got a carburetor problem on a 2-stroke - /o/ (#28505068) [Archived: 570 hours ago]

Anonymous
7/9/2025, 2:29:26 AM No.28505068
not it
not it
md5: c4238085716fe00260c1a080497cc6b5🔍
ok. I can't figure out why I cant get my carburetor tuned.

What the problem is is at 3/4 throttle, it is too rich. I have the needle at the leanest setting. it is the leanest needle Dellorto makes for this carburetor. The only other option is to lean the atomizer. But I did the math. The change in atomizer would be about 1/4 of the change 1 step of a needle change would give me in the area lost- between the needle and atomizer. There is no way this is going to be enough. I need about 4 or so needle change to make it run right.

The bike just has no consistency in the throttle change. from idle to 1/2 throttle, it has great pull, good power. But then I get to 3/4 throttle and it just bogs down. I had it richer before and it was even worse. I went up basically a total of 5 clip positions up on the needle (by swapping to 1. a leaner needle and 2. moving the clip position

This is the best I can think of to do to get it right now (besides the 1/2 step clip up position from the atomizer change) that I can get.

https://files.catbox.moe/bfr0du.mp4

Here was the same with 5 steps basically richer clip positions on the needle before.

https://files.catbox.moe/ldhbxp.mp4

Way worse as you can see.

Can anybody think of something I'm forgetting here that would make it do this, and be practically untunable?

Details: Honda Elite 2001 SA50, Dellorto PHBG carburetor. Some aftermarket exhaust, kind of small but free flow non-restrictive deal. Cone type air filter. Malossi reed/reed cage.

Pretty sure there are no airleaks. And the main jet is probably 1 or 2 sizes too small right now too since I just upgraded the cylinder kit. BEfore with the stock or a not as race-ey bbk I had the same problem.

And it seems before with this same kit previously or other bigborekit's I always have had the same problem.

Its been over 10 years but when I first got this I remember first getting it and flooring it first thing and it wheelied with me.
Replies: >>28505088 >>28505093 >>28505110 >>28505637 >>28505702
Anonymous
7/9/2025, 2:47:46 AM No.28505088
>>28505068 (OP)
Ditch the dellorto and get a Polini CP instead. And change the crank seals just because you probably should. Iirc, leaking seals can push air out but not let it leak in but don't take my word for it.
Replies: >>28505105 >>28505697
Anonymous
7/9/2025, 2:50:36 AM No.28505093
>>28505068 (OP)
your petal reed valves might be worn out and theyre essentially experiencing 'valve float' at the top end. Im pretty sure they still sell them but if not people have cut their own reeds out of steel shim stock iirc. I think the first video sounds like its running great and unless you have an AFR measurement you wont know for sure if its actually faltering at the top end
Replies: >>28505100 >>28505106 >>28505697
Anonymous
7/9/2025, 2:55:49 AM No.28505100
>>28505093
This too. I think in mine I have .4mm reeds and they work fine at high rpm.
Anonymous
7/9/2025, 2:58:37 AM No.28505105
>>28505088
>5
fresh rebuild. I did it right, measured the old ones before I took them off, on the depth.

