4 stroke with nt help please

[sissytrikerider]

Ok ive searched and didnt find my answer. I have a 4stroke that i have put a nt carb and k&n style air filter like the two strokes run. I have a 1 in exhaust header pipe about 18 in length in to a custom muffler i made out of stainless 2 1/8 in exhaust tubing about 12in long. After trial and much error i have the bike running i have a 69 main jet and the needle clip set 2nd from bottom. It sounds nice, idles fat but responsive and plug burn on 3/4 throttle is nice and chocolatety.
But my issues start there while tunning durring all testing once i hit 3/4 throttle it dies, no matter jet size or needle clip setting. Now from what i under stand the needle controls idle-3/4 throttle an the main jet is 3/4 throttle-wot.i have a tach, so im setting checking main jet burn at 7100rpm range. Once i crack that throttle all the way she dies. I plan tomorrow to try some more fine tuning, and some iridium plugs just for a slight improvement.
This setting of a fat idle and main jet size (69) is the best results ive had up on the kick stand. Now on the road its very flat and slow to speed, where im thinking that extra 1/2 in of throttle twist would come in handy.
Any suggestions???

 

[Venice Motor Bikes]

The stock NT carb needs to be jetted a little larger to use on the 49cc HS engines.

The engine dying like that when you fully open the throttle is because there isn't enough gas in the air flow.

 

[sissytrikerider]

I have a jet kit from 60 -80 and from what i can tell the stock in the carb was a 60(no markings, just comparission into light ). So with the needle in the middle (out of 5) i went from range 60-80 in increments of 5 -65,70,75,80 70 seemed about right so i tried a 69 and liked the color a little better, so then next i bumped the needle clip up and down one from middle and tried the 65,70 and 75, with the same results putting me again 68/ 69. I too thought the kill was due to not enough fuel but i got the same results through out range and it ran best by riching the neddle clip to 2nd lowest. I plan on doing a little more plug chops tomorrow, i jut ran out of plugs, and sand in the plug restorer (a little pnumatic self contained blaster you pop a plug end into and hit the button, fresh plug) i even set the bowl height at 20 mm due to not being able to remove the bowl gasket. Is the maybe a better height for the 4 stroke. I got that from the thread floating on that other site everyone directs us to lol. It calls for 22mm no bowl gasket. I dont see that affecting much off mm or few, but mine was off to start.
Am i right in the rpm range 7100 7300 playing sorta safe on the high side. Thought i read the 142 4stroke maxing out at 8000?

 

[Venice Motor Bikes]

I don't do plug chops, that doesn't work well on these little engines... instead jet it by 'feel'.
You want it to have the largest jet possible while still running good.

Also, here's a great thread on rebuilding the carb... http://motorbicycling.com/showthread.php?t=302

 

[YesImLDS]

I agree with vmb. Richen her up and give it a test. Sounds like you are leaning out up top.

 

[Agreen]

Flip the choke on when you get ready to hit 3/4 throttle. If it doesn't die, open the jet up more and drop the needle to compensate at partial throttle.

I'd spring for a pz16 carb if you can make an intake manifold for it. They have a separate idle jet, which is adjustable with a screw. They also have a main jet with a needle. Much better carb in my opinion. The intake also seals with an oring against the flange. Much better than relying on the NT's metal-on-metal gasketless seal. If you can't make one, send me a pencil rubbing of the HS intake flange and some pictures. I can fab one for you for the cost of materials and shipping.

 

[sissytrikerider]

Green i will research that carb.
I did some more testing and up to 80 jet. Wot on kick stand, almost on a test ride. Will write more tomorrow, as i wrote up a post twice for my stupid tablet to log me out and loose all i wrote.

 

[Venice Motor Bikes]

Don't test in on the kickstand! Get on it & ride it so you can really feel what it's doing.

 

[sissytrikerider]

I do both. I see on the kick stand is different. I actually got wot on the stand at the 77 jet but not so on the ride but close. So i went to the 80 jet and a little closer. So after sum hunting and sourcing i came across the smallest drill bit, to the eye it looked close. Took the 79 jet and drilled it out. Enough resistance to feel its bigger then the 80 but went thur with ease. Put in an all back together, hit wot a few times and died, assumed no need for a test ride as the jets to big, ok ill get a micro bit set the next day. Picking up tools and cleaning up the garage i find the "primer" button laying on the floor............ causing a air leak and not giving proper mix.
So that suckers getting so gas proof epoxy and sealed up cause ill never use it. All it does is push down the float and open the seat to allow gas into the bowl.
So today i will get a bit set cause i doubt im that lucky with the drill bit on hand but retest for proper results. Plus i still want to try one of those plugs kc raves about (ngk 7544) Found them on both ends of town that i will hit today at work.
Ill get some pics togethers also. I still need to finish my other build thread. Heres a few no motor, tested bicycle functionalability . As long as i dont break a bicycle chain im confidant i can pedal anywhere home if necessary.

