1949 350 Inter main jet size

Thanks for your reply, Robert.

The needle is a no. 106 in position 1. So it's as low as it can go. I'm having the slide changed to the equivalent of a 4.5.

I guess it's just trial and error from here?

Paul

Thank you Jon and Robert. I'll let you know how I get on.

Do you know whether there is a particular spark plug that works best in these bikes, perhaps one that works at a higher temperature?

Paul

Update on how I am getting on.

Went out today as it is gloriously sunny here. Bike started easily and sat at a slow idle while I got my gear on. Setting off was a bit strange with the engine threatening to stall. Advanced the ignition and that seemed to do the trick until I reached the end of the road and slowed down - cut out on me, but I managed to bump start it while I still had some momentum.

The first mile and a half were fine, but then I got the mother of all mis-fires. Missing and back firing like crazy and throttle position made no difference. Stopped to turn for home, engine cut out and wouldn't restart. Of course I didn't have a spare plug and spanner with me. Called home and my wife came to get me (I keep a collapsible trailer in the boot of my car for just this eventuality!).

When trying to restart, I noticed what looked like steam waffting out of the carb bell mouth. What could this be? Water in the fuel?

Got home and removed the plug (NGK) black with soot. I hadn't had a chance to use a lot of throttle, so I guess I can't accuse the main jet. Will try a Champion plug (does it come with the correct gap? If not, what should it be?) and see if that makes any difference, then start playing with the carb settings.

Paul

Previously robert_tuck wrote:

If it will idle happily from cold then its too rich. Weaken off the pilot till it falters then turn back in a 1/4 turn.Could also have a too high fuel level.

Thanks Robert. Yes, it was cold, but the idle was very slow, barely one "spark" per second with the ignition about half way advanced. Where would you have the ignition advance set?

How do I adjust the fuel height?

Paul.

Previously Paul Knapp wrote:

Letting the engine idle while you get your clobber on, isn't a good idea. This will allow the plug to start to have soot deposited on it and if there is a weak sparkthe plug will start to short out under load which will then add more soot from the unburned petrol. Though, reading above brings to mind of a very similar problem I once had. It wasn't until Iobserved the magneto throwing a feeble yellow spark across a 1/4" (6mm) gap I set up,(which a health mag shoulddo with a loud, strongblue spark),that it was evident the magneto was faulty.I had the bobbin re-wound which had initially showed no fault atmy localmaggy doctor, now all back togetherand it hasn't missed a beat since.

read all about it here. http://www.brightsparkmagnetos.com/DIY/12.htm

Dan, Paul, thanks for your responses.

The magneto was overhauled in August last year (and I've only done 100 miles since then), which doesn't necessarily mean the spark is good, but on the balance of probabilities, it should be OK, unless Sod has been at it again. I'll check it anyway. Any suggestions on how I go about this single-handedly?

I certainly didn't hang around getting my gear on - not much more than being held at a red traffic light!

Thanks

Paul

Previously Andy Marks wrote:

Hi Paul

A mate of mine has a 28mm MK1 concentric that he used when he was running his 350 Inter in before going over to the TT carb. It has since done the rounds in our local VMCC section and anytime anyone is having trouble with an Inter they put that carb on as we all know it just goes on and works so if your still having problems then you know they are elsewhere!

I've just checked and when I borrowed it I made the following notes:

No. 4 Slide

220 Main

Needle in the middle

28mm bore

If you set yours up like that I wouldn't have thought you'd be far out at all. That carb has been on several bikes and once everything else is set up it starts, idles and runs perfectly. What most people have then done is put the TT carb back on and worked purely on that to try and get back to the type of running they had with the concentric.

Good luck

Andy

George, Andy,

Thank you.

George, the Mk1 was brand new in August, so unless anyone has experience of porous floats from new, I'll assume for now that it is OK. If it is floating OK, could there still be a problem if it floats at too high a level?

Andy, I'm now running a 230 main, 106 needle (middle pos) and No5 slide (ground for me because Burlen only goes to No4). So far, I'm pretty sure the main hasn't come into play. If it isn't electrical, pilot is looking likely.

BTW, my bike is a clubmans model, in case that makes any difference.

Thanks again to everyone who has responded. New plugs arrived today, so when my knee has recovered from my restarting efforts earlier in the week, I'll try that and also check for a strong blue spark. What should the spark plug gap be?

Paul

Update.

I have changed the plugs as suggested to N5C and weakened the pilot by turning anti-clockwise (is that the right way?). Also now running on premium unleaded.

I have been out for two rides, one of 20 miles and one of 32 miles which included a run up Kop Hill just to see if I could (and I could!).

On both rides there was some misfiring but mainly only in 3rd or 4th gear at speeds above 40mph. Accelerating in first or second seemed absolutely fine, even though the throttle was probably more open than at 40mph in 3rd or 4th. Puzzling. Anyway, about two miles from home I got the dreaded mother of all misfires again and the engine died. This was just after climbing a steep hill. At this point the plug was 50 miles "old". I changed it for a new one and got home. Still misfiring, but this time probably because I forgot to advance the ignition after restarting (doh!).

Plug is still soothed up with absolutely no sign of the light brown colour I want.

So, first question, did I turn the pilot screw the correct way for weakening? Secondly, I think it's time to go smaller on the main jet, but in what increments? It's a 230 now. How big a change is it in real terms to reduce to the 220 that Andy used? Maybe I should just get a 220 and 210 and do some trial runs?

Any advice gratefully received.

Thanks for reading this missive.

Paul

Thank you both.

Robert, the soot is matt black. There is no choke fitted. So I was actually making the pilot richer!

John, good idea. I'll mark up the throttle in the morning.

Paul

Previously robert_tuck wrote:

Forget messing with the main jet ,that is not your problem. Make sure the choke is up and clear away. Screw the pilot air screw all the way in (gently!) how many turns was that? should be at least one and a half/two turns , Is the soot a matt black or slightly shiny? ,if shiny then the issue is oil,not fuel.

Robert,

If by a "turn" you mean 360 degrees, it was 2 and 1/4.

Paul

Previously barry_stickland wrote:

Your problem is to do with the piston, piston rings, or cylinder bore.

Barry Stickland

Barry, I haven't had the engine apart since I've had the bike, so I don't know for sure the condition of the piston/rings/bore, butif this were the case, would I not expect to see smoke from the exhaust? I'm not aware that there is any. Also, when I remove the spark plug it is dry. Wouldn't it be wet and or shiny if oil were the problem?

Maybe I should do a compression test? Would that tell me anything?

Paul

It has been a while (!!), so I thought I'd let you know what's been happening in the last year. I gave up trying to find a suitable setting for the carb and as I knew nothing about the bike's previous service history or use, decided to get the engine stripped down so that I could eliminate piston, rings etc.. As it turned out, that was a good decision. It was like a coal mine in there! Obviously hadn't had any TLC, probably for decades. Completely worn out. No amount of carb fettling would have made this engine run well.

It's all back together again and looks fantastic. I have reverted to its original TT carb and am in the process of learning how to ride with it.

Haven't totally mastered the starting process, but I'll post elsewhere on that subject.

My thanks to all who commented on this thread.

Paul