TT250 hiccup

[moparrob]

Originally Posted by Ariel Red Hunter

Hiccups.

Aha.

[Ariel Red Hunter]

Originally Posted by moparrob

Aha.

I should have said hiccups when running at a steady speed. A roll-off hiccup is caused by a too rich Main jet.

[moparrob]

Well I just put some 117 jets in and it seems to be running better for the short ride tonight. This was achieved by drilling out the stock 108 jets with a .046" drill bit, yielding 1.170 mm = 117 jet.

For those interested in making their own new jets the following sizes apply:

.043 = 110 jet

.044 = 112 jet

.045 = 114 jet

.046 = 117 jet

.047 = 120 jet

I will check it out on a longer ride this week and report back. Fingers crossed.

[rojo_grande]

I had a similar hiccup at 3/4 to WOT with the stock carb. I'm at ~5,500 ft and trying to jet for 8000+. The stock jet is a 108. I got 105 down to 98 trying to get lean enough. The bike ran well enough but had an inconsistent sputtered/hesitated at near/WOT. Tried a number of different jets, idle screw adj., and needle positions. Never really resolved the issue until I swapped to the Mikuni carb everyone else is running. I believe I'm using a 100 main and 25 slow jet (haven't looked at it in a few months). Have the after market exhaust, de-smogged, stock intake/air filter, stock gearing (17/50). Still not getting the advertized top end speed but I am getting up to 64 - 65 MPH per GPS (190# rider + gear) and does pull hills in top gear much better.

Rojo

[Weldangrind]

One of our fine members shared a trick with me. Once you've dialed in the jetting combo for your bike, write it on the bowl with a Sharpie. It's especially helpful if you've been drilling jets, rather than buying them.

[mtiberio]

Originally Posted by Weldangrind

One of our fine members shared a trick with me. Once you've dialed in the jetting combo for your bike, write it on the bowl with a Sharpie. It's especially helpful if you've been drilling jets, rather than buying them.

if you drill a jet, take a file and mark a line through the stamped number...

['16 TT250]

Originally Posted by moparrob

Well I just put some 117 jets in and it seems to be running better for the short ride tonight. This was achieved by drilling out the stock 108 jets with a .046" drill bit, yielding 1.170 mm = 117 jet.

For those interested in making their own new jets the following sizes apply:

.043 = 110 jet

.044 = 112 jet

.045 = 114 jet

.046 = 117 jet

.047 = 120 jet

I will check it out on a longer ride this week and report back. Fingers crossed.

Drilled to 117 will not flow the same as a 117 jet. If it works for your engine it's not a problem, but everyone should know that buying a 117 is unlikely to yield the same flow as one drilled to 117.
BTW, it's a jet not jets.

You can't suck all the fuel out of the bowl unless there's a restriction not allowing fuel in, at that point it would bog out and not just hiccup. If the float level is low or there's any restriction in the fuel delivery to the carb there's a possibility that the level could reach a point of being just a hair off between good and not good giving inconsistent mixtures so I'd check them just to be sure. Unlikely to be the air injection. Raising the needle along with a bigger jet might make the mid throttle too rich. Once you determine the proper main jet I suggest doing a mid throttle cruise and reading the plug.

[moparrob]

Drilled to 117 will not flow the same as a 117 jet. If it works for your engine it's not a problem, but everyone should know that buying a 117 is unlikely to yield the same flow as one drilled to 117.

I disagree completely. If the size of the orifice is exactly the same size between two jets the laws of physics mandates they will flow exactly the same volume of fluids. The jet drill size chart above is not my own compilation - it comes from experienced motorcycle tuners and I simply used and applied the info contained therein.

BTW - my reference to 'jets' refers to the fact that I have two TT250's and I needed to drill 2 jets. My command of the English language is sufficiently developed to the extent I am able to distinguish the singular tense from the plural tense.

[Ariel Red Hunter]

Originally Posted by '16 TT250

Drilled to 117 will not flow the same as a 117 jet. If it works for your engine it's not a problem, but everyone should know that buying a 117 is unlikely to yield the same flow as one drilled to 117.
BTW, it's a jet not jets.

