Piston port derbi puchgila tops out at 30 fast

So I'm thinkin it might be related to my gila being pushed out so much

I have a .7metal base gasket and 2 autozone grey gasket gaskets I cut myself around em. Timing is 2mm on hpi. No leaks it just falls off the pipe around 30 and doesn't go any faster. Hits the pipe pretty early like it should but it just falls off. Tried tuning the variator.

If anyone thinks it's related to the kit being pushed out how's my gaskets and to what thickness do you think should be placed there. (edited)

Re: Piston port derbi puchgila tops out at 30 fast

Where's the piston at BDC? Squish? Compression? Something's not right.

Re: Piston port derbi puchgila tops out at 30 fast

My squish is probably over 2 mill. My timing is 2.0 btdc

Re: Piston port derbi puchgila tops out at 30 fast

over 2 mil? woof, start there. how did you tune the vario? you have a 6 roller or tjt? did you add weight? because you might not be varitating at all.

Re: Piston port derbi puchgila tops out at 30 fast

you only need the one base gasket that the gila kit comes with, or something similar. your huge base gasket is the issue.

Re: Piston port derbi puchgila tops out at 30 fast

Yeah man, that 2mm squish is definitely not helping you...the 1.2 to 0.8 range is where you wanna be. BDC = bottom dead center aka where's the piston at the bottom of the stroke? You want it flush with the exhaust port. I sense this may play a large role in your lack of power due to your base gaskets and squish.

30 is still wicked slow...sounds variator related as well.

Tune up and report back.

Re: Piston port derbi puchgila tops out at 30 fast

i'm guessing you have super light weights in the variator and it's not closing all of the way, due to that.

Re: Piston port derbi puchgila tops out at 30 fast

I started the post on my phone I'm on a comp now and ill give a more thourough break down of this.

I got the bike with a treats cdi that was pretty fucked up, because you have to dremel it a ton to get it timed right. well basically it had been dremeled so much that it cracked. so at that point the bike was misfiring so I figured id do some work to it in general. before it started misfiring the bike had 21grams of poilini rollers in a tjt with a red contra. the kit had three auto zone roll up gasket paper gaskets and a weakendz pipe, and a gila head gasket with a derbi head. It topped out at 55 with stock gearing. not bad

so

i put a hpi mini on there and one thin gila stock base gasket.

my squish was at .7 ..rad. ran the bike at 1.8 btdc rad

had head tapping with load at around 20+ and cracked the piston.

so Im guessing rod stretch led to that.

I talked to steve brown at the buzzards rally for abit about running lower compression for higher top end and cooler temps. so i went back to my current ideology of mad base gaskets which results in a non racey squish band.

in its current condition (.7metal base with 2 relatively thick hand cut gaskets) when i look down the cylinder and the piston is at the bottom of the stroke its not flush with the exhaust opening its past it about 5mm. I ran it at 1.8 btdc with the variator untouched from the previous owner at 21 grams. i could only hit the power band a couple of times, so i lightened the weights to 18 grams. hit the power band every time and variated all the way .. still but maxed out at 30 both times. retimed it to 2.0 btdc bike felt better but same results 30 mph.

so I'm left knowing that if i run one thin gasket my piston will tap my head. thats at .7 squish.

and now if it sounds right if i have my gila pushed out with one metal and 2 paper base gaskets my cylinder timing is off.

so I'm thinking that ill try 2 thick grey paper gaskets.

Re: Piston port derbi puchgila tops out at 30 fast

i would grab a Gila head to match that kit. I'm not sure which Derbi head you're running, whether it be aftermarket, modded stock, etc., but I would think an ill-matched head could be a more likely cause of that tapping. plus, Gila head will allow you to eliminate decomp (one less potential leak). your port timing is not so hot with all that base gasketry going on. my 2¢

Re: Piston port derbi puchgila tops out at 30 fast

oh right I got the gila head on there.

so like less base gaskets cool.

what do you think a good timing is?

