Porting and blowdown

[pudvah]

ya man thats awesome, I remember the day I got mine back from Ken and doing heat cycles I was like WOW. Love the pap pap pap of the toomey. I have had too much going on lately to ride and need to rejet because it was tuned in 85-90 degree weather and now its 50. I can't wait for the ride report from you I promise you're gonna be shocked how friggen hard she pulls when that bad mamajama of a pipe hits.

 

[deeeebeeeeee]

I frigging stoked , looks like my driveline parts: clutch,chain, rear cog, swingarm extension are going to make it today. We sold some property just in time to cover bills, and hold us over until my 2nd job starts paying. This allowed me to go ahead and replace the some parts that probably wouldn't hold up to the new motor. I forgot how good that Toomey sounded, I run it for a bit before the rebuild, but when it sparked to life, I was quite surprised. I think the rechambered head made a huge difference. It definitely sounds built.

 

[deeeebeeeeee]

Got to ride a little bit today, a little weak around idle but pulls stronger off the pipe at low rpm, not sure how it pulls thru midrange because I can't get out of 3rd in my yard and every time the band hits it either blows the tires off of it or lifts the front until I am looking at the stars.

Float height was fine, I ended up using a spare carb body and the needle valve seat wasn't tight.

Might mention it in the carb support sub as well but I had to drop to a 32.5 Pilot jet and still had to go a full 2 3/4 to 3 turns out on the air screw, does it make sense to have to go to a 30 pilot in this sort of motor (double metering at idle?).

Had a vitos needle in it, but went back to the stock 5j22, since everything was so screwed up, it's running a little rich for the most part, will have to drop it one clip. 380 main jet is god awful rich but once I get it broke in a bit more and jetted properly otherwise, and out on the trail I will work down for 360, I am guessin about 320, 330 is where I will end up.

My wife said it didn't sound right, and that it was louder, and much more offensive sounding to her ears. That just tells me all is well.
I won't know until I get it broke in but it seems like the band comes on sooner, it also idles a little faster to keep it smooth, so it's hard to tell and I won't know until I start getting close on the main jet, worst case scenario if the band is too bad low, I will buy new top end gasket set and adjust the porting a bit.

I have a second cylinder and will be starting on it soon

 

[OConnor Racing]

Your main jet is way too rich. Run the stock needle, middle position, and a 320 main. Sort it out from there.

 

[deeeebeeeeee]

Thanks I was a little lost since I swapped to a vm28. The only comparable I have seen was a vm30 that needed to go up 2 sizes coming from stock carb, seems like maybe one size bigger going to the vm28 should do it?

Initially I went puposely large with the main jet so as to be sure not to mask what the needle was doing, bit I don't think that is working quite as expected.

I really don't have any space around the house to do much, I need to build a path corner wise across my little acre.

 

[deeeebeeeeee]

Soooo. frustrating, ended up having to switch the needle valve out on the carb, I tightened the seat down and with my finger on the float it didn't leak, then I got called away and left the gas on for ten minutes, came back and it was leaking out the over flow again.

Dropped the needle one clip and it lined it out at 1/4 throttle but way lean above half.
Went to the Yamaha shop to get a #30 pilot jet and the one box the pilot jets were in was missing and probably somewhere in the shop. That's what the lady at the counter said.
I did order one but it might be Friday of next week before it shows up. So I am basically screwed until the correct pilot jet arrives because it's throwing everything else off,running a 32.5 at over 2 1/2 turns 0 on the airscrew.

To compound that i am afraid I went a little farther than I realized to on the main transfers, and possibly brought the blowdown down below stock by a half of a degree or more. I hope this didn't kill the upper end of my rpm range. Once again it's hard to tell because the carb is off and I really don't have enough time on the motor or room in my yard to see how she winds out.

Once I get my pilot jet in and the lair screw set right, then I think the needle will be ok, then I can worry about the main I have a 310, 330,340, I lost the 350 jet along with the O-0 needle jet, and I thought I had a 320 as well but don't see it.
It's pretty bad with the little one around. You set something down and next thing you know it's gone, they are especially interested in anything that I am working on.