You can't suck all the fuel out of the bowl unless there's a restriction not allowing fuel in, at that point it would bog out and not just hiccup. If the float level is low or there's any restriction in the fuel delivery to the carb there's a possibility that the level could reach a point of being just a hair off between good and not good giving inconsistent mixtures so I'd check them just to be sure. Unlikely to be the air injection. Raising the needle along with a bigger jet might make the mid throttle too rich. Once you determine the proper main jet I suggest doing a mid throttle cruise and reading the plug.

I don't have a dog in this fight but you are correct. A factory made jet has transition cones to avoid the hard edge that comes with a drilled jet.

[moparrob]

I suppose if you want to split hairs down to the transitional surface of the tapering cones of a 108 jet drilled to 117 vs. a standard 117 jet there probably is some infinitesimal difference on that surface. However, there was already a taper on the 108 jet and the orifice was only opened up .004", about the size of a hair.

Anyhow, I'm not looking to debate something which I really have no expertise in. I'm just searching for practical answers to get an inexpensive Chinese motorcycle to run smooth without hiccups.

All positive input is appreciated.

[2LZ]

I've drilled tons of jets over the years without mishap. I drilled the main jet in my X-Moto (163FML CG 200cc) and it cleaned it up nicely.
Worst thing you can do is go too big. Can't cut the lumber longer.....

['16 TT250]

Originally Posted by moparrob

I suppose if you want to split hairs down to the transitional surface of the tapering cones of a 108 jet drilled to 117 vs. a standard 117 jet there probably is some infinitesimal difference on that surface. However, there was already a taper on the 108 jet and the orifice was only opened up .004", about the size of a hair.

Anyhow, I'm not looking to debate something which I really have no expertise in. I'm just searching for practical answers to get an inexpensive Chinese motorcycle to run smooth without hiccups.

All positive input is appreciated.

Aside from the transitional, the drilled hole is unlikely to be as smooth as a factory made one and can be crooked or otherwise imperfect. I've seen jets drilled and go leaner. The other caveat is that using a .046" bit doesn't guarantee a .046" hole. Bit and chuck quality, how the jet is secured, how the drilling is executed, whether the hole is de-burred, etc.; all can lead to different results.

I'm not knocking the practice, I've drilled fuel and nitrous jets many times, it just can't be reliably compared to a factory made jet's flow potential. This doesn't matter since you're tuning for yourself, it's just not a reliable recipe for someone else to follow.

['16 TT250]

Originally Posted by 2LZ

I've drilled tons of jets over the years without mishap. I drilled the main jet in my X-Moto (163FML CG 200cc) and it cleaned it up nicely.
Worst thing you can do is go too big. Can't cut the lumber longer.....

You can fill it with solder and re-drill. I don't completely fill, just coat the hole with solder. Not something you wanna have to do, but when you're in the desert for a 5 day trip nowhere near a parts store some solder might be your only option. Luckily someone brought a set of small diameter hole files, turns out a guitar serves multiple purposes.....well, at least the strings do.

[Weldangrind]

I was recently trying to drill out a slow jet with a 61-80 numbered drill set (and a pin vise), when it all went pear shaped on me. I couldn't make any sense out of what was happening with the motor, since it was behaving like it was getting way more fuel than I was providing. It hit me a few days later; the drill bits were incorrect from the factory. I had drilled the jet out way too far.


I took each bit out and measured with a vernier, and discovered that of the 19 bits in the index, I only had six sizes (which were triplicated). I've learned to measure the bit before I happily drill away, so I don't unwittingly go too far.


I didn't think I'd have any success in filling a slow jet with solder. Since I had another virginal jet, I drilled it to the correct size (according to Mr.Vernier) and the motor was happy.

[Ariel Red Hunter]

Originally Posted by moparrob

Drilled to 117 will not flow the same as a 117 jet. If it works for your engine it's not a problem, but everyone should know that buying a 117 is unlikely to yield the same flow as one drilled to 117.

I disagree completely. If the size of the orifice is exactly the same size between two jets the laws of physics mandates they will flow exactly the same volume of fluids. The jet drill size chart above is not my own compilation - it comes from experienced motorcycle tuners and I simply used and applied the info contained therein.

BTW - my reference to 'jets' refers to the fact that I have two TT250's and I needed to drill 2 jets. My command of the English language is sufficiently developed to the extent I am able to distinguish the singular tense from the plural tense.

H-m-m, I thought the reference to two jets was to the pilot jet and the main jet. Thanks for clearing that up.