Re: Piston port derbi puchgila tops out at 30 fast

did you swap heads after the piston cracked, or before? if it happened before, I'd now go to a default Gila gasket or similar, as Ryan suggested, and give it a shot

Re: Piston port derbi puchgila tops out at 30 fast

will do, I was running the derbi head with a slim stock gila base gasket when it cracked. ill try the slim stock gila base gasket with the gila head. currently I'm running a hand made copper head gasket. its kinda thick even after the heat treatment. so idk if my squish will be good prob over 1.0mm but at least my port timing will be what the kit is suppose to have. thanks for the all the help ill report back sometime next week.

Re: Piston port derbi puchgila tops out at 30 fast

Downhill Harvey (OFMC) /

when i look down the cylinder and the piston is at the bottom of the stroke its not flush with the exhaust opening its past it about 5mm.

5mm? Yeah, reduce your base gaskets by 5mm. With that much base gaskets, your squish has to be more than 2mm.

Re: Piston port derbi puchgila tops out at 30 fast

Downhill Harvey Wrote:

-------------------------------------------------------

> when i look down the cylinder and the piston is at

> the bottom of the stroke its not flush with the

> exhaust opening its past it about 5mm.

>

> 5mm? Yeah, reduce your base gaskets by 5mm. With

> that much base gaskets, your squish has to be more

> than 2mm.

so the goal is to have the piston flush with the end of the exhaust port?

Re: Piston port derbi puchgila tops out at 30 fast

Downhill Harvey (OFMC) /

so the goal is to have the piston flush with the end of the exhaust port?

yep, kinda mopeds 101, nooblet,

...............................and why would you mess up a bike that went 55 already, is beyond me.

Re: Piston port derbi puchgila tops out at 30 fast

Sorry to hear about your troubles, but yeah, your squish/port timing/compression is way way off.

Try using just the dykes ring for less friction and flutter, which will yield higher RPMs. Gap it between .009-.012". Doing this for me helped me (not sole contributor) gain +1500 RPMs.

Give the cylinder a run down and get rid of any inconsistencies and asymmetrical ports. My Gila had a nice hump in the ex port (now gone/polished) and had asymmetrical intake and exhaust port openings (widened left side of ex and right side of intake, 2mm each. Yours may be different). Give it a good chamfer and move along to the gaskets.

Run the Gila head and Gila gaskets to start. Be sure to match up the base gasket to the transfers since it's most likely hanging over them a bit.

See where the piston sits at BDC - if it's flush with the ex port, check squish. If not, adjust until this is achieved, then check squish.

If squish is between .8 and 1.2mm, check compression. If not, adjust head gasket until this is achieved, and then check compression.

If compression is in the 155-175psi range, move to timing. If it's too high/low, look in to getting the head milled and re squished to keep it kosher, then move to timing.

Time the bike between 2 and 2.75mm BTDC. 1.8 is WAY too low for the HPI Mini. Keep an eye on temps/performance and adjust if necessary.

And mess with your variatior weights. Easy 60+ after all of that.

Re: Piston port derbi puchgila tops out at 30 fast

^^^^^. What he said and check

your variator and rear pulley

You might have a weight jammed or a rear spring problem

Re: Piston port derbi puchgila tops out at 30 fast

i dont see any pics of .. stuff?

Re: Piston port derbi puchgila tops out at 30 fast

Variator is smooth and checks out because it variates full each time.

In agree that my port timing is off and down hill Harvey

I stated above that the only reason I am going through this is because the previous owner left me with a really jacked up cdi that the mounts snapped on

Re: Piston port derbi puchgila tops out at 30 fast

ok so i did some work to the derbi yesterday.

original gila base gasket is on with a little oil on both sides

exhaust port is flush with bottom of stroke.

but

the squish is 1.3-1.4 sometimes the micro meter reads 1.0 but it usually reads that number.

is 1.3-1.4 ok in the end?

that read is with the gila aluminum gasket.

i had a handmade copper one in before but took it out cause it was reading 1.5+

timing is 2.4 on the hpi mini

I haven't started it yet because I'm waiting for the honda bond to dry. but I'm about to go to my garage to fire it up in a bit.

