 

They actually perform quite well as set up stock. Keep in mind that manufacturers had to deal with fairly restrictive emissions requirements, without all the advantages of knowing exactly how to deal with those requirements. It was quite a challenge given that the U.S. was still a huge market for motorcycles at the time (impacting most of the engineering and production decisions), and political pressure meant that emissions regulations were constantly changing. Motorcyclists were fairly lucky to be allowed higher emissions numbers, and vastly less complex carburetors as a result (have a look at what a mid '80s U.S. passenger car had for emissions equipment in comparison).

Once set up correctly they work wonderfully. Unfortuantely most owners get to deal with them after decades of neglect and abuse from prior owners.

 

Or send them to Hogfiddles, wet set, tune, then ride.

Best $400-$500 bucks I have spent...

 

Now this I have to agree with. I wonder how this would work re import duties etc?

 

Gifts are duty free

 

Fix your stuff however you choose. You asked, got responses, now take action based on whichever responses you choose are within your capabilities.
If your successful share your findings with everyone here so they can benefit also.

So over this nauseating thread.
Done and out.
Peace.