2 STROKE Questions (air leak?)

[erectordale]

I've been working on my Tiger 500 trying too find why it pulses when running rev's about 3,000 rpm then want's too dy give a little throttle and it revs and want's too die out. I have just replace the crank seals, re -sealed the cases, head and base gasket I had this running great last summer just wouldn't kick start. we adjusted the timing and it will kickstart now put you have too give it a shout of gas or ether at this point and time I thought I would ask for some advice as I've lost my patientance with it. I really thought I had this figured out . things that are differant than most 2 strokes are as follows

1 no case gaskets I used yamabond,hondabond
2 I used yamabond on the base gasket too be sure
3 rotax used a aluminum head gasket I found this leaked horribly so I used yamabond on it as well
4 I sprayed starting fluid every where and can not find a air leak
carb is totally rebuilt with all new parts
5 the piston only has around 20hrs if that on it


I have done a bunch of honda 250r motor's and never have ever had this kind of trouble I only want too tear in too this 1 more time I'm really curious what else it could be Thanks in advance Dale

[Louis Mielke]

Um I didn't think you could use yamabond on ahead gasket.

[Huffa]

Would a leak down test possibly be your next step? I forget exactly how that is accomplished, somehow by pressurizing the engine and watching with a guage to see how long it holds the pressure ?

Here it is ........... (maybe you did that already though?)

http://www.xs11.com/tips/misc/misc3.shtml

http://www.google.com/search?hl=en&client=firefox-a&channel=s&rls=org.mozilla:en-US:official&hs=nNJ&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=2+stroke+leak+down+test+&spell=1

[Erics350x]

sounds like you arent getting enough fuel. i'd try going through the carb and petcock.
Dont use starting fluid on 2 strokes it'll cause some serious wear to the topend. Use some premixed gas instead.

[Billy Golightly]

Dale you need to build a leak down tester, that would be my first place to start. You can use the directions from Macdizzy as a guide: http://macdizzy.com/leakdown.htm Or you can build one a little bit differently. I used a radiator pressurizing tester as a base, I had the end adapter that fits onto radiator caps removed and had my local napa make a new hose with a 1/4inch male pipe fitting on the end that swivled. I then turned a block of aluminum that fit the intake, drilled a hole all the way through it and threaded it where the hose would go in. I then made a plate that bolted onto the 250R cylinder in place of the exhaust flange. Another thing you could use those is those expanding rubber pipe plugs that plumbers use, would probably even work better.

After all thats done, pump it up. Its got to hold 7psi, for ATLEAST 7 full minutes without dropping any. If it drops at all you got a leak. Find it and seal it, pressurize it again. Repeat until its perfect. I've spent a lot of time cleaning and leveling surfaces, sealing up places extremely well on my flat tracker and I've got it where it will hold 12psi over night, but this is a little on the extreme side and not really needed. Just part of my obsessive compulsiveness I have :)


Do that first...and if your holding good pressure inside the engine then we need to start looking at other things like the carb and maybe the rotary valve, but I don't know much of anything about those :(


EDIT: Wrong link before :lol:

[iowarotax]

Dale, does that have the Bing carb or did you put something else on it? My buddys ice bike has the same engine and it has always revved like that. I would try a different carb. I think I read somewhere that the Bings have to be replaced sometimes, rebuilding them doesnt help.

[erectordale]

Yes I have a bing carb on here this has every part possible too change brand new I have a compression tester that won't work guage busted I can build off that I'll try the leak down as I'm really lost at this point I do have a 40mm sled carb that I could try

[erectordale]

It can't be overhaeting as it's doing it from the start-up cold

[erectordale]

I'm going too build a leak down tester now I have everything here too build it be back in a while

[iowarotax]

On my friends, you would be riding it and come out of a corner and hammer the throttle and when you went to let up on it it would stay WIDE open. You had to jack the throttle once and it would be normal. Does your Bing have a choke or the tickle button?

[Bryan Raffa]

I would try and replace that bing...

[Huffa]

Dammit ..........:banned: the BING! :D

[erectordale]

well I found the main issue The head might as well not be on there I never seen 1 leak this bad we could not even build 1# of air too register on the gauge. now what can I use for a sealant on the head don't tell me the copper stuff as it just stays slime and never seals up hondabond of course won't work

[Huffa]

What about sending your head out and have a custom gasket made?

http://www.headgasket.com/gaskets.html

How in the world did it even run then with no compression :crazy: :confused:

[Louis Mielke]

I'd have ronnie or someone level that head, and them find someone to cut you a copper head gasket. You might be able to do it yourself if you get some really small sheet metal snips

[erectordale]

I can get soft copper locally and make 1 as this has no bolt holes or anything its just a ring I guess I will try that as all else has failed so far

[Daddio]

Just imagine how it will run with good compression.
:rolleyes: I have some sheet copper Dale.:rolleyes:

[erectordale]

How thick is it Daddio

[Daddio]

That is a very good question. I'm not sure of the answer though. It is across town at my old mans shop.

[erectordale]

I have a local sheet metal shop I will hit monday can't be that costly

[Daddio]

Probably not. You might even see if they could cut one out while you're there.

[Billy Golightly]

You gotta get the surfaces level first before you worry about a gasket. Don't even bother taking it to a machine shop unless its someone that definitely knows what the hell their doing and keeps all their tooling dialed in constantly. You need a certified piece of granite (or a real thick, straight and level piece of glass) with some 180grit sand paper taped to it. Do the bottom of the head, remove the studs and then do the top of the cylinder.

[Erics350x]

Some machine shops can cut a groove in the head for a copper o-ring. My brother has this done on really high compression or boosted engines all the time.

[erectordale]

the top of the cylinder is next too impossible too level the head sets down in on the top of the sleeve thats the only spot that makes contact with the head its about 6mm down in side I thought hat it was sleeved wrong but I have 3 top ends and they all are set up the same way , I 'm trying too scan this parts diagram I have for the 500 too show how this head has a step in it

[erectordale]

Her's the diagram of the top end for the 500 if you lookk closely the only thing in there is 2 little orings

[erectordale]

I found out today from a old time racer that on this type set-up you need too lap the head in like you would valves then use high tac or spray copper sealant

[Daddio]

The old aircooled VW engines didn't have head gaskets either, must be the German influence:crazy: .

[erectordale]

after lapping the head for 3 hrs and making a thin gasket out of aluminum the *&^^%* still leaks enough it won't go. I guess another day of lapping tommorrow

[erectordale]

Finally I have this head sealed. the head calls for a o-ring on 2 studs. we added a o-ring and sealed them with sealant too be sure cut 2 -1 thousands brass shim stock head gasket and sealed it with a aircraft gasket maker type sealant.

we now can hold 9# of presure for 10 mins :w00t: the 500 will be at trikefest for sure now :D

[Mosh]

This is great news Dale.I love that machine.

[Billy Golightly]

That is great to hear Dale, glad you got it squared away!