Potato's PK ver. 2.0 - PK130 "Polish rocket"

[Jimmy D]

Love it - but that engine stand I wouldn't trust as far as I could throw it!

[thezapper]

The carb shouldn't leak like that, any chance you can get your hands on a different carb? a kiehn pwm or pwk would be a nice addition, they are super easy to set up too. it seems to me perhaps the float needle be acting up. You can lean up the idle jet abit to see if that cleans up the stumble, seems a bit rich.... but like you mentioned about the inlet timing being to aggressive that could have some effect on it loading up at idle... + 1 with ditching that stand, weld it up so it doesn't flop all over...

[potatopl]

The stand was intended to be foldable for travel reasons (I'm working abroad, and if there is a possibility I take my "toys" with me). The pivot option if useful when assembling the engine. I forgot it also should be rigid, if I want to use it as a test station and kickstart the engine a lot. It also was the first thing I've welded up in my life so don't be suprised it's a bit $hitty. I'll fabricate a more solid one when I come home, I promise, but now I have only this one.

Finished reading this great manual for tuning dellorto PHB carbs, and now I know i did't start the jetting process correctly.
www.thisoldtractor.com/mg_manuals/dellorto_manual_a_guide_1.1.pdf
I'll start from the scrap, with the new knowledge I have.

First of all, the float height was inproper. Too high fuel level in the bowl + vibrations caused the flooding. The floats on PHB carb should be set between 23,5mm and 24,5mm.

I hope the smoke comes from excess of the fuel in the mixture, not from damaged simmering and gear oil additive.

Will keep you informed about the jetting progress.

[Jimmy D]

Ah, didn't mean to knock your welding skills matey, I have none!

[potatopl]

Had another try on the idle setting, but no good news.

The float adjustment helped a bit with flooding from the overflow channels. The engine is still shaking quite much and it overflows from time to time, but I'm not sure if it's caused by the needle valve sealing badly (visual check of the rubber needle tip seems positive), or the vibrations of the engine on the stand. I assume, that when the engine is bolted down to the scooter, the total mass increase will lever the vibrations significantly.

Main problem is the blowback at idle. The idle speed has to be quite high in order to keep the engine running. The petrol that is pushed back from the manifold condenses on the slide and is dripping down. It is then sucked back causing extra rich mixture. There is no visible response to the idle jet size or air/fuel regulating screw. I can totally close the screw, which cuts out the fuel added to the idle circuit, and the engine is still running at idle. I Belive, that it's because so much petrol is condensed at the slide and sucked back and forth, that it does not require any more from the idle jet.

The problem should vanish at high rpm's, however I'd prefer to keep the idle in expense of some peak power. The engine was supposed to have a sporty spirit and good acceleration, but I wanted rather a street than a track racer, so I'd need it to run on idle and mid revs as well in the traffic or while waiting at the lights.

I think I've gone a bit over the top with the inlet closing time, I've opened the sealing pad to the max as most of you do, but didn't take into consideration the pad length. This, together with smaller carb, worse pipe and not so aggressive port timing has put me in this place. If you want to perform, you have to go for the max with in all areas - mixing "sporty" components with "race" timings not work out

I see 3 options now:
-keep it as it is, and loose the idle
-remove the pad completely and go reed
-open the casings and close the pad partialy with JB Weld

What do you think?

Since I still have some time and

[thezapper]

Go with a reed valve you wont be disappointed, no more setbacks.... just install and the motor will run better but you would still have to open up the motor and remove the pad, or the massage the crank to let the gasses flow, and as far as the carb goes im not completely convinced that the float circuit is working 100% in one of the videos of the close up of the carb, fuel is seeping out of the vents, with the float needle seated (closed) and the engine level I don't see how this can happen? other than something be wrong there, please just try a different carb, again keihn are very nice to work with perhaps you have a defected unit.... just trying to help you out...

[potatopl]

The overflow from the front vents is not a problem anymore, it was caused by bad float height and flooding the bowl.

Going reed will definitely solve the blowback problem, but it's the most expensive option since I'd need to buy new manifold and carb, for which I don't have the budget right now.

I'll source a PHBL24 from my collegue and will give it a try.

[potatopl]

Got the 24mm carb from my friend, I'll try the bigger slide cutaway.

I've also found the 3-stud reed manifold that goes with my 25mm carb rubber connector - I thought Polini makes only versions for 24mm clamp fixing. I might go the way Zapper suggested.

[potatopl]

Didn't write anything as there was nothing to be proud of
In fact I've made a few mistakes I'm ashaed for, but will say them loud so somebody else can learn from them.

