Ariel Owners Motorcycle Club

Let us know what you find and how it goes.
Do you have the service tools needed.
Where in the country are you?

Evening All

I am struggling to cure the continuing problem, on this Arrow. As mentioned above the issue is a reluctance for the engine to run unless with either full choke or a very wide throttle opening.

I received the bike without any history or other evidence of its condition. After some work on the electrics I got the engine running though only with the symptoms as described above. After checking and eliminating the carb and ignition, I assumed crankcase seals were failing, causing a loss of crankcase pressure so I stripped & replaced these along with the main bearings. (I noted that the original outer RH seal was brittle so imagined that I'd discovered the root of the problem). I also, at the same time, re-bored the barrels & fitted new 'Japanese-origin' pistons.

When reassembling the bottom end, I followed the directions regarding crank run-out and, although I persevered with a dial gauge, piece of chalk and a longish tube, I was unable to achieve anything like the 0.001" figure stated in the manual. The best I could achieve was something like 0.008"!!

So, having completed the rebuild, disappointingly, I found there was no difference to the original symptoms. Ie. the engine will only run on full choke or a very wide throttle opening - it sounds 'strangled' on opening the throttle if it isn't choked or the tickler depressed to enrich the mixture.

Clutching at straws, I removed the silencers (even though these seemed to be clear) and re-ran the engine to eliminate excessive back-pressure as the cause. I found there was no difference to the symptoms, but a few curtains twitched at neighbours' windows!

The carb has been thoroughly cleaned, the flange re-faced and its spec verified as correct for the model. Ignition timing is as per the book and the spark is good.

I noted, when I dismantled the engine, that the inner main bearing journal on the LH crank had been sleeved (in fact, this remained in the inner main bearing when I removed the crank); I believe this is not standard. Although the sleeve doesn't extend as far as the taper (which locates in the RH crank) I am wondering whether this has affected my success in achieving satisfactory crank run-out. Anyway, I am wondering whether the excessive crank run-out is affecting the crank case pressure. Personally, I'd have thought that the seals would tolerate this - even if the main bearings would protest!

Any ideas you have on how I might proceed would be gratefully received.

Evening All

I am struggling to cure the continuing problem, on this Arrow. As mentioned above the issue is a reluctance for the engine to run unless with either full choke or a very wide throttle opening.

I received the bike without any history or other evidence of its condition. After some work on the electrics I got the engine running though only with the symptoms as described above. After checking and eliminating the carb and ignition, I assumed crankcase seals were failing, causing a loss of crankcase pressure so I stripped & replaced these along with the main bearings. (I noted that the original outer RH seal was brittle so imagined that I'd discovered the root of the problem). I also, at the same time, re-bored the barrels & fitted new 'Japanese-origin' pistons.

When reassembling the bottom end, I followed the directions regarding crank run-out and, although I persevered with a dial gauge, piece of chalk and a longish tube, I was unable to achieve anything like the 0.001" figure stated in the manual. The best I could achieve was something like 0.008"!!

So, having completed the rebuild, disappointingly, I found there was no difference to the original symptoms. Ie. the engine will only run on full choke or a very wide throttle opening - it sounds 'strangled' on opening the throttle if it isn't choked or the tickler depressed to enrich the mixture.

Clutching at straws, I removed the silencers (even though these seemed to be clear) and re-ran the engine to eliminate excessive back-pressure as the cause. I found there was no difference to the symptoms, but a few curtains twitched at neighbours' windows!

The carb has been thoroughly cleaned, the flange re-faced and its spec verified as correct for the model. Ignition timing is as per the book and the spark is good.

I noted, when I dismantled the engine, that the inner main bearing journal on the LH crank had been sleeved (in fact, this remained in the inner main bearing when I removed the crank); I believe this is not standard. Although the sleeve doesn't extend as far as the taper (which locates in the RH crank) I am wondering whether this has affected my success in achieving satisfactory crank run-out. Anyway, I am wondering whether the excessive crank run-out is affecting the crank case pressure. Personally, I'd have thought that the seals would tolerate this - even if the main bearings would protest!

Any ideas you have on how I might proceed would be gratefully received.

It is too much run out, You'll notice it in the smoothness of the engine. The low down running issue is due to either the carb. idle system not working properly or a crankcase air leak most likely. Nev

Hi Clive
Let us know what you find when you get there

Ok, it looks like I shall have to strip the engine back down to investigate further. I'll report back when/if I discover the cause...

Well, in an effort to investigate the possibility of leaking seals, and before resorting to a more extensive mechanical exercise, I devised a rather unscientific approach as follows...

I stripped down both alternator and primary sides, as far as poss, to reveal the crankcase 'doors' then blocked off the exhaust pipe ends with gaffer tape. My thinking was that gas could be drawn into the crankcases but, as there would be no escape through the exhaust ports, this would help increase crankcase pressure and reveal any leakage more noticeably through a faulty seal. Comments, please!

I then smothered all suspect locations with soap suds (the time-honoured tyre-fitters' choice for leak detection) and spun the engine over on the kick-starter. I carried this out several times but could see no bubbles emerge from any location (though less easy to observe on LH side due to the flywheel partially obstructing my view).

I know this doesn't verify the centre seals but, it would seem, the outer ones are fine. As the engine is so dramatically affected and just won't run without full choke (or wide open throttle) I'd have thought any leakage through the seal(s) would have been very obvious. But, hey, the darned seals were renewed during the very recent rebuild!!

I cannot imagine the problem is due to the carb as I have checked it over several times now. I suppose the only way of eliminating that is to borrow one that is known to be good, if I can find one...

Ahh, having reviewed my test method, I see a flaw in my reasoning. The crankcases won't pessurise if the inlet Is left open to atmosphere. Whoops!

Coming back to the carb. Having experienced very poor running on my W/NG recently, and having checked the carb over, I replaced one or two parts. With new bits, I was able to ascertain that although the old parts appeared correct, one was excessively worn when compared to a new one, and one of the jets had apparently been drilled out - it fooled me because the number was correct.

So the question is, are you sure the carb is OK? Some of the bits might look right but be damaged. It doesn't take much wear to ruin a needle and it's hard to see it with the naked eye.

Second question - are the needle jets for the two stroke engines the same as the ones for the four strokes?

Update. In order to test for crankcase leakage I made up and fitted the following items...

* A pair of rubber-faced discs to plug the exhaust ports (I used the standard exhaust roses to compress and retain them)
* A blanking plate (with an 'o' ring groove) for the carb flange. I fitted, to this, a schrader valve to take an air line.

When I attempted to pressurise the cases, surprisingly, the gauge remained resolutely at zero - the chamber seemed to be vented direct to atmosphere! on investigation I realised that this was, indeed, so. Air was venting straight out of the crankshaft centre which would normally be occupied by the alternator rotor bolt. I didn't realise that the RH crank was hollow in this way. Having plugged the hole with the rotor bolt, I could then see a substantial leak around the 'top-hat' shaped collar on which the RH seal bears - a poor design, eh!

I'll fix the leaks I've discovered and check again...

Regarding the carb (Simon). Jets are generally no different to 4 strokes as far as I know. There is a range of needles, of course both in length and profile. So, it can be something of a mine-field if you've not got access to Burlen's catalogue! However, the spray tube is different on a two-stroke - being bevelled off (on the engine side). Having said that, I know that there is at least one 4 -stroke which employs a similar arrangement in order to avoid using a very large main jet - the Norton 850 Commando.