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 Post subject: 750 running for the first time!
PostPosted: Sun Feb 10, 2013 11:49 am 
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Joined: Mon Jan 07, 2013 9:52 am
Posts: 7
Location: UK
model: 750 Sport
year: 1990
Have had the Sport for a couple of months and needed to do a few things to it prior to starting so was pleased to hear it run for the first time. It needs a belt replacement and want to remove the motor from the frame for clean up and general check over along with valve clearance checks. I ran it with the air filter removed, once it warmed up it idled smoothly and I reved it up slowly to about 5000 RPM. There was a fairly consistent stumble around 3500 to 4000 RPM. Is this the common short fall of the Weber carb? I'm not sure on the direction I want to go with the bike, I do really enjoy working and fiddling with bikes and this little bike has not cost me a lot. It is all there as originally sold but a bit long in the tooth. Do not see the 750 Sport as an highly sought after model or one that will ever be collectible. Do like it's ties to the F1. I do want to make it run smoothly through out the rev range and this may be the deciding factor for the bike. If I can do that with the Weber and patience and effort on my part will keep it original. If that is not possible would like to convert to carbs with vertical cylinder carb mounted on rear rather than central feed. Convert to 17" wheels as well. Has anyone changed vertical cylinder head to allow rear carb? If so what parts were used to accomplish. Your comments on any or all of the above are appreciated.


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 Post subject: Re: 750 running for the first time!
PostPosted: Sun Feb 10, 2013 12:35 pm 
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Joined: Wed Sep 19, 2012 11:33 am
Posts: 75
Location: Taunton, England
model: 750 Sport
year: 1990
I know that fitting a Pantah rear cylinder head is possible on these engines, but they are extremely rare (read expensive), would need machining (bigger bores on the 750), and the cam has to be meddled with (not sure if someone told me that a front cam can be used) then make an exhaust...

I'm no carb expert, and there's plenty here who seem to have succeeded with the Weber, but after investing £200 on a rebuild the Weber on mine was still ghastly. I've just finished making throttle and choke cables for the PHF 36 Dell'Ortos I fitted (as recommended by Phil and Maico88 on here) and hope to see an improvement in starting and a reduction in flat spots.

My bike came with 17" wheels and it rides superbly. Interesting to note that the 1989 900SS was almost the same bike as the 750 Sport, but came from the factory with 17" wheels, and was praised for its handling by contemporary road testers. Fitting 17" wheels also allows you a choice of tyre that the 16" Oscams don't.

As for originality - I'm of the opinion that as they stand the Sports aren't really special enough to command big money, which is why there's no crime in changing them to suit riding style and budget.


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 Post subject: Re: 750 running for the first time!
PostPosted: Sun Feb 10, 2013 2:17 pm 
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paso grand pooh-bah
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Joined: Sun Jul 18, 2004 12:00 am
Posts: 5227
Location: southern Germany
model: 750 Paso
year: 1987
If you like to work on the bike and keep the Weber the best way for starting would be to put the airfilter back in. Then clean the carb, sync it and set mixture correctly, clean all electrical contacts, do the relay mod and eventually swap the coils.
viewtopic.php?f=1&t=5823
Adding a fuel pressure regulator is said to be a further improvement while I do prefer an underpressure fuelpump from a SS/Monster or Yamaha TDM/TRX.
All this doesn`t cost much more than some time. It may not solve everything but it will definetely make things a lot better.

G.


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 Post subject: Re: 750 running for the first time!
PostPosted: Fri Feb 15, 2013 12:47 am 
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paso grand pooh-bah
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Joined: Sat Sep 03, 2005 12:00 am
Posts: 1318
Location: SF Bay Area
model: 750 Sport
year: 1990
Steve at LoudBikes has used donor Paso/Sport motors to refresh his F1, using the original F1 heads. You can search his blog to see how he did it after the F1 blew up fantastically some years back. I think one of your challenges will be getting the carb to fit into the frame, but I'm not sure.

Much easier is to change carbs if you find the stock carb too much of a challenge. But swapping heads is a huge undertaking with a big chance of something going very wrong. Its a grand project with very little upside, besides being supremely odd. There won't be one like it.

If you want more power, simply get a 900SS motor and swing arm and drop it into the Sport. Drops right in, and fixes many shortcomings, such as displacement, small valves, old ignition, old carburation, etc.

If you are going to do the 17"wheel swap, go all the way and just get a wrecked 900ss and make a 900 Sport. Use the full 900ss front end and you'll have 320mm rotors and 4 pot calipers. There have been a few of those done, and all of them love the bike. Search the archives for pics.

Cheers, Phil

_________________
Duc in the Bay
1990 750 Sport x2-Rosso Blanko (900ss copy) & Nuovo Nudo (Scrambler project)
1991 907 -mostly stock
2002 ST4s - Lots of mods.


Last edited by ducinthebay on Sun Feb 17, 2013 6:01 pm, edited 1 time in total.

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 Post subject: Re: 750 running for the first time!
PostPosted: Fri Feb 15, 2013 10:44 am 
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Joined: Mon Jan 07, 2013 9:52 am
Posts: 7
Location: UK
model: 750 Sport
year: 1990
Thank you for all your replys. Think I will play with the Weber and see if I can sort it out and thus keep bike standard. Failing that will go with the 900 option. Will keep you posted.


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