TY175 / NEW BORE / CARB LEAKING PREMIX - FLOAT BOWL GASKET

[Tuzi]

'75 TY175B - NEW BORE - MIKUNI VM22SS/1 LEAKING PREMIX AT FLOAT BOWL GASKET

I want to ask for recommendations before I take action.

I searched the archives but did not find any similar posts. Sorry if I missed any.

Just had a new bore done on my '75 TY175B and now find premix leaking from the float bowl gasket. Never a problem for the 2 years I've owned it, or any bike previously.

NOTES

1. Before the bore premix at 50:1 (previous owner/myself). Mix Golden Spectro / VPR racing fuel. Ran as smooth and sharp as the second hand of a Rolex. Carb is jetted for 50:1.

2. For break-in my Tech mixed a batch of Maxima (either their castor or petroleum) / premium pump gas at 32:1. Okay for break-in, but rough enough to prevent delicate moves (as expected).

3. Tech asked me from now on to replace Golden Spectro (afraid of carbon build up though I've used it for years without problems) with Bel-Ray H1-R at 32:1. Mixed a batch of H1-R / VPR at 32:1, got 2 20 minute sessions then found the float bowl gasket leaking and it will not start (spark is fine).

4. Suggestions? I want to maintain 50:1 to keep my performance and would like some clarification on using either of the above oils though I don't want to open an "oil can of worms," just GS and H1-R.

As always, thanks for your support,

Lloyd...

[David Lahey]

Hi Lloyd the oil and fuel products mentioned in your posting are not well known here in Australia so it might help if you describe what sort of oils and fuels they are especially what is VPR?
Whatever the fuel and oil in use, I would be looking for a different reason for why the float bowl gasket started leaking.
The oil/fuel ratio thing is a personal thing and if you got a long run from the rings and bore with whatever you used before, maybe it is fine for you and that bike.
You didn't comment on the condition of the motor before the rebore. Maybe your tech saw something when the motor was apart (gummed/stuck rings maybe, lots of carbon on the hot bits maybe) hence the advice to use the BelRay oil.

[Tuzi]

Hi David,

Thank you for your response. Following find clarifying info. Noted in the original post, I want to get some feedback first before diving into the carb.

1. Golden Spectro is a blended synthetic/petroleum oil. It is recognized as one of the very best for vintage. I've used it for over 20 years with no problems. Recommended 50:1 and has been the only oil used with the TY until the top-end rebuild.

2. Bel-Ray H1-R is a racing 100% synthetic ester oil formulated for power-valve 2-strokes. It also has an excellent reputation as one of the best synthetics. 40:1 is recommended. This is the oil the tech recommended at 32:1.

3. VP Racing Fuels is one of the leading manufactures in the US. VPR is a Leaded/Oxygenated fuel with a 101 octane rating. Vintage is one of it's applications as a pump-grade gas equivalent from the 1970's (it's also used for for other applications). Spoke to their representative on this one.

The combination of Spectro/VPR at 50:1 has been prefect.

No issues with carbon prior to the bore, new piston/rings, etc. Plug always clean. The carb has been cleaned and adjusted several times (last time about a month ago) with no issues prior to this situation.

I will go back to my 50:1 after I figure this out. I did see in several US forums where 2 riders had the exact same problem after new top end, 50:1 prior (coincidence - using the 2 identical oils I mention above), 32:1 break-in, followed by float bowl gasket leak. Recommendations were to check the needle seating or replace it, new gasket, or re-jet if staying with 32:1. There were no further post of their solution's, and they're outdated.

I was hoping that some other vintage TY (or Mikuni) riders would have experienced similar conditions.

Thanks for your follow up.

Lloyd...

[Guy53]

I use 25 % VP mixed with no ethanol Shell Ultra ( Canada ) in very hot weather with BellRAy at 50/1 with no problem for 4 years, when temp is lower than 80 degree I don't use VP.

Guy

[David Lahey]

There are very few people running leaded or oxygenated fuel in their air cooled trials bikes out here, so if your gasket problem is related to the use of VPR, then there will be little experience of it here. The most commonly used fuel here for air cooled two stroke trials bikes is 98 octane (ethanol-free) from the bowser. Leaded fuel and indoor ELF fuel are easily available in drums but are not normally used for trials bikes. Full synthetic and semi-synthetic are the most commonly used two stroke oils in air cooled trials bikes.

One possibility for your carby gasket leak to consider is that different fuels have different SG, so the fuel level in the bowl will be controlled to different heights unless the float tangs are adjusted to suit the fuel. I know for example that the leaded fuel sold here has a significantly different SG to that of pump unleaded so maybe your tech set the float height to suit the pump unleaded and now it is much higher with your VPR mix in it. (in our case, the unleaded fuel has a higher SG than the leaded fuel)