Benelli 250 2C

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Re: Benelli 250 2C

Postby Lotus54 » Sat May 13, 2023 7:00 pm

I took it for a longer ride today- ran great!
I found out why cold start was poor- the cable going to the ‘splitter’ that opens both of the starter valves had broken.

I need to get some 3mm screws to bolt down the handlebar switch, a few other little things and ready to put some miles on it to break it in.
I turned over 5,000 miles on the speedo.

I forgot to take a picture on the ride.
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1976 OSSA Super Pioneer- 78 Benelli 750 sei,72 250 2C Benelli, 68 Benelli Dynamo trail, 76 OSSA GPII Phantom, Beta XTrainer 300, Lotus Elan S3
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Re: Benelli 250 2C

Postby Lotus54 » Thu May 18, 2023 5:55 pm

Great day for a ride up the Elwha (and other places)
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Re: Benelli 250 2C

Postby Lotus54 » Thu May 18, 2023 7:30 pm

The throttle cable adjuster had broken. I’m going to replace the throttle and splitter with a two-cable setup, but in the meantime, I made a new adjuster. The knurling is not very good- but it is functional
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Re: Benelli 250 2C

Postby John H » Fri May 19, 2023 7:25 am

Knurling takes some practice to get a perfect pattern. What brand is the throttle?
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Re: Benelli 250 2C

Postby Lotus54 » Fri May 19, 2023 8:30 pm

Tomeselli.

I’ve done a lot better knurls before, but this was a different tool, different lathe and different material.
1976 OSSA Super Pioneer- 78 Benelli 750 sei,72 250 2C Benelli, 68 Benelli Dynamo trail, 76 OSSA GPII Phantom, Beta XTrainer 300, Lotus Elan S3
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Re: Benelli 250 2C

Postby Lotus54 » Wed May 24, 2023 5:56 am

I got a dual cable Tomeselli throttle. This is not the desmodronic type that many modern 4-stroke bikes use, but both cables are pull to open.
I made up both cables from some Venhill kits I have. The throttle is quite a bit lighter without the splitter (and old upper cable), smoother also.
I then made up the ‘top’ cable for the two enrichers on the carbs. It had broken in the spitter. So now I can just pull the lever on the handlebar for cold starts. It starts really easily with that active, but not won’t start without it. I was just pulling on a cable until I got it fixed- much better now.

I got one new silencer in from Germany, that is all they had. But it does replace the rustier one. I will keep looking for a right now, but will start working on cleaning up the old ones really well and see about rechroming. The baffle system comes completely out.
1976 OSSA Super Pioneer- 78 Benelli 750 sei,72 250 2C Benelli, 68 Benelli Dynamo trail, 76 OSSA GPII Phantom, Beta XTrainer 300, Lotus Elan S3
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Re: Benelli 250 2C

Postby John H » Fri May 26, 2023 6:34 am

Tomaselli accessories are always high quality unlike some Amal items. I like the idea of changing to twin throttle cables
all the way too.
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Re: Benelli 250 2C

Postby Lotus54 » Sun May 28, 2023 7:42 am

The manual has a very slow breakin recommendation. On this one, mostly the pistons (rings) that would require it. Tolerences are fairly snug so I don’t want to push it.
I have a spare headpipe, so I think I will weld an O2 sensor bung on it and go ride it with my readout box, so I can verify mixture. I think that is the most important on a 2-stroke, get too lean and it gets hot and…
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Re: Benelli 250 2C

Postby John H » Sun May 28, 2023 9:04 am

I know what 'lean' does to 2 strokes, put the wrong gas in the Lawnboy last year and stuck it. How do you adjust the oil mix on the Benelli 250?
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Re: Benelli 250 2C

Postby Lotus54 » Mon May 29, 2023 7:51 pm

The Benelli is pre-mix. I’ve been using Motorex full synth 2-stroke at 50:1
My KTM 300 called fro 60:1, my Beta averages about 88:1 (oil injected).

With the oils in 1972, they called for 5% - but even back in the later 70s, I ran much leaner (I think 40:1) with the oils that had come out.
BUT, I want to make sure not too lean. That will kill it a lot faster than lean oil (well, from what I’ve seen). Plus oils avaliable now are very good.
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