revs wont die down

[drillam]

When I come to a halt my MK1 over revs for quite a while until slowly dying down to normal tickover speed. I can force the revs down by holding it in gear (2nd) for slightly longer than I would normally and forcing the engine speed down before I de-clutch and it immediately settles to a normal tickover.
The throttle cable seems fine and turning the bars doesn't induce revs such as an overtight or badly routed cable might. The throttle slide can be heard and felt snapping shut when I close the twistgrip.
Any ideas please?
I've done a search but can't find anything.
thank you.
millard

[knackeredMk1]

You might be overheating because of running lean. Have you changed anything on the bike or taken the carb/airbox off How far out from all the way in is your air screw

If you are running lean you need to sort this out otherwise it could seize.

[fallenmikethebike]

You might be overheating because of running lean. Have you changed anything on the bike or taken the carb/airbox off How far out from all the way in is your air screw

If you are running lean you need to sort this out otherwise it could seize.

+1, That does sound suspiciously like an air leak, engine side of the Carb.
Do you know when the top end was last de-carbonised?
Mike

[drillam]

Hiya
Well the filter is standard as far as I'm aware and I just cleaned it last week.
Last time out, which was also my first time off road with the bike, it started to show this symptom and has been getting steadily worse. The previous owner told me he had set everything up and it initially felt very good.
I had a look at the air screw and it was only turned out one full turn, so I corrected it and took it round the village a few minutes ago. It's good on a rising throttle but rough when the throttle is closed down or backed off for built up areas.
I put it on the stand and set the tickover speed and played around with the air screw but at that engine speed it appears to have very little effect. I'm begining to suspect blocked pilot jet, but would that cause the engine's reluctance to stop reving when the throttle's blipped?
I'm just off to the shed to strip and blow the carb throw.
Any other suggestions more than welcomed, thanks guys.
millard

ps
No idea as to the last decoke, but had a look down the plug hole recently and the piston crown looked very clean. I'm not at all familiar with two strokes so don't be scared of "teaching granny to suck eggs" here.
Feel free to state the obvious.

[knackeredMk1]

It could be that your throttle cable is on the way out and frayed ends are slowing the return of the carb slide even though the throttle itself had been let go.

Take the cable off and look at the inner where it comes out at both ends. If it is frayed, rusted or kinked this could be the problem. Change the cable if it is wrong but oil it anyway before putting it back if no problem.

[drillam]

Throttle cable is good but there must have been nearly a flat teaspoonful of mud'ncrud in the carb from where I drowned it during last week's trail ride.
The surprising thing is that the wee bugger ran at all, let alone poorly.
I'm blowing it all through and cleaning it up now and will hopefully have it running tonight for tomorrow's trail ride.
I'll get back to you later. Thanks for your suggestions.
millard

[drillam]

I put the carb back together and the jets are as per spec but the needle is marked J35D (sounds like a bra size) and has four slots. The clip is in the second from top.
Started it and let it run for a minute then blipped the throttle a few times and there was no improvement. After a wee while it decided to rev all by itself. While doing so I sprayed WD40 over the inlet stub in an attempt to temporarily eliminate any leaks, but to no avail.
In spite of this I suspect the inlet stub may to be to blame here as it might have been disturbed and any cracks worsened by removal and replacement of the carb. Any thoughts would be most welcome at this stage, thanks fellas.
Millard.

[drillam]

Well I've removed the inlet stub and reed block. The gaskets weren't too good so I'm making new ones.
The stub looks good, I can see no evidence of perishing nor cracks.
The amount of crap in there was scary though, just as the carb was.
I'm beginning to wonder if all that muddy water going through the engine when I drowned it last week could have damaged the crankcase seals. There was mud on the plug when I took it out to try and get it running again and this was the state of the airbox.


<img src="http://i14.photobucket.com/albums/a340/ ... rymud1.jpg">

[IMG]http://i14.photobucket.com/albums/a340/ ... rymud1.jpg[/IMG]

Other than the inlet stub/reed block, crank seals and head/base gaskets, are there any other possibilities for air ingress after carburation?

