Bore kit still having high-speed problems!

ok, remember a while back i said my 70cc kit on my tomos was popping at high speed, and i thought it was the pipe? Well despite what most people said, i was convinced it was the pipe, and got a brand new one. What do ya know? i didnt do a damn thing. It still pops at top-end. IT DOES RUN ABSOLUTELY FLAWLESS UNDER 45 MPH! the problem only happens past 45 mph. i have played with the mixture til my eyes were bleeding, but nothing helped. I even took apart the entire cylinder and carburator. Couldnt find a damn thing wrong with it. I am stumped at this point. I will take any suggestions.

RE: Bore kit still having high-speed problems!

like i said its probably the kit itself like the piston is a little too big for the cylinder. happende on a n old bike of mine

RE: Bore kit still having high-speed problems!

Two things to check...

First.... run it till its warm... then run it at 40 mph for like 1 mile... then stop fast and pull the spark plug and take a look at the color.... if it is not too white... run it wide open (45) for a mile.... and stop fast again and pull the plug again to check color again.

Second.... get or borrow a strobe timing light and check the timing of the ignition while running... I am assuming you have no points... if it DOES have points.. then clean and set them correctly.

Once you check those things you will know better what might be wrong.

Hey.... Did it ever go faster than 45 mph?.

RE: Bore kit still having high-speed problems!

HA! the speedo needle used to hit zero pretty hard and stop. This is about equal to 60 mph on a tomos speedo

RE: Bore kit still having high-speed problems!

oh, by the way, this kit didnt always do this. it was fine until about a month or so ago, when the old pipe broke in the middle, and i welded it back together. Since then it hasnt worked right, even with the new pipe.

RE: Bore kit still having high-speed problems!

Reeperette /

Tim, if you would, more details, exact definition of the noise, when and more specifically, where it occurs, and what plug you are using.

The only guess I could hazard would be the plug not vaporizing the gasoline at the right moment, and that would be either timing or plug type/heat range.

Do you have an advanced ignition on it ?


RE: Bore kit still having high-speed problems!

i think it has an electronic ignition. When i only use like 3/4 throttle, its about where the problem start, and theres a kind of tapping, like metaly hitting metal really hard. Then, if you floor it, it begins to pop and sputter, but not backfire. these problems only occur past 40-45 mph. my plug is an NGK, which is only a few months old.

RE: Bore kit still having high-speed problems!

I think it's your ignition. Some ignition systems have a spark-retarder on it, wich causes the sparkplug to fire a bit later to limit the revs. Is the spark is retarded too far the exhaust will be popping and the bike won't accelerate very good anymore. The retarding system only kicks in at certain revs, so you wont notice antything at lower revs. If you block the retarding system (mechanical retarding system as seen on old Honda's) or cut the earth-wire on the rev-limiter (electronic ignition) the spark wont be retarded anymore, wich will make the engine run more smoothly, make it able to do more revs and it'll stop the popping in the exhaust and lack of acceleration when it pops.

I recently had another ignition problem myself wich caused poor running and a popping exhaust. The high-voltage ignition coil was getting old (27 years old!) so I had to replace it and that was the end of the problem. I now have a coil mounted for a motorcycle, so it's of better quality that the original coil, it cost me $15.

RE: Bore kit still having high-speed problems!

Reeperette /

Replace that NGK plug with a Bosch Platinum, as well....NGK plugs have never worked well for Tomos, though they do allright for most of the far east mopeds, they've never done that hot in the Euro's.


RE: Bore kit still having high-speed problems!

yo, ivo. your probably right since you've helped me with nearly every other problem ive had with my many peds. However, if it is the ignition, why didnt this problem occur 3 months ago when it ran fine?

RE: Bore kit still having high-speed problems!

Well, I'm not absolutely sure about it, but it could reaaly well be the ignition. Those ignition coils are really weird when they break down. One day I drove to a friend on my bike and all was well. When I started my bike to get home it did start, but it ran very poorly. So those coils don't break down gradually, they just stop working propperly at once. My bike did still run, but the ignitiontiming was eratic, sometimes the spark came on time and sometimes it was too late. I tried adjusting the points to an earlier ignition, but the sparks that first came on time now came too early and if you run your bike with pre-ignition you'll really screw up the engine, the piston will overheat and deform and the sparkplugs electrodes will melt. I suggest you just replace the ignition coil for a new one (and check your points). If it wasn't the coil you'll still have the coil for when it does break down, eventually all ignition coils break down, mine took 27 years but they will break down.

RE: Bore kit still having high-speed problems!

like i said once those pipes leak it will wear at the cylinder and make a gap between the piston and it. hapened on my old bike. you need a new cylinder and piston DO NOT MESS WITH THE ELECTRONIC IGNITION!!!!!!!!!!!!!!!!!!!!!!!! if you fail to listen to me u will fuck up your whole moped. (plz excuse my french) well hope that helps.


RE: Bore kit still having high-speed problems!

