G2 idle and running issues - with videos!

[BultacoBen]

Hello!

I'm having some issues with my little G2. Bought as non-runner I've got some life back into it but never with great success. The two times it's been on the road on its way to MOT it was 8-stroking and then loss of power and then death...

The timing was some way off correct (but I can't remember in which direction... Remedied now.) and checking the fuel level using a cover I laser-cut in perspex I diagnosed it as too high and added a 0.7mm shim to the top of the float:

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This has brought to the fuel level to the top of the pip when on the sidestand and the bottom of the pip when stood vertically:

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I haven't yet had it on the road to see if it loses power like it did before but once warm it struggles to idle happily. Here are two videos that may help with diagnosing what's going on:


It starts after 9 kicks with the choke applied, and I then raise the choke, after which it seems to idle reasonably happily. At 1:00 I fiddle with the idle screw to see where it is and find it is fully wound in. Winding out a fraction causes the bike to stop. I also stand it vertically as this used to make the bike stop, I suspect because it effectively raised the fuel level in the bowl from the carb's perspective.
Re-starts happily enough at 1:08 and idles OK, idle slows a bit when I stand it vertically at 1:20 but keeps running. Idle speeds up when it returns to the sidestand at 1:38.


Later, nothing has changed except the engine has warmed up a bit. When I stop holding a fast idle with the throttle or revving it, the idle is very slow and the engine stops.

With the idle screw wound fully in I'm surprised the idle isn't faster... (but then, I had to make modifications to the float to get the fuel level right so who knows with these old carbs...)

The jets and needle are all new so precluding me having been sent the incorrect jets by AMAL I don't think this is the issue. I think I remember checking them when installing but am not certain.

Any suggestions for a happier idle when warm?

[BultacoBen]

Unrelated, there also seems to be air and a dribble of oil blowing out of the small hole in the right hand cap, normal? (May have to scroll to the right to see this in the picture, apologies for the size am uploading from my mobile and can't decrease the size)

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The filthy engine is mainly down to oil leaking from the other side of the engine and then running round and dripping down with the two main sources appearing to be screw controlling oil feed to the inlet valve, and the inspection cover. The screw is in the correct position (all the way in and then 1/8th of a turn out?) so could this be remedied by tightening the nut, which is already pretty well done up? Not sure how to resolve the inspection cover leak as it is as tight as I can get with fingers and the rubber gasket seems in reasonable condition....

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[clanger9]

Hi bbenxe,

Some thoughts:

If it's 8-stroking then it's running much too rich. You mention you've changed the jets: did you replace/check the gasket under the jet block? It'll run horribly rich if there's any leak here.

What is the idle mixture set to? It should be a 1 1/2 turn out (or thereabouts). If it's a lot different from his then something else is wrong...

Finally, if it starts up and runs fine, but the warm idle is "a bit rubbish" then it may be that the main carb body is worn and the throttle is too loose a fit. You can get it re-sleeved, but it's probably best just to get a new carb in that case.

On your second post, I can't think why there would be "air" coming out of the clutch cover cap. The chain case isn't pressurised (it's pretty much open at the back around the sliding seal). How much oil is in there? It should just touch the bottom run of the chain. It's a mystery to me why there would be a hole in the couch cover cap. I'm sure it's not supposed to be there!

[Rob Harknett]

You need to check you have the correct carb number, then check it is fitted with all the correct parts, not just the main jet. Throttle slide must be correct and needle position. I have never bothered checking fuel height on any bike. You also appear to have a lot of spare thread on the fixing stud. Have you longer studs or wrong thickness spacer, not that that would make too much difference. The only time I have had a bike 8 stroke was on my 1936 AJS 250. Had a bit of a job to climb the hill back to the Jampot rally site at Oakhampton. Having just done the Sunday run over the moors to Princetown and back 2 up. It started 8 stroking on the last 1/2 mile. The carb was very loose, one nut almost off. Tightened up the nuts, but that did not cure the problem. I took the bottom nut off the carb and the main jet fell out. I once had a 2 stroke 4 stroke, that was due to a blocked exhaust. Is your silencer clean.

[Janet]

It shouldn't have a fibre washer underneath the banjo fitting on the fuel intake.


Edit: Please see Duncan's later post for correction. Possibly.

[Les Howard]

I don't recognise your float as the correct one...they are usually drum shaped. BUT ...even the correct AMAL float is not always free of problems....A little while ago I identified the dimension of their plastic one as being a little to big in diameter and it caused it to stick or jam as it moved by the internal thread boss of upper float chamber cover screw opposite the pivot...Cure is to file away part of the casting. I questioned AMAL and they admitted I was right and sent me another one from their latest batch in which the float is slightly smaller....I don't know if your float is not buoyant enough or it is sticking but if it is then it could cause flooding and a rich mixture and maybe it only occurs when the engine is running due to vibration. If the 8 stoking occurs when on a run. Shut the engine immediately and examine the fuel height, but note the fuel level can drop after you stop the engine as a high fuel level tends to drain off automatically via pilot jet to a certain extent so you need to do the check with no delay....Les

[SideValve]

Just a thought but might be worth double-checking the timing. If it went a long way out before it might be that its moving on the taper or the back-plate isn't secure. I had a G2 before where you could twist it on its mounting.
Another mistake I made was timing it in the wrong direction - not one of my brighter moves.....

[Ozmadman]

Simple... you are using the choke lever incorrectly... Pulling it toward you will take the choke off.. you are pushing it away from you which is putting the choke on!!! no wonder it is choking and not running properly. Mine will start without the choke as most lightweights will unless it is extremely cold. Push the choke away from you to start it and pull it toward you once started and I reckon that will solve your problem The float is not right as it should be a brass one and there should be no hole in that primary case cap

[Ozmadman]

Hi bbenxe,
Finally, if it starts up and runs fine, but the warm idle is "a bit rubbish" then it may be that the main carb body is worn and the throttle is too loose a fit. You can get it re-sleeved, but it's probably best just to get a new carb in that case.

If the slide/bore is worn then you will probably hear it rattling, if so get it re-sleeved by Matryn Bratby, far better and cheaper and longer lasting than a new carb which are of dubious quality these days. Had mine done and it ticks over like a Swiss watch now

and this was before my recent engine strip and rebuild to cure an engine knock at revs

On your second post, I can't think why there would be "air" coming out of the clutch cover cap. The chain case isn't pressurised (it's pretty much open at the back around the sliding seal). How much oil is in there? It should just touch the bottom run of the chain. It's a mystery to me why there would be a hole in the couch cover cap. I'm sure it's not supposed to be there!

What do you mean "sliding seal?? + there may be a bit of pressure build up if the engine breather is naff/blocked as there is no crank seal on that side of the engine

[Ozmadman]

The filthy engine is mainly down to oil leaking from the other side of the engine and then running round and dripping down with the two main sources appearing to be screw controlling oil feed to the inlet valve, and the inspection cover. The screw is in the correct position (all the way in and then 1/8th of a turn out?) so could this be remedied by tightening the nut, which is already pretty well done up? Not sure how to resolve the inspection cover leak as it is as tight as I can get with fingers and the rubber gasket seems in reasonable condition....

Only have the screw out a tad (1/16th), just enough to let a little oil through under pressure and put a bit of gasket goo on the thread of the screw, something liquid like Wellseal but not anything that is liable to block up the hole. Make sure the gap in the cover rubber seal is at the top!! and put some Wellseal on it if you can't stop it leaking. I tighten my screws up a bit more than finger tight with pliers, just to nip them up as I have lost these before due to vibration if only done up finger tight