I've swapped the new engine with my mate. Dropping the old motor didn't take more than an hour. My mate was curious about the condition of the old motor, so we've stripped the top end to find a lot of coke (unfortunately the black one ), and dying rings. This explains problems with cold start and idle running. But I've got a brand new build 130cc engine, so why to care about 75cc old shite...

Putting the new one was not that quick though. First, there was a lot of fiddling with connecting all the cables and their regulation.

Then we had a puzzle with the wires from the stator to the main loom, although there were only 3 of them, they were not the original ones, and their colors were not

standard. We had to take off the flywheel to identify the cables.

The DIY intake manifold was a bit too long, so the carb could not be mounted. We had to cut the pipe, so we've stuffed a ball made of paper towels inside for

protection, cut it with flex, and sucked all the debris. The carb could now be mounted, but only without a filter. The angle of the manifold made the carb be

positioned just in front of the joining of two halves of bodyshells, leaving no space for the filter.

After we've overcome those problems we tried to start the engine. It did not want to start after few kicks. We've checked the spark and it was OK. With or without choke - nothing. Decided to bump-start it - nothing. Then after about hundert kicks it started, but would die when throttle was added. When the exhaust spitted a piece of paper towel, we knew what was the problem:

MEMO 1: Remove all plugs before fitting the engine!

After short test ride I've stopped in front of the garage to set up the idle. Then suddenly the flywheel started to hit it's cover. I've immediately turned off the engine, but it was too late. The flywheel nut got loose and shreaded the woodruff key and the slot in the cone.

MEMO 2: Always make sure you torque down the nuts properly.

After removing the flywheel I've kicked the engine a few times and felt that the piston is being blocked a bit. Decided to strip down the engine and look for possible damage inside.

At this point I wanted to put the old engine back in, but forgot that it's already stripped So there was me, an owner of 2 scooters, 3 engines - non of them working.

MEMO 3: Always keep at least one scoot running while working on the other one or you end up riding a cycle.

Fortunately my mate has put the old 75cc engine back for me while I was at work abroad, and I've put it back when I came back, so at leas I've got something to ride on, but I feel the scoot beaing weaker and begging for rebuild.

I've also stripped the 130cc engine, luckily no damage inside (I don't know where did the "blockikg" come from though). The key slot in the crank is also not that bad - I've removed the burr with a file and lapped the flywheel again using grinding paste. I will wait with the swap untill I finish rebuilding my PX.

By the time I've bought an XL2 frame with tank and Piaggio Sfera forks with disc brakes. The frame doesn't have papers and is rather molested, but I'm planning to make sort of cutdown-rust-racer or crosser from it.

[triffid]

Good to share Potatopl, you won't be the only one on here with some embarrasing rebuild stories

[jonnysnatchsniffer]

i reckon the rich carb is most likely from fuel not shutting of properly, as i had exactly the same problem, that and the jets were too big, i too have taken my inlet pad out to about 0.8mm - 0.5mm in some dodgy places, and my crank has been cut, giving 215 degrees and even with racy settings and a 1kg wheel it ticks over lovely, if its to rich and the pilot jet is smaller than it really should be, around 40 on phbl should be on the lean side and 60 rich, but if fuel is still geting past the floatvalve, fuel will then flow up the pilot jet regardless of airflow over it making it rich, some people even set float height to make this happen, im well below the floatheight of the keihin just due to the fact that at its normal height it just dumped fuel everywhere and down the inlet, this made for a very rich ride, ok past half throttle , but shit upto
i just dont reckon its the inlet,

[potatopl]

I guess you've nailed the problem JSS. I've just turned the engine on a stand again yesterday evening, and after 1 min of running the carb has overflown and the fuel came out of all possible holes

Now the question is why is that happening, and how to prevent it?

-I've checked the rubber tip of the needle valve and it was ok, the brass inlet (jet?) oth the needle valve also looks ok
-float height was checked and adjusted according to dellorto manual

Possible causes and solutions:
-vibrations of the engine on a stand are opening the needle valve - if the engine is put into the frame, the intertia of the connected system (engine+frame) will be bigger and it won't shake that much??
-the length of the fuel hose is too big and the fuel in the hose creates too big pressure, that the needle valve can't seal - shorthen the fuel hose
-the float height is set incorrectly - the level of the fuel in the bowl is too low which causes not enough pressure on the needle valve from the bottom - adjust float height

Any other tips from you guys?

Aug 8, 2014 15:51:10 GMT jonnysnatchsniffer said:

im well below the floatheight of the keihin just due to the fact that at its normal height it just dumped fuel everywhere and down the inlet

That higher/lower float is a bit confusing. You normaly check the float height with the carb upside down, so if you set them to be "higher" in this position, you actually make less fuel to go into the float bowl. Can you specify, how did you set the floats?