Worst case I take the head back off and add a degree or two to the exhaust port and the secondaries which AR almost at stock and that should line it out

 

[jus_me]

Not to sound rud or anything but why not just get a stock carb? Sounds to me like your chasing your tail trying to get this carb to work (considering all the time spent etc...) when a stock carb would work 1000x better and you would be good to go as far as running/jetting specs..

 

[deeeebeeeeee]

I ended up giving my stock carb to abother member here, who was without, the frustrating part was mostly with the needle valve first being loose, then not seating properly. The next issue is that I don't have the right pilot handy, which would be the same on either carb. The vm28 is really about the same as the vm26ss, except for the lack of TORS, and it needs one size larger main jet.

In hindsight I wish I would have kept my stock carb, because I knew it was all good, but now that I have went to the trouble of fixing up the vm28, I suppose I will stick with it. All in all its not to bad, it's just frustrating not having the right pilot jet as it kind of puts a damper on the whole thing.

I got a little obviously amateur vid of it running and revving, gotta figure out how to post it up.

 

[deeeebeeeeee]

Just a quick vid of it running and revving, keep in mind the motor is bone cold and the air screw is at 3 turns out and on a 32.5 Pilot.
It's 58 degrees and rainy and no choke was needed. I do have a #30 on order as I have said before.

Ok so the little poof sounding backfire on second kick, has to do with the gas being left on and the needle valve oozing fuel it doesn't even overflow out the vent it is just full of vapors, if you leave it in for a few hours

But if you listen closely at around a minute when it revs fairly it sounds like the microphone is breaking up but it actually sounded like that, it seems like where it should be really hitting hard it breaks up, but it may be fine under power or once jetted.
Anyone with a fine ear care to comment, because honestly despite the fact that the extra compression sounds awesome, I feel like it's off somehow. Any suggestions are welcome.

Other than that I am going to ride it and not worry about it, it's got hells of power, (enough to spin donuts on damp concrete just off idle), so maybe it just needs run and possibly jetted.

If all went well my little vid is above,

 

[joeak47]

Not to sound rud or anything but why not just get a stock carb? Sounds to me like your chasing your tail trying to get this carb to work (considering all the time spent etc...) when a stock carb would work 1000x better and you would be good to go as far as running/jetting specs..

What he said /\ /\ /\ /\ /\ /\
The stock Mikuni VM26 works flawlessly, is easy to tune, and FITS the intake boot and air boot!
Here's one here... best offer should get it cheap >>> http://www.ebay.com/itm/Yamaha-Blas...ash=item1c5b368ce6:g:jQAAAOSwwbdWIPcv&vxp=mtr

 

[jvb]

Nice Deeebeeee!
1 or 2 sizes smaller on the main jet and good to go!
Can't wait for a vid. when it hits the powerband!

 

[deeeebeeeeee]

The vm 28 is nearly identical to the vm26, same OD, on both ends, uses the same slider, same jets(except NJ), it's really the same body, bored out 2mm, and drilled for a different Needle jet. I wish I would have kept my stock carb, then I could have robbed the inlet needle and seat (which has been the source of my carb headaches) from it.

The vm28 is fine other than the fact the needle seat was worn. I am fairly convinced that if I would have had a chance to get the bugs worked out and jetted when it was running before, it would have been no different than the vm26 to get jetted.

Now that I have a tors delete cap to fit a stock carb, and an extra idle screw, I wish I still had the stocker,but I gave it to a kid here on the forum who needed it right then because the threads on top of his were stripped. No regrets, my biggest frustration is not having any space at the house to ride.
Maybe I should get the guy I gave my carb to to send me his old one of at least the inlet needle and seat.

Anyhow gotta go over to my rental property to mow and get my wheel dolly out of the shed, so I can unload the big arse fridge from my trailer, then I can load up and get out of here, with my jet kit and toolbox in hand. I have got my self sooo convinced that the porting is off, I am "fingers pinched nearly together" this close to pulling the jug. So I can raise the exhaust port by 2 degrees and the secondary transfers up to match the primary.

