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Discussion Starter #1 (Edited)
Just rebuilt a 98 Blaster, and now it won't idle.
Here's the details.
Split cases, new crank bearings/seals, crank and rod were in spec, countershaft bearing, all seals all gaskets, clutch, clutch springs, and plates (fibers and steels), all new bolts, brand new cylinder(stock bore), ring gap is right on(.011 if I remember correctly). Everything is mechanically sound, I have no doubts.( I have been working on cars, bikes, atv's, 2 and 4 strokes for over 25 yrs, and I am a competant mechanic).
I am almost 100% certain it is a carburetor problem.
It has an FMF Fatty pipe and silencer, Boyesen Rad Valve with carbon fiber dual stage reeds, stator plate holes grooved to rotate clockwise and advance timing, flywheel turned in lathe and lightened 5 ounces, K&N style air filter with no airbox lid, using 100 octane with Klotz synthetic 2-stroke oil. Oil pump is still on and working properly.
As far as I know it is the stock carb(Mikuni) with stock jets, and air screw is 1.5 turns out/counter clockwise. Adjusting the idle screw either direction makes a small difference. A half turn out(leaner) chokes it and it dies almost instantly. Up to 2.5 turns out(richer) slightly improves it, but it still won't stay running. I am 800' above sea level.
Before the rebuild it ran and idled perfect, but, it did not have the lightened flywheel(no way that's the problem), did not have the K&N air filter(had a foam filter, still without airbox lid), it did have Boyesen cf dual stage reeds, but in the stock reed cage, no Rad Valve. Reeds in Rad Valve now are also a new set.
I am aware that now with the Rad valve and K&N air filter(coupled with the other mods), could cause a need for a jetting change, or needle adjustment.
However, I did not think it would cause it not to idle at all.
It will idle for 5 to 10 seconds and die. Giving it slight throttle will help keep it running a few more seconds, but more than 1/4 throttle will cause it to bog and stall.
The choke on makes it worse.
Any advice would be greatly appreciated.

Also, something is wrong with this site for me.
This has taken a very long time to type, as I'm having to type many of the letters multiple times.
The screen will flash and freeze momentarily.
I am using Windows 7, and having problems on no other sites and Word is working properly on my computer.
Is there a setting(s) I need to turn on/off for this forum? I have not posted here in a long time, but had no issues in the past.
Thank you.
 

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I would start with a leak down test to make sure that you don't have an air leak. Is the pickup gap at the flywheel set correctly? Do you have a good strong spark? Float level at the carb set correctly?
 

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Discussion Starter #3
I have not done a leak down test yet, but evey seal and gasket were double or triple checked on assembly, and everything was torqued to spec.
The spark is very strong(coil is new, stator is original).
I am going to double check the float later.
I'll pull the flywheel too.
Thanks
 

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Discussion Starter #4
In hindsight, I see no need to pull the flywheel at this point, as the spark is strong. I do not belive this is an electrical problem.
I also do not think it is an air leak. I am confident in proper assembly, and it does not surge at idle like a lean condition ususally causes.
I guess what I really want to know is; even with the modifications that I have, shouldn't it still idle and stay running with stock jetting? I find it hard to belive that the difference in a Rad Valve and stock reed cage, as well as a K&N air filter vs a foam filter(the only 2 changes since the rebuild), would upset things enough to cause it not to idle or stay running.
I will double check the float level later when I get time.
Thank you
 

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Discussion Starter #5
Ok, since I was so positive it was the carburetor, and not an air leak, I checked everything again today.
I finished everything late last night with a tired brain. So, guess what...it's an air leak.
I torqued the head to spec, and in a star pattern. It looked good. I also checked the head and cylinder with a straight edge before assembly, and they appeared fine. The head is original, the cylinder is brand new. The copper gasket was new.
After a closer look, I could see light between cylinder and head, at the rear center! RRRR! Stupid me for missing it. I know better than to work on things tired.
My Dad took the head and is going to check it properly tonight or tomorrow. I'll go from there. The head was fine on the old cylinder, so I'm not past saying that the new cylinder is not squared and perfectly flat either.
So, with that said; Does anyone know how much material(thickness, thousandths) can be removed from the head and/or cylinder, and not cause any issues? Higher compression/detonation shouldn't be an issue either, as I'm running 100 octane.
I'm also not concerned about the port timing changing either, peak hp should just move in the rpm range, I can't think of any major negatives. Is there an ideal squish number for a stock bore and stroke Blaster? Does anyone sell specific thickness base gaskets, and in different sizes?
Sorry for so many questions, but after a lot of searching(here and on the Blaster forum), I can't find the answers.
Thanks for any advice, info, or links.
 