[jonnysnatchsniffer]

how about rust ? that was part of my problem

[henri]

how about back to basics ,stick the float in warm water an look for bubbles ,as it only takes a few drips of petrol to stop it floating an working the valve properly ,an are ya sure its moving freely an squarely on its pivot ,youve set the height so much you'd prob of noticed any mis-alignment.
an connect the carb to remote tank an hold over a bucket with the bowl off an see that the needle stops flow with finger pressure holding the float up,tho mostly if i suspect a needle valve i just throw a new one in ,but doing this if needle valve stops flow hold it shut for a min or 2 an see if fuel is bypassing it some how ,never seen it but have heard of a carb with a casting flaw that allowed fuel into bowl bypassing the needle valve .H

[jeanshorts]

I had that. Casting slag on the bottom of my float bowl "spearing" the float when I hit a big bump. Take apart the carb , clean it prob solved till I hit a bump. Must've cleaned the carb 50x before I noticed 50 little nicks in the float and figured it out.

[jonnysnatchsniffer]

i just kept bending the tab till it didnt flood, i done what henri suggested and took the bowl off and used the float manually to see when it shut off and aimed for 1/2 full bowl, the good thing about the keihin is you can take the bowl off without loosing the fuel, the 1/2 full is because of the float and jets that are in the bowl, be carefull that you dont make it run too lean when on wot
if the valve is letting by, you can get some toothpaste on a cotton bud and twist it in the valve to flatten it off, its like a very fine grinding paste
nobody really pays attention to float height but ive been told its very important, it can affect running at all throttle positions which is why manufacturers of one make will give a different height for different models, most bikes have a fuel pump that only works when used so fuel flow to the carb will stop when not running, as our wanky scooters are gravity fed fuel will flow all the time its turned on and a float height for an rs aprillia will be different to that of a gas gas

[henri]

yep def agree with johnny ,mostly, on standards i just set float by eye , the height of fuel in bowl affects the height of fuel in jet's ,on a tuned motor the variation can affect mix enuff to cause bogging or lean-seizer ,on standards there forgiving enuff to survive ,tho i think gravity feed is best when it will deliver enuff,less to go wrong ,unlike vacumn pumps which when diaphram splits pore fuel into inlet ,like vacumn worked taps, or mechanical pumps that under feed coz of week springs or overfeed coz of wrong springs .guy i got my car off had re-built the mech pump with the cheaper 6psi kit ,shud of had 3psi type , mpg was down to 10-12 coz of fuel spraying round engine bay ,mobile bomb scene, went lectronic an 15000 miles later still sweet.
i think ya could try johhnys toothypeg paste trick ,but maybe use old needle valve an then rinse an replace as it will/should have the right profile still.does this flooding only happen when scoot is running or also when not-running ,as if only when running ya might be on right track with the vibration theory ,weigh the stand down with weights/sandbags/fat mate an see.H

[potatopl]

Thank you all for your tips! I'll disassemble the carb again, clean it and check the valve and float as you suggested.

THe 75cc engine was dying, so decided to put in the 130cc, just for now I've put the old SHBC 19.19 carb.

The first jets I've put are idle-42, main-88 + polini airbox without filter. It idles a bit high, but it's steady. When throttle added it doesn't rev up smoothly (can't say if it's too rich or lean), but goes down with rpms nicely. After the test ride I can say it accelerates fine on 1st and 2nd gear, a power boost starts above 5krpm and you can feel it On 3rd it could not go above 7krpm and on 4th it struggled to accelerate. I guess it's all because of the small carb. I hope everything will improve when I sort out the 25mm one.

[henri]

the symptoms of not reving out over 5-7 k is fuel starvation or low jets for main ,the high idle suggest a lean mix on idle circuit or air leak, have ya still got the flooding issue ,reckon youve got more than 1 problems simultaneously, its a back to basics moment , start from beginning an take nothin for granted ,doubt everything even your own recent work, prob wont actually find problem but will cure it ,1 of the great unknowns eh, dont matter if it goes away , H

[potatopl]

I've sheared the flywheel key for the third time and damaged the cones. Swapped the motor back with the short stroke one.

In the meantime, I bought a 3-hole Malossi reed manifold from revdevil on here. The top lad has thrown into the package a Worb5 crank which he didn't need anymore.

When I finally find time I need to open the engine, remove the sealing pad, stick the new crank in and cose it again. Will also use another flywheel this time.


I've also bought a battered XL2 frame with tank for some silly money from a friend. I've cut out the rotten and jagged edges. It still needs straightening, welding and painting but when it's finished there will finally be no more engine swapping (which pi$$es me off a lot).





I would be VERY happy if I manage to finish this project by the end of this year, but we all know how it usually ends up.