Thu May 20, 2021 4:24 am

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Thu May 20, 2021 4:24 am linkquote
So, I need some jetting help.

This is the bike:

PK100xl
Malossi MHR 132 aluminum direct reed
Malossi MHR expansion
Port times 122 /176
VHSH 30mm.

I had a run on an inertia dyno and this was the result. I seem be be rich, then lean in the mid rev range (at both 1/2 and full throttle positions). Although the bike goes well enough both these elements can be felt on the road, and I feel it could be better. Here is what the bike was jetted with on the dyno
Main 150
Needle U16 (3.5 clips from top)
Pilot 42
Emulsion tube 48
Atomiser DP265

Since then I have tinkered. Bike was definitely rich on idle or 1/8 throttle so went to 42 emulsion tube and 40 idle jet. Pick up definitely better

Aso have tinkered with a richer needle. I had a K21 and on the same clip setting it seems much better mid range. But I how have a slight stutter pickup on transition from 1/8 to 1/4 throttle. I'd like some advice on how to jet this engine to be the best it can. Willing to do the work myself and jet it on the road.
thanks
Olly





Thu May 20, 2021 8:05 am

Jet Eye Master
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Thu May 20, 2021 8:05 am linkquote
I would imagine a PK with 20bhp is a lot of fun. Does it get to 9000rpm in 4th?

Do you have an rpm and CHT readout fitted?
How many degrees is the timing strobed to? Is it variable/which one?
What is the squish clearance?

VHSH is a great 30mm carb. Many would say the best. Get these jetting issues sorted and it will come to life. You may not appreciate the difference to other cabs until jetted correctly.

U16 and K21 are way different but I would think the K21 should be the first to try and set up.

If you want me to talk you though it will take a while.
Thu May 20, 2021 8:31 am

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Thu May 20, 2021 8:31 am linkquote
Yes please!

I would love for you to help - I've seen your advice on other threads and I really want to understand how this works.

I built this motor myself- a Labour of love - I have made every mistake in the book. But we are here now and yes 20hp in a PK is great, but I just feel it has so much more potential!

Squish is 1mm Malossi recommends 1mm

Ignition is Vape Sport. It has a funny curve (advances about 2 degrees from idle to about 4000 and then retards) and I set it up a while ago and it probably needs checking but the idea is that by 9000 RPM we are at 15 or 16 degrees, so that's what I think I have.

Crank is 51/105. Transfers are matched to the cases via the 8mm spacer.

Gearing is long 1st, long 2nd and short 4th. Not revved it out on the road in 4th yet as I live in London, so the opportunity is limited, but it got there no problem on the dyno (I'll post the in gear chart soon).

I really want to get on top of this jetting so I'm all ears starting from the beginning! thanks

I will be fitting SIP Speedo this weekend so will have rpm and CHT functionality
Thu May 20, 2021 10:55 am

Jet Eye Master
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Thu May 20, 2021 10:55 am linkquote
Ok lets begin. Few bits of housekeeping first.

Timing may or may not be too far advanced. If too far advanced it will never jet in. Set it by strobe to 16 degrees @ 6000 for now. The Vespa timing marks can be way off and it has to be set by strobe light.

Check the fuel flow from the hose at the carb, with half a tank and not on reserve. At least 0.5L/min or it will never jet in. Check the filter within the carb body is either clean or missing.

Have a look at the piston crown and make sure its in good condition. If you've been running with weak jetting and high timing there might be melting, that would need attention.

Check the float height is at 11mm.

Lets assume the rest of the engine is in good condition. SIP speedo will give you the best chance. If you get the SIP sensor speedo cable add on it will save a lot of grief.
Fri May 21, 2021 12:56 am

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Fri May 21, 2021 12:56 am linkquote
Super - I will do all that this weekend.

Just for info, I also have Malossi sold VHST 28mm which they sell for this kit.

Dyno guy said it was too weak and he preferred to work with the VHSH.

interesting thing is that Malossi's settings are from the factory for this kit. The bike seemed to run well with this carb in this set up.

These are Malossi's VHST spec

main jet140
idle jet 033
needle D37 (I think 2nd clip from top need to check).
atomiser HH 271
slide 55

What do you make of it?
Fri May 21, 2021 6:51 am

Jet Eye Master
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Fri May 21, 2021 6:51 am linkquote
VHST is more like a 4 stroke carb but for a 2 stroke. Supposed to be more economical but that means slower and that is immediately is less interesting.