I don't know what I was thinking trying some odd stuff first time around, but I am almost certain that I ended up with an initial blowdown below stock, and I got a feeling it's not gonna rev out well. I know I keep saying it and I keep hoping I am wrong, but I just can't shake the thought that I should have come up on the exhaust and puttied in the intake.

Anyhow I should get to ride today, and will know whats up soon enough.

 

[deeeebeeeeee]

Holy Halloween Batman, was that a rocket, or was he really trying to do a superman without a ramp.
I knew the jetting was off but who knew dropping in a 300 would bring it too life like that, to be fair I did go back up to 310.
But wow I was testing lugging it in second giving it a little more I probably should have and BAAAM Baby that thing hit the band layed black marks down the driveway, and pulled the fronts a foot and a half in the air before I let go of the gas.

Wow, it's now just a matter waiting for the #30 Pilor (one size lower) and I think i will need to run my needle one clip rich, got a 310 in it now might have to go to 320. But shhhzamm she's mean. It does have a little bit of an issue getting on up to the top of the power band unless the motor is loaded, like if it's spinning hard it kinda hits a wall and breaks up, but if there is load on it it rips pretty hard.

I am gonna guess that the 28mm carb has a little better venturi effect because it seems like I am going a step leaner on jets not a step richer, once again time will tell.
This last little ride was with a new plug, gonna have a look at it just to get an idea of where I am at overall.

 

[deeeebeeeeee]

OK so I got tired of the motor starting to break up and fall on its face at around 7.5 or 8k ( guessing), so I did what I said I would earlier in the thread.
Pulled the head and took some proper measurements with a feeler guage and caliper, found out this morn that i had went .2 or .3mm to high on the primary transfertransfers than intended. So I did the math (thanks again for making me take better notes than normal), pulled the head and went about .6mm higher on the exhaust port rechamfered, and cleaned up with some 400 grit around the edges of the port, also touched the secondaries lightly and hit em fairly hard with the 400 grit, just to make up for the fact that the primaries and now the exhaust were higher than originally planned.

Heat cycled it once re-torqued, I noticed when I fired it up it was immediately idling better but a bit lean, now the #35 pilot is happy at 2 1/4 to 2 1/2 turns out (before it was rich at 3 turns).
Made a quick pass in my driveway, which only has enough room for second (if you tach 3rd you better hope the is no traffic b/c you are going to overshoot the end of the driveway .) and immediately noticed it revved to what I can only say is higher than stock, (before it was lower than stock), also I noted that a 300 main jet seemed quite lean I wet up to 320 and it pulled stronger still.
I feel like it's time to get out on the trails, burn the last gallon or so of the first tank of fuel, then really break it in.

 

[deeeebeeeeee]

Haven't made It to the trails yet maybe tomorrow, but I did do some adjustment on the needle (which is now a 5j11, it matches the larger Q-2 needle jet , and 2.5 IIRC slide cutout quite well), and ended at #4 clip with a 1/2 clip spacer as 5 was too rich, 4 was actually ok but 4 and 1/2 makes almost the same power. In the end I could go with either. Main jet is up to 330 and might still take a 340, just depends on how things go when I out the #30 pilot in and get the air screw back closer to 1 1/2 or 2 .
It has been a pain re-jetting the '92 yz80 carb for the blaster, especially since the needle jets are yamaha only and can only be had in certain sizes from yamaha, and N-8 and O-0 from Mikuni.

Anyhow things are coming along nicely, I am a bit concerned about cylinder head temps, but I am gonna guess it is to be expected as more power is more heat and or more efficiency,


Can anyone comment as to what expected head temps should be, and what a safe maximum is?

I did inspect the piston, plug, and head dome for any detonation damage when it was apart and found none. I think the biggest problem is my little 80 or so foot long driveway with a 40 x30 L at the end. It doesn't leave much room to get any cooling speed up. I believe I better either take some thin plate steel and cut out a couple deflectors or just buy them.

