My 1957 International 500cc has a 10tt9 carb fitted which is proving troublesome for regular riding and difficult starting issues. Has anyone fitted a Monobloc or Concentric instead? Recommendations please.
I am not familiar with the International Models so I would have the following questions:
How is the TT carb fitted? Flanged connection or threaded?
Is there an adapter between the head and the carb?
If there is an adapter is it thread X thread, thread X flange, or flange x flange?
As an aside, I would think that any carb originally specified for an ES2 or Model 19 would suffice for an International as far as air handling capabilities are concerned. Of course, you will probably have to make adjustments to the jets as necessary.
If you have a spare £500+ you can get a new 10TT9 from Burlen.
For the rest of us a 930 Premier Concentric would be a good choice.
i have one on my ‘37 500 Inter engined post war plunger Manx. Purchased from Surrey Cycles all jetted ready to go. Price I think was about £160/180. If you go for it I can let you know the settings that worked for me.
My 37 Inter MS suffers from poor starting. It has its original well worn10TT9 fitted and runs ok on it but starting especially in this current temp is a right pain. Ignition timing, valve timing, carb cleaning, jet changing, same issue.
Decided to try it with a concentric I had left over from another project. It was jetted 280,106, slide 3.5 need position one. That was my starting point. The change over involves replacing the fixings as you can’t get the bolts in past the tickler so fit studs and nuts (cycle thread). Change cables to the levers to preserve the originals and as a tip fit an inline adjuster for the throttle cable as access under the tank is limited. Fuel hoses needed replacing as the TT has 1/4 bps the concentric push on banjo.
Here we go, the motor is fresh, the mag is rebuilt, the sump is dried and I have a folding kickstart fitted, (it’s a CR box which was bump started all it’s life). Flood, choke, retard, nothing... flipped the advance up to full and she bite me, ok, I got life, retard a quarter, she tries to bite again, ease it back to half. Bang she is on, warm at low revs, set the pilot and idle (that will be new to you as a TT user). Stop, restart, yes. Ok now hook up the strobe to see where I am on ignition, it you got the flat air advance levers you have a much greater range, open to closed, so make sure you don’t get to carried away with max advance. I noted 55 degrees of control.
So now it’s a starter it’s not a clean runner. I recognise I’m down on jet sizes and needle low so I started with main jet up to 320 as per TT, no better, (8 stroking), 310 same. Back to 280 lift the needle, no start. Back down with needle, work the choke setting and ignition to get some indication on where I’m going wrong. Cam timing is giving a lot of spit back as it’s set up for open pipe. I’m tempted to back it off to give less overlap but I’m still playing with the carb combinations. But getting it to start reliably is a milestone. I’ll get the right combination eventually but its all a learning curve for me so it takes time. Will update you on progress. If you have success let me know where I’m going wrong. I intend to go back to TT once that has been sleeved and I have the motor bedded down and running well. It’s a little bit of a legacy with cammy motors, but can be cracked.
To confirm the settings that worked for me were as follows and as recommended by Surrey Cycles
main - 310, 106 needle, slide 3, pilot jet 30. Can’t remember what setting the needle is at probably in the middle
As previously mentioned though this is just a starting point. Just so happens for me it worked out perfectly, just had to set the idle.
Starting is normally a 1 or 2 kick affair, around 1/2 advance, tickle till floods bring kickstart up to compression, ease over with decompression lever a rad then a good kick through does the job
...a Monobloc or Concentric is that it's very easy to fit an air cleaner, in my mind a necessity. I recently started up my '48 Inter for the first time with a new Monobloc and she fired off after a few kicks and runs really well. I prefer the look of the Monobloc to the Concentric and believe it's a superior device in many ways. I poached jetting off someone else here and so far, so good.
389 Amal Monobloc Jetting for International Model 30:
Main jet 340
Idle jet 30
Needle jet 106
Needle D middle notch
Throttle slide 3
with Atlas manifold bored to correct size to get carb in same relationship to head.
When I acquired my Inter about 18 months ago I had terrible starting problems. Now it seems to have been sorted, mostly by familiarity. The biggest improvements I made to the TT carb were
Careful adjustment of the pilot screw. It's a turn or more further out now to increase fuel on pick up
Most helpful, an effective throttle stop. Now when it gets going, it stays on a reliable tickover even when I get off to open and close the gate. Attached photo shows it.
Don't flood. Tickle to feel bowl is full, no more, and very small throttle.
My ignition is 37. Retard about1/4" as seen on the disc on top of the lever. Advance as soon as it fires and open throttle gently. Don't blip the throttle because that just gives it big gulps of lean mixture.
I currently have a foam sock type air filter on the intake stack. By Ramair. Ugly thing but neutral colour and it's easy to remove.
If I were to change the carb, I think it would be to monobloc because they look a bit better to my eyes. The Amal 'standard' 289 is available at the correct size. BUT the angled float chamber seems to be unavailable, so you'd need to fit your TT one...if it fits and if it's the correct level.
Best of luck!
... have proved good for me though I only had a 20cc pilot, 30 on order long with screw on filter.
Michael; that looks a very nice finish on your machine.
Dave; is the threaded jet block a through hole for the "stop" screw? and is there a reason for its radial position? Its a mod I would like to incorporate with the new 5 slide. My original 7 is drilled...
Snow prevented a road test but it will come soon.
The little cheese head screw stops the slide from falling all the way down. There is a reason why it is so close to the edge, but I can't remember what it is! I think it becomes obvious once it is all in pieces. My PO fitted it but he didn't make it thick enough. I think you could pop a blob of blutak in (on the bench) and look for a small air gap...my tickover on advance is a bit quick (maybe 1200rpm) but falls to about 700 on retard. I'm sure it could be slower. I have a photo down the carb throat and I'll dig it out.
Some writers here talk about drilling a hole in the slide. But at about £70 each, I don't want anything irreversible. Now I can stop at the end of the road and wait for traffic etc, and not lose the motor if I make a hand signal. I don't think TT riders did much signalling.
David has certainly made his Inter much more civilised than could be expected. In his shoes I would probably have plumped for a pre-monoblock carb similar to the 289 that I have on my big single and got round any float issues with a remote float from a later bike. I will probably adopt Davids stop detail on an Italian SSI ( TT type) that I need to civilise for practical classic use.