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Rita Ignition, Tire Tubes and Carburetors Q and A with Keith

Lucas Rita ignition, tire tubes, Triumph and Mikuni carburetor are this month’s featured questions Keith answers.

Keith_Garage
by Keith Fellenstein

Lucas Rita ignition

Q: Hi Keith. I read your article on Triumph T140E wiring and the Lucas Rita ignition. My 1976 Triumph T140, which has been heavily customized, has this system fitted. The bike is being recommissioned, very slowly due to time, but I’m working on the electrics at the moment. I noticed when I was testing the ignition that when a spark is triggered both plugs spark each time. Is that correct? Thanks.

Michael Atkinson via email

A: Both coils firing is normal for the twin Rita, as it is a wasted spark ignition. One cylinder is on the compression stroke ready to fire and the other is on the exhaust stroke with nothing to fire. I wanted to check my memory so I just looked at the wiring diagram and the giveaway is that the coils are wired in series. The first time I see the Rita show up in the parts books is for the 1979 range of twins so yours was indeed added later.

Triumph carburetor issue

Q: Hi Keith, you are my “go to guy” for British motorcycles, so here are a few questions for you. My 1965 Triumph is winterized every year, but I still start it up every few weeks. I use a fuel stabilizer and have never had any problems. This year, I had trouble starting it. When it did start, it backfired and ran rough. Eventually, it smoothed out and I took it for a ride. After a few miles, it died and wouldn’t start. Fortunately, I was only a couple of blocks from my shop so I pushed it there. While checking it out, I noticed the battery was weak. The battery was several years old so I wasn’t going to waste my time with it. I installed a new one and it started right up. I drove it several miles and it was fine. When I returned, I left it running on the side stand. As I walked away, it loaded up and died. It acted like it ran out of gas. I started it back up, and when I leaned it over to put on the side stand, it died again. I started it back up. Every time I leaned it over to the left, it started sputtering. When I returned it to upright, it lined out. I then leaned it to the right, and engine speed increased. OK, what’s going on? I looked both carburetors over, and remembered that it had two identical carburetors on each side. They are both left hand carburetors. Same numbers, float bowl cover installed on the left side, ticklers on the left side. Do you think this bike left the factory like this, or do you think someone might have changed the right carb out and replaced it with a left one? I was going to check the float on the right carb, but would have to remove the carburetor as the cover is on the inside. Have you ever heard of anything like this? Could the wrong carburetor be part of the problem? I know you’ll have the answer for this, you’re the best! Thanks in advance.

John Botts/Ponca City, Oklahoma

A: On the Monobloc, the jet is on the right side of the carburetor, while the bowl is on the left. If leaned over to the left, it is possible to reduce the fuel flow to the jet, leaning it out and causing your stall. They were both left hand bowls from the factory.

Tires and tubes

Q: Hello sir, I just read your excellent article in response to a guy with an alloy rim. I just bought a 1972 Triumph Tiger and I need to know if tubeless tires will work on there with a tube installed and what I should know about this combo. I tried putting a tube in a tubeless car tire once and it blew out on the freeway during a 300 mile high-speed trip the next day. I figured it was heat build-up. I’d hate to have that happen on a motorcycle. I’m not 19 anymore. Thanks.

Farley/via email

A: It’s not ideal, but it is often necessary due to a limited choice of tires in the right size. I’m using Avon tubeless with tubes in many of my classic bikes. It’s probably safest to consider that putting a tube in a tubeless tire drops the speed rating one whole classification.

Carburetor adjustments

Q: Hi, Keith, I’m working on a Mikuni carburetor. Does it have just one adjustment screw? If there are more, where are they located?

Jimmy Webb/via email

A: Mikuni carburetors, and many others, have two adjustment screws, one controls the air/fuel mixture at idle and the other controls the throttle opening at idle. You use both to achieve the optimum idle, smooth and not too fast. I’m going to describe the common VM series. The first screw is closer to the air intake side of the carburetor, which makes it an air bleed screw. This controls the air relative to the amount of fuel, the amount of fuel being metered by the idle jet inside the carburetor. A common starting point from which to make adjustments is 1½ turns open from lightly closed. The second screw is located right at the midpoint of the round slide and is the throttle opening screw. That one is usually set to one turn in from the slide bottoming out in the carburetor body. Start the engine and adjust the throttle screw to achieve your desired idle speed, then turn the air screw in and out in ½ turn increments to see where the idle is smoothest. This may raise or lower the idle speed, so you may again have to manipulate the throttle screw to get to your desired idle. A few times going back and forth between these 2 screws will give you the best idle speed. If the bike hesitates accelerating off idle, you may have to compromise the mixture by richening it to accommodate the sudden increase in airflow from opening the throttle. With an air screw like the Mikuni, richening it means turning it in, about 1/4 turn at a time to find the sweet spot. Adjust the idle speed screw again to achieve your desired turnover speed.

Published on Oct 20, 2020

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