1975 TY-175B Running Issue - Lose Idle - Motor Races

Tuzi · Post by **Tuzi** » Mon Jul 23, 2012 8:39 am

1975 TY-175B Running Issue - Lose Idle - Motor Races

Spec: 1975 TY-175B - Mikuni/VM22SS/1 - Golden Spectro 50:1

Condition:
--- Choke out - starts (always 1st/2nd kick) - warm - choke in - wil not idle and dies - try again (choke in) and after several minutes the motor will begin racing for maybe 10-15 seconds and dies.

Now this is what I cannot figure out. The carb has been looked at, cleaned/adjusted 3 times. After it's examined each time, the bike runs like a charm, and idles perfectly. The first time out (1 hr) it's great. The 2nd time out (1 hr), the idle goes away. The 3rd time is when - with the idle gone - the motor begins racing after about 2 or 3 minutes.

Other:
--- The original manual spec calls for the the air screw to be out 1.5 turns before fine-tuning mixture and idle. When I got it, and each each time it has been worked on, it's at 10 o'clock, from the full 12 closed (slightly open). The technician (vintage experience) say's it's okay as long as it runs fine. During the above conditons, I've adjusted the mix and idle with absolutely NO affect. Will say that it seems to be leaning out a little more after each event. Checked plug and it looks good, and did not see any header leaks or anything else. No matter what, always starts on the 1st, 2nd kick.

Note: Between the 1st and 2nd events, I had all the motor gaskets and seals replaced.

Help ---- Suggestions?

BTW, use the Sammy Miller pegs. A must for all TY's! :-)

Thank you,
Lloyd...
Tallahassee, FL

Post by **David Lahey** » Mon Jul 23, 2012 10:01 am

I think you might have more than one problem
Check fuel tank venting system for free flow
Check fuel tap for free flow
When it plays up, take the float bowl off with the petrol still inside (take it off and keep it upright until the bowl has been removed) and look for water or particulate matter.
If the pilot circuit is working correctly the idle air screw should be somewhere between 1 and 2 turns. If it only idles properly with the screw just off the seat, then there is something wrong with the pilot circuit. Check the size of the pilot jet is standard size and the tiny hole through it is clear. Also check for free flow of compressed air/WD40/whatever through the pilot system. There are four places the check the pilot circuit for flow. Where the air goes in at the entry bellmouth, where the pilot jet screws in, where the idle air screw screws in, and a tiny hole inside the air venturi near the inward side of the throttle slide.
Another possible reason for the idle air screw needing to be so far in could be air leakage into the crankcase. The effect of an air leak is more pronounced when the motor is fully warmed up so see if you can tell if the problem is engine temperature dependent. Possible leak sites are the rubber thing the carby attaches to the reed cage with, crankshaft seals, centre joint between the crankcase halves, the oil injection nipple and the cylinder base gasket joint.

FM350 · Post by **FM350** » Mon Jul 23, 2012 6:18 pm

Remove generator cover, and check for play in main bearings. Sounds like you have an air leak of some sort, and in most cases worn bearings is the cause of this.

gilly · Post by **gilly** » Mon Jul 23, 2012 7:01 pm

If you have already replaced the main bearings & seals it sounds like a main seal has been damaged or faulty when the seals were replaced.

pop · Post by **pop** » Mon Jul 23, 2012 8:27 pm

Id be looking for an air leak in bottom end also :-k

Tuzi · Post by **Tuzi** » Tue Jul 24, 2012 5:57 am

Re: 1975 TY-175B Running Issue - Lose Idle - Motor Races

I want to thank everyone for your quick reponses to my TY-175 problems.

Thanks for providing the carb details and brining up the main bearings.

I remember now that I had the main bearings replaced along with the gaskets and seals at the same time. Had the problem before and after the replacments.

With each subsequent carb check, the bike runs fewer minutes before the condition starts again. Now, every time within several minutes.

Thanks again, I'm off to work on it!

Lloyd...

FM350 · Post by **FM350** » Tue Jul 24, 2012 5:36 pm

See if you can borrow another carb and try that, if its still the same pressure test the motor for air leaks, and also very carefully check the ignition system.

Tuzi · Post by **Tuzi** » Wed Jul 25, 2012 6:47 am

Thank you for the suggestion. Will do...