Tomos A3 sputtering and backfire

Had (relative) stock A3 running well before putting this kit on it. https://www.treatland.tv/tomos-A3-airsal-kit-p/tomos-a3-airsal-kit-02210544.htm

Bike fired up easily and idled beautifully. I took it for few rides at 1/2 to 3/4 throttle after doing a bit of the recommended kit break in. Performance was great and was consistent. I didn't want to do plug chops or any aggressive riding though until I was able to resolve airleak at base gasket I found w/ carb cleaner.

So I got a better gasket off treats, took off: intake, carb, studs, and top end of engine. Gasket went on well, followed by studs, top end w/ rings aligned, and reed/intake/card. Fired up, idles seemingly well, no more air leaks detected. However attempting to ride now is sputtering on me, and today trying a quick ride I got one backfire.

I first thought, timing... Timing light confirms 1.9mm BTDC, which is where it was before and running very well. I'm also wondering how anything timing or really electrical in general could have been impacted by removing top end to replace gasket.

What could I have influenced when replacing this gasket? Could this be a symptom of perhaps the rings not aligned properly? Reed? I think reed could only be installed the one way anyways... What else could I have potentially done that stopped this bike from running beautifully as it was just before this gasket replacement?

Re: Tomos A3 sputtering and backfire

Condenser is bad most likely. Bypass the one on the stator and mount one to your high tension coil bracket with the wire going straight to the ht coil lead. Pretty common problem with 40+ year old ignitions. The part can be had at auto zone for 5-10 bucks. I like to get the 70s super beetle condenser, it comes with a little bit longer wire and an m6 mounting bracket. Most of the other one are m4 or smaller.

Re: Tomos A3 sputtering and backfire

> Daniel '' Wrote:

> -------------------------------------------------------

> Condenser is bad most likely. Bypass the one on the stator and mount one

> to your high tension coil bracket with the wire going straight to the ht

> coil lead. Pretty common problem with 40+ year old ignitions. The part

> can be had at auto zone for 5-10 bucks. I like to get the 70s super

> beetle condenser, it comes with a little bit longer wire and an m6

> mounting bracket. Most of the other one are m4 or smaller.

I can certainly see why this would be first thought, but what gives me doubts about this are...

- bike ran consistent and beautifully right before taking off top end, intake, carb to simply replace gaskets

- should have mentioned, replaced condenser earlier in season, has ~100 miles on it

Another potentially helpful comment and I can't comment on how it was before all this as I just received my timing light... Timing light sits perfectly on 1.9mm BTDC, does have an intermittent blip where it momentarily falls out of place and bounces right back to 1.9mm BTDC

Re: Tomos A3 sputtering and backfire

try a new plug, problem might be that crank seal behind stator plate. whats yr carb n jetting?

Re: Tomos A3 sputtering and backfire

Plug relatively new, but simple thing to test - will do

Crank seal behind stator plate was replaced brand new this season, unless for some reason my install was poor and it's slipping out

15.15 dellorta SHA

70 jet

techno estoril

Re: Tomos A3 sputtering and backfire

u can temporarily run an ex condenser just to test, if u dont see any wet ness when u peer into flywheel hole then yr new seal should be holding up. try cleaning the points 3 times, and double check timing is btdc, not aftdc.

Re: Tomos A3 sputtering and backfire

How did you time it at 1.9 mm s

What's that piston travel before top dead center or flywheel rotation before top dead center?

Re: Tomos A3 sputtering and backfire

Thanks Pat will give it a shot.

Sean I use a micrometer, also my flywheel is 360mm circumference so 19mm is 1.9mm BTDC. Just purchased a timing light as well to ensure I’m hitting that spot on the money

Re: Tomos A3 sputtering and backfire

♣Slew Foot♣ /

You are retarded too far. Check if you are super cool on top but the pipe is cherry. Your gasket quacks the. Timing

Re: Tomos A3 sputtering and backfire

maybe now that you've fixed the air leak you need to downjet a bit.

what's yer plug look like ?

sometimes it's the simple stuff

Re: Tomos A3 sputtering and backfire

Thank you all for response. Helpful for this specific issue but also great learning experience talking through it... Sorry for delay, have been out the garage w/ change in seasons and holiday seasons... Plan to get back in and try some of these suggestions soon.

Pat Splat - definitely before TDC, points cleaned recently and in great condition

Crazy Wayne - 1.9 mm BTDC is cross referenced both at the piston head w/ micrometer and from what I gather on this bosch flywheel at 360^, 19mm of flywheel travel BTDC hits the 1.9mm at piston head

Slew Foot - Will look into this. What do you mean by gaskets quacking timing?

Evgdboy - I hear ya, that sounds logical and like simple solution right? I tried downjetting a bit with the same mindset before I even post this - no real change in performance.

I am thinking it's electrical/timing. I just got timing light and what I'm noticing at idle is that it does sit nicely right on the 1.9 BTDC mark I make, but like once every second it falls out of line and right back into place

Re: Tomos A3 sputtering and backfire

♣Slew Foot♣ /

Quacked...

Falsified.... With the thickness of the gasket it makes the port map raised

Re: Tomos A3 sputtering and backfire

Update - replaced my recently installed condenser with external superbeetles condenser recommended by deesal. Don’t ask me why my last one failed so quick... but I guess that was the big issue.

Quick test run cause of rain, but bike seems to be running very well like before. Only thing I still notice that I would like to understand and hopefully address is that my timing light still bounces out of position intermittently... not as strong or often as it appeared to before. I am going to replace points even though they look to be in great shape and I’m going to double check the connection on my grounds, perhaps even run a second one. Any other suggestions to consider that might contribute to the timing light behaving like this?

Tough to see we’ll in video cause of frame rate, but you’ll get the point after watching

Re: Tomos A3 sputtering and backfire

PROBLEM SOLVED

Only posting this as a thank you to those who chimed in and in hopes to help someone with similar symptoms in the future.

Condenser was replaced which resolved my sputtering and backfire. Excited to convert to external condenser and will consider on my puch as well for ease of access and diagnosing.

My intermittent misfire on my timing light was resolved today w/ installation of new points. My old points looked to be in excellent condition and well aligned, however they must have had just enough going on to cause a disruption in spark.

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