I'm going to reassemble the carb, check head and base nuts for tightness and try it again with my fingers crossed that I don't have to tear the cases apart to fit new seals.

cheers
Millard

[drillam]

Before replacing the reed block I started to clean out the inlet tract which was mucky. I had a look down the hole with a wee torch and could see the flywheels and conrod/big end etc. They all seemed clean enough from what I could see, but there was oil on the flywheels, as if they were dipping into a puddle of oil at the bottom of the cases. This didn't register at first as it's normal on a four stroke. But then I remembered it's a 2 stroke, surely there shouldn't be any oil in the crankcases on a 2 stroke?
Could this be my problem? damaged crank seals pulling in oil from,,,where? I'm not familiar enough with these engines to know if that's a possibility, but it looks like I will be, very soon.
I put it back together and it's getting worse every time I start it. This time I let it idle for a minute and started fiddling with the throttle stop as I'd just rebuilt the carb. The engine's response to any adjustment to the throttle screw's position was hardly noticeable until I screwed it all the way in when it VERY suddenly started screaming. So much so that I hit the kill switch, but nothing happened. I turned off the petrol tap and then remembered the ignition key, turned it off and it finally died.

I'm stumped, don't know what to try next. I don't mind if I have to replace the seals but don't really want to make a start on it until I can eliminate all the other possibilities.
Any ideas please?
cheers
Millard

[fallenmikethebike]

Bad news i think mate, by all means replace the crank seals,it may make a temporary difference,and if sourced from a bearing factor place they will be cheap enough not to worry.
Oil in the bottom of the crankcase is not that unusual on a 2T, it's a residue from the walls and other surfaces, and shows the autolube is working fine.
Unfortunately,, if your bike,s had that big a drink out of a muddy puddle, and the crud has ingressed the inner workings to the degree you described, it,s more than likely a full rebuild time , but try the seals first, however, you will be very lucky if it does not let go in the near future, very sorry, and i hope i am wrong.
Mike

[knackeredMk1]

My strong suspicion is to go with FMtB .

There was one instance of similar symptoms to that which your bike is showing but is very unlikely - viewtopic.php?f=6&t=4763

[drillam]

Meaning that I've possibly/probably shagged all the bearings ??
Mains wouldn't be too bad but big end would be pricey I'd guess .

If there's no other explanation for the over-revving then i'll try the seals first and see what happens. I had a look through some old posts and it appears to be a relatively easy job as the cases don't have to be split so it can be done in frame.

Could you guys give me a pointer as to what other gaskets and seals will be disturbed in the process please?
I'll figure out from that which will likely need replacing and which I could re-use or make myself.
Also I had a look to see what sizes the crank seals are and although I found one post with that question I couldn't find an answer, any pointers please?

I very much appreciate your responses fellas.

cheers
Millard

[fallenmikethebike]

Meaning that I've possibly/probably shagged all the bearings ??
Mains wouldn't be too bad but big end would be pricey I'd guess .

If there's no other explanation for the over-revving then i'll try the seals first and see what happens. I had a look through some old posts and it appears to be a relatively easy job as the cases don't have to be split so it can be done in frame.

Could you guys give me a pointer as to what other gaskets and seals will be disturbed in the process please?
I'll figure out from that which will likely need replacing and which I could re-use or make myself.
Also I had a look to see what sizes the crank seals are and although I found one post with that question I couldn't find an answer, any pointers please?
Crank side, 22mm =bore x 34mm =dia x 7mm thickness , i haven't, done the other side , yet.
You will need a magneto puller, the seal is best taken out on that side by screwing in a couple of self tapping screws, Carefully, and then using these to evenly pull out the old seal.
Order both sides, but start on the mag, side first to see if it improves the problem, before diving into the other side, which will require a casing gasket, at least, carefully easing , the hoses should mean not disturbing the water pump.
Mike

I very much appreciate your responses fellas.

cheers
Millard

[drillam]

Thanks Mike
I read this by Knackered in another thread :-


""Re: Main bearings and crank seals
I believe seals are - 38x52x10 & 22x34x7
Bearings - 63/28
Someone confirm?""



So I'll get the double lipped version which someone else mentioned and see what happens.
BTW
I've read both YES & NO to the question of whether the seals can be replaced in frame without splitting the cases, gut feeling would be yes but can anyone confirm this please?
thanks
Millard

[fallenmikethebike]

Thanks Mike
I read this by Knackered in another thread :-


""Re: Main bearings and crank seals
I believe seals are - 38x52x10 & 22x34x7
Bearings - 63/28
Someone confirm?""



So I'll get the double lipped version which someone else mentioned and see what happens.
BTW
I've read both YES & NO to the question of whether the seals can be replaced in frame without splitting the cases, gut feeling would be yes but can anyone confirm this please?
thanks
Millard

Did mine on the crank side with engine in situ, can't see why the other side should be any different.
Mike