I have the stock dio carb; changable pilot jet compared to the elite stock carb, too.
Ive done this before but had no success, swapping carbs
also have an arreche 21mm spigot and a 17mm flange carb. but as i said, never been successful with any of the carbs and this bike ever since as from what I can recall, since the rebuild.
>but i used hondabond ht
>I used the tools to install the crank with from honda
>Im running stock oil pump so no airleaks from there.
>manifold gets changed along with the carburetor if i swap to a flange carb so shouldnt be any issues.
the only part that is completely different is the malossi reed cage over the stock. there the same style tho. 2-petal.
Replies: >>28505106 >>28505111
Anonymous
7/9/2025, 3:00:05 AM No.28505106
>>28505093
ok so maybe the reeds might be worn out? I have a set of new malossi reeds, also I have practically brand new stock reed cage i could try too. I'll try it.. can't hurt >>28505105
and as i was just saying, its the only aftermarket part i cant vouch the best for. but everything seems like its no problem.. thats the one thing id cast the most of any doubt on
Anonymous
7/9/2025, 3:02:08 AM No.28505110
>>28505068 (OP)
OP here
for detail the first video, when Im going along, its at 1/4-1/2 throttle. when i rev it up a little at first i hit 3/4 then i quickly went up to full cause i passed a guy on the road; i was showing off.
then later i cruised along at 1/4 then went to 3/4 where it sounds boggy for a bit. then i floored it for a little. 3/4 is the problem. full to me seemed a little lean btw yknow but wtv.
Anonymous
7/9/2025, 3:02:16 AM No.28505111
>>28505105
>there the same style tho. 2-petal.
What thickness?
Replies: >>28505113
Anonymous
7/9/2025, 3:04:42 AM No.28505113
>>28505111
.30 carbon
stock is.. IDK. they're fiberglass.
Replies: >>28505140
Anonymous
7/9/2025, 3:18:28 AM No.28505140
>>28505113
Beats me. I think you're going to have to ask the Facebook gurus with this one. Sorry bro. I noticed you haven't mentioned anything about main jets. You did change those too, right?
Replies: >>28505299
Anonymous
7/9/2025, 5:44:25 AM No.28505299
>>28505140
They're possibly lean 1 or 2 sizes. It was floored on that video near the end of the throttle pull
Think reeds could make it 3/4 rich? Best guess I've got so far.
Anonymous
7/9/2025, 9:46:56 AM No.28505637
>>28505068 (OP)
Get on a stretch of long road, change your plug for a fresh one, then do a longass 3/4 throttle pull. Long as you can keep it at 3/4 throttle with the bog like miles long, get to the end and kill the bike and stop quick. Pull the plug and look at it.
Replies: >>28505694
Anonymous
7/9/2025, 10:11:48 AM No.28505655
Stupid question: Does this machine have a power valve?
Replies: >>28505694 >>28505933
Anonymous
7/9/2025, 10:55:17 AM No.28505694
>>28505655
like a 4-stroke? on the carb? no.
>>28505637
i can ttell its rich. i have richer needles and it bogs even worse with the richer ones. check the 2nd video in the Original Post. I was goosing it up to full throttle when the bog clears after the little rev up; it almost sounds like im letting off the throttle its so bad, but then it hits like its on another gear.. thats the main jet.

watch the second video. I could test by richening the 3/4 needle setting, and I have. its worse absolutely. idkwtf to do really. never read anywhere about something like this.

questions came to mind: do yamaha and honda use different carbs? are they interchangable? does honda and yamaha tune their bikes different and maybe the carb just can't be swapped, sometimes?

but this was negated when I found a honda motor jetted and running fine with a dellorto phbg 21mm carb, and the keihin 30mm carbs.

the reed idea, i read that it affects idle more than 3/4 throttle. but its osmething I could try. the reeds have about 5000 or so miles on them.

I dont know i really hate this. ive swapped cases even cause i fo9und one in a junkyard to see if that was any problem. but i remember i think pretty clearly that 3/4 never had a problem when i first got the bike, and it would even wheelie stock.

Any ideas? I usually always tune the main jet using a CHT guage. Temps hit no more than 350 at wide open throttle, on hills, everything, its the right main jet. i dont want to overheat, and any richer jetting when i do this, it runs bad you know.
Replies: >>28505717
Anonymous
7/9/2025, 10:58:23 AM No.28505697
>>28505088
its totally not lean tho. >>28505093
would this apply at 3/4 throttle too? valve flutter..hmm have to search wtf that is.

the more i screw with this thing the more chances i have of f'ing something up
Replies: >>28505718
Anonymous
7/9/2025, 11:10:08 AM No.28505702
chyna
chyna
md5: 1fcf417bb69ed8e412f079435110146d🔍
>>28505068 (OP)
assume you're a retard, did you check for air leaks behind the carb and at the crank seals? is the exhaust tuned to your engine, do you use the right air filter? are your reed valves clean or leaking light?
does it get enough fuel, is the float bowl height set right?
did you mess with the emulsion tube/is it worn out?
id get an air/fuel sensor kit from fleabay for 40ish bucks, weld a bung into the exhaust, and start from there.
always assume you're stupid and you missed something basic like not tightening the spark plug.
Replies: >>28505713
Anonymous
7/9/2025, 11:24:11 AM No.28505713
>>28505702
ive pressure tested for airleaks. none.
vacuum, notta, dont have one. wouldnt assume there is anything that would leak since its basic default gaskets like everything that would come on it stock. gaskets are new everywhere. its not lean. its rich. too rich.
when its on the stand and holding throttle at 3/4 it smokes big out the back..