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Roll the Play-Doh turd & check the Squish height. “How it”s Done” Page 37, I’m working on the index again. 2-Stroke Performance Tuning page 17 has great info, if you don’t have a copy it’s around 20 bux on ebay.

As far as the text goes; This site is probably overloaded. I do all of my text entries in MS Word, then past it into E2S. You’ll also need to boot Fire Fox into your system so the print won’t show up in black.
 

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Discussion Starter #7
Roll the Play-Doh turd & check the Squish height. “How it”s Done” Page 37, I’m working on the index again. 2-Stroke Performance Tuning page 17 has great info, if you don’t have a copy it’s around 20 bux on ebay.

As far as the text goes; This site is probably overloaded. I do all of my text entries in MS Word, then past it into E2S. You’ll also need to boot Fire Fox into your system so the print won’t show up in black.
I do know how to check squish. I also have the book!( I read your recommendation for it here over a year ago, great stuff).
What should the squish be on a Blaster? I wanted to check that when I put it together, but couldn't find the specific info anywhere.
Also, how accurate can it be with a used copper gasket?
The used gasket shouldn't matter since it's compressed to a set thickness already, correct?
I do have a new gasket ordered for reassembly again too.
My Dad's a mechanical engineer, he resurfaced the head for me yesterday. Very little material removed, as it wasn't warped(as I thought). I set the head on the cylinder tonight, and there is still a small gap(obviously, since the head was good). Light can be seen and it rocks slightly. Going to resurface the cylinder, hopefully tomorrow. Pretty bad, considering this is a new cylinder.
Thank you sir for the time and info.

Strangely enough, the site issues I were having went away on their own. Copying from Word was going to be my next step too.
 

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So, with that said;
I'm also not concerned about the port timing changing either, peak hp should just move in the rpm range, I can't think of any major negatives. Is there an ideal squish number for a stock bore and stroke Blaster? Does anyone sell specific thickness base gaskets, and in different sizes?
Simply milling the head will not affect port timing, nor change the rpm where the peak torque occurs. These changes will only occur if the cylinder itself where machined on either the top or bottom surfaces. That being said, with the ideal compression and proper piston to head clearance, which has not been determined yet, you will be able to achieve maximum power output, but not at a different power band.
 

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Is the piston hitting the head when you turn it over? Is that copper gasket the stock head gasket? Try using no gasket , as a test, with piston at BDC, and put the head back on and look for the gaps you have been seeing when the copper gasket is in place. If the surfaces are flat they should mate up. Could the head gasket be a problem?
 

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Discussion Starter #12
Simply milling the head will not affect port timing, nor change the rpm where the peak torque occurs. These changes will only occur if the cylinder itself where machined on either the top or bottom surfaces. That being said, with the ideal compression and proper piston to head clearance, which has not been determined yet, you will be able to achieve maximum power output, but not at a different power band.
Yes, that is correct.
Moving the cylinder up or down by different thickness's of base gaskets would.
Sorry, brain fart.
 

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Discussion Starter #13
Is the piston hitting the head when you turn it over? Is that copper gasket the stock head gasket? Try using no gasket , as a test, with piston at BDC, and put the head back on and look for the gaps you have been seeing when the copper gasket is in place. If the surfaces are flat they should mate up. Could the head gasket be a problem?
No, the piston isn't hitting the head.
I'll check the squish tomorrow or Friday night when I have some more time.
Resurfaced the top of the cylinder tonight.
Much better.
Should be fixed.
Won't know until hopefully Saturday, that's when the new head gasket I ordered is supposed to be here.
I did use a new head gasket when I reassembled the engine, but I don't want to use that one again.
Given the improvement in how the head fits to the top of the cylinder without a gasket, I'm confident that the copper will fill in any imperfections.
I'll heat cycle the engine 3 times(bring it up to 190 to 200 f, while slightly repeatedly revving, checking temp with temp gun, let cool to air temp, repeat), then I'll re-torque the head bolts.
...if it runs, lol.
Thanks for your time.
 