Erin Lassley from Nebraska /

With my experience in air cooled engines involving VWs and my moped, plugs make a major difference. I have NGK plugs break down on me due to heat in the summer time. I think the guy that suggested Bosch Platinum is on the right track - a good high quality high dollar plug is a cheap and easy way to start diagnosing you problem.

A metal to metal sound is suggesting to me you might have detonation problems. This is referred to as 'pinging' in the automotive world and can suggest a problem with fuel either igniting by bad timing or simply from heat.

The next step would be to do as the other guy stated to ride it hard for a mile and with insulated gloves on, inspect the color of the plug. You say you had no problems 3 months ago. What were the ambient temperatures you were riding in back then compared to now? Temperature makes a big difference in how an engine operates.

I'm also curious that obviously since a bigger displacement engine is going to be turning much higher RPM's (due to no change in gearing in the moped to match the newfound engine displacement) - what is done to adjust the spark? Just like a small engine, the timing is fixed. Is it possible that for higher speeds, you will need to advance the spark ahead and run a faster idle? It will start harder too. This is why you'll find on some older engine designs (non-moped) that they have a spark setting for "start" and then a spark setting for "run" which was simply a 2 place timing adjustment. Today's modern automobiles and almost every mass produced engine today have constantly variable spark to match the various conditions, loads, and speeds the engine works under.

I'm under the assumption that a big bore kit should also include some kind of device or instructions that allows you to vary your timing. Electronic ignition would do it for you automatically.

Erin in Nebraska.

RE: Bore kit still having high-speed problems!


NOBODY can wave a magic wand and divine what the heck is wrong with your ped from over the net...especially when you don't help much.

Anybody you take it to to get it fixed will go through a process of elimination based on what you tell them.. and their experience.

You HAVE to pull the main jet out and look through it.

You HAVE to check the plug and report back on what you find.

You HAVE to check ignition timing.

So far you are not even sure if you have an electronic ignition or points.

Pull the dang ignition cover and LOOK at it !!... then tell us!

If it has points they prob just need to be cleaned and set.

And... "why would the ignition be bad now when it ran fine 3 months ago"?

Because ...SHIT HAPPENS !.... Just because I didn't have the Flu 6 months ago doesn't mean I won't have the Flu tomorrow !!

The "piston is too small for the bore" is most likely not true ... it was a new piston recently..right?...Then it is not the piston and bore UNLESS it had a seizure (or the bore guy was a total hack).. you said you had the piston and cyl off to look for what might be wrong... did the piston have ugly scuffs and scrapes on it's skirt ?... if it didn't .. then the piston and bore should be fine.

However.. I did see you said where it doesn't have an air filter.. and if you ride where there is much dirt your piston and ring life will be drastically shortened.

If I had your ped in my hands.. I would figure out what is wrong within 1 hour...(but I have all the tools too)... they are NOT mysteries.

When you asked before .. I told you twice. it wasn't the pipe.

RE: Bore kit still having high-speed problems!

ok, as for all that junk about "look at the plug! check the timing! chech your spark plug!" I DID!!! I'm not a moron on this subject, i already checked that stuff out. This forum is my last resort. I was hoping i could find kind people here that might understand my problems. I asked for help, not a load of crap from somebody who thinks they are a moped god.

RE: Bore kit still having high-speed problems!

Reeperette /

Basic premise of mechanics - check the simple things first.

You chose not to provide the details of your exact actions such as checking these things, and there is no logical way for anyone of this forum to have known whether you checked them or not - so we start from the ground up when giving advice, because not everyone who asks is an experienced mechanic.

That being said, if your only response to honestly and freely given assistance is an attitude problem, bugger off, we don't need it.

If you wish to consider help offered by people who ride these things every friggin day a "load of crap" go to your local cycle shop and pay THEM $60.00 an hour to tell you the same damn thing.

I've offered you all the assistance I am going to, guy...and as for that, some here have advised against speed kits because of the possible carnage factor, and some actually have speed kits that DO work, cause they have made them work - so your commentary on lack of skill would be extremely misplaced, but I digress.

In short, take your busted 'ped, and your funky attitude, and hit the road, preferably face first.


RE: Bore kit still having high-speed problems!

Ron Brown /


Not to be out done in the dumb question department. Did you check the tire pressure, odometer accuracy....oh yes, I almost forgot, did you check that the flywheel nut is a up tight as the one riding the ped?


RE: Bore kit still having high-speed problems!

Well that is part of your problem... If you think that was a "load of crap"... then you missed the good advice in there.

And if you had paid attention back when I told you "it wasn't the pipe" we could have found your problem before your crank destroyed itself.

But you know better.

All I know is us "moped gods" aren't sitting around with blowed up motors !... LOL

I'll buy it for......$50.... deal?

Harm and Destroy wasn't what you were supposed to do to yer ped !

RE: Bore kit still having high-speed problems!


RE: Bore kit still having high-speed problems!

John Purchase /

Well, alright Erin! Where'd you come from? I didn't know there were that many ped-smarts out yonder in Nebraska! :) (jk)

Glad to have ya!


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