Triumph Rat Motorcycle Forums banner
1 - 7 of 7 Posts

·
Registered
Joined
·
122 Posts
Discussion Starter · #1 ·
I'm trying to get my dad's Tiger 90 running a bit better and having stripped and cleaned the carb have managed to get it pretty good once started. It rides perfectly on the road so I'm guessing the basic size, main jet and needle are about right. The trouble is its a pain to start, not too bad cold but a nightmare when hot. I'm wondering if this could be to do with the pilot jet as to get it running ok I've had to screw it right in.
From my limited experience of Monoblocs I presume that this means it is running lean on the pilot and could do with a slightly bigger jet. Is that right? I'm hoping a bigger jet will allow the adjuster to be screwed out more to give more chance of adjustment.

Starting from cold needs a big flood on the tickler and when hot the usual no throttle-no tickle doesn't work. A little tickle is needed even when hot or it usually won't fire.

It has to be said that the bike has been tuned up a bit from standard (and has always been hard to kick!) so there aren't really any basic settings to go from. It's the same 1" 1/8 carb as standard but it originally would have been a pre monobloc horizontally mounted.

So am I right in thinking it seems too lean because the pilot adjuster is screwed right in and am I right in thinking I need to go bigger ie from a 35 to a 40 for example to make it richer?

Thanks in advance
 

·
Registered
Joined
·
122 Posts
Discussion Starter · #3 ·
TT, yes a 1937 big single. My thinking is that if the only way I can get it to run half decent is to have it screwed right in then perhaps its not rich enough and I don't have the adjustment available. Plus having to tickle when hot isn't ideal as if you over tickle then you risk flooding it.

Forgot to mention that the plug is very light in colour and even when you think you've flooded it, it turns out to be fairly dry. Maybe I'll try lifting the needle a notch or two though I don't think that will alter much at small throttle openings.

I'd like to get it to the stage where I can ride it somewhere and stop the engine without fear of 10 minutes of embarrassing kicking to get it going! It doesn't help being fairly flat round here so no option of bump starting without a push!!
 

·
Registered
Joined
·
122 Posts
Discussion Starter · #4 ·
Here is the beast in question:
 

Attachments

·
Registered
Joined
·
2,965 Posts
Are you sure the pilot jet is clear? Have you seen the sky through it?

Air leaks into the joints between carb and head are betrayed when you have the engine idling and spray WD40 at the joints.

If you have no such faults, I don't see what can be wrong with trying a bigger pilot jet. It's more common to try a slide with a smaller cutaway, but I can't say which fix would be better for your bike.

Nice, game-looking bike.
 

·
Registered
Joined
·
122 Posts
Discussion Starter · #6 ·
I'll have a look at the slide but I think its the smallest cutaway already, more research required on that though as the numbers on it don't seem to relate to the sizes available.

Pretty sure the joint is good, its nice and flat and has a new O ring, I'll try the WD40 trick though.

As for the pilot jet I've not actually removed it as it seemed like it might break the slot as it was very tight. I gave it a good blast with air and it was coming through the body of the carb. I'll have a proper go at removing it to confirm it's clear, if I'm changing it I'll HAVE to get it out anyway!

It's a game bike to ride, it was built as a sprinter but ended up as a road bike. It goes, stops and handles amazingly well for an 80 year old machine.

Thanks for the help
 

·
Registered
Joined
·
1,131 Posts
While you might have a hole in your #35 jet after blowing through it, a hole "does not a jet make."

Pretty close works well when working with hand grenades, it does not work at all when working with jets. This is especially true when working with pilot jets who's orifices can be as small as .016" in diameter.

Continue to treat a jet's orifice as a hole and frustration will continue to follow you throughout your days working on these instruments.

Blow, squirt and poke and frustration will follow!

Oh, the point replace the pilot jet, and adjust the size to suit. This pilot air screw orifice works best when the pilot air screw is 1 1/2 turns out. If it is less increase the pilot jet size. If it is more decrease the pilot jet size. Then make small adjustments to the pilot air screw and slide cutaway to get a smooth transfer from the idle carburetor to the main carburetor.
 
1 - 7 of 7 Posts
Top