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Discussion Starter #14
New head gasket, back together, same problem.
It will idle the longest with the air screw completely closed/clockwise. It will also take about 1/4 throttle that way.
Runs about 15 seconds and dies.
Stock jets, clean carb, needle in position 2.
I put the airbox lid back on and it'll run a little longer.
Makes me think it needs a larger pilot jet, but I would still think it should idle.
I'm going to move the needle down to the 3rd position, but am doubtful, as the needle should control the midrange.
I've never had a 2 stroke give me problems like this.
As I mentioned before, the thing ran great before it seized(just age, worn out, ran great for a long time).
The only changes since the rebuild are a Rad Valve(had the cf reeds in it before too, a new set now), and the K&N style air filter, where it had a foam filter before.
I can see those flowing more air, but I still think it should idle.
The further counter clockwise I turn the air screw, the worse it gets. It won't idle nearly as long at 1.5 turns out as it will fully closed.
I know now it does not have an air leak anywhere, and it has a lot of compression.
Other than a jetting change, I'm out of ideas.
 

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Discussion Starter #15
Needle in 3rd position(richer), but no change.
Since turning the air screw clockwise richens it, and it runs longer with the air screw all the way clockwise; as well as it running longer with the airbox lid on(air restricted some, so richer), I would think it needs to be richer.
However, Boyesen's instructions with the Rad Valve say that the main jet(but that controls upper rpms) may need to be one to three sizes leaner.
I had thought originally I may need to change the main or pilot, but not just for it to idle. If I cant get it to idle, I have no reference point to start from.
I'm going to call Boyesen Monday, as they're closed on weekends.
 

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Hello sixpack; Can you please explain how you surfaced your head & cylinder. Since we all do these operations differently, perhaps some of the readers will learn different ways to do this important work.
JT
:Thumbsup2:
 

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Will it run better with the choke pulled out a little? Is the TORS system still hooked up? I still think you need to do a leak down test to rule out the possibility of an air leak.
 

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Discussion Starter #18
Will it run better with the choke pulled out a little? Is the TORS system still hooked up? I still think you need to do a leak down test to rule out the possibility of an air leak.
Runs worse with choke out.
The TORS system being the idle control above the carburetor cap? Yes.
 

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Discussion Starter #20
Hello sixpack; Can you please explain how you surfaced your head & cylinder. Since we all do these operations differently, perhaps some of the readers will learn different ways to do this important work.
JT
:Thumbsup2:
My Dad did both, he's a mechanical engineer.
We checked them both with a square, criss cross across the bolt holes and studs, they appeared level.
He then said that the next way to check, while removing the least amount of material, is as follows.
He has a 12"x12"x1" piece of steel that is squared and true.
120 grit emory cloth was then clamped tightly across it.
The mating surfaces of the head and cylinder were both colored with a black sharpie.
Each piece was slowly turned in a circle around the center.
After only a few turns part of the shaded area revealed the bare aluminum again, indicating the high and low spots.
After a couple more turns, the entire area was bare aluminum again.
With calipers, at the same reference points around the mating surfaces, from the top of cylinder and bottom of head, to the bare aluminum mating surfaces themselves, showed only a couple thousandths removed from each part.
Prior to doing this I had seen where Vitos sells a stock replacement head gasket that is .014" thinner than stock.
I knew as long as less material than that was removed from both pieces combined, there would still be enough piston to cylinder head clearance. I have .008" to .009" to spare.
Even with such little removed, the difference was immediately noticeable once the head was placed on the cylinder, and without the gasket. With the new gasket on and the head torqued to 20 ft lbs, the visible gap(miniscule, but enough to see light from behind it)was now gone.
It may sound crude to some, but worked quite effectively.
The head and cylinder were also square on the trued piece of steel after.
 
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