I got a compression tester today and for some reason,, (ice cold motor, or the 20 inch hose maybe) I couldn't get the compression to read over 60 psi no matter how hard I kicked or held the throttle. Took the guage off out the plug in started second kick, so of course it has more than 60 psi. I don't know if I get someone to hold one of the short extensions with the rubber tip tight against the plug hole if it would get a closer reading?

 

[pudvah]

Supposedly harbor freight compression testers are notorious for testing 60 psi, junk right out of the box. Not sure if that's where you got it but if it's not a good quality tester it could be the issue.

 

[Awk08]

I did inspect the piston, plug, and head dome for any detonation damage when it was apart and found none

what does /\ that mean ?
you've had it apart already since assembling this new engine ?
if so, did you anneal the head gasket or use a new one ?
re-leakdown test ?

I'll second the cheap compression testers as garbage, I have 2 of them, a harbor freight and an ebay special.
they worked a few times each, then sh-it the bed. new o-rings did nothing.
you do want to buy/beg/borrow/steal a good tester to get a basline for future tests to track wear as compression drops, or not.
compression is the best indicator as to whats going on in there piston/ring/cylinder wise

 

[speedyslyder]

a auto parts store for 30 bucks with a option to bring it back
for full refund is better then a online compression gamble.

i did not read entire book... above but
invest in some gorilla black duct tape for the seat lol

in my opinion and experience
you raised the compression on the blaster sooo
it would be like sitting on a 125 yz revving it,and sitting on a yz250 and revving it.
IT will sound and fell different

IN response to a few of your statement/\

 

[deeeebeeeeee]

what does /\ that mean ?
you've had it apart already since assembling this new engine ?
if so, did you anneal the head gasket or use a new one ?
re-leakdown test ?

I'll second the cheap compression testers as garbage, I have 2 of them, a harbor freight and an ebay special.
they worked a few times each, then sh-it the bed. new o-rings did nothing.
you do want to buy/beg/borrow/steal a good tester to get a basleine for future tests to track wear as compression drops, or not.
compression is the best indicator as to whats going on in there piston/ring/cylinder wise

Yes I had to take it apart, long story short i screwed the pooch and went further thsn intended on main transfers, it wouldn't idle for crap, and was taching out where I hoped it to hit the second wind of the toomey. Had to go in and raise the exhaust port to compensate for the low blowdown and high transfer. It worked and it also gave me a chance to get proper measurements with the piston in cylinder on, feeler guage, etc.
Yes, I originally used a new head gasket because I had it, and set the one I had annealed aside, which I used this, time.
Yes, shhh but I had to use a less than ideal base gasket, so I did test it, only went 5 minutes because I had to hold pressure against the intake insert to keep it sealed, will have to wrap it with a little tape or plasti-dip it before next time, I didn't break the intake seal this time, but did tape over intake ports.

I actually bought the guage from a brick and mortar harbor freight store, it's going back in the morning, and getting g swapped out for the next one up. Which probably uses the same position guage.

I need to get a seat cover, when I top it out in 6th that loose duct tape has got to be holding me back, but I hate to loose the racer boy graphic .

Actually I have a bad habit about that kind of thing, should have seen my cars back in the day never would replace that dented left fender but the motor, stayed fully tuned, clean K&N, secret fuel treatment (1 cup methanol per tank) works great on fuel injected engines with the base timing bumped (chrysler/Mitsubishi 3.0l v6 w/ dist.) Hard to see a dirty dingy black car in the dark turning triple digits down curvy 2 lane back roads. I was like catch me if U can mother truckers. Then one day I got caught

 

[deeeebeeeeee]

I found my answer on Cylinder head temps, looks like anything under 350°F is no sweat as long as you are not detonating, running lean, or any other issues
http://www.blasterforum.com/threads/temperature-compression.49492/
Here aND the thread it links to has some information about cylinder head temps.