What is every component in your VHSH and what other jets/slides/needles etc. do you have for it?
Fri May 21, 2021 7:35 am

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Fri May 21, 2021 7:35 am linkquote
For the VHSH I have:

Random selection of main jets -140, 150, 152, 158 165 168, 170, 172
Selection of idle jets 40, 42, 45, 48, 50
Needs U16, K21, K98 (one it came with)
I have a DQ266 atomiser in addition to the DP265 in there at the moment
I have 42 and 48 emulsion tubes.


that's it I think.

What are you thinking?
Fri May 21, 2021 7:58 am

Jet Eye Master
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Fri May 21, 2021 7:58 am linkquote
Slide number? Bushing height? Float jet?

A fair selection of bits. Will need some smaller pilots.
Fri May 21, 2021 8:27 am

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Fri May 21, 2021 8:27 am linkquote
Sorry - what's the bushing height?

will take the carb apart tomorrow.
Olly
Fri May 21, 2021 9:55 am

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Fri May 21, 2021 9:55 am linkquote
It's the brass bit that sticks up into the Venturi. 3, 7, 8mm are the usual sizes. It's likely 7mm.
Fri May 21, 2021 10:41 am

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Fri May 21, 2021 10:41 am linkquote
Thanks!

I also have a DP268 atomiser!

What idle jet sizes should I get?
Fri May 21, 2021 10:59 pm

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Fri May 21, 2021 10:59 pm linkquote
Get a 30 and a 35. They're not cheap so we'll try to work with those until we know more.
Sun May 23, 2021 3:07 am

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Sun May 23, 2021 3:07 am linkquote
Right - ordered idle jets.

Need valve and seat size 300

One piece floats 9g

Slide -looks like a 50?

Bushing 7mm

No fuel filter fitted

Float height looks to be about 11mm (but not sure how to measure)

Tap has passed the fuel flow test

Finally, what's the deal with air filters? not running one as advised not to but now have a ram foam thing. Bit worried about crap getting in.





Sun May 23, 2021 9:57 pm

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Sun May 23, 2021 9:57 pm linkquote
All sounds nearly good to get started. Did you reset and strobe the timing? Where is it set?

Where is your carb mounted? If in the tunnel and it was me, I would leave it open with no filter. The ram air filters are ok, as long as they are not squashed up.

You have tippex marks on your throttle grip? Need to know zero to WOT and each 1/4 position.

SIP speedo working ok?
Mon May 24, 2021 4:46 am

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Mon May 24, 2021 4:46 am linkquote
Thanks!

Carb is in the tunnel yes

Didn't get to fit sip speedo this weekend. Most likely next weekend I'll get to it and then we can start!
Olly
Mon Jun 07, 2021 8:47 am

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Mon Jun 07, 2021 8:47 am linkquote
hi jack

fitted sip speedo - seems to be working

will adjust timing next,]]

Out of curiosity I fitted

35 pilot
DQ266 atomiser in place of DP265
K21 needle 3.5 clips

seems much more zingy from 1/8 throttle - all rich hesitation is gone. But I bet its lean everywhere!
Mon Jun 07, 2021 8:48 am

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Mon Jun 07, 2021 8:48 am linkquote
am waiting for your instructions
Mon Jun 07, 2021 1:26 pm

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Mon Jun 07, 2021 1:26 pm linkquote
As needle position seems quite good, maybe lean when coming on to pipe I went up from 152 main jet to 155. Pulling harder. Not bogging on full throttle so may go up again to 158 tomorrow -see if I can get it too rich

this is amateur stuff and I'm really flailing around but I'm enjoying the warm weather on the scoot!
Mon Jun 07, 2021 2:23 pm

Jet Eye Master
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Mon Jun 07, 2021 2:23 pm linkquote
Ok, let's start at the beginning before you blow it up.

Have you reset the ignition timing yet? If you leave it high it's like working without a safety net.

The K21 would be the needle to try first. Clip 2. Biggest atomiser you have DP268. Smallest pilot jet 30. Inner pilot B42. No main jet.

Get all this in and adjust the airscrew at fast tickover. Aiming for as weak as possible. Under 2.5 turns would be great.

Edit: Expecting it to be too rich everywhere, all speeds, all positions, which is the best place to start.
Thu Jun 10, 2021 10:34 am

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Thu Jun 10, 2021 10:34 am linkquote
OK

timing now set to 16 degrees at 6000 rpm.