its literally is not any at all lean. i just spent years learning and found an airleak from some chinese oil plug i got was splitting o-rings that they engineered to seal like a distributor on an old car, that slides into the head with an o-ring on a little carved out slot around the shaft, and verytime the plug was pulled back out, it was split.
never got any help on forums, and told them about this and noone said a single word. decided ok even tho everyone else uses these, this is fucked, your "gaskets" dont split. and who thought of this stupid idea o ring around the shaft.. replaced it with the stock oilpump and lean stopped

if your not going to believe me until i do it, well im not going to do it. i can test by changing to every single needle phbg's have to find out. I can see the smoke, hear the bog, hear it improve as i change jets. not going through that to prove it to you. i have 2 videos. want cleaner vids? i'll replace needles when it gets light out and make one with a longer hold at 3/4. its not lean, its rich.

this is retarded. its a bike like everyone else has. no leaks. im too damn rich. how the hell did it get so damn rich!?? I even have multiple carbs. was going to swap and try and put a new set of reeds in. gauranteed it wont work. ive done this before. i never get the pull this bike should get like everyone else.

heres a video of the 21mm phbg and a keihin 30mm on the same bike.

and theres not anything worng with the exhaust, just tune the carb/cvt. ive seen this same bbk on the stock exhaust...? exactly what would be wrong? https://youtu.be/kHSM6S8RTNE
Anonymous
7/9/2025, 11:26:07 AM No.28505717
>>28505694
No, like on the header very close to the engine's exhaust port. Running pig fucking rich at 3/4-wot sounds like symptoms of a stuck power valve. I wouldn't expect one on a scooter but I could easily be wrong. Also, a carb is a carb. As long as they're designed for approximately the same size engine you can tube for ideal running with jetting.
Replies: >>28505723
Anonymous
7/9/2025, 11:28:51 AM No.28505718
DSCN0275_01
DSCN0275_01
md5: 97190fc6169f2799cfc8e2e52db62c36🔍
>>28505697
essentially the reed valve isn't closing and shutting properly because the power pulses at that rpm outpace the valves ability to open and close causing it to instead hang open, remember, being a two stroke its all vacuum related. The easiest way to check for a worn valve is to hold the basket up to the light and check for a light gap like pic related.

Even a tiny chip can cause it to malfunction too. My DT175 had a 'wandering zero' problem where it was hard to start, hard to keep running at idle, it ran like aids and i couldn't adjust the idle mixture to compensate at all, and when i took the jug off to investigate there was a tiny chip in the valve. I replaced it, put the top end back together and it was like a brand new bike again.
Replies: >>28505720 >>28505723
Anonymous
7/9/2025, 11:32:40 AM No.28505720
autismpress (2)
autismpress (2)
md5: b41b27f6fdbb66013ac4f0a139b2da57🔍
>>28505718
this, assume you're missing something simple.
Replies: >>28505723
Anonymous
7/9/2025, 11:34:44 AM No.28505723
1723070113758690
1723070113758690
md5: d6445e5a14272aa40d5e93d0eaafd3e7🔍
>>28505717
i dont think this is part of this bike. its a single cylinder 2-stroke. and if your talking about heads like one on a 4stroke, this isnt anything but a combustion chamber with a gasket bolted to the top of the cylinder, with ports carbed out on the sides for exhaust, intake/boost.

just an exhaust connects off the back -side of the cylinder, curves around back and around to the side and out the back
>>28505718
yea but from what i've read, ive not seen it would affect 3/4 operation.