 

[Agreen]

I'm confused.

An 80 jet is the smallest one. It goes up in diameter as you go down in number. A 61 jet would be the biggest.

Unless it's measured in mm. Is it a 0.80mm jet? If that's the case, the diameter of that jet would be 0.0315". But an 80 jet is 0.0135".

What size drill bit did you use?

 

[sbest]

The primer button hole does not need to be completely sealed, air getting in there is not a problem.

Most 2 stroke carbs are not directly interchangeable with 4 strokes, especially piston port 2 strokes. It has to do with intake pulse, messing up much more than just the main jet. If you don't know how to tune all those systems (pilot, emulsion tube, cut out, etc) you would be wise to pick up a proper 4 stroke carb.

Steve

 

[YesImLDS]

The primer button hole does not need to be completely sealed, air getting in there is not a problem.

Most 2 stroke carbs are not directly interchangeable with 4 strokes, especially piston port 2 strokes. It has to do with intake pulse, messing up much more than just the main jet. If you don't know how to tune all those systems (pilot, emulsion tube, cut out, etc) you would be wise to pick up a proper 4 stroke carb.

Steve

This is a very popular modification for the 4 strokes and should work just fine

 

[Agreen]

This is a very popular modification for the 4 strokes and should work just fine

Not sure what the benefit of it would be. The NT is a garbage carburetor in my opinion. It has no idle circuit, it's only 14mm, and it has sealing issues. I switched to a pz16 on my 48cc 2 stroke and never looked back. The pz19 works like a dream on my gx200. They crank faster, idle better, and have better power with them vs their respective stock carbs.

They do work, and I'll give you that. They're relatively cheap, but so is the pz carb. The NT is also very simple, but that's also a drawback because it makes tuning difficult.

 

[sissytrikerider]

Well today (just an hr ago) put the stock carb on and its still very flat under load and no top end power, so im thinking i might have a gearing issue possibly? But heres some pics.
I do like that pz carb and might be a thought if i cant tune this one.

So what i have is the 4g tranny which i believe is the 100 t configuration, the standard sbp shift kit back to a 3 speed hub with a 18t sprocket. Now i have to find that nifty site that explains how to figure out my gearing.
All my testing has been in first which is .75 the additional gears are 2nd 1.0 and 3rd being 1.33

Last pic is just to show we dont only build bicycles in south buffalo, and that just the tip lol

 

[sissytrikerider]

Duh forgot to upload last pic

 

[Venice Motor Bikes]

I also have to agree that the NT carb switch works extremely well with these 49cc 4-stroke engines.

I wish you were near Los Angeles so you could bring the bike to my shop... I'm sure I could get it running good if i had it in front of me. :/

 

[sissytrikerider]

Well after the stock carb with no guts either im thinking the problem isnt the carb. Its fresh ethnol free fuel. I wont even put that corn in my silverado with a 6.0 on 35s.
I had this same motor on a previous bike (diff. exhaust) with a shift kit and ran excellent so im familiar with what performace should feel like. Ill figure it out , maybe with a little help and this will be a thread we all point to for the same problems im having.
So one other thing i played with was can anyone tell me the correct spacing for the magnito? I had it off, set it to the thickness of a beer case(didnt have any matches, see beer always solves the problem) and i set the valve lash to some thread i saw here. Maybe .06, .08 ????.
I did also notice a high rev diffrence between carbs. Stock hits 6000 and nt was hitting 9s on ocassion which i bet isnt good.

 

[Agreen]

Never had an issue with fresh E-10. So long as it's not over a month old.

How's the spark plug? Maybe it's worth a shot to replace it? If your valves are set right, the carb is probably not the issue (either one, really) then I'd start looking at ignition. And how is the compression?

Was it dying, or just low on power?

 

[sissytrikerider]

Ok sorry . Busy busy busy. I made it to the car show memorial day weekend, some cook outs and a bday last weekend now im ready to figure this think out. After talking th sbp the say that the gearing sounds correct, they recommend a 19t on the rea9 im running a 18 currently so that may not be the issue. I still ordered a 25t for my rear to try just for my own curosity mostly. I am going to the hf and grab a compression tester and will report my findings. I am also going to recheck thevalve lash just as a pecaution.

Spark is good as far as i can tell. I was doing plug chops so its fresh, ill clean up the used ones for spares and when warming up the bike to do a fresh chop. But like i mentioned i did play with the magnito pulling off cooling covers and cleaning the motor. Does anyone know the proper spacing?

 

[sissytrikerider]

And what kind of compression reading should i get? I got 30 which sounds low to me.