Will adjust carb at weekend as per instructions, but what's the first step - what will I be testing for?

Edit: just seen rich everywhere


thanks
Sat Jun 12, 2021 8:41 am

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Sat Jun 12, 2021 8:41 am linkquote
Ok Jack

Done what you said.

DP268
42 inner pilot
30 pilot
K21 2nd clip
no main jet


Air screw 2 1/4 turns out - idles at 1100 -1200 rpm

The bike is rich at 1/4 throttle (stutters)
1/2 throttle it seems rich around 5-6000 rpm and then it comes on pipe and really goes
Same for 3/4 throttle rich as it comes on pipe then clears and goes.
Full throttle obviously mega rich and won't go.

What next?
Olly
Sat Jun 12, 2021 10:36 am

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Sat Jun 12, 2021 10:36 am linkquote
You have any smaller pilot atomisers, B42 is too big. Should be idling slower.

Other than that it sounds as expected. Next, drop the clip half at a time until 1/2 throttle cleans up but only nearly cleans up. If you're at 3000 rpm up a very slight hill in 3rd, open to 1/2 (exactly half throttle, not more, not less) and hold it, it accelerates briskly up to 1/2, then stutters faintly and is just about continuous splutter while held there.
Sat Jun 12, 2021 10:52 am

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Sat Jun 12, 2021 10:52 am linkquote
Hi Jack,

Not got lower than b42 should I get a lower one and if so which one?

Should I do this before adjusting the needle?

Is the aim adjusting the needle to get 1/2 and 3/4 throttle to be too rich in the upper rev range?

thanks
Olly
Sat Jun 12, 2021 10:54 am

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Sat Jun 12, 2021 10:54 am linkquote
Also just curious about the process. What are we aiming for and what are the stages?

Also how does one know which atomiser / needle combo to start with?

thanks
Sat Jun 12, 2021 2:18 pm

Jet Eye Master
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Sat Jun 12, 2021 2:18 pm linkquote
Get a B35. That should be it.
First need to get 1/2 done. If 3/4 is an issue it will need another needle but that we will know soon.
Sun Jun 13, 2021 1:52 am

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Sun Jun 13, 2021 1:52 am linkquote
So I've been out this morning tinkering with needle clip positions.

3000 rpm 1/2 throttle 2nd gear up slight hill and hold it there.

4th clip is where it stutters comes on pipe and just about clears

4.5 clips is where it stutters comes on pipe clears a bit and then starts stuttering again. Pretty much unrideable on this clip setting.

Olly

EDIT have ordered B35. Should I retest when it arrives?

EDIT 2 what I am getting is 3000rpm lots of spluttering, then on pipe at 6000rpm and clears (just about clears on 4th clip- definitely does not clear on 4.5 clips)
Sun Jun 13, 2021 2:25 am

Jet Eye Master
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Sun Jun 13, 2021 2:25 am linkquote
Just to check. Clip 4 is the bottom clip lifting the needle as high/rich as it goes?

What you want is just to hold 1/2 throttle continuously from 2000rpm and it will accelerate well, then level out and start to splutter very mildly. This is the clip position you are looking for. Above and below 1/2 throttle doesn't matter at this point.
Sun Jun 13, 2021 4:24 am

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Sun Jun 13, 2021 4:24 am linkquote
Yes clip 4 bottom clip.

Clip 4.5 with little washer below circlip so lifting a bit higher.

I'm not getting the characteristics you describe at any position. From 3k rpm I have spluttering at 1/2 throttle (more spluttering the richer the needle). Then at 6k rpm it clears and I have clean acceleration in all positions except for clip at 4.5 .

This follows the pattern of the dyno print out above which was observed on the dyno. Rich before 6k rpm and then lean afterwards.

Any ideas?

Edit : this was why I felt a DQ atomiser might work better than a DP as the DQ leans out the mixture in the early rev range I believe
Sun Jun 13, 2021 6:17 am

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Sun Jun 13, 2021 6:17 am linkquote
Clip 4 is very rich for your 132. The idea of this test is to only hold the throttle at 1/2 and not move it in any direction. All other positions will splutter; not interesting. If it splutters badly at 2000rpm half throttle weaken the clip until it doesn't. Let it accelerate up until it levels out, then should start mild spluttering at higher rpm.
Can't move on until this test is exactly as described. When the clip is correct, it will be.
Sun Jun 13, 2021 8:41 am

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Sun Jun 13, 2021 8:41 am linkquote
Ok I think I understand. I am holding it steady at 1/2 throttle.