I guess I'm just curious in the effects of going a little over the squish recommendations. (edited)

Re: Piston port derbi puchgila tops out at 30 fast

Topping out at 30 is all tranny or gearing.

It's not squish or timing, even very very retarded and no squish you should be going much faster.

Re: Piston port derbi puchgila tops out at 30 fast

JBOT: Fear is the Mind Killer Wrote:

-------------------------------------------------------

> Topping out at 30 is all tranny or gearing.

> It's not squish or timing, even very very retarded

> and no squish you should be going much faster.

red contra

hpi mini 2.4

weak ends

24mm mikuni 155 main

dayco belt

tjt vario/ramp

stock gila base gasket

stock gila head gasket

stock gila head

I agree with you Jbot...

squish 1.3

ran the bike today no leaks, compression test 120 psi.

when i first ran it the vario had 21g's of polini weights in it. ran a sluggish 40

ended up with 16.5 g's of weight and to be honest i could probably go lighter.

i only have 30 miles on this new piston so I'm not going to try and go 60+ on it yet.

The bike feels good though which is a relief because I've been working on it for awhile.. It doesn't really feel as responsive as when I first got it though a little boggy when i open it up. The bike had a 145 main in it when i got it, so I might move back down to that. That might lean it out correctly.

The plug is coffee colored which is good. and I took a flash light to my spark plug hole to see if there were marks from the piston tapping the head, there weren't any.

running temps were around 360-420ishh i wasn't really paying close attention.

idle temps from a hot engine 360-380 ishh

Do derbi rear pulleys get jammed? Mines not, but I'm wondering if they jam up like all my hobbits pulleys. just so i can know if i should be careful with my throttling from a stop.

Re: Piston port derbi puchgila tops out at 30 fast

try the old contra again? might be too tight.

Re: Piston port derbi puchgila tops out at 30 fast

Downhill Harvey (OFMC) /

timing is 2.4 on the hpi mini

The manual says 1.8mm or or 21 degrees

idle temps from a hot engine 360-380 ishh

That is way too hot for an idle temp.

Re: Piston port derbi puchgila tops out at 30 fast

ORLY harvey, you read the hpi manual and it says to run it at 1.8? that would put you at like .3 or 5*at 10k

they recommend 2-4mm

his timing is fine.

Re: Piston port derbi puchgila tops out at 30 fast

Hopeless.

Re: Piston port derbi puchgila tops out at 30 fast

Downhill Harvey (OFMC) /

My "all stocker" does 37, 40 in a tuck, 20z front. Full throttle temps of 360, all at 6k, according to the tach.

Re: Piston port derbi puchgila tops out at 30 fast

stock cylinder has like 15* blowdown so yes it will make really great power in the low rpms. a gila however has 28* of blowdown and has a very narrow powerband, from about 8k-10.5.

i'm still convinced your variator tuning is all of it. a couple grams makes a huge difference. you should probably just throw a kstar/dmp on it, something with a broader powerband and more forgiving with the tuning. it's a crazy set-up that is always breaking shit and i've never seen one that shreds any harder than a regular kitted derbi.

Re: Piston port derbi puchgila tops out at 30 fast

Yea I'm pretty sure it's a combo of vario tuning and jetting.

When I first got it it had a diff cdi and it had 21 grams in it. It did fine 55mph

Now the power band is all diff and 15 grams is what it takes now, maybe even less I'm gonna be tuning in abit.

Thanks for all the help guys

Re: Piston port derbi puchgila tops out at 30 fast

soft seized today, chipped the piston slightly. temps hit 450ish.

I took the head off and saw that the exhaust port was flush with bdc but the boost and intake ports were covered up a good percent. Im starting to think it was all my timing at first and that maybe I should of just places 3 handmade gaskets like the bike came with.

I had my hpi timed to 1.8 but as some have said that is retarded for a hpi so that may have been the issue all along.

The last image is from myrons mopeds, it shows 3 base gaskets. Im starting to think I had the port timing right all along. but my squish would still really suck if i kept 3 base gaskets in.

unnamed.jpg
unnamed-2.jpg
Screen Shot 2014-08-10 at 11.27.03 PM.png

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account