heres diagram of how the jet works on phbg. at 3/4 its controlled by needle and atomizer. it works on 1/4 up to 3/4. at 1/4 other things. not a problem there. theres 2 big parts of the needle that change for jetting. besides the clip you stick on at the cut outs along the top-blunt end of the needle, there is- the place where it begins to thin down to the pointy end. thats 1/4. that can change by swapping to another needle which begins "sooner" or "later". and the tip, which affects 3/4, by its thickness or thiness. also you can adjust it randmonly by moving the clip.
>>28505720
really.. must be cause i don't have any idea. its something maybe ive not tried before.
I have old vids from before with the same setup, when i had an airleak. it never ran well at top end either or had the smooth acceleration no matter, and always ran i faintly remember, a bit boggy at 3/4; but id have to look
Replies: >>28505728 >>28505739
Anonymous
7/9/2025, 11:39:23 AM No.28505728
>>28505723
i think youre throwing too much theory into the diagnostics process and overthinking the carb. Yes it doesn't make sense but its because another part isn't doing its job thats throwing the carb adjustment process out for a loop. Usually most people dont even think about carburettors outside of squirting brake cleaner through its passages after cleaning the bowl since they just work even if its not pinpoint accurate.
Anonymous
7/9/2025, 11:56:27 AM No.28505739
PowerValves
PowerValves
md5: 4e4e4c16a33f2d31e75c2799f9b57f66🔍
>>28505723
I am referring to a two stroke component. I didn't think this engine would have it. It's basically a cheat designed to give the engine two different exhaust port shapes to optimize for a wider range of RPM.
Replies: >>28505743
Anonymous
7/9/2025, 12:12:30 PM No.28505743
1751628651299933
1751628651299933
md5: 128cc4bb3d7373a6a34980e540ba5edc🔍
>>28505739
no, i dont think so. just a single oval-ish port, bolted down 2 bolts to the cylinder, 2 on the side to hold up the exhaust to the frame
Anonymous
7/9/2025, 12:30:33 PM No.28505749
If you have changed the induction geometry before or after the carb it can cause issues. I've had a 2 stroke with a restriction hole post air filter but before the carb. You take that out and it runs like rubbish and backfires out the carb.
Replies: >>28505798
Anonymous
7/9/2025, 1:33:25 PM No.28505798
>>28505749
ok so i just need to find which specific air filter dellorto says works with their phbg carburetor them im gold?

This doesnt make any sense, there must be some stupid engineering behind it, and explaining that would make more sense. so in that case, someone would have already figured this out, 21k other carb/filter combinations wouldnt have already worked on this bike, ,and make all these specifications in some upgraded/larger carburetor.

This is a very well known engine with tons of mods and tons of people using them, with no problem.
the air filter is basically a UNI filter. a foam filter with a plastic cap over it for rain and holes on the side all around for rain protection, made by polini. i just took it off out there and blew through it and felt no blow back.

And i just took the reeds off and checked them. not sticking up but, i dont think this matters very much but it had about 4-5 pin holes shining through one of the reeds. LIterally think my pressure testing popped through the carbon reed and that this would not matter but just a tiny bit and during the pressure test wouldnt have mattered for it since I capped it off at the carburetor spigot.

mentioning air flow. I tried to tune it with the airbox once first thing and it was impossible. way too rich.. So then I took off the airbox and it was wayy much easier to tune.. Should not be impossible tho. Bet without any air filter it will scream. Too loud tho, jeez wtf no filtering? I mean, why?

Maybe I will try the stock carburetor/airbox combo since that was made together with its intake manifold. 14mm carb
Replies: >>28505805
Anonymous
7/9/2025, 1:53:34 PM No.28505805
>>28505798
youd be surprised about how much an airbox can affect two stroke running, ive seen plenty of people put on pod filters on old two smoke trail bikes and suddenly it runs like ass because theres some black magic to do with its induction path and an airbox is actually 'tuned' to the motor for power pulses, back pressure and resonance. Absolutely you can retune a carb to accept an aftermarket filter but bikes can be really sensitive to it, and with a 50cc it'd make more of a difference. Engineers know what theyre doing sometimes

>holes in the reed valves
that would certainly affect it too, maybe try going back to the stock steel ones?
Anonymous
7/9/2025, 3:50:45 PM No.28505933
>>28505655
No power valves on these tiny things. It would be cool, though.