If the idea is to stop it spluttering at low rpm then I need to weaken it from 2nd clip.

Will give it a go and report back.
Sun Jun 13, 2021 8:52 am

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Sun Jun 13, 2021 8:52 am linkquote
Ride at 2000rpm 3rd gear and low throttle. Suddenly open to 1/2 throttle and hold it. No splutter just acceleration, then mild splutter when it levels off at higher rpm.
Think that explains it better.
Has to be done with no main jet fitted.
Sun Jun 13, 2021 9:35 am

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Sun Jun 13, 2021 9:35 am linkquote
Ok so I've been out again.

2.5 clips clear and virtually no discernible stuttering anywhere in the rev range

3 clips and stuttering before coming on pipe noticeably.

So 2.5 is the setting?

EDIT 2nd gear and 3rd gear the same

EDIT 2 andI went down to 1 clip, 1.5 clips, 2 clips etc. Clip 3 was the first appearance of noticeable stuttering.
Sun Jun 13, 2021 12:42 pm

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Sun Jun 13, 2021 12:42 pm linkquote
Sounds like you got it. I think clip 3 is the setting. Needs to be rich but only just. As you do the rest of the jetting it that 1/2 point needs to stay rich.

This test confirmed that the K21 needle is not terrible. And the DQ268 can stay in.

Does it splutter at 1/4 throttle on clip 3? I suspect it does, need to work on the pilot next.
Sun Jun 13, 2021 1:16 pm

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Sun Jun 13, 2021 1:16 pm linkquote
Yes it does splutter on 1/4 throttle on clip 3 .

what next?

thanks

EDIT just to be clear its a DP268 in there not a DQ
Sun Jun 13, 2021 2:40 pm

Jet Eye Master
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Sun Jun 13, 2021 2:40 pm linkquote
daolski wrote:
Yes it does splutter on 1/4 throttle on clip 3 .

what next?

thanks

EDIT just to be clear its a DP268 in there not a DQ
Yeah, DP. DQ are better on the road. If you do a lot of miles, changing to DQ would pay for itself in a month.

Splutters at 1/4 on clip 3 but not at 2.5?

Need to get that pilot jet down lower. Hopefully it will fudge in with the 50 slide.

In the meantime we can see if the needle is ok. And make it a bit more rideable. Fit a main jet that is big enough to just splutter at 3/4 throttle.
Mon Jun 14, 2021 2:40 am

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Mon Jun 14, 2021 2:40 am linkquote
Happy to get DQ268 if you think that's the right one?

Should I get other pilot jets? I have 30,35 and 40 at the moment.


Yes 1/4 throttle splutters only on clip 3.

Should I test 3/4 throttle in 2nd or 3rd gear?

thanks
Mon Jun 14, 2021 3:10 am

Jet Eye Master
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Mon Jun 14, 2021 3:10 am linkquote
Do 3/4 in all gears. Will be the same as doing 1/2 , open quickly to 3/4, should accelerate with no splutter, then mild splutter when the rpm catches up. Keep the clip on 3 all the time. Only change the main jet.

Leave the DQ until the end. Atomisers are expensive and might need a between size atomiser , which can be brought for VHS carbs.

Let's see how 30 B35 works out before buying anything else.
Mon Jun 14, 2021 12:42 pm

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Mon Jun 14, 2021 12:42 pm linkquote
So I've been up the road testing 3/4 throttle, clip 3.

160 main jet leaves a murmur of spluttering just before coming on pipe in 2nd gear and no spluttering at all in 3rd or 4th gear. 162 is slightly worse.
Mon Jun 14, 2021 9:58 pm

Jet Eye Master
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Mon Jun 14, 2021 9:58 pm linkquote
If you leave it at clip 3 and 160 main, what happens at WOT in 3rd?
Hoping for, revs right out and slightly splutters.

Has the clip 3 half throttle splutter gone yet?
Tue Jun 15, 2021 2:25 am

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Tue Jun 15, 2021 2:25 am linkquote
Hi Jack,

WOT in 3rd revs right out (and we are doing 60mph by that point!!) but very slight splutter 5000-5600 RPM just before coming on pipe

Still spluttery in all gears at 1/4 throttle.

Still a bit spluttery 1/2 throttle.

2nd gear WOT revs right through no spluttering.
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