1972 T500 - One Cylinder

[quidger]

Beginning stages of a restoration.
Bike hadn't been started for 20 years.
So far, relined tank, new battery, new plugs, thoroughly cleaned carbs even though they were in excellent condition. Set float heights by using both a micrometer and tube in drain oriface. Changed oil and fresh gas.
I have excellent spark both sides.
However, it's only firing on one cylinder. I checked the plug on the non-firing side and it looks like it has not seen any gas at all - plug electrode is virtually shiny new.
I haven't checked compression with my gauge but it seems to have strong compression. And the cylinder that is firing runs strong.
I think it has to be a carburation issue since the non-firing cylinder seems to be getting no gas. In cleaning the carburetors the only thing that looked the slightest bit suspect was that the Spring in the valve needle seemed a little soft.
Any suggestions are much appreciated.

Thanks

[rngdng]

My guess would be pilot jet clogged. The passages are very small, and easily clogged. It's not always obvious.



Lane

[quidger]

It seems logical since the pilot is the final delivery point for the fuel.
I've had this carb off three or four times to check floats and to re-clean the passages and jets.
But I cannot disagree with you. Pilot jet would seem like the main suspect.
So I'll take the carb off and give it another thorough cleaning.
I'll let you know if this solves the problem.

Thanks

[quidger]

Okay, re-cleaned the right carb and reinstalled.
I think blowing out and using carb cleaner on the pilot jet and carb passages may have done the trick.However, I can't say for certain because after I installed the newly cleaned right carb the bike starts on the third kick every time , runs for about 3-4 seconds and then dies. I'm fairly certain that the right cylinder with the cleaned carb is now firing because I now have some smoke coming from right exhaust.
Before I took the right carb off and cleaned it, the bike started right up and would run, albeit only on one cylinder.
Now the bike appears to be firing on both cylinders but it won't stay running. It starts consistently now, always on the third kick and under choke. I say appears to be running on both cylinders because it doesn't keep running long enough for me to tell for sure. When I give it some throttle it also dies.
Any more ideas or thoughts are greatly appreciated.

Thanks

[tricky1962]

Could it possibly be a faulty fuel tap? - clogged filter for example?

It now sounds like fuel starvation to me

[quidger]

I have also replaced the original diaphragm style petcock (leaking badly) with a new manual petcock. And, I have plugged the vacuum inlet on the carburetor with a cap to seal it off. So I'm fairly certain that the issue is elsewhere.
I would agree that it appears that lack of fuel to keep the engine running is the problem. What I'm not understanding is how the bike ran well on one cylinder and when I got it firing on both cylinders (at least I think it is firing on both now) the bike only runs for 4 or 5 seconds and then dies. And it only runs with the choke/enhancer on.
I'm really scratching my head at this point and hope someone has a suggestion to help me get the old gal running and back on the road.

[tricky1962]

Once it's died, will it restart immediately?
If not, how long do you have to wait before it will start 3rd kick?

[quidger]

It will start again almost immediately but always on the 3rd kick and always with choke on.
Since it runs for such a short period of time it's hard for me to 100% verify this but if I try to give it throttle as soon as it starts to run, the application of throttle seems to kill it even quicker.

[Alan H]

Clean the carbs again and make sure the slides have the flat side to the engine (cutaways to the filters).
Have you got a standard air filter on?
It sounds as if it's very weak mixture wise or even part blocked exhaust.
How many turns out are the air screws?
Are the exhausts and silencers clear?
What plugs are you running?

[jabcb]

Start from the assumption that the PO might have parked the bike 20 years ago because of some problem he couldn't fix.

Get new pilot jets — some PO might have trashed them.
Make sure the slides are in correct, go down all the way & work smoothly. (One of my bikes was parked years ago because of a frayed throttle cable.)
Make sure the choke plungers operate smoothly, and are adjusted to actually open & close. (One may be stuck open so that only one cylinder runs when hot. Also happened to me.)

There are drain bolts under each cylinder for draining the bottom end. Consider draining the lower end because it may be too full to get a good vacuum. (This spring I had a bike with a loose plug cap. The plug was pretty dry. After fixing the loose cap & installing new plugs, that cylinder became a neighborhood fogging machine. Seems that the low end was so full that the plug wasn’t getting very wet.)

[quidger]

I bought the bike last September and it shows only 1500 miles on the odometer. It had been stored for 25 years. They had the good sense to drain the gas tank and carbs. The tank had a small bit of rust but I lined it with Caswell anyway because in the long run it will need to have it done some day. Even though the carbs were extremely clean I still totally disassembled them, ran them through the ultra sonic cleaner, shot carb cleaner through them and blew them out with compressed air.
I believe the mileage to be accurate based on the original redline tires with very little wear and the chain has never been adjusted. I've restored several 1960's , 70's and '80's bikes over the past 15 years and this a unique situation that I'm having trouble solving.
I'm positive that slides have cutaways to the intake side. I have totally cleaned the carbs twice now. Standard original air filter has been cleaned and blown out with compressed air. It is in very good condition and was not that dirty.
Air screw is out 1 1/4 turns per the manual.
I haven't removed the mufflers to check for blockage of some type because of the way it was running when it was firing on one cylinder. The left cylinder was the one that was firing and it had a strong exhaust output. The right cylinder was not firing but it was still had out put , albeit not as strong as the left, which is logical.
I put in new NGK plugs - can't remember but it's either B8 or B7.
I can't think of any possible explanation as to why when it was running on one cylinder it was firing perfectly and when the carb for the second cylinder is re-cleaned and installed that the right cylinder will now not run for more than a few seconds.
I appreciate you guys giving me your input and ideas as we work to find a solution.

[quidger]

Jabcb might have hit the nail on the head with the idea that 25 years ago the PO may have had the same issue, thus bike was parked with the low miles and never saw the light of day until the auction last Fall.
I'll take you up on the suggestion to get new pilot jets . I think OEM Mikunis are still available. Hate using Keyster parts in carbs.
Slides are installed correctly, functioning properly and in very good condition.
I removed the two drain bolts from the case, drained old oil and refilled with new.
What about the new manual petcock I installed? Could there be a relationship between my issue and the new petcock? I put a cap on the carburetor vacuum inlet to plug it.

[tricky1962]

I would temporarily stick the old fuel tap on and give it a go.

I replaced mine with a new non-vacuum tap, purchased from the US but I think of Chinese origin. If the tap is not in exactly the right position, it will only fuel one carb

[quidger]

Tricky, I'll give it a go.

[jabcb]

There is a tendency for the T250/T350/T500 to run on one cylinder when the battery is flat. So you may have an electrical problem.
You know you have a problem if you don’t get a spark when you manually operate the points. But getting a spark when you manually operate the points doesn’t guarantee that you have a spark when the engine is running.

Check the coil primary & secondary resistances.

Start with a good battery that’s fully charged.
Measure voltages with the left points closed & right open: coil primary battery side for both coils, coil primary points side for both coils, and the points (metal part that moves) for both sides. Then repeat with the left point open & right closed.

A comparison